Effect of some waste additives on the physical and mechanical properties of gypsum plaster composites

Gypsum plaster composites were synthesized by blending plaster with 0.2–10% of unburnt rice husk, blast furnace slag, calcium carbonate or commercial poly vinyl alcohol polymer (PVA). The normal consistency (NC) and setting time (ST) in addition to apparent porosity (AP), bulk density (BD) and compressive strength (CS) of the composites were determined after 7 and 28 days. Results indicated that rice husk, polymer and calcium carbonate increased while slag decreased NC. All additives delayed the setting time, increased the AP and decreased BD of their corresponding composites. The effect of their addition is exaggerated with increased added ratios of either of them. Their compressive strength, on the other hand, increased with slight addition of either of them then it decreased by further increased additions. Physicomechanical properties elucidated that the added wastes exist in the interstitial pores and spaces of the plaster matrix in the composites without any sign of interaction between either of them and set plaster. The formed composites although did not much improve their mechanical properties yet they consume in their formation either cheap available materials or some wastes. The synthesized plaster composites help to clean environment and can be used for low-economical cheap lightweight units suitable for load bearing non-concrete low-height walls of buildings.