Strength Performance of Concrete Produced with Volcanic Ash as Partial Replacement of Cement

Abstract

There is global need for the preservation of natural resources, reduction of carbon dioxide emission and sustainability of concrete structures; this and other problems associated with material production have fuelled the search for alternative cementing material to produce environment-friendly construction materials. The mining of cement raw materials leads to depletion of natural resources and degradation of environment. Cement production also pollutes the environment due to the emission of CO2. Volcanic ash is suitable material for replacement of cement in concrete production. Chemical composition of volcanic ash as well as the specific gravity, bulk density, workability, compressive strength split tensile strength and flexural strength properties of varying percentage of volcanic ash blended cement concrete and 100% cement concrete of mix ratio 1:2:4 and water-cement ratio of 0.5 were examined and compared. Slump test and compacted factor test was carried out to check the effect of volcanic ash on the workability of fresh concrete. Volcanic ash partially replace cement in the order of 0%, 5%, 7.5%, 10%, 12.5%, 15% and 20% were cast. The concrete were tested at the ages of 7, 14, 21 and 28 days. The results showed that volcanic ash is a good pozzolan with combined SiO2, Al2O3 and Fe2O3 of 74.8%. The highest compressive strength at 28 days was 29.2N/mm 2 and 28.3N/mm 2 at for 10% and 7.5% respectively, as compared to plain concrete which was 27.8N/mm 2 ; in addition 5% replacements of cement with volcanic ash present same value with the control concrete. The highest split tensile strength at 28 days was 3.48N/mm 2 and 3.45N/mm 2 at for 10% and 7.5% respectively, as compared to plain concrete which was 3.42N/mm 2 ; in addition 15% replacements of cement with volcanic ash present same value with the control concrete. The highest flexural strength at 28 days was 4.91N/mm 2 and 4.83N/mm 2 at for 10% and 15% respectively, as compared to plain concrete which was 4.70N/mm 2 ; in addition 5% and 7.5% replacements of cement with volcanic ash both present higher value of 4.75N/mm 2 which is higher than the control concrete. The strength test results indicated that volcanic ash concrete gave better strength compared to control samples. A 10% replacement of cement with volcanic ash was found convincing and indicate the optimum replacement level of cement. However can be used up-to 15% replacement level due to its promising result. The research recommends use of volcanic ash as partial replacement of cement in aggressive environment, increased water cement ratio.