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The Chemistry of Concrete Biodeterioration
Published in Thomas Dyer, Biodeterioration of Concrete, 2017
Carbonic acid undergoes very little by way of interaction with ions encountered in Portland cement, as shown in Table 2.13. However, its interaction with calcium is of great importance. Under higher pH conditions, calcium carbonate (CaCO3) is formed (Figure 2.12). The most stable form of calcium carbonate at normal ambient conditions is calcite, although vaterite is often also formed, gradually converting to calcite. The aragonite form may be precipitated at elevated temperatures. At lower pH values, calcium forms CaHCO3+, with the charge balanced by a bicarbonate ion. This means that calcium in this configuration can be viewed as being present as Ca(HCO3)2—calcium hydrogencarbonate (also referred to as calcium bicarbonate).
Practical insights into the recycling of green mussel shells (Perna Viridis) for the production of precipitated calcium carbonate
Published in Environmental Technology, 2022
A. Prihanto, S. Muryanto, R. Ismail, J. Jamari, A. P. Bayuseno
SEM analysis revealed a non-uniform polyhedral and cubical-like morphology with 3–5 m size and calcite and vaterite agglomeration. The current synthesis proposed that by increasing the reaction time of the CO2 stream, the vaterite content of the PCC structure could be increased. The powder products contained calcium carbonates in a variety of polymorphic forms, which could be used to synthesize calcium orthophosphate for biomedical applications [36]. Furthermore, the rate of agitation during the precipitation process may have a significant impact on vaterite particles for vascular medicine. Vaterite is suitable for use in biomedicine due to its biocompatibility [48,49] and low toxicity [22,50]. The high purity of vaterite with homogeneous spherical particles is essential for ensuring marketability in the medical industry. These distinguishing particles are required for drug delivery to the lung to achieve the desired level of penetrance [51–53]. In particular, powder processing procedures could produce vaterite with particle sizes ranging from 300 nm to 6 m.
Evaluation of self-healing performance of concrete containing fly ash and fibres
Published in Australian Journal of Structural Engineering, 2021
Seyedehtina Sajjadi, Rahmat Madandoust
As was observed in previous sections, self-healing has happened almost to all mixtures, but the important issue is what did make healing happened? The factor that filled the cracks can be seen in Figure 6. This agent has grown out of cracks and it can be seen at the outer surface of the cracks. Also, when the secondary tensile test was carried out, after the failure of the specimens, this white substance was observed at the inner surface of the specimens. To investigate the infrastructure of this substance, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS) were carried out. The self-healing agent has been identified in Figure 7. In Figure 7(a), a five hundred times magnification, and in Figure 7(b), a three thousand times magnification of rhombus calcite crystals are observed based on identified morphologies in previous studies (Choi, Inoue, and Sengoku 2018; Escoffres, Desmettre, and Charron 2018). Also, calcium carbonate is observed in the form of vaterite in Figure 7(c) (Choi, Inoue, and Sengoku 2018; Escoffres, Desmettre, and Charron 2018).
Identification of Bio-Minerals and Their Origin in Lime Mortars of Ancient Monument: Thanjavur Palace
Published in International Journal of Architectural Heritage, 2021
Sriram Pradeep, Thirumalini Selvaraj
Along with biological calcium oxalates, Rodriguez et al. 2007 have stated the influence of bacterial species and organic molecules in the precipitation of vaterite. The bacterial walls are composed of carboxyl, hydroxyl, phosphite sites (Schultze-Lam et al. 1996). These functional groups have greater control over the crystal stabilization and promote the precipitation of vaterite. As discussed earlier the mortars are prepared with fermented plant extracts that exhibit the supersaturation state along with bacterial species. Hence, the predominate presence of vaterite in palace samples could be due to the control of bacterial cell surface along with organic molecules. Ravi, Thirumalini, and Taher (2018) have discussed the role of vaterite in ancient structure, Charminar, Hyderabad, India and identified vaterite as a major polymorph in the lime mortars. They concluded that due to the mitigation of calcium carbonate to vaterite, the structure longevity is improved. Hence, the presence of calcium oxalates and vaterite in Thanjavur palace could be one of the reasons for long-term durability of the structure.