CS269363B1 - A method of preparing a concrete mixture with a low water coefficient based on gypsum-free Portland cement - Google Patents

Abstract

A method for preparing a concrete mixture with a low water coefficient based on gypsum-free Portland cement is solved for cases of using the mixture, especially in "prepakt" technologies. The essence of the proposed method consists in pouring the slurry or mortar into aggregate containing at least 1 to 3% by weight of moisture, preferably moistened before preparing the mixture, and this aggregate has a minimum grain size of 8 mm when pouring with mortar or 4 mm when pouring with slurry.

Description

The invention relates to a process for the preparation of a concrete mixture with a low water content based on gypsum-free Portland cement, which achieves high initial and long-term strengths.

The basic prerequisite for achieving high concrete strengths is the preparation of a mixture with a low ratio of water to cement. The effort of research work in the field of special and common concretes is therefore to find a way to reduce the value of the water coefficient, below the value w = 0.35 without loss of workability. For the preparation of concretes with a low water coefficient, gypsum-free Portland cements are suitable, which can be processed at a very low water coefficient w = 0.20. The properties of these BS cements, respectively the possibility of preparing concretes from these cements, have been described in US 3,689,294, US 4,168,985, US 4,551,176 and in MS. Author's Certificate No. 253,499. Even in the preparation of BS cements, the preparation of concretes with a water content below 0.28 to 0.26 is not an easy matter. One of the possibilities of using the excellent Theological properties of BS cements is the preparation of concrete mixtures in a separate way. With this technology, for example, coarse aggregate is first placed in the formwork or space for concreting, which is poured with a special mortar or slurry after possible compaction. Pouring can be supported by vibration or pressure injection of mortar or slurry into pre-stored aggregate. This technology is used in a number of special concrete works, for example in road construction or in the preparation of piles. The advantage of this separate concreting - also called a prepact - is, as Jílek and Novák: Betonové stavitelství I, 1986 state, in that the coarse aggregate does not pass through the mixer. The mixer is then protected from intense wear and coarse aggregate from increased bruising.

The use of prepact technology with conventional Portland cement faces a number of disadvantages. First of all, it is necessary to ensure a high fluidity of the mortar or slurry, which must penetrate between the coarse aggregate. This high flowability of the mortar or slurry can be ensured by increasing the cement content in the mixture up to 700 kg / nP of the concrete mixture, then by using plasticizing additives or by increasing the water coefficient above 0.50. With this technology, it is often necessary to use activation mixers to overcome the negative effect of the high water content of the mixture. Another condition for success in prepakt technology is the use of aggregates with large grains.

The above-mentioned drawbacks are eliminated by the process for the preparation of a concrete mixture with a low water coefficient based on gypsum-free Portland cement according to the invention. First, a slurry with a water content w <0.30 is prepared or a mortar sw <0.35 is prepared, the ratio of ground clinker to fine aggregate being 1: 0.30 to 1: 2.7 by weight, and then the slurry or mortar is it is poured or conveyed under pressure, possibly under vibration, into a layer of crushed or mined aggregate. The essence consists in that the slurry or mortar is poured into an aggregate containing at least 1 to 3% by weight of moisture, preferably moistened before preparing the mixture, this aggregate having a minimum grain size of 8 mm when pouring the mortar or 4 mm when pouring the slurry.

A necessary condition for carrying out this technology with mortar or slurry made of BS cements is therefore the prevention of undesired suction of water from the mortar or slurry with aggregate. It is therefore necessary to use wet aggregate during preparation, or to moisten the aggregate before preparing the mixture. Such aggregate allows a smooth passage of mortar or slurry of BS cements. An advantage of the process according to the invention is also the fact that, in contrast to the previous restrictions on the size of coarse aggregate - when using Portland cement - coarse aggregate mined and crushed from size 4 mm for slurry and from size 8 mm for mortars can be used. The importance of the water contained in the wet aggregate lies in the fact that it can serve as an additional source of water for hydration and allows to achieve a high degree of hydration in the matrix, which consists of cement stone and a low water coefficient. It is also an advantage that when pouring a layer of coarse aggregate with a highly liquid mortar or slurry of BS cements

