Spark plasma sintering using calcareous waste concrete powder

Abstract

• Spark plasma sintering (SPS) of milled calcareous waste concrete was investigated. • Waste mortar powder (WMP) and waste coarse aggregate powder (WCAP) were prepared. • The flexural strength of the WMP and WCAP was higher than the ISO 13,006 standard. • Spurrite, gehlenite, wollastonite, larnite, and magnetite were synthesized by SPS. In this study, spark plasma sintering (SPS) was performed using calcareous waste concrete powder. In particular, we examined the sintering temperature for SPS. This improved the flexural strength and flexural modulus. Two types of calcareous waste concrete powders were prepared: waste mortar powder (WMP) and waste coarse aggregate powder (WCAP). The characteristics of the sintered bodies were evaluated using a three-point flexural test and powder X-ray diffraction (XRD). As the main crystalline component of the raw powder, WMP included calcite and quartz, and WCAP included calcite and hematite. Regarding the flexural strength of the sintered body, WMP had 52.6 MPa at a sintering temperature of 900 °C, and WCAP had 42.4 MPa at a sintering temperature of 850 °C. These values are higher than the value of 35 MPa of ISO 13,006 standard, which prescribes porcelain stoneware tiles. XRD analysis reveals the synthesis of spurrite, gehlenite, wollastonite, and larnite in WMP, and in WCAP, spurrite and magnetite are confirmed. The synthesis of these chemical compounds is attributed to the decarbonation reaction of calcite at 760 °C. Therefore, calcareous concrete can be used as a raw material for construction ceramics when applied to SPS.