Improved processes for the production of soil-cement building blocks

Abstract

Stabilised-soil cement building blocks are an established building material in many areas of the Less Developed World. This thesis has been split into three parts. Part A presented an overview of the process of soil-stabilisation and outlined the roles which soil structure and curing play in stabilisation. It examined methods of testing soils, highlighting errors presented in the published literature and presenting corrected testing procedures and unified plans for their implementation. Part B examined the conventional quasi-static block compaction process (slowly applied pressure) and established that no cost-effective increase in the compacted block density can be achieved by altering such moulding configurations as mould-wall roughness, mould-wall taper, number of applied pressure cycles and double-sided pressure application. The tests were also used to assess the plausibility of several theoretical mechanisms underlying quasi -static compaction. Cement may be traded against compaction pressure for a given final cured strength. The relation of compaction pressure and cement content to well-cured strength was established for 50 mm diameter cylinders and used to assess the financial benefit of high-pressure compaction. It was shown that savings in the cost of cement associated with high-pressure compaction were outweighed by the additional cost of such machinery. However there were additional benefits found to high-density compaction, beyond the saving in stabiliser costs. It was established that a highdensity moulding machine in the range £1000 - £1500 would allow these benefits to become cost competitive. Part C examined both experimentally and theoretically an alternative dynamic (impact blow) compaction process, establishing that optimised dynamic compaction may produce strength equivalent to quasi-static high-density moulding while requiring only 25-50 % of the energy. Five theoretical models of the process were developed and the Combined Airlock/Friction/Compression Wave Model was shown to have the most explanatory power