Feasibility of recycling fly ash and aluminum by-product wastes for lightweight concrete

The objective of this study is to investigate parameters to formulate these wastes into useful construction products. Autoclaved cellular concrete, SSH high strength binder mixture and mine backfill technologies are employed for feasible products and versatile applications.; Aluminum metal is mixed with alkali solution, and soluble aluminum hydroxide product and H2 gas are produced as a result of the hydroxide-metallic aluminum gas forming reaction. Porous structure is developed by means of the entrapment of H2 gas in the fly ash based concrete mixture. The foamed concrete consists of about 75% as pores and 25% as solids in volume. The degree of expansion is dependent on the pH value and the quantity of aluminum metal.; The factors governing H2 gas generation are pH value of alkalis, the amount of aluminum metal and the degree of oxidation of aluminum metal in the slag. NaOH reveals high pH value (0.1M→pH13) and induces vigorous H2 gas generation reaction. CaO has a lower alkalinity potential than NaOH and contributes to late strength progress. Gypsum slurry is an effective additive for H2 gas holding potential in the concrete mixture. Blending procedure removes the outer oxidized layer of the aluminum slag and leads to quick H2 generation reaction. Successful results were obtained from aluminum slag with sufficient amount of H2 gas generation.; After a foamed concrete undergone setting and hardening, hydrothermal treatment induces rapid reaction of C-S-H. This autoclaving process under the operation pressure of 300 psi at the temperature of 420°F incurs 2.5 times the strength of the concrete cured for 28 days in the saturated lime solution. As aluminum slag is applied to the fly ash based binder mixture which has a pH value over 13.6, highly porous concrete product is created as a result of H2 gas generation. The high pH value is according to the high alkalinity of NaOH and Na2SiO3·5H 2O. This product yields high strength value by means of an elevated curing procedure in a radient oven. This cellular concrete displays 35--40 pcf in density and 300--600 psi in strength. This lightweight concrete has a potential to replace gypsum products with the properties of 45--50 in density and less than 100 psi in strength.; The aeration process in a concrete structure provides outstanding properties of thermal resistance and acoustic insulation coupled with a lower density level. The cellular concrete behaves similar to wood product without combustibility, decay and termite damage. Also this product has a high rating on fire resistance due to the inherent concrete nature. (Abstract shortened by UMI.)...