Salt Freeze-thaw Cycles Research Articles

Study on Performance Deterioration of Asphalt and Asphalt Mixtures Containing Mafilon under Internal Salt Freeze-Thaw Cycles

The purpose of this work is to determine the implications of internal salt freeze-thaw cycles on performance deterioration to asphalt and asphalt mixtures containing Mafilon (MFL). The deterioration to different numbers of F-TCs and different MFL contents on asphalt properties and mechanism were investigated by physical properties tests and microcosmic tests. Then the damages of road performance indexes of asphalt mixtures containing different MFL contents were studied by road performance tests. The experimental results show that asphalt containing MFL after F-TCs has a remarkable decline in ductility and penetration, while growth in softening point. Internal salt F-TCs are most damaging to the cryogenic properties of asphalt. Chemical reactions and salt aging effects occur in salt F-TCs, raising the glass transition temperature of asphalt. Road performance tests indicate the deterioration of internal salt F-TCs to high temperature stability and water stability is the most pronounced, with 29.18% and 21.78% reduction, respectively.

Salt frost resistance of concrete with crushed asphalt particles: Experiments and modelling

Asphalt coating is widely utilized for its excellent impermeability on marine structure surface. However, in high latitude regions, the coupling effect of freeze-thaw cycles and chemical aging rapidly diminished the protective effect, significantly increasing the risk of structural damage. Therefore, to maximize the impermeability and durability of asphalt, we homogeneously intermixed the crushed asphalt particles into the concrete instead of surface coating. A series of crushed asphalt particles concrete (CAPC) with different asphalt content were prepared and subjected to up to 30 salt freeze thaw cycles (SFTCs) in a 3.5 wt% NaCl solution. Experimental results revealed that addition of asphalt particles improved pore structure and impermeability, mitigating frost damage and chloride diffusion. Optimal performance is observed at 2 % asphalt content, showcasing a notable 22.0 % reduction in porosity, a substantial 47.3 % decrease in chloride concentration at 10 mm depth after 30 SFTCs, with only a 3 % slight reduction in strength. Moreover, a multi-phase chloride diffusion model was proposed, considering matrix/asphalt damage and time-varying porosity. The influence of aggregate shape and volume, data-processing methods, long-term prediction under different regions were discussed. Compared with asphalt coating and classical concrete, the proposed CAPC is recommended for use under marine environment, especially in cold marine regions.

Seepage characteristics and mechanism of double damage basalt fiber reinforced concrete under three-dimensional variable stress states

Concrete experiences a three-dimensional variable stress state during its service life. To explore the permeability evolution and mechanism under such conditions, a permeability test was conducted on double damage basalt fiber concrete subjected to loading and unloading of twice confining pressure. Pore structure and microstructure of specimens were analyzed before and after permeability test. The findings reveal that the reduction in permeability after primary cycle of confining pressure loading and unloading is significantly higher than that after secondary cycle, and residual deformation is also more pronounced after primary cycle. Both high temperature and salt freeze-thaw cycles induce initial damage to specimens, consequently altering internal pore structure and subsequently impacting initial permeability. Notably, initial permeability decreases in the case of 10th salt freeze-thaw cycles, while it increases under other conditions. The greater the initial extent of damage to the specimen, the higher the permeability damage coefficient and the permeability damage rate. As the confining pressure decreases, the attenuated permeability increases, with the permeability decay rate reaching a significant 88.53 %. Plastic deformation of pores during loading and unloading process cannot be fully reversed, leading to the development of macropores and mesopores into smaller pore sizes, resulting in a remarkable 87.17 % increase in the proportion of micropores. Microscopic observations reveal smaller pores within the matrix, shorter crack lengths, and narrower crack widths in the specimen. The application of confining pressure reduces permeability channels within specimens, ultimately causing a decline in permeability.

