3.4.1. Effect of crushed quartz filler on water reduction
The idea of adding crushed quartz filler to M-S-H binder is inherited from replacement of Portland cement with quartz filler to improve the rheology of cement paste  due to the less water absorption and smooth texture of finely ground quartz particles.
Fig. 9 described water reduction effect as adding crushed quartz filler (QF) to MgO-SiO2 binary system to maintain a fixed flow of MgO-SF-QF ternary system (Series 3, 4, 5). It is obvious that the replacement of cementitous materials by crushed quartz filler improves rheology considerably, expressed by the consistent reduction of water content while maintaining a fixed flow of …show more content…
Samples without filler, although contain highest gel volume but also requires highest water content in the series (w/b=0.36) and consequently has lowest 28-day compressive strength of 43.7 MPa. The introduction of filler content, as at only 10%, is able to reduce water content dramatically to w/b=0.27, leads to the impressive improvement of compressive strength to 85 MPa. Further increase of filler content to 40% results in higher reduction of water content to as low as w/b=0.21 with only a marginal increase of compressive strength to 87 MPa. Testing results have shown that ternary M-S-H binder systems of MgO-SF-QF have higher compressive strength, compared to binary system without fillers. Crushed quart filler is mainly “inert”at room temperature, however, is able to improve workability considerably in M-S-H ternary system (MgO-SF-QF). Fillers content is effective from 10-40% of the binder without clear optimal …show more content…
In this paper, M-S-H mixtures have been prepared and tested to suggest the optimal binder composition to obtainhigh compressive strength paste and mortar with M-S-H binder system. The following concluding remarks have been found from the optimization process:
The binary M-S-H binder system composed of MgO and silica fume containing very high microfine content requires extremely high water content. The use of suitable superplasticizer is critical to reduce water demand in which the optimal dosage of Viscocrete-5-555 (a polycarboxylate SP) is about 3-4% (1-1.5% solids).
The formulation of M-S-H-gel is not the only contributor to thestrength of the binder. The MgO/SiO2 ratio for optimal strength is also dependent on other factors including optimized workability and packing density. Selection of binder composition is therefore complicated and should results from total effect of those factors above.The MgO/SiO2 ratio for optimal compressive strength is found at mixture containing 60% MgO-40% SF.
Use of crushed quartz filler is of utmost important to reduce water content of silica fume. Replacement of M-S-H binder by crushed quartz filler from 10-40% results high strength mixture with very low water to binder