Geopolymer binders are a promising alternative to ordinary Portland cement (OPC) because they can significantly reduce CO2 emissions. However, to apply geopolymer in concrete, it is critical to understand the compatibility between the coarse aggregate and the geopolymer binder. Experimental studies were conducted to explore the effect of the size of the coarse aggregate on the mechanical properties and microstructure of a metakaolin-based geopolymer (MKGP) concrete and ordinary concrete. Three coarse aggregate size grades (5–10 mm, 10–16 mm, and 16–20 mm) were adopted to prepare the specimens. The microstructure of the concretes was investigated with scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and mercury intrusion porosimetry (MIP). Results showed an opposite coarse aggregate size effect between OPC and MKGP specimens in terms of compressive strength. SEM/EDS analysis indicated that the MKGP concrete has a weaker microstructure compared to OPC concrete induced by a higher porosity. The differences in mechanical properties and pore structure between the MKGP and OPC concrete are attributed to the greatly differing shrinkages triggered by the large surface area and penny-shaped particles of metakaolin. The findings in this work help tailor the mechanical properties and microstructure of MKGP concrete for future engineering applications.
Marine concrete structures are subjected to a harsh environment and potential climate change variables. Deterioration of the structure demands drastic measures for repair and rehabilitation. Advanced composite materials exhibit unique advantages compared to conventional construction materials. Over the years, carbon fiber reinforced polymer (CFRP) composite material has been used widely for the repair and rehabilitation of structures. Many studies have been conducted on the performance of FRP flexural strengthened reinforced concrete (RC) members. Still, experimental studies investigating the performance of shear strengthening under real environmental conditions are lacking. This paper helps fill this gap because it is an experimental investigation of the behavior of CFRP shear strengthened RC beams under a marine environment. Specimens were exposed to cyclic (wet/dry) and full exposure to the elements for a 3-month period. Six strengthened beams and one unstrengthened beam were tested; the tested control beam failed due to a diagonal-tension crack. The increase in the concrete shear capacity of the strengthened specimens was in the range of 14-18% compared to the control beam. Thus, the results lead to the conclusion that CFRP strengthening increases the shear capacity of specimens considerably.
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