The physical, chemical, and microstructural characteristics and strength relationships of fired bulk and clay fraction (< 2 μm size) samples of two Cambodian clays (C1 and C4) and a Malaysian clay (BBC) were investigated. The < 2 μm particles were separated from the bulk samples by a repeated sedimentation method and Stokes' law. The physical properties were characterized by particle size distribution, specific surface area (SBET) and cation exchangeable capacity (CEC). To evaluate the strength relationships, the prepared samples were fired at temperatures from 950 to 1200 οC. Results showed that all the clay fraction samples pronounced higher SBET and CEC values than those of the bulk samples. The clay fraction samples showed a decrease of SiO2 (about 6 wt.%) and Fe2O3 (0.5 - 5.1 wt.%) while an increase of Al2O3 (about 3 wt.%) compared with the bulk samples. Both Cambodian clays produced a red body color after firing while the Malaysian clay produced a moderate white color. Firing at ≥ 1050 οC led to the formation of new phases such as mullite and hematite (all samples) and cristobalite (only in C1). The microstructures of all the samples revealed that liquid phase formation occurred at ≥ 1050 οC and became more pronounced at 1200 οC, especially in the clay fraction samples. The relationships of the flexural strength to the bulk density, water absorption, and firing shrinkage were highly correlated at ≥ 1050 οC. Judging from these relationships, as a whole, it can be seen that 1050 οC was considered as the minimum firing temperature for Cambodian clays.

Keywords: Cambodia, Ceramics, Clay, Microstructure, Strength relationship.