Performance Criteria design of mixture proportions for laterite-cement bricks using the Schéffé Mixture Approach

Abstract

A guideline to select variable proportions produce laterite-cement bricks meeting a user defined requirements was developed using the Scheffe’s theory. Using this Mixture experimental design approach, five blends of a three component mixture using water, cement and laterite with percentage sand replacement to produce building bricks was carried out with cement content ranging between 8-20 percent by weight of laterite. The physical, and geotechnical properties of the laterite samples were determined. The machine mixing, compaction using Hydraform Twin-M7 machine and curing were carried out in a laboratory environment. The compressive strength at the specified ages of 7 and 28 days were measured using Testometric FS300CT Universal Testing Machine and responses were modeled as a second order quadratic polynomial. Guidelines for development of constraint formulation were carried out. An inverse relationship for strength was obtained and compressive strength achievable ranges between 7.46 - 18.85N/mm2. Two analytical methods using the Genetic Algorithm stochastic search technique, and an approximate method are presented with examples and were found adaptable computationally, to obtain response prediction, satisfying the constraints of strength, cost, component proportions and durability. This method is intended to replace the trial method of mixture proportioning which is incapable of developing specifications writing procedure to meet user defined requirements.