Freeze-thaw Environment Research Articles

Study on dynamic mechanical properties and meso-damage mechanism of carbon fibers recycled aggregate concrete under freeze-thaw environment

The uniaxial compression mechanical properties tests of carbon fibers recycled aggregate concrete (CFRAC) were carried out in order to investigate the effect law of coupling freeze-thaw cycles (FTCs) and dynamic strain rates on the mechanical properties of CFRAC. Two cases of carbon fibers (CFs) doping of 0% and 0.3% were considered. The full CFRAC uniaxial compressive stress-strain curves at different strain rates (10−5/s, 10−4/s, 10−3/s, 10−2/s) after different FTCs (0, 50, 100) were obtained. The microscopic characteristics and microcrack propagation process of the specimens were analyzed by means of nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and acoustic emission (AE). The results showed that the specimens still had significant strain rate sensitivity after FTCs. With the same amount of CFs doping and strain rate, the strength and elastic mode (E) of the specimens kept decreasing as the number of freeze-thaw cycles (N) increased. With the same N, the strength and E of the specimens increased and the deformation capacity decreased as strain rate increased. With the addition of 0.3% CFs, the frost resistance and crack resistance of the specimens were significantly enhanced. Combined with the statistical damage constitutive model, the influence of FTCs and dynamic strain rates coupling on the meso-damage mechanism of CFRAC was analyzed. The meso damage evolution process was characterized by five characteristic parameters E0, εa, εh, εb and H. The results showed that there was an obvious regularity between the change of characteristic parameters and CFs content, dynamic strain rate and the N. An effective link between the fine-scale damage mechanism and the macroscopic nonlinear intrinsic behavior was established. The phenomenon of AE signal lag in uniaxial compression was explained from the perspective of effective stress.

Study on dynamic response characteristics of impact of freeze-thaw saturated marble in plateau area.

To study the effects that the perennial freeze-thaw environment exerts on the dynamic mechanical properties of marble, which characterizes the Qinghai-Tibet Plateau, impact tests were conducted, and saturated marble was utilized; thus, we analyzed the effect of different loading rates on its dynamic compressive strength, fragmentation pattern, and energy-absorbing density. The results indicate the following: (1) When 42.02s-1 ≤[Formula: see text]≤ 49.20s-1, the degree of fragmentation and the fractal dimension of saturated state marble is greater than that of the dry state marble; when [Formula: see text]<42.02s-1 or [Formula: see text]>49.20s-1, the dry state marble exhibits greater fragmentation than the saturated marble; (2) When the saturated state marble is subjected to a specific fractal dimension, the energy-absorbing density of the marble that characterizes the saturated state is great compared with the dry state, and when the fractal dimension increases, the energy-absorbing densities that characterize the two states gradually converge. (3) The effect of water on the mechanical properties of marble has an obvious rate dependence, showing a weakening effect at low strain rates and a strengthening effect at high strain rates. In regard to the analysis pertaining to the dynamic fracture mechanism of marble under the influence of the freeze-thaw environment that characterizes the plateau, the aforementioned experimental results exhibit considerable significance.

Interfacial strength characteristics between modified iron tailings and profiled fibers under dry–wet and freeze–thaw environments

