JPH0124740B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for delaying the dehydration and solidification speed of cast-in-place mortar piles, which is made by injecting mortar into a pile hole drilled underground and inserting reinforcing bars, shaped steel, etc. into the mortar. This type of pile is commonly used as foundation piles or column retaining walls. However, in ground with a high permeability coefficient such as sandy ground, the water in the mortar injected into the pile hole is absorbed into the surrounding ground, and as a result, the mortar dehydrates and solidifies, making it difficult to insert reinforcing bar cages or sections to a specified depth. There are many cases where this is not possible. Especially recently, as underground structures have become larger, it has become necessary to construct long piles.
Countermeasures against the above-mentioned large solidification phenomenon are required. Conventional countermeasures against dehydration and solidification include making the pile hole walls watertight, which is done by using an auger after the pile hole is excavated with an auger. In this conventional construction method, in addition to the work of excavating pile holes, injecting mortar, and inserting rebar cages, it is necessary to operate an auger to prevent dewatering before or while pouring mortar. Moreover, dewatering prevention treatment depends on the permeability coefficient of the ground, and the work required differs from place to place, requiring considerable skill, and further improvements are needed to create highly reliable mortar piles. has been done. The difficulty in working with the above-mentioned conventional means lies in the fact that the pile hole wall itself is artificially made impermeable. Therefore, in order to create mortar piles that are more workable, economical, and reliable than conventional methods, the injected mortar must have a slow dehydration and solidification rate and still maintain the required quality. This invention uses an admixture known as a fluidizing agent,
The purpose is to obtain a cast-in-place mortar pile that is used as an admixture to retard the rate of water dehydration in mortar, thereby increasing the water retention of the mortar and preventing dehydration and hardening due to water absorption in the surrounding ground. Furthermore, even if the ratio of water and cement material is reduced to 40% by adding an admixture, the flow value can be adjusted to allow pressure feeding with a normal pump, which is not possible with the commonly used "pump". The objective is to obtain a cast-in-place mortar pile that does not require particularly high material costs compared to "Pact Mortar" and has a strength greater than the design standard strength of mortar. The features of the present invention for the above-mentioned purpose include a binder made of cement with fly ash added, water and sand,
When a mortar consisting of an admixture is filled into a hole in the ground with a large permeability coefficient and a reinforcing steel material is inserted into the mortar to create a cast-in-place mortar pile, the weight ratio of the mortar mix described above is such that the amount of water and The ratio of the admixture and binder, whose main ingredient is polymeric aromatic hydrocarbon sulfonic acid, should be at least 40%.
There is a method for delaying the dehydration and solidification rate of cast-in-place mortar piles by retarding the dehydration and solidification rate of mortar by adding 0.6 to 1.0%. The mortar composition according to the present invention is based on various conditions such as the material cost being approximately the same as that of normal prepact mortar, the design standard strength of the mortar being CK=300Kg/ ^cm2 or more, and the possibility of pumping. It is necessary to do so. Table 1 below shows the test results of a conventional "prepacto mortar" and a mortar used in the present invention using an admixture containing a polymeric aromatic hydrocarbon sulfonic acid or a salt thereof. That is, Blend Example Nos. 1 to 13, 16, and 17 are mortar examples of the present invention, and Blend Examples 14 and 15 are conventional "prepact mortar" examples.

