Recent progress in low-carbon binders

The interfacial transition zone (ITZ) has a major detrimental impact on the structural performance of concrete. This negative impact can be modulated by introducing mineral admixtures to a concrete mix, which fill the excessive voids within ITZ and react with portlandite to form more compact products. The approach described here, consisting of characterization of phases and micromechanical modeling, enabled assessment of the effect of silica fume, fly ash, and metakaolin on ITZ thickness and strength. The proposed model was based on the Mori-Tanaka scheme coupled with an estimation of deviatoric stress within ITZ. This study suggests that silica fume is efficient in reducing ITZ thickness, while the addition of fly ash more significantly contributes to ITZ strength. Moderate replacements of Portland cement for silica fume or fly ash, up to 20%, can positively influence concrete performance; in case of metakaolin, replacement up to 10% is recommended.

Impact of silica fume, fly ash, and metakaolin on the thickness and strength of the ITZ in concrete

Effects of chemical composition of fly ash on compressive strength of fly ash cement mortar

Municipal solid waste incineration (MSWI) generates bottom ash, fly ash (FA), and air pollution control (APC) residues as by-products. FA and APC residues are considered hazardous due to the presence of soluble salts and a high concentration of heavy metals, and they should be appropriately treated before disposal. Physicochemical characterization using inductively coupled plasma mass spectroscopy (ICP-MS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) have shown that FA and APC have potential for reuse after treatment as these contain CaO, SiO2, and Al2O3. Studies conducted on treatment of FA and APC are categorized into three groups: (i) separation processes, (ii) solidification/stabilization (S/S) processes, and (iii) thermal processes. Separation processes such as washing, leaching, and electrochemical treatment improve the quality and homogeneity of the ash. S/S processes such as chemical stabilization, accelerate carbonation, and cement solidification modify hazardous species into less toxic constituents. Thermal processes such as sintering, vitrification, and melting are effective at reducing volume and producing a more stable product. In this review paper, the treatment processes are analyzed in relation to ash characteristics. Issues concerning mixing FA and APC residues before treatment, true treatment costs, and challenges are also discussed to provide further insights on the implications and possibilities of utilizing FA and APC as secondary materials.

Characteristics of incineration ash for sustainable treatment and reutilization

Towards ternary binders involving limestone additions — A review

Effects of the fineness of limestone powder and cement on the hydration and strength development of PLC concrete

Effects of the physicochemical properties of fly ash on the compressive strength of high-volume fly ash mortar

Superabsorbent polymers as internal curing agents in alkali activated slag mortars

Self-healing cement composites are generally produced by using materials such as inorganic powders, bacteria pellets, and microcapsules. Among them, inorganic powder-type healing materials tend to decrease in healing performance over time because they react relatively quickly. Accordingly, this study encapsulated self-healing inorganic reactive powders in solid capsules (SC) in order to delay their reaction. The capsule surface was coated with a membrane to prevent moisture from permeating it. SC were utilized to provide the self-healing effect to the repair mortar. SC were mixed at three rates (0%, 5%, and 10%) by the binder mass of the repair mortar. The fundamental properties, including rheology, table flow, strength, and length change, and the self-healing performance of the self-healing repair mortar mixes were investigated. It was found that the rheological and mechanical properties of the repair mortar decreased slightly as the amount of SC increased. On the other hand, for a crack width of 0.25 mm and crack inducing age of 28 days, the healing performance of repair mortar specimens containing SC was at least 20 pt% better than that of plain repair mortar after a healing period of 28 days.

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Fundamental Properties and Self-Healing Performance of Repair Mortar with Solid Capsules Made Using Inorganic Reactive Powder

*In this research, isothermal conduction calorimetry analysis has been conducted to investigate the reactivity of alkali activated slag binders. In order to secure the reactivity and workability of alkali activated slag binders, experiences with various types and concentrations of alkali activators were performed. Isothermal conduction calorimetry were measured with different alkali activators and mass ratio of SO3 to binders as variables, and sodium tripolyphosphate (Na2P3O10) and hydrated sodium borate (Na2B4O710H2O) were used to control setting time. As a results, alkali activated slag binders required alkali activators with 4 to 5 percent of concentration to accelerate the formation of calcium silicate hydrate(C-S-H) by alkali-activation, and overall heat generation rate delayed as accumulated heat decreased due to the high SO3 contents. Moreover, the use of hydrated sodium borate as setting retarder causes elongated setting time due to delaying heat generation, so it can be considered that setting retarder played an important role in delaying total heat generation rate.

http://koreascience.or.kr:80/article/JAKO201534853187661.pdf

Sungwoo Oh

Papers

Effects of the fineness of limestone powder and cement on the hydration and strength development of PLC concrete

Effects of the physicochemical properties of fly ash on the compressive strength of high-volume fly ash mortar

Superabsorbent polymers as internal curing agents in alkali activated slag mortars

Fundamental Properties and Self-Healing Performance of Repair Mortar with Solid Capsules Made Using Inorganic Reactive Powder

Isothermal Conduction Calorimetry Analysis of Alkali Activated Slag Binder