AU452995B2 - Altering the properties of concrete by altering the quality or geometry ofthe intergranular contact of filler materials - Google Patents

Description

10.340 no This invention relates to concrete, and embodiments

of the invention, it is believed, can offer substantial

advantages over prior proposals. One important character- istic which can be obtained is a high strength to weight ratio

compared with prior products.

In this specification, the term "concrete" is used

to mean a product formed from aggregate, which may be

solely a fine aggregate such as sand or a mixture of a

coarse aggregate and a fine aggregate, and a hydraulic

cement.

The term "mortar" means a- product comprisinga-fine aggregate such as sand and a hydraulic cement as a binder,

and thus is within the scope of the meaning of the

term "concrete".

The term "graded aggregate" means a collection of

solid particles capableof being bonded together with a

hydraulic cement, the range of particle sizes being

within certain limits. The range of sizes may be small or large but in the context of the present invention,

the aggregate is a graded aggregate if the range of

particle sizes is such that the aggregate can be compacted

so that adjacent particles directly bear against one

another and retain this feature when a concrete structure

is formed by the method according to the invention.

The term "hydraulic cement" means a substantially dry.powder like substance which on receiving water under-

goes a chemical action taking up water and then sets or oures to form a solid binding material.

The invention, briefly, is based on the appreciation

that a hitherto unexpected and surprising improvement in

strength or strength to weight ratio of a concrete or

452. 995

10.340 no mortar may be realised if relatively strong particles

(such as aggregate particles) in the concrete or

mortar are made to bear against each other and

relatively weaker particles (such as cement particles and

any similar sized particles such as specially added

light-weight particles mixed with the cement) are

confined substantially within the voids between the

relatively strong particles. In the past, incorrect

formulation, or method of mixing the ingredients, or

a combination of these have, it is thought, prevented

the realisation of the high strengths or strength to

weight ratios which the present inventors have

discovered to be possible.

Basically, the present invention provide9sa method

of producing a concrete structure involving a novel

process of formulation, compaction, and water addition,

this process extending to the use of both conventional

and non-conventional concrete making materials.

Furthermore, embodiments of the invention include

significant alteration of the properties otherwise to

be found in the product through the addition in a novel

manner of relatively large quantities of materials able

to impart desired properties. For example, the normal

density can be significantly reduced through the

addition of a very low density material, while

causing only a imparting relatively small adverse

affect on the strength of the concrete.

In an important embodiment of the invention, the

method permits the prevention of an optimum configuration-

and mixture from being dissipated by partial separation

of some components of the mixture from others.

a *452995

340 no

Concrete is normally mixed wet before pouring, and forms a paste of the cement and water which coats all of the aggregate particles. When the wet mixture is poured into a mold, the aggre- gate particles are not in direct Contact with each other but are of necessity separated by a film or larger quantity of cement and/or water. This separation is quite independent of the degree of compaction of the mixture, both during and after pouring, and we have found that it may impart a fundamental weakness to the concrete.

Another difficulty arises because wet mixes require the addition of considerably more water than that which is actually required for hydration, the additional water being used to increase the flowability of the wet mix, so as to permit proper handling and filling of the mold or formwork. As a result, the excess water eventually evaporates, leaving voids; hence, the cured cement is left weaker than it would have been if the excess water had never been present. Also, large or small voids are left as a consequence of entrapping air during the placing process.

A further difficulty heretofore has arisen because the quantities and sizes of aggregates chosen for a wet mix are based primarily on obtaining such workability in the wet mix as is commensurate with the quantity of cement chosen for the desired strength. This basis of choice of aggregate sizes and quantities, coupled with the excess water, has often led to excessive segrega- tion.

10,340 no

The present invention in one aspect enables these

problems to be overcome by a

340 no

novel dry-mix procedure.

Among the advantages which can be achieved

by embodiments of the invention are improved

compressive strength, improved tensile strength,

reduced porosity, greater resistance to subsequent

wetting, better as-molded surface appearance and

uniformity, better texture both on the surface and in

the body, better receptivity to paints, and better

control of properties in general.

According to a first aspect of the invention, there is provided a method of forming a concrete

structure comprising dry mixing graded aggregate with

a material being hydraulic cement or a mixture of hydraulic cement and other particles having a size of the same order of magnitude as the cement particles, the quantity of cement in said mixture being such that in

the structure produced by the method the cement will bind together said other particles in spaces between the

particles of said aggregate, the volume of said material

being such that after compaction the volume would be no/ ot aubt nOtiAlly/greater than the void space that would

occur in the dry aggregate after compaction and not so much less than said void space that ineffective bonding

and excessive void space remains, filling a mold with the resultant dry mixture, compacting the dry mixture in the mold to an extent such that particles of said

aggregate bear on one another, adding water such that

the water is distributed by seeping into the compacted

mixture, thereby ejecting air into the atmosphere, and curing the resultant wet compact mixture in the mold to

6. 452, 995

10 340 no produce said structure, the method being carried out

such that particles of the aggregate bear directly

on adjacent particles in the cured concrete structure,

the cement acting to bond the particles to one another.

When water is added in the method, distribution

of the water will occur under the force of gravity if

the mold is static or under centrifugal force if the

mold is rotated. However, it is thought that capillary

action in addition will always assist the distribution

of the water.

According to a second aspect of this invention,

there is provided concrete comprising: a cured compacted

mixture of graded fine aggregate,

and a material being hydraulic .cement or a

mixture of hydraulic cement and other particles having a

size of the same order of magnitude as the cement particles,

the quantity of cement in said mixture being such that

said other particles are bound together in spaces between

the particles of said aggregate, the volume of said material

being such that in the dry compacted state the volume

would be net Ubtontizllgreater than the amount of void

space in the compacted fine aggregate and not so much less

than said void space that ineffective bonding and excessive

void space remains, said cement being located almost

entirely in the voids between the fine aggregate particles

so that aggregate particles bear directly on other

aggregate particles. The cement 'material may be pure hydraulic

cement such as portland cement (although other hydraulic

cements may be used) or the material may be a mixture

of hydraulic cement and other particles, such as light-

weight particles of a size of the same order of magnitude

as the hydraulic cement particles when dry. 7. 452 995

34 Ono The invention extends to embodiments

in which any addition to the presence of fine

aggregate, graded coarse aggregate is used, this

being dry-mixed with the fine aggregate. Preferably,

the volume of the fine aggregate when dry and compacted

is approximately equal to and no less than the volume

of the voids in the coarse aggregate when dry and

compacted.

It is also possible for embodiments of the

invention to include aggregate comprising two components

one of which is much lighter in weight than the other

component. Preferably, the lighter-weight component

is small enough in particle size relative to the size

of the other component so that the forces of apparent

viscous drag in the fluid-like dry mixture exceed the

apparent buoyancy forces in the dry mixture.

Reference will now be made to the accompanying

drawings for the purpose of explaining embodiments of

the invention. In the drawings;

Figure 1 is a sectional diagrammatic elevation

of a mold containing a column of compacted aggregate,

illustrating some aspects of an underlying theory of the

invention.

Figure 2 is a diagram showing a Mohr envelope

for certain relationships between shear stress and normal stress.

Fig. 3 is a similar diagram for another instance. Figure 4 is another similar diagram for yet

another instance.

452.995

10.34 Ono

Fig. 5 is a diagrammatic representation of a loose

50-50 pack of structurally strong and structurally weak

particles.

Fig. 5A is a force diagram of a balanced loaded

particle of Fig.

Fig. 6 is a similar diagram of a denser pack of the

same types of particles.

Fig. 6A is a force diagram of an unbalanced loaded

particle of Fig. 6.

Fig. 7 is a similar diagram of a pack of structurally

strong particles around only one structurally weak particle.

Fig. 7A is a force diagram of the unbalanced loading

of the particles adjacent to the weak particle of Fig. 7,

shown in two different unbalanced loadings.

Fig. 8 is a graph obtained from the data of Example 1

below, showing the relationship between the percent voids in

compacted sand aggregate completely filled with compacted

cementA cnA prc) s s op raW

Fig. 9 is a graph of the compressive strength obtained

per amount of cement in a mix of cement and phenolic

microballoons.

Fig. 10 is a diagram showing how the beams of

9. 452,995

10.340/70 Example 5 are tested.

Fig. 11 is a view in cross-section of one of the beams tested according to Fig.

Fig. 12 is a comparison of compressive strengths obtained from two basic mixtures of this invention with

varying amounts of calcium chloride in the water added to

capillary action.

Fig. 13 is a graph where compressive strength has been plotted against days of moist cure for two basic mixes

made according to the principles of this invention.

Fig. 14 is a graph of flexural strength plotted against days of moist cure for two basic mixes prepared accord-

ing to the principles of this invention.

Fig. 15 is a Mohr envelope diagram comparing the shear stress per normal stress of two mixes differing only in

cement content, the solid line envelope and circles represent-

ing a concrete having less cement per aggregate than the

broken-line envelope and circles.

Fig. 16 is a graph wherein compressive load is

compared with the angle of the Mohr envelope of failure for

a series of sand-cement concretes differing only in the sands

used.

Fig. 17 is a graph plotting compressive strength

452.995

10,340 no

against the water-to-cement ratio for two different types of con-

crete both made according to the principles of this invention.

Fig. 18 is a graph showing the increase in compressive strength corresponding to increased shrinkage in concrete of the

present invention which incorporates calcium chloride as a cure accelerator.

Fig. 19 is a graph showing the increase in flexural tensile strength corresponding to the increase in shrinkage in the same concrete as for Fig. 18.

Fig. 20 is a Mohr envelope diagram comparing the qualities of concrete with and without an accelerator that quickens cure and

increases shrinkage.

In one embodiment of the invention, graded fine and coarse aggregates, preferably with angular grains, are mixed to- gether. If these aggregates were to be densely compacted, they would have a certain percentage of void space between particles.

