Structural strength and performance of cement - stabilized murram blockwalls

Abstract

The thesis gives figures by the Central Bureau of Statistics showing that for a reasonably decent residential house,wall construction materials account for 25% of the total cost of materials. It therefore concludes that by reducing the cost of walling materials, a significant reduction in the overall cost of the building can be realised. The thesis then gives a recapitulation of the standard formats and requirements for masonry building units in Kenya and also looks specifically at the potential use of stabilized soil blocks as possible masonry units. The test soil was classified as a sandy gravel in the

particle size range of 0.2 mm - 2 mm , with a plastic limit of

46%, a plasticity index of 9,maximum dry density of 1500 kg/m3 and an optimum moisture content of 26%. The effect of adding cement of upto 10% by weight was investigated to determine whether suitable compressive strengths could be achieved. It was established that strengths of upto 8.3 N/mm2 were attainable.

The possibility of replacing part of cement with lime was investigated and it was found that loss of strength would occur unless the blocks were oven baked for 48 hours immediately after manufacture. The effect of sand as an additive to the mixture of the test

soil with cement was investigated and it was found that the strength of the blocks could almost be doubled by adding 60% by weight of sand.

(ii i)

various methods of manufacture of the stabilized soil blocks were investigated and it was found that methods of direct compaction of the soil using a drop hammer or a Kango hammer were most effective. Manufacture by tamping with a rod or vibration in an automatic block making machine gave only 70% of the strength attained by the Kango hammer. Manufacture by squeezing in a Cinva Ram block press gave a strength of only 44% of that attained by the Kango hammer. Water absorption, wet strength and drying shrinkage tests

were carried out on selected blocks. It was found that well designed stabilized murram blocks will be stable in water logged conditions with a loss of strength of less than 30%. Drying shrinkage of upto 0.17% were however recorded which were well in excess of 0.05-0.07% allowed for concrete blocks. This showed that the blocks may be prone to shrinkage cracking in varying moisture and temperature conditions. In tests carried out on wall panels, 74% of the predicted

load capacity was realised which was found to be encouraging.

The cost effectiveness of cement-stabilized murram blocks was assessed vis-a-vis concrete blocks of mix ratio 1:4:8 and it was found that savings of between 35% and 57% can be made. The thesis concludes that cement-stabilized murram blocks

can be used in wall construction with significant savings over traditional concrete blocks. Cement contents of between 6% and 10% with possible sand additions of 25% to 50% is recommended for better water resistance. As a precaution, cement stabilized murram block walls should be protected from constant moisture to ensure greater durability.