『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