Infrastructure Engineering - Research Publications

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    A Comparative Study on the Degradation of Alkali-Activated Slag/Fly Ash and Cement-Based Mortars in Phosphoric Acid
    Ren, J ; Zhang, L ; Zhu, Y ; Li, Z ; San Nicolas, R (FRONTIERS MEDIA SA, 2022-03-09)
    This study compares the degradation behavior of the alkali-activated slag/fly ash (AASF) and ordinary Portland cement (OPC) mortars exposed to phosphoric acid with different pH values. The experimental results show that AASF mortars exhibit better resistance than OPC mortars against surface damage, although both systems get white deposits on the surface in phosphoric acid with a relatively high pH level. AASF mortars obtained lower mass loss than OPC mortars in phosphoric acid with pH at 2 and 3. The strength reduction in AASF mortars after immersion in phosphoric acid is more significant than that in OPC mortars. However, total degradation depth of AASF was smaller than that of OPC regardless of the pH of the acid solutions. Based on the experimental data, linear relationships were identified between the slope of degradation depth–mass loss curves and the Al/Si and Ca/Si ratios of the binders. This may indicate a new way to assess the degradation behavior of AASF and OPC based on their chemical compositions.
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    Constructing a novel nano-TiO2/Epoxy resin composite and its application in alkali-activated slag/fly ash pastes
    Ren, J ; Guo, S-Y ; Zhao, T-J ; Chen, J-Z ; San Nicolas, R ; Zhang, L (Elsevier, 2020-01-30)
    A novel in-situ synthetic method is developed for fabrication of inorganic-organic hybrid structured TiO2/Epoxy resin composite without adding any surfactants. It is discovered for the first time that the inorganic-organic micro-structured TiO2/Epoxy composite can be homogeneously dispersed in one type of alkali-activated binders: alkali-activated slag/fly ash (AASF) pastes with slag/fly ash at 50/50. Besides, it is found that TiO2/Epoxy composite is capable of enhancing the mechanical properties including compressive and flexural bending strengths, improving porous structures and reducing drying shrinkage of the AASF paste. Moreover, scanning electron microscopy results showed that the AASF binder enhanced by TiO2/Epoxy resin composite has a smooth and flat morphology with fewer cracks as compared to the control paste, leading to a denser microstructure. It is assumed that both TiO2 and epoxy resin are beneficial in improving the microstructure and hence the macroscopic properties of AASF binders were also improved. Since the preparation of TiO2/Epoxy composite through in-situ polymerization method is attractive because of its simple manufacturing procedure and cost-effectiveness, its modified AASF binders have an appealing potential to be used for large-scale production and field applications in the foreseeable future.
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    Degradation of Alkali-Activated Slag and Fly Ash Mortars under Different Aggressive Acid Conditions
    Ren, J ; Zhang, L ; San Nicolas, R (ASCE-AMER SOC CIVIL ENGINEERS, 2021-07-01)
    Acidic environments constitute serious chemical threats to concrete-like cementitious materials. The purpose of this study is to experimentally investigate the degradation of alkali-activated slag/fly ash mortars with different slag/fly ash ratios: 80/20, 60/40, and 40/60 in acidic environments. Mortar samples were exposed to three different types of aggressive acidic solutions: phosphoric acid, sulfuric acid, and a mixture of phosphoric acid and sulfuric acid maintained at a constant pH value of 2.5±0.5 for a period of 150 days. Results showed that, for all mortar samples, the aggressivity of the phosphoric acid is greater compared to the other acids. Moreover, samples with a slag/fly ash ratio of 60/40 demonstrate the highest resistance against the three types of acidic environments. In addition, it shows that the degradation process of alkali-activated mortars can be divided into two degradation stages: an early stage and a subsequent stage. The chemical-reaction dominated early degradation stage is described by using Hill function, whereas a diffusion process-dominated subsequent stage is simulated with Fick's second law. Finally, the results of theoretical analysis predicted that the degradation depth of alkali-activated slag/fly ash mortars exposed to sulfuric acid environment (pH=2.0) for 50 years could be reduced by about 52%-60% compared to that of an ordinary Portland cement (OPC)-based mortar.
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    Degradation resistance of different cementitious materials to phosphoric acid attack at early stage
    Ren, J ; Zhang, L ; Walkley, B ; Black, JR ; San Nicolas, R (PERGAMON-ELSEVIER SCIENCE LTD, 2021-10-06)
    Sewer wastewater systems pose great threats to OPC-based concretes used for pipes due to the presence of various acids. Phosphoric acid can cause as much damage as sulphuric acid but has been very lightly studied. This study focuses on the early stage of the degradation process of different cementitious materials in phosphoric acid. Three types of cementitious materials are compared: OPC (100% cement), slag-blended OPC (slag/cement mass ratio at 65/35) and alkali-activated slag/fly ash pastes (slag/fly ash mass ratio at 50/50). Samples were exposed to phosphoric acid solution with a constant pH at 2.0 ± 0.2 for 44 days. The degradation kinetics, chemical and microstructural properties as well as dissolution rate of these binders are analysed. The results show that the alkali-activated slag/fly ash binder has the lowest degradation rate compared to the other cement-based binders. The intrinsic characteristics of the binders lead to significant changes in the kinetics of degradation. The chemical properties of the binders are the critical influential factor of the early stage behaviour. A conceptual degradation process is proposed to describe the early-stage kinetics of degradation for the cementitious materials studied.
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    Degradation process of alkali-activated slag/fly ash and Portland cement-based pastes exposed to phosphoric acid
    Ren, J ; Zhang, L ; Nicolas, RS (Elsevier, 2020-01-30)
    High costs are currently involved in the repair and replacement of sewage concrete pipes due to the severe damage caused by the acid-rich aggressive environments of sewage and drainage wastewater. Although it is known that, a high concentration of phosphoric acid exists in some sewer pipes, very few studies have been focused on its impact on various cementitious materials. The purpose of this study is to experimentally investigate the resistance of alkali-activated slag/fly ash-based pastes and compare them to ordinary Portland cement-based pastes exposed to phosphoric acid with different pH values (pH = 2, 3 and 4) for a period of 150 days. The experimental results revealed that alkali-activated slag/fly ash-based pastes are more resistant to phosphoric acid attacks compared to ordinary Portland cement-based peers. Furthermore, it is also observed that the kinetics of degradation of the pastes are vastly different, depending on their binders: the degradation process of ordinary Portland cement-based pastes can be described by using Power law, while the degradation process of alkali-activated slag/fly ash-based pastes is divided into an early stage and a later stage which can be described by using the Hill function and the Power law, respectively. The theoretical model developed in this study predicts that, under strong phosphoric acid condition for a period of 50 years, alkali-activated slag/fly ash-based pastes could potentially reduce the degradation depth by around 70%–80% in comparison to ordinary Portland cement-based pastes.