JP7243982B2 - Concrete repair agent - Google Patents

Description

The present invention is a concrete for application, impregnation, injection, etc., for promoting the performance recovery of concrete that has been subjected to high-temperature heating due to fire or the like, or for modifying or repairing general concrete that has not been subjected to high-temperature heating. It relates to a restorative.

When concrete is heated to a high temperature due to a fire, etc., the cement hydration reaction products decompose and degrade, and uneven expansion and contraction occur between the cement paste and aggregates. Mechanical performance such as elastic modulus is degraded. Also, when calcium hydroxide decomposes at high temperatures, concrete loses its alkalinity. Furthermore, since cracks frequently occur on the surface of the concrete, the material penetration resistance is lowered, and carbon dioxide gas, oxygen, salt, water, and the like easily enter and diffuse into the concrete. As a result, the neutralization resistance of the concrete is lowered, and the reinforcing bars in the concrete are likely to rust.

On the other hand, the performance of concrete that has been subjected to high-temperature heating recovers over time through recuring, but it cannot recover to the level before high-temperature heating. Therefore, the Architectural Institute of Japan's "Fire damage diagnosis and repair/reinforcement method guidelines and explanations for buildings" recommends that the core strength is less than the design standard strength and the concrete of the severely deteriorated part where the width of the crack is several millimeters or more is removed and recast. , stipulates to repair cracks in concrete whose core strength is greater than or equal to the design standard strength.
However, recasting concrete takes time and effort. In addition, cracks of 0.2 mm or more can be repaired with epoxy resin or polymer cement, but it is difficult to repair fine cracks of less than 0.2 mm and fine damage, so large cracks should be repaired. Also, the performance of the concrete is inferior to that before it is subjected to high temperature heating.

Therefore, it has long been desired to develop techniques for repairing concrete that has been subjected to high-temperature heating. Methods have been proposed to restore the performance of subjected concrete.
However, since this performance recovery agent does not sufficiently penetrate into the interior of concrete, there is a demand for a more excellent performance recovery promoter and repair agent. In addition, repairing agents such as excellent modifiers and performance recovery agents are also required for ordinary concrete that has not been subjected to high-temperature heating.

Lee Ju-guk, Lee Kyung-tao: Research on Performance Recovery of Concrete Heated to High Temperature, Structural Transactions of Architectural Institute of Japan, Vol. 76, No. 666, 2011, pp. 1375-1382

The problem to be solved by the present invention is to provide a concrete repair agent for application, impregnation, injection, etc., which has excellent permeability into the interior of concrete and restores or improves the performance of the concrete.

In order to solve this problem, the present inventors conducted various tests and found that a mixed aqueous solution of silicates and alkali metal hydroxides has a high ability to penetrate into the interior of concrete. It was confirmed that it is possible to restore the performance of concrete that has been deteriorated by being heated to high temperatures and general concrete that has not been heated to high temperatures.

That is, one aspect of the present invention provides a concrete repairing agent comprising an aqueous solution containing a silicate and an alkali metal hydroxide .
In addition, the term "repair agent" as used in the present invention is a concept that includes performance recovery promoters and modifiers.

The repairing agent of the present invention has high permeability into the interior of concrete, and can re-react cement hydration reaction products decomposed at high temperatures to repair minute damage. Therefore, the coating, impregnation, or injection of this repair agent can restore the performance of concrete that has been heated to a high temperature. In addition, since the repairing agent of the present invention has high permeability into the interior of concrete, it is possible to improve the performance of general concrete that has not been heated to a high temperature.

