Experimental study on mechanical behavior of steel fiber reinforced geopolymeric recycled aggregate concrete

Abstract

Steel fiber-reinforced geopolymeric recycled aggregate concrete (SF-GRAC) was proposed as a high-performance green concrete, and the mechanical properties were investigated experimentally to promote the use of SF-GRAC in structural engineering. A series of SF-GRAC specimens were prepared with different contents of steel fibers and recycled aggregates, and compression tests, splitting tensile tests and four-point flexural tests were conducted. Meanwhile, the microstructure was observed through scanning electron microscope (SEM) for the interfacial transition zones (ITZ) between the geopolymeric matrix and the recycled aggregates or steel fibers. The results showed that the compressive, tensile and flexural strength of recycled aggregate concrete obviously increased when the original Portland cement (OPC) was replaced with ground granulated blast furnace slag-fly ash based geopolymer, but the ductility and toughness also decreased. By adding up to 1.5% steel fibers, the compressive, tensile and flexural behavior of SF-GRAC were obviously improved, and more premium than OPC concrete with natural aggregates, which made it eligible for structural application. SF-GRAC with 100% recycled aggregate and 1.5% steel fibers had 38% higher compressive strength, 83% higher tensile strength, and 41% higher flexural strength than OPC concrete with natural aggregates, while the compressive and flexural toughness indexes increased over 160% and 170% respectively. Micro morphological analyses illustrated that the microstructure of geopolymeric matrix was denser and more uniform than OPC matrix, and there was no obvious cracks and pores in the ITZs of geopolymeric matrix-aggregate and geopolymeric matrix-steel fiber, indicating a good bonding behavior. Through data-fitting, a series of regression models were proposed to predict the elastic modulus, splitting tensile strength and flexural strength of SF-GRAC, which fit reasonably well with the experimental results. Carbon emission analysis was also conducted on SF-GRAC, which was proven to be a green construction material with over 26% reduction on carbon emission compared to OPC concrete.