Abstract:
Concrete is the most widely used construction material in the world. The situation in the country is not an exception as most of the infrastructures in Kenya such as build-ings, bridges, drainage among others, are constructed using concrete. Sadly, the fail-ure of buildings and other concrete structures is very common in Kenya. Portland Pozzolanic cement type 32.5 N/mm2 is the most widely used concrete binder material and is found in all parts of the country. Despite blended cement CEM 32.5 being the most commonly used cement type in construction industry in Kenya and most devel-oping countries as a result of its low price and availability locally, its strength gain has been proven to be slower compared to when other types of cement are used due to quantity of pozzolanic material added to the blend. This thesis outlines findings of an experimental investigation on the effect of cypress tree extract as an accelerator to enhance rate of gain of strength on Kenyan Portland pozzolanic cements. Six differ-ent blended cement brands locally available were used during the study. Cement chemical analysis was done using X-ray diffraction method while for the cypress extract, Atomic Absorption Spectrometer machine was used. Physical and mechani-cal properties were checked based on the British standards. The generation of the concrete mix design was done using the British DOE method and concrete was test-ed for the compressive strength at 7, 14, 21, 28, 56 and 90 days. Cypress tree extract was added at 5%, 10%, 15% and 20% dosage expressed as a mass percentage of ce-ment content. It was observed that 15% dosage gives the most improved compressive strength of concrete: 10.4% at 7 days and 9.5% at 28 days hence the optimum. It was further noted that when Cypress tree extract is used as an accelerator in the mix, the Portland pozzolanic cement concrete achieves the design strength at 27 days saving 10 days of the project duration compared to when no accelerator is used while the ultimate strength was achieved at 67 days. The study therefore recommends the use of the cypress tree bark extract at a dosage of 15% by mass of the cement content as an accelerator when the structure is to be loaded at 28 days and waiting upto 39 days before loading the structure if no accelerator is used for blended cement concrete.
