Abstract
This study investigated the reactivity properties of self-leveling hybrid alkali-activated cements, such as ordinary Portland cement (OPC) and its residual precursors, coal bottom ash (BA), and rice husk ash (RHA). Due to the relatively low reactivity of BA, binary mixes were produced with OPC using contents of 2.5–30% in the treated BA samples. Furthermore, ternary mixes were prepared in proportions of 25%, 50%, and 75% with RHA as a replacement material for the OPC (mix with 90%:10% BA:OPC). For all of the mixes the spreading behaviors were fixed to obtain a self-levelling mortar, and dimensional changes, such as curling and shrinkage, were performed. Mortars with 30% OPC reached a compressive strength of 33.5 MPa and flexural strength of 7.53 MPa. A scanning electron microscope (SEM) and X-ray powder diffraction (XRD) were used to indicate the formation of N-A-S-H and a (N,C)-A-S-H gel, similar to the gel with trace of calcium. The best performance was achieved when the binary mix produced 10% OPC. A hybrid mortar of OPS-BA presented 10 times lower susceptibility to curling than an OPC mortar. The results showed that both ashes reduced the shrinkage and curling phenomena.
Highlights
Alkali-activated materials (AAM) are widely known as an eco-efficient cement due to its low CO2 emissions and reuse of waste residue, achieving physical and mechanical properties similar to ordinary Portland cement (OPC) [1,2,3,4]
scanning electron microscope (SEM) analyses showed that hybrid mortar with more than 10% of Portland cement produced gels with traces of calcium, which increased the durability and than 10% of Portland cement produced gels with traces of calcium, which increased the durability strength of mortars
Even with very low content, the presence of calcium provided from OPC was the key to achieve mortars with good mechanical and durability properties
Summary
Alkali-activated materials (AAM) are widely known as an eco-efficient cement due to its low CO2 emissions and reuse of waste residue, achieving physical and mechanical properties similar to ordinary Portland cement (OPC) [1,2,3,4]. An aluminosilicate mineral and an alkaline solution are required for activation [5]. Industrial waste, as the fly ash (FA), blast-furnace slag (BFS), and bottom ash (BA) are commonly used as aluminosilicate minerals in alkaline activation [6,7,8,9]. To ensure the sufficient reactivity of this precursor material, a larger amount of amorphous silica and relatively small particle size are required [14,15,16]. To develops a greater mechanical strength AAM-based depends on ash reactivity [6,11,12], and a higher rate of dissolution in alkaline medium [5]. If the dissolution and solidification process of calcium is faster than Si/Al, acceleration hardens [17,18,19]
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