The interfacial properties of fibers and matrix materials have an important effect on the mechanical properties of fiber-reinforced materials. To study the role of fiber morphology and the environmental effects on the interfacial properties of fibers and matrix materials, the interfacial strength characteristics of undulation polypropylene fiber (UPF) and serrated polypropylene fiber (SPF) with cement-modified iron tailings (CIT) were analyzed through single-fiber pullout tests. The effects of curing age, freeze–thaw cycles, and dry–wet cycles on interfacial strength were analyzed. The energy dissipation during fiber pullout under different environmental conditions was verified, and the microscopic mechanism of interfacial strength change was determined. The results show the following: (1) The interfacial strength of UPF and SPF is positively correlated with curing age, while freeze–thaw and dry–wet cycles can impair their interfacial properties; also, the interfacial strength decreases substantially and tends to flatten out after 3 cycles. (2) The dissipation energy of UPF and SPF increases with curing age, but decreases as the number of dry–wet cycles and freeze–thaw cycles increases. The critical reinforcement length of UPF is better than that of SPF by 363% and 50% under freeze–thaw and dry–wet cycles, respectively. Also, its performance and reinforcement effect in reducing crack development under freeze–thaw and dry–wet environments are better compared to SPF. (3) The interfacial strength of the profiled fibers consists of adhesion and friction. Freeze–thaw cycles cause a significant damage to adhesion and friction, while dry–wet cycles mainly affect adhesion. Interfacial strength is related to the curvature of the fiber and the unconfined compressive strength of CIT, which follows a linear function.

Study on the Permeability of GCL Materials in Coupled Environment

As a new-type anti-seepage material, Geosynthetic Clay Liner (hereinafter referred to as GCL) has been applied in various anti-seepage projects and achieved good benefits. Based on different salt solution types, concentrations, dry-wet, and freeze-thaw cycles, this paper designs a permeability test of GCL after aging, and the result shows that: (1) under the influencing factors of single salt solution, there is a threshold concentration of 0.15 mol/L, which means that the increase rate of GCL permeability coefficient suffers a significant decrease above this concentration. (2) With fewer numbers (<4 ) of dry-wet cycles the GCL permeability coefficient shows faster growth and then returns gradually to stability. (3) Compared with dry-wet and freeze-thaw environments, cation concentration and valence have a more prominent inhibition effect on the anti-seepage property of GCL. The research results can provide data reference and reasonable advice for the deterioration of various indicators of GCL material and its service life in corresponding projects in saline soil areas.

Static pressure and dynamic impact characteristics of filled jointed rock after frozen-thaw cycle damage

In the construction project, rock mass is often destroyed from the joint plane, and the jointed rock mass is easy to be eroded by freeze-thaw environment. Therefore, the damage mechanical properties of filled jointed rock mass under freeze-thaw action are very important for construction disaster prevention, engineering safety evaluation and reinforcement. In order to research the effect of the freeze-thaw cycle on the mechanical deterioration properties and damage characteristics of filled jointed rocks, prefabricated filled jointed rock samples are tested with different numbers of freeze-thaw cycles under the temperature range of -20°C~20°C. Then the wave velocity test, static compression test and SHPB impact test are conducted on the rock samples after freeze-thaw. Based on the test results, the change regularity of wave velocity degradation, static compression mechanical properties and dynamic compression mechanical properties of filled jointed rocks under the effect of freeze-thaw cycles were analyzed. The results show that the wave velocity, static compressive strength and dynamic compressive strength of the filled jointed rocks all show a downtrend with the increase of the number of freeze-thaw cycles, and each parameter is positively correlated with the strength of the filling materials. Among them, the decrease in the wave velocity of the rock sample after 30 freeze-thaw cycles is greater than 30%, and the strength loss of the static peak compressive strength exceeds half of its initial strength. The static peak strain rises exponentially with the increase of the number of freeze-thaw cycles while the dynamic peak strain does not show a clear trend. The dynamic peak strain is about 1/10 to 1/5 of the static peak strain. Under the same freeze-thaw action, the lower the strength of filling material, the more serious the damage.

