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Chemical and Physical Interactions between Chlorides and Cement Hydrates
Published in Shi Caijun, Yuan Qiang, He Fuqiang, Hu Xiang, Transport and Interactions of Chlorides in Cement-Based Materials, 2019
Shi Caijun, Yuan Qiang, He Fuqiang, Hu Xiang
Birnin-Yauri and Glasser (1998) presented that chloride ions can be also adsorbed by AFt phase even under the condition of low chloride ion concentration. However, no experimental results were obtained to confirm the validity of this assumption. Hirao et al. (2005) studied the chloride binding capacity of AFt phase and found that chloride ions in external solution cannot be bound by AFt phase and the morphology of AFt phase (Figure 3.8) were unchanged after being exposed to chloride solution. Elakneswaran et al. (2009a) reported that the chloride binding capacity of AFt phase lied between Friedel’s salt and C-S-H gel, and the interaction between AFt phase and chloride ions belongs to physical adsorption. The differences of chloride concentration in these studies and the reversibility of physical adsorption may be responsible for the different conclusions drawn in these studies. Generally, the AFt phase in cement paste can decompose into Friedel’s salt at high concentration of chloride ions (Hirao et al. 2005). However, the content of AFt phase in cement paste is much less than that of C-S-H gel; the chloride binding of AFt phase can be mostly neglected.
Literature Review
Published in Habeeb Lateef Muttashar, Sustainable Construction Materials, 2019
The discrepancies in NaOH or sodium silicate are ascribed to the different Si/Al ratios produced and to the larger or smaller quantities of (zeolitic) crystalline phases present in the matrix. In addition, the existence of silicate ions leads to the creation of more dense structures, with gels richer in Si (Duxson et al., 2005; Fernández-Jiménez and Palomo, 2005b; Fernández-Jiménez, 2006; Criado, 2007). Sulfate attacks in OPC-based concretes or mortar are mostly ascribed to the generation of expansive ettringite (AFt phase) and gypsum. The sulfate ions interfere inside the concrete and react with portlandite Ca (OH)2 to form gypsum. In the existence of enough sulfate, the metastable mono-sulfo-aluminate converts into ettringite, which subsequently absorbs moisture to undergo expansion cracking and spalling (Žarnić et al., 2001). Generally, GP products are devoid of Ca(OH)2 where mono-sulfo-aluminates are formed from resource materials that enclose little or no Ca. Finally, upon exposure to sodium sulfate solution, the growth of gypsum and ettringite ceases. This in turn results in the expansion of the matrix, implying that the GP samples have become resistant against sulfate attack.
The Chemistry of Concrete Biodeterioration
Published in Thomas Dyer, Biodeterioration of Concrete, 2017
Additionally there are two groups of compounds containing aluminium and iron known as the AFt (‘aluminoferrite-tri’) and AFm (aluminoferrite-mono) phases. The most commonly encountered AFt phase in plain hydrated Portland cement is ettringite, which has the formula 3CaO. (Al,Fe)2O3(CaSO4)3.32H2O. The most commonly encountered AFm phase is monosulphate (3CaO.(Al,Fe)2O3.CaSO4.12H2O). These phases contain sulphate, which derives from the calcium sulfate added to the clinker. However, under different chemical conditions the sulphate can be replaced with a wide range of different anions, and the quantity of chemically combined water can also vary.
Durability of concrete with nano-particles under combined action of carbonation and alkali silica reaction
Published in Journal of Asian Architecture and Building Engineering, 2019
Maohua Zhang, Wenyue Zhang, Yanyu Sun
Inductively, the high pozzolanic activity of nano-SiO2, the intense absorbability and substitution effect of nano-Fe2O3 can reduce the concentration of Ca2+ and the PH of pore solution, as well as make CH to form C-S-H gel with low Ca/Si, AFm and AFt phase hydration products to enhance the durability of concrete under the combined action of carbonation and ASR.