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As a material for road deicing and snow removal, electrically conductive concrete (ECON) can convert electrical energy into thermal energy to automatically melt ice and snow, avoiding manual and mechanical operations. However, to achieve ideal electrical conductivity, the content of single-doped conductive fillers in ECON needs to be high, which leads to poor workability of ECON and agglomeration of conductive fillers. Combing conductive fillers with different scales helps reduce the content of single-doped conductive fillers in ECON. This study prepared composite conductive concrete using multilayer reduced graphene oxide (RGO), carbon fiber, and steel fiber as conductive fillers. The effect of multilayer RGO on composite conductive concrete's compressive strength, flexural strength, and electrical conductivity was investigated. Besides, the mechanism of RGO on composite conductive concrete's conductive network was analyzed by scanning electron microscope (SEM). Results showed that the 28-day mechanical properties and electrical conductivity of composite conductive concrete first increased and then decreased. Composite conductive concrete containing RGO with 0.4% cement weight (RGO-0.4) exhibited better mechanical and electrical properties. The improvement of the performance of composite conductive concrete was attributed to the filling effect of RGO on the gaps of concrete matrix and the wrapping effect of graphene flocs on fibrous conductive fillers because these effects increased the compactness of the matrix and conductive contact area, respectively. Also, a snow melting test was carried out using an RGO-0.4 slab at an ambient temperature of −15°C. The snow melting efficiency was improved, showing that 20-cm-thick snow melted in 1.2 h. In conclusion, the hybrid addition of RGO and fibrous conductive fillers has positive effects on ECON, providing a new way to develop ECON. [ABSTRACT FROM AUTHOR]

Recycled fine aggregate (RFA) produced from concrete waste is commonly used in the construction industry; however, its use for structural concrete members has not been extensively studied. Moreover, its durability in a drying–wetting cycle environment still needs to be examined. In this study, the intrusion process of chloride in concrete under the drying–wetting cycles is experimentally characterized. Chloride penetration tests are carried out on concrete with the incorporation of different RFA replacement rates and mineral admixtures (i.e., fly ash and silica fume). The results show that the chloride penetration of recycled fine aggregate concrete (RFAC) is dependent upon the performance of the concrete itself, while the deterioration of chloride ion erosion resistance is due to the combined action of the replacement rate of RFA and the drying–wetting cycles. The incorporation of RFA degrades the properties of RFAC owing to its drawbacks in the degradation of interfacial properties of RFAC. Exposure to the drying–wetting cycle environment causes the content of free chloride ions in RFAC to increase initially before decreasing with the erosion depth, thereby showing an obvious convection zone and diffusion zone. The incorporation of the mineral admixture can effectively improve the compactness of the concrete microstructure and make concrete less susceptible to chloride ions ingress. RFAC mixed with 15% fly ash and 10% silica fume has a comparable resistance to chloride penetration as a natural aggregate concrete, which is a feasible method for the application of RFA. [ABSTRACT FROM AUTHOR]

Construction and demolition wastes (C&DWs) have raised a large number of ecological and environmental problems. Recycling C&DWs into arecycled concrete aggregate (RCA) will help save natural resources effectively and reduce the negative impact of C&DW on the environment. Innovative pervious concrete (IPC) can mitigate extreme weather disasters, such as rainstorms, and overcome the low strength and poor durability of traditional pervious concrete. In this study, innovative recycled pervious concrete (IRPC) is prepared by combining RCA with IPC, which has broad application prospects and ecological friendliness. This study investigates the effect of RCA quality grades and replacement rates on the mechanical property, permeability, sulfate resistance and abrasion resistance of IRPC. IRPC mixtures were prepared with three different quality grades (high, medium and low qualities) of aggregates named as NA, RCA1 and RCA2. Moreover, the replacement rate of RCA for NA varied as 0%, 25%, 50%, 75% and 100%. The IRPC specimens were tested for compressive strength, mass loss and abrasion resistance after different sulfate wetting-drying cycles of 0, 30 and 60. The results exhibited that the initial compressive strength of all types of IRPC was more than 40 MPa. The compressive strength and mass of most IRPC increased first and then decreased slightly with the passage of a number of sulfate wetting-drying cycles, indicating IRPC has good resistance to sulfate attack. Sulfate attack and the addition of RCA will reduce the abrasion resistance of IRPC. However, when the replacement rate is lower than 50%, and the RCA quality is better (attached mortar content < 25%), the abrasion resistance of IRPC will be improved under sulfate attack. The experimental results might be useful as a reference and design methodology for employing IRPC in pavement applications in the future. [ABSTRACT FROM AUTHOR]

