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Engineering geopolymer composites (EGC) are promising environmentally friendly building materials with excellent mechanical properties. However, the durability of EGC is compromised by gradual carbonation from atmospheric exposure. For the first time, this study provided an insight of the carbonation of EGC by comprehensively investigating the effect of mix design, such as fly ash/ground granulated blast furnace slag ratio (FA/GGBS ratio), alkali content, water/binder ratio (W/B ratio) and polyethylene (PE) fibre content, on its carbonation resistance. Our results showed the components in EGC affected the carbonation through the alternation of microstructures. An increase of FA content and W/B ratio significantly increased the carbonation depth by 206.6 % and 116.3 % respectively due to the increased porosity and transition pore fraction, resulting in more than 30 % reduction in tensile strength and 15 % reduction in compressive strength. However, increased alkali and fibre content prevent carbonation with around 60 % and 26 % decrease of the carbonation depth, leading to a less loss of the mechanical properties. Furthermore, we tested the pH values of the EGC along the carbonation depth, proposing a novel approach to assess the carbonation degree by dividing the area into completely carbonated area (pH around 9.21–10.44) and non-carbonated area (pH around 12.58–13.37). These findings provide insights for mitigating carbonation effects in EGC and facilitate the widespread use of this sustainable material in construction applications, ensuring long-term durability and reliability. • Effect of various components of EGC on its carbonation resistance. • An optimal mixed design of EGC for maximizing its carbonation durability. • Microscale characterization for investigating the mechanism of EGC carbonation. [ABSTRACT FROM AUTHOR]

• The ambient cured EGC with local PVA fiber was developed. • The impact behaviors of EGC was investigated under cold temperatures. • The influences of different parameters were discussed. This paper was intended to investigate the impact resistance of engineered geopolymer composite (EGC) in cold temperatures. The ambient cured EGC based on local PVA fibers, which has favorable environmental and economic benefits, was first developed and tested under uniaxial compressive and tensile loading conditions. The drooping hammer test machine retrofitted with a liquid nitrogen canister was applied to conduct the impact tests of EGC specimens under different cold temperatures, i.e., −10 ℃, −20 ℃ and −50 ℃. The conventional engineered cementitious composite (ECC) specimens and the corresponding cement mortar were also tested as the control groups. The influences of alkali concentrations on the compressive, tensile and impact behaviors of EGC were investigated. According to the experimental results, it was found that the developed EGC could have comparable compressive strength and tensile behaviors with ECC. For both EGC, ECC and their corresponding matrixes, the impact load increased while the ultimate displacement decreased when the temperature dropped from −10 ℃ to −50 ℃. It was also found that the energy dissipation coefficient of EGC specimens increased with the decrease of temperature, indicating that EGC materials have preferable impact resistance under low or ultra-low temperature environments. [ABSTRACT FROM AUTHOR]

• The ambient cured EGC with local PVA fiber was developed. • The impact behaviors of EGC was investigated under cold temperatures. • The influences of different parameters were discussed. This paper was intended to investigate the impact resistance of engineered geopolymer composite (EGC) in cold temperatures. The ambient cured EGC based on local PVA fibers, which has favorable environmental and economic benefits, was first developed and tested under uniaxial compressive and tensile loading conditions. The drooping hammer test machine retrofitted with a liquid nitrogen canister was applied to conduct the impact tests of EGC specimens under different cold temperatures, i.e., −10 ℃, −20 ℃ and −50 ℃. The conventional engineered cementitious composite (ECC) specimens and the corresponding cement mortar were also tested as the control groups. The influences of alkali concentrations on the compressive, tensile and impact behaviors of EGC were investigated. According to the experimental results, it was found that the developed EGC could have comparable compressive strength and tensile behaviors with ECC. For both EGC, ECC and their corresponding matrixes, the impact load increased while the ultimate displacement decreased when the temperature dropped from −10 ℃ to −50 ℃. It was also found that the energy dissipation coefficient of EGC specimens increased with the decrease of temperature, indicating that EGC materials have preferable impact resistance under low or ultra-low temperature environments. [ABSTRACT FROM AUTHOR]

• The effect of sand-to-binder (S/B) ratio on the bond performance of EGC with concrete and steel reinforcement is reported. • Increasing the S/B ratio improves the bond strength of EGC/concrete substrates. • Direct correlation exists between elastic modulus of EGC and their bond strength with concrete substrates. Engineered geopolymer composites (EGC) have recently emerged as a greener and more environmentally friendly alternative to conventional engineered cementitious composites (ECC), achieving excellent mechanical and durability properties. This study investigated the effect of sand to binder (S / B) ratio on the bond performance of EGC repair material with concrete and steel reinforcement. The S / B ratio of EGC mixes was varied from 0.3 to 1.0, and its effect on the physical and mechanical properties was evaluated. It was found that increasing the S / B ratio decreased the micro-cracks at the EGC-concrete interface and, increased the bond strength. A direct correlation was observed between the elastic modulus of EGC and its bond strength with concrete substrate. The EGC-steel rebar pull-out strength initially increased and then decreased with the S / B ratio. The EGC repair material with S / B ratio more than or equal to 0.8 achieved the minimum EGC-concrete bond strength value of 1.5 MPa, as recommended by the BSI code. [ABSTRACT FROM AUTHOR]

• The ambient cured EGC with local PVA fiber was developed. • The impact behaviors of EGC under elevated temperatures was investigated. • The influences of different parameters were discussed. Engineered geopolymer composite (EGC) is a novel fiber reinforced geopolymeric material with ultra-high ductility, which is more eco-friendly than engineered cementitious composite (ECC) due to the substitution of cement. This paper was intended to investigate the impact behaviours of EGC exposed to elevated temperatures. The ambient cured EGC with local PVA fibers was first designed and tested under compressive and flexural loading conditions. The comparisons between ECC and EGC were made concerning the compressive and flexural behaviours. Then, the drooping hammer tests of EGC, ECC, cement and geopolymer matrixes were conducted under different environment temperatures, i.e., 50 °C, 100 °C and 150 °C. As the temperature increased from 50 °C to 150 °C, the impact resistance of cement decreased while the impact resistance of geopolymer increased gradually. It was also found that EGC has higher maximum impact load and impact duration than ECC as the environment temperature increased, indicating that EGC may be more suitable for the impact protection of structures under high temperatures. At the environment temperature of 50 °C, the energy dissipation capacity of EGC increased with the increase of alkali concentration, while the alkali concentration was recommended to be lower than 12 mol/L when the environment temperature is above 100 °C. [ABSTRACT FROM AUTHOR]