Abstract
The influence of KOH concentration (8 and 12 M) and curing conditions as temperature (40℃ and 60℃), time (7 and 28 days) and relative humidity (85% and 95% RH), on compressive strength of metakaolin-based geopolymers (MK-based GP) was evaluated. Derived from the experimental design technique, and using a factorial design 2K with two replications in the center point, eighteen experiments were conducted. The results reveal that the best performance conditions of geopolymerization to develop a higher compressive strength of 20 MPa are 12 M KOH to 60℃ and 85% RH at 28 curing days. With these conditions, the value of relative humidity of 85%, promotes high strength compact samples, and a maximum of 42 MPa at 90 days. The results of significant, compressive design of GP showed that KOH concentration and curing relative humidity were the most important factors, followed by curing time and temperature. The GP were characterized by XRD, and their evolution on compression strength was followed by SEM.
Highlights
Inorganic materials called geopolymers (GP), which could potentially replace conventional cements and many mineral based products are becoming important in the reduction of CO2 footprint, and energy consumption
Noting that 83.03% of the model explained the variability of the compressive strength, this value represents a good fit, so the model is considered suitable for further optimization [27] [28]
The design of experiments based on the 2K + 2 model was proposed to study the influence of four parameters: concentration, time, temperature and % RH on the synthesis of GP by MK activated with KOH
Summary
Inorganic materials called geopolymers (GP), which could potentially replace conventional cements and many mineral based products are becoming important in the reduction of CO2 footprint, and energy consumption. Experiment design in the MK-based GP was developed in systems activated with NaOH or NaOH/sodium salts [1] [20] [21] [22] [23] [24], where compressive strength values vary largely from 7 to 75 MPa, and results published cannot be compared due to differences in precursors (high degree or low degree kaolin; MK obtained from kaolin at different temperatures); in high or low alkaline activators concentration, and in the large number of processing factors that are different from study to study [20]. The experimental design uses a factorial 2K + 2 to improve the performance of the parameters, such as an alkaline activator concentration, and curing conditions as relative humidity, temperature and time on the compressive strength of MK-based GP
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