EFFECT OF ADMIXTURES ON SHRINKAGE PROPERTIES IN SELF COMPACTING CONCRETE

Abstract

With the rapid advancement in concrete technology, demand for sustainable building materials has increased manifold in last few decades. High strength concrete such as Self compacting concrete (SCC), also known as Self consolidated concrete, is considered one of the finest and highly modified concrete material. SCC represents a major evolution in the building industry. The increased use of SCC for construction and repair purposes lies in the fact that it is semi-flowable in nature and possess several advantages such as environmental, human, technological and economical. This paper mainly focuses on the effect of various shrinkage properties such as drying shrinkage, autogenous shrinkage and plastic shrinkage on performance of SCC. Detailed literature review suggests that early age shrinkage in SCC has been a major setback in attaining it’s desired strength. Expansive cracking and capillary tension are considered as two main phenomena behind shrinkage in SCC. It is found out that factors like lower water/cement ratio or decreasing limestone filler/cement ratio leads to reduction in autogenous shrinkage. It is considered that cracks are one of the pivotal reasons behind the poor durability of concrete as they help in entering hazardous fluids. Hence cracks causes specific problems like plastic shrinkage. The effect of shrinkage reducing admixtures (SRA) on SCC was observed to be positive. SRA along with paraffin based curing compounds helps in reducing cracks. It was observed from rheological tests conducted on concrete as well as fresh SCC that, as far as drying shrinkage is concerned usage of SRA was found out to be effective while hydrophobizing admixtures tends to be useless. Along with addition of such admixtures, limestone fines in SCC mixes shows a reduction in autogenous shrinkage in SCC as compared to normal vibrated concrete (NVC). More importantly results show that total shrinkage in SCC mixed with limestone filler is slightly higher (not >9.2%) than in NVC, while SCC made with viscous Modifying Agents (VMA) shows 7.7% less shrinkage than in NVC, due to lower autogenous and drying shrinkage.