The Coexistence of the Poly(phospho-siloxo) Networks and Calcium Phosphates on the Compressive Strengths of the Acid-Based Geopolymers Obtained at Room Temperature

• Published in: Journal of inorganic and organometallic polymers and materials Vol. 31; no. 8; pp. 3301 - 3323
• Main Authors: Riyap, Hamed I., Tazune, F. Kenne, Fotio, Daniel, Tchakouté, Hervé K., Nanseu-Njiki, Charles P., Rüscher, Claus H.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.08.2021; Springer Nature B.V
• Subjects: Acids; Aluminosilicates; Aluminum oxide; Aluminum silicates; Bauxite; Bayer process; Calcium aluminate; Calcium oxide; Calcium phosphates; Calcium silicate hydrate; Chemistry; Chemistry and Materials Science; Compressive strength; Geopolymers; Inorganic Chemistry; Organic Chemistry; Phosphoric acid; Polymer Sciences; Reagents; Roasting; Room temperature; Silicon dioxide; Slaked lime; Waste fired brick; Brushite; Acid-based geopolymers; Poly(phospho-siloxo); Calcium sources; Monetite
• ISSN: 1574-1443; 1574-1451
• DOI: 10.1007/s10904-021-01949-8

This work aims to investigate the coexistence of the poly(phospho-siloxo) networks and calcium phosphates on the compressive strengths of the acid-based geopolymers obtained at room temperature. Waste fired brick and phosphoric acid were used as an aluminosilicate and chemical reagent, respectively. Calcium aluminate hydrate was prepared by mixing calcium hydroxide from the calcined eggshell and calcined bauxite. Calcium silicate hydrate was obtained by the mixture of rice husk ash and calcium hydroxide. The molar ratios CaO/Al 2 O 3 and CaO/SiO 2 in the calcium aluminate and calcium silicate hydrates are equals to 1.0. The X-ray patterns of the acid-based geopolymers indicate the broad hump structure between 18 and 38°(2θ). In addition to this broad band, those from the mixture of calcium sources show the reflection peaks of monetite and brushite. The compressive strength of the reference is 56.43 MPa. Those obtained with the addition of 10, 20, 40 and 50 g of calcined eggshell are 30.15, 22.85, 21.16 and 13.47 MPa, respectively. The ones from calcium aluminate hydrate are 32.62, 31.58, 17.83 and 16.33 MPa, respectively. Whereas those containing calcium silicate hydrate are 44.02, 42.71, 40.19 and 18.59 MPa, respectively. This work demonstrates that the formation of calcium phosphates in the structure of the acid-based geopolymers decreases the poly(phospho-siloxo) chains and therefore reduces their compressive strengths. The moderate addition of calcium silicate hydrate reduces slightly the compressive strengths of the acid-based geopolymers which can be comparable to the one of CEM II 42.5R.