Mix Proportion Optimization of Grouts Used in Two-Stage Concrete

Two-stage concrete (TSC) is known as preplaced aggregate concrete, which is defined as concrete produced by placing coarse aggregate in the formwork, then filling the voids with a special grout mixture. The strength performance of grout and the ability of grout to flow around the aggregates is essential for TSC. In this study, a new grout for TSC was analyzed; it is composed of cement, water, and various admixtures. Using the response surface methodology, the result of the fluidity test was analyzed, regressing the relationship between the content of each admixture and fluidity. The results show that the water reducer has the greatest effect on fluidity, followed by silica fume and then fly ash. In addition, according to the results of the strength test, the relationship between the strength variability and content of each additive is regressed by the binary logistic regression analysis. Moreover, the mix proportion optimized by the logit model is verified to effectively reduce the variability of the compressive strength. Based on the obtained results, an optimal composition is proposed.