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Information about the thermal conductivity of sprayed concrete is useful for calibration exercises using sprayed panels, where heat flows need to be estimated, and future enhancements to the method to include estimates of concrete temperature across the thickness of the lining. However, the necessary information about thermal conductivity of sprayed concrete is rare, and no information about the early age thermal conductivity of sprayed concrete has been found. The thermal conductivity of sprayed concrete aging from five hours after casting to 20 days was continuously measured by a transient method. Thermal conductivity was found to be higher than expected at early age and decreased to the mature value as the concrete cured. Based on these results it is hypothesized that early age thermal conductivity is mainly influenced by free water content, while at a mature stage the key determinants are the structural features of the cement matrix. Thermal conductivity is discovered to have an exponential relationship with density, regardless of mix constituents. A convenient numerical approach is proposed to estimate thermal conductivity for concretes and its accuracy has been verified by data from tests on a wide range of concretes with density ranging from 0.2 g/cm 3 to 2.5 g/cm 3 . [ABSTRACT FROM AUTHOR]

It has become a common practice to use composite cement instead of pure Portland cement in many construction applications, then acknowledging the long-term microstructures and compositions of the composites, to ensure a long term stable performance and durability, becomes essential. Thus, this paper is presenting the characterisation of three 20-year-old cement-GGBS-blended pastes which experienced a curing history of at 40 °C for the first five years and then room temperature for the rest years. The main existed phases included C–S–H gel, portlandite, AFm, and hydrotalcite-like phase as hydration products, as well as the products from the carbonation occurring during storage, including ettringite (this ettringite was from the carbonation of AFm.), calcite, vaterite, hemicarbonate and monocarbonate. The comparison among the results obtained for three pastes indicated that increasing GGBS contents enhanced the substitution of bridging SiO 4 4− tetrahedra by AlO 4 5− tetrahedra in the aluminosilicate structure of C–S–H gel, the incorporation of proton ions into the chains to balance the charge differences caused by the substitution, as well as the chain growth. The chain length was found to be direct proportional to GGBS contents, which was enhanced by higher curing temperatures. Through comparing to the results obtained for parallel pastes but hydrated at room temperature for the whole 20 years, a similar hydration degree was observed for OPC in each paste, but higher hydration degree for GGBS in the paste with the experience of hydration at 40 °C, as well as morphological and compositional differences were caused by the different hydration histories. In addition, calcium hydroxide functioning as “a catalyst” in the process of pozzolanic reaction of GGBS was suggested by similarity between calcium contents but different hydration degrees of GGBS in both parallel pastes with and without hydration experience at 40 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • The development on PFRC during three decades are studied. • PFRC has various advantageous properties over ordinary concrete. • Plant fibre reinforcement causes the loss of compressive strength and durability. • Premodification on plant fibres improves the inferior properties of PFRC. • Theoretical studies of PFRC are still lacking. As one of the most important supporting technologies to economic development and urbanisation, concrete becomes a crucial link to reduce the global carbon emission and confronts with an unprecedented challenge of decarbonation. The reinforcement by plant fibres in concrete is one of promising approaches to decarbonise concrete. This paper combines scientometric and manual analysis to study the research progress on plant fibre reinforced concrete (PFRC), revealing the development scale, the prevailing research domains and focuses on PFRC and the knowledge progress of PFRC. The main challenges confronted by PFRC are discussed and future research scope are proposed. [ABSTRACT FROM AUTHOR]

• Isothermal microwave curing was effective for preparing RPC. • Microwaves accelerated strength development significantly. • The optimal curing process was obtained. • The contributed reactions were identified. A combined application of microwaving curing and reactive powder concrete (RPC) may provide an accelerated development of outstanding mechanical and physical properties, which has great potential to improve the quality and efficiency of production. In this work, a custom-made microwave oven was used to isothermally cure RPC with steel fibre reinforcement at 40 °C, 60 °C and 80 °C for 30 min. Compared to phased nonisothermal microwave curing, the isothermal microwave curing is equally effective, yet more energy efficient to operate and easier to control. The microwave-cured specimens at 1 day gained up 72.0% and 127.6% of the 28 days compressive and flexural strength achieved with standard curing, respectively. The acceleration rates varied with material characteristics and initial temperatures. The characterisation data obtained from STA, XRD and SEM-EDS analysis indicated that the beneficial effects of microwave curing temperature on strength development were due to the accelerated cement hydration and pozzolanic reaction of silica fume. The products resulting from this acceleration strengthened the interfacial zone between hydrated regions and aggregates, and the interfacial zone between the cement and silica fume. Besides C-S-H, AFm, AFt, CH, C C - , Al-tobermorite, a CO 3 2−-contained fukalite-like phase was found to be formed, which may be produced by the pozzolanic reaction of silica fume at the expense of calcium carbonate under microwave curing. [ABSTRACT FROM AUTHOR]