The photograph which shows the state of the pressurization injection test of a repair agent. Graph showing the relationship between injection amount and injection time for each repair agent. Series no. 1 is a photograph showing the penetration depth of the concrete to be repaired in No. 1 to the prism specimen. Series no. 1 is a graph showing the results of strength recovery after injecting a repair agent into concrete to be repaired (normal strength) of No. 1; Series no. 2 is a graph showing the results of strength recovery after injecting a repair agent into the concrete to be repaired (high strength) of No. 2. FIG. Series no. 3 to No. 5 is a graph showing the results of strength recovery after the concrete to be repaired (normal strength) of No. 5 was immersed in the repair agent. Series no. 3 is a scanning electron microscope (SEM) photograph showing changes in the internal structure of the concrete to be repaired in No. 3 after being immersed in the repair agent.

The concrete repairing agent of the present invention (hereinafter also simply referred to as "repairing agent") contains silicates such as lithium silicate (Li ₂ O.nSiO ₂ , n=3 to 8) and one of alkali metal hydroxides. It consists of an aqueous solution containing a seed or two or more. As shown in the test results to be described later, this repair agent has a high ability to penetrate into the interior of concrete and exhibits an excellent performance recovery effect.

Alkali metal hydroxides typically include sodium hydroxide (NaOH) and potassium hydroxide (KOH).

In addition, from the viewpoint of fully exhibiting the effects of the present invention (permeability improvement effect and performance recovery effect), the molar ratio of silicates and alkali metal hydroxides is silicates:alkali metal hydroxide=0. .5 to 5.0:5.0, more preferably 0.5 to 3.0:5.0, more preferably 0.5 to 2.0:5.0 preferable.
Similarly, the total mass concentration of silicates and alkali metal hydroxides is preferably 5 to 80%, more preferably 5 to 20%, and more preferably 7 to 13%. preferable.

Furthermore, the repairing agent of the present invention includes other components (water-soluble substances) other than silicates and hydroxides of alkali metals, such as antirust agents for preventing corrosion of reinforcing reinforcing bars in concrete and alkaline bones of concrete. A chemical that prevents material reaction may be mixed. The repairing agent of the present invention mainly exerts the effect of making concrete denser, but by mixing other water-soluble substances such as those mentioned above, it also exerts the anti-corrosion effect of reinforcing bars and the effect of suppressing alkali-aggregate reaction. can do.

A repair agent was prepared by the following tests, and the permeability and utilization effect in the case of pressurized injection were evaluated.
1. Test Overview 1.1 Preparation and Heating of Concrete to be Repaired A cylindrical specimen of concrete to be repaired was prepared according to the formulation shown in Table 1. Series no. 1 and No. 2 are close to medium-strength concrete and high-strength concrete, respectively. Table 2 shows the materials used. A specimen having a size of 10 cm in diameter and 20 cm in height was cured in water at 20±3° C. for 28 days. After that, it was left in a room at 20±5° C. until heating. A compression test was performed immediately before and after heating to measure the compressive strength. Table 1 shows the compressive strength immediately before heating.
Before heating, a hole of 60 mm in depth and 10 mm in diameter was drilled in the center of the driving surface of the concrete specimen to be repaired. Next, the temperature was raised at a rate of 2 to 3° C./min, and the heating temperature was maintained for 5 hours after reaching the target temperature (450° C., 550° C., 650° C.). Although the core temperature of the concrete was not measured, it is considered that the core temperature of the concrete reached the target temperature because the rate of temperature increase was small and the target temperature was maintained for 5 hours.

1.2 Repair agent used A test for selecting a repair agent (hereinafter referred to as "selection test of repair agent") and a pressurized injection test to verify the effectiveness of repair agent (hereinafter referred to as "injection of repair agent"). Table 3 shows the raw material (raw material solution) of the repair agent used in the test.
The water glass aqueous solution (WG) is a mixture of JIS K 1408 No. 1 water glass and water at a volume ratio of 1:1.
The molarity of aqueous sodium hydroxide (NH) is 10M.
The liquid glass (S) is obtained by mixing the undiluted solution of the liquid glass and water at a volume ratio of 1:2. The composition of the liquid glass is a trade secret and unknown.
The molar ratio of lithium silicate (Li) is 7.5, the content of silica (SiO ₂ ) is 20-22% by mass, and the content of lithium oxide (LiO ₂ ) is 1.3-1.5% by mass. .
Sodium aluminate (AN) is a liquid product made from aluminum hydroxide and sodium hydroxide.

