The Damage Mechanism and Strain Induced in Frost Cycles of Concrete (original) (raw)
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Effect of Freezing-Thawing Cycles on the Physical and Mechanical Characteristics of Concrete
2010
Concrete is the most used construction material in practically all of civil engineering fields due to its economical and technical advantages. However, its microstructure is porous and may be completely or partially water saturated. In severely cold climates, this water freezes and degradations develop gradually with the freezing-thawing cycle’s number, in forms of internal cracking, chipping and scaling. Frost behaviour is based on the coupling between the 9% volumetric increase during water transformation into ice, the cryo-suction phenomena, the non frozen water transport within the porous network and the thermo-mechanical behaviour of each component of the frozen media. It is thus obvious that the frost resistance depends on the microstructure (pore size distribution and permeability) and the mechanical characteristics of the material. In this paper, physical and mechanical characteristics evolution during freezing-thawing cycles was followed. The results show that the reduction...
Stress Analysis for Concrete Materials under Multiple Freeze-Thaw Cycles
Journal of Advanced Concrete Technology, 2015
Once ice forms in highly saturated concrete material, internal tensile stress will be generated and causes damage to the material, which is a serious problem for concrete structures in cold and wet regions. On one hand, each component (porous body, ice and liquid) should satisfy the compatibility of stress and strain, which has been discussed by the poromechanical theories. On the other hand, if some empty voids exist, the hydraulic pressure will release when liquid water escapes from the expanded area according to Darcy's law. Recent closed freeze-thaw tests on the saturated mortar showed a consistent tendency: as the number of freeze-thaw cycles (FTC) increases, the deformation changes from the expansion to the contraction. In order to make clear the physical and mechanical changes during this process, a more comprehensive hydraulic model is developed, which combines both the mechanisms mentioned above. The estimated strain behavior by this model is in a good agreement with experimental measurements, and also, it has good potential and is more flexible to be applied to different cases such as different saturation degrees and cooling rates. The permeability change can be also considered in this model as a reflection of frost damage level.
Internal and surface deterioration of concrete due to frost action
Concrete deterioration due to frost action in non-saline environment will be studied statistically and by using a deterministic approach based on thermodynamics. The statistical approach can also be used in evaluating the serviceability life expectancy of concrete structures. The approach based on thermodynamics will be applied to a case of façade concrete panel in which the moisture and temperature loads have been acquired from real climate data.
Prediction of fracture parameters and strain-softening behavior of concrete: effect of frost action
The aim of this study is to investigate the effect of frost damage on the strength and fracture properties of concrete formulated according to the standard NF EN 206-1 without air entraining agent. Prismatic 8 9 15 9 70 cm and cylindrical 16 9 32 cm specimens were subjected to various repeated freeze-thaw cycles according to the standard NF P 18-425 to induce different degrees of deterioration and the change in material properties was evaluated. Mechanical experiments were carried out on the specimens before and after their exposure to freezing-thawing cycles. The Young's modulus was determined through compressive tests conducted on 16 9 32 cm cylindrical specimens. Flexure strength and fracture parameters were obtained according to RILEM recommendations from three point bending tests conducted on prenotched samples. Tensile strengths were obtained by split tensile tests conducted on 16 9 32 cylindrical specimens. The correlations between the number of freezing-thawing cycles and the mechanical properties reveal that the change in the tensile strength gives a better indication of degradation due to frost action. From force-crack mouth opening curves, F-CMOD, the intrinsic fracture properties were obtained using the cracked hinge model based on a power law strain-softening curve and an inverse analysis algorithm. It was observed that the fracture energy, G RILEM F ; calculated according to the RILEM recommendations decreases by increasing the ratio a 0 H (notch length/beam's height). When a 0 H exceeds 0.45, G RILEM F reaches a value of 0.15 N/mm which is equal to the one obtained using the inverse analysis. Moreover, it has been established that the fracture energy, G F , and the critical crack opening displacement, w c , increase with freezing-thawing cycles.
