Utilization of OPC and FA to enhance reclaimed lime-fly ash macadam based geopolymers cured at ambient temperature

One kind geopolymer composite cementitious material was synthesized under the activation of modified water glass, using reclaimed lime-fly ash macadam powder (RLFMP) as basic raw material, fly ash (FA) and ordinary Portland cement (OPC) as compound additive. The effects of OPC content, alkali content, water glass modulus and water-solid ratio on the setting time, compressive and flexural strength of the geopolymers cured at room temperature were investigated by orthogonal experiment. In addition, the mineralogical phases, micromorphology and pore distribution characteristics of the final products were characterized through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and Mercury Intrusion Porosimetry (MIP). The results indicated that the OPC content had the most significant effect on the setting time and mechanical properties of geopolymers. With the increase of OPC content, the setting time of geopolymer mortars was greatly shortened, and the compressive strength and flexural strength were obviously improved. When OPC content was 10% of the total cementitious powder mass, alkali content was 11%, water glass modulus was 1.4, and water-solid ratio was 0.35, the 28 day compressive strength of geopolymer pastes cured at room temperature reached the highest of 43.2 MPa. Microstructure analysis showed that the incorporation of OPC promoted the full dissolution of silicaalumina raw materials in alkaline environment, improved the degree of geopolymerization and formed the C(A)-S-H gel products in the reaction system. The C-(A)-S-H gel products were synergistic with the N-A-S-H gel products generated by pure geopolymerization to enhance the compactness and adhesion of the matrix, which was conducive to the improvement of the mechanical properties of geopolymer. This study demonstrates the feasibility of preparing geopolymer with RLFMP at room temperature, which widens the source of geopolymer raw materials and provides a new type of geopolymer composite.