International Concrete Abstracts Portal

Carbon-based nanomaterials such as graphene oxide sheetreinforced cementitious composites have attracted extensive interest owing to their improved post-fire mechanical properties. However, the role of graphene in anti-thermal detriment is still unclear. In the current study, the mechanical characteristics, pore structure, and interface evolution of graphene-toughened cementbased materials under high temperatures are investigated. Scanning electron microscope analysis showed that graphene implanted in the cement matrix had out-of-plane deformation at elevated temperature. The deformation caused the evolution of the interface between graphene and the cement-based material with respect to temperature. Correspondingly, the toughening effect of graphene on cement-based materials decreased first and then increased. The reinforced domain of graphene switched from mesopores to capillary pores when the temperature was beyond 400°C, contributing to the enhanced reinforcement efficiency of the cement mortar. The interfacial evolution process with an in-depth analysis based on multiple scales would benefit from optimizing the design of graphene composites at high temperatures.

The durability performance of geopolymer concrete against severe environmental conditions is important for implementing geopolymer binders as alternatives to ordinary portland cement (OPC). In this experimental investigation, the impact of adding graphene on the durability characteristics of geopolymer concrete was examined. Graphene was added at 0.5% by weight of aluminosilicate precursors in geopolymer concrete. Permeability, salt ponding, capillary sorptivity, and immersion in chemical agents were performed to assess the durability characteristics of geopolymer concrete without and with graphene, which were also compared with the durability characteristics of OPC concrete without and with graphene. It was found that the addition of graphene in geopolymer concrete reduced the permeable voids by 12% and water absorption by 9%, and improved the resistance against chloride penetration and sulfuric acid exposure. The compressive strength of geopolymer concrete increased by 20% with the addition of graphene. Also, an approximately 70% reduction in the initial and final rate of water absorption was observed in geopolymer concrete with the addition of graphene.

Thermal-cured alkali-activated binders (AABs) are a potential replacement for traditional portland cement (PC) in concrete, primarily for precast applications. To avoid this energy-intensive regime and encourage wider application, this study investigates the development of ambient-cured AABs by adding graphene oxide (GO) nanoparticles. The mechanical strength and durability characteristics are determined for alkali-activated slag (AAS) mortar specimens prepared using 4, 6, and 8 molar (4, 6, and 8 M) concentrations of sodium hydroxide in the alkaline activator. The different percentages of GO by weight of slag are 0.0, 0.03, 0.06, and 0.09%. The mechanical parameters considered are compressive, flexural, and splitting tensile strengths. The durability parameters investigated are the rapid chloride permeability test (RCPT), sorptivity, and acid resistance. The performance of ambient-cured AAS mortar specimens containing GO is compared with thermalcured AAS mortar specimens (without any GO inclusions) and the control cement mortar (PC) to evaluate the effect of GO on the mortar characteristics. The strength of AAS mortar is observed to be higher both with and without GO inclusions for the molarity of sodium hydroxide greater than 4 M. The mixture containing 0.06% GO with a 4 M activator is found to exhibit optimal mechanical and durability characteristics. Mineralogical, chemical, and microstructural investigations confirm that the addition of GO to the ambient-cured AAS accelerates the rate of hydration, even at a lower concentration of the activator (4 M) due to its high specific surface area and consequent formation of a greater number of nucleation sites. Hence, ambient-cured AAS mortar prepared using 4 M sodium hydroxide and 0.06% GO is recommended for practical use.

In this study, the effects of graphene oxide/isobutyltriethoxysilane (GS) composite emulsion, ordinary fly ash (OFA), and silanemodified fly ash (SFA) on the mechanical and waterproofing performances of hardened cement pastes (HCPs) were investigated. In addition, the influence of OFA and SFA on the protective effect of GS was studied. The results showed that GS decreased the compressive strength of the HCPs and significantly improved their waterproofing performance. The compressive strength and waterproofing performance of the HCPs decreased because of the replacement of cement with fly ash (FA), but its toughness improved owing to the effect of FA refining the crystal size of calcium hydroxide. Compared with OFA, SFA was conducive to forming a denser gel network structure composed of SFA, GS, and calcium-silicatehydrate (C-S-H), significantly improving the performance of the HCPs and the protective effect of GS.

An environmentally friendly pervious concrete was developed by using fly ash as the sole binder modified by graphene oxide (GO). The density, void ratio, mechanical strength, Young’s modulus, infiltration rate, deicer salt scaling, and degradation resistance of this pervious concrete were measured against three control groups. The test results indicated that the addition of 0.02% GO (by weight of fly ash) significantly increased compressive strength, split tensile strength, Young’s modulus, deicer salt scaling resistance, and degradation resistance of the fly ash pervious concrete. Overall, this innovative fly ash pervious concrete showed a comparable performance to portland cement pervious concrete. A microscopic investigation using an electron microprobe was also conducted to obtain more insights on the effects of GO and chemical activators on the fly ash pervious concrete.