A quantity of cement calculated to be approximately equal to the volume of that void space when the dry cement is in a compacted

dense array, is added. The dry aggregate is then mixed with the added cement, and the dry mixture is poured into the mold or forms,

the pouring being done, for best results, in a manner minimizing

segregation. The dry mixture is

10.340/n then compacted as much as possible in the mold or forms,

as by a combination op vibration and tamping, so as to

approach the volume which the well-compacted argregate

would have had without any cement being present; i.e.,

the cement completely fills all the voids between the

aggregates. Water is then added by exposing a portion

of the concrete to water, for instance, through small

holes at the bottom of the mold. Capillary action is

sufficient to draw the water throughout the concrete mix,

sweeping the air in the minute capillary-size void spaces

ahead of the water and eventually out of the mold.

Additives, such as calcium chloride, may be included.

The concrete is then cured in the normal manner.

A very important feature for optimum use of

this invention is that the water seeps in to displace the

air from the voids into the atmosphere without disturbing

the packed aggregate and cement. Capillary action can

conveniently be relied upon to cause such seeping of the

water, although other forces such as gravitational forces

and hydraulic pressure may be utilised. Therefore for

best use of the invention, the mold or casting bed should

be carefully designed bearing in mind that trapped air

inhibits the full penetration of water to the region of the

entrapped air and tends to prevent the formation of

concretes which meet the expected standards. For instance,

in the application to a slab, water should not be

introduced simultaneously to both the top of the slab

and the bottom of the slab; if it were so introduced,

there would be too much risk that the cement hydrating

or at near the top and bottom surfaces would seal against

12 452, 995

3 4 0Ono the exit of air from within. The infusing

developing air forces would bc opposed by the

pressure within the slab until an equilibrium

were established, and

2. 995

10.34 no

then no more water would infuse. If, however, the water is intro- duced at the bottom only, and if the top is exposed, then it is possible to sweep all the air upwards and out in advance of the infusing water. If the water is to be introduced at the top, then the bottom forms should be provided with vents of sufficient fre- quency and capacity as to enable the orderly exit of air in advance of the infusing water.

If a section of concrete is so thick that there is a possibility that the infusing waters might cause the hydrating cement to seal the water courses prior to complete infusion, then preferred practice of this invention includes introducing the waters of infusion from within the dry mix in a manner timed to permit the orderly exit of air. The use of such internal conduits for the infusion from within as will enable infusion along the length of the conduit, such as for example, a "stocking" of sand or the use of B-X cable, is in accordance with the proper exercise of this invention under these circumstances, when internal infus- ion is warranted or is otherwise desired.

The term "BX cable", as used herein, designates a type of conduit of the kind used for electrical wiring and made by conti- nuous spiral winding of a metal strip into a non-watertight conduit from which water can leak in a substantially even spiral pattern.

Thus, for example, a positive escape path for the air may be provided along mould surfaces, the water being added through

2 995

10.34 Ono

perforated conduits inside the mould and surrounded by the compac- ted dry mix. Alternatively in the method of the invention in which

cement is in its most dense array, as defined above, in the finished concrete, the water may be added through perforated

conduits directly surrounded by sand separating them from the

compacted dry mix.

If the section of concrete of this invention does not

warrant internal infusion, and if infusion is to be from without

and from a formed surface, such as for example, the face of a wall or the bottom of a slab, then a course to distribute the water

along the face of the form or mould should preferably be provided.

Water distribution courses such as those provided by corrugated or

screened contact surfaces are examples of recommended practice of

this invention.

If water is to be distributed along a free top surface,

such as for example, the top of a slab, then it is to be expected

that, initially, the compacted top surface will be slightly dis- turbed by the exit of air upwards (air being lighter than water).

This undesirable disturbance can be inhibited by surcharging the

top surface with a load such as, for example, sand. A surcharge

load will prevent the disturbance of the top surface of the con-

crete. As an alternative, the initially disturbed top surface may

be recompacted while the mixture is plastic and the cement still

has a significant portion of its hydration ahead of it. Very

often, troweling of the top surface, after water has been infused

10,.340 no

from the top, provides the required amount of recompaction. A further alternative is to add water to the top surface sufficiently

slowly to prevent the air near the surface from being trapped within the water and tending to bubble upwards rather than to exit

downwards. Finally, these three alternatives can be coupled on any

combination of any two or all three of them.

The proper compaction of the dry mix in the mold or forms prior to the addition of water causes the particles of cement

to be contained within the void spaces that necessarily exist bet- ween the aggregate particles. Thus a separating film of either water or cement between the aggregate particles is avoided. More- over, the dry mix aerates and flows almost like a fluid, enabling excellent mold definition even superior to a very wet mix. After compaction, the remaining void spaces are so small as to afford

entry of only a small quantity of water, which comes in under the influence of capillary action. Very little more than the minimum required for hydration is used, and the process is self-metering.

This invention also extends to embodiments in which aggregates of different size ranges are used in the concrete.

Preferably, quantity of each size of aggregate used in formulating

the dry-pour concrete is chosen so that each size range fits into

the void spaces between the particles of the next larger size. Therefore, with proper proportioning of quantities, the most

compact state of the dry-pour mix can only exit with no segrega-

tion, and the very act of compaction tends to create the correct

Lnsegregated distribution of particles.

452.995

10.340 no

Dry mixes formulated and poured into molds in the manner

stated above have yielded compressive strengths far in excess of

what might be expected from the more usual wet mix formulations of the same cement content and same manner of cure. For example, laboratory test results shown in Fig. 13 were obtained from cement-

aggregate mixes that included no chemical additives and there was

no accelerated cure. This figure shows that 28-day compressive

strengths of approximately 10,000 psi have been obtained for a

nominal 7-sack mix, and strengths of about 11,000 psi for a nominal

8-sack mix. Twenty-eight day compressive strengths 12,000 psi

have been obtained for 10.5 sacks of cement per cubic yard,instead

of the more usual 6,000 psi for a'Vet mix of the same formulation--

an improvement of about 10.0%. Other dry-mixes of this invention have given comprssive strengths of 6,000 psi for 5.5 sacks of cement

per cubic yard instead of the more usual 2,500 psi for the wet

mix; and 5,000 psi for 5 sacks of cement per cubic yard instead

of the more usual 2,000 psi for a wet mix. The wet mixes described above are those formulated for 3 to 4 inch slump. This marked improvement in compressive strength is only one of the advantages

of this invention. A considerable increase in tensile strengths

also results. For the cement of this invention having a 12,000

psi compressive strength, a tensile strength in excess of 1,000

psi.was obtained.

Particular note should be taken of the very high early

strengths of concrete formulated in the manner of this invention.

Fig. 13 also showsjthat compressive strengths in excess of 4,000

452,995

10.340 no

psi have been achieved after one day of non-accelerated curing for both the 7-sack and 8-sack mixes of this example. These strengths are far in excess of those attainable by the usual wet mix formu-

lations of similar composition and subjected to similar curing.

A considerable increase in the flexural tensile strength may occur when this invention is employed to manufacture concrete.

Hitherto unattainable flexural tensile strenghts in excess of 1,000 psi for a nominal 6-sack mix and strengths in excess of

1,400 psi for a nominal 8-sack mix have been obtained, without

using any chemical additives. Fig. 14 shows that remarkable one- day flexural tensile strengths of approximately 600 spi have been

obtained without any accelerated cure of the beam specimens. This example serves to illustrate that a distinct quality of

high flexural tensile strength, which is not obtainable by similar formulations of the more usual wet mix methods, may be obtained by

the dry-pour process embodying ithis invention.

1. 452.995

10,34 Ono Another noteworthy property is that the total

included porosity for a dry-pour concrete which is an

embodiment of this invention can be in the order of

only 3.6 percent, which is almost an order of magnitude

less than the porosity expected for conventional wet

mixes. Consequently, such dry-pour concrete can be

virtually waterproof, approaching the permeability of

a fired ceramic, which has 2 percent porosity. This

quality is important for waterproofing, and it also

enables painting without having to seal the concrete

first and it imparts the ability to achieve a high-gloss

finish with one coat of paint. Embodiments of the invention may provide a dry-

pour concrete having an as-poured molded surface which is

-smooth, and, when -formed in a proper mold surface, the

as-poured surface may give a virtually polished

appearance, completely free of visible honeycombing and

air bubbles, thereby distinguishing it from the undesirable

honeycombed surface of a stiff wet mix. This surface

quality is of particular interest when it is further

recognised that immediately upon wetting, such dry-pour

concrete has considerably greater strength than any

possible wet mix, no matter how low the slump of the wet

mix.

Since water is not added to the dry-pour concrete

until the concrete mix is already placed in the mold

and since no movement of the wet material is required,

considerably more rapidly curing mixes, such as

34 Ono

high-early-strength cement and solutions of calcium chloride in the

water, 8% solutions) may be used with excellent results. Five-foot-square panels, varying in thickness from 3/4 of an

inch to two inches with an average thickness of one inch, have

been poured by this technique and, without heating or steam curing,

were stripped from their forms and stood upright within ten hours of pouring--a time that by no means represents the lower time limit

for the time could have been substantially reduced.

Another very important result which can be achieved is a dry-pour concrete which is considerably more dimensionally stable than the conventional wet-pour concrete. For example, a normal wet-mix concrete shrinks considerably during cure, so that a cold joint cannot bond well. In fact, one normally expects such a cold joint to crack along the pour line. In contrast, thicknesses of concrete as little as a quarter of an inch have been patched with

dry-pour concrete of this invention compacted in place against

partially cured concrete, and the resultant structure appears to

have suffered no reduction in strength through the cold joint. No crack or other characteristic readily distinguishes the patched

areas.

The substantial reduction of both shrinkage and creep which can be obtained results from the fact that substantially all

of the aggregate particles are initially in contact with each

other and upon the addition of water cannot

2. 995

10.34 Ono

be moved closer together by shrinkage in the cement or in the mix.