Investigations on the shear performance degradation of ECC-NC grooved interface under salt freeze-thaw cycles

This study aims to clarify the mechanical behavior of engineered cementitious composite (ECC)-normal concrete (NC) grooved interface under salt freeze-thaw cycles. A comprehensive analysis was conducted to study the effects of the cycle number, interface agent, and ECC strength on the interface shear performance. The results showed that, compared with specimens in room temperature conditions, after 200 cycles, the shear strength and shear stiffness of all specimens decreased by no less than 37.8 % and 52.7 %, respectively. Moreover, using different interface agents or increasing ECC strength improved the interface salt freeze-thaw resistance significantly. Among all specimens using interface agents, fly ash had the best-enhancing effect on the interface shear performance. Additionally, considering interface area corrosion and degradation of material properties, a damage model was established. Based on the damage model, an equation for calculating the interface shear capacity was proposed, providing a valuable reference for the engineering application of ECC reinforcement in extreme environments.

Experiment study on flexural performance of steel concrete composite beams under salt freeze-thaw cycles in negative moment sections

Bridge structures in cold climates face significant challenges due to freeze-thaw cycles and salt-induced corrosion. This study investigates the degradation mechanisms of the negative bending behavior of steel-concrete composite beams using normal concrete (NC) and ultra-high performance concrete (UHPC) under salt freeze-thaw cycles (SFTC), considering the impact of different stud arrangements. The results indicate that UHPC significantly enhances the cracking performance in the negative bending region of the composite beams and demonstrates high resistance to SFTC. Before undergoing SFTC, the cracking moment of the UHPC beams increased by an average of 210.5%, and stiffness by 37.3%, compared to the NC composite beams. After 150 SFTCs, the NC beams showed a significant decline in performance, with a 62.1% reduction in cracking moment, a 6.2% decrease in load-carrying capacity, and a 5.6% reduction in stiffness. In contrast, the flexural performance of the UHPC beams was almost unaffected, with only a 17.5% reduction in cracking load. Moreover, beams with a double-row stud configuration exhibited better negative bending resistance compared to those with a single-row stud configuration. Based on experimental results and data from reference, a reasonable formula for predicting the composite beams under the effect of SFTCs was proposed and proved to have satisfactory accuracy.

Microstructural damage characterization of NC-UHPC composite under salt freeze-thaw cycles based on ex-situ X-ray computed tomography

In the harsh environment of extreme salt-freezing conditions, concrete structures face secondary durability issues after undergoing repairs, making it a critical yet challenging topic. This paper employs a novel ex-situ X-ray computed tomography approach to explore the mechanism of damage evolution in normal concrete (NC) to ultra-high performance concrete (UHPC) composites under salt-freezing conditions. For the first time, we consider evolution in both external and internal pores to quantitatively assess the damage. Additionally, slant shear tests, Mercury Intrusion Porosimetry (MIP) were also employed to validate the damage mechanism of NC-UHPC. Finally, empirical formulas summarizing the bond strength and pore changes in NC-UHPC were derived. The results reveal a crucial factor influencing the progression of damage in the NC-UHPC composite: the presence of external pores that directly interact with the salty solution. Damage initiation primarily occurs within the NC-UHPC composite due to these external pores located in the NC region, subsequently extending into the overlay transition zone (OTZ) and UHPC sections. Remarkably, the resistance of the OTZ, previously identified as the weakest zone in the NC-UHPC composite, surpasses that of the NC. This exceptional performance can be attributed to the higher porosity of the OTZ, offering additional space for the dissipation of pressure caused by freezing. What's even more important is that this highlights the consistent origin of damage in the NC-UHPC composite, emphasizing that it always begins within the NC. Considering this perspective prompts the question of whether the exceptionally high strength and durability of UHPC may lead to an excess of repair capabilities?

