EFFECT OF REVIBRATION ON THE FLEXURAL STRENGTH OF CONCRETE USING MAHOGANY SAWDUST ASH AS A PARTIAL REPLACEMENT FOR CEMENT

Abstract

Introduction: The paper addresses the effect of revibration on the flexural strength of reinforced-concrete beams using mahogany sawdust ash (MSDA) as a partial replacement for ordinary Portland cement (OPC). Beam specimens of sizes 150 mm x 150 mm x 600 mm reinforced with 12 mm diameter steel bars (Y12) and 8 mm diameter steel bars (Y8) as links, were used to cast each of 0%, 5%, 10%, 15% and 20% replacements of cement for SDA. The beams were revibrated after the initial vibration for 20 s at 10-minute successions within one hour. Fifty beams were cast in total and cured for 28 days: 35 revibrated and 15 non-revibrated. Methods: Based on the chemical analysis of MSDA, the following major chemical oxides were found in cement: SiO2 (39.87%), Al2O3 (18.05%), Fe2O3 (6.92%). Flexural strength tests were carried out for each beam using the three-point load method, and the result shows that the peak flexural strength occurred at 0% followed by 5% replacement at the 20-minute revibration time interval. The revibrated beams show the peak flexural strength of 10.50 N/mm2 and 10.00 N/mm2 at the 20th minute for 0% and 5% replacements; for the nonrevibrated beams, 8 N/mm2 and 7 N/mm2 were obtained for 0% and 5% replacements, respectively. Results: According to the flexural strength test results, revibration has improved the flexural strength of the concrete beams produced, and MSDA as pozzolana is recommended to comfortably replace cement by not more than 5%.