Environmental properties of cement-free concrete using ground granulated blast-furnace slag

Abstract

To develop the alternative green concrete, alkali-activated slag (AAS) concrete was investigated considering the fundamental properties, durability, and sustainability. For the fundamental properties, physical and chemical properties were considered. To assess the physical properties, the compressive strength, setting time and pore characteristics were investigated. To assess the chemical properties, the hydration products were detected by X-ray diffraction together with scanning electron microscopy to calculate the hydration rate. For the durability, corrosion behavior of mortar specimen was monitored with galvanic current and the factors influencing the corrosion of steel were investigated such as critical chloride contents, binding capacity, chloride transport and threshold corrosion current. Visual test with pore solution was performed to investigate the threshold chloride level and threshold corrosion current. For the sustainability, CO2 emission and alkali leaching were considered comparing with ordinary Portland cement mortar. As a results, it was found that the compressive strength, setting time and porosity were strongly dependent on the OH concentration. Hydration products were different with the activator type. It was also found that the corrosion behavior was strongly dependent on the activator types: Ca(OH)2 used AAS was the most passive in monitoring of the galvanic corrosion, while AAS with KOH and NaOH indicated a similar resistance to the corrosion of steel with Portland cement mortar. Despite AAS paste had a lower chloride binding capacity, it had a higher resistance to chloride transport in chloride profiling test and rapid chloride penetration test. This presumably due to a lower level of pores at capillary range, which was ensured by the pore characteristics of AAS mortar in mercury intrusion porosimetry. For sustainability of AAS, it was found that it was much greater than ordinary Portland cement both CO2 emission and alkali-leaching.