Research on the Anti-corrosion Performance of Corrosion Inhibitor under Salt Freeze-Thaw Cycles

In this study, a multifunctional corrosion inhibitor (referred to as CI) was incorporated into C30 concrete. The effect of CI on the free chloride content, Tafel curves of reinforcement, and quality loss rate (QLR) were investigated under salt freeze-thaw cycles (SFTCs). Additionally, the scanning electron microscope (SEM) was employed to examine the corrosion of the reinforcement surface. The results indicated that CI was beneficial in reducing the internal free chloride content within the concrete. It could also form an adsorption film on the reinforcement surface, effectively lowering the corrosion rate and minimizing QLR, and providing excellent protection for the steel reinforcement.

Effect of load on bonding properties and salt freeze-thaw resistance of bridge expansion joint concrete

In the seasonal frozen regions, the bridge expansion joint concrete (BEJC) is susceptible to damage during its service life, not only from vehicular loads but also from chloride salt erosion and the effects of freeze-thaw cycles. This study investigates the basic physical and mechanical properties of BEJC under different curing conditions. A rapid chloride permeability test was conducted to comparatively analyze the concrete's chloride ion penetration resistance. The microscopic crack width on the concrete bond surface is evaluated to assess the concrete bond performance under different loading durations. Additionally, the study explores the coupled effect of wheel loads and single-sided salt freeze-thaw cycles (WL-SFT) on the freeze-thaw resistance of BEJC, delving into factors such as spalling mass, water absorption rate, and pore structure characteristics (including air content, specific surface area, spacing coefficient) and connectivity. The results indicate that for specimens subjected to loading at 1–14 days and 3–14 days, the average crack widths on the bond surface are 14.36 µm and 10.09 µm, respectively, representing 5.27 times and 3.70 times those of unloaded specimens. The bond strength also decreases by 34.8% and 14.2%, respectively, compared to unloaded specimens. The increase in crack width leads to a reduction in bond strength, highlighting the importance of bond strength as a consideration for the actual opening time of roads in engineering projects. Furthermore, due to its smaller and more stable pore structure, the study suggests that WL-SFT almost does not damage standard curing (SC) concrete; however, it slightly disrupts the pore structure of natural curing (NC) concrete. In comparison, WL-SFT leads to the generation of more microcracks in both the surface and deeper layers of low-temperature curing (LC) concrete, resulting in the destruction of its pore structure and connectivity.

Salt scaling resistance of pre-cracked ultra-high performance concrete with the coupling of salt freeze-thaw and wet-dry cycles

Wet-dry cycles and cracking are unavoidable problems of concrete structures and reduce durability by enhancing the penetration of harmful ions and water, which may have a synergistic adverse influence with severe surface damage caused by salt freeze-thaw cycles. This study aims to investigate the salt scaling resistance of ultra-high performance concrete (UHPC) under multiple harsh environments including wet-dry cycles and pre-cracking. The relationship between workability, absorption behavior, and scaling resistance with fiber content increases is assessed. Mass loss, chloride binding behavior, pore structure, and pore morphology are analyzed to describe the influences of pre-cracking and wet-dry cycles. The results reveal that the workability of fresh concrete and the distribution of steel fibers are the key factors in determining the salt scaling resistance of UHPC. Pre-cracking and wet-dry cycles inhibit the rapid scaling damage of UHPC by accelerating chloride accumulation, which reduces the icing pressure of pore liquid and refining the micropores (<200 nm) capable of remaining non-frozen at low temperatures through the chemical binding of chloride. However, the combined effect of pre-cracking and wet-dry cycles can lead to the corrosion of internal steel fibers and more scaling damage, and the crack width should not be greater than 0.1 mm.