The extreme lack of porosity and the stable particle arrangement

enforced by intergranular contact prevents severe dimensional

changes from occurring upon either the wetting or the drying of

the concrete, and there is virtually no warpage in curing.

A theory which may explain these remarkable characteris-

tics is offered, though the invention is not to be limited by such

a theory and the applicants do not assert that the theory is correct

Consider an arrangement of granular particles, such as sand, in which every particle is in contact with one or more ad-

jacent particles and in-which-the-entire arrangement of particles is constrained so as to inhibit movement outward from the mass of

the particles in contact. This may be accomplished, for example, by placing the sand in an infinitely rigid constraining cylinder

as shown in Fig. 1. Furthermore, consider that the column 11 of sand has been compacted to its most dense array so that further

compaction--without fracture of the particles--is not possible.

Such a column 11 of sand will then support a surcharge loading 12

without inelastic deformation, provided that there is no fracture

of the particles

2,995

10.34 Ono in contact. In this case, thc energy contributed by the surchai~ge loading 12 is stored internally and is available for use to effect complete elastic rebound vhen the surcharge loading 12 is removed.

-The column 11 of particles in contact has some properties of a fluid, dts can be seen by imagining the cylinder walls 10 suddenly removed. The column 11 of sand would then "flow" out from under the surcharge loading 12. Without lateral restraint, the column 11 of sand obviously has negligible strength. Thus, the strength of the column 11 of sand depends upon the quality of the constraining medium, in addition to the quality of the-sand. If the cylinder walls 10 were to be thin and flexible, then the maximum surcharge loading 12 causing failure would be less than if the walls 10 were thick and rigid. The column 11 of sand can oper ate well as a structure if and only if the outward movement (flow) of the mass of particles is inhibited, therebyrenabling transfer of load through the particles in contact.

The preceding description of the column of sand is compatible with the Mohr-Coulomb strength theory, first expounded by Coulomb in the year 1776. The Mohr-Coulomb strength theory as applied to granular soils takes into account that a certain relationship exists between normal stresses and shear stresses, such that when a permissible combination of such stresses is exceeded, failure occurs. This relationship is given by a Mohr envelope, as show..n in Fig. 2. By plotting the confining pressure, the minimum principal stress on the axis-of principal stress, and then drawing a circle tangent to

22 45 2.995

10.3 4 0no

the Mohr envelope passing through this point and extending in the

direction of increasing stress, the maximum principal stress a2will

occur where the circle crosses the axis of normal stress. The deviator stress 02 o- is the load carried by the soil structure

I Suppose the confining pressure r' 1 is increased to I1 The tangent circle is drawn and o2 is noted on the axis of normal

stress. Note that an increase in confining pressure enables an increase in load-carrvinq capacity. That is, the deviator stress for the second case 02 ~1 is greater than the deviator stress for the first case o2- ir

A second way of increasing deviator stress, the load carrying capacity of the sand structure, is to increase the angle k n of the Mohr envelope. This is shown in Fig. 3, where o2 -l is greater than o- o for the same confining pressure, oa.

A third way of increasing the load-carrying capacity of the sand structure is to build into the structure a shear capacity

quite independent of the intergranular contact. This shear strength is marked C on the ordinate of shear stress, and Fig. 4 shows that

for the same confining pressure and slope of the Mohr envelope, the

deviator stress 0-1 is greater for that material with initial shear capacity than is the deviator stress o o- for the same material but without the initial shear capacity.

One example of the invention will now be discussed. The concrete is composed

452, 995

10.3 4 0no of a compacted structure of granular material (which for the moment may be called sand, though applicable to all granular media) which depends heavily on the character and quality of the intergranular contact betvcen particles. The cementitious material (portland cement is used as an example) serves to provide both a constraining force (confining pressure) and an initial shear capacity independent of the intergranular' contact.

When the sand and cement is mixed dry, the cement (being many orders of size smaller than the sand) will most conveniently and most naturally fill the voids between the particles of sand, when the mixture is compacted to a dense array of the sand. The geometry of contact then taken is preserved after water is added for hydration of the cement, for the self-metering aspect of feeding the water by capillary attraction provides only that water which is needed to fill the remaining void spaces between the cement particles and this turns out to be little more than that required for hydration of the cement. The cement during its hydration period first expands largely filling its own void spaces, bonds itself to the particles of sand, and then contracts during the latter part of the hydration period. The contact force (or pressure) between the sand particles is increased due to this shrinkage of the bonded cement and to the disposition of the sand to maintain its geometry due to its already dense array. This prestressing of the sand structure provides the confining pressure indicated by 0 in the previous examples of the~ M~ohr strength theory. The very presence of the cement binder itself also provides the initial shear capacity C noted by the 24, 45 2,995-

10.340 no

ordinate of shear stress in Fig. 4.

Eor the optimum execution of this invention, thcre

should be a controlled relationship .between the volumes

of aggregate and cement. If the mixture is such that the

voids between the aggregate particles are not completely

filled with cement, then opportunity for the largest

possible initial shear strength and opportunity for the

largest possible pre-stress of the sand structure will

be lost. Such a condition of a lean mix lean in cement content) precludes the optimization of the

quality of high compressive strength, though it may be

desirable for some other reason and though great

improvements over conventional wet mixes are still obtained.

By contrast, in the usual wet process for the

manufacture of concrete, the particles of sand are

forced apart by the water-cement phase in order to provide

to provide the workability required for the wet process.

The strength advantage of intergranular contact of the

sand is not inherent in the wet process and is not likely

to be obtained. In addition, in the wet process,

shrinkage of the cement due to hydration causes

shrinkage of the concrete and dimensional instability.

2, 995

10.340mno

As shown in Fig. 3, increasing the angle of the Mohr envelope increases the load-carrying capacity of the sand structure. As is well known in the field of solid mechanics, an increase in the angularity of the particles and the use of a well-graded mixture

one with many sizes of appropriate quantities), other

things being equal, increases the slope of the Mohr

envelope. It is reasonable to expect that for very dense

angular well-graded sands the slope of the Mohr envelope

will approach 45 degrees. This angle if present initially, will remain during the dry process of this invention,

since the structure has no tendency to change its

geometry. The literature suggests that for concrete of the wet process of casting concrete, a slope of only degrees might reasonably be expected. This unfavourably

low angle is due to the unquestionably poor state of intergranular contact.

The idealized Mohr envelope of failure may again be used to provide a theoretical explanation as to why large tensile strengths occur as a consequence of this invention and why these tensile strengths increase with increasing cement content, provided that the cement content is not so great that it would force separation of the sand particles in contact, thereby removing the strength

derived from the intergranular contact of the sand

particles, which is represented by the Mohr envelope

of failure.

The solid lines of Fig. 15 describe an idealized

452,995

10.3 4 Ono Mohr envelope of failure and the Mohr circles w1hich are compatible with this envelope. The broken lines of Fig.

describe a similar condition of compacted aggregates, with an

increase of cement content beinv the only ifference. Note

that increasing the cement contentfiile the other variables

are held constant causes an increase in the initial shear

capacity (the intercept n the shear stress axis) and in the

shrinkage forces during the latter stages of the hydration.

If the compacted aggregate particles are in intimte contact,

then these additional shrinkage forces serve to further

increase the confining pressure from c to It is noted

that this would cause an increase in the compressive strength

compare with (a and also,a rather

significant increase in the tensile strength a'

compare with In the prior-art wet process for

making concrete, it is not possible to get the tensile strength

attainable by this invention, because the shrinkage of the

hydrating cement is not effectively resisted by the aggregates

(which are not in intimate contact, but rather are separated

by a coating of cement and water). As a consequence,

little confining pressure is set up by the shrinkage forces.

Study of Fig. 15 shows that as or, approaches zero, not only

does the compressive strength reduce, but so

does the tensile strength and rather significantly

at that. In the prior-art wet process, this condition of the

confining-pressure approaching zero exists, seriously inhibit-

ing the development of load-sustaining tensile stresses.

In summary, this -inv.ention/appear- to proide "aggregate

27 452.995

10.340/70 with voids filled with cement and the resultant

concrete can at least in some embodiments sustain remarkably high loads and have good dimensional stability.

In addition, since the Mohr-Coulomb strength theory

may be applicable, it is thought that predictions of quality of performance may be possible, based upon laboratory study of the sand or other aggregate to be

used in thl. basic structure. However, it must be understood that aggregates can be added to the fine

aggregate or to the sand-cement mixture discussed above.

The strength of the concrete is dependent on the strength of the aggregate particles and, therefore,

higher strength requires sound aggregate with adequate

compressive strength. An angular shape, such as tends to result from crushing larger particles, leads to greater

strength than a rounded shape occurring in older sand

and rock where sharp points have been worn off. Furthermore, within a given stratum, there should, preferably, be a variation in size, for the strength theory shows that

such variation increases the slope of the Mohr envelope,

thereby leading to greater strengths. Basically, greater angularity and greater size variation causes

greater interlocking when the dry mixture is compacted,

and hence greater resistance to deformation and movement.

For determining the proper proportioning of aggregates and cement, it is recommended that the compacted void

volume in the aggregate structure be calculated or

determined by experiment. Preferably this volume is then approximately equal to the quantity of cement used in the

final mix. Adding additional cement

28. 452995

.10.34 0n requires proportioning aggregates so that the compacted void

volume is adjusted to be large enough so as to properly

receive the additional cement and yet preserve the integrity

of the intergranular contact. In such a case it is possible to increase the strength of the final concrete product.

However, adding that much additional cement which is in excess

of the capacity of any compacted aggregate void volume to

receive this additional cement, decreases the strength--for there is an excess of cement over the void spaces to be filled

and the integrity of the intergranular contact of the

aggregate structure is destroyed. For any particular distribution of aggregate sizes and shapes, there is an optimum cement content--that is densest in a compacted dry state and

fills the aggregate voids. The optimum compacted aggregate structure lies in between the densest possible arrangement and

the loosest possible arrangement.

