Influence of fly ash on the compressive strength and young's modulus of concrete

Abstract

This experimental research focus on determining how the addition of industrial waste affects the mechanical properties of concrete when partially replacing cement. The cement industry is currently one of the most polluting industries, contributing negatively and significantly to the emission of toxic gases into the atmosphere. There is, therefore, a general need to reduce the dependence and the use of cement in order to mitigate its effects on the environment. One way of reducing its needs is partially to replace it by waste or industrial by-products in the form of supplementary cementing materials (SCM). Therefore, the proposed project focuses on the influence of the cement substitution by SCM in the concrete manufacturing and establishing a relation with the characteristics of a standard concrete. The SCM used in this study is an in-nature fly ash, a by-product of Brazilian thermoelectric plants. The influence of fly ash on the concrete was analysed according to the substitution content at the age of 28 days. This study comprised the production of 50 specimens casted with 0%, 10%, 20%, 40% and 50% cement replaced by fly ash and with a water/binder ratio of 0.4 and 0.6. Slump, compressive strength and Young's modulus tests were carried out on the mixes. Experimental results indicated an increase in compressive strength at the age of 28 days for 10% and 20% in-nature fly ash replaced cement and reduced for 40% and 50% in-nature fly ash. A drop in the modulus of elasticity was also noted in accordance with the increase in the ash substitution rate. Relationship between Young's modulus and compressive strength were also determined.