Effect of Freeze–Thaw Cycles and Initial Water Content on the Pore Structure and Mechanical Properties of Loess in Northern Shaanxi

Spalling disease caused by freeze–thaw cycles often occurs on the loess cut-slopes in northern Shaanxi. The deterioration of the pore structure and mechanical strength of loess under a freeze–thaw environment is one of the critical reasons underlying the occurrence of spalling disease in the slopes. In order to explore the effects of freeze–thaw cycles on the pore structure and the mechanical strength of loess, four initial water contents (7%, 9%, 12%, and 14%) and six freeze–thaw cycles (zero, one, three, five, 10, and 20) were considered in this study. Nuclear magnetic resonance (NMR) and triaxial compression tests were carried out to analyze and reveal the mechanisms of effect causing the deterioration of the soil strength that affects the stability of loess cut-slopes. The results showed that the porosity growth increased with the initial water content and continued to increase during the freeze–thaw process until a later stage of the freeze–thaw cycle, when it gradually stabilized. The stress–strain curves were primarily influenced by the number of freeze–thaw cycles, the initial water content of the samples, and the confining pressure. Both the cohesion and the internal friction angle exhibited a decay law that showed a significant decrease, then a slow decrease, and finally stabilization during the freeze–thaw process. Small and micropores were predominant among the pore structures of the loess, while medium pores were the second most common, and large pores were the least common. With the increase in the initial water content, the pores transformed from micropore structures to medium and large pore structures. The soil strength deterioration was primarily driven by the phase changes of the pore water, as well as the water migration during the freeze–thaw process. This study will be beneficial for identifying the characteristics and types of freeze–thaw disease in cut-slope engineering in seasonally frozen loess areas and providing a theoretical reference and design basis for achieving green and sustainable development in slope engineering, management, and maintenance.

Experimental investigation and prediction model of permeability in solidified coarse-grained soil under freeze-thaw cycles in water-rich environments

In freeze–thaw and water-rich environments, high-speed railway subgrade systems experience significant changes in their moisture field due to the combined effects of temperature and pore pressure gradients. This poses a serious challenge to the long-term safety of high-speed railways. To address this issue, the permeability of high-speed railway subgrade fill materials before and after modification was tested using a self-developed infiltration instrument. Modifications included increasing the fine particle content and adding self-developed solidifying additives. Based on experimental results and discussions on the solidification mechanism of the fill, a model for predicting the permeability coefficient of the fill was proposed and analyzed. Results show that the self-developed additive is an efficient material for reducing permeability, with effects reaching up to the order of 107. The additive also demonstrates excellent resistance to freeze–thaw environments. Mineral-based cementitious materials have a greater impact on permeability coefficient than cement-based materials. The permeability coefficient prediction model was validated, showing a 92.3% consistency level with laboratory test results. Parameter analysis revealed that the model's parameters effectively characterize the pore structure, fluid environmental temperature, pore pressure, and other characteristics of porous media. The findings have important implications for stable control and moisture field guarantee in high-speed railway subgrades under freeze–thaw and water-rich conditions.

Study on Anchoring Characteristics and Freeze–Thaw Degradation Law of the Cement-Based Early-Strength Anchor in Freeze–Thaw Regions

This article focuses on the effect of freeze–thaw cycling on a cement-based early-strength anchor material, the compressive strength of which at 24 h is 14 times that of ordinary cement, and the compressive strength at 7 h is twice that of ordinary cement. The setting time required to achieve the expected strength is 1/7 of that of ordinary cement. Through indoor freeze–thaw cycling tests, the appearance changes, quality loss, strength loss, and microstructure changes in the early-strength anchor after 0, 5, 15, 25, 50, 75, and 100 cycles were studied, revealing the evolution of the mechanical properties and micromechanisms of the cement-based early-strength anchor material under freeze–thaw cycling conditions. The sample freeze–thaw failure criteria were determined, evaluation indicators reflecting the degree of damage were defined, and their relationships with the number of freeze–thaw cycles were fitted to assess the durability of the cement-based early-strength anchor material under freeze–thaw environments. This provides a theoretical reference for further improvements in material properties and adaption to different environments.