• Utilization of RGFA as an alternative material for river sand is feasible. • RGA mortar showed comparable properties compared with NA mortar. • Unreacted metakaolin in RGFA was activated by alkali solution anew. • High bond strength of GP-RGFA ITZ lowered the decline tendency of CS. Geopolymer has been viewed as a potential, ideal and green material to replace cement. The recycling of Portland cement-based concrete as recycled aggregates was investigated diffusely, while the reuse of geopolymer was paid little attention. Exploring the feasibility and interfacial evolution of utilizing recycled geopolymer fine aggregate (RGFA) produced from waste geopolymer as the alternative for river sand (RS) was the core object in this research. Metakaolin to RS ratio of 1:2 and NaOH/Na 2 SiO 3 ratio of 0.5 by weight, and 12 M of NaOH solutions were adopted to prepare the referenced geopolymer mortar. Then five RGFA replacement rates (0%, 20%, 50%, 80% and 100%) were used to prepare the NA (RGFA) mortar. The tests of compressive strength, flexural strength and water absorption of mortars were performed. SEM was used to observe the interfacial transition zone (ITZ) between RGFA and new generated geopolymer paste. Results proved that RGFA mortar exhibited comparable mechanical properties compared with the RS mortar when replacement rate was less than 50%. Furthermore, more compact ITZs were obtained in RGFA mortar. The decreasing mechanical properties of RGFA mortar was primarily attributed to the weak properties of RGFA itself. The filler effects and compact ITZs relieved the decline tendency of mechanical property of RGFA mortar. It was convinced that utilizing RGFA to replace RS as fine aggregates in the construction activities was promising. [ABSTRACT FROM AUTHOR]

• An innovative ACP was prepared applied as tunnel fire resistant coating. • ACP has a lower thermal conductivity, excellent mechanical and durable properties. • ACP can defend effectively SCC from spalling in tunnel fire accidents. • 40 mm thickness of ACP can effectively withstand tunnel fire up to 2.5 h. Self-compacting concrete (SCC) widely used in tunnel structure is prone to spalling when it is subjected to the fire disaster. The fire-resistant materials coated on the surface of concrete are considered as an effective way to prevent concrete from being destroyed in a fire accident. However, current these coatings are difficult to withstand a high temperature, for example, tunnel fire temperature, and a longer-term fire. In this paper, a 40 mm thickness of SiO 2 aerogel cement paste (ACP) coating was prepared to investigate the protective effect for SCC in a simulated tunnel fire with the maximum temperature of 1100 °C for 2.5 h. The mechanical properties, thermal conductivity and fire resistance of SiO 2 ACP, and the compressive strength of SCC with or without ACP coating in the simulated tunnel fire were tested. The results showed that ACP exhibited excellent mechanical and durable performances and low thermal conductivity. The 40 mm thickness of ACP has a strong thermal insulation capacity and can effectively withstand tunnel fire up to 2.5 h. The SCC samples under the protection of ACP did not undergo compressive strength degradation and destruction of microstructure. The interfacial temperature of ACP and SCC was much lower than the critical value (380 °C) in a 2.5 h tunnel fire. Therefore, ACP can provide a good choice for protection of SCC in a tunnel fire with a high temperature and long time. [ABSTRACT FROM AUTHOR]