In this study, a multi-scale model called DuCOM (Durability COncrete Model), which is developed by the Concrete Laboratory at the University of Tokyo, is extended by coupling the geochemical code PHREEQC. The coupled numeri-cal framework can address physicochemical and geochemical processes such as the hydration of cement particles, pore structure formation, multispecies transport, activity effect, thermodynamic reaction between aqueous solution and solids, etc. in cementitious materials, and therefore, it can potentially be used to assess the long-term durability of concrete structures. The model prediction for the composition of cement hydrates, pore solution chemistry, calcium profiles for the cement paste exposed in pure water, and calcium and sulphur profiles for the cement paste immersed in the sodium sulphate solution are qualitatively and quantitatively compared with experimental results obtained from literature. Fi-nally, the importance of the strong coupling among various processes and mechanisms in the DuCOM-PHREEQC sys-tem is discussed.

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Ground treated ultrafine-POFA obtained from palm oil industry was heat-treated to remove excess carbon. The varied proportion (17%, 30% and 40%) of UPOFA was incorporated into the ultra-high strength concrete (UHSC) to study its effects on the UPOFA-UHSC (U_x-UHSC) in comparison with OPC-UHSC (U₀-UHSC) engineering and transport properties. The U_x-UHSC has an increasing workability tendency with a retarded setting times as compared to U₀-UHSC. Besides, U_x-UHSC registered higher compressive strength than the U₀-UHSC. The 90-d strength of 156 MPa was achieved in U₁₇-UHSC which was 4.7%, 7.5% and 12.2% higher than the values obtained for U₃₀-UHSC, U₄₀-UHSC and U₀-UHSC, respectively. The U₄₀-UHSC exhibited the greatest improvement at 90 days in transport properties such as porosity, water absorption, initial surface absorption, rapid chloride permeability, gas permeability and water permeability while the highest strength was recorded with U₁₇-UHSC. Thus, the pozzolanic UPOFA is capable of improving the engineering and transport properties of UHSC.

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