Cement and Concrete Research(2024 - 2024)
Unified hydration model for multi-blend fly ash cementitious systems of wide-range replacement rates
Yu Y.; Gunasekara C.; Elakneswaran Y.; Robert D.; Law D.W.; Setunge S.
Cement and Concrete Research, Elsevier Ltd., Vol.180, 2024, MAY.
(https://doi.org/10.1016/j.cemconres.2024.107487)
Abstract
Developments of binary, ternary, and even quaternary cementitious binder materials have been widely recognised in research and practices to elevate the sustainability of modern construction industry. To this end, a robust method to predict the hydration of novel binder systems is essential to facilitate informed material designs, yet extremely lacking. In this study, focusing on fly ash cement binders, a unified hydration model, applicable to multi-blend systems that further incorporate hydrated lime and/or nano silica, is freshly established. The proposed method features kinetic models to predict reaction degree for each binder component that are further coupled with a thermodynamic model to evaluate phase assemblage during hydration. The proposed model is carefully calibrated and verified against separate sets of experimental data. It is demonstrated to be applicable to binders incorporating up to 80 % of total cement replacement, and capable of robustly assessing the influence of multi-blend compositions on the hydrating systems. c 2024 The Authors
Modeling the ionic diffusion coefficient of unsaturated hardened cement paste: A micromechanical approach
Zhang M.; Lin D.; He Z.; Yang R.
Cement and Concrete Research, Elsevier Ltd., Vol.177, 2024, APR.
(https://doi.org/10.1016/j.cemconres.2023.107415)
Abstract
Most of the concrete structures in service are unsaturated, estimating the ionic diffusion coefficient of unsaturated cement-based material is of paramount significance to assessment of corrosion of reinforced concrete. Taking account of the contributions from different water configurations at multi-scale (water films, interlayer water, large gel pore (LGP) water and capillary pore water) and the corresponding diffusion mechanisms of each type of water, a micromechanical model for estimating the ionic diffusion coefficient of unsaturated hardened cement paste (UHCP), is developed in this study. Model results show that the interconnectivity of the spheroidal capillary pore water is closely related to the aspect ratio of spheroidal capillary pore, the slender the prolate pore, the higher the interconnectivity of the capillary pore water; when the capillary pore water is totally drained, water films and interlayer water within C-S-H governs the ionic diffusion, the higher the water to cement ratio (w/c), the less the contribution of interlayer water, and the greater the contribution of water film, to ionic diffusion within UHCP. Application on saturated hardened cement paste and UHCP shows the capability of the model to accurately reproduce the experimental results. c 2023 Elsevier Ltd
Retardation effect of the pozzolanic reaction of low-calcium supplementary cementitious materials on clinker hydration at later age: Effects of pore solution, foreign ions, and pH
Wang T.; Medepalli S.; Zheng Y.; Zhang W.; Ishida T.; Bishnoi S.; Hou D.; Shi Z.
Cement and Concrete Research, Elsevier Ltd., Vol.177, 2024, FEB.
(https://doi.org/10.1016/j.cemconres.2023.107416)
Abstract
Clinker hydration at later age in blended cement pastes was found to be retarded by the pozzolanic reaction of low-calcium supplementary cementitious materials (SCMs). Various mechanisms were explored, including the consumption of pore solution, the presence of foreign ions, and pH-related effects. Experimental results indicated that the dissolution of the foreign ions from SCMs was a secondary effect. The primary cause of the retardation effect was the reduction in pH caused by the pozzolanic reaction. Aqueous precipitation tests yielded the following findings related to pH: (1) At lower pH levels, the precipitation of C?A?S?H gel was reduced due to the decreased nano-adhesion force. (2) The morphology of aluminium-incorporated calcium silicate hydrate (C?A?S?H) gel consisted of small spherical particles at lower pH levels, resulting in a denser capillary pore structure. The latter led to increased water retention within the fine gel pores but a reduced amount of pore solution available in the capillary pores for cement hydration. c 2023 Elsevier Ltd