These raw materials (raw material solutions) were prepared and used for selection tests of repair agents. Table 4 shows the composition of the repair agents used in this selection test.

1.3 Injection Test Method of Repair Agent into Concrete A cylindrical specimen of concrete to be repaired (normal strength) of No. 1 was heated at 450°C. After that, using the injection equipment (packer and acrylic capsule, see the following reference) used for the ASR (alkali aggregate reaction) suppression method, the injection pressure was set to 0.5 MPa, and the four types of repair agents shown in Table 4 were used. was injected from the above-mentioned drilled part. Water was also injected for comparison.
Reference Kazunori Era: ASR Suppression Method Using Lithium Nitrite, Suppression of Alkali-Silica Reaction by Injection of Lithium Inside, Concrete Engineering, vol. 2, pp. 155-162, 2012

In the injection test of the repairing agent, the series No. 1 was heated at three temperature levels (450, 550, 650° C.) of the repairing agent (mixed aqueous solution of lithium silicate and sodium hydroxide) selected in the above selection test. 1 and No. 2 was injected at a pressure of 0.5 MPa into the cylindrical test piece of the concrete to be repaired. After that, mortar of the same formulation as the matrix mortar of each cylindrical test piece was kneaded to fill the drilled portion. Furthermore, 20±3° C., R.I. H. After curing for 28 days by leaving it in a 60% room, the compressive strength was measured according to JIS A 1108. Compressive strength was the average value of three specimens. In addition, in order to compare the effect of promoting performance recovery, water was poured into the cylindrical specimen of the concrete to be repaired at each heating temperature. Fig. 1 shows the appearance of the injection test of this repair agent.

2. 2. Test Results 2.1 Results of Repair Agent Selection Test FIG.
In about 140 minutes, 250 mL of water was injected and began to seep out onto the surface of the cylindrical specimen. As a result, series no. It was found that when the concrete to be repaired in No. 1 was heated to 450° C., the amount of liquid that could be injected into one cylindrical test piece was 250 mL. Moreover, as shown in FIG. 2, it was confirmed that the permeability of the repairing agent of "Li+NH+water" is higher than that of other repairing agents.

Moreover, the series No. heated at 450°C. The prismatic test piece of concrete to be repaired in 1 was divided into approximately three equal parts, and (a) 10M sodium hydroxide aqueous solution (NH), (b) lithium silicate (Li), and (c) "Li + NH + water" were repaired. It was immersed in the agent for 10 hours. A cross-sectional photograph after immersion is shown in FIG. As shown in the figure, the penetration depth was the smallest when immersed in lithium silicate (Li). On the other hand, the "Li+NH+water" repair agent was able to completely permeate the specimen.

Thus, it was confirmed that the repair agent of "Li + NH + water" has high permeability. I used a restorative.

2.2 Results of Repair Agent Injection Test Repair agents consisting of liquids A, B, and C as shown in Table 5 were prepared by changing the ratio of water in "Li + NH + water" suitable for pouring into heated concrete. That is, the ratio of water is A liquid < B liquid < C liquid.
Cylindrical test piece of concrete to be repaired (concrete test piece for effect verification) heated at 450°C, solution B and solution C, and cylindrical test piece of concrete to be repaired (concrete test piece for effect verification) heated at 550°C and 650°C (concrete test piece for effect verification) A solution and B solution were injected into the . Three cylindrical specimens were injected for each heating temperature level and liquid type.
Table 6 shows the molar ratio of lithium silicate and sodium hydroxide (lithium silicate:sodium hydroxide) and the total mass concentration of lithium silicate and alkali metal hydroxide in solutions A, B and C.