Deterioration law of flexural performance of RC beams with initial cracks under alternating action of salt freeze-thaw cycles and fatigue

Reinforced concrete (RC) bridges in cold regions are continuously exposed to the combined challenges of traffic loads, freeze–thaw cycles, and salt corrosion. This research delves into the deterioration mechanics and flexural performance of damaged RC beams when subjected to the dual stresses of salt freeze–thaw cycles (SFTCs) and fatigue loading. We conducted performance degradation tests on cracked RC beams subjected to alternating SFTCs and fatigue loading, followed by evaluations of their residual flexural capacities. In-depth analysis considered the impact of the number of alternating cycles and the initial crack width. The results indicate that the combined effects of alternating SFTCs, fatigue loading, and initial cracks significantly diminish the RC beams' flexural strength. As the number of alternating cycles and the initial crack width increased, there was a notable rise in mass loss, rebar corrosion, and a reduction in residual load carrying capacity and stiffness. Particularly, beams without initial cracks saw a 3.61 % reduction in load carrying capacity and a 24.06 % decrease in stiffness after four alternating cycles. In contrast, beams with an initial crack width of 0.10 mm experienced an 11.15 % decline in load carrying capacity and a 38.38 % drop in stiffness. The study concludes that while the combined effects of fatigue loading, SFTCs, and initial cracks are significant, initial cracks exhibit a more pronounced negative influence on load carrying capacity than on stiffness and ductility.

Research on Performance Deterioration of Internally Cured Pavement Concrete under the Coupling Effect of Salt Freeze-Thaw.

This paper aims at solving the material durability problem caused by spraying deicing salt on pavement concrete in the northern winter. Super absorbent polymer (SAP) was adopted as an internal curing agent to enhance the durability of pavement concrete. Curing parameters including particle size and dosage of SAP and curing condition were optimized based on mortar tests by means of the grey target decision method. The deterioration rule of durability and mechanical properties of pavement concrete internally cured by different SAP dosages after salt freeze-thaw cycles were explored through rapid freeze-thaw test. Combined with the characteristics of pore structure, hydration and microstructure, the influence mechanism of SAP on the salt freeze-thaw resistance of pavement concrete was revealed. The experimental results showed that: (i) The reduction in mass loss rate and relative dynamic modulus was significantly improved by SAP internal curing with moderate dosage; (ii) The more freeze-thaw cycles the specimen underwent, the greater the increase in strength; (iii) After 75 cycles, the chloride ion erosion depth could be decreased by approximately 23.18%. Moreover, the addition of SAP could refine the pore size, inhibit the generation of shrinkage microcracks, and promote the degree of cement hydration in the late stage, which improved the internal density of the cement concrete structure. Therefore, the deterioration of pavement under the coupling effect of salt freeze-thaw was reduced.

Research on The Chloride Diffusion Modified Model for Marine Concretes with Nanoparticles under The Action of Multiple Environmental Factors

Marine concrete structures are subject to the action of multiple environments during their service time. This leads to increased deterioration in the durability of marine concretes under the combined action of bending load and dry–wet cycles, salt freeze–thaw cycles, and salt spray erosion. The main reason for the damage of concrete under the action of the above three environments is Cl- attack. The free Cl- content (Cl-f) and the free Cl- diffusion coefficient (Df) of concrete can explain the diffusion of Cl- in concrete. This paper considers the actual environment of marine concrete structures and develops the Cl- diffusion modified model for nano-marine concretes under the action of dry–wet cycles, salt freeze–thaw cycles, and bending load and salt spray erosion. The nano-SiO2, nano-Fe2O3, and nano-Fe3O4 were firstly incorporated into ordinary marine concrete, then the Cl- content of each group of marine concrete was measured at different depths, and the Cl- diffusion coefficients were calculated; finally, the Cl- diffusion modified model was established under different environmental factors. The test results show that the total and free Cl- diffusion coefficients of nano-marine concretes were lower than those of ordinary marine concrete, and the nano-SiO2, nano-Fe2O3, and nano-Fe3O4 of the optimum dosage were 2%, 1%, and 2%, respectively. The fitting results of Cl- content have a good correlation, and the correlation coefficient (R) is basically above 0.98.

Experimental Evaluation of the Concrete Damage and Pore Characteristics under Salt-Freezing Cycles.