Consider a container of dry cement subjected to a

compactive effort composed of tamping, vibration or other

mechanical means. For this cement there is a particular lower bound of volume to which any given quantity of cement will

compact. This lower bound is a stable figure which is a

consequence of the equilibrium established between the tendency of the particles to draw closer due to the mechanical

effort expended during the compaction process, the tendency of the particles -to spread apart due to the air pressures in

the voids (aeration) during the compaction process, and the geometric and frictional impedence to both contraction and

expansion in the neighborhood of this state of equilibrium.

This particular equilibrium point will be called herein the 29. 452.995

10.340 n0 "most dense array", and it lies between the theoretical "dense pack" and theoretical "loose pack" arrays of spheres in contact. For example, the specific gravity of the most dense array of Type I cement was found to be in the neighborhood of 1.8.

The quantity of cement which fills the voids of the fine aggregate so that the cement is in the most dense array is the quantity which aids in maximizing the strength of the finished product. When designing a mix for maximum strength, it is an uf Lh ivi tbjetapproach.this most dense to array for the cement in the voids of the fine aggregate. It is compatible with the strength theory of this invention that this will develop maximum shear intercept (Figure and maximum confining pressure, o; of the fine aggregates due to shrinkage of the hydrating cement after the infusion of water. Friction at the interface between the fine aggregates and the cement will act to impede the realization of the most dense pack of the cement during compaction. It therefore becomes desirable to minimize this frictional impedence, and this may be accomplished by a number of methods. One method is to remove the smaller particles of fine aggregate so that large void spaces (with fewer opportunities for surface contacts) result. Another method is to design a mix such that the volume of voids in the fine aggregates which is filled with cement is large enough to permit compaction of the dry cement to a point approaching

its most dense array and yet preserve the integrity of the particle contact of the fine aggregates. Reflecting again on the strength theory of this invention, enlarging the void space of the fine aggregates will flatten the slope of the 452. 995

10.340no Mohr envelope, thcreby reducing the load carrying capacity. However, this diso'dvantage may be partially or fully offset.by increasing thc opportunity for approaching the most dense pack of the dry cement, thereby increasing the load carrying capacity. The amount of increase of void spaces in the fine aggregate which will produce the optimum strength (load carry- ing capacity) depends upon, among other variables, the compactive effort, the distribution of sizes of fine aggregate, the surface texture of the aggregate, and the type of cement. It has been found that when a washed and dried Del Monte sand was used with the following proportions: 26.5% 16 mesh 26.56, 20 mesh 26.51 30 mesh that 34.5t of Type I cement provided optimum voids in the structure of fine aggregates. This volume of voids is approximately 25%, greater than the volume of the voids when the sand is compacted to it-s "dense pack" state and is less than the volume of voids in the sand where the sand is in its "loose pack" state.

Example 1: To show that the optimum arrangement of a compacted aggregate structure lies between the densest possible arrangement and the loosest possible arrangement.

Cement and a sand aggregate were chosen, having the following specific gravities:

.31 45 2, 995

.10.34 0no Specific gravity of the well-graded compacted sand .ggregate in its most dense arrangement Specific gravity of the 1.65 well-graded compacted sand pggregate in its most loose arrangement Solid specific gravity 1.40 of the sand aggregate =2.50

Three dry mixtures were then made, as follows: .ixture A: 1 part cement, I part sand (by weight) .Mixture B: 1 part cement, 2.25 parts sand (by weight) .Mixture C: 1 part cement, 3 parts sand (by ;eight)

By calculation, Mixture A was found to have the following volume relationships: Volume of voids of compacted loose arrangement 0.32 units Volume of compacted dry cement 0.61 units Thus, in Mixture A there is a substantial excess of cement over the void space available to receive this cement. The ratio of the volume of the cement to the total volume was 66%. This mixture was tested and found to have a compressive (28 day) strength of only 2,800 psi.

By calculation, Mixture B was found to have the following volume relationships: Volume of voids of compacted sand 0.61 units Specific gravity of compacted dry cement 1.58 Specific gravity of compacted sand 1.49 In Mixture B, the specific gravity of the sand lies in between the loosest arrangement (1.40) and the densest arrangem3nt and all the voids are 32 452, 995

10.34 0 no just filled with dry compacted cement. Tests showed

that the compressive strength (28 day) of this

Mixture B was 10,000 psi.

By calculation, Mixture C was found to have the

following volume relationships:

Volume of voids of compacted sand 0.62 units

Specific gravity of compacted dry cement 1.37

Specific gravity of the compacted sand 1.65

The specific gravity of the sand in Mixture C lies

at the densest arrangement, and all the voids are

essentially filled with compacted dry cement. The

compressive strength (28 day) was found by test to

be 5,200 psi.

Example 1 thus indicates that a gradual increase in

strength is to be expected with increase in cement content, as

long as the sand aggregate forms a competent compacted structure.

When the loosest possible arrangement of sand structure is no

longer possible and intergranular contact is compromised, a

decrease in strength follows even with an increase in cement

content. These results show consistency with the strength theory

of this invention. For, when the integrity of the intergranular

contacts of the aggregates is compromised, the effect is to

markedly decrease the slope of the Mohr failure envelope and,

as previously discussed, to decrease the deviator stress, which

is the measure of the failure load. By increasing the void

volume and yet keeping the integrity of the intergranular contact

of the sand, although the slope of the Mohr envelope may

decrease slightly, the 'effect of the added cement at increased 33. 452,995

10.340mfl density is to increase the initial shear stress intercept (shown in Fig. 4 as C on the ordinate axis) as well as to increase

the confining pressure a of the aggregates in contact clue to increased shrinkage forces of the cement gel. Both these effects of the additional cement add more to the deviator stress (the measure of failure load) than the slightly flatter slope of the failure envelope detracts from the deviator stress. The net result is to show an increase in load-carrying capacity, which is indicated graphically in Fig. 8) a plot of the results of this example.

Example 2: To show that increasing the quality of intergranular contact increases the strength of the resulting concrete product.

The literature of soil mechanics shows that sand aggregates of uniform size will not have as steep a slope for the Mohr failure envelope as will a well-graded mixture of the same sand, other things being equal. Therefore, because the w~ell-graded mixture is known to have a higher quality of intergranular contact, as a soil, then it is predicted by the theory discussed above that the well-graded mixture w3ill1 produce a higher-strength concrete. This is borne out by the information supplied in the table below. The source of the sand aggregate was the same in both cases. The compacted dry density of the cement was constant for the tests of each case.

Vods Compete~ -Compressive Strength (28 da s Case filled wiith comipacted gnred Ce-ment Well-graded sand gradedsan D 34 5,200 3,700 E 40 10,000 7,600

34 45 2, 995

10.34 Ono Example 3: The following example is offered to illustrate that the copr-ossive strength of t concret of this invention is improved with increasing .slope of the Mohr envelope of failure (a measure of the quality of intergranular contact). Tests were conducted on three different types of sands to determine the Mohr envelope of failure under similar conditions of compaction. All other variables such as quantity and type of cement, size and. shape of sample, compaction of dry material, technique of curing, etc., were kept constant, so as to effectively isolate the variable of interest the slope of the Mohr envelope of failure of the sand phase. The three sands used were an Ottawa 20/30, an Amador 70, and a well graded Silica. The results are charted on Fig. 16 and clearly demonstrate the principle that as the slope of the Mohr envelope increases so does the compressive load-carrying capability of the concrete of this invention.

Example 4: To show that when other considerations are kept constant (including the volume of voids in the sand aggregate), that the strength of the finished product of concrete increases with increasing specific gravity of the dry compacted cement.

Four mixtures were used', differing only in the specific gravity of the dry compacted cement as follows:

Specific Gravity of dry compacted cement (identical Compressive cement except for Strength in Mixture compaction) psi (7 day) F 1.16 2,260 G 1.37 3,140 H 1.48 4,200 I 1.54 5,360

35 452,995

10.340Ono

The specific gravity of the dry compacted cement is rel- ated to the amount of water that can be absorbed by capillary act-

ion. Exclusing absorption of water by the aggregates, the amount of water which may be admitted by this dry pour and subsequent

wetting process can be no more than the space between the particles

of cement. The greater the specific gravity of dry compacted cement, the smaller the volume of void space between the cement

particles, and hence, the smaller amount of water admitted.

Consequently, the denser the compacted dry cement, the smaller

the quantity of water admitted and, therefore, the lower the water-cement ratio. The water-cement ratio is a significant parameter which relates to the strength of concrete. The lower the water-cement ratio, the greater the strength, other things being equal. Whereas, in the usual process of manufacturing wet mix concrete, water-cement ratios are rarely less than 4 gallons

per sack of cement and this ratio is achieved only by reducing work-ability, surface smoothness and form definition the concrete of this invention can achieve water-cement ratios less than 3

gallons per sac)of cement without such negative factors. This low water-cement ratio does not introduce the likelihood of marred

surfaces due to trapped air, as it does in the wet process. Figure 17 illustrates the improvement in compressive strength of

cement-fine aggregate-coarse aggregate concrete of this invention with reduction in water-cement ratio. The low water-cement ratios obtained and the related high compressive strengths are not possi- ble with prior-art concretes of the same material formulation.

In addition these qualities are obtained with the same excellent

452,995

10.340M

form or mold definition discussed in other parts of this

specification.

That which is true for the proportioning of cement to

sand (fine aggregate) is likewise true for the proportioning of fine aggregates to coarse aggregates (rock). If the cement sizes

are completely telescoped within the sand-size voids and completely

fill these voids, and if the sand sizes are completely telescoped within rock-size voids and completely fill these voids, then the quantities which result can be adjusted to achieve optimum propor- tions for maximum strength. That quantity of rock, which when

compacted to the state of inter-rock contact but which admits large quantities of mortar which completely fill the voids but do

not over-fill them approaches the optimum quantity.

