Characterizing the suitability of selected subgrad materials for use as subgrade materials in jimma zone

Abstract

Because of the development of construction industry in Ethiopia, consumption of construction materials is increasing from time to time. Concrete is an important and most widely used material in the construction industry. One of ingredient material in the production of concrete which is solely used for, beside manufactured sand, a long period of time without any substitute materials is river sand. As a result, searching for alternative materials which can satisfy both the quality requirements and other aspects such as cost, accessibility, workability and environmental considerations is an important task for the engineering community. Volcanic light weight aggregates are available in Ethiopia, especially in Great Rift Valley. But the practice of using those materials in concrete production is very low due to the absence of confidence and concern on the final output of the material. Therefore the main objective of this research was to compare the properties of concrete by partially replacing river sand by scoria fine in concrete production. The methodology followed under this research was passing through laboratory experimentation and cost comparison. The experimental laboratory procedure of the study includes; material selection, material preparation, material testing, preparing mix design, mixing, freshly and harden concrete test. There were six mix proportion of the two materials (i.e. 100%RS+0%SFA, 80%RS+20%SFA, 60%RS+40%SFA, 40%RS+60%SFA, 20%RS+80%SFA, 0%RS+100%SFA) at uniform W/C ratio of 0.62. The hard concrete test was done at the age of 7th and 28th days to determine the compressive strength as well as cost comparison for Hawassa town. For the minimum compressive strength requirement of 25MPa, the 28th day compressive strength test at the mix proportion of 20%RS+80%SFA failed the minimum strength requirement but up to mix proportion of 40%RS+60%SFA, scoria added concrete attain the minimum required strength. The slump test result showed when the percentage of SFA increases workability of concrete decreases this is due to the surface roughness, irregularity and absorption capacity. The cost comparison result also showed that, for 1m3 concrete cast by SFA, 8.1% reduction in the total cost of concrete for the study area. Therefore this research can conclude that in areas where river sand is expensive and scoria deposit abundantly available, can be used for concrete production.