Development of specification writing procedure for mixture proportions for laterite cement bricks using the Central Composite Design Approach

Abstract

A specification writing procedure was developed to obtain component mixes to produce laterite-cement bricks meeting a user defined requirements. The procedure was developed using the Central Composite Design (CCD) of the Response Surface Methodology (RSM) of experimental design. It essentially focused on selecting component proportions to obtain response prediction for a three component mixture for building bricks production using water, cement and laterite with percentage sand replacement. Compaction was carried out using the commercially available Hydraform Twin-M7 machine exerting a compactive effort of 10MN/m2. Five blends of bricks were investigated with cement content ranging between 8-20 percent by weight of laterite and 0-20 percent silica sand replacements. At the specified ages of 7 and 28 days, the compressive strength was measured using Testometric FS300CT Universal Testing Machine and responses were modeled as a second order quadratic equations. An inverse relationship for response prediction for strength was obtained and compressive strength achievable ranges between 7.00 -19.00 N/mm2. A specification writing form is proposed which will enable the selection of constituent materials and acceptance criteria to be met to enable both cement and plastic bonds achievable.