Mechanical and durability properties of concrete subjected to early-age freeze-thaw cycles
Materials and structures, 2021
Early-age frost damage to concrete used in winter construction or in cold environments negatively affects the development of the hydration process and the performance of the concrete, thereby reducing the service life of the building structure. Experimental research was carried out to investigate the compressive strength, resistance to chloride penetration and resistance to freeze-thaw of concrete specimens subjected to earlyage freeze-thaw cycles (E-FTCs). The effects that different pre-curing times of concrete and mineral admixtures have on the properties of early-age frostaffected concrete were also analyzed. Results show that the earlier the freeze-thaw cycles (FTCs), the poorer the later-age performance. Later-age water-curing cannot
Stress-Strain Model of Concrete Damaged by Freezing and Thawing Cycles
Journal of Advanced Concrete Technology, 2004
This study investigates the dependence of the mechanical behavior of concrete, such as strength, stiffness, and deformation capacity on the damage caused by freezing and thawing cycles (FTC). A stress-strain model for concrete damaged by freezing and thawing prior to the application of mechanical loading was proposed based on plasticity and fracture of concrete elements. The FTC fracture parameter was introduced to explain the degradation in initial stiffness of concrete resulting from freezing and thawing damage. Based on experimental data, the FTC fracture parameter was empirically formulated as a function of plastic tensile strain caused by freezing and thawing with the assumption that the plastic strain was caused by the combined effects of FTC and mechanical loading damage. The stress-strain relationships obtained by the proposed model were compared with the experimental data.
Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens
Construction and Building Materials , 2016
The pore structure of the hardened concrete and the microscopic changes of a few selected pores throughout the freeze-thaw test were investigated by a method combining RapidAir and digital metalloscope. Traditional tests were also performed to evaluate the macroscopic change caused by freeze-thaw cycles (FTCs). The investigation shows that the concrete material, of which the spacing factor is 0.405 mm and the air content is 2.38%, can still withstand more than 300 FTCs. Severe microscopic damages occurred after approximately 200 FTCs and the freeze-thaw damage were gradually aggravated afterwards. Prestress forces have a remarkable impact on the failure pattern under FTCs. It was further found that the compressive strength as an indicator is more reliable than the relative dynamic modulus of elasticity in evaluating the freeze-thaw damage on concrete material. In addition, the test and analysis show that the measured prestress losses of bonded specimen are larger than that of unbounded specimen under the attack of FTCs due to the duct grouting effect. The ultimate freeze-thaw prestress loss is about 5% of rcon of for both the bonded and unbonded specimens because the grouting cement paste will eventually be completely destroyed.
Application of fracture energy for the assessment of frost degradation of high-strength concretes
Budownictwo i Architektura, 2021
Knowledge of fracture mechanics parameters can help for a more accurate assessment of frost degradation of high-strength concrete. High strength concretes, despite the tight structure, are characterized by increased brittleness. Cracks in the concrete structure are places of accumulation of significant stresses. Additional stresses resulting from cyclic freeze/thaw stimulate the material destruction processes. The basic strength parameters of concrete do not take into account structural defects of the material and do not give a complete description of susceptibility to damage caused by, e.g., frost degradation. This study aimed to determine the relationship between frost degradation of high-strength concretes and changes in the value of their fracture energy associated with the initiation of cracking after 150, 250, 350 and 450 freeze/thaw cycles. The research was carried out using 100 × 100 × 400 mm samples, with a pre-initiated 30 mm deep notch. The I load model under a three-poin...
2014
During the last decades durability issues gained more interest and the necessity of reliable and suitable models for the prediction of concrete behaviour on time has grown. One of the most severe deterioration processes that may affect concrete structures is caused by freezing-and-thawing cycles. The causes and mechanisms of frost damaging process have been deeply studied during the last decades and different theories have been developed to describe the physical process of damaging due to frost action. Nevertheless very little attention has been given to the effect of frost attack on the behaviour of reinforced concrete (R/C) structures and on the material characteristics and bond properties of concrete. Recent studies showed that frost action leads to a reduction of compressive and tensile strength, an increasing of peak strain and fracture energy and a reduction of bond strength. In the present work an innovative formulation recently proposed by the authors within the framework of...