Effect of quartz powder on mid-strength fly ash geopolymers at short curing time and low curing temperature

Abstract

Geopolymers are recommended as an alternative to Portland Cement, which has high CO2 emissions. Geopolymers are a more environment-friendly construction material produced using the precursor aluminosilicate powders. In this context, fly ash rich in SiO2 and Al2O3 is frequently used in geopolymer design. In this study, geopolymers were obtained using different quartz powder proportions (0, 50, 75 and 100%) instead of river sand. The produced geopolymer mixtures were subjected to heat curing at 40–60 and 80 °C for 6, 8 and 10 h. The physical, mechanical, transport and microstructural properties of geopolymers produced at low curing temperature and short curing time were investigated. Within the scope of the experimental study, 36 different geopolymer mixtures were produced. The hardened unit weights of geopolymer mixtures vary between 2170–2250 kg/m3. Unit weights are relatively low since the fly ash content in the mixtures is 1000 kg/m3. The compressive strength (1-day) of geopolymer mixtures varied between 7 and 60 MPa, and flexural strengths varied between 3 and 9.7 MPa. The mechanical properties of the mixtures improve as quartz powder, curing time and curing temperature increase. While the capillary water absorption of geopolymer mixtures cured at 40 °C exceeds 1 kg/m2, the capillary water absorption of mixtures cured at 80 °C is below 0.40 kg/m2. Since the fly ash rate is high in geopolymer mixtures, the alkali activator rate has also increased and therefore, the CO2 emission has exceeded 400 kgCO2/ton. However, as the compressive strength of the mixtures increased, the emission factor decreased. The N-A-S-H and crystal zeolitic phases were formed in the geopolymer matrix, as an observation of SEM, XRD, and FT-IR analysis. Withal, as the quartz powder increased, the crystal phase of the geopolymer matrix increased, also. As a result, it was determined that fly ash geopolymers with 60 MPa compressive strength could be obtained by using quartz powder in a short curing time of 10 h.