Herein, ordinary silicate concrete specimens are prepared to study the damage law of a cement-concrete material under the effects of salt erosion and a freeze–thaw environment. NaCl, NaHCO3, and Na2SO4 solutions are separately produced, according to the characteristics of saline soil, to conduct an experimental study on the concrete characteristics during quick salt freezing cycles, and to analyse the changes in its compressive strength, mass loss, and dynamic elastic modulus (DEM) under freeze–thaw cycles. Low-field nuclear magnetic resonance (NMR) and scanning electronic microscopy are used to investigate the change in the microstructure of concrete specimens under salt freeze–thaw cycles (FTCs). The results show the loss in compressive strength, mass, DEM, and NMR spectrum signal increased by 1.5–3 times, 3–5 times, 1.5–2.5 times, and 2–4 times, respectively, for concrete specimens under 50–100 FTCs in 6.8% composite salt solution, in comparison to fresh water. Apparent spalling, decreases in the DEM, and reductions in the compressive strength occur in concrete when increasing the number of salt FTCs. The number of internal cracks in the concrete structure increase under the combined action of salt crystallization, moisture absorption, and freeze–thaw. The changes in the internal microscopic pore volume in concrete structures exhibit the same trend with changes in the macro mechanical properties of concrete. The correlation coefficients between the changes in each peak in the NUR spectrum and the changes in the compressive strength of concrete specimens under FTCs in freshwater or low-concentration salt solutions are both larger than 0.7, calculated using the grey correlation degree method. Therefore, these changes could be used as a potential evaluation index for salt frozen damage to concrete structures.

A time-dependent diffusive model for the simulation of chloride penetration in concrete considering the effect of natural salt freeze-thaw cycles

In marine cold regions, reinforced concrete (RC) structures are affected by the coupling action of chloride erosion and freeze-thaw (FT) cycles. The coupling effects will lead to the concrete deterioration, accelerate the chloride diffusion process, and significantly reduce the service life of RC structures. In this investigation, a chloride diffusive model considering the time-varying effects of FT damage and temperature was proposed to quantify the diffusion of chloride in concrete under the action of natural salt freeze-thaw cycles (SFTCs) or under the action of alternating environment, in which the salt FT cycling environment and the pure chloride diffusion environment appear alternately. In addition, a natural salt FT cycling experimental method was put forward, which can simulate the actual salt FT cycling process of concrete in tidal zone. Chloride content and the dynamic elastic modulus (DEM) of specimen were determined after corresponding exposure duration, i.e., 30 d, 60 d, 80 d, 100 d and 120 d. Meanwhile, during the exposure time, the temperature at different positions (air temperature, water temperature, central temperature of the specimen in atmospheric area, tidal zone, and underwater area) was monitored continuously. The results show that the maximum number of FT cycles in this experiment is 36, and the average FT minimum temperature is −4.3 °C. The cycle of FT action is 24 h, and the ratio of freezing time and thawing time is about 5:1. After the initiation of FT action, the DEM decreases linearly with exposure time, with maximum loss of about 3% in one winter. Compared with the previously reported rapid FT cycling test data, the loss of DEM caused by one rapid FT cycle is about 9.3 times of that caused by one natural salt FT cycle. Besides, the mass loss of concrete under natural SFTCs for one winter in Tianjin area is about 0.3%. And chloride profiles in concrete deepened with exposure duration. Subsequently, the proposed model was used to simulate the diffusion of chloride in concrete under the experimental conditions. The chloride contents simulated by the proposed model agree well with the test results, showing that this model is applicable to predict the diffusion of chloride in concrete exposed to the action of alternating environment.

Concrete Durability after Load Damage and Salt Freeze-Thaw Cycles.

