COMPRESSIVE STRENGTH AND DURABILITY OF CONCRETE WITH COCONUT SHELL ASH AS CEMENT REPLACEMENT

Abstract

The durability of concrete is the ability to withstand induced damages over a long period of time. It can be measured by means of sorptivity or rate of water absorption and resistance to sulfate attack (RSA). Concrete with larger voids is more susceptible to deterioration through absorption of chemicals, such as sulfate found in soil and seawater, which forms gypsum and ettringite. Gypsum and ettringite cause reduction of strength, cracking, and expansion of concrete. To improve the durability of concrete exposed to
sulfate, the National Structural Code of the Philippines (NSCP) suggests increasing the strength of concrete to 31 MPa, which would require more cement. This study aims to investigate the effects of partially replacing cement with coconut shell ash (CSA) in its compressive strength, sorptivity, and RSA. CSA in this study was classified as a Class N pozzolan, a cementitious material that makes a cheaper substitute for ordinary Portland cement (OPC). Results showed that the sorptivity of all concrete with CSA is within the acceptable limit. Based on the relationship of compressive strength with the CSA content, the optimum percentage replacement of OPC with CSA is 10%. From statistical analysis, it was determined that there is no significant difference in the compressive strength and expansion of concrete between the conventional and 10% CSA concrete. The strength of 10% CSA concrete is 92.10% of the strength of conventional concrete. The study reveals that CSA at 10% cement replacement is an effective pozzolan, which neither compromises
the compressive strength and RSA of concrete.