Bond Properties of FRP-concrete Interface with Nano-modified Epoxy Resin under Wet-dry Cycles

Yue Li,Xiongfei Liu,Jiaqi Li 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.4

The interface bonding properties of FRP-reinforced concrete under wet/dry conditions are studied by performing the interface bond test. The effects of the number of wet/dry cycles and FRP layers, and FRP reinforcing sequence on the efficiency of reinforcement are studied. The microstructure of FRP-concrete interface is observed by SEM. The variations in bond properties of FRP-concrete interface under extreme conditions under tension are investigated. Experimental results show at the early stage of wet/ dry cycles, the strengths of concrete and epoxy resin increase, and further interface bond strength enhances. As wet/dry cycles forward, defects and loose microstructure form in both FRP and concrete, and the interface bond strength decreases. Under identical conditions, the interface bond strength of sample strengthened by FRP after wet-dry cycles is higher than that of sample strengthened before wet-dry cycles. FRP-concrete bond strength is related to the number of wet-dry cycles.

Influence of Wet-Dry Cycles on Uniaxial Compression Behavior of Fissured Loess Disturbed by Vibratory Loads

Jian Xu,Liyang Zhou,Ke Hu,Yanfeng Li,Xiangang Zhou,Songhe Wang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.5

In this study, the influence of wet-dry cycles on the uniaxial compression behavior of fissured loess after vibration was investigated by small shaking table tests, wet-dry tests, and uniaxial compression tests. Results show that the initial elastic modulus and peak strength both decline after wet-dry cycles while the morphology of stress-strain curves shows insignificant changes. Except for samples with a fissure angle α = 45°, where the bimodal stress-strain curves were observed, all show softening trend. The failure mode can be classified into four main types: fracture failure (α = 0° and 15°), slip-fracture coupled failure (α = 45°), slip failure (α = 60°), and compression shear failure (α = 30° and 90°). The failure modes of samples at α = 0°, 15°, 45°, and 60° are independent of wet-dry cycles but strongly depend on fissure angle, while those at the other fissure angles are more susceptible to wet-dry cycles. The uniaxial compressive strength (UCS) of fissured loess samples before vibration are greater than those after vibration. The relationship between UCS and fissure angle before and after vibration show double-valley pattern. A binary medium model for fissured loess considering vibration and wet-dry cycles was constructed, which was verified by test data.

Effect of Dry–Wet Cycling on the Residual Strength Characteristics of Coal Measure Soil

Gang Huang,Mingxin Zheng 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.11

Coal measure soils are the main component in the slip zones of landslides along the Changli highway in China. Therefore, exploring the residual strength of coal measure soil affected by dry–wet cycling is helpful for evaluating landslides. However, very few researchers have reported on the residual strength behavior of coal measure soil subjected to dry–wet cycling. In this study, we performed three tests (ring shear test, scanning electron microscopy test, and mercury intrusion porosimetry test) to evaluate the residual strength behavior of coal measure soil under different dry–wet cycles. Our results indicated that the peak strength decreased with increasing dry–wet numbers and that dry–wet cycling had no evident effect on the residual strength. Moreover, the residual strength in the slip soil was approximately proportional to the normal stress. Furthermore, the degeneration of peak cohesion exponentially increased, and the porosity and fractal diameter also increased with the dry–wet numbers. The connection between mineral particles changed from a stable layered structure to an unstable chain structure. Consequently, we inferred the failure mechanism of K213-type shallow landslides and formulated appropriate preventive measures. This study is of great significance for understanding the mechanical behavior of the slip zone of coal measure soil and predicting the re-emergence of coal measure soil landslides.

Evolution of Tensile Properties of Compacted Red Clay under Wet and Dry Cycles

Ling Zeng,Hui-Cong Yu,Qian-Feng Gao,Jie Liu,Zi-Han Liu 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.2

Tensile strength is an important soil parameter that affects the stability of structures built on clayey soils. This paper presents an experimental study of the change of tensile properties of red clay during wet-dry cycles. Cyclic wet-dry tests were performed on compacted red clay specimens with different initial water contents and dry densities. Direct tensile tests and Brazilian split tests were then conducted on these specimens to determine the soil strengths. The effects of initial water content, initial dry density, number of wet-dry cycles, and crack rate on the tensile properties of red clay were investigated. The results demonstrate that the tensile strength of red clay is generally 1.566 times the splitting strength. Both the tensile strength and splitting strength are negatively correlated with the initial water content but are positively correlated with the initial dry density. Because of the presence of desiccation cracks, the tensile strength goes on reducing under wet-dry cycles. The tensile strength can be expressed by a power function of the initial water content, initial dry density, and crack rate. The proposed equation is useful to evaluate the tensile strength of cracked soils subjected to wet-dry cycles.

Durability of CFRP Strengthened Steel Plates Under Wet and Dry Cycles

Shan Li,Jiyue Hu,Yi-Yan Lu,Hong-Jun Liang 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.2

This paper presents tensile test results of CFRP strengthened steel plates (CS) after wet and dry corrosion. The number of cycle times and strengthened schemes