Problems on Concrete Aggregate

Abstract

Concrete is the most important material for construction industries. Performance of concrete depend on the kind of the components and on the environmental conditions involved. The neccesity of conservation of materials and energy plays a great role on the durability of concrete. As the result of the new tendency for cement production, to which suspension pre-heaters are widely installed, alkali content in cement is higher than it was used to be. On the other hand, because of the shortage of riverbed materials, aggregates with proven quality are becoming limitted. More over, the recent design of mixing proportion in concrete industries makes more cement and less water in unit volume of concrete. These three factors are unfavorable in the view of notorious reaction in future concrete.
It was already 40 years ago that the alkali-silica reaction was found to be one of harmful phenomena for concrete structures. In the first 20 years, the cause and the mechanism were investigated in order to prevent the reaction. During the next 20 years, a world-wide spread of the phenomena was reported in spite of the preventive efforts, and the further study continued.
This paper introduces the examples of damaged concrete structures, and points out the need to counter-attack the phenomena. As only few petrographers are engaged with the investigation into the deleterious aggregates, the author expects that the members of the clay society should pay attention to the problem. The summary of 20 years study is given in this report. The next report deals with alkali-silica reaction, alkali-carbonate rock reaction, aggregates with sulfides and sulfates, aggregates with clay minerals and laumontite and shrinkage-causing aggregates.