Journal article

Synthesis of calcium silicate from selective thermal transformation of waste glass and waste shell

Building materials Recycling Waste minimization


This study details a new pathway for successfully synthesising calcium silicate compounds using 100% waste inputs and processing temperatures significantly lower than conventional approaches. Using a solid-state reaction of two common wastes – powdered float glass from building demolition and sea shells discarded by the food industry, wollastonite (β-CaSiO3) and pseudo-wollastonite (α-CaSiO3) were obtained at 1100 °C and 1200 °C respectively. By comparison, a minimum processing temperature of 1436 °C has previously been required to achieve the same result. For both products, the optimum ratio of powdered glass to CaO derived from the mixed sea shell waste was 75:25. SEM analysis showed the wollastonite produced was dense with small sized porosity. By increasing the temperature to 1200 °C, smoother surface of pseudo-wollastonite was achieved with an acicular crystal structure observed at the fracture surface. Interactions between glass and CaO powder at 1000 °C, 1100 °C and 1200 °C were also studied using confocal microscopy. This revealed that the solubility and viscosity of the glass plays key roles in the production of the calcium silicate compounds. The hardness, flexural and compressive strength of the products increased in line with increases in temperature from 1100 to 1200 °C, with maximum values of 198.6 N/mm2, 30.1 and 110 MPa achieved, respectively. By measuring the mechanical properties of the calcium silicate compounds produced, we confirmed these 100% ‘made from waste’ slabs are potential low cost, energy-saving alternatives to ceramic tiles.


  • Calcium silicate compound made from 100% waste materials is proposed.
  • Wollastonite and acicular crystal pseudo-wollastonite were successfully produced at 1100 and 1200 °C respectively by using solid state reaction.
  • Particle interaction among the powder filler, mechanical properties and microstructure of the final product were reported.
  • The prototypes demonstrated superior mechanical performance that is comparable to ceramic tiles.
Publication Details
20 January 2018
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