JPS62212276A - Alkali aggregate reaction control for concrete - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for suppressing alkaline aggregate reaction in concrete.

(Prior Art) In recent years, many cases of early deterioration of concrete structures due to alkaline aggregate reactions have been reported and are attracting social attention.

Until now, the three major factors that cause the alkaline aggregate reaction have been considered to be A0 reactive aggregate B and alkali C0 moisture in concrete. The goal has been to eliminate one or more of the contributing factors.

The following specific measures have been proposed.

a. Removal of alkali-reactive aggregates 1) Based on various evaluation tests or past results, select aggregates that have a risk of causing an alkali-aggregate reaction, and no longer use those aggregates as concrete materials. .

b. Removal of alkali from concrete 1) Use a low-alkali cement in which the alkali concentration in the cement (NazO equivalent, ratio of Il to cement) is 0.6% or less.

11) Use pozzolans such as fly ash and silica hume as a partial substitute for cement to reduce the alkali content in concrete to 3 kO/■3 or less.

Removal of C0 moisture I) To prevent water from penetrating from the outside, pour dense, high-quality concrete using an AE agent, etc.

11) For the same purpose, an impermeable layer is formed on the surface of concrete using paint, etc.

(Problems that @- attempts to solve) However, each of the above methods has the following problems.

First, regarding the removal of alkali-reactive aggregates, testing to determine the toxicity of aggregates requires specialized techniques and a long period of time.
There are problems such as the fact that the alkali reactivity varies depending on the part of the aggregate collected within one volume or at the 1i & 1 aggregate collection site. Furthermore, aggregate is also a limited resource, and it is desirable to utilize it effectively even if the aggregate is suspected of being alkali-reactive.

Low-alkali cement is currently being standardized in the JIS standard, but there is an unavoidable problem in that it is relatively expensive. Additionally, there may be cases where pozzolan or furnace slag cannot be used depending on the type of structure, environmental conditions, etc.

Finally, waterproofing with paint is expensive, and in the case of large structures and retaining walls, waterproofing may trap moisture inside the components and encourage aggregate reaction. There is a problem.

An object of the present invention is to provide a method for suppressing an alkali aggregate reaction in concrete, which can suppress an alkali aggregate reaction without being influenced by the type of aggregate or the type of cement.

(Means for Solving the Problems) To explain in detail the present invention for achieving the above object, the present invention is characterized by performing initial drying after pouring concrete and before performing main curing. .

(Function) It has been confirmed through experiments that by performing initial drying after pouring concrete in this way, the alkaline aggregate reaction can be suppressed.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure shows a flowchart of the method for suppressing alkaline aggregate reaction in concrete according to the present invention. As shown in the figure, concrete is placed in step 1, concrete is compacted in step 2, concrete is demolded in step a, and concrete is initially dried in step 4.

Initial drying is carried out, for example, by placing the concrete product in a drying curing chamber and evaporating χ% of the moisture in the product. χ
The value of is set through preliminary experiments depending on the alkali reactivity of the aggregate used.

The initial drying time is 1M! Initial drying is carried out within about 10 minutes [1, main curing of the concrete is performed in step 5] Next, it is put into service in step 6.

The feature of the method for suppressing alkali aggregate reaction according to the present invention lies in the "initial drying" step. Approximately 30% of the mixed water layer in the concrete is removed from the mold and then dried and cured (e.g., 25°C, 40°C).
%R, H,) to evaporate and suppress expansion due to aggregate reaction during later use. Due to the need for initial drying, we believe that small precast members made of concrete or mortar are particularly suitable for application. However, it may be possible to deal with cast-in-place concrete by drying the surface with a heater or the like.

Next, the effect of suppressing alkali aggregate reaction by the method of the present invention will be described below based on experimental results.

Pyrex glass #7740, which is also specified by ASTM, was used as the aggregate that caused the aggregate reaction. A 1lfll measurement test was conducted for the specimen dimensions and aggregate particle size in accordance with ASTM C227 (mortar bar method). Table 1 shows the composition of each mortar sample (■-184,4013).

Table-1 Mortar specimen composition table (per specimen) Amount of alkali retained in cement: Q, 636% (N820) Moisture reduction rate (W, L, - Water reduced by drying after demolding/supply) 37.8°C, 100% R, H, The materials were cured under conditions that tend to cause alkaline aggregate reactions.

A list of experimental cases is summarized in Table 2.

Table 2 List of Experimental Cases The relationship between the expansion amount and material age for cases W, L, -0 to 49% is shown in FIG. Initial drying W, L, -0 ~ as shown in Table-2
Figure 2 shows the relationship between the amount of expansion and the age of the material in the 49% case.

Although the initial drying curing conditions are different as shown in Table 2, as is clear from Figure 2, the moisture reduction rate W,
As L becomes larger, the amount of expansion becomes smaller. especially,
W.

In the cases where L is 36% and 49%, the specimen is not only shrinking, but its value is also stable, and III
There is no tendency to turn to the l side. In the case where W and L are 0%, the expansion amount is extremely large at 0.265% at 8 years of material age, whereas the effect of suppressing the aggregate reaction due to initial drying is clear.

In addition, according to ASTM C227 (mortar bar method), the risk of causing an alkaline aggregate reaction is determined to be 0.1% at 6 months (26 weeks) and 0 at 3 months (13 weeks).
．． This is when the amount of expansion is 0.05%.

In the case of W, L, -49% in Fig. 2, the curing after drying is 80°C, 100% R, H.

Experiments were also conducted under very severe conditions such as at 20° C. and in water, but i1#I did not occur.

Continuous measurement results are required for final judgment, but this experiment revealed that the alkali aggregate reaction can be suppressed by setting W and L to about 30%.

On the other hand, by setting W and L according to the size of the alkali reactivity of the aggregate used, other cases can also be accommodated.

Although the method of the present invention can be applied to concrete in general, it is thought to be particularly suitable for use in small precast members such as curb blocks, concrete sleepers, and interlocking blocks, which are still frequently damaged by alkaline aggregate reactions.

(Test results) A specimen subjected to conventional standard curing and a specimen with the same composition but subjected to initial drying according to the above embodiment of the present invention were prepared. When observing the situation at the boundary with the object using scanning electron microscope scissors, it was found that a reaction product of 15 to 20 μm was observed at the boundary in the conventional specimen, but no reaction product was observed in the specimen according to the present invention. There wasn't.

The aggregate reaction inhibition effect due to initial drying in the present invention can be considered as follows.

b) The generation of reaction products (which cause expansion and deterioration) due to alkaline aggregate reactions is greatly influenced by the amount of moisture inside concrete for several days after it is placed. If the product is initially dried, the amount of reaction products produced is small (afterwards, even if moisture is supplied, no reaction products are generated or progressed).

0) The internal micropores created by the initial drying absorb the expansion of the reaction product.

Although it is judged that the aggregate reaction is suppressed by the synergistic effect of the above a) and O), it is thought that the effect of a) is mainly large.

(Effects of the Invention) As explained above, according to the method for preventing alkaline aggregate reaction in concrete of the present invention, which involves performing initial drying according to the present invention, the following effects can be obtained.

(a) It can be used as aggregate for concrete even in volumes where there is a risk of an alkaline aggregate reaction.

(b) Only one process (drying process) needs to be added to the existing flow of precast member production.

(c) By appropriately setting the water reduction rates W and L, it is possible to cope with the case where the alkali reactivity of the aggregate changes.

(d) Once a preliminary experiment is conducted to determine the drying curing conditions that satisfy the target moisture reduction rate, it is sufficient to repeat the drying curing mechanically thereafter.

(e) By simply performing initial drying, no matter what kind of conditions are likely to cause an alkaline aggregate reaction thereafter (e.g. 37.
8℃, 100%R,H,・80℃, 100%R,H,・
(20°C, in water), the aggregate reaction suppression effect persists.

(f) For initial dry curing, moisture reduction rate W, L.

The curing conditions (WA degree, humidity) for reducing moisture can be set freely, with only the value of .

[Brief explanation of drawings]

Fig. 1 is a flowchart diagram showing an example of the implementation steps of the method according to the present invention, and Fig. 2 is a comparison diagram of the alkaline aggregate reaction suppression effect consisting of the relationship between the age of the material and the volume of swelling related to the moisture loss rate due to initial drying. It is. Patent applicant: Pentayo Construction Co., Ltd. Agent
Patent Attorney Isao Sasaki 2nd
figure

Claims (1)

[Claims] 1. A method for suppressing alkaline aggregate reaction in concrete, which comprises initially drying the concrete after pouring the concrete and before curing the concrete.