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Concrete structures usually contain cracks or microcracks. Under dynamic loading, such as impacts, blasts and earthquakes, these cracks may initiate and propagate, weakening concrete strength and structure’s stability. It is thus necessary to carry out the research on the crack dynamic fracture behavior and to develop crack arresting technique for cracked concrete structures under dynamic loads. In this study, impact tests were performed using a drop-weight impact device. A single crack emanating from a semicircle and a V-shaped bottom (SCESVB) specimen was proposed. The V-shaped bottom has the function of arrest on the propagation of the pre-crack. Crack propagation gauges (CPGs) were used to measure crack propagation parameters. Three angles 120°, 150° and 180° were designed for the V-shaped bottom of the SCESVB specimens. The crack propagation behavior was simulated by the finite difference code AUTODYN, and the dynamic stress intensity factor (DSIF) was calculated by the finite element code ABAQUS. The critical DSIF was determined by the crack initiation time and the propagation time measured by the CPG. The experimental and numerical simulation results show that the SCESVB specimen is suited to studying crack propagation behavior and crack arresting behavior for concrete under dynamic loads. During the crack propagation process, the crack may arrest in a short time, and the critical DSIF at initiation is higher than that at propagation for the concrete.

In order to investigate the deterioration of the elastic modulus and fracture toughness of corroded concrete, three-point bending (TPB) tests were conducted by using corroded concrete specimens. The initiation load, the maximum load, the P-CMOD (loads versus crack mouth opening displacements) curves and the stress-strain curves were measured. Meanwhile, the deterioration near crack tips of the corroded specimens was observed with the aid of scanning electronic microscopy (SEM). Under the simulated acid solutions, the corrosion depth near crack tips gradually grows with the increase of corrosion time, and finally the concrete microstructures are porous and loose and microcracks are developed, which will deteriorate concrete material parameters, such as elastic modulus and fracture toughness. The test results show that subcritical propagation occurs during the loading progress from the initiation load to the maximum load, and the initiation toughness is about 80%–85% of the fracture toughness of the corroded concrete. For the specimens immersed in pH 2.5 and 3.5 solutions, both the fracture toughness and the elastic modulus increase in the early stage and then decrease with the increase of corrosion time, whereas for the specimens immersed in pH 1.5 solutions, both the elastic modulus and fracture toughness decrease almost linearly with immersion time. H+ and SO 4 2 - are two main factors in the deterioration of concrete in the simulated acid solutions.

Lauric acid (LA) is a common used phase change materials (PCM), and has been attracted considerable attentions for conserving waste energy and improving efficiency of energy utilization in building. In this paper, asphalt/LA blends are obtained through direct impregnated technology. The morphology, compatibility, crystalline properties, phase change properties, thermal reliability and stability of obtained asphalt/LA blends are extensively studied by scanning electron microscope, X-ray diffraction, differential scanning calorimetry, accelerated thermal cycling testing and thermogravimetric analysis, respectively. The asphalt exhibits a good compatibility with LA, and the phase separation is not detected in obtained blends. The obtained asphalt/LA blends demonstrate an excellent performance of storing and releasing heat during phase change process. Meanwhile, accelerated thermal cycling testing results indicate that the modified asphalt exhibit good thermal reliability and LA cannot leak from the blends after 100 times thermal cycling treated. The good thermal stability implied a practical application of blends in the construction industry. The obtained blends show great potential for conserving waste energy and regulating the indoor temperature in the field of construction and building.

This paper presents an experimental study on the effects of very early age loading of concrete-filled steel tubular (CFST) short columns on their long-term axial compression behaviors. The specimens include CFSTs wrapped in FRP (fiber reinforced polymer) cloths and bare CFSTs. When concrete is at an age of 1d, 2d or 3d, the circular CFST column specimen is loaded with axial compression, unloaded after reaching the peak value, and then put into the curing room to continue curing. At the age of 28d, the axial compression bearing capacity is tested and the load–displacement curve is obtained. In the tests, five CFST columns are set as the control group, which are directly cured until 28d. The effects of initial loading age, steel tube wall thickness and constraint level are investigated. The results show that very early age loading can improve the long-term load bearing performance of CFST columns. For the configurations applied in the present study, the ultimate bearing capacity are increased by 1.01% to 24.59%, the yield loads by 2.33% to 52.53%, and the combined elastic moduli are also increased.

There are some concrete structures subjected to both impacts of acid rain and cyclic wetting-drying, such as the concrete bridge pier and dam in an acid rain zone, and therefore, it is of great significance to study the deterioration of concrete material parameters under such combining impacts. The parameters investigated in this paper mainly include the corrosion depth, mode II fracture toughness, compressive strength and elastic modulus. Additionally, the chemical composition and thermal stability of corroded products distributed in severe, mild and free corrosion zones were measured by using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). To study the pure mode II fracture toughness of deteriorated concrete, anti-symmetrical four-point bending (ASFPB) tests were conducted on the corroded concrete specimens. The test results indicate that the dissolving corrosion caused by H+ occurs in the corrosion zone of concrete, while the swelling corrosion caused by SO42- mainly occurs in the severe corrosion zone. The thermal stability of corroded products distributed in the severe, mild and free corrosion zone of concrete decreases gradually. The pure mode II fracture toughness of concrete almost decreases linearly with increasing the number of cyclic wetting-drying, and increase with increasing the pH value of simulated acid rain. Moreover, there is a good linear relationship between pure mode II fracture toughness and compressive strength of concrete under both impacts of simulated acid rain and cyclic wetting-drying. The elastic modulus of corrosion concrete decreases with the increase of wetting-drying cycles, and it decreases with decreasing the pH value of simulated acid rain solutions.