Accelerated curing

Abstract: Steel slag has been used as supplementary cementitious materials or aggregates in concrete. However, the substitution levels of steel slag for Portland cement or natural aggregates were limited due to its low hydraulic property or latent volume instability. In this study, 60% of steel slag powders containing high free-CaO content, 20% of Portland cement and up to 20% of reactive magnesia and lime were mixed to prepare the binding blends. The binding blends were then used to cast concrete, in which up to 100% of natural aggregates (limestone and river sands) were replaced with steel slag aggregates. The concrete was exposed to carbonation curing with a concentration of 99.9% CO2 and a pressure of 0.10 MPa for different durations (1d, 3d, and 14d). The carbonation front, carbonate products, compressive strength, microstructure, and volume stability of the concrete were investigated. Results show that the compressive strength of the steel slag concrete after CO2 curing was significantly increased. The compressive strengths of concrete subjected to CO2 curing for 14d were up to five-fold greater than that of the corresponding concrete under conventional moist curing for 28d. This is attributed to the formation of calcium carbonates, leading to a microstructure densification of the concrete. Replacement of limestone and sand aggregates with steel slag aggregates also increased the compressive strengths of the concrete subjected to CO2 curing. In addition, the concrete pre-exposed to CO2 curing produced less expansion than the concrete pre-exposed to moist curing during the subsequent accelerated curing in 60 °C water. This study provides a potential approach to prepare concrete with low-carbon emissions via the accelerated carbonation of steel slag.

Abstract: Microwave heating is a highly efficient technique for various thermal processes. Advantages of microwave heating compared to conventional processing methods include energy-saving rapid heating rates and short processing times, deep penetration of the microwave energy (which allows heat to be generated efficiently without directly contacting the work-piece), instantaneous and precise electronic control, clean heating processes, and no generation of secondary waste. Microwave energy processes for heating, drying, and curing have been developed for numerous laboratory-scale investigations and, in some cases, have been commercialized. Microwave energy use should theoretically be advantageous in the processing of cement and concrete materials (e.g., hydraulic Portland cement, aggregate, and water). These materials exhibit excellent dielectric properties and, therefore, should be able to absorb microwave energy very efficiently and instantaneously convert it into heat. This paper provides a comprehensive review of the use of microwave energy to process cement and concrete materials, as well as a critical evaluation of currently utilized microwave heating mechanisms and high-performance microwave systems. The current status of microwave applications and future research and development trends are also discussed, including such thermal processing methods as the hightemperature sintering of cement materials, the accelerated curing of precast concrete products, as well as the drilling and cleaning of decontaminated concrete surfaces by the built-up internal pressure. The results of this review indicate that microwave heating is directly associated with dielectric loss by the cement and concrete. Microwave processing can be used to improve clinkering and to reduce the clinkering temperature by about 100 1C. Considerations when constructing mathematical models of microwave heating for cement and concrete should include the influences of heat and mass transfer during microwave curing on the temperature difference in the concrete, the degree of uniformity of the internal structure, and the ultimate performance of the product. Future studies of microwave energy in cement and concrete applications might include investigations of adaptive (time-dependent) dielectric properties, coupling chemical reactions in the presence of microwave energy, the design and construction of suitable microwave systems, and the prediction of related phenomena (e.g., thermal runaway, as a highly regulated safety issue).

Abstract: In this study, a monofunctional benzoxazine monomer was synthesized by condensation reaction of aniline and formaldehyde with cardanol, a by product of cashew nut shell liquid (CNSL). The monomer was characterized by FTIR and 1H NMR spectral analysis. Curing characteristics were studied by differential scanning calorimeter. The exothermic peak associated with curing was observed from 230 °C to 291 °C with a peak maximum of 272 °C. Adding a small percentage of cardanol as phenolic initiator reduced the onset of cure as well as peak maximum temperature due to accelerated curing. Thermo gravimetric analysis indicated a peak decomposition temperature of 432 °C and a char yield of 24% at 800 °C. The viscoelastic properties of the neat cardanol benzoxazine, its jute fiber composite and the acrylonitrile modified jute fiber composites were studied with dynamic mechanical thermal analyzer (DMTA). The storage modulus (E′) value increased with fiber loading and showed a higher value for treated composite indicating an increase in interaction between fiber and resin matrix. On the other hand, the tan δ which is associated with glass transition, shifted to lower value compared to neat resin with incorporation of jute fibers.