The dry mixture of aggregate and cement acts in many ways

like a fluid. The segregation of the aggregate particles can be

thought of as representative of a phenomenon very similar to, and

analogous to, solids suspended in a fluid. If they are small

enough, the viscous drag of forces on the particles predominate

over dynamic or buoyancy forces, and the mixture acts in a manner analogous to a colloidal suspension. During normal mixing and

handling, if the aggregate and cement are reasonably close to the

same density there is no segregation except at the free surface.

The free surface of the dry mixture has an effect not

unlike surface tension of a liquid. An aggregate particle near the'

452.995

34 no

surface, when some form of agitation exists, has a certain pro- bability of being moved to the top of the free surface. Because of the analogous apparent surface tension, the probability of the particle re-entering the surface is less than the probability of its leaving the mix. Therefore, for any given mixture of sizes of aggregate, there is a sort of scum of free particles of aggregate created on the surface. The total number of particles of a given size on the surface remains nearly fixed and is equal to the quantity required to overcome the lower probability of the particle re-entering, and thus a state of equilibrium exists. Since this is a surface phenomenon, then thnix immediately below the surface lacks somewhat that amount of aggregate resting on the surface. Therefore, the act of compaction tends to restore the mixture to the proper state.

The dry mix is, therefore, quite free from segregation problems so long as the surface "scum" is not removed. If the material is allowed to flow down a long open chute, whose angle of fall is steeper than the angle of repose of the aggregate on the surface, the aggregate on the surface will outrun the mixture and the true segregation tends to occur. The same effect occurs from material being poured from a spout and allowed to build Up, forming a cone, sides of which have an angle greater than the angle of repose.

These problems can be overcome by limiting the chute angle to no greater than approximately 30 degrees above horizon-

452. 995

10.3407o

tal, the precise angle depending on the angularity and size of

particle. For angles greater than this, a closed conduit made to run full, having no free-surface, is also an adequate solution.

In pouring into the mold, care must be taken not to build up a cone or mound with sides that are too steep. If a storage vessel is to be used, then it should be filled from one side at the top

and removed from the opposite side at the bottom, or it should be slightly agitated or some other provision made, such as a de-

segregation cone in its bottom.

Thus, though some segregation is possible, proper handling can and does largely eliminate it. In any case, the presence of the dry cement drastically reduces the degree of segre-

gation that would be found in handling the dry aggregate by itself.

In the design of a mix for the dry-pour technique, two competing alternatives must be considered and evaluated for maximum efficiency. A mix whose sizes are such that, during the act of compaction, the cement-size particles are telescoped com-

pletely within the void spaces of the sand-size aggregate and

the sand-size particles are telescoped completely within the void spaces of the rock size aggregate will be relatively more

costly for compaction and relatively less costly for cement than

a mix;: designed for transportation and placement, without segre-

gation except for surface scum.

10.340 no

Example

Mixture J: Telescoping sizes moderate compaction required. A mixture of 1 part cement Type II, 2 parts sand and 4 parts rock made according to this inven- tion, developed a compressive strength (28 day) of

6,100 psi. The cement content was 6.4 sacks per cubic yard.

452. 995

10.340/70 Mixture K: Transportable without segregation

light compaction required.

A mixture of 1 part cement Type I, 2.3 parts

sand, and 2.77 parts rock made by the process of this invention developed a

compressive strength (28 day) of 5,000 psi.

The cement content was 7.4 sacks per cubic yard.

In Mixture J, the cost of the moderate compaction

would be offset by the savings in cement. In Mixture K, the cost of additional cement would

be offset by the savings in compaction cost.

The capillary forces are considerable, and the water,

once exposed to a surface of the concrete in its dry form, can

be raised a considerable height. With the entry of the water, a potential difference is developed, which forces the air to

the free surface of the dry mix. There is, therefore, consider- able latitude in the manner in which the water is added, so

long as the hydration rate is not accelerated so rapidly

through the use of high early cement, calcium chloride, hot

water, etc., that the capillary passages are shut off by the

expanding cement gel before the addition of the water is

complete. If the water is added to the upper surface, this

surface may have to be troweled or brushed subsequently, for

appearance sake. If the water is added through internal

tubing, the surface can be brought to a smooth troweled finish

prior to. the addition of water.

The process of adding water is self-metering, in 41 .452,995

10.340 no

that the void spaces can hold only the right amount of water. So long as the water is not added with sufficient turbulence to form a wet mixing action, the process may be speeded up by raising the pressure on the entering water. This pressure must, however, be sufficiently low so as not to disturb the pre-formed intergranular contact of the compacted dry-pour. The process may, of course, also be speeded up by increasing the number and area of entry points for the water.

The self-metering aspect means that no consideration.need be given the porosity or hydrophilic nature of the aggreate. This, coupled with the fact that the water is not added until after the concrete is placed, gives considerable additional advantage to the process beyond the achievement of the better properties.

The invention also extends to embodiments in which con- crete of specific design requirements is produced. It may be possible:

to maximize the strength of a given or specific formulation of component materials, or

To minimize the segregation of the component mater- ials in a given or specific formulation, particularly where there is a difference in densities, or

to maximize a quantity of one or more cf the compo-

42

10.34 no

nent materials weaker in strength than the other components, while

a minimum decrease in strength of the resultant c6mposite product

is desired, or

452 995

10.34 Ono

to si;gnificantly alter one or more of the properties or qualities of a composite cementitious

material, or

to minimize the quantity of one or more of the strong component materials or the cement with a minimum decrease in strength.

This may be accomplished through the selection of particle sizes, the selection of specific quantities

and proportion of these particle sizes, and the

selection of component materials.

For example, if the segregation of a very lightweight component is to be prevented, then one of the following

may be done:

The lightweight particles may be made small enough so that the forces of viscous drag exceed the

apparent buoyancy forces in the dry mix.

The size and quantity of lightweight particles may be chosen so that they fit completely within the

void spaces between particles of aggregate of a larger

and heavy kind, and the quantity and proportion of the

larger particle size may be chosen so that the larger

particles tough each other in the completed mix.

452,995

10.34 0 no This means that the lighter particles would

have to shove aside the heavy particles in order

to segregate an unlikely event.

A number of component materials have been

added to concrete such as sawdust, phenolic and other

microballoons, foamed silica, foamed polystyrene,

and foamed ceramics. Embodiments of the invention

have been tested with each of these materials and have been successful.

Densities as low as 80 pounds per cubic foot,

depending on the lightness of the particles added, have

been obtained with compressive strengths of

approximately 4,000 psi. Young's modulus has been

reduced by an order of magnitude. Shrinkage has been

both increased and decreased, according to what is

desired. Densities as low as 50 pounds per cubic foot,

with 1,500 psi compressive strength have been achieved.

Machinability has been increased to a point where the

concrete can be cut with a carpenter's saw or threaded

on a lathe with the normal high-speed tool bit shaped

for the cutting of steel.

452.995

10.340 nOm

Many other properties may be drastically changed. For

example, the nuclear shielding properties may be improved. As

another example, brighter colors may be obtained through the

addition of larger quantities of color pigment. In another

instance, forty percent of the cement specified in a given mix

has been replaced by lightweight particles while retaining

percent of the original compressive strength. In other instance

particles in densities as low as one-half pound per cubic foot h been added and contained in the mix without segregation.

Commonly, concrete consists of four components: coars

aggregate, fine aggregate or sand, cement particles, and water.

In the usual wet mix, the sand is at least partially contained

within the void spaces of the coarse aggregate. The cement par-

ticles, are at least partially contained within the void spaces

of the sand. The excess water is at least partially contained

within the void spaces of the cement. The spacing between the

particles of a particular component is defined by the total volu

assumed by the smaller-particle components. In the particular c

where there is no smaller-particle component, the component will

compact to a point where all of its particles are touching. De-

pending on the amount of compaction, the form of structure achie will vary. Perfect spheres, all of the same size, can exist in

structurally stable arrays where there can be as much as 48 perc void space and as little as 28 percent void space. These are re

ferred to herein as loose pack and dense pack, respectively. A

normal aggregate is not and preferably should not be perfectly

452 995

34 0M

spherical, nor are all of the particles of a given component of exactly the same size. Consequently, the approximate usual per-

cent of void space for a dense pack is 35 percent and for a loose

pack 55 percent. These exact percentages, of course, may vary

considerably.

When concrete is mixed with water in the normal wet mix,

a paste is formed between the water and the cement; this paste

coats all of the particles with a certain minimum coating, depend-

ing on the wetness of the mix. Thus, in a normal wet mix, the

cement is never wholly contained within the void space of the aggre- gates. A compressive load through a cured wet mix concrete must,

therefore, in part be assumed by the cement.

Cured Portland cement, even packed as dryly as possible,. may sustain a compressive load of only approximately 2,800 psi.

We have discovered that when flexible particles (such as resinous

microballoons) of approximately the same size and size distribu-

tion as the cement particles and almost no structural strength

are mixed with cement in various proportions, surprising results

are achieved. Cement in its normally packed density of 94 pounds

per cubic foot contains approximately 50 percent void space and is, therefore, nearly in a loose packed condition. (Because of the

large specific surface area and the adhesion to air molecules,

the cement can, of course, be aerated to a much lower density,

but the very fluidity of aerated cement particles comes from the

fact that the particles are not in contact with each other, and

452.995

1034070no

this condition does not constitute a true pack.)

What we found is that when, by absolute volume, a wet mix of 10 percent flexible particles of the same order of size and

of insignificant structural strength and 90 percent cement is

cured, the structural strength is reduced below the 2,800 psi of

the cement above. However, in a dry mix, as the percentage of flexible particles increases to a point of approximately 40 per-

cent to 60 percent, the compressive strength increases to a peak

at this point of 3,500 psi, a magnitude greater than the undiluted

strength of the cement. As the amount of flexible particles is further increased, the strength begins to diminish, quite rapidly

after there were 60 percent flexible particles reaching a point

of almost no ompressive strength with close to 100 percent flexi- ble particles. Tests have been made with phenolic microballoons, foamed silica and foamed polystyrene. The curve in Fig. 9 des- cribes these results in more detail.

