Development and performance evaluation of diatomaceous earth-based geopolymer concrete incorporated with sisal fibres and high-density polyethylene wastes

Abstract

The building industry is facing challenges in terms of resource management, excessive energy consumption, and CO 2 emissions resulting from the extended usage of concrete made primarily of Portland cement and ceramic bricks. Geopolymer technology has caught the attention of many researchers in an attempt to promote the development of sustainable concrete. This study investigates how to utilize diatomaceous earth as a resource for geopolymers. Little research has been conducted on the use of diatomaceous earth as a stand-alone geopolymer precursor or in combination with natural fibres and/or polymeric additives, although, it has become a significant source of industrial waste that ends up in landfills. The primary goal of the study was to develop and analyse the performance properties of diatomaceous earth-based geopolymer concrete incorporated with sisal fibres and high-density polyethylene wastes. The specific objectives were: to characterize diatomaceous earth in relation to chemical, physical, thermal, and mineralogical features; fabricate geopolymer concrete from alkaline activated diatomaceous earth with the addition of sisal fibres and HDPE waste; analyze the effect of incorporating sisal fibres and HDPE wastes on the performance properties of the geopolymer concrete; and to generate correlational and predictive models for the developed geopolymer performance properties. The methodology involved using standard techniques to characterize diatomaceous earth that had been calcined at 600 °C and in its raw state. After 28 days of curing, the alkaline (lime)-activated specimens were tested for their mechanical, physical, and thermal characteristics. The geopolymer performance correlation and predictive models were developed using linear and polynomial regression approaches. The chemical composition showed that silica was the main constituent, making up 88.12% of the raw sample and 89.92% of the calcined sample. The optimum material mixture for the lime- activated geopolymers was found to contain 83.75 %wt diatomite, 15 %wt lime, and 1.25 %wt sisal fibres yielding 2.72 MPa of compressive strength, 0.72 g/cm 3 bulk density and 0.110 W/mK thermal conductivity. In comparison to the acceptable standards for the concrete masonry units, as stated in ASTM C1634 and ASTM C129, the properties of the lime-activated diatomite-based concrete suggested the necessity for modification. The optimum performance outcomes of the modification, which comprised substituting sodium hydroxide and sodium silicate activation for lime activation, were a compressive strength of 34.10 MPa, a bulk density of 1.32 g/cm 3 , water absorption of 13.93 %, and 0.322 W/mK thermal conductivity. Bulk density and water absorption showed a strong correlation with compressive strength. The diatomite under investigation is a class F pozzolan, and it can be used to produce sisal-fibre reinforced geopolymer concrete with acceptable performance for masonry walling materials. There was a strong correlation between certain performance characteristics and the amount of sisal fibre incorporation. Additionally, strong correlations between performance properties were found. The practicality, economic viability, and durability of cellulosic fibre-reinforced geopolymer composites were however deemed to require further study. The development of standards and specifications for the manufacturing of geopolymers as well as their functional properties was also recommended.