Comparative Study of Alkali-Activated Fly Ash Manufactured Under Pulsed Microwave Curing and Thermal Oven Curing

Abstract

This paper compares the alkali-activated fly ash (AAFA) manufactured with thermal oven curing and pulsed microwave curing methods. Fly ash activated by 8M NaOH solution at a liquid to solid ratio of 0.3 was cured by thermal oven at 85°C and domestic microwave oven, respectively. Apart from compressive strength test, the temperature profiles of AAFA samples were captured by thermal camera. Reaction products of AAFA were characterised with XRD, FTIR and TG/DTG, while the microstructure of AAFA was analysed by MIP and SEM. The results showed that with much shorter curing duration, the compressive strength of AAFA samples under microwave curing was comparable to those samples under thermal oven curing. The XRD results demonstrated that different reaction products were generated from thermal oven curing (hydroxysodalite) and microwave curing (chabazite-Na) respectively. The FTIR spectra showed that aluminosilicate with higher degree of polymerization was formed in the sample with microwave curing. MIP indicated equivalent total porosities from both curing methods, while a well-distributed matrix phase under thermal oven curing were found in the SEM results. Overall, the results demonstrate that microwave curing has great potential to be an alternative curing method for manufacturing AAFA.

Difference between Internal and External Hydration of Hardened Cement Paste under Microwave Curing

“…erefore, much attention has been paid to the application of microwave curing for the precast concrete production [9][10][11] or rapid repair of cement-based materials [12]. Application of microwave curing also shows a broad perspective on the alkali activated materials [13,14]. With the development of society, economic and ecological needs have to be considered.…”

Confined-Direct Electric Curing of NaOH-activated fly ash based brick mixtures under free drainage conditions: Part 1. Factorial experimental design

“…However, geopolymer binding technology used in fly ash mixtures is frequently associated with conventional thermal curing. The main drawback of conventional thermal curing is that it inevitably increases the energy consumption, offsetting the benefits that can be obtained from alkaliactivated fly ash [10]. It is possible to synthesise an alkali-activated fly ash based binder at an ambient temperature, but it is impractical, due to delayed setting, intensive efflorescence formation, very slow mechanical strength development and relatively low strength at 28 days of age [11].…”

“…Compared to conventional thermal curing, such as oven curing, it is generally agreed that microwave curing is a low-energy heating source [10]. Chindaprasirt et al (2013) [12] showed that early-stage microwave curing followed by conventional oven curing reduced the curing duration and energy consumption and, hence, the associated cost.…”