MODELS FOR PREDICTING THE STRUCTURAL CHARACTERISTICS OF SAND-QUARY DUST BLOCKS

ABSTRACT Model equations for predicting the structural properties and cost of laterite-quarry dust concrete were developed. The properties of interest were the compressive strength, flexural strength, shear strength, water absorption, and static modulus of elasticity. The research; characterized the physical and oxide properties of laterite and quarry dust; developed mathematical models that predicts the structural properties and cost of laterite-quarry dust concrete; determined the relationship between the compressive strength and cost of laterite- quarry dust concrete; developed a table that gave various mix ratios and their corresponding strength properties; compared the cost of river sand concrete and model predicted laterite- quarry dust concrete. Experimental research design was adopted and the materials were; Water, Ordinary Portland cement, Laterite, Quarry dust and Crushed rock. River Sand was used for the purpose of comparison. Purposive and convenience sampling techniques were employed and samples were drawn from Umuchigbo in Enugu East Local Government of Enugu State and Ezillo in Ishielu Local Government of Ebonyi State. An (5, 2) augmented extreme vertices design was used. The design matrix consisted of fifteen (15) design points and seven (7) check points with replications of the vertices and the centroid, given a total of twenty eight (28) runs. A total of one hundred and seventy seven (177) specimens were produced. Eighty four (84) of laterite-quarry dust concrete cubes of 150mm, eighty four (84) of laterite-quarry dust beams of 600 x 150 x 150mm, and for the purpose of comparison nine (9) of river sand concrete cubes of 150mm were produced and tested respectively for their compressive strength, flexural strength, and water absorptions after 28 days of curing. The sample preparations and tests were done in accordance with the relevant British Standards. The results of the various test were used to formulate the model equations, notably, the compressive, flexural, and shear strengths, static modulus of elasticity, water absorption and cost per m3 of laterite-quarry dust mixes. Data analysis was done using Minitab 17. Adequacy of the models were tested using ρ-value, F statistics and normal probability plots at 95% confidence limit. Two (2) research hypotheses were tested using regression and correlation equation. The ρ-value of less than 0.05 indicated high level of significant and results were presented in tables and figures. Major findings revealed that the physical and chemical property test of laterite and quarry dust fell within acceptable limits. The bulk densities and specific gravities of laterite and quarry dust were found to be 1240kg/m3, 1695kg/m3, 2.60 and 2.79 respectively. The model equations were all found to be adequate. The minimum and maximum compressive strengths of laterite-quarry dust concrete ranges from 10.01N/mm2 to 26.13N/mm2, flexural strength ranges from 2.44N/mm2 to 4.95N/mm2, shear strength ranges from 0.20N/mm2 to 0.41N/mm2, static modulus of elasticity ranges from 18.51N/mm2 to 28.87N/mm2, and water absorption ranges from 2.82% to 6.34%. Minimum and maximum cost were also predicted and ranges from ₦19,834.02 to ₦31,804.70 respectively. The relationship between the compressive strength and cost was found to be positive and strong with the correlation value of 0.896. Comparative of the model predicted laterite-quarry dust concrete and river sand concrete shows that the model predicted laterite-quarry dust concrete is cheaper and cost effective than concrete produced with river sand as fine aggregate. It is therefore recommended that the use of laterite and quarry dust in concrete production be encouraged and other items in different stages of building construction be modelled. Construction mixture experiment should also be introduced in the tertiary curriculum. This research has contributed a broad knowledge on the area of study.