(1) Injection time As mentioned above, the cylindrical specimen (concrete specimen for effect verification) was completely wet, and 250 mL of water could be injected until the liquid oozed out to the surface. The injectability of liquids A, B, and C was considered. Tables 7 and 8 show the injection time of 250 ml of each solution.

As shown in these tables, the higher the heating temperature of the concrete specimen, the shorter the pouring time. In addition, although there was some variation, there was a tendency that the larger the proportion of water, the shorter the injection time. Furthermore, it was found that the higher the strength level before heating, the shorter the injection time when heating at 550° C. or less. That is, the time to complete injection depends on the concentration of the repair agent and the heating temperature and pre-heating strength of the concrete.

(2) Compressive strength Assuming that the compressive strength of the concrete specimen before heating is 100%, the residual compressive strength (%) of the concrete immediately after heating and after pressurized injection and recuring of the repair agent are shown in FIGS.
Series No. shown in FIG. In the case of the concrete to be repaired in No. 1, the compressive strength of the specimen heated at 450°C decreased to about 70% after heating, and the strength was recovered by injecting liquid B and liquid C. Especially in the case of liquid B, it recovered to about 90% of that before heating. The compressive strengths of the specimens heated at 550° C. and 650° C. decreased by 50% and 40%, respectively, after heating. However, by injecting liquid A, the strength recovered to about 80% and 70% of that before heating, respectively.

On the other hand, the series No. shown in FIG. In the case of the concrete to be repaired in 2, the compressive strength of the specimen heated at 450° C. decreased to about 50% immediately after heating, and recovered to about 85% before heating by injecting liquid B. The compressive strengths of the specimens heated at 550° C. and 650° C. decreased to about 38% and 28%, respectively, immediately after heating. However, by injecting the B liquid, the strength recovered to about 90% and 70% of that before heating, respectively.
It should be noted that, for any of the specimens, no promotion of recovery of strength was observed due to the injection of water.

The following test was used to evaluate the permeability and utilization effect of immersing (impregnating) concrete in the repair agent.
1. 1. Outline of Experiment 1.1 Composition of Repairing Agent The aforementioned lithium silicate undiluted solution (Li), 10M sodium hydroxide aqueous solution (NH) and water were mixed in a volume ratio of 2:1:2. Here, it is called D liquid.

First, in order to confirm the penetration ability in the case of immersion, the series No. shown in Table 9 was tested for this repair agent (solution D). No pressure penetration test of the repairing agent (Liquid D) was conducted using normal strength concrete No. 4. Specifically, series No. 1 heated at 300°C. A concrete columnar specimen (10 cm in diameter) of No. 4 was immersed in D solution, and the specimen was split at intervals of 24 hours to confirm penetration to the center.

1.2 Preparation and Heating of Concrete to be Repaired 3 to No. 5 normal strength concrete. Formulations are as shown in Tables 9 and 10. Ordinary Portland cement and siliceous aggregates were used. A cylindrical specimen having a size of 100 mm in diameter and 200 mm in height was prepared, cured in water at 20±3° C. for 56 days, and then stored indoors. After that, the specimen was heated in a small electric furnace. The temperature was raised at a rate of 2-3° C./min, and the target temperature (300° C., 500° C., 650° C.) was maintained for 5 hours. After heating, it was naturally cooled in the air.

1.3 Repair after heating After charging the D solution into a container that can be sealed, series No. 3 to No. The specimen after heating in 5 was immersed for 7 days. After the immersion, the specimen was air-cured for 21 days in a room at a temperature of 20±2° C. and a relative humidity of 60±5%. The heating temperature is set according to the series No. 3 is 300° C.; 4 is 500° C., and No. 5 was set at 650°C.

1.4 Measurement before and after repair Compressive strength was measured before heating and after repair according to JIS A 1108:2018 (concrete compressive strength test method), and the compressive strength residual rate immediately after heating and after repair was calculated. Compressive strength was taken as the average value of three specimens. Further, the internal structure of the test piece immediately after heating at 500° C. and 650° C. and after repair by immersion was observed with a scanning electron microscope (SEM).

