Optimization of the rice husk ash production process for the manufacture of magnesium silicate hydrate cements

Different types of amorphous, silica-rich materials can be employed as supplemental cementitious materials (SCM) in Portland cement compositions that are more common. SCMs react with Ca(OH)2 in the presence of Portland cement and a water solution to create calcium silicate hydrate (C-S-H). When produced under specific circumstances, rice husk ash (RHA) contains a high concentration of amorphous silicon dioxide and is utilized as SCM in Portland cement formulations. Similar to this, materials high in amorphous silica, like RHA, encourage the production of hydrated magnesium silicate gels (M-S-H) in reactive magnesium aqueous solutions. Studies examining RHA's capacity to generate M-S-H under various temperature settings, however, are scarce. For the creation of cellulose-reinforced cementitious composites, M-S-H cements, which have superior mechanical qualities and reduced alkalinity (pH 9-10) as compared to Portland cement, are a suitable option. Because of this, the current study assesses the hydration reaction of magnesium oxide with silica produced from RHA and processed by various heat treatments (500, 550, 600, and 650 degrees C) to generate M-S-H. There were tests for mechanical stability, electrical conductivity, calorimetry, XRD, TG, pH, and more. As benchmarks, compositions containing MgO and commercially active silica (SF) were employed. The findings demonstrate that, in comparison to previous thermal treatments, RHA generated at 500 degrees C (RHA500) enabled the creation of an increased M-S-H concentration. The axial compressive strength of this composition (MgO/RHA500) in the initial phases is comparable to that of the reference composition (MgO/SF). Since the paste consisting of MgO/RHA500 had the lowest pH values at 30 days of curing, even when compared to the pH of the reference composition MgO/SF (pH 10.04), the calcination of RHA at 500 degrees C is also the best treatment to lower the alkalinity of the created system. The MgO/RHA500 composition's decreased alkalinity will enable the RHA generated at lower temperatures to be applied in a new way. The RHA, which is already a by-product of the agro-industrial sector with some added value, serves as a predecessor for the creation of M-S-H cement, which will promote both technical and environmental benefits for non-conventional cementitious materials.