INVESTIGATION OF ALKALI SILICA REACTION OF WASTE GLASS AS AGGREGATES IN FOAMED CONCRETE

Abstract

Foamed concrete is a special type of lightweight concrete which has given attention due to its low consumption of energy, good thermal insulation, and excellent sound absorption. It is well known that concrete industry consumes natural raw materials, therefore using waste glass in concrete may be one of the solutions to reduce natural resources consumption, reduce solid waste stream as well as inhibit environmental pollution. This research focused on examining Alkali-Silica Reaction phenomenon of foamed concrete mixes containing different types of crushed waste glass incorporating as fine aggregate, coarse aggregate and powder with different chemical compositions and at different percentages 0%, 25%, 50%, 75% of sand volume. In this study, foamed concrete mixes were designed at density of 1200 kg/m3 and 0.49 w/c ratio. Four types of waste glass (soda-lime glass, boro-silicate glass, green glass and lead silicate glass) were added as partial replacement of sand volume. All have been used as fine aggregate with maximum particle size of 2.36mm, coarse aggregate with particles sizes between 4.75mm and 9.5 mm and glass powder. Polypropylene fibers 12mm long with aspect ratio of 667 were used at 0.5% by the total volume of foamed concrete mix. A homogenous distribution of coarse aggregates glass was achieved due to manual distribution. The reactivity was determined in sodium hydroxide solution by adopting mortar bar test. Then, scanning electron microscopy and energy dispersive X-Ray technique were used to investigate microstructure of some mixes. The effect of crushed waste glass on hardened properties including porosity, water absorption and sorptivity were studied and mechanical properties were investigated as well. Finally, thermal conductivity and ultrasonic pulse velocity of mixes were examined. The results of this study showed occurrence of Alkali-Silica Reaction (ASR) phenomenon in conventional foamed concrete mixes (without waste glass). Also, it was noticed that the expansion in conventional foamed concrete is considerably less than that of normal concrete mix by about 24% due to the porous structure of foamed concrete. The recorded expansion due to ASR in foamed concrete mixes increased by about (26%-66%) with increasing the percentage of added waste glass as a replacement of sand volume. In addition, the chemical composition of recycled waste glass (glass type) significantly influenced the reaction of alkali-silica. Lead-silicate glass exhibited the higher expansion of about 83% while green glass had the lower effect a round 49%. Furthermore, it was found that the use of coarse aggregate glass resulted in higher expansion than that of fine aggregate glass. While using powder glass and polypropylene fibers helped in solving the ASR problem by decreasing its reaction by approximately 64% and 55%, respectively. Certain decrease in porosity, water absorption and sorptivity was noticed with incorporation the four types of waste glass in foamed concrete mixes. Mechanical properties of foamed concrete mixes were enhanced with incorporation waste glass Also; the results showed decreasing in thermal conductivity with using the four types of waste glass as aggregate In general, the results showed a good enhancement in properties of foamed concrete with increasing the addition of waste glass. In addition to use aggregate glass, using waste glass as a powder and adding polypropylene fibers was proved as a good solution to overcome the ASR phenomenon problem in foamed concrete made with waste glass as aggregate.