Setunge,S., Nguyen,N., Alexander,B.L. and Dutton,L.(2009): Leaching of alkali from concrete in contact with waterways. Water Air Soil Pollut.: Focus, 9, 381-391.

『水路に接触したコンクリートからのアルカリの浸出』


Abstract
 Concrete is usually the preferred material for construction of structures in contact with water during their service life. Early age exposure to water is beneficial for curing of concrete structures. However, the pollution of water from freshly cast concrete in contact with water has not been investigated in detail. A significant increase in the alkalinity has recently been observed in a stream in contact with freshly installed concrete culverts. High alkalinity has caused distress to fresh water fish in the stream. A preliminary laboratory study was commenced to explore the effect of leaching of alkali into water from freshly placed concrete. Freshly cast concrete specimens were exposed to fresh water, covering a range of conditions observed in the field such as volume of concrete/volume of water, age of exposure and cement content. Analysis of the results indicated that early age contact with fresh concrete can lead to an increase in the pH levels of water up to 11, similar to the levels of pH observed in pore water inside freshly cast concrete. It was noted that until an age of 4 days from casting of concrete, the age of exposure does not significantly affect the changes in the peak pH levels of water. Continuous monitoring of water in contact with concrete also indicated that the pH levels diminish with time, which is attributed to the possible reaction of calcium hydroxide with atmospheric carbon. The paper will present the experimental study, the results, analysis and outcomes as well as planning of a more comprehensive study to observe possible ways of reducing the leaching of alkali from freshly placed concrete.

Keywords: Leaching of alkali; Concrete construction; Cement hydration; Water pollution』

1. Introduction
2. Major variables affecting water contamination
3. Experimental programme
4. Methodology
5. Results
 5.1. The effect of ratio of volume of concrete/volume of water on the change of pH
 5.2. The effects volume of concrete/surface area/volume of water on the change of pH
 5.3. The effect of cement content of the concrete mix on the pH change in water
 5.4. Effect of age of exposure on the pH changes in water
6. Underlying reason for the observed changes in pH
7. Continuation of the work
8. Conclusions and recommendations
References


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