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 buildings ,
bridges, concrete drainage among others, are constructed using concrete. Sadly, the failure of buildings and other concrete structures is very common in Kenya. Blended Portland cement type 32.5N/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 developing countries as a result of its low price and availability locally, its strength gain has been proven
to be lower compared to when other types of cement are used due to quantity of pozzolanic material added to the blend. This paper outlines findings of an experiment investigation on the use of cypress tree extract as an accelerator to enhance rate of gain of
strength on Kenyan blended cements. Six different 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 mechanical 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 tested for the compressive strength at 7, 14, 21, 28, 56 and 90 days. It
was observed that 15% dosage of the extract expressed as a mass percentage of the cement content 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 blended 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 is 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