【table】

[Table] From the above blending examples and test kneading results, the flow value immediately after kneading becomes smaller as the water-to-cement ratio W/(C+F) increases and the sand binder ratio S/(C+F) increases. Considering the construction conditions on site, the mixing ratio is 0.6 ~
1.0 is most desirable. Next, the dehydration speed is quite slow compared to conventional prepact mortar, and the dehydration completion time is 2 minutes and 15 to 20 seconds for standard mortar, whereas Ad/(C+
F)=0.6%, regardless of W/(C+F), 4 minutes 45~
At 5 minutes 30 seconds and 0.8%, the time increases from 5 minutes 30 seconds to 10 minutes as W/(C+F) decreases. In other words
In a poured mortar containing an admixture with Ad/(C+F)=0.8%, the time for dehydration and solidification of the same amount of fresh mortar is delayed by about 2.5 to 4.5 times compared to a normal prepact mortar. From the above results, W/(C+F)=40~50%,
It was found that in the range of Ad/(C+F) = 0.6 to 1.0%, the higher the mixing ratio, the slower the mortar dehydration rate, the lower the flow value immediately after kneading, and the smaller the change in flow value thereafter. did. On the other hand, if the mixing ratio is large, Ad/(C+F)
= 1.0%, a separation phenomenon in which sand settles in a stationary mortar is observed, but such a phenomenon is not observed at 0.6% and 0.8%. From the above, if mortar separation is taken into account, the optimum positive miscibility of the admixture is Ad/(C+F)=0.8%. Next, the mortar was dehydrated and the dehydration rate was measured, and the results of comparing the dehydration properties with normal prepact mortar will be explained. Table 2 shows examples of mortar formulations used in this measurement, and several examples are extracted from Table 1. As a test device, a mortar pressurized dehydration test device developed by the present inventor (see Japanese Patent Publication No. 1709/1983) was used. This test device mainly consists of a pressure vessel in which a lid with an air supply pipe is airtightly attached to a bottomed tube. A rotary shaft with cutting blades at its tip that rotates horizontally on the virtual ground penetrates from the lid into the tubular body. In addition, the mortar dehydration speed is greatly affected by the mortar dehydration film with a thickness of approximately 3 cm that is formed around the earth auger as a result of pressurized dehydration during the construction of prepact mortar piles. After artificially creating a virtual ground and a 3 cm thick dehydration membrane in the interior and measuring their hydraulic conductivity, we poured the target flexible mortar onto the dehydration membrane and measured the dehydration solidification rate of this mortar. Measurements were made as dehydration rate. The above-mentioned measurement of the hydraulic conductivity involves the preparation of a hypothetical ground using standard sand, the measurement of the hydraulic conductivity of the virtual ground, the injection of mortar onto the virtual ground, the dehydration film formed by pressurizing the mortar and removing the excess mortar. Fabrication,
Measurement of the permeability coefficient of a dehydration membrane is carried out using the following procedure. For details of this procedure, please refer to the specific examples described in the above publication. Next, to measure the dehydration rate, the mortar placed on the dehydration membrane is pressurized for a certain period of time, and the water in the mortar passes through the dehydration membrane and dehydrates to the bottom of the tube, and then a weight is applied into the mortar from above the tube. This is done by penetrating the reinforcing bar. Penetration of the reinforcing bar was carried out at regular intervals, and the solidification rate of the mortar over time was measured from the penetration resistance (Pr=1 Kg/cm ² ) and the high retention amount of the reinforcing bar (4 Kg/cm ² ). This measurement result is shown in Figures 1 to 3.
As shown in the figure. Note that P in the figure is shown in FIGS. 1 to 3.
In addition, P in the figure is a pressurizing force.

