Utilization of Industrial Waste Slags to Enhance Ground Waste Concrete-Based Inorganic Polymers

Abstract

Recycling and utilization of waste concrete and industrial waste slags is a significant step towards the protection of the environment and sustainable development. Industrial waste slags including ferronickel (Greece) and fayalite (Finland) slags were mixed with ground waste concrete for the production of inorganic polymers (IPs). The effects of different parameters during alkaline activation such as solution concentration (6 to 12 M NaOH), curing temperature (60 to 80 °C), and aging period (7 to 28 days) upon the uniaxial compressive strength of the produced specimens were determined. The optimum conditions for ground concrete waste-based inorganic polymers were found to be the use of alkali activator with mass ratio of Na2SiO3 to NaOH 1 and L/S 0.3 cured at 80 °C for 24 h and aged for 7 days with compressive strength of 16 MPa. Molar ratios of $$\frac{{{\text{SiO}}_{2} }}{{{\text{Al}}_{2} {\text{O}}_{3} }}$$ and $$\frac{{{\text{H}}_{2} {\text{O}}}}{{{\text{Na}}_{2} {\text{O}} + {\text{K}}_{2} {\text{O}}}}$$ in the reactive paste were 16.03 and 13.02, respectively. IPs produced from ground concrete waste (GWC), fayalitic (FS), and ferronickel (LS) slag mixtures; in particular, a mix ratio of 25GWC-25FS-50LS (Na2SiO3 to NaOH 1 and L/S 0.2, cured at 60 °C for 24 h and aged for 7 days) obtained high compressive strength (47 MPa). Molar ratios of $$\frac{{{\text{SiO}}_{2} }}{{{\text{Al}}_{2} {\text{O}}_{3} }}$$ and $$\frac{{{\text{H}}_{2} {\text{O}}}}{{{\text{Na}}_{2} {\text{O}} + {\text{K}}_{2} {\text{O}}}}$$ in the reactive paste were 9.59 and 16.81, respectively. Structural integrity of selected IPs (25GWC-25FS-50LS) was observed when immersed in acidic H2SO4 and salt Na2SO4 solutions of 0.5 M and/or subjected to high-temperature firing (up to 400 °C).