CS 269363 B1 with a low water coefficient - often in the range w = 0.23 - 0.27 according to the invention all gaps between the aggregates are fully filled, even on the underside of the part without the occurrence of clumps of unconnected aggregates. The simultaneous use of vibration is advantageous. In this way, high-grade concrete with a low water content can be prepared without the use of special mixers, even with a low BS cement content in the mix. In this case, simple mixers can be used to prepare the mortar. The process according to the invention eliminates the difficulties caused by the necessary regulation of the onset of setting of concrete mixtures from BS cements, or the consequences of measuring larger volumes of concrete mixtures from BS cements to shorten the onset of setting. The process according to the invention furthermore makes it possible to prepare a concrete mix with aggregate, the properties of which are distributed according to the depth of the concrete mix, where, for example, the top layer may contain a highly abrasion-resistant filler. According to the method of the invention, it is furthermore possible to use a different dose of cement according to the profile of the concrete mixture. It is also possible to prepare fibrous reinforcement parts in this way. Another possibility is to use a highly liquid slurry with fly ash, for example when creating piles where access with vibrators is difficult.

The invention is illustrated by the following examples, which do not limit the invention in any way.

Example 1

BS cement was prepared from clinker from the Štramberk cement plant by grinding to a specific surface area of 502 m ² / kg with the addition of 0.1% by weight of ethylene glycol clinker. From this BS cement, a low-dose cement was prepared with the advantage that can be used for precast units and technology using separate concreting. The preparation of the concrete mixture took place in two stages. In the first phase, a mortar was prepared in the ratio cement: sand = 1: 2, l, when this mortar contained 1% Νβ2θθβ - mass. BS of cement - and 0.92% by weight of NagCO 2 sand and further 0.75% by weight. BS of sodium-ferrous polyphenolate cement, 3 wt. BS of SiOg fly ash from Mníšek and 0.01 wt. BS of ethyl silicate cement 40. The water coefficient of the mortar was 0.27. Sand from the locality Káznějov fraction · 0.5 to 4 mm was used as a filler for mortar. The consistency of this mortar was very plastic to liquid. In the second phase, coarse aggregate was prepared from the Rejta locality - granular grains of leaf character - 80% of grains with unsatisfactory shape index of fraction 8 to 16 mm with sub-sieve 15.3 with over-sieve 8.7.

The procedure for preparing the concrete mix was as follows. A layer of coarse aggregate up to a height of 6 to 7.5 cm, dosed by weight, was loosely poured into a mold measuring 150,150,150 mm. The aggregate was used in two treatments: a / in the dry state, b / moistened. An aliquot of mortar was poured onto the aggregate layer and vibrated at a frequency of 50 Hz on a vibrating table. After about 15 seconds, the mortar filled the space between the grains of the coarse fraction and the resulting concrete mixture behaved as a composite prepared in the usual way. Another layer was added to this layer until the mold was completely filled. The total vibration time ranged from 35 to 55 seconds. The total dose of cement was 284 kg / m 2. The bulk density was determined on the prepared bodies, the standard deviation of which was around 4%. The results of cubic strengths are given in the following table. The bodies were treated for 24 hours under a damp cloth and for 2 to 28 days in an environment with a relative weight of 55 to 75% at a temperature of 20 + 3 ° C.

Table 1 Compressive strength Cement dose per m ^ Consistency Mass. kg / m 3 . Aggregate treatment / MPa / 24 hours 2 days 22 28 284 ♦ / 1 800 ,, + / dry / 14 - - - 284 very soft to soft 2 390 wet 24 40 57 75

CS 269363 Bl 3 + / When using dry crushed aggregate, the mixing water was sucked out during pouring and vibration. The concrete mixture had a low bulk density and inside the body there were clumps of coarse aggregate not connected by a bonding mortar.