Numerical Simulation of Frost Heave Deformation of Concrete-Lined Canal Considering Thermal-Hydro-Mechanical Coupling Effect

This work presents a comprehensive coupled thermal-hydro-mechanical model to explore the frost heave mechanism of the concrete-lined canal under a freeze–thaw environment. Unlike previous models that regard concrete as a homogeneous material, this model considers concrete a porous medium and considers the effect of the concrete pore structure, as well as the water content, ice content, and ice-water phase transition, on the mechanical deformation of the canal. Firstly, based on the theories of unsaturated soil mechanics, thermodynamics, and poroelasticity, the thermal-hydro-mechanical coupling equations of the soil under the freeze–thaw condition are established. Then, based on the theories of thermodynamics, poroelasticity, and permeability mechanics of porous media, the thermal-hydro-mechanical coupling equations of the concrete under the freeze–thaw condition are established. Finally, the freeze–thaw simulation of a canal is carried out and compared with the referred indoor model test, in which the evolution behavior of temperature, frost depth, and frost heave deformation of the canal are studied. The results show that the freezing process of the soil foundation is a unidirectional process that develops from the surface to the bottom, and the thawing process of the soil foundation is a bidirectional process that thaws from the surface and bottom to the center. The frost heave deformation of the soil foundation at the 1/2~1/3 slope height area is the largest, which may easily lead to frost heave damage to the concrete lining in this area. The frost heave deformation of the canal obtained by the numerical simulation is consistent with the experimental results, which illustrates the validity of the established model for predicting the frost heave deformation of concrete-lined canals.

Bearing capacity and seismic performance of Y-shaped reinforced concrete bridge piers in a freeze-thaw environment

Bearing capacity and seismic performance of Y-shaped reinforced concrete bridge piers in a freeze-thaw environment

Study on mechanical properties and damage mechanism of recycled concrete containing silica fume in freeze–thaw environment

In order to study the uniaxial compressive mechanical properties and damage evolution of recycled aggregate concrete (RAC) containing silica fume (SF) under freeze–thaw cycles, the RAC with SF replaced partial cement was prepared. The replacement rates were 0% and 9%. The RAC were subjected to 0, 50, 75, 100, 125 freeze–thaw cycles and uniaxial compression tests. The microstructure, micro-crack propagation process and reaction products were observed by acoustic emission (AE) and scanning electron microscope (SEM). The statistical damage theory was used to explore the mesoscopic damage evolution mechanism of RAC. The results showed that the peak stress and modulus of elasticity of the specimen tended to decrease, the peak strain and mass loss rate gradually increased with the increase of the number of freeze–thaw cycles(N). The compressive strength of RAC with S = 0% decreases from −41.52MPa to −11.23MPa when N increases from 0 to 125. The addition of SF produced additional volcanic ash reactions, resulting in an increase in ettringite (AFt), which reduces the porosity of RAC and is able to increase the compressive strength at different N significantly. Compressive strength increases by 21.84% and 12.06% at N = 0 and 125, respectively. Considering the existence of two mesoscopic damage modes of fracture and yield, the deformation failure mechanism of RAC was analyzed from the perspective of effective stress. The all five characteristic parameters characterizing the mesoscopic damage show significant regular change with increase of the number of cycles. The relationship between the macroscopic mechanical properties of RAC and the mesoscopic damage mechanism was established by analyzing the evolution law for the characteristic parameters.

Effect of coupled chloride salt erosion and Freeze-thaw on the dynamic mechanical properties of EPS cement soils

