Effect of Using Shell Molding Sand and Sodium Silicate Sand as Substitute Sources for Cement Raw Materials

Abstract

Abstract

The goal of this study focused on determining the optimal substituting percentage for producing cement from recycled waste foundry sand (including shell molding sand and sodium silicate sand). Raw materials that were used in preparing the pre-determined recipes were heated to 1,400°C for 6 h during the clinkerization process. Resultant clinkers were mixed with limestone to prepare the four types of cement (referred to as FEC-I, FEC-II, FEC-III, and FEC-IV). Proposed results were compared with those of ASTM type I ordinary Portland cement (OPC). Results demonstrate that the major components of OPC, including C₃S, C₂S, C₃A, and C₄AF, were present in all clinkers. Compressive strength of the FEC pastes cured for 28 days was higher than that of the OPC paste. However, the compressive strengths with curing time between 28 and 90 days increased negligibly. X-ray diffraction analyses of the hydrates of the OPC and the FEC pastes revealed that they comprised Ca(OH)₂ and C-S-H gels. Signals in the ²⁹Si magic-angle spinning/nuclear magnetic resonance (²⁹Si MAS/NMR) spectra of the FEC pastes demonstrated increases in intensity from Q¹ and Q² peaks in the hydrated pastes. The degree of hydration and the average length of the linear polysilicate anions in OPC pastes and the FEC pastes increased with time up to 90 days. This study demonstrated the feasibility and safety of utilizing waste shell molding sand (7.6 wt.%) and sodium silicate sand (10.8 wt.%) in the cement manufacturing process.