Water Demand And Workability Of M-S-H Binder Case Study

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3.1 Water demand and workability of M-S-H binder system
3.1.1 Optimization of superplasticizer
M-S-H binder contains high content of very fine silica fume particles and therefore requires much higher water demand than Portland cement (PC) for workability (Zhang et al (2009)). Also, the reactive magnesium oxide particles were found to have cells lattice structure and therefore require higher water demand than PC (Eubank, 1951). For those reasons, tests with superplasticizers using the procedure as described in (2.2) were performed to select the most effective superplasticizer type and optimal dosage for M-S-H binder (as shown in figure 1 and figure 2). Figure 1. Water content for fluid paste samples with M-S-H binder.
Figure 1 describes water content to achieve flowable paste mixtures containing 50% MgO + 50% SF with varying superplasticizer types and dosages. It was shown that the mix without superplasticizer (non-SP) required highest water content of
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Similar to PC concrete, w/b ratio significantly affects the strength of M-S-H mortar mixtures, demonstrated by the increase of compressive strength at all testing ages as water content decreases. The mortar samples at 28 days age obtained low strength of only 20 MPa with w/b = 0.50 (w/s=0.40) but achieved high strength of approximate 70 MPa as w/b was reduced to 0.34 (w/s=0.27). The effective range of w/b to achieve high strength of over 50 MPa at 28 days age was found to be lower than w/b=0.375 (w/s=0.30). By using superplasticizer and crushed filler, it was able to produce M-S-H mortar to have 90 days compressive strength of up to 90 MPa. The compressive strength of M-S-H mortar are comparable to a number of Portland cement mortar mixes produced by Allena and Newtson (2010) and Al-Jubory (2013) at similar water to binder

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