Effect of Mineral Admixtures on Mechanical Properties and Chemical Resistance of Lightweight Coconut Shell Concrete

The effect of cement replacement with mineral admixtures such as silica fume and fly ash on the mechanical and chemical resistance of lightweight coconut shell concrete was studied. The lightweight concrete was made with full replacement of conventional coarse aggregate with crushed coconut shell aggregate of size less than 12.5 mm. Coconut shell treated with 20 % poly vinyl alcohol improved the resistance against aggressive environment. But concrete made with treated shell aggregate gave 5 % improvement in compressive strength. Hence, coconut shell may not degrade once it is bound with concrete. The properties such as compressive strength, splitting tensile strength, flexural strength and elastic modulus were studied. The durability properties such as sulphuric acid (pH1 & pH2) resistance and sulphate (sodium and magnesium sulphate) resistance were studied on 120 days. The density of the coconut shell concrete satisfied the limit of structural lightweight concrete, which is less than 2000 kg/m3. The optimum compressive strength of coconut shell concretes with 10 % silica fume in 28 days is 31.78 N/mm2, and it meets the requirement of structural lightweight concrete. The other mechanical properties such as flexural strength, split tensile strength and elastic modulus for the optimum mix in 28 days were 5.65 N/mm2, 2.98 N/mm2 and 8450 N/mm2, respectively. The weight loss and strength loss were less in CSC with 10 % FA, which is found to possess higher acid and sulphate resistance than SF and control mix. The weight loss and strength loss caused by magnesium sulphate seem to be slightly higher than that caused by sodium sulphate environment.