Development, engineering properties and potential applications of unfired earth bricks reinforced by coal fly ash, lime and wood aggregates

Abstract

The current study developed and evaluated the engineering properties of improved low-cost UEBs reinforced with various lime (L)-coal fly ash (F)-wood aggregate (W) mix ratios. The objectives were; (1) to determine the effects of lime-coal fly ash-wood aggregate mixtures on mechanical strength and water resistance properties of UEBs; and (2) to determine the comparative cost of the improved UEBs to that of the control (10% cement). Four UEBs with various lime (L)-coal fly ash (F)-wood aggregates (W) mix ratios (L4%-F16%-W1.5%; L4%-F16%-W3%; L8%-F12%-W3%; L10%-F10%-W1.5%) were fabricated and their engineering properties compared to those of unstabilised (negative control) and 10% cement stabilized (positive control) unfired earth bricks. Dry compressive strength (DCS) of UEBs stabilized by L10%-F10%-W1.5% (8.3 MPa) was significantly higher (p < 0.001) than that of 10% cement stabilized unfired bricks (7 MPa). DCS and dry density of the four UEBs conformed to the British Standards for low-density clay masonry units. DCS increased with lime-fly ash ratio according to a power function (y=−5.41x2+11.18x+2.22; r2 =0.95, p = 0.018), attaining a maximum of 8.3 MPa at a ratio of 1: 1. However, UEBs had low wet strength, but incorporation of 4% cement significantly increased (p < 0.001) the wet compressive strength of UEBs to 0.94 MPa. UEBs stabilized by 10% lime, 10% coal ash, 1.5% wood aggregates and 4% cement (L10%-F10%-W1.5%-C4%) had water absorption (15.8%) similar to that of 10% cement stabilized UEBs. Moreover, unfired earth bricks reinforced by L10%-F10%-W1.5%-C4% conformed to British Standards engineering specifications for low-density clay masonry units, while the cost was 50% lower than that of cement stabilized bricks, demonstrating the low-cost of the UEBs. In summary, the results demonstrate that improved low-cost UEBs can be developed by incorporating lime, coal fly ash and wood aggregates, but a little cement (4%) may be required to increase the wet compressive strength. Potential applications of the UEBs include, (1) internal partitioning; (2) construction of low-cost housing for low-income households in developing countries, and (3) the provision of temporary or short-term low-cost shelter for displaced persons in humanitarian emergencies.