Guoxue Zhang

This article investigates the influence of B2O3 dosage on the rheological properties and mechanical properties of geopolymer cement mortar. The results showed that B2O3 slightly reduced the fluidity of geopolymer cement mortar, whereas the yield stress and plastic viscosity of geopolymer cement mortar increased with the increase of B2O3 dosage, besides the thixotropy of geopolymer cement mortar also increased. Moreover, the appropriate amount of B2O3 was found to improve the mechanical properties of the 3, 7 days geopolymer cement mortar. Compared to the specimen without B2O3, with 1 wt. % B2O3 geopolymer cement mortar, the 3, 7 days flexural strengths were increased by 18.15 % and 15.03 %, the 3, 7 days compressive strength were increased by 4.95 % and 11.28 %, respectively. Furthermore, infrared spectrum analysis indicated that the formation and propagation of the amorphous aluminosilicate gel phase were improved, which can explain the improvement in the mechanical strength with the incorporation of B2O3. Hence, it is found that the incorporation of B2O3 particles can enhance the rheological properties and mechanical properties of geopolymer cement mortar.

In the present study, in order to examine the impact performances of ordinary reinforced concrete bridge piers which have been replaced by stainless-steel bars of equal cross-sections under the protective condition of anticollision material, the impact dynamic responses of the ordinary reinforced concrete bridge piers, with replacements under the protection of closed-cell aluminum foam, were compared and analyzed using an ultrahigh drop hammer impact test system. The results showed that when the impact velocity was small (for example, less than 1.42 M/s), after the implementation of equal cross-sectional replacements, the closed-cell aluminum foam had been in an elastic or yield stage. During that stage, the impact forces of the stainless-steel reinforced concrete piers were larger than those of the ordinary reinforced concrete piers, and the relative ratios were stable at approximately 28 to 34%. In addition, the relative ratios of the displacements at the tops of the components were also found to be stable at approximately 22%, and the change rates of the concrete ultrasonic damages were approximately the same. However, when the impact forces had increased (for example, more than 1.67 m/s), the closed-cell aluminum foam entered a densification stage, and the peak impact force ratios decreased sharply. It was also observed that the relative peak displacement ratios at the tops of the components displayed increasing trends, and the change rates of the concrete ultrasonic damages had displayed major flux. Therefore, the replacement of the ordinary piers with stainless-steel bars had increased the possibility of shear failures.

To study the impact resistance of the stainless steel reinforced concrete after reinforced with CFRP (Carbon Fibre Reinforced Plastic), the multifunction ultra-high heavy drop hammer test system was adopted to conduct multiple horizontal impact test research on three stainless steel reinforced concrete piers before and after they are reinforced. The test results showed that with equal impact energy, the maximum impact force of the stainless steel reinforced concrete piers was larger than that of the stainless steel reinforced concrete piers that were reinforced with CFRP, while after the concrete piers were reinforced, the peak displacement of the piers was obviously smaller than that before they were reinforced and the residual deformation also became smaller, which improved the flexural rigidity of the section. And the local anti-damage capacity can be improved so as to lengthen the life of structures by reinforcing the stainless steel reinforced concrete pier with carbon fiber.

In this research study, horizontal impact tests were carried out on five reduced scale pier models using China’s most advanced multifunctional ultrahigh heavy drop hammer impact test system and DHDAS dynamic signal acquisition and analysis system. Due to the fact that the traditional measurement method can only be used for local measurement damage, and the volatility is high, this paper proposes a test method for the modal frequency identification of the overall damage of reinforced concrete pier and applies the ultrasonic damage measurement method to verify the results. The tests analyzed the modal frequencies and ultrasonic velocity identifications for the purpose of evaluating the impact damages of bridge piers, as well as the relationship between them. The results showed that the modal frequencies were consistent with the ultrasonic waves in identifying and evaluating the damages to the piers. Also, the modal frequency damage factors were determined to be functions of the ultrasonic wave velocity damage factors. Therefore, the results of this study confirmed that it was feasible to characterize the impact damages of piers using a modal frequency method.

In this experimental study, for the purpose of furthering the understanding of the effects of different reinforcement ratios on the impact resistance behaviors of reinforced concrete (RC) beams, a series of vertical impact tests were conducted on five RC beams with different reinforcement ratios using a domestically advanced ultrahigh heavy drop hammer impact testing machine system. The impact velocities and force of the drop hammer during the impacts, displacements, and strain of the test points, as well as the crack propagation process, were collected and analyzed. The experimental test results revealed the following. (1) When the reinforcement ratios ranged between 0.58 and 1.63 %, the RC beams had mainly suffered bending failures. However, when the reinforcement ratios were increased, it was observed that the overall stiffness of the beams had been effectively improved; displacements, steel strain, and damages were reduced; and the impact resistance abilities of the beams had been enhanced. (2) When the reinforcement ratios had ranged from 1.63 to 2.57 %, shear failures were found to be the main failure mode of the RC beams. It was found that increases in the reinforcement ratios could not effectively reduce the damages and were not conducive to the beams’ resistance to impact loads. (3) It was determined that because of the shearing effects of the impact loads, the shear force of the RC beams had increased.

