# Novel Processing Methods of Low-Clinker Multi-Component Cementitious Materials--A Review
## 4 Microwave Treatment (MW-T) Methodology
### MW-T of Cementitious Materials/Concrete and SCMs
According to the current investigation, the microwave approach may increase the stability and durability of the prepared CTB structures. The timing of the MW-T implementation is also crucial; therefore, the interval between the implantation of the CTB and microwave heating is considered. In the CTB at an early age, a shorter delay time is linked to greater mechanical performance. At a curing age of 7 days, microwave heating (for 7 min) with a 0 h delay period can also boost the CTB's strength [145]. To ensure safe and effective mining, the CTB strength and gain rate should also be ensured. The CTB heated with MW-T is described in work by [PERSON] et al. [146] as using a coupled electromagnetic heat transfer model. This suggested model considers the processes of heat conduction and convection, as well as pertinent temperature variation. Energy is converted from electrical to electromagnetic and then thermal. The practical application of the microwave approach to the CTB technology can thus advance, thanks in part to the findings of this investigation. This work is anticipated to contribute to the practical implementation of microwave technology in mine backfill operations. A summary of the major effects of microwave treatment MW-T on concrete curing effectiveness is given in Table 3. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Aggregates (F-Fine, C-Coarse)** & **SCMs/Replacement Levels (\%)** & **Main Findings** & **Treatment Refs.** \\ \hline F: quartz sand & Limestone powder/(21.1) & - In comparison to the reference specimens, the fc displays increments of 30 MPa, 53 MPa, 74 MPa, and 89 MPa with microwave exposure times of 60 s, 120 s, 180 s, and 240 s at the age of 8 h. Here, microwave pre-curing for 240 s results in the highest fc of 105 MPa. & MW-T [137] \\ \hline F: quartz sand & SF, FA & - Due to MW-T curing, it is possible to generate materials with very high early strength up to 420 MPa after just one day and a total microwave-curing time of two hours. & MW-T [138] \\ F: quartz sand & SF, FA & - The hydration and pozzolanic reactions were accelerated at the same time by MW-T curing and the application of very reactive pozzolanic additives. & MW-T [138] \\ \hline \multirow{3}{*}{-} & \multirow{3}{*}{GGBFS/(15, 30, 45)} & - The carbonation of composite binders can be promoted more quickly with MW-T curing than with steam curing. Along with the acceleration of hydration at early ages, an important factor in improving the fc of composed with cement mortar-GGBFS composite binder is the decrease in the number of harmful pores. & MW-T [140] \\ \hline F: quartz sand & SF/(25.9) & - Aluminosilicate chain length for C-S-H phase with more branches and cross-linking are created during hydration at a high output energy of MW-T curing. & MW-T [147] \\ \hline \multirow{3}{*}{-} & Graphene-oxide (GO) & - The synergetic effect of combining GO-doping and MW-T curing & MW-T curing \\  & doping/ (0.05, 0.1, 0.5) & resulted in the maximum fc (32.4 MPa), which is about 126.6\% more than what would have been possible without GO-doping and MW-T curing. & MW-T [148] \\ \hline \multirow{3}{*}{-} & \multirow{3}{*}{FA/(50)} & - In contrast to the very low early-age strength of the cement-FA blended paste under air curing (11 MPa at 1 day), cement-FA blended paste gained 51.5 MPa under MW-T curing for 5.29 h. & MW-T [149] \\  & & - Low energy low-carbon concrete can be produced via MW-T curing. & MW-T curing. \\ \hline \multirow{3}{*}{F: river sand} & \multirow{3}{*}{Coal gangue/(30)} & - The optimal MW-T curing temperature range was 600 \({}^{\circ}\)C-700 \({}^{\circ}\)C, and microwaves can stimulate the activity of coal gangue powder. & MW-T [150] \\  & & - The high temperature of MW-T curing also led coal gangue powder to dissolve, which resulted in the particles becoming fine and moist. & MW-T [151] \\ \hline F: nonreactive sand & Bamboo culms/ (1, 1.5) & - Alkaline treatment with MW-T increased the ductility and toughness of prepared composites. & MW-T [151] \\ \hline \end{tabular}
\end{table}