JPH0421578A - Deterioration of concrete - Google Patents

Abstract

PURPOSE:To change qualities of concrete and to deteriorate concrete in a relative short period, by exposing part of concrete to be deteriorated in a electrolyte solution and impressing an electric current to a pair of electrodes oppsingly set to the exposed part. CONSTITUTION:Part of concrete to be deteriorated is exposed in an electrolyte solution, a pair of electrodes are set oppsingly to the exposed part. Then DC voltage is impressed to the electrodes and calcium ion is eluted from concrete in the electrolyte solution to deteriorate concrete. Water is preferable as the electrolyte. The electrolyte may contain chloride and/or sulfate ion.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of altering concrete and deteriorating its strength.

(Background of the invention) Although the precise details of the mechanism by which concrete develops strength have not been elucidated, it is generally understood that it is achieved by hardening of cement between bamboo materials, and in this case, cement The curing is mainly caused by calcium silicate hydrate (
It is based on a hydration reaction in which fine crystals of CS H) are produced.

Therefore, it is predicted that the strength of concrete after hardening is closely related to the cement hydration structure, and the alteration of the hydration structure is a factor that greatly influences the strength.

By the way, research and development regarding concrete to date has focused on increasing its strength, and the reality is that there has been little research into weakening concrete.

This invention was made in view of this background, and its purpose is to provide a method that can alter and deteriorate concrete in a relatively short period of time.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a concrete deterioration method in which a portion of the concrete to be deteriorated is exposed in an electrolytic solution, and a portion facing the exposed portion is provided. A pair of electrodes is installed, and a DC voltage is applied to the electrodes.
The method is characterized in that calcium ions are eluted from the concrete into the electrolytic solution.

Water is suitable as the electrolyte.

The electrolyte may also contain chlorine and/or sulfate ions.

(Operations and Effects of the Invention) According to the method for degrading concrete having the above configuration, when a DC voltage is applied between a pair of electrodes installed opposite to the portion exposed in the electrolyte, an electric field is formed in the electrolyte. Since the calcium ions contained in concrete are positively charged, they are attracted to the negative electrode side and eluted into the electrolyte, thereby forming cavities in the concrete and reducing its strength.

The degree of elution at this time is approximately proportional to the DC voltage between the electrodes, so the degree of calcium ion elution can be easily changed by adjusting the magnitude of the DC voltage between the electrodes.
It is possible to make concrete deteriorate in a short period of time.

In addition, if you select normal water as the electrolyte and dissolve chlorine or sulfate ions at an appropriate concentration in this water, the chlorine and sulfate ions are negatively charged, so they are the opposite of the calcium ions mentioned above. Since calcium ions are attracted to the positive side of the electrode, in addition to elution of calcium ions, these ions can be caused to enter concrete by electric force, thereby further accelerating the deterioration of concrete.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows the status of a test conducted to confirm the effects of the method of the present invention.

In the test shown in the figure, a container C containing water A as an electrolytic solution and a cylindrical mortar test specimen X with a diameter of 5 cm and a height of 1 mark were prepared.

For test specimens X, three specimens No. 1 to No. 3 were prepared, each of which was embedded in a support F made of PVC with both end surfaces exposed, and this was immersed in water A. .

Then, a pair of electrode plates B and D made of carbon are installed so as to face each exposed surface of the test specimen Each was connected to the negative electrode side of power source E.

Here, the mortar composition of each test specimen It was cured in water.

Note that the device designated by the symbol H shown in FIG. 1 is a heater for keeping the water A at room temperature.

The electrical test conditions were initially planned to be constant current, but as the elution of calcium ions increased, it was not possible to maintain constant current conditions, so
A constant voltage of V was used.

Figure 2 shows the results obtained from this test.

In the figure, the circles indicate the measurement results when no DC voltage is applied.

As is clear from the results shown in the same figure, it can be seen that applying a DC voltage between electrodes C and D greatly promotes the elution of calcium ions from the mortar.

In this test, test specimens No. 2 and No. 3 were taken out at 93 days and 48 days, respectively, and the properties of their cross sections were observed.

In the No. 3 test specimen, the area within 2 to 3 mm from the + side surface exhibited a dark gray color, and its structure was dense.

On the other hand, the other areas exhibited a pale gray color, and the texture was coarser than that of the former.

This condition suggests that calcium ions are gradually eluted from the negative side.

In addition, No. 2, which promoted elution more than No. 3 test specimen.
In the test specimen, no dense parts were observed, all the specimens were pale gray in color, and the structure was coarse.

This is considered to be because most of the calcium ions in the test specimen were eluted during the test.

FIG. 3 shows the X-ray diffraction patterns of the NO, 2, No, 3 test specimens.

As shown in FIG. 3(A), in the sample before the test, diffraction lines of C a (OH) 2 and CSR, which are the main cement hydrates, are clearly observed.

However, upon visual observation, the part exhibited a dark gray color and was determined to have a dense structure (Fig. 3 (B), No. 3, + side of specimen).
Now, as before the test, Ca(OH)2 and C5H
A diffraction line with .

On the other hand, in the part that exhibited a pale gray color and was judged to have a coarse structure by visual observation (Fig. 3 (C), No. 3, one side of the specimen), only the C5H diffraction line showed Ca (OH).
The diffraction line 2 was not observed, and this part was Ca(OH)
2 has already finished eluting, and it can be determined that the quality has changed.

In addition, in the N022 test specimen shown in Figure 3 (D, E),
C
Only the 3H diffraction line was observed, and it was determined that all of the Ca(OH)2 had been eluted from this test specimen.

Furthermore, changes in unit volume weight and water absorption were measured for the NO.2 and No.3 test specimens.

The table below shows the measurement results.

As is clear from these results, the unit volume weight of the specimen after the test decreased by approximately 8% compared to that before the test, and the water absorption rate decreased by approximately 38%.
% has increased.

This result shows that the elution of Ca (OH) 2 and C3H increases the void space, which reduces the unit volume weight.
It is thought that the water absorption rate increased.

In addition, in the above explanation, only the elution of calcium ions was explained, but if chlorine or sulfate ions are dissolved in water A, the chlorine or sulfate ions are negatively charged, so
Contrary to the above-mentioned calcium ions, these ions are attracted to the positive side of the electrode, and using the same principle as in the above embodiment, these ions can be made to penetrate into the concrete by electric force, and the concrete is damaged by the action of the chlorine or sulfate ions. Since it is well known that concrete deteriorates, it can be fully predicted that the elution of calcium ions and the interaction with chlorine and/or sulfate ions will accelerate the deterioration of concrete.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a test conducted to confirm the effects of the concrete deterioration method according to the present invention, Figure 2 is a graph of the test results, and Figure 3 is an X-ray diffraction graph of the test specimen. It is. 0...... Pillar 4... Water (electrolyte) 6... Electrode 8... DC power supply

Claims (3)

[Claims] (1) In a concrete deterioration method, a portion of the concrete to be deteriorated is exposed to an electrolytic solution,
A method for degrading concrete, which comprises installing a pair of electrodes facing the exposed portion, applying a DC voltage to the electrodes, and eluting calcium ions from the concrete into the electrolytic solution. (2) The method for degrading concrete according to claim 1, wherein the electrolyte comprises water. (3) The method for degrading concrete according to claim 1 or 2, wherein the electrolyte contains chlorine and/or sulfate ions.