The medium to long term engineering performance of high-strength geopolymer concrete systems are largely dependent on fluid ingress and the transport phenomena that govern permeability of structural members exposed to aggressive environments. For the purpose of analysing durability performance, both high pressure water and gas permeability testing of fly-ash geopolymer(GP) concretes have been assessed for samples cured under ambient and steam exposure conditions at 65OC. The observed mean permeability coefficient values for gas(k) and water(Kw) of steam-cured structural grade concrete was respectively 6.19E-17m2 at 300kPa gas pressure and 1.52E-10m/s at 525kPa water pressure. While mean gas permeability values were comparable to reference steam-cured ordinary Portland cement(OPC) systems, the corresponding water permeability coefficient data for geopolymer concrete was ten-fold higher. The transport properties of OPC concrete systems are typically governed by water-to-cement ratio and the degree of hydration which is linked to the level of porosity and pore interconnectivity. However, corresponding permeability of geopolymer concrete appears to be dictated by an inherent mesoporous capillary pore network structure for which transport properties appear to be partly dependent on mode of concrete curing. The Paper examines global implications of increased permeability and key durability parameters such as chloride diffusion, carbonation rates and steel reinforcement corrosion on long-term engineering and durability performance.
Based on the temperature rise caused by adiabatic process and the viscosity of the metal under the impact of steel, the Johnson-Cook constitutive relation of structural steel in civil engineering was modified. Applying the Split-Hopkinson Pressure Bar (SHPB) testing technique, the impact experiment under elevated temperatures (25, 350, 450 and 750℃) and high stain rates (2300 and 3200s-1) of Q345 steel was performed. Johnson-Cook constitutive model of structural steel was modified on the basis of adiabatic warming effect and Perzyna constitutive model. Based on the result of the experiment, the fitting curves were drawn and compared with the revised constitutive model. The results showed that Q345 steel has obvious strain rate hardening effect and temperature soften effect, and the curves of the modified constitutive model and the experimental results matched very well. The modified Johnson-Cook constitutive relationship can precisely describe the dynamic characteristic of Q345 steel under the impact of temperature effect and strain rate effect.
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