Effects of Retarders on Concrete Properties

Abstract

This is a study on the effect of three different brands of concrete set retarding admixture. The study was divided into 2 parts, the first consisted of slump test, determination of air content in concrete, setting time and compressive strength of microstructure of cement paste with and without retarding admixture by using optical microscope, scanning electron microscope and X-ray diffractometer. The results revealed that all three different brands of retarding admixture increased the slump of concrete, air content in concrete and delay in setting time of concrete. However, the effectiveness varied with the brand and dosage of the retarding admixture. Compressive strength of concrete with retarding admixture developed faster than concrete without admixture at the early age. No difference in the compressive strength of concrete was found at 28 days at the significant level of 0.01 percent.Concerning microstructure, it was found that there better dispersion of cement particles in the cement paste with retarding admixture. The scanning electron microscope study revealed that the morphologies of calcium hydroxide and two types of C-S-H Gel, Fibrous particles type and small equant grain type in the cementpaste with retarding admixture was not different from those of normal concrete. The x-ray diffraction experiment revealed that patterns of X-ray diffractograms of cement paste with and without retarding admixture are similar.