PREDICTION EQUATION OF DRYING SHRINKAGE STRAIN OF CONCRETE WITH LOW QUALITY RECYCLED COARSE AGGREGATE

Abstract

The goal of this research is to establish the concrete mix design containing both low quality recycled coarse aggregate and CfFA（Carbon-free Fly Ash）. CfFA is high quality fly ash which has unburnt carbon of less than 1%, and the use of CfFA is very effective for the improvement of flowability of concrete and the prevention of alkali-silica reaction of recycled aggregate. In this paper, the fundamental data on drying shrinkage strain of recycled coarse aggregate concrete were discussed in detail. As a result, the factors influencing drying shrinkage strain of concrete were cement content, water content, coarse aggregate content and the dosage of CfFA. In particular, for recycled coarse aggregate concrete, the effects of high absorption of recycled coarse aggregate and the amount of mortar adhering to coarse aggregate should be concerned. Then, the effects of these factors on the values of the final drying shrinkage strain at the age of 6 months were discussed, by introducing the apparent water content defined as the sum of water content and the absorption of aggregate（W´＝W＋W_G）and the apparent coarse aggregate content subtracted the adhered mortar content from coarse aggregate content（G´＝G－M）, instead of water content and coarse aggregate content in the mix proportion of concrete. In this paper, the multiple regression analysis was applied to calculate the final drying shrinkage strain as well as the prediction equation proposed by AIJ. It was found that the proposed equation for drying shrinkage strain of recycled coarse aggregate concrete can express the experimental data.