These results can be explained by two different factors. The first is that the structure formed at peack strength is appro-

ximately that of a loose pack with every other particle a struc- tura cement particle and the balance the non-structural flexible

particles as illustrated in Figs. 5 and 5A. In this array, the transmission of the compressive force from the upper surface down can be achieved in a balanced condition through the cement parti-

cles, so that none of the particles have an unbalanced component,

causing shear stress. Contact is achieved between the cement

452,995

10.340 no

particles through a non-point of tangency because of the swelling

of the cement during early hydration.

A denser pack, as shown in Figs. 6 and 6A, would assume a geometric configuration such that the forces would be unbalanced

and failure planes would develop at the interface between the strong

and weak particles. Had the quantity of microballoons been greater than that shown in Fig. 5, concentration of weaker particles would

cause unbalanced loading thereby weakening the structure. These considerations of particle quantity and arrangement indicate why the strength of the mixture peaked at a particular quantity of microballoons. The use of fewer microballoons causes unbalance and hence shear forces, as shown in Figs. 7 and 7A. The use of more microballoons reduces the total quantity of cement available to

assume compressive load and increases the likelihood of two adjacent

particles being both weak particles.

The above considerations of the form of the structure does not, however, explain the apparent increase in compressive

strength of the cement. This increase appears to be due to a second factor, namely the shrinkage of the cement during the last stage of

cure. The initial paste of cement and water settles, releasing some of the free water, whilecontaining the balance to form what

is called the gel. The volume of the gel is greater'by far than the original volume of the cement particles (absolute volume),

and it is greater than the final volume of the fully hydrated

cement, since the volume of cement plus free water is reduced as

452 995

34 Ono

they chemically combine.

In the early stages of hydration, the cement gel is not structurally sound and cannot exert appreciable forces. Thus, the initial expansion due to the formation of the gel takes place

largely by filling the void places initially existing between the

cement particles. However, as the gel becomes more structurally competent, the hydration has usually reached the stage where the

cement gel begins to shrink. Whether or not there is aggregate present, the initial particle structure (such as the cement par-

ticles themselves in contact with each other) resists any shrink- age. The resistance to the shrinkage causes the cement to be preloaded or prestressed in such a manner that the additional

capacity of the cement to support a compressive load is signifi-

cantly reduced.

In the structure of Figs. 5 and 5A the very limited bear ing capacity of the flexible particles enables a uniform shrinkage

in all directions without a significant prestressing of the cement This structure and this effect are quite important. From it three important points follows:

To maximize the compressive strength of concrete, the cement should not be required to bear a compressive load. Rather, the more competent aggregate should be relied upon to

perform this task.

452.995

34 0 no

If a desired structure requires the cement to bear load, then the cement should be allowed to shrink without excess-

ive preload caused by inhibiting much of the shrinkage at the

microscopic level.

Since the sand and coarse aggregate have many times the compressive load-carrying ability of the cement even when unprestressed, then, using a structure like that shown in Fig.

nearly half of any given component of the aggregate can be re- placed by non-structurally bearing particles without significant

reduction in strength, provided that either the non-structural

particles or other particles added in some other component sub-

stantially let the cement shrink without preload. In the case of the aggregate, the load transmits from particle to particle, as shown in Fig. 5, through the components having smaller particles

and in the case of sand, through the cement itself.

Therefore, the results indicate the desirability of a dense pack for maximum strength when the particles of any one size are of uniformly high strength and the desirability of a loose pack

of there is a mixture of strengths of particles of the same general

size. Further, where a mixture of strengths is used, to maximize the strength, approximately 60 percent should be of high strength

in order to reduce the probability of two weaker particles touching.

Acceleration of the rate of cure tends to cause increased

shrinkage of the concrete, and when acceleration is used in the

2. 995

10.340 no

process of this invention such shrinkage leads to improvement in

the flexural, tensile, and compressive strengths of the concrete.

For example, calcium chloride, when used as an additive

to accelerate the rate of cure, tends to improve the flexural ten-

sile and compressive strengths of the resulting product. In the

dry process of the invention, as well as in the prior art wet

process, the use of calcium chloride will increase the amount of shrinkage when curing. For example, the use of 3% calcium chloride

(by weight of water) increased the 28 day shrinkage by 45% for a mortar mixture of 25% cement (Permanente Type II) and 75% sand.

Fig. 18 illustrates that with increasing shrinkage, the compressive

strength increases significantly. Likewise, Fig. 19 illustrates

that with increasing shrinkage the flexural tensile strength

increases.

The fact that an increase in shrinkage produces an

increase in both tensile and compressive strength is consistent

with the theory of this invention as previously developed. Fig.

again shows an idealized Mohr envelope of failure. Due to

the shrinkage of the hydrating cement, a, represents the pre-

stress acting on the sand particles in contact due to this shrink-

age. The deviator stress (a2 a1) represents the compressive

strength and (0l o3) represents the tensile strength. When

calcium chloride is added o1 increases to 1' due to the

increase of shrinkage forces acting on the sand particles in

contact. As shown, the compressive strength shows an increase

2 995

10.3 4 Ono

C(02' oi') over the previous (02 01 Likewise, the tensile strength (o1 03') shows an increase over the previous (01 03). The theory predicts an increase in both compressive strength and tensile strength. The theory also predicts that the increase in compressive strength is greater than the increase

in tensile strength. Examination of Figs. 18 and 19 shows experi- mental verification of this theory.

Normal aggregates and cement may be used, and different component materials added when a particular property is desired to be changed and where the normal component materials do not contain that property. When high strength is desired in hydraulic concrete, the normal aggregates are capable of takinghigh compressive loads, and no other material is required. If tensile strengths higher than those achievable by improving the ordered structure are de- sired, new materials, such as epoxies, other resins, or fibres, may be added.

When light weight is desired, normal aggregate is repla- ced, at least in part, by other materials of similar size but lighter weight, such as foamed silica, foamed ceramic, phenolic microballons, foamed polystyrene, sawdust, or wood flour. Depend- ing on the structure created, the addition of this material is also useful for increasing shrinkage or reducing Young's modulus. Many sawdusts are sufficiently fibrous in nature and sufficiently light in density to make a

2.99

10.340 norm

good material for reducing weight or, because of the fibers, in-

creasing tensile strength.

Porosity may be reduced by using the dry-pour technique of this invention, and, through it, obtaining the most compact

mix. Further reduction in porosity is achievable by using mate-

rials, such as silica flour, with particle sizes in the order of less than one micron in diameter. This size of particle fits into the void spaces between the cement particles, and, so long as the quantity used does not reduce the water content in a dry-

pour below that needed for hydration, the porosity can be reduced below the 3.6% prosotiy that has been achieved without the use of this size particle. When it is desired to color the concrete, most pigments are of a similar size range, and they can therefore

also be used to reduce porosity.

When organic materials, such as sawdust, cotton linters, or hemp and sisal fibers ar-Csed, care must be taken that possible deleterious content of the organic material does not weaken the cement. A concrete containing organic material is probably best used in an interior application, since the wetting of the concrete

could accelerate the attack on the cement. The damage may be reduced by presoaking the organic material in a waterproofing material or in sodium silicate. The reaction of the lime content in the cement with the sodium silicate tends to petrify the organic material. Of additional advantage is the inherent low porosity

of the dry-pour process, significantly inhibiting the wetting of

452,995

10.34 Ono

the concrete.

The cement itself can be diluted with other particles without significantly reducing the strength. The choice of par-

ticles used is dependent on the structure to be formed. Thus,

where the structure requires the cement strata to bear uniaxial

compressive load, particles of the same size but of little strength

can be added so as to reduce residual preloading of the cement, and, because of this, gain sufficiently to make up for the reduc-

tion in cement. For purpose of economy, it may be desirable to

substitute a hard particle for some of the cement in order to preserve some of the properties best supplied by hard and unyielding

particles. For maximum efficiency of such a substitution, the particlepelected should be of the same order of size as the cement

particle and bond well to the cement. An example is ground lime-

stone which has not been fired in a kiln and is thus fully hydrated. Even in a structure where the cement bears compressive load, up to

percent of the cement particles may be replaced by fully hydrated ground limestone while retaining 80percent or more of the strength.

When a significant improvement in tensile strength is

desired, an epoxy resin or other glue may be added to the cement. When this has been tried in a wet mix, using a liquid form of

epoxy, the epoxy coated the cement particles and significantly inhibited the curing of the cement. The advantages of the greater

strengths similar to those achieved in the dry-pour process are not

then realized. According to the present invention a dry-pout with a

452.995

10.34 0 no

reduced cement content, so as to produce a porous concrete, could

be followed after curing by spraying the surface with a liquid

epoxy or other synthetic resin, preferably under pressure. This technique causes the resin to penetrate and produce high tensile

strength on the surface sprayed. Thus, in a normal beam, where a high tensile strength is required on only one surface, the opposite

surface being in compression and the center being close to the neutral axis, the quantity of the costly resin can be significantly reduced and the curing of the concrete left unimpaired while still

improving the tensile strength where improvement is needed. Another way of incorporating resins is by addition to the dry-pour

concrete mix of powdered dry resins or glues. These resins or glues could be water soluble or activated after curing of the

cement with some other solvent or activator.

By predetermining the appropriate structure, segregation due to differences in densities can significantly be reduced.

The basic mechanism is to hold the lighter particles down with

the weight of the heavier particles or in some cases with an ex-

ternal restraining force. Where there is a mixture of light and heavy particles within a given particle size range, a structure with the particles all approximately in contact, and where there

are approximately half of each density, the lighter particles

cannot rise without lifting the heavier particles enough to

spread them sufficiently apart for escape of the lighter parti- cles. Conversely, the heavier particles are equally restrained

from sinking.

