Overgrinding of Portland cement brings excessive shrinkage and poor self-healing ability to concrete. In this paper, through the ultrasonic test and optical micrograph observation, the self-healing properties of concrete prepared by cement with different particle size distributions were studied. Besides, the effect of carbonation and continued hydration on self-healing of concrete was analyzed. Results show that, for the Portland cement containing more particles with the size 30~60 μm, the concrete could achieve a better self-healing ability of concrete at 28 days. For the two methods to characterize the self-healing properties of concrete, the ultrasonic test is more accurate in characterizing the self-healing of internal crack than optical micrograph observation. The autogenous self-healing of concrete is jointly affected by the continued hydration and carbonation. At 7 days and 30 days, the autogenous self-healing of concrete is mainly controlled by the continued hydration and carbonation, respectively. The cement particle size could affect the continued hydration by affecting un-hydrated cement content and the carbonation by affecting the Ca(OH)₂ content. Therefore, a proper distribution of cement particle size, which brings a suitable amount of Ca(OH)₂ and un-hydrated cement, could improve the self-healing ability of concrete.

Gait abnormalities have been widely investigated in the diagnosis and treatment of neurodegenerative diseases. However, it is still a great challenge to achieve a comfortable, convenient, sensitive and high-pressure resistant flexible gait detection sensor for real-time health monitoring. In this work, a polyaniline (PANI)@(polyacrylic acid (PAA)–polyvinyl alcohol (PVA)) (PANI@(PVA–PAA)) ternary network hydrogel with a uniaxially oriented porous featured structure was successfully prepared using a simple freeze–thaw method and in situ polymerization. The PANI@(PVA–PAA) hydrogel shows excellent compressive mechanical properties (423.44 kPa), favorable conductivity (2.02 S m⁻¹) and remarkable durability (500 loading–unloading cycle), and can sensitively detect the effect of pressure with a fast response time (200 ms). The PANI@(PVA–PAA) hydrogel assembled into a flexible sensor can effectively identify the movement state of the shoulder, knee and even the sole of the plantar for gait detection. The uniaxially oriented porous structure enables the hydrogel-based sensor to have a high rate of change in the longitudinal direction and can effectively distinguish various gaits. The construction of a hydrogen bond between PANI and the PVA–PAA hydrogel ensures the uniform distribution of PANI in the hydrogel to form a ternary network structure, which improves the pressure resistance and conductivity of the PANI@(PVA–PAA) hydrogel. Thus, PANI@(PVA–PAA) hydrogel flexible sensor for gait detection can not only effectively monitor some serious diseases but also detect some unscientific exercise in people's daily life.

Due to low early strength and high shrinkage, ordinary Portland cement (OPC) has difficulty meeting the actual needs of modern construction projects, while belite calcium sulfoaluminate cement (BCSA–OPC) composite cement provides a new solution. The mechanical and the drying shrinkage properties of the BCSA–OPC mortar were determined, the hydration heat of the BCSA–OPC was studied, and the pore size distribution of the mortar was investigated. In addition, the hydration products of the BCSA–OPC were analyzed by X-ray diffraction (XRD) and simultaneous thermal analysis (TG-DSC), and the microscopic morphology of the BCSA–OPC mortar was observed by scanning electron microscopy (SEM). The results show that with the increase in BCSA dosage in the BCSA–OPC, compared with OPC, the flexural strengths of the mortar of 50% dosage of BCSA at the hydration age of 1 d, 3 d, 7 d, and 28 d are improved by 33.3%, 36.6%, 23.6%, and 26.8%, and the compressive strengths are improved by 50.8%, 35.7%, 13.4%, and 27.7%. The drying shrinkage and total porosity of the mortar at the hydration age of 28 d are reduced by 117.4% and 21.55%, respectively. It is attributed to the filling effect of a large amount of ettringite (AFt) and intertwined with the fibrous C-S-H gel to form a network. This study will provide a theoretical basis for the application of the BCSA–OPC engineering.

Rapid calcium sulfoaluminate cement concrete (RCSACC) has received increased attention of late because it can be manufactured with less CO2 emissions than ordinary Portland cement. In previous studies, RCSACC performed poorly when subjected to elevated temperatures, to which fiber-reinforced concrete (FRC) is a potential alternative. This study investigated the impact of incorporating two types of fibers, i.e., copper-plated steel microfilament (CPM) and shear corrugated steel (SC), on the engineering, mechanical, and microstructural features of RCSACC after exposure to elevated temperatures. Pore size distribution, microstructure, and mechanical properties were tested after exposure to temperatures of 100, 200, and 300 °C. The content of each type of fibers represented 1% of the concrete. The results showed that the mechanical properties were affected by the addition of either type of steel fibers. Adding CPM or SC steel fibers could ensure an adequate resistance of RCSACC when exposed to high temperatures, in addition to improving its residual mechanical behavior, spalling resistance, and ductility after heating. Steel fibers contribute to enhancing both mechanical properties and resistance to heating effects. However, adding steel fibers also appears to increase microstructure damage with heat, reduce workability, entrap air and water, and reduce cracking related to drying shrinkage.