Investigation of the Effect of Chemical Admixture on the Drying Shrinkage of Concrete

The work reported in this paper, which was carried out in the Technical Faculty of the University of Mazandaran was an attempt to investigate the effect of chemical admixture on the drying shrinkage of concrete. Various amounts of superplasticiser (SP) was introduced into the concrete mixes (of various strength). The water/binder ratio, the aggregate/cement ratio and the addition of silica fume (SF) were all variables. Two of the mixes i.e. Mix1 and Mix2 could be considered as reference mixes and were without admixture, whereas the other three mixes contained admixture and with increasing dosage as the strength was increased. This aspect of the study extended over a period of 210 days for the high strength concrete (HSC) mixes (with and without fibers). In the case of the medium strength concrete (MSC) mixes, 350 and 210 days of drying was imposed on the plain concrete and fibre reinforced mixes respectively. The overall variation in the relative humidity showed that the average trend suggested a small reduction in shrinkage when a small dosage of SP was added and an increase in the relative ultimate shrinkage as the SP dosage was increased. The main conclusion, however, was that shrinkage is not appreciably affected by the addition of the SP, although the predominant type of shrinkage may be autogenous and not drying shrinkage as the strength is increased

Keywords:

Drying shrinkage , Autogenous shrinkage , High-strength concrete , Fibre