2,9

10.34 Ono

Where the particles of one size range are all light- weight particles and the next larger particles are heavier, the heavier particles may be used to restrain the lighter, smaller particles. The spacing of the larger particles should again be such that they are approximately touching, and the size should be sufficiently larger so that the smaller, lighter particles fit within the void spaces between the larger particles. In this case, it is possible for the smaller particles to rise without spreading the heavier particles, but they cannot rise in a straight line; they would have to travel in a series of curved paths pro- vided by the void spaces between the larger particles.

The tendency of larger particles to segregate from smaller ones at the free surface under agitation is reduced in a wet mix, because the cement paste has a much greater apparent vis- cosity than the dry aerated cement powder. However, the floating to the surface of lighter particles just below the free surface is possible in a wet mix. This tendency to segregate increases as the mix gets wetter. Consequently, much better results with much less segregation can be achieved by using a dry-pour. In a dry-pour, the aerated mixture of cement and sand is sufficiently fluid so that with some vibration it can pour through a bed of large aggregate whose void spaces are large enough to permit the passage of the sand particles. Therefore, in the case where the largest aggregate is of very low density, another mechanism is preferably employed to prevent segregation. The mold can be filled with the largest size aggregate and that compacted and re-

10.340 no

strained from any upward movement by a screen across the top of the mold. The cement and sand mixture under vibration can then pour down into the mold flowing through the opening in the screen

and the void spaces in the aggregate.

Example 5: To show the manner in which lightness in weight may be effected and yet improve the flexural capability by a novel

method of prestressing, and to show another means of achieving lightness in weight and comparing strength to weight ratios.

All the beams described in this example have a gross cross-section of 3 1/8" x 3 1/8" and a length of 32 Each of them is placed on simple supports 30 inches apart, as shown in

diagrammatic manner in Fig. 10, load P placed at the midpoint of

the span. There is no reinforcement for the beam.

Beam 1 was made in square solid uniform cross-section o 3 1/8" on each side and wasmade from Mixture L, as follows:

Type I cement 34.5 pounds 16 mesh sand 26.5 pounds mesh sand 26.5 pounds mesh sand 26.5 pounds

Calcium chloride, 5% by weight of the water used when t dry mix was set by capillary action. On test, as per Fig. 10, th flexural stress at failure was 1,080 psi. The Unit weight of Beam 1 was 145 lbs./cu.ft., and its Strength-to-weight ratio was

7.45.

452. 995

10.3 40 no

Beam 2 was made from two different materials, Mixtures L and M, its cross-section being shown in Fig. 11. Mixture L was the same as was used for Beam 1. Mixture M was as follows: Type III cement 15.0 pounds Phenolic microbaloons 15 ounces Polystyrene expanded

pellets (Sp. Gr. 0.039) 2 ounces

The beam 2, when tested had the following qualities: Flexural stress at failure 1,310 psi Unit weight of beam 103 lbs./cu.ft. Strength-to-weight ratio 12.7

Beam 3 was solid, like Beam 1, but was made from the following Mixture N;

Type I cement/phenolic microballoons

(60/40 volumetric proportions 0.334 cubic feet) 16 mesh sand 26.5 pounds mesh sand 26.5 pounds mesh sand 26.5 pounds Calcium chloride, 5% of water by weight

For Beam 3 the test results gave the following results:

Flexural stress at failure 720 psi Unit weight of beam 119 lbs./cu.ft. Strength-to-weight ratio 6.05

2. 995

10.3 4 Ono

The above beams will serve to illustrate that by mobiliz ing and controlling shrinkage effects, prestressing of composite

sections of different materials can be effected. The advantage of the shrinking middle section is to provide the prestressing force which occurs so as to equilibrate the restraint to shrinkage. Thi is in addition to the advantage of lightness in weight of the resulting composite section. Some stress relaxation of the stres- sed middle core is to be expected in this case and hence some loss

of prestress. Shrinking cores with a minimum of stress relaxation can be designed with more competent sectional cores; a non- lightweight core section.

Using the dry-pour technique, it is possible to gain significantly better form or mold definition. As-cast surfaces can be produced in an almost polished condition, reproducing the surface of the mold to within a few times the diameter of the ce-

ment particle, which is of the order of 20 microns. Thus, on a production line, using photographic techniques, the mold surface

may be made to have raised surfaces for one shade of color and depressed surfaces for another shade. The piece having been cast and cured with one color of pigmentation may then have its de- pressed areas filled or partially filled with a concrete of another pigmentation and, because of low shrinkage, the different-

ly pigmented concretes may be bonded together. Hence, a realistic imitation grained wood surface or marble surface, or the effect

of a brick veneer may be produced. Artistic designs may be duplicated.

2,995

10.34 Ono

It is also possible to use to advantage centrifugal

casting techniques and this, particularly combined with techniques

for improving tensile strength, can lead to the production of

pipe, competitive not only with normal concrete pipe but also with cast iron pipe in the larger dimensions. However, capillary

action will still tend to cause water distribution.

For the same reasons that chemical accelerators are used

in the usual wet-pour mix, these accelerators can be used in the

dry-pour mix. These reasons include, but are not limited to:

enabling earlier removal of forms, shortening the curing period,

advancing the time when a structure can be placed in service,

offsetting the retarding effects of low temperatures, and compen- sating for the retarding effects of some other admixture. These

accelerators can be used to greater advantage in the dry-pour mix

than in the prior art wet-pour mix. In a wet-pour mix, there must

be little or nor delay in casting the concrete, or else early

stiffening or loss of slump will occur and the concrete will be- come unworkable. In the dry-pour concrete no such disadvantage

occurs, for the material is placed and compacted prior to the

introduction of water with the chemical accelerator in solution.

Evidence of the effectiveness of chemical accelerators is given in the following example:

Example 6: Mixture O was made as follows:

Type I cement 34.5 pounds

16 mesh sand 26.5 pounds

2 995

34 Ono

mesh sand 26.5 pounds mesh sand 26.5 pounds Calcium Chloride as indicated in Fig. 12

The cure was for two days at 100% humidity at 140°F and for one day drying at 140°F.

The compressive strengths (28 day) of Mixture O are plotted in Fig. 12 against varying proportions of calcium chloride in the water which was added by capillary action, according to this invention.

Mixture P had the same proportions as Mixture O.but was cured for six days at 100% humidity at 70°F and then for one day, drying at 140 F.

The results shown in Fig. 12 indicate the effectiveness of using a chemical accelerator such as calcium chloride. The results also indicate that approximately 5% to 6% of calcium chlo- ride (by weight of water) seems to be most effective for this mix.

It is hypothetical that the use of a chemical accelerator is most beneficial when the cement used is not fresh. A hydrated film of calcium carbonate is assumed to have formed as a shell about each particlebf cement, thereby inhibiting the action of the cement until the shell is broken by the expanding cement in the initial process of hydration. The older the cement, the more com-

452.995

10.34 Omno

petent the hydrated shell. This shell can be broken by mechanical action by the physical act of compaction or by reaching the reso-

nant frequency of the shell by vibration. The shell of calcium carbonate, which acts as a film surrounding the cement particle, may be broken by chemical means, the chemical additive being called

the accelerator. For example, if calcium chloride is added in solution, the calcium ion and the chlorine ion separate--the calcium

ion being used in the hydration process of the cement. The free chlorine ion finds a free hydrogen ion, and hydrochloric acid is

formed. This hydrochloric acid attacks the calcium carbonate shell, under which action the calcium and chlorine combine to form calcium

chloride as one product, and the cycle starts all over again. This way, by destroying the calcium carbonate shell, the process allows

for more rapid hydration of the cement and results in less reduction

in strength where an old or partially hydrated cement is used.

Example 7: To show that rapid curing attends the use of calcium chloride.

Mixture Q was made from 1 part cement, 2.3 parts sand,

as follows:

Type 1 cement 34.5 pounds 16 mesh sand 26.5 pounds mesh sand 26.5 pounds mesh sand 26.5 pounds

2. 995

34 Ono

One sample was made without calcium chloride and had a compressive strength (28 day) of 9,900 psi.

Another sample was made with 3% calcium chloride (by weight of water) and was cured at 70°F ambient temperature.

after 22 hours, its compressive strength was 2,170 psi

after 49 hours, its compressive strength was 4,500 psi

after 13 days, its compressive strength was 8,750 psi

It is unnecessary to add water admixtures, as it often is required in the usual prior art wet process, for the following

purposes; to improve workability, to reduce the water required, to cause dispersion of cement particles when mixed with water, to re- tard setting, to reduce or offset shrinkage during setting and hardening, and to reduce bleeding. The use of admixtures in the wet process is sometimes expensive and very often is coupled with a reduction of strength in the final product.

64 452 995

Claims (1)

10.34017o THlE CLAIMS DEFINING TIM INVL.NTION ARE AS FOLLOWS:

1. A method of forming a concrete structure

comprisin- dry mixing graded aggregate with a material

being hydraulic cement or a mixture of hydraulic cement

and other particles having a size of the same order of

magnitude as the cement particles, the quantity of cement

in said mixture being such that in the structure produced

by the method the cement will bind together said other

particles in spaces between the particles of said aggregate,

the volume of said material being such that after compaction

the volume would be not sbt nt-1--11-greater than the void

space that would occur in the dry aggregate after compaction

and not so much less than said void space that ineffective

bonding and excessive void space remains, filling a mold

with the resultant dry mixture, compacting the dry mixture in the mold to an extent such that particles of said aggregate

bear on one another, adding water such that the water is

distributed by seeping into the compacted mixture, thereby

ejecting air into the atmosphere, and curing the resultant

wet compact mixture in the mold to produce said structure,

the method being carried out such that particles of the

aggregate'bear directly on adjacent particles in the cured concrete structure, the cement acting to bond the particles

to one another.

2. The method of claim 1 wherein the aggregate is f'ine

aggregate and additionally graded coarse aggregate is dry

mixed, the dry compacted volume of the fine aggMrcgate being

approximately equal to and no less than the volume of the

voids in the dry coarse aggregate when dry and compacted.

