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Bun Kim Ngun 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.5
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 ο C. 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 ο C 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 ο C and became more pronounced at 1200 ο C, 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 ο C. Judging from these relationships, as a whole, it can be seen that 1050 ο C was considered as the minimum firing temperature for Cambodian clays.
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Zainal Arifin Ahmad,Bun Kim Ngun,Hasmaliza Mohamad,Etsuo Sakai 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.3
The effects of rice husk ash (RHA) and fume silica (SF) in both binary and ternary systems on the properties of cement pastes and the compressive strength of concretes were studied. The amount of cement replacement in both systems was 15%. The free calcium hydroxide (Ca(OH)2) content was analyzed using XRD and TG/DTA for the hardened cement pastes. The results showed that the amount of Ca(OH)2 decreased significantly the curing ages for all blended cement pastes. At 28 days, the amount of Ca(OH)2 in OPC is 17.31%, 8.18% in RHA and 6.43% in SF replacements, respectively. The ternary system similarly indicates a significant reduction of Ca(OH)2 content. The compressive strength of concretes was improved significantly by blending the aforementioned materials in both systems. In the ternary system, the concretes containing 7.5%SF and 7.5% RHA gave remarkable improvement in the compressive strength. For example after 90 days curing, the strength is 57.8 MPa whilst only 47.5 MPa for OPC. Therefore, the application of proper ratios of RHA and SF in a ternary system is able to increase the properties of the concrete.
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