EPS cement soil is a type of material widely used in engineering, but it is often in a complex engineering environment. Freeze-thaw cycles and chloride salt erosion have a large impact on the strength of cement soils in engineering, and it is a very important subject to investigate the strength trends of cement soils under severe conditions of salt erosion and freeze–thaw environments. In this study, the apparent characteristics and dynamic mechanical property characteristics of the EPS cement soil after different numbers (0, 3, 6, 9, 12, 15) of freeze–thaw cycles in different concentrations of NaCl (0 g/L, 4.5 g/L, 18 g/L, 30 g/L) solutions were investigated by chlorine salt erosion and freeze–thaw cycle coupling test and SHPB test. The changes of appearance morphology, dynamic stress–strain curve, dynamic compressive strength and energy dissipation after impact were analyzed, and the mechanism of strength change of the cement soil was explained from the microscopic perspective. The results of the tests show that the cement soil mainly undergoes elastic deformation, plastic yielding and damage stages during the impact damage process; with the increase of chlorine salt concentration and the increase of the number of freeze–thaw cycles, the dynamic compressive strength of the cement soil specimens decreases continuously, and the rate of strength loss gradually slows down first, and when the number of freeze–thaw cycles is more than 9, the rate of strength loss begins to increase. In the 30 g / L chloride erosion environment, after 3,6,9,12, and 15 freeze–thaw cycles, the dynamic compressive strength decreased by 16.48 %, 22.35 %, 28.77 %, 34.36 %, and 55.87 %, respectively. Under the immersion environment of clear water and low concentration (4.5 g / L) chlorine salt, when the number of freeze–thaw cycles exceeds 12 times, the absorption energy and energy absorption efficiency of the sample decrease sharply. Under the immersion of high concentration (18 g / L and 30 g / L) chlorine salt, the absorption energy and energy absorption efficiency decrease rapidly after more than 9 freeze–thaw cycles.

Experimental Study on Creep Characteristics of Unloaded Rock Masses for Excavation of Rock Slopes in Cold Areas

Seasonal freeze–thaw environments are one of the key factors that aggravate the mechanical strength decay of excavated and unloaded rock masses on reservoir banks in cold areas. To study the time-dependent mechanical properties of an excavated and unloaded rock mass on a bank slope under freeze–thaw action, triaxial unloading tests were carried out on sandstone, freeze–thaw tests simulating freezing strength were conducted, and triaxial creep tests were implemented with graded incremental loading on unloaded specimens subjected to freeze–thaw action. The test results showed that the total deformation of the unloaded specimens is significantly increased compared with the conventional specimens, and the lateral direction is more likely to produce creep behaviour than the axial direction. The level of confining pressure determines the level of creep deformation of unloaded specimens and affects the variation law of creep rate. The creep behaviour of the unloaded specimens is aggravated by freeze–thaw action and, the longer the freezing period, the larger the creep strain share, and the creep rate increases significantly. The creep damage pattern of the unloaded specimens subjected to freeze–thaw action is mainly manifested as shear damage, and the creep process intensifies the derivation of tension-type cracks in the specimens. The higher the confining pressure of the unloaded specimen, the more obvious the plastic characteristics and the weaker the brittle characteristics during creep failure. The freeze–thaw action significantly reduces the long-term strength of the unloaded specimen, which is approximately 50~55% of the instantaneous strength. The long-term strength decays significantly with an increasing freezing period, and the research results can provide a theoretical reference for the evaluation of the long-term stability of excavated and unloaded rock masses in cold areas.

Degradation of the bond performance between composite limestone powder concrete and steel bars under a sulfate freeze–thaw environment

An experimental investigation was conducted to explore the degradation of the bond performance between five types of composite limestone powder concretes and steel bars under a sulfate freeze–thaw environment. The failure model, ultimate bond strength, peak slip and bond–slip curve were researched. Three types of anchorage lengths were adopted in the investigation. The results indicated that limestone powder and fly ash reduced the ultimate bond strength and increased the peak slip of split failure. Slag increased the ultimate bond strength and reduced the peak slip. The bond performance between the composite limestone powder concrete and steel bars decreased with increasing anchorage length. Limestone powder exacerbated the degradation of the bonding performance of concrete under freeze–thaw cycles, while slag slowed the reduction in ultimate bond strength and corresponded with lower peak slip and more brittle failure. The constitutive relationship between the conventional environment τ (s, d/L) and the sulfate freeze–thaw environment τ (s, fts) was established, and the correction factor for the critical anchorage length of the sulfate freeze–thaw environment was derived. Thus, the influences of limestone powder, fly ash and slag on the critical anchorage lengths were analysed.

