Evaluation of Compressive Strength of Uncalcined Dredged Sediment and Fly Ash-based Geopolymer Using Response Surface Method

Dredged sediments from dredging operations pose environmental hazards and disposal challenges. The geopolymerization method for treating these sediments offers an eco-friendly alternative to Portland cement. This study develops geopolymer materials using uncalcined dredged sediment, fly ash, and an alkali activator (sodium hydroxide and sodium silicate). The compressive strength of the geopolymer was tested after 7 days curing under two conditions (ambient and at 60°C for the first 24 hours) and analyzed using Box-Behnken Design and Response Surface Method. The study examined three variables: sodium hydroxide molarity (6M to 12M), sediment-to-total solids ratio (0.3 to 0.9), and sodium silicate solution-to-sodium hydroxide solution ratio (1 to 3). High-accuracy prediction models were established, and the desirability function was used to optimize the mixture proportions for the two curing conditions. The multi-objective optimization aimed to meet the strength requirement of TCVN 6477:2016 standards for concrete bricks, maximize dredged sediment content, and minimize sodium silicate usage. The optimal mixture achieved a compressive strength of 7.5 MPa at 7 days, with 37.53% dredged sediment for ambient curing and 45.59% for drying curing. Compared to ambient curing, drying curing enables a higher sediment content and a reduced use of NaOH. Furthermore, the geopolymer reactions and gel matrix formation of the optimal mixture were confirmed by FTIR spectra and SEM observations.