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Concrete deterioration mechanisms (A)
Published in Brian Cherry, Green Warren, Corrosion and Protection of Reinforced Concrete, 2021
Hydrated tricalcium aluminate (C3A) can also react with calcium sulphate to produce ettringite, 3CaO.Al2O3.3CaSO4.31H2O. This renders the hardened concrete susceptible to attack by soluble sulphate ions which may be present in penetrating water. Initially a soluble sulphate, for example sodium sulphate, can react with the calcium hydroxide in the pore water to produce calcium sulphate: Na2SO4+CaOH2→CaSO4+2NaOH
Mechanisms of Concrete-Polymer Interactions
Published in Satish Chandra, Yoshihiko Ohama, in Concrete, 2020
Tricalcium aluminate (C3A) is present in cement in small amounts (7 to 8%), but it influences setting and hydration of cement significantly. During hydrolysis, C3A produces C4AH13 and C2AH8 (see Section LA). These are two metastable hexagonal phases. Many organics interact with C4AH13 and form interlayer compounds;37,38 this prevents transformation of C4AH13 to C3AH6. It is considered that incorporation of organic additives into the hydrate lattices could be responsible for this hindrance. Consequently the rate of ettringite formation will be delayed, and small ettringite needles will be formed instead of big ones (Figure 7.15A and B).37
Lime, cement and concrete
Published in Arthur Lyons, Materials for Architects and Builders, 2019
Sulphates are frequently present in soils, but the rate of sulphate attack on concrete is dependent on the soluble sulphate content of the groundwater. Thus, the presence of sodium or magnesium sulphate in solution is more critical than that of calcium sulphate, which is relatively insoluble. Soluble sulphates react with the tricalcium aluminate (C3A) component of the hardened cement paste, producing calcium sulphoaluminate (ettringite). This material occupies a greater volume than the original tricalcium aluminate; therefore, expansion causes cracking, loss of strength and increased vulnerability to further sulphate attack. The continuing attack by sulphates depends on the movement of sulphate-bearing groundwater, and in some cases delayed ettringite formation may not be apparent for 20 years. Delayed ettringite formation is sometimes observed in precast concrete that had been steam-cured, or when the temperature within the in situ mass concrete had risen excessively during the curing process. With magnesium sulphates, deterioration may be more serious as the calcium silicates within the cured concrete are also attacked. The use of sulphate-resisting Portland cement or combinations of Portland cement and fly ash or granulated blast furnace slag reduces the risk of sulphate attack in well-compacted concrete. In the presence of high soluble sulphate concentrations, concrete requires surface protection. The criteria that increase the resistance of the cement matrix to sulphate attack are described in the document PD CEN/TR 15697: 2008.
Biochar as a cost-effective and eco-friendly substitute for binder in concrete: a review
Published in European Journal of Environmental and Civil Engineering, 2023
Carbonaceous matter is in use for construction material (cement, asphalt and bitumen) since early 1960s, but the application of biochar for this purpose was initiated around two decades back in United States (Zhao, Huang, & Shu, 2014). Cement comprises of silicates (tricalcium silicates: C3S: 50–70% and dicalcium silicates: C2S: 15–30%), tricalcium aluminate (C3Al) (5–10%) and tetracalicum aluminoferrite (C3AlFe) (5–15%) with small amounts (<5%) of sodium oxide, potassium oxide and gypsum (Mindess & Young, 1981). Silicates are responsible for the formation of hydration products, viz. calcium hydroxide and calcium silicate hydrate gel with C-S-H linkage during cementing process (Barron, 2010).
Concrete sulfate corrosion coupled with hydraulic pressure
Published in Marine Georesources & Geotechnology, 2020
Researchers have studied several approaches to improve the sulfate corrosion resistance of concrete, such as reducing tricalcium aluminate content in cement, lowering the water/cement (w/c) ratio of concrete, and adding pozzolanic mineral admixtures. Djuric et al. (1996) found that incorporating fly ash could improve the sulfate resistance of concrete. González and Irassar (1997) discovered that reducing tricalcium aluminate content in cement could reduce the risk of concrete sulfate corrosion. Qiao et al. (2006) observed that concrete incorporated with 10 wt.% replacement ratio of cement by fly ash and 20 wt.% replacement ratio of cement by ground granulated blast furnace slag exhibited better resistance to wet/dry cyclic sulfate corrosion than normal concrete. Long, Xie, and Tang (2007) conducted experiments on concrete sulfate corrosion under wet/dry cycle and fully submerged conditions. They found that decreasing the w/c ratio of concrete and increasing the replacement ratio of cement by fly ash and silica fume could effectively reduce sulfate corrosion damage on concrete. Yang et al. (2016) found that air entrainment and incorporation of silica fume could increase the resistance of concrete to wet/dry cyclic sulfate corrosion.