To determine how the performance of concrete changes after initial load damage and salt freezing, concrete samples were first subjected to loading and unloading, and were then put into salt solutions to carry out rapid freeze–thaw cycle (FTC) experiments. Salt solutions were created based on the saline soil of western Jilin, China, for use in salt freeze–thaw testing. This determined the change law of the compressive strength and the dynamic elastic modulus (DEM). Additionally, low-field nuclear magnetic resonance technology and a scanning electron microscope were applied to investigate the pore characteristics and microstructure of concrete samples after FTCs. This study found that when the concrete specimens were subjected to an initial load of 0.3f under 50 FTCs, the loss in the compressive strength increased by 24% when the concrete was subjected to freeze–thaw cycles in freshwater and increased by 24% when concrete was subjected to freeze–thaw cycles in a 6.8% composite salt solution compared with the specimens without the initial load. When the concrete was subjected to FTCs in a 6.8% composite salt solution 50 times, the loss in the compressive strength increased by 110% for concrete without an initial load and increased by 109% when the concrete was subjected to an initial load of 0.3f compared with the specimens under FTCs in freshwater. The persistent effect of the FTCs also aggravated chloride ion erosion in the concrete, which gradually reduced the concrete’s permeability resistance. Internal pores in the concrete, especially the proportion of above-medium-sized pores, gradually increased along with the increase in the number of FTCs. There is a good linear correlation between the change rule of compressive mechanical properties and the change rules of mass, DEM, and pore characteristics inside the concrete under rapid FTCs in different salt solutions.

Service Life Prediction of Basalt Fiber Reinforced Concrete under Salt Freeze-thaw Cycles

To address the reduced durability of concrete structures under salt freeze-thaw erosion in Northwest China, basalt fiber reinforced concrete and common concrete with different mixing amounts were selected to predict their service life in three freeze-thaw conditions. Results showed that the damage on concrete under fresh water freeze-thaw condition is lower than that caused by salt freeze-thaw erosion, the addition of basalt fiber can effectively slow down the degradation of mechanical properties of concrete under salt freeze-thaw erosion, and the lowest degradation rate is reached when the content of basalt fiber is 0.15%. Fiber hinders the expansion of cracks and reduces the pores, and in turn improves the frost resistance durability of concrete. The service life prediction results obtained with Gray Model and Weibull Model are roughly similar, among which, Gray Model needs less sample volume, while Weibull Model presents more accurate prediction results.

Coupling Effect of Salt Freeze-Thaw Cycles and Carbonation on the Mechanical Performance of Quick Hardening Sulphoaluminate Cement-Based Reactive Powder Concrete with Basalt Fibers

The effect of salt freeze-thaw cycles coupled with carbonation on the mechanical performance of quick hardening sulphoaluminate cement-based reactive powder concrete combined with basalt fibers was investigated. The ratios of basalt fibers in sulphoaluminate cement-based reactive powder concrete (SAC-RPC) were 1%, 2%, 3% and 4% by the volume of concrete. The mechanical strengths (compressive strength, flexural strength and bonding strength) of SAC-RPC were investigated after curing for 5 h, 1 d, 14 d and 28 d, respectively. Meanwhile, the mechanical strengths of resultant concrete were detected, when different NaCl freeze-thaw cycles and carbonation were adopted. Results showed that the addition of basalt fibers could effectively improve the mechanical strengths, especially the flexural strength of SAC-RPC. The dosage of 3.0% was the threshold value affected mechanical strengths. The flexural, compressive and bonding strengths of SAC-RPC were higher than 8.53 MPa, 34 MPa and 3.21 MPa, respectively. The mass loss and mechanical strengths loss of SAC-RPC increased in the form of quadratic function with the increasing number of NaCl freeze-thaw cycles and varied in the form of quadratic decreasing function. Meanwhile, the effect of carbonation on the mechanical strengths of SAC-RPC can be ignored. Additionally, the coupling effect of salt freeze-thaw cycles and carbonation could accelerate the attenuation of concrete strength. The mechanical strengths loss demonstrated a decreased quadratic function with the increasing volume of basalt fibers.

