Mechanical and durability properties of structural grade heavy weight concrete with fly ash and slag

Abstract

The paper investigates the fundamental mechanical and durability properties of a M50 strength grade heavy weight concrete (HWC), with replacement of cement by fly ash at 15 %, 25 % and 35 % levels and slag at 40 %, 50 % and 60 % levels. The mechanical properties studied include compressive strength, elastic modulus, flexural and split tensile strengths, and the durability properties include water permeability, drying shrinkage and carbonation behavior. Although extended curing improves mechanical strength and water permeability properties of fly ash and slag blended HWCs, fly ash replacement reduces the modulus of elasticity of HWC to some extent. A simple relationship was used to estimate the elastic modulus of fly ash and slag based HWCs from their density and compressive strength, and the estimated values agreed well with the experimental results. Experimental investigation shows that the long term drying shrinkage strain for all fly ash based HWCs (15 %–35 %) is lesser than that for the 100 % ordinary portland cement (OPC) and all slag based HWCs. The resultant hardened density variations of fly ash and slag blended concretes exposed to long term controlled environment discussed in this paper can be used for estimating shielding thickness of HWC members against ionizing radiations. The carbonation resistance of fly ash and slag HWCs exposed to 3 % CO2 condition for 146 days is also evaluated. Accelerated carbonation coefficients (kacc) estimated for all types of HWCs show that the carbonation resistance of HWC prepared with 15 % fly ash and 40 % slag is comparable. The rate of accelerated carbonation of HWCs increases for the increase in replacement level of fly ash and slag. In addition to the higher rate of carbonation, increase in calcium carbonate content estimated through micro analytical studies also suggest that a higher level of slag replacement reduces the carbonation resistance of HWC significantly.