Mix-Proportion Design Methods and Sustainable Use Evaluation of Recycled Aggregate Concrete Used in Freeze–Thaw Environment

Recycled aggregate concrete (RAC) has been gradually used in practical engineering owing to the maturity of waste-concrete recycling technology. However, the disposal of waste RAC in different environments remains challenging. Second-generation recycled concrete aggregates (second RCAs) prepared by crushing waste RAC can further promote the sustainable development of the construction industry, in which the mix-proportion design method of RAC used in different environments is key in determining the feasibility of recycling second RCA. In this study, to investigate the usability of second RCA, five typical concrete mix-design methods were selected to prepare RAC with a service life of 50 years for freeze-thaw (F–T) environments in cold regions: the ordinary concrete design method, high-performance method, saturated surface-dry aggregate design method, equal mortar volume method (RAC-E), and overall calculation method (RAC-A). The frost resistance of RACs and the physical properties of second RCAs were investigated, and the economy of recycling waste RAC with different mix-proportion design methods was evaluated via value engineering analysis. The results showed that after 350 F–T cycles, the mass loss and relative dynamic modulus of elasticity of RAC-E and RAC-A were better than those of specimens prepared via other methods. Compared with the original RCA, the second RCAs obtained using waste RAC in the F–T environment performed better, and their water absorption was reduced by 23%. A value analysis of the RAC–waste RAC–second RCA circulation system showed that RAC-A exhibited the highest value coefficient. Both the equal mortar volume and overall calculation methods can be used for the mix design of RAC in the F–T environment; however, the latter is a better method owing to its higher value coefficient and lower calculation error.

Moisture Damage Characterization of Rubber-Modified Asphalt Mixture Containing Waste Steel Slag under Multiple Freeze–Thaw Cycles

Recycling waste materials has become popular in the pavement industry because of its potential for significant environmental benefits, conservation of natural resources, and sustainability. This study investigated the feasibility of simultaneously recycling waste steel slag and tire rubber in bituminous pavements and analyze the moisture susceptibility of asphalt mixtures made of these solid wastes. The physical and chemical characteristics of the aggregates and the adhesive behavior of the aggregate–bitumen system were explored to determine their impact on moisture sensitivity. Accordingly, two different methods, freeze–thaw splitting test and fracture energy tests, were employed to assess the moisture stability of mixes in a multiple freeze–thaw environment. The microstructure of the interface between the aggregate and bitumen was investigated, and the long-term moisture damage process of the mixes was clarified and verified. The results indicate that the natural hyperalkalinity and porous structure of the steel slag have a favorable effect on the adhesion performance. Cohesive failure was found to be the primary mode of failure of loose asphalt mixtures in a multiple freeze–thaw environment. We tentatively propose that the adhesion energy loss is a secondary failure mode of the loose asphalt mixtures. The addition of 100% steel slag and asphalt rubber had the greatest impact on improving the long-term moisture resistance of the asphalt mixtures. The present work is beneficial for the practical application of waste tire rubber and steel slag in highway engineering.

Deterioration mechanism on Micro-structure of unsaturated polyester resin modified concrete for bridge deck pavement under salty Freeze-thaw cycles

To investigate the dynamic evolution characteristics on the microstructural deterioration of unsaturated polyester resin modified concrete (UPMC) for bridge deck paving layer in the salt freeze–thaw environment, the four-stage experimental layout under two freeze–thaw (FT) cycles regimes (i.e., FT-fresh water and FT-salty water) were schemed. The dynamic deterioration rule and mechanism of the interior pore structure, microcrack and interfacial transition zone (ITZ) under different FT stages were analyzed through quantitatively characterizing the corresponding characteristics parameters utilizing mercury intrusion approach (MIP), SEM, digital image processing and energy dispersive spectrum (EDS) test. The test results demonstrated that FT cycles would exacerbate the damnification degree of the interior pores and microcracks and the ITZ expansion inside concrete, especially under FT-salt water, due to crystallization pressure and expansion stress and a pumping effect from FT cycles, as well as chloride-induced corrosion. Nevertheless, the introduction of unsaturated polyester resin (UPR) could restrain the germination, propagation and nucleation of interior microdefects, diminish the morphologic irregularities of crack structure, exert a replenishing and refinement effect on the internal micropores and retard the expansion in ITZ width range irrespective of FT types.

