Abstract:
ABSTRACT
Aggregates being major components of concretes have appreciable effect on their properties and cost. Gravels are often used as coarse aggregate for concrete due to its low cost and availability. However, technical data on concrete produced from gravels in southwestern Nigeria is sparse. This study was designed to identify gravels in selected locations in south western Nigeria and determined properties of the resulting concretes.
Preliminary investigations were carried out in five purposively selected states (Ogun, Oyo, Osun, Ondo and Ekiti) in southwestern Nigeria to determine registered gravel mining pits. Fifteen gravel mining pits based on age and scale of mining operations were selected for this study. The physical properties [size distribution, Moisture Content, Water Absorption Capacity (WAC) and Specific Gravity (Gs)]; mechanical properties [Aggregate Impact Value (AIV), Aggregate Crushing Value (ACV) and Aggregate Abrasion Value (AAV)]; and chemical properties [pH, chloride, and alkali reactivity] of the gravels were determined using ASTM methods. Appropriate gravel constituents in concrete mix were determined using Gs factor. Concrete 150mm cubes and 150 x 150 x 750mm3 beams were cast with the gravel collected from the fifteen gravel pits. Density, water absorption, compressive, flexural and split-tensile strengths of the concrete were determined after 28 days using ASTM methods. Data were analysed using coefficient of variation, ANOVA and linear regression at p = 0.05.
Seventy registered gravel mining pits were identified. Maximum particle sizes of the gravels ranged from 19.0 to 37.5 mm while Fineness Modulus (FM) was 6.9±0.7. Moisture content, WAC, Gs, AIV, ACV and AAV of the gravels were 2.0±0.9%, 0.7±0.5%, 2.5±0.5, 39.4±11%, 32.9±7.5% and 41±2.3% respectively. Size distribution, AIV and ACV of the gravels varied significantly with pit locations. The pH, chloride, and alkali reactivity of gravel were 7.2±1.2, 0.9±0.6% and 0.004±0.002% respectively. Appropriate concrete mix design was 1:2:4 (cement: sand: gravel, with water/cement ratio of 0.6). Density, water absorption, compressive, flexural and split-tensile strengths of concretes were 2335.8±93.8kg/m3, 5.0±1.2%, 17.2±7.0N/mm2, 2.9±0.7N/mm2 and 2.30±0.6N/mm2 respectively. High concrete strengths resulted from high FM, low AAV and average Gs of gravels. Gravel location with highest compressive, flexural and split-tensile strengths of concretes had 24.8N/mm2, 3.5N/mm2 and 2.8N/mm2 while that with lowest strengths had 9.6N/mm2, 2.2N/mm2 and 1.7N/mm2 respectively. Coefficient of variation of ACV, pH, FM and AAV values of 10%, 10%, 6% and 3% respectively showed good performance. Sources of gravel highly influence compressive, flexural and split-tensile strengths of the cubes and beams (R2 = 0.99). Density and water absorption of the concretes were not significantly affected by gravel sources.
Mechanical properties of concrete cube and beam produced from gravel sourced from different locations in southwestern Nigeria varied. Gravelly concretes with high strengths could be used in construction of low rise buildings and rural roads while those with low strengths could be employed in applications (walkways) where high strengths are not required.
