ABSTRACT
This project work aims at assessing and investigating the effect of local aggregate size and grading on the flexural strength of concrete.The loss of flexural strength of concrete is largely responsible for cracks in the structure. This test method is used to determine the modulus of rupture of specimens prepared and cured in accordance with Practices of Standard Practice for Making and Curing Concrete Test Specimens in the Field beam specimen. The study will be carried out with the following objectives; To determine the effects of various aggregate sizes on the flexural strength of concrete, To determine the Flexural Strength of Concrete, To determine the corresponding workability (slump values) associated with the aggregate sizes, To draw conclusions and give recommendations based on the research findings and compare to the compressive strength of concrete.
The study investigated 27 sets of concrete beam samples made from aggregates of uniform sizes of 10mm, 14mm, 20mm. Apair of 4 moulds, each of internal dimensions 100mm by 100mm by 500mm for the concrete beams. A concrete mix of 1:2:4 with a constant water-cement ratio (w/c) of 0.5 was used. Concrete beams were produced, cured and flexural strength test carried out at 7, 14 and 28 days.
The result showed that the concrete made from the local aggregate sizes of 10mm, 14mm, 20mm gave average flexural strengths of 0.8N/mm2, 0.78 N/mm2, and 0.765 N/mm2 respectively for 7 days; 1.36 N/mm2, 1.34 N/mm2 and 1.30 N/mm2, respectively for 14 days; 1.65 N/mm2, 1.50 N/mm2 and 1.45 N/mm2, respectively for 28 days. It was concluded that that flexural strength of concrete made from uniform size aggregates increases with increasing aggregate size. The slump values recorded for aggregate sizes of 10mm, 14mm, and 20mm were 30mm, 50mm, and 90mm respectively. It can be said that the slump values increases with an increase in aggregate size.
