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Industrial minerals
Published in Francis P. Gudyanga, Minerals in Africa, 2020
Natron is an admixture of sodium carbonate decahydrate Na2CO3·10H2O, sodium bicarbonate NaHCO3 together with small quantities of sodium chloride and sodium sulphate. It occurs in saline lake beds in association with thermonatrite, nahcolite, trona, halite, mirabilite, gaylussite, gypsum, and calcite. It is the source of soda ash (sodium carbonate anhydrate N a2CO3) as a result of calcination.
Mosaics
Published in Claudio Alessandri, The Restoration of the Nativity Church in Bethlehem, 2020
Natron is a sodium carbonate mineral associated to low amounts of other salts such as chlorides and sulphates extracted in Egypt, used to produce glass. It was mixed and melted together (glass batch) with a silica-lime sand in which quartz and calcium carbonate were present in suitable ratios to make glass. Sands with such properties were quarried in a few sites, identified up to now in the Levantine area and in Egypt (Freestone, 2005).
Salt Decay and Salt Mixtures in the Architectural Heritage: A Review of the Work of Arnold and Zehnder
Published in International Journal of Architectural Heritage, 2022
To discover which types of salts were present in efflorescence, Arnold would start by using simple field tests. These included manipulating the salts to see if they would dehydrate with the heat of the skin, taste tests (whose safety is not discussed by the author), and tests with pH test paper. The pH tests helped him detect alkaline salts, namely carbonates, and distinguish natron which is alkaline from mirabilite which is not. Their usefulness and simplicity suggested Arnold it would be of interest to include pH data in the tables of characteristics of salts. This was apparently not achieved by the author but would be a useful future development. For deeper qualitative evaluation of the salts, Arnold developed a methodology combining polarizing light microscopy with microchemical tests. He recommended keeping at hand in the lab a collection of salt crystal forms for possible reference and presents a list of their refractive indexes and optical properties, enriched with critical observations derived from his practical experience. He thought this list should in the future be extended to other types of salts, which is another possible and interesting future development of his contribution.
Engineering behavior of ambient-cured geopolymer concrete activated by an alternative silicate from rice husk ash
Published in European Journal of Environmental and Civil Engineering, 2023
Jhon Cárdenas-Pulido, Fernando Ramirez, Diego F. Velandia, Juan C. Reyes, Julian Carrillo, Willian Aperador
The 28-day compressive strength of the GC, GA and TC concretes are shown in Table 6, while the evolution of this parameter is depicted in Figure 9. Overall, the highest strength was exhibited by TC concrete with 24.3 MPa, while GC and GA were 23.2 MPa and 21.0 MPa; strength variations between the GC and GA concretes with respect to TC concrete were only 4.4% and 13.4%, respectively (the difference between GC and GA concretes was only 9%). These similar values allow to reliably compare GC, GA and TC concretes in other engineering properties being the point of reference. Commercial sodium silicate enhances the mechanical strength of geopolymers, along with reduced permeability and a stable structure (Fernandez-Jimenez & Palomo, 2005). Nonetheless, the results in this study demonstrate that alternative sodium silicate from rice husk ash can be used instead of the commercial one for manufacturing ambient-cured geopolymer concrete, since both provide comparable 28-day compressive capacities. The 28-day compressive strength of the GA concrete is also higher than the 17 MPa lower bound prescribed by the ACI 318 Building Code (ACI 318-19, 2019), and hence is acceptable for structural practical applications. Results of this study match well with earlier research (Passuello et al., 2017; Bernal et al., 2012; Kamseu et al., 2017; Bernal et al., 2015), which identified that total replacement of commercial sodium silicate by alternative silicate from rice husk ash does not drastically reduce the compressive strength of geopolymer pastes and mortars, but rather provides comparable behaviors. The comparable 28-day compressive strength of the GA concrete with respect to the GC could be ascribed to: (i) a high release of silicate species at later ages from the alternative silicate capable of participating in the geopolymerization reaction (Hajimohammadi & van Deventer, 2017); (ii) presence of unfiltered residues and remanent undissolved rice husk ash particles in the alternative silicate that fill the porosities of the geopolymer concrete and cause a densified microstructure by packing (Kamseu et al., 2017); and (iii) slight filler effect of the natron and beta-sodium carbonate efflorescence formed (Zhang et al., 2014).