Example 2.

In a control experiment with the same composition as in Example 1, a gradient mixer was used. A mixture of the same composition as in Example 1 had a very solid to solid consistency. This mixture was very difficult to thicken, both when using dry and wet aggregates. '

Example 3

BS cement was prepared from clinker from the Štramberk cement plant by grinding with additives of

0.03% by weight of Abeson TEA clinker with a specific surface area of 430 m / kg. Concrete suitable for prefabrication and separate concreting was prepared from this cement as in Example 1. In contrast to Example 1, the cement dosage and the aggregate used were cast. Cement mortar was prepared in a mixing ratio of 1: 1.6, where the additives were dosed as follows: 1 wt.

BS of Na 2 CO 2 cement and 0.15% by weight, NagCO 3 aggregates, 0.75% by weight. BS of Bodno-ferrous polyphenolate cement, 3 wt. B3 of SiO 2 fly ash from Mníšek to 0.01 wt. BS of ethyl silicate cement 40. The water coefficient of the mortar was 0.26. Sand from the Halámky locality with a fraction of 0.5 to 4 mm was used as fine aggregate. The consistency of the prepared mortar was very plastic to liquid. Mined aggregate from the Petržalka locality - crushed pebbles - fractions 8 to 16, sharply sorted with a gap of 32%, determined by infusion, was used as coarse aggregate. Coarse aggregate was used in two variants a / heavily moistened on the surface b / moistened. The results of the cubic strengths are in the following table, where the bearing was the same as in Example 1.

Table 2

Order weight kg / m ^-3 batch of cement aggregates strength in 24 hours pressure 3 days / MPa 28 days 2 430 342 kgm ^-3 wet 31.1 48 78 2 397 342 strong wet 34.1 55 60

Example 4

The control experiment showed that in order to achieve the same cubic strength of concrete after 28 days, ie about 75 MPa in pressure at the same composition, it is necessary to increase the cement dose by 50 to 80 kgm ^-3 using a conventional mixer due to workability of the mixture.

Example 5

BS cement was prepared from the clinker of the Štramberk cement plant by grinding to a specific surface of 450 m Ag with the addition of 0.05% Abeson TEA. A free-flowing slurry with a water content of 0.25 was prepared from this cement with the addition of 1% by weight, NajCO3 cement and 0.6% sulfonated polyphenolate. Aggregate was poured into a container measuring 20.20.10 cm and shaken loosely. The aggregate was used in both dry and wet conditions. A slurry was poured onto the aggregate layer, which flowed freely through the aggregate layer. The following table shows the onset of solidification of the entire mixture. In the case of the use of dry aggregate, cavities were formed which were not permeated by mortar.

CS 269363 Bl

Table 3

aggregates onset of solidification Vlineves 4 to 16 170 min Predonin 8 to 16 170 min Kneeling 16 to 22 125 min Vojkovice 6.3 to 8 mm 200 min Chžín 6.3 to 8 190 min Suchdol 6.3 to 8 190 min Dřenice 2.7 to 4 145 min the control experiment itself slurry 190 to 200 min

The process for preparing the concrete mixture according to the invention can be advantageously used in the construction industry, in particular in prepact technologies.

Claims (1)

OBJECT OF THE INVENTION Method of preparing a concrete mixture and a low water coefficient based on a non-gypsum Portland cement, ice is first prepared a slurry with a water coefficient w <0.30 or a mortar sw <0.35, the ratio of ground clinker to fine aggregate is 1: 0.3 up to 1: 2.7 wt. The slurry or mortar is then poured or conveyed under pressure or vibration to a layer of crushed or drawn aggregate, characterized in that the slurry or mortar is poured into an aggregate containing at least 1 to 3% by weight of moisture, preferably moistened prior to preparing the mixture. wherein this aggregate has a minimum grain size of 8 mm when pouring mortar or 4 mm when pouring slurry.