Development of alite calcium sulfoaluminate cement for smart cement-based materials application

Abstract

Different compositions of alite calcium sulfoaluminate (ACSA) clinkers were synthesised for use as an alternative, more environmentally friendly binder than ordinary Portland cement (OPC). ACSA clinkers have a lower firing temperature than OPC clinkers, thus reducing carbon dioxide emissions during processing. Calcium fluoride (CaF2) and copper oxide (CuO) were added to the raw materials and the resulting phase formation for clinkers was compared with and without these additives. Three different compositions of ACSA clinkers as well as six different firing temperatures were tested and evaluated. Results revealed that the additives accelerated initial formation of alite at as low as 1,100°C. The ability to process ACSA at such a low temperature enabled the coexistence of alite - ye'elimite phases in the clinker, while SO3 content greatly influenced alite crystal formation. Unexpected CaSO4×2H2O loss due to evaporation in the firing process initially reduced the ye'elimite phase content below the designed target. Using additional CaSO4×2H2O subsequently increased ye'elimite content to the target level when the experiment was repeated using the optimal composition and temperature.

New smart composites as sensors and actuators in civil engineering for structural health monitoring were fabricated and investigated. A novel 0–3 piezoelectric composite is presented which consists of (K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3 (KNLNTS) as the piezoelectric phase and alite calcium sulphoaluminate cement (ACSA cement) as the matrix phase. Since they are new types of materials, the synthesising processes for each material is intensively investigated. ACSA cement was successfully prepared using an appropriate composition and fired at 1250oC for 30 minutes. The Rietveld refinement technique was used to determine the amount of each quantitative phase, calculated through the XRD patterns from the model structure. Characterisation of the KNLNTS sintered ceramics was investigated by XRD patterns, SEM, dielectric properties, and piezoelectric properties. The optimum synthesising conditions provided sintered KNLNTS ceramics that had dielectric constant and dielectric loss at room temperature values of 1,386 and 0.022, respectively. The KNLNTS/ACSA cement composites were prepared with various KNLNTS content in the range of 30-70 vol.%. The hardened density, acoustic impedance, microstructure, dielectric properties, and piezoelectric coefficient of the composites were also investigated.

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