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Self-Healing Cementitious Materials
Published in Ghasan Fahim Huseien, Iman Faridmehr, Mohammad Hajmohammadian Baghban, Self-Healing Cementitious Materials, 2022
Ghasan Fahim Huseien, Iman Faridmehr, Mohammad Hajmohammadian Baghban
It was demonstrated that the geopolymer was formed due to the addition of the geomaterial with a content of 71.3% SiO2 and 15.4% Al2O3 to the expansive material through a separate polymerization of the aluminate and silicate complexes [20]. The presence of the alkali metals caused the dissolution of the polymerized aluminate and silicate complexes at the alkaline pH. As uncovered by an extensive examination, the geopolymer gel particles were less than 2 µm in size, and a large number of hydro-garnet or Aft phases were produced by the cracked interfacial phases associated with the original ruptured zone (Figure 3.1). In comparison to the hydro-garnet phase, the dense phase contained most of the altered geopolymer gel as revealed by the EDX spectra. According to the additional analysis of the chemical additives, an improvement was achieved by the supplementing regular concrete enclosing the NaHCO3, Na2CO3, and Li2CO3. Such composition triggered the cementitious re-crystallization and concrete particle precipitation [20]. The conclusion reached was that the crack self-repair could be greatly enhanced through the addition of sufficient quantities of the carbonates and expansive agents.
Chloride Binding and Its Effects on Characteristics of Cement-Based Materials
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
Besides C-S-H gel, chloride binding can also have some effects on other hydration products. Ekolu et al. (2006) reported that at a specific chloride concentration, AFm phase in cement-based materials would be destroyed while most of the AFt phase remained unchanged. As the chloride concentration continually increased, the AFm and AFt phases were both decomposed and transformed into Friedel’s salt and gypsum. Balonis et al. (2010) studied the interaction between chloride ions and AFm phases within hydrated cement, and a comprehensive picture of phase transfer with the increase of chloride concentration was provided, as shown in Figure 4.9. When chloride ions are introduced under service conditions, chloride ions can readily displace the OH, SO4, and CO3 ions in AFm phases and transfer into Kuzel’s salt or Friedel’s salt. Meanwhile, ettringite with lower density is formed and results in the increase of solid phase volume (Jensen and Pratt 1989; Shi et al. 2016).
HPCs and Alkali Silica Reactions. The Double Role of Pozzolanic Materials
Published in Yves Malier, High Performance Concrete, 2018
Solid species formed during the hydration of binders (CSH, portlandite, ettringite, AFm and AFt phases) incorporate a large proportion of initial mixing water into their structure. The composition of the residual fluid is rapidly stabilised (approx. one week) when Portland cement is used. Hydration of certain additions (natural or artificial pozzolanas) is slower, and corresponding soluble species are liberated more slowly in solution.
Effect of type and particle size of superabsorbent polymers on the hydration mechanism of pavement concrete
Published in International Journal of Pavement Engineering, 2023
Yawen Tan, Huaxin Chen, Rui He, Zhe Yang
It can be seen from Figures 11–16, Table 5, and Table 6 that the Wdeh values of ref-2 at 1 d, 3 d, and 7 d are 0.96, 1.04, and 1.03 times of ref-1 respectively. Therefore, the content of C-S-H, AFm, and AFt phases at1 d is slightly higher than ref-2, whereas the content of C-S-H, AFm, and AFt phases at 3 d and 7 d increases with the increase of w/c ratio. Also, weight loss of the dehydroxylation of Ca(OH)2 phase (Wdeo), chemically bound water (Wcb), and hydration degree (α) have the similar variation characteristics (Liu et al. 2017). It is explained that cement-based materials with a high w/c have more abundant hydration products and a higher degree of hydration after 3 d due to a higher w/c ratio is generally more contributed to the full hydration of cement.
Influence of pH on the leaching behavior of a solidified arsenic contaminated soil
Published in Environmental Technology, 2023
Wenjie Zhang, Haisheng Yu, Jinxiang Huang, Weiguo Jiao
The XRD patterns of the specimens before and after leaching are shown in Figure 4. Quartz, albite, potassium feldspar, and cordierite were the main phases in the solidified soil before leaching. The iron oxides/hydroxides which peaked at 54°–56° (2θ) could strongly adsorb and/or co-precipitate with As and thus immobilize it [48]. Peaks of the portlandite phase and Ettringite (AFt) can be observed in the XRD patterns, which are the hydration products of cement. The AFt phases appeared at 9°–10° (2θ) and 15°–16° (2θ), which have a strong ion exchange capacity and are considered to have the potential to immobilize As [49,50]. Another hydration product, the CSH phase, was not observed in the XRD patterns because it is mainly an amorphous gel [51]. After leaching, the density of portlandite, AFt, and iron oxide/hydroxide phases decreased as the pH of the leaching solution decreased, owing to the dissolution or erosion under acidic conditions [24]. The density of the portlandite and AFt phases increased slightly in the weakly alkaline leachant due to promotion of the hydration process of cement [43]. In addition, the density of the iron oxide/hydroxide phase of the specimens decreased slightly in the strongly alkaline leachant (pH 11) as compared to that in the weakly alkaline leachant (pH 9). This indicated that some iron oxides/hydroxides dissolved and hence led to As desorption [47]. The leaching behaviors in the semi-dynamic leaching tests were consistent with the variations in the XRD spectra.
Very high early strength calcium aluminate based binary and ternary cementitious systems: properties, hydration and microstructure
Published in European Journal of Environmental and Civil Engineering, 2023
Murat Saydan, Ülkü Sultan Keskin, Burak Uzal
In addition, when all binary and ternary systems were examined, it was observed that the increase in cement ratios was reduced the expansion of the specimens and even it was caused shrinkage in most cases at late-ages. On the contrary, the expansions dominated the dimensional properties in systems using less cement by ratio. Considering to this situation, it is evaluated that the increase in the CAC/Hh ratio in the mixtures was caused shrinkage. On the other hand, although the decrease of this ratio was generated the expansion in late-ages, the shrinkage occurs in the early stages of hydration. In addition, it is understood from the graphs given in Figures 7–9 that SF does not have a direct effect on the length changes of the specimens in terms of expansion and shrinkage. However, it can be seen that the length changes in the specimens using 60% CAC, 30% SF and 10% Hh in all CAC types were proportionally lesser than containing 60% CAC, 30% Hh and 10% SF. In particular, this supports the idea that the addition of SF not only shows a filler effect but also reduces the amount of metastable or expansion-sensitive AFm-AFt phases in the systems, thus limiting expansion and shrinkage.