Effect of Coconut Shell Aggregate on Shrinkage Cracking in Concrete using Modified Ring Test

Abstract

This study investigates the effect of coconut shell aggregate (CSA) as partial replacement for natural coarse aggregate on the restrained shrinkage cracking behavior of concrete. Concrete specimens with 0%, 10%, 20%, and 30% CSA were cast to simulate restrained drying shrinkage conditions in accordance with AASHTO PP34-99. Crack initiation, width and length were monitored for 70 days. Results show that increasing CSA content delayed crack initiation and reduced crack severity. Crack width and length reduced from 0.2mm and 87mm in control concrete to 0.15mm and 72mm respectively when 10% CSA was added. Notably, at 20% and 30% CSA, no shrinkage cracks were observed, indicating a significant improvement in cracking resistance. Split tensile strength decreased by 8.5%, 13.4% and 17.1% for 10%, 20%, and 30% CSA respectively. These findings demonstrate the potential of CSA as a sustainable alternative aggregate that enhances concrete durability under restrained shrinkage conditions.