Modeling and Optimization of Some Mechanical Properties of Lateritic Concrete

Abstract

The success in the technological growth of any area depends heavily on the ingenious use of the readily available local materials. This is so because low low-cost production is assured while production process optimization is enhanced for the best quality product. In some areas, laterite is more readily available and cheaper than sand especially where sand is sourced by only river dredging. This work, Modeling and Optimization of Some Mechanical Properties of Lateritic Concrete, involves the replacement of sand with laterite. The aim is to predict the component mix proportions at which the lateritic concrete compressive strength, elastic and rigidity moduli and the poisson’s ratio are optimal. To carry out the task, we embarked on experimentation and design, applying the second order polynomial characterization process of the simplex lattice method. Disturbed samples of laterite materials were collected from the Vocational Teacher Education Department Site of the University of Nigeria, Nsukka, at the depth of 1.5m below the surface. These were assembled together with the Ordinary Portland Cement and pure water, in the Soil/Concrete Laboratory of the Civil Engineering Department of the Institute of Management and Technology, Enugu. Using the 3-component, second degree polynomial lattice structure, the Scheffe’s Simplex Lattice Design Optimization theory was applied to arrive at the actual component proportions for the lateritic concrete mix for the cubes and blocks that were cast in 150mm x 150mm x 150mm and 220mm x 210mm 120mm moulds, respectively. Two replicate samples of cubes and blocks were made for each of six test points and three control points required for the test. The prepared samples were cured for 28 days. The 18 cubes were crushed to obtain the compressive strength, and the 18 blocks were tested for lateral and longitudinal elongation and compressive stress under vertical compression. Mathematical models were formulated for the compressive stress, elastic modulus, modulus of rigidity and poison’s ratio as follows: Y = 2.70X1 + 2.525X2 + 2.295X3 +1.11X1X2 +1.25X1X3 – 0.64X2X3 for the compressive strength; Y = 4569.01X1 + 4501.31X2 + 4941.92X3 – 65.12X1X2 + 680.60X1X3 + 25.74X2X3 for the elastic modulus; Y = 1371.48X1 + 1459.38X2 + 1362.68X3 – 816.84X1X2 +49.80X1X3 - 54.00X2X3 for the rigidity modulus; and Y = 0.338X1 + 0.27X2 + 0.45X3 + 0.52X1X2 +0.00X1X3 + 0.00X2X3 for the poison’s ratio. The model adequacy is checked using the control factors on the raised regression equations. Finally softwares were prepared and run to select the optimized properties of the mix, and generate the best mix ratios for the desired properties. From the models, the 28-day maximum compressive strength was 2.896 N/mm2, the elastic modulus was 4976.685 N/mm2, the modulus of rigidity was 1459.38 N/mm2, and the poison’s ratio was 0.45. Henry Scheffe’s simplex design was applied successfully to show that the properties of the lateritic concrete are functions of proportions of the ingredients and not the quantities of the materials.