Study and improvement the effect of internal sulphate on properties of normal and light weight concrete

Abstract

Sulphate attack is a major difficulty which has a local effect on the constructional materials, specially the concrete. Internal sulphate attack takes place due to the source of sulphate being incorporated into the concrete at the period of mixing, while adding gypsum in the cement etc. This project aims to investigate the influence of internal Sulphate Attack (ISA) on some characteristics of light weight (LWC) and normal concrete (NC). In this study, two types of concretes have been prepared, light weight and normal concrete. Two levels of sulphates (3% and 6%) are added as a part of sand to determine the influence of sulphates on NC and LWC that produced a local material and compared it with control normal mix. These added ratios of sulphate are highly convergence of the actual reality of internal sulphate. To decrease the harmful effect of internal sulphate coming from 3 and 6% by weight of sand, two ways have been utilized in this study. First one, using type I cement with 20% of silica – fume as replacement with a part of ordinary cement, second one by SRPC instead of type I is preferred to resist internal effect of sulphate. Light weight concrete has been prepared by total replacement for gravels by crushed bricks. As a result of this research, it concluded that the increment of SO3 amount caused a decrement in the compressive strength by 43.81% at 90 days and by 33.5 % at 60 days but there is a slight effect appear at 28 for samples consist of OPC with presence of 3% SO3. When sulphates increased to 6%, compressive strength decreased by 49.3% at 90 day, and by 38.3% at age of 60 days with very slight effect at age of 28 days. Tensile strength of NC follows same the behaviour as that of the compressive strength. For light weight concrete, the reduction in compressive and tensile strength will result from combined effect of the ettringite formation and high porosity due to introducing crushed bricks as total replacement for gravels. LWC was highly effected by sulphate attack even at early ages and it concluded that the increment in the SO3 amount by (0-3) % by weight of sand, the compressive strength of LWC, decreased by 20.11 % at age of 28 days, 29% at 60 days, while they decreased by 44 % was at 90 days. Using of 20% silica fume with type I cement heals the effect of 3% and 6% calcium sulphate in the A4 and A5 samples and produced a compressive and tensile strength approximately equal to that of control samples. Using of SRPC with 3% and 6% calcium sulphate in the A7, A8, L7 and L8 samples prevented the effect of internal sulphate in both NC and LWC and gave compressive and tensile strength higher than that of standard samples (without sulphate).