Utilization of by-product waste silica in concrete - based materials

Abstract

The usage of waste silica from AlF 3 production is limited due to admixtures of fluoride in its composition. The negative effect of admixtures was eliminated by thermally activating this silica gel. After thermal activation the mineralogical composition of silica gel changes. Fluorine is binding in low-reactive compounds, which insignificant effect on the cement hydration process. The possibilities of using waste by-product silica in hardened cement paste were investigated. Silica gel could be used as additive of the hardened cement paste after thermal activation (1 hour at 800 °C temperature). It was discovered that the optimum content of thermally activated technogenic silica gel additive under the conditions explored was up to 10% of the total quantity of the cement. After 28 days of hardening, the strength of hardened cement paste increased 7 MPa when the quantity of the additive was -10% of the total weight when compared to the strength qualities of the samples with no additives used.

The Prospective Approach for the Reduction of Fluoride Ions Mobility in Industrial Waste by Creating Products of Commercial Value

“…Large amounts of silica gel waste contaminated with fluoride ions are generated in the industrial production of aluminum fluoride [13,14]. In fact, one of the main fertilizer producers in Lithuania, a joint-stock company "Lifosa", generates approximately 15 thousand tons per year of the mentioned waste during the manufacture of 17 thousand tons of AlF 3 [15].…”

“…In fact, one of the main fertilizer producers in Lithuania, a joint-stock company "Lifosa", generates approximately 15 thousand tons per year of the mentioned waste during the manufacture of 17 thousand tons of AlF 3 [15]. In the process of obtaining AlF 3 , the latter compound is formed in the reaction of neutralizing hexafluorosilicic acid with aluminum hydroxide [13,14]: H 2 SiF 6 + 2Al(OH) 3 → 2AlF 3 + SiO 2 •nH 2 O + H 2 O + Q…”

“…According to the literature, untreated silica gel waste can be immobilized in concrete stone [14,19]; however, due to effect of F − ions on the environment, the application in cement industry is limited. Also, F − ions can be bound into stable compounds during the hydrothermal synthesis of lower basicity calcium silicates hydrates [17,18,34].…”

Combined Removal of an MTBE and BTEX Mixture Using Indigenous Microbe Immobilized on Waste Silica Gel

“…In organosilicone products, when R/Si ≈ 2 (R for organic substituents and Si for silica), they are known as silica gel. Even though the simultaneous aerobic removal of a mixture of BTEX, cis-1,2-dichloroethylene (cis-DCE), and trichloroethylene (TCE) using an indigenous bacterial isolate identified as Pseudomonas plecoglossicida immobilized on waste scrap tyres was investigated [14], the reutilization technology for the waste silica gel has not been widely used yet and the waste is commonly stored at landfill sites instead [15]. To the best of our knowledge, this is the first time the waste silica gel was used as a matrix for the simultaneous adsorption and bioremoval of BTEX and MTBE mixture in aqueous solutions.…”

Impact of vibrations on the final characteristics of normal and self-compacting concrete

“…The best is electrofilter SiO 2 (micro silica) that has an average particle size of a few micrometres. Due to its small spherical shaped particles, micro silica insures good cohesion and improved resistance to segregation and is effective in the elimination of bleeding [7][8][9][10] . The other often used additive -flying ash is very efficient in increasing cohesion and reducing the sensitivity to changes in the amount of water.…”