Abstract
In order to investigate the effects of microwave curing on the microstructure of the interfacial transition zone of mortar prepared with a composite binder containing glass powder and to explain the mechanism of microwave curing on the improvement of compressive strength, in this study, the compressive strength of mortar under microwave curing was compared against mortar cured using (a) normal curing at 20 ± 1 °C with relative humidity (RH) > 90%; (b) steam curing at 40 °C for 10 h; and (c) steam curing at 80 °C for 4 h. The microstructure of the interfacial transition zone of mortar under the four curing regimes was analyzed by Scanning electron microscopy (SEM). The results showed that the improvement of the compressive strength of mortar under microwave curing can be attributed to the amelioration of the microstructure of the interfacial transition zone. The hydration degree of cement is accelerated by the thermal effect of microwave curing and Na+ partially dissolved from the fine glass powder to form more reticular calcium silicate hydrate, which connects the aggregate, calcium hydroxide, and non-hydrated cement and glass powder into a denser integral structure. In addition, a more stable triangular structure of calcium hydroxide contributes to the improvement of compressive strength.
Highlights
Curing period reduction of precast concrete production has many advantages, e.g., reduction of workshop area, capital saving, and productivity improvement
The hydration of glass powder will be accelerated, ratio of 15% is slightly higher than the controls, which is attributed to the filling and nucleation effect the hydration ofisglass powder is much slower than that ofthe thehydration cement
The dissolved Na+ enters into the calcium silicate hydrate (C-S-H) around the glass powder to form alkali-silica reaction (ASR) gel with a high Na/Si atomic ratio as shown in Table 1, which is in agreement with the findings reported by Serpa et al and Redden et al [26,37]
Summary
Curing period reduction of precast concrete production has many advantages, e.g., reduction of workshop area, capital saving, and productivity improvement. Microwave curing exhibits the characteristics of energy saving, rapid stripping for precast concrete [2,3] or concrete repair [4], which is effective in accelerating the hydration of cement [5,6,7,8] or improving the pozzolanic reaction of supplementary cementitious materials (SCMs) [9,10,11,12,13,14]. According to the research of Wu et al, microwave curing increases the early strength without any detrimental effect at later ages [15]. Leung et al showed that early strength at 4.5 h and later age strength at 7 days of concrete prepared with type III Portland cement under microwave
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