2, 9

10.340 n 3. The method of claim 1 or 2 wherein said material

in a dry compacted state approaches its densest possible

state.

4. The method of any one of claims 1 to 3 wherein one

component of said aggregate is much lighter in weight

than another component thereof and the lighter-weight

component is small enough in particle size relative to

the particle size of said other component so that the

forces of apparent viscous drag in the fluid-like dry mixture exceed the apparent buoyancy forces in the dry

mixture.

The method of any one of claims 1 to 3 wherein one component of said aggregate is much lighter in weight than

another component thereof and the size and quantity of the

lightweight component are such that it can fit completely

within the void spaces of said other component, the quantity

and proportion of said other component being such that the

particles thereof touch each other in the completed mix. 6. The method of any one of claims 1 to 5 wherein the

water is added internally of said dry mixture and sweeps

the air outwardly.

7. The method of any one of claims 1 to 5 wherein the

water is added to one face only and sweeps the air out

principally through the opposite face. 8. The method of claim 7 wherein the water is added

to the bottom of the mold, along watercourses provided by

the mold.

452. 995

340 no 9. The method of claim 7 wherein the water is

added on a top surface, the step of adding water being

preceded by covering the top surface with a layer of

sand, to hold said top surface in place while the water

is added.

The method of any one of claims 1 to 9 wherein the

cure is accelerated, thereby increasing compressive and

flexural tensile strength of the finished concrete.

11. The method of claim 10 wherein the acceleration

is accomplished by adding calcium chloride to said water

before distributing it.

12. The method of any one of claims 1 to 11 wherein

the aggregate particles are generally angular in shape

rather than well rounded.

13. The method of claim 6 wherein the water is

added through perforated conduits inside the mold and

surrounded by the compacted dry mix.

14. The method of claim 13 wherein said conduits are directly surrounded by sand separating them from the

compacted dry mix.

The method of claim 13 wherein said conduits comprise BX cable.

16. The method of any one of claims 1 to 5 wherein

the water is added to the top surface, slowly at a rate

slow enough to prevent water entrapment of the air in

the mixture's voids.

17. The method of claim 16 wherein the top surface

is recomposed after the water is added.

2, 995

10.34 0no 18. The method of claim 17 wherein the recomposition

is done by troweling.

19. Concrete comprising

a cured compacted mixture of graded fine

aggregate, and a material being i e Yecement or a mixture

of hydraulic cement and other particles having a size of

the same order of magnitude as the cement particles, the

quantity of cement in said mixture being such that said other

particles are bound together in spaces between the particles

of said aggregate, the volume of said material being such

that in the dry compacted state the volume would be no

greater than the amount of void space in the compacted fine

aggregate and not so much less than said void space that ineffective bonding and excessive void space remains, said

cement being located almost entirely in the voids between

the fine aggregate particles so that aggregate particles

bear directly on other aggregate particles.

Concrete as claimed in claim 19 wherein the

aggregate particles are generally angular in shape rather than well rounded.

21. Concrete as claimed in claim 19 or 20 wherein the

amount of cement in a dry compacted state approaches its

densest possible state.

22. Concrete comprising a cured compacted mixture of

graded fine and coarse aggregates with a material being

lrto cement or a mixture of hydraulic cement and other

particles having a size of the same order of magnitude as

2, 995

10.3 4 Ono the cement particles, the quantity of cement in said

mixture being such that said other particles are bound

together in spaces between the particles of said aggregate,

the volume of said material being such that in the dry no compacted state the volume would be ntsubstantially

greater than the amount of void space in the compacted

fine aggregate and not so much less than said void space

that ineffective bonding and excessive void space remains,

said cement being located almost entirely in the voids

between the fine aggregate particles so that fine

aggregate particles bear directly on other fine aggregate

particles and the combined volume of said fine

aggregate and said material being no less than the volume

of the void space that would lie between the particles

of said coarse aggregate were said coarse aggregate

compacted by itself.

23. A lightweight concrete according to claim 19

wherein said aggregate includes a first component and

a second component which is of much lower density and is

smaller in particle size than said first component to

such an extent that the forces of apparent viscous

drag in the fluid-like dry mixture of cement and aggregate

from which said concrete is made exceed the apparent

buoyancy forces in the dry mixture so that said dry

mixture remains geometrically stable and is constrained

when water is infused to convert said dry mixture to said

concrete.

69. 452, 995

10.34 Ono

24. A lightweight concrete as claimed in claim 23,

wherein the size and quantity of the lightweight component

are such that as a consequence of proper compaction, it

fits completely and for all time is constrained within the

void spaces of said other component, the quantity and

proportion of said other component being such that the

particles thereof touch each other in the completed mix. Concrete as claimed in any one of claims 22 to

24, and containing a cure accelerator.

26. Concrete as claimed in claim 25 wherein said cure

accelerator is calcium chloride.

27. Concrete as claimed in claim 23 or 24 wherein said

lighter-weight component consists of material chosen from

the group consisting of foamed silica, foamed ceramics,

foamed polystyrene, phenolic microballoons, sawdust and

wood flour.

45 2. 995

10.340no

28. Concrete as claimed in any one of claims 19 to 22,

wherein said material is a mixture of cement and other

particles in the order of less than one micron in

diameter, said other particles fitting within the voids

between the particles of said cement, thereby reducing

the porosity of the concrete.

29. Concrete as claimed in any one of claims 19 to 28,

wherein the volume of said material or cement is approximately

equal to and not greater than the volume of void space of

the aggregates when compacted.

DATED this 13th day of AUGUST, 1974

LESTER H. GABRIEL and WILFRED ERNEST WILLIS By their Patent Attorneys:

GRIFFITH, HASSEL FRAZER Fellows Institute of Patent Attorneys of Australia.

71 452995

10.3 4 0Ono

SURCHARGE LOADING

CONSTRAINING CYLINDER

FIG-] COLUMN OF SAND COMPACTED TO ITS MOST DENSE ARRAY

PLATFORM

MOHIR ENVELOPE SHEAR STRESS FI G-2 NORMAL STRESS

sc SHEAR MOUR ENVELOPE STRESS FIG-...3 ff2 I0't' NOMLSTRESS

NORMAL STRESS

452, 995

.10.340m

STRUCTURALLY WEAK PARTICLES

STRUCTURALLY STRONG PARTICLES

FIB BALANCED PARTICLE LOADING DUE TO PROPER CHOICE OF COMPACTION AND NUMBER OF STRUCTURALLY WEAK PARTICLES DISTRIBUTED COMPRESSIVE LOAD

STRUCTURALLY WEAK PARTICLES

PARTICLES

O FIG_6 SOMPRESSVE j 'COMPONET -UNBALANCED PARTICLE LOADING DUE TO IMPROPER AMOUNT OF SHEAR COMPACTION COMPONENT FIG..6MATO

STRUCTURALLY STRONG PARTICLES

(FGFIG_7 FIG_7a UNBALANCED PARTICLE LOADING DUE TO INCLUSION OF TOO FEW STRUCTURALLY WEAK PARTICLES

452. 995

10.3 4 0no

-DENSEST POSSIBLE ARRANGEMENT (SG= 10,00 LOOSEST POSSIBLE 10,000 ARRANGEMENT 1.40)

§ceJ 5.000 FIG-8

3435 40 44 VOIDS IN COMPACTED SAND AGGREGATE uimr-LI.I L rlLLED WITH COMPACTED CEMEN1r 4000 3'jv z2 3000 MATERIAL L i( cD 2000 ;c a: MATER IAL M ooo FIG. .11 8 0 100 50 o F IG-9 CEMENT INCEMENT-MICROBALLOON MIX 9000

S 8000 MIXTURE P z 7000 m 6000 5000 S*ooo 4000 MIXTURE 0

3000 I 2000 1000 0 0 I 2 3 .4 5 6 7 8 9 CALCIUM CHLORIDE (BY WEIGHT OF WATER) P ,aM FIG-12

2, 995

10.3 4 no

12.000 II

I a. ii SCOMPRESSIVE STRENG1U1 S VS DAYS MOIST CURE w S4,000 I-7+ SACK MIX BEAR RIV. A(GG.e CL .1-8+SACK MIX-BEAR RIV. AGG. 0 0. 7 14 21 28 8 o I I 1I I I I I I I I I S 10 20 30 40 50 60 DAYS MOIST CURE (FOG)

FIG-13 1500

I U

O 1000 -a .EXURAL STRENGTH

V/ u a

VS I- ii) DAYS MOIST CURE

-J 500 I SACK MIX -HEALDSBURG AGG.B

x 8+ SACK MIX BEAR RIV. AGG. 0 w 7 14 21 28 J I I I I 0 I I I I c 10 20 30 40 DAYS MOIST CURE (FOG) FIG-14

2, 995

10.3 4 0no

16,000 FIG_16 15,000

14,000

13,000 '1 I I I I I 24 25 26 27 28 29 30 31 ANGLE OF THE MQHR ENVELOPE (DEGREES)

12,000

COMPRESSIVE STRENGTH 10,000 VS WATER/CEMENT RATIO

8,000 SI- 28 DAY a H- 7 DAY 0

6,000

I I I I I I I 2 3 4 5 6 7 8 WATER CEMENT RATIO GALS/SACK

FIG-17

8t 452. 995

10.34 0 no

o w FIG-18 -,w

Ir §1i§L w00 2 z o o I I 0 20 40 INCREASE IN SHRINKAGE USING 3 BY WT. OF WATER) CALCIUM CHLORIDE TO ACCELERATE CURE

4. ws 40 cs cow w 7 Z 0 FIG-19 WI--- 20 Z

OltW 0 20 40 INCREASE IN SHRINKAGE USING 3 BY WT. OF WATER) CALCIUM CHLORIDE TO ACCELERATE CURE

T SHEAR STRESS

\I 'Tn NORMAL STRESS

452, 995