In this study, the impact test of two groups of reinforced concrete piers protected by closed‐cell aluminum foam is carried out by using the ultrahigh drop hammer impact test system. The purpose of this study is to explore the impact resistance and protective performance of closed‐cell aluminum foam under the impact load on the concrete bridge pier after replacing the ordinary reinforcement with stainless steel reinforcement. The study results show that the impact force is related to the overall stiffness of the specimen, as well as to the failure mode. When the impact velocity is less than 1.42 m/s, the closed‐cell aluminum foam is in an elastic or yielding stage. The change rate of impact force (231 and 97.5, respectively), tip displacement (33.5 and 18, respectively), and ultrasonic damage rate of the concrete in the two groups of specimen is relatively small, while the change rate of the two groups of specimen remains approximately consistent. In addition, when the impact is greater than 1.42 m/s and the closed‐cell aluminum foam is in the densification stage, the change rate of the impact force (increase from 231 to 819 and from 97.5 to 984.5), the tip displacement (increase from 33.5 to 67 and from 18 to 62), and ultrasonic damage rate of concrete are larger, which results in an increase in the dynamic response of the structure.

In this study, an ultrahigh drop hammer impact test system was adopted for multiple horizontal impact tests on stainless steel-reinforced concrete columns and ordinary-reinforced concrete columns with the same longitudinal reinforcement diameter. The damage performance after impact was studied, and the finite element model was established. The test measured the impact force, displacement, cracking of the specimen during the impact, and the concrete damage near the bottom of the specimen. The test results showed that the failure mode of the stainless steel-reinforced concrete specimen under multiple impacts was the same as that of the ordinary reinforced concrete specimen. Under the same impact conditions, the maximum impact force, the maximum displacement, and the damage degree of stainless steel-reinforced concrete column specimen were lower than those of the ordinary reinforced concrete specimen.

The reinforced concrete structure of a port wharf is affected by steel corrosion and ship docking impact. Replacing an ordinary steel bar with a stainless steel bar can solve the corrosion problem of the steel bar while ensuring the bearing capacity of the structure. However, the research on impact resistance of stainless steel-reinforced concrete structure is not perfect. In this paper, impact mechanical properties of reinforced concrete beams before and after equal strength replacement of stainless steel bars are analyzed by theoretical analysis and drop hammer impact test, and the possibility and applicable scope of equal strength replacement of stainless steel bars are put forward. The results indicated the following: (1) when the reinforcement ratios were small (0.21% to 1.32%), the stainless steel-reinforced concrete beams with equal strength were able to effectively reduce the stiffness losses of the beams undergoing impact loads, as well as improve the elastic resilience abilities, and reduce the structural damages. Therefore, the corrosion and impact problems of reinforcements could be solved by replacing ordinary reinforcements with stainless steel reinforcements and (2) when the reinforcement ratios were large (1.32% to 2.57%), the shear failures of the stainless steel-reinforced concrete beams were observed to be relatively serious, and the impact resistance performances had worsened. The research results provide technical support for the engineering application of stainless steel-reinforced concrete structure design.

In this research study, the characteristics of ship–bridge collision force formulas, in Chinese standards as well as international standards, were analyzed. By considering the damage situations of bridge piers under the cumulative ship collision conditions, a method of combining theoretical deduction with numerical analysis was adopted in this study. The goals of this study were to analyze and examine the sizes of the ship–bridge collision forces, along with the damage situations of piers, in order to propose a collision force calculation formula which took cumulative pier damages into consideration. Also, experimental verifications and an applicability analysis of the proposed formula were performed.

Stainless reinforced equal-strength replacement piers are used to solve the problems of steel corrosion, surplus strength, and resource waste for piers in marine environments. In this study, an ultrahigh drop weight impact test system was applied for a comparative experimental model of the horizontal impacts between two groups of stainless reinforced replaced concrete piers. The impact forces and displacements, strain time–history curves, crack propagations and distributions, and concrete damages, were analyzed during the experimental test. The results showed that the original specimen had consistent change trends with the stainless reinforced equal-strength replaced specimens in regard to maximum impact, steel bar and concrete strains, displacement peaks, and other aspects. Furthermore, under equal impact energies, the relative ratios were found to all range at ±5%, and the fracture quantities and distributions, as well as the concrete damages, were approximately consistent. These research results will potentially provide technical support for the future designs of anti-impact stainless reinforced concrete piers.