Design, processing and properties of fly ash-based lightweight geopolymer using foaming agent for brick application

Abstract

Lightweight concrete reduces the overall self-weight of the structures resulting in the reduction of the foundation size, cost, and other specification. However, the conventional lightweight concrete production causes several environmental impacts and produce low mechanical properties, so there is a clear need of searching and replacing for more efficient and durable alternatives beyond the limitations of the conventional lightweight concrete. Geopolymer represents a great opportunity to ensure greater sustainability in the construction industry especially for the use of industrial waste such as fly ash. This research focuses on the preparation of fly ash-based lightweight geopolymer using superplasticizer as foaming agent. The superplasticizer (Polyoxyethylene alkyether sulfate) was prepared using pre-formed method by combination with water and air pressure. The effects of geopolymeric synthesis parameters such as the NaOH concentration (6 M, 8 M, 10 M, 12 M and 14 M), ratio of foaming agent to water (1/10, 1/20, 1/30 and 1/40) by volume, ratio of foam to geopolymer paste (0.5, 1.0, 1.5 and 2.0) by volume, curing temperature (40 °C, 60 °C, 80 °C and 100 °C) and curing time (6, 12, 24 and 48) hours on the lightweight geopolymer paste that affect the mechanical and microstructure properties were studied in detailed. The compressive strength, water absorption, density, were studied to determine the mechanical properties of lightweight geopolymer. The thermal insulation properties was investigated through the effects of thermal conductivity, thermal diffusivity, and specific heat of lightweight geopolymer at different ageing time (3, 7, 28, 60 and 90) days. The microstructure properties of lightweight geopolymer were tested by using Scanning Electron Microscope. The results indicated that the lightweight geopolymer have an optimum NaOH concentration of 12 M, with highest compressive strength of 15.2 MPa at 7 days, an optimum ratio of foaming agent to water (1/10) and ratio of foam to geopolymer paste (1.0) with highest strength of 16.6 MPa (7 days), optimum curing temperature (80 °C) and curing time (24 hours) showed the highest strength and lowest density of 15.6 MPa and 1400 kg/m3, respectively. The thermal conductivity and thermal diffusivity of lightweight geopolymer are substantially lower with value of 0.63 W/mK to 0.83 W/mk and 0.26 mm2/s to 0.35 mm2/s, respectively. A potential new lightweight construction material can be produced by using low cost of foaming agent and easy to process for addition to geopolymer paste. The fly ash-based lightweight geopolymer produced in this work exhibit compressive strength in accordance to the standard for masonry lightweight applications at considerably lower curing temperature (80 °C).