Principle Instigator
Makena Mbaabuh

This study examines the effect of addition of retarders into a concrete mix. With new admixture patents on the rise there is a need to study the effects of these admixtures. A proper study should be done to study these new admixtures.
The addition of retarders confer beneficial properties that enable the retardation of initial and final set that facilitate hot weather concreting operations, mass concreting, roller compacted mass pours and piling concrete.
This research study utilized the Vicat Apparatus test to evaluate the initial and final setting times of Mombasa cement and the resultant effect when chemical retarders are added. The retarder to be used is MasterPozzolith 55R. The experiment conducted on the cement pastes indicated that the addition of retarders increased both the final and initial setting times of concrete. The cement used was Pozzolanic Portland Cement as it has a lower heat of hydration, it is the most widely used cement in Kenya and is of lower cost than Ordinary Portland Cement.
In this research the mechanical properties of concrete were examined using the cube crushing test. The experiment was conducted on the cubes with various dosages of the retarder of 0%, 0.1%, 0.3% and 0.5%. By testing the cubes the following was concluded; the addition of retarders delayed strength gain in concrete at early ages and for dosages between 0.1% and 0.3% the 28 day strength was greater than that of the control mix.
However more research needs to be done on the water reducing capabilities of the retarder and the design procedures for addition of retarders need to be standardized.

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