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The Chemistry of Concrete Biodeterioration
Published in Thomas Dyer, Biodeterioration of Concrete, 2017
Oxalic acid is capable of forming a number of salts with calcium of relatively low solubility, the only difference in composition being the amount of associated water of crystallization. Three of these compounds are naturally occurring minerals: the monohydrate (whewellite), the dihydrate (weddellite) and the trihydrate (caoxite). The aluminium and iron (III) salts are highly insoluble in water, with the iron (II) salt being slightly more soluble. The solubility products are given in Table 2.29.
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
Yang et al. (2009) has studied the chemistry behind the incorporation of sticky rice in lime mortars and proved that their addition has improved adhesive strength, waterproof and toughness of mortars due to controlled crystal growth of calcium carbonate. Fang et al. 2013investigated the role of Tung oil in lime putties and concluded that the interaction of unsaturated fatty acids with calcium hydroxide made mortars more stable and greatly influenced the properties of mortars. The behaviour of lime mortars in the presence of cactus mucilage and volcanic ash was studied and justified that their incorporation has greatly improved mechanical properties and reduced porosity due to the precipitation of weddellite (Martínez et al. 2014). Calcium oxalates (Weddellite, whewellite) are important biominerals found in nature, and they are the most plenteous category of organic minerals identified in sediments and hydrothermal veins (Ruiz-Agudo et al. 2017). Hess et al. (2008) have investigated the prehistoric paints in lower Pecos region, Texas and isolated 20 bacterial strains from 8different sites out that majority of strains were bacillus species. After conducting wide range of investigation on bacterial strains, they found that the strains are capable to produce oxalates under vitro conditions. The effective role of jaggery (Unrefined sugars), kadukkai (Terminilachebulia), kulamavu (PerseaMacrantha) in lime mortars has been analysed and found that the addition of fermented organics leads to the formation of weddellite in lime mortar, that drastically increased the physical and mechanical properties (Thirumalini, Ravi, and Rajesh 2018). Again Thirumalini and Sekar 2014 stated that along with conventional formation of calcite, the fermented kadukai and jaggery further enhance the precipitation of calcite by means of bacteria bacillus Subtilis. Now a days in cement mortars, the soil living bacteria such as bacillus cereus, bacillus megaterium, bacillus pasteurii, bacillus sphaericus, bacillus subtilis were incubated in sophisticated facilities and were incorporated in the mortars for self-healing of shrinkage cracks by microbial precipitation of calcite. Also, as a secondary advantage, other properties such as compressive strength, permeability, chloride penetration and water absorption were enhanced (Castanier, Le Metayer-Levrel, and Perthuisot 2000; Krishnapriya and Babu 2015; Siddique et al. 2016; Wang et al. 2017; Huynh et al. 2017). Though many researchers have discussed about the presence of bacterial strains in lime plasters and stone surfaces, still no research work has been done on the bacterial precipitation of calcium carbonate in organic modified lime mortars. Generally, the precipitation of calcite happens in two ways namely, by atmospheric carbon-di-oxide as expressed in Eqn.1(Hearn 1998) and by microbial precipitation. The presence of plant extract in the mortars may accelerate biomineralization due to the presence of bacterial colonies, shown in Eqn. 2. (Dhami, Reddy, and Mukherjee 2014).