[Table] As is clear from Figure 1, the amount of dewatered water changes over time for all formulations A, B, C, and S in Table 2. Naturally, the greater the pressurizing force, the greater the amount of dehydrated water. There is. Also, in formulations A, B, and C, formulation S
The amount of dehydration is extremely small, about 1/4 to 1/6 compared to the previous model. For example, if the pressurizing force P = 5 Kg/cm ² and the pressurizing time is 20 minutes, the amount of dehydration will be approximately 1200 cm ³ for formulations A and B,
For formulation S, the pressure was approximately 5000cm ³ , and the pressure P was 2Kg/cm ² .
When the pressurization time is 40 minutes, the amount of dehydration is approximately for formulations A and B.
600 cm ³ , and about 3650 cm ³ for formulation S, and the ratio of dewatering amount is about 1/4 and 1/6, respectively. Figures 2 and 3 show penetration resistance Pr = 1 and 4.
This shows the change over time in the dehydration layer thickness measured by the high retention amount of a reinforcing bar of Kg/cm ^2. According to this, the dehydration solidification layer thickness that occurs around the pile is
C is 1/4 to 1/15 of the formulation S, and as is clear from Figure 2, the time it takes to reach the dehydrated solidified layer thickness (6 cm) where it becomes difficult to penetrate the reinforcing bar is as follows. For S, which pressure force, P=2,
3 and 5 are also within 10 minutes, but formulation A,
For B and C, P=5 for 30 minutes, P=3 for 45-70 minutes, P
=2 has a delay of more than 100 minutes. Here, the pressurizing force P is the pressure difference between the weight of the mortar in the drilled hole and the groundwater pressure around the mortar pile, and this pressurizing force P acts on the mortar to dehydrate the mortar. Further, the larger the pressure P is, the faster the dehydrated and solidified layer is formed. In the range of normal pile lengths, this pressing force is P=2 to 5 (Kg/cm ² ). For this reason, in the formulations A, B, and C, there is more time to insert the reinforcing steel material than in the formulation S. Moreover, the time required to reach the same solidified layer thickness is 6 to 10 times longer. From this point of view, the injection mortar according to the present invention is
The resistance to dehydration is considerably superior to that of the above-mentioned ordinary prepact mortar, and this is thought to be due to the difference in the dispersion mechanism of cement particles between the two. In other words, in the case of intrusion aid, the admixture mainly consists of lignin sulfonate, which enhances the water reduction effect mainly through air entrainment, but it has almost no dispersion effect on cement. In this case, the surface charge of cement particles increases due to the adsorption effect of an admixture mainly composed of polymeric aromatic hydrocarbon sulfonic acid or its salt, such as naphthalene sulfonate, and the mutual repulsion between cement particles increases. Due to the dispersion and fluidization of cement particles.
Therefore, the dehydration solidified layer of mortar has a small clearance ratio, that is, a small hydraulic permeability coefficient, and the dehydration rate becomes slow. The effects of the present invention will be described below. The injection mortar has a slow dehydration solidification rate, excellent fluidity, and little change in flow value over time. Furthermore, if the flow value is 16 to 20 seconds, it is possible to construct cast-in-place mortar piles using a combination of existing construction equipment. Furthermore, judging from the pile body strength, the design standard strength of mortar with a water-cement ratio W/(C+F) = 45% is CK = 300Kg/cm ² (28 days old) and CK = 390.
Kg/cm ² (91 days old), water-cement ratio W/(C+F)
=40% 〓CK=385Kg/cm ² (wood age 28 days) and 〓
Approximately CK=500Kg/cm ² (wood age 91 days) can be secured.
In other words, by using this invention, a pile with a regular moment of resistance can be obtained by properly inserted reinforcing steel.

[Brief explanation of drawings]

The drawings show the test results of the prepact mortar used in this invention. Figure 1 shows the relationship between the amount of dehydration and pressurization time, and Figures 2 and 3 show the relationship between pressurization time and dehydrated solidified layer thickness. FIG.

Claims (1)

[Claims] 1. When creating a cast-in-place mortar pile by filling a hole in the ground with a high permeability coefficient with mortar consisting of a binder made of cement with fly ash added, water, sand, and an admixture, reinforcing steel is inserted. In terms of the weight ratio of the above mortar composition, the ratio of water to binder is 40% or more, and the ratio of admixture containing polymeric aromatic hydrocarbon sulfonic acid as the main ingredient to binder is 40% or more.
1. A method for delaying the dehydration and solidification rate of cast-in-place mortar piles, the method comprising delaying the dehydration and solidification rate of mortar by adding 0.6 to 1.0%.