Search

• A self-sensing ultra-high-performance fiber-reinforced concrete (UHPFRC) is fabricated by incorporating few-layer graphene (FLG) • In the composite with 0.5 wt% FLG, the enhancement on compressive strength can reach to more than 25%. • The possible polarization and conduction mechanisms of the FLG/UHPFRC composites are proposed according to the dielectric polarization theory. • The FLG/UHPFRC composites exhibit distinct piezoresistive behavior from the ordinary cement-based sensors. Graphene nanomaterials have demonstrated tremendous prospects in the preparation of smart ultra-high-performance fiber-reinforced concrete (UHPFRC). However, few relevant researches are available on the piezoresistive behavior of the UHPFRC reinforced by few-layer graphene (FLG). In this research, the mechanical, electrical and mechanical–electrical behavior of the FLG/UHPFRC composites were investigated, and the possible polarization and conduction mechanisms of the FLG/UHPFRC composites were proposed. The findings showed that FLG was equably dispersed in the matrix, which enhanced the mechanical properties of the composite materials through the crack arresting effect, pinning effect and seeding effect, etc. FLG improved the conductivity and relative permittivity of the composites, but did not change the topology of the Nyquist plot. Moreover, the FLG/UHPFRC composites exhibited distinct piezoresistive behavior from ordinary cement-based sensors due to the coupling effect of the interfaces and microcracks. [ABSTRACT FROM AUTHOR]

• Limestone calcined clay cement (LC3) is adopted in UHPC. • D-optimal design is used to optimize the recipes of LC3-based UHPC. • LC3 can provide a high substitution ratio for ordinary Portland cement. • LC3 can promote the engineering properties of UHPC. Limestone calcined clay cement (LC3) is believed to be able to substitute Portland cement and promote low-carbon development in the concrete industry. Ultra-high performance concrete (UHPC) features high proportions of cement. Herein, an LC3-based UHPC with high cement substitution was designed and optimized based on the D-optimal method, and its engineering properties, including workability, mechanical properties, hydration process, microstructural evolution, and carbon emission were evaluated. Results show that with an increase in LC3, the dynamic yield stress increases and the water film thickness decreases, which indicates that the workability of LC3-based UHPC reduces. When the substitution ratio is about 55 percent, the optimized LC3-based UHPC achieves the maximum compressive strength, about 146.05 MPa. XRD and TG results show that LC3 consumes portlandite by the pozzolanic reaction, which generates additional gel products. However, as the substitution ratio exceeds 55 percent, the degree of pozzolanic reaction drops, resulting in a decrease in the count of hydration products and compressive strength. The pore structure of LC3-based UHPC is refined, with fewer air voids and a larger percentage of gel pores compared to the normal UHPC. The optimized LC3-based UHPC with a substitution ratio higher than 50 percent in this study achieves high integrated performance with engineering applications and low carbon environmental value. [ABSTRACT FROM AUTHOR]

Secondary hydration is the main driving force of autogenous self-healing and directly impacts the closure of cracks in damaged cementitious materials. In fiber-reinforced cement composites, secondary hydration also dominates the regeneration of the fiber-matrix interface during the self-healing processes. As an important factor influencing the cement hydration, silica fume (SF) addition can be crucial to the self-healing performance of cementitious materials and composites. In this paper, the effect of SF on the autogenous self-healing of ultra-high-performance fiber-reinforced concrete was investigated. With a ≥20% SF addition, the secondary hydration the cement matrix adjacent to the cracks was accelerated. The dissolution of amorphous silica and the formation of Si-containing healing phases was observed. These effects predominated the closure of the mouth and the inner part of the cracks. SF addition also enhanced the regeneration of fiber-matrix interface by promoting the growth of self-healing products in these areas. The closure of cracks and the regeneration of fiber-matrix interface are both responsible for the restoration of flexural properties. • The secondary hydration acceleration of the cement matrix after cracking was found with a ≥20% SF addition, which promoted the self-healing of the cracks in UHPFRC. • The effect of SF on the structural regeneration of the cracks in UHPFRC was elucidated with a self-healing mechanism of the amorphous Si dissolution. • The self-healing of the deep matrix crack and fiber-matrix interface together induced the flexural property restoration of the SF-containing UHPFRC. [ABSTRACT FROM AUTHOR]