Experimental study of the durability of high-performance cementitious composites with amorphous metallic fibers

Amorphous metal fibers (AMF) can significantly enhance the mechanical properties of cementitious composites, however, research on the durability properties of cementitious composites containing AMF is still incomplete. In this study,(AMF)were strategically utilized to enhance the durability of cementitious composite. The long-term performance of amorphous metal fibers reinforced cementitious composites (AMFRCC) with four fiber contents (0.4%, 0.8%, 1.2%, 1.6%) was systematically evaluated under chloride corrosion, sulfate cycling, and free-thaw cycling conditions, using conventional Steel fibers reinforced cementitious composites (SFRCC) as a control group, and the reliability life of AMFRCC under freeze–thaw conditions was predicted. The results showed that SF and AMF volume fractions above 1.2% are detrimental to cementitious materials' chloride ion penetration resistance. After dry and wet sulfate cycles, AMF is not corroded, while the uniformly dispersed AMF can fully exploit the crack arresting effect and reduce internal defects in cementitious materials. However, in long-term sulfate environments and freeze–thaw environments, corrosion of SF causes severe degradation of SFRCC performance. Furthermore, the Wiener model can more accurately predict the lifetime of AMFRCC and SFRCC in freeze–thaw environments when the relative dynamic modulus of elasticity is used as an indicator of degradation.

Effects of the liquid rubber modified adhesive on the bond-slip response of the CFRP-steel interface

This paper presents an experimental and analytical study, purposely exploring the effects of the liquid rubber incorporation into epoxy resin on the bond performances between the carbon fiber reinforced polymer (CFRP) plate and steel. The experiment consisted of 36 double-shear bonded joints, and the investigated variables were the liquid rubber contents (i.e., 0, 5%, 10%, and 15% by weight) and adhesive thickness (i.e., 0.5 mm, 1.0 mm, and 2.0 mm). The failure mode, ultimate load, strain distribution, as well as the load-slip response were compared and discussed between specimens using the non-modified and liquid rubber modified epoxy adhesives, respectively. On the basis of the experimental results, a bi-linear bond-slip model considering the influence of liquid rubber content was proposed, and the critical parameters including the maximum interfacial shear stress, initial slip, fracture energy, and the maximum slip were identified, respectively. The present study lays a foundation for the subsequent research on the long-term bond enhancement for the CFRP-steel interface under freeze-thaw environment.

Experimental investigation and finite element analysis on lateral behavior of reinforced concrete columns subjected to freeze-thaw cycles

In cold regions, lateral load-deformation response of reinforced concrete column exposed to outdoor freeze-thaw environments may be significantly deteriorated. In this paper, a method is developed to model the lateral load-deformation response of reinforced concrete column that may experience strength deterioration due to freeze-thaw cycles. The proposed model accounts for uneven distribution of freeze-thaw damage within the cross-section of structural components. The model captures the uneven progression and extent of strength degradation at a given depth in the cross section as a function of number of freeze-thaw cycles. The model is developed using the experimental data from pseudo-static testing of six large scale reinforced concrete columns subjected to freeze-thaw cycles. The column specimens have different concrete strengths and are subjected to different axial loads. An existing model that only considers even distribution of freeze-thaw damage is used to validate the proposed model. Furthermore, the performances of the models are assessed, including monotonic and cyclic responses. Overall, the proposed model can capture the monotonic and cyclic responses of frost-damaged reinforced concrete column relatively well while accuracy is slightly lower for large axial loads. Also, the results reveal an important limitation of the existing even model in modeling freeze-thaw effects.