Ternary Systems Case Study

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Ternary systems MgO-SF-QF
3.4.1. Effect of crushed quartz filler on water reduction
The idea of adding crushed quartz filler to M-S-H binder is derived from a study of Portland cement replacement with quartz filler to improve the rheology [25] due to the less water absorption and smooth texture of finely ground quartz particles.
Fig. 9, 10 described water reduction effect of adding crushed quartz filler to maintain a fixed flow of MgO-SF-QF ternary systems (Series 3, 4, 5). The replacement of cementitous materials by crushed quartz filler improves rheology considerably, expressed by the consistent reduction of water content while maintaining a minimum flow of 120-125 mm for workability. The amount of reduced water is proportional to the increase
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13 shows dependence of compressive strength on water content of ternary systems. As w/s decreases, total water content in the mix decreases and results in increased strength, except two mixes in series 4 (S4.30 and S4.40). These two mixes include very high filler content at 30-40% in which the decrease of water content might not compensate the strength loss due to the reduction of cementitious materials (MgO + SF). From this figure, the effective range of w/s to achieve the highest strength is found in each series. To achieve the optimal compressive strength of over 80 MPa, the mortar mixtures required low SF content (MgO/SiO2 = 60/40) in combination with low water content of w/s = 0.21-0.27 (equivalent to w/cm = 0.30-0.35 (Table …show more content…
High SF content binder might contain unreacted silica fume particles in low water content mixtures, results in poor particle packing and reduces strength. As testing both binary and ternary systems, the optimal binder composition for strength was observed with mixture of 60/40 MgO/SF ratio instead of 40/60 MgO/SF ratio as required by stoichiometry for chemical reactions to form M-S-H gel. The optimal binder composition, therefore, is dependent not only on the MgO/SiO2 ratio for maximum formation of M-S-H gel, but also the MgO/SiO2 ratio for maximum packing density characterized by particle size and shape of each constituent in the binder. By adding crushed quartz filler from 10-40% binder, the compressive strength and workability improves considerably. Compressive strengths of Q20 and Q30 samples indicate the effective crushed quartz filler content of between

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