2. 2. Test Results 2.1 Compressive Strength Series No. 1 was heated at 300° C., 500° C., and 650° C. and immersed in a repair agent for 7 days. 3 to No. Fig. 6 shows the compressive strength before heating and after heating/repairing (immersion/curing) of No. 5 and the residual rate compared with the strength before heating. As shown in Fig. 6, the compressive strength after repair recovered to 93%, 87% and 86%, respectively. The repair effect of the repair agent was also confirmed in the case of immersion.

2.2 Changes in internal structure after repair Fig. 7 shows SEM (500x) photographs immediately after heating and after repair. Cracks and voids were observed in the specimen immediately after heating. Especially series no. 5 is a series No. 5 heated at 500°C. The cracks were larger than those of the specimen No. 4, and there were many voids. However, after the repair by immersion in the repair agent, it became dense. That is, series No. 1 heated at 500°C. Cracks and voids were hardly seen in the specimen No. 4, and series No. 4 heated at 650°C. The specimen No. 5 had less cracks and voids.

3. Investigation on the mechanism of high permeability of repair agents Silicate-based surface impregnation materials (aqueous solutions), which are mainly composed of lithium silicate, sodium silicate (water glass) or potassium silicate, have long been widely used for waterproofing and surface protection of concrete. It is This is because the dried solidified impregnant and the CSH gel, which is a reaction product of Ca(OH) ₂ produced by the hydration of the cement and the dried impregnant, fills the voids of the concrete to produce a modifying effect. However, since these conventional silicate-based surface impregnating materials can penetrate only up to several millimeters into the surface layer, their application range has been limited to modifying, waterproofing, and protecting the surface layer. The reason why the silicate-based surface impregnating material cannot penetrate deeply is that the impregnating material reacts with the hydration product Ca(OH) ₂ of cement to form a C—S—H gel, blocking the permeation pathway.

In order to elucidate the mechanism of the high permeability of the repair agent of the present invention, the viscosity of the repair agent was measured and the reactivity between the repair agent and Ca(OH) ₂ was experimentally confirmed.
Specifically, the viscosities of NH, Li, and WG of the raw material solutions shown in Table 3 were measured at 20°C. The results are shown in Table 11. In addition, the viscosities at 20° C. of liquid D and a mixture of WG and NH (WG+NH, volume ratio 1:1) used in the immersion experiment were also measured. The results are also shown in Table 11. It was confirmed that the viscosity of liquid D was the lowest.

If the viscosity of the lithium silicate aqueous solution is not affected by the addition of NH, the viscosity of solution D (Li: NH: water = 2: 1: 2) at 20 ° C. is 47.2 (viscosity of Li) × (2 /5) + 34.9 (viscosity of NH) x (1/5) + 1.00 (viscosity of water) x (2/5) = 26.3 mPa s, but the measured value (12.7 mPa ·s) is smaller than the calculated value (26.3 mPa·s). From this result, it can be seen that the addition of NH reduces the viscosity of the lithium silicate aqueous solution. This is presumed to be due to the addition of NH to make lithium silicate smaller molecules. On the other hand, the calculated value of the viscosity of the mixture of WG and NH (24.8 × (1/2) + 34.9 × (1/2) = 30.0 mPa s) is the measured value (31.0 mPa s) is almost the same as

Examination of reactivity between repair agent and Ca(OH) ₂ In the experiment, five types of alkaline solutions (Li, NH, WG, D solution, WG+NH) were used. The WG+NH solution is the same as in Table 11. 5 g of special grade reagent Ca(OH) ₂ (purity of 96.0% or more) was dissolved in 100 mL of alkaline solution. After one night, the liquid was filtered with filter paper (JIS3801 Type 5 A quantitative analysis filter paper), the filtered filter paper was dried at a temperature of 105°C, and the weight of the solid matter remaining on the filter paper was measured. Table 12 shows the measurement results.

The solids produced by mixing Ca(OH) ₂ with Li and WG, respectively, were believed to be reaction products of silicate ions and calcium, yielding 38.4 g and 80.7 g of solids, respectively. On the other hand, in the D solution in which NH was mixed with Li, the solid matter remaining on the filter paper decreased from 38.4 g to 12.9 g. Mixing WG and NH in a 1:1 volume ratio reduced the solids from 105.5 g to 41.1 g. Assuming that Ca(OH) ₂ and silicate ions do not react and are calculated by volume ratio, the filtered solid matter of solution D is (2/5) × 38.4 (g) + (1/5) × 16.9 (g ) + (2/5) x 5.3 (g) = 20.9 (g) and the filtration solids of WG + NH is (1/2) x 80.7 (g) + (1/2) x 16 .9(g)=48.8(g). This indicates that the addition of NH suppresses the reaction between silicate ions and Ca(OH) ₂ . Also, the reduction rate of reaction is (48.8-41.1)/48.8=15.8% for sodium silicate and (20.9-12.9)/ 20.9=38.3%. Lithium silicate shows a larger rate of decrease in reaction. Therefore, the permeability of liquid D is high.

Like lithium silicate, sodium silicate (water glass) becomes less reactive with Ca(OH) ₂ with the addition of sodium hydroxide. Therefore, if mixed with an appropriate amount of water, aqueous solutions of sodium silicate or potassium silicate and sodium hydroxide have high permeability and are considered to be applicable to internal repair of concrete.

As mentioned above, silicates (lithium silicate, sodium silicate or potassium silicate) are often used as surface impregnants for modifying and protecting concrete. On the other hand, the repairing agent of the present invention has a high ability to penetrate heated concrete as described above, and it is thought that this high penetrating ability is exhibited similarly to unheated concrete. The repair material of the invention can also be applied to repair or modify unheated concrete.

Here, the repair agent of the present invention can also be used as a repair agent for geopolymer concrete. Geopolymer concrete containing CASH gels can decompose the CASH gels when subjected to high temperature heating. In addition, as with concrete using Portland cement, cracks and damage occur at the interface between the paste portion and the aggregate portion due to differences in the amount of expansion due to high temperature heating and the amount of contraction due to cooling. When the repair agent of the present invention is applied, immersed, or injected into the geopolymer concrete that has been degraded by high-temperature heating, the CASH gel is regenerated by alkali stimulation, and is unreacted before high-temperature heating. A polycondensation reaction occurs in the active filler, which can repair damage and cracks after high-temperature heating. In this way, the repair agent of the present invention can promote recovery of the performance of geopolymer concrete that has been deteriorated due to high-temperature heating. Therefore, in the present invention, "concrete" shall include geopolymer concrete.

4. Conclusion According to the repair agent of the present invention, the penetration into the concrete is improved regardless of whether or not the concrete is subjected to high temperature heating. As a result, it is possible to recover the performance of the concrete deteriorated by being heated at a high temperature, and it is possible to reform even the inside of the concrete that has not been heated to a high temperature.

Claims (3)

A concrete repairing agent comprising an aqueous solution containing a silicate and an alkali metal hydroxide ,
The silicates comprise lithium silicate, and the alkali metal hydroxide comprises only sodium hydroxide,
A concrete repairing agent , wherein the total mass concentration of the silicates and the alkali metal hydroxide is 5 to 20% . The molar ratio between the silicates and the alkali metal hydroxide is
The concrete repair agent according to claim 1 , wherein the ratio of silicates: hydroxide of alkali metal is 0.5 to 5.0:5.0. The concrete repairing agent according to claim 1 or 2 , which is obtained by mixing a water-soluble substance other than said silicates and said alkali metal hydroxide.

Images