Abstract
Magnesium silicate hydrate (M–S–H) formed on reaction of MgO and reactive SiO2 imparts binding characteristics similar to Portland cement (PC). Limited knowledge is available on the long-term mechanical and durability performance of M–S–H binder systems. In this study, the performance of MgO–SiO2 binder was assessed up to 365 days. In addition to silica fume (SF), the most widely used silica source with MgO, calcined clay (CC) with kaolinite content of ~ 40–50% and industrial grade metakaolin (MK) were also investigated. Mortar specimens were prepared with all the three silica sources at three different proportion levels of MgO and silica source. Thermodynamic modelling was carried out to further understand the changes occurring in the phase assemblage during hydration for the adopted proportions. Concrete mixes comprising of MgO and MK or SF in a ratio of 1:1 and PC as a control mix were cast a water to binder ratio of 0.4. The compressive strength and porosity were measured at 7, 28, 90 and 365 days on mortar and concrete specimens. In addition, elastic modulus and electrical resistivity was also measured on the concrete samples at all the above-mentioned ages. MgO mixes with CC and MK showed a continual increase in compressive strength until 365 days whereas strength retrogression was observed in MgO–SF mixes after 90 days. The durability indicators for MgO–MK concrete showed better or similar performance as compared to PC. The aluminum present in the CC and MK helps to improve the overall characteristics of the MgO–SiO2 binder.
Highlights
Magnesium silicate hydrate (M–S–H) is one of the most recently developed and least investigated binders among the various MgO cementitious systems [1] whose current state-of-the-art uses a formulation that is based on the hydration of light burnt MgO in the presence of reactive SiO2
This study investigates the long-term performance of the M–S–H binder consisting of silica fume, along with widely available kaolinitic clay and metakaolin alongside MgO
The dissolved silica subsequently reacts with brucite to form M–S–H assisting in further strength
Summary
Magnesium silicate hydrate (M–S–H) is one of the most recently developed and least investigated binders among the various MgO cementitious systems [1] whose current state-of-the-art uses a formulation that is based on the hydration of light burnt MgO in the presence of reactive SiO2. In the pursuit of an environmentally sustainable alternative to the Portland cement (PC), the dominant binding material for modern day-concrete, M–S–H binders are attracting considerable attention. Zhang et al [11] were able to formulate a paste with compressive strength as high as 70 MPa at 28 days. Similar encouragement can be identified from the study of Tran and Scott [12] who obtained 28 days strengths as high as 87 MPa in their mortar formulation and Sonat et al [13] reported strength around 75 MPa in their concrete formulation
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