# 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  
Because of its significant benefits of non-contact heating, volumetric and selective heating, user-friendly control, clean heating processes, and no formation of secondary waste, MW-T has recently received much attention [104; 105; 106; 107; 120; 121]. Unfortunately, this may significantly impede the implementation and advancement of such technology in the pavement engineering of the typical cement concrete's low microwave absorption efficiency, which may reduce the microwave heating speed [104; 105; 106; 107; 108; 109; 122]. According to research on the electrical field curing approach, C-S-H products' electroosmotic swelling occurs, and pore connectivity decreases in a DC field [123; 124]. Most of the studies mentioned concentrated on using microwave absorbents and absorption aggregate to increase the MW-T efficiency of cement and concrete. This makes it possible to increase the effectiveness of microwave heating of cement concrete in applications like accelerated concrete curing [125], road de-icing [122; 125], asphalt concrete repair [125], and the high-performance nondestructive testing of cement and concrete structures [119] with a low cost, a wide range of sources, and excellent performance. Microwaves can be partially absorbed by dielectric components contained in concrete, boosting temperature and hastening cement hydration. Additionally, mixed water that has been bound in cement hydrates is microwave-resistant. In contrast to heat curing, the hydrates are less easily decomposable. Because it is prone to MW-T, water is necessary for the heating process [126; 127; 128]. In turn, concrete quality might improve. As a result, microwave energy is suitable for accelerating the early hardening of concrete and mortar mixes. Because it employs electrical energy rather than combustion, which requires more time and energy, it might be called an environmentally beneficial, green, and clean technology [111; 112]. Microwave curing may modestly increase the total porosity of mortar [129] when compared with normal curing and steam curing at 80 \({}^{\circ}\)C (under different curing regimes at the age of 28 days). To better understand mortar pore size distribution under various curing regimes, Figure 11 shows four size ranges [129]: large capillary pores (>100 nm), middle capillary pores (50-100 nm), mesopores (4.5-50 nm), and gel micropores (<4.5 nm). It can be stated that MW-T curing may reduce the pores in the range of >100 nm. Figure 10: Schematic of a hypothesized approach that would combine magnetic field, high-intensity ultrasound, and microwave processing to produce concrete with increased homogeneity and enhanced early strength. Different power dissipations are produced by the microwave electromagnetic field's interactions with the constituents of concrete in the MW-T of concrete [119]. Due to varying scales, porosity, aggregates with different mineral compositions, and moisture migration, the distribution of dielectric losses is uneven as microwave radiation is transformed into heat energy inside concrete [103; 111; 112]. Additionally, rather than only being a thermal-mechanical coupling problem, the MW-T of concrete is a multi-field coupling and multi-phase mixed nonlinear problem. Compared to traditional steam heating, MW-T can speed up the curing process and boost the early strength of concrete [120; 128; 130]. When exposed to such an electromagnetic field, the dielectric components of concrete vibrate and resonate with the applied field. These interactions prevent the vibration that microwaves cause, which leads to internal friction heating the concrete [130; 131]. [PERSON] et al. [132] investigated the temperature distribution for concrete structures under different heating parameters of MW-T in the diagonal direction (Figure 12).