| dc.description.abstract | In Kenya soil is the basic house construction material for low-income groups. However, its lack of durability and low strength, are limi ting factors to its use. The aim of the current research programme was to establish, for lime-stabilised murram (from Kenya), the optimum lime content, compaction pressures and curing conditions which are necessary to achieve the minimum strength required by the Kenyan standard for stabilised soil building blocks.
A comparative study was also done on murram-cement and murram-lime-gypsum.
Initially mixtures of murram containing different amounts of lime ( i . e. 5, 1 0 and 1 Swt%) and murram containing different amounts ff cement ( i . e. 2, 4 and 6wt%) were compacted at 5N/mm and cured at 300C and 100% relative humidi ty for periods ranging from 1 to 4 weeks. In the extended work mixtures of murram containing different amounts of lime and lime-gypsum ( i . e . 5, 1 0 and 1Swt% lime and Swt% lime-1.Swt% gypsum, 10wt% lime-3.0wt% gypsum and lSwt% l~e-4.5wt% gypsum) were compacted into cylinders at 10N/mm and cured under the same conditions. The chemical and microstructural changes which occurred during curing were determined using thermal analysis, x¬ray powder diffraction and scanning electron-microscopy. The strength of lime-stabilised murram increases with both increase in curing time and increase in lime conte~t. Addition of up to 6wt% cement and compacting at SN/rnm pressure appears to be less effective with regard to strength deve~opment. I~creasing the compaction pressure from SN/mm to 10N/mm increases the compressive strength of the cured murram-lime material by amounts ranging from 50 to 100%, although only the 15wt% lime addi tion material meets the Ken2an standard requirement for minimum strength (1.5N/mm). Addition of small amounts of gypsum produces very significant increases in strength which meet the Kenyan standard requirement, however, this weakens the lime stabilised murram when exposed to wet-dry durability tests. Diluting murram with 30wt% sand enabled higher strengths to be achieved wi th the same lime content. Stabitising the murram with 10wt% cement and employing 10N/mm pressure also enabled the minimum strength to be achieved, but the material disintegrates when soaked in water. In wet conditions therefore, gypsum addition is not recommended. Also cement stabilisation in the current work fails.
Reaction of lime with murram results in the formation of calcium silicate-aluminate hydrate (C2ASH8) and carbonate substituted calcium aluminate hydrate (C4,ACO• 5H12). When gypsum is present the principal reactlon product is ettringi te which is a calcium sulpho-aluminate hydrate (C3A3CSH32) . | en |
