Fly ash based geopolymer as lightweight aggregate with low processing temperature for structural insulating concrete application.

The lightweight aggregate in concrete has been broadly used nowadays due to its low density with great mechanical properties. These lightweight aggregates can be produced by thermal treatment from either naturally resource or from industrial by-product. However, the current production methods usually involving high energy due to high sintering temperature used despite of giving a great mechanical properties. Hence, there is a clear need of searching and replacing for more competent and proficient methods beyond the limitations of the current methods. Geopolymer becomes an attractive research due to its improving concrete properties and preserves the environment by using industrial waste such as fly ash. This research focuses on producing a fly ash geopolymer lightweight aggregate with good thermal insulation properties for structural concrete application with minimal sintering temperature by using geopolymerization methods. The 1effects of geopolymeric synthesis parameters such as the NaOH concentration (6 M, 8 M, 10 M, 12 M and 14 M), ratio of fly ash/alkali activator (2.0, 2.5, 3.0 and 3.5), and sintering temperature (400 °C to 1200 °C) to the fly ash geopolymer lightweight aggregate on mechanical and microstructure properties were studied. The optimum aggregate properties in term of highest impact strength with low density and water absorption then tested its thermal insulation properties through the effects of thermal conductivity, thermal diffusivity and specific heat capacity of aggregates. The results indicated that the fly ash geopolymer aggregate have an optimum NaOH concentration of 12 M with AIV of 22.43 % and an optimum ratio fly ash/alkali activator of 3.0 with AIV of 21.43 %. For the effect of sintering temperature, the results showed aggregate with sintering temperature of 900 °C gives the lowest AIV value (14.77 %) indicating highest impact strength with lightweight density (1730 kg/m3) and lowest water absorption (4.50 %). For thermal properties, at the aggregate of 900 °C shows the lowest thermal conductivity and diffusivity of 0.585 W/mK and 0.358 mm2/s, respectively. The performance of fly ash geopolymer lightweight aggregate in OPC concrete were tested for its mechanical and thermal properties and compared with the concrete of commercial lightweight aggregate. The results of concrete with fly ash geopolymer lightweight aggregate has shown better properties in term of strength with 43.71 MPa of compressive strength at 28 days, water absorption of 8.36 % and density of 1735 kg/m3 which can be classified as structural lightweight aggregate concrete according to ACI 213R. Concrete with fly ash geopolymer lightweight aggregate presented good thermal insulation properties through thermal conductivity results as low as 0.28 W/mK which makes it suitable for use as a good thermal insulation material. This work expands the findings contribution of microspheres in fly ash and the effect of iron (Fe) content to the geopolymerization process as well as produces a geopolymer lightweight aggregate with good thermal properties and high impact strength at low processing temperature.