A Central Composite Design method for design of mixture proportion for a laterite-cement bricks

Abstract

An attempt is made in this paper to present a guideline to produce laterite cement bricks meeting a user-defined requirement. Using the Central Composite Design (CCD) of the Response Surface Methodology of experimental design, a response prediction for a three component mixture for building bricks production using water, cement and laterite with percentage sand replacement was carried out. Five blends of bricks were investigated with cement content ranging between 8-20 percent by weight of laterite and 0-20 percent sand replacements. The machine mixing, compaction using Hydraform Twin-M7 machine and curing were carried out in a controlled laboratory environment. At the specified ages of 7 and 28 days, the compressive strength of bricks was measured and responses were modeled as a second-order quadratic model. Guidelines for the development of constraint formulation for mixture proportioning and optimization formulation were carried out. An inverse relationship for response prediction for strength was obtained and compressive strength achievable ranges between 7.46 - 18.85N/mm2. Two analytical techniques, using the Genetic Algorithm (GA) stochastic search technique, and an analytical method were presented with examples and were found adaptable computationally, to obtain response prediction, satisfying the user-defined constraints of strength, cost and durability.