COARSE AGGREGATE

This project aims to evaluate the strength of concrete by partially replacing the coarse aggregate by Blast Furnace Slag (BFS). The primary objective is to determine the effect of replacing natural granite with BFS in varying percentages (2.5%, 5%, 7.5%, and 10%) on the strength and durability of concrete. The research is motivated by the need to find sustainable alternatives to natural aggregates, reduce construction costs, and promote the reuse of industrial by-products in the construction industry. The methodology involved preparing concrete mixes with BFS replacing granite at 0%, 2.5%, 5%, 7.5%, and 10% by weight. The materials to be used include Ordinary Portland Cement, fine aggregates (sharp sand), coarse aggregates (granite and BFS), and potable water. Standard laboratory tests were conducted, including sieve analysis for particle size distribution, slump test for workability, compressive strength and flexural strength tests at curing ages of 7, 14, and 28 days, and Aggregate Impact Value (AIV) and Aggregate Crushing Value (ACV) tests to assess aggregate quality. A constant mix proportion was maintained for all specimens, with curing performed under controlled conditions to ensure comparability of results.The results revealed that the control mix (0% BFS) achieved the highest compressive strength of 21.08 N/mm² and flexural strength of 9.60 N/mm² at 28 days, while 2.5% BFS replacement yielded comparable strengths of 19.29 N/mm² and 8.56 N/mm², respectively. Workability decreased with increasing BFS content, with slump values reducing from 30 mm (control) to 16 mm (10% BFS). The AIV and ACV values confirmed that both aggregates were mechanically durable, though granite performed slightly better. It was concluded that BFS can be used as a partial replacement for granite up to 2.5% in structural concrete without significant loss of performance, while higher percentages are more suitable for non-structural applications.

The increasing demand for sustainable construction materials has prompted the
exploration of alternative resources to conventional aggregates. This study investigated
the effect of using periwinkle shells as a partial replacement for coarse aggregate in
concrete, combined with chemical admixture.
The study utilized the following materials: cement, fine aggregate(sand), coarse
aggregate (granite), water, and periwinkle shells. The method involved preparing
concrete mixes with varying proportions (0%, 10%, 20%, 30%, and 40%) of granite
replaced by periwinkle shells. Standard laboratory tests were carried out, these include:
The physical properties of cement (consistency, initial and final setting time), aggregate
(fineness modulus, silt content, moisture content, specific gravity, aggregate crushing
value, and aggregate impact value test) and mechanical properties of the concrete
produced (compressive strength, split tensile strength, flexural strength) at 7, 14 and 28
days curing period. Slump test and water absorption tests, were also assessed to evaluate
the suitability of periwinkle shells as coarse aggregate substitutes.
The results showed that compressive strength decreased with increasing replacement but
remained satisfactory at lower levels. At 28 days, the control mix achieved 20.85 N/mm²,
while 10% replacement recorded 19.56 N/mm², representing a 6% reduction but still
retaining over 90% of the control strength. Similarly, split tensile strength reduced from 3.87 N/mm² (control) to 3.60 N/mm² (10%), and flexural strength decreased from 5.96 N/mm² to 4.13 N/mm² at 28 days. Water absorption increased slightly from 2.68% .(control) to 3.04% at 10% replacement, remaining within acceptable durability limits. Based on these findings, the optimum replacement level is 10%, as it offers improved sustainability while maintaining structural adequacy and durability for practical applications.