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Test method for evaluating actual risk of alkali-aggregate reaction of hydraulic concrete

A hydraulic concrete and test method technology, applied in the direction of material inspection products, etc., can solve the problems of the decrease and change of alkali content in concrete, and the small expansion rate of test pieces, so as to achieve the effect of reducing the precipitation of alkali

Active Publication Date: 2012-07-11
NANJING HYDRAULIC RES INST
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0011] As mentioned above, there are many methods at home and abroad to judge the type of alkali activity of aggregates, the degree of alkali activity and the effectiveness of suppression measures. However, if it is used to evaluate the actual risk of alkali-aggregate reaction in hydraulic concrete, there are still the following Three relatively concentrated problems: (1) The existing method is generally to fix a certain mix ratio and the type of raw materials for testing, but the actual concrete is often changeable, including aggregate particle size, water-binder ratio, alkali content, Cement type, admixture quality and dosage, admixture type and dosage, air content, etc., under the condition that all these parameters change, what is the risk of alkali-aggregate reaction damage in actual concrete? Currently, there is no effective, Feasible test method
(2) The test conditions of some existing methods are too harsh, resulting in a qualitative change in the alkali-aggregate reaction mechanism inside the concrete
(3) Some test methods, such as the 38°C concrete prism method, due to the relatively small cross-sectional area of ​​the specimen, the alkali inside the concrete is easy to seep to the surface, resulting in a gradual decrease in the alkali content inside the concrete, and the measured expansion rate of the specimen will be small
[0018] In the prior art, there is no technical solution to solve the above problems

Method used

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  • Test method for evaluating actual risk of alkali-aggregate reaction of hydraulic concrete
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  • Test method for evaluating actual risk of alkali-aggregate reaction of hydraulic concrete

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0048] Example 1: A certain dam concrete mix ratio is used, see Table 2. The mix ratio of No. 4B is the mix ratio of four-grade normal dam concrete, and the maximum particle size of the aggregate is 150mm. The mix ratio numbered 3B is a three-graded normal dam concrete mix ratio, and the maximum particle size of the aggregate is 80mm.

[0049] Table 2 Dam concrete mix ratio (kg / m 3 )

[0050]

[0051] Concrete is mixed with a self-falling mixer according to the mix ratio given in Table 2, and the equivalent Na of the cement is reduced by adding NaOH 2 Adjust the O content to 1.25%, pass the evenly stirred concrete through a 40mm sieve until no slurry or fine particles fall from the sieve within 1min. Pour the wet sieved concrete under the sieve into the 100mm×100mm×515mm prismatic cast iron test mold with the measuring head installed, and ensure that the concrete around the measuring head is squeezed and compacted, and then the test mold is placed on the vibrating table ...

Embodiment 2

[0053] Example 2: See Table 3 for the mix ratio of anti-scouring concrete for a flood discharge tunnel of a hydropower project. The mix ratio of the number "2CM" is the mix ratio of the secondary normal anti-scouring concrete, and the maximum particle size of the aggregate is 40mm. The mix ratio of the code "2BM" is the mix ratio of the secondary pumped anti-scouring concrete, and the maximum particle size of the aggregate is 40mm.

[0054] Table 3 The mix ratio of anti-scouring concrete for a spillway tunnel (kg / m 3 )

[0055]

[0056] Concrete is mixed with a forced mixer according to the mix ratio given in Table 3, and the equivalent Na of cement is reduced by adding NaOH 2 The O content was adjusted to 1.25%, and the uniformly stirred concrete was poured into a 100mm×100mm×515mm cast iron test mold with a measuring head installed, and the rest of the operations were the same as in Example 1. "2CM" and "2BM" mix proportion measured expansion rate of each age is attach...

Embodiment 3

[0058] Embodiment 3: Except that the surface of the test piece is not wrapped with self-adhesive aluminum foil, the rest is the same as that of Embodiment 2.

[0059] Compared with Example 2, as a result, the measured expansion rates of "2CM" and "2BM" at the age of 90 days were reduced by 0.28% and 0.35% respectively, and white alkaline substances were precipitated on the surface of the test piece.

[0060] This shows that wrapping aluminum foil can effectively avoid the precipitation of alkali inside the specimen to the surface.

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Abstract

The invention relates to a test method for evaluating the actual risk of an alkali-aggregate reaction of hydraulic concrete. The test method comprises the following steps of: (1) mixing actual raw materials according to mix proportions to form concrete, adjusting equivalent Na2O content of cement to 1.00-1.50 percent by adding NaOH, screening aggregate with the grain size of being more than 40mm out, and forming a test piece from the concrete subjected to wet screening; (2) pre-burying stainless metal measuring heads in the test piece; (3) demolding the test piece and soaking the test piece in a saturated calcium hydroxide aqueous solution the equivalent Na2O concentration of which is close to that in a concrete hole solution, wiping the test piece till reaching a saturated and surface-dry state, and wrapping the test piece by aluminum foil in a sealed vessel for curing; (4) carrying out testing according ages of 7 days, 14 days, 28 days, 56 days and 90 days, taking the test piece out of a curing environment at 24h ahead of test age arrival, and measuring the length of the test piece after temperature is stable; and (5) evaluating the actual risk of the alkali-aggregate reaction of the hydraulic concrete. The test method disclosed by the invention can achieve the purposes of ensuring that the mix proportions, the raw materials and the test environment of the concrete are identical with those of the actual engineering to the greatest extent, and the test cycle can be shortened.

Description

technical field [0001] The invention relates to a test method for evaluating the actual risk of alkali-aggregate reaction disease in hydraulic concrete. Specifically, it relates to a test method for evaluating the actual risk of alkali-aggregate reaction of hydraulic concrete by using wet-screened concrete specimens. Background technique [0002] Alkali-aggregate reaction is one of the major problems causing damage to concrete engineering. The damage to concrete structures caused by alkali-aggregate reaction was first discovered in the United States. It was built in the King City Bridge in California from 1919 to 1920. Cracks were found on the top of the pier in the third year after completion. After that, the cracks gradually developed to the bottom. By 1924, the top of all pier All cracks occurred. In February 1940, Stanton of the California Highway Bureau published the article "The Influence of Cement and Aggregate on the Expansion of Concrete" through a large number of...

Claims

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Application Information

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IPC IPC(8): G01N33/38
Inventor 白银丁建彤蔡跃波
Owner NANJING HYDRAULIC RES INST
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