An experimental study of the effects of some commercial admixtures on the properties of concrete

Abstract

This thesis is the study of the effects of several commercial admixtures on the properties of concrete in the plastic and the hardened state. The project is divided into two parts. Part I deals with the laboratory investigation and Part II takes into account the theoretical study of Part I.

Three standard concrete mixtures at different water-cement ratios and approximately at constant slump were designed without the addition of admixtures to serve as a parameter for the test mixtures.

Eighteen different test mixtures were made with local aggregates. Three test mixtures for each individual admixture and combination admixtures were used for comparison purposes.

From the results obtained in the laboratory study, it was found that all the admixture used, separately and in combination, the test mixtures with an air entraining agent produced the greatest improvement in the plastic state as compared with their standard. In the hardened state, the cement dispersing agent (normal set) and the accelerator produced the greatest increase in the compressive strengths at all ages of testing as compared with their standard. It is further revealed that the accelerator imparted the greatest influence when used in rich mixture.

In the theoretical study, by making alterations in the water-cement ratio so as to obtain a desired slump of four inches, the theoretical test mixtures so designed predicted a further increase in the compressive strengths, except in the case of the accelerator. It is noteworthy that the accelerator produced the same magnitude of compressive strength as was produced by the cement dispersing agent (normal set) at 28 days in the rich mixture, but in the case of the poor mixture, the latter was more effective.