Impact of sustained load on damage characteristics of reinforced concrete beams under the combined action of salt freeze-thaw cycles and corrosion

A large number of reinforced concrete (RC) structures in cold regions are attacked by the combined action of sustained load, freeze-thaw cycles and steel corrosion. The combined effects accelerate the deterioration process of RC and significantly reduce the service life of RC structures. This paper presents an investigation of the damage characteristics of RC beams under combined action of salt freeze-thaw cycles (SFTCs), load and corrosion. By using the large artificial climate chamber and the RC beam reverse loading device, three RC beams were subjected to SFTCs and corrosion tests under different load levels, and one beam was subjected to corrosion tests under normal temperature without load. The test results showed that the second-order natural frequency can be used as an index to evaluate the freeze-thaw damage of RC beams. The higher the load level, the greater the amount of concrete spalling and the faster the second-order natural frequency decreases. Affected by the freeze-thaw damage, the surface of test beams is not prone to rust crack, but the stress cracks become wider with the increase of SFTCs. In addition, freeze-thaw damage aggravates the non-uniformity of longitudinal reinforcement corrosion, accelerates the corrosion ratio of reinforcement. With the increase of load level, the average corrosion ratios of longitudinal rebar and stirrups increase, and the local corrosion of longitudinal reinforcement is more serious. The coupling effect is obvious when the load, SFTCs and corrosion work together, and the evaluation of the damage characteristics of concrete members should pay attention to the interaction between various factors.

Influence of the Coupling Effect of Ocean Currents and Waves on the Durability of Pier Structure of Cross-sea Bridges

Xie, Y.P. and Li, X.H., 2020. Influence of the coupling effect of ocean currents and waves on the durability of pier structure of cross-sea bridges. In: Al-Tarawneh, O. and Megahed, A. (eds.), Recent Developments of Port, Marine, and Ocean Engineering. Journal of Coastal Research, Special Issue No. 110, pp. 87–90. Coconut Creek (Florida), ISSN 0749-0208.In the marine environment, under the action of ocean currents and waves, the piers of cross-sea bridges face a series of durability problems such as salt erosion and salt freeze-thaw cycles. The durability of the pier structure directly affects the service life of cross-sea bridges, so the research and test on the durability are of important significance for the design of cross-sea bridges. Based on the coupling effect of ocean currents and waves in the marine environment, this paper explores its influence on the durability of the pier structure of cross-sea bridges. The research results show that the durability analysis includes environmental index calculation, durability index calculation and durability evaluation. The damage of the bridge pier concrete structure is related to the material composition and the deterioration of the macro performance of the microstructure under the action of special environment. The pier concrete of the target cross-sea bridge measured in the laboratory has a salt-freeze resistance greater than F300. This paper provides an important theoretical basis for the research on the safety of marine concrete structures.

Investigation on interface fracture properties and nonlinear fracture model between ECC and concrete subjected to salt freeze-thaw cycles

The work aims at investigating on interface fracture properties and nonlinear fracture model between ECC and concrete under salt freeze-thaw cycles. Based on the interface nonlinear fracture mechanism, a three-parameter nonlinear fracture model was proposed to comprehensive and accurately reflect the degradation law of interface fracture properties under salt freeze-thaw cycles. The experimental results showed that the salt freeze-thaw erosion had a very negative effect on interface fracture properties. Moreover, the occurrence of interface fracture under salt freeze-thaw cycles was affected remarkably by ECC strength grade, and the higher ECC strength always leads to later occurrences of interface fracture. Regardless of cycles, the fracture propagation process of all specimens included three phases: initial crack, stable crack propagation, and instability failure. Moreover, the three phases all occurred at the interface, and the crack did not extend to ECC or concrete substrate. Meanwhile, the fibers bridging effect was very significant at the phases of crack stable propagation and instability failure. Only one kind of wedge-splitting load-crack mouth opening displacement (CMOD) curve was observed. As number of cycles increased, slope of rising section curve and ultimate wedge-splitting loads all gradually decreased, while the CMOD corresponding to ultimate splitting load had little change. The salt freeze-thaw erosion had a very negative effect on three fracture parameters. Moreover, the three fracture parameters all decreased continuously with the increasing number of cycles.