Evaluation of the engineering and physicochemical properties of a novel geopolymer binder from red mud, rice husk ash, and diatomaceous earth using sodium silicate solution as alkaline activator

• Main Author: Nguyen, Hoc Thang
• Format: text
• Language: English
• Published: Animo Repository 2015
• Online Access: https://animorepository.dlsu.edu.ph/etd_doctoral/434
• Institution: De La Salle University

Geopolymers, also known as alkali-activated pozzolan cements, have been recently gaining attention as an alternative binder for concrete because of its potential to lower the environmental impact of construction, to utilize waste as raw materials of alumino-silicates, and to enhance the material performance. In this study, engineering properties of sodium silicate activated geopolymer-based material produced from the ternary blend of red mud (RM) waste, rice husk ash (RHA) and diatomaceous earth (DE) which was optimized with statistical design of experiment and multi-response surface method. Using the augmented simplex lattice mixture design, ten mix proportions of RM, RHA, and DE were prepared and mixed with 15%, 20%, 25%, and 30% (by weight of the solid) water glass solution (WGS) to produce the specimens. After 28 days of curing at room temperature, these specimens were tested for compressive strength (MPa), volumetric weight (kg/m3), thermal conductivity (W/m.K), water absorption (kg/m3), and thermal stability including the mass loss (%), volumetric shrinkage (%) and change in compressive strength (%) when subjected to an elevated temperature of 10000C. By using the desirability function approach on multiple responses, the optimum ternary blend was found in ranges of 14.47-17.07 % RM, 63.43-67.19% RHA, 17.23-21.66% DE mixed with 20-25% WGS to obtain the desirable engineering properties of sodium-silicate activated geopolymer-based material. The predicted engineering properties are in the range of 12-15 MPa for compressive strength, 1297-1307 kg/m3 for volumetric weight, 55-63% for heat resistance in terms of strength gain, 7-8% for volumetric shrinkage, 7.6-8.3% for mass loss, 190-206 kg/m3 for water absorption, and 0.29-0.32 W/m.K for thermal conductivity, respectively. Confirmatory experiments were also carried out an optimal mix (OM) formulation of 15% RM, 65% RHA and 20% DE with WGS concentration in the range of 10 to 30%. Confirmatory runs were also done and the experimental values were found to be in g The study also proposed the reaction mechanism for the formation of the amorphous alumino-silicate geopolymeric networks in the sodium silicate activated geopolymer from the ternary blend of RM, RHA, and DE based on the results provided by SEM-EDS, XRD, and FTIR. This proposed mechanism showed that the tetra-silicates or acid silicic (Si(OH)4 or H4SiO4) dissolved and reacted with the iron oxide (Fe2O3) in RM and DE to form the oligomer precursor (-Fe3+[SiO4]4--). Aside from the formation of precursor tetra-silicates or acid silicic (Si(OH)4 or H4SiO4) from the dissolution of SiO2 of raw materials (RHA and DE), the precursor (-Fe3+[SiO4]4--) was reacted with others precursors (sialate -O-Si-O-Al-O-, sialate-siloxo -O-Si-O-Al-O-Si-O-, sialate-disiloxo -O-Si-O-Al-O-Si-O-Si-O-, tetra-silicate [SiO4]4-, and tetra-aluminate [Al(-)O4]4-) to form the sodium alumino-silicate iron hydroxide polymeric network. The concentration of sodium silicate solution influenced the geopolymer network structure resulting to either an Al-rich or Si-rich geoplymer. Si-rich geopolymer produced stronger geopolymer binder as shown in the findings of the engineering properties of optimized geopolymer at 25% WGS (OM25) which had ratios of Si/Al and Na/Al at 3.5 and 0.8, respectively. OM25 has the highest compressive strength at 17.04 MPa and the lowest water absorption at 191.20 kg/m3 among the geopolymer specimens. Results from the evaluation of physicochemical properties indicated that sodium silicate activated geopolymer from the ternary blend of red mud, rice husk ash and diatomaceous earth produces a lightweight and heat resistant material. These can be used as thermal insulating material for panel building and refractories with minimal environmental impact. A systematic method of optimizing the engineering properties of the geopolymer was proposed and used for a given application with multiple response surface method. Moreover, the proposed reaction mechanism for the formation of the alumino-silicate geopolymeric networks in the geopolymer products was elucidated based on the scientific evidences with complementary results of XRD, FTIR, SEM-EDS, DTA-TG, and MIP. Future studies will therefore explore its potential used as a binder for concrete, and deeper understand the microstructure in relation to its durability performance.