OPTIMIZATION OF WATER TREATMENT PLANT SLUDGE AND SLAG-BASED GEOPOLYMER CONCRETE TO PRODUCE AN ENVIRONMENTALLY FRIENDLY ALTERNATIVE TO TRADITIONAL CONCRETE

Annually, 635 million cubic meters of water treatment plant sludge (WTPS) is produced in Egypt and is treated as waste and disposed back to the Nile River. Alternative disposable routes, such as using WTPS as a binder in construction applications, are under consideration. Also, industrial by-products such as ground granulated blast furnace slag (GGBFS), fly ash, and other aluminosilicate sources are commonly used as binders for geopolymers, which are explored as potential replacements for cement due to their lower carbon dioxide emissions, with reduction of approximately 800 kg/ton compared to traditional cement production. Utilizing WTPS and GGBFS as binders for geopolymer concrete provides an economical and environmentally friendly alternative to cement. This study investigates the optimum geopolymer concrete mix using a combination of WTPS and GGBFS as a binder to investigate their mechanical properties to be used for construction applications. Various mixing ratios of GGBFS to WTPS (50:50 and 25:75) were studied. The activator solution consisted of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), with a solution modulus of 1.0 for all developed mixes. The Na₂O to binder ratio varied between 10%, 12%, and 14% for each GGBFS-WTPS ratio. Workability was assessed using the slump test, while compressive strength was determined using cubic specimens from each developed mix. The optimum geopolymer concrete mix was identified as having a 50:50 WTPS to GGBFS ratio, with the optimum Na₂O to binder ratio of 10%. The optimum mix gave a slump value of 22 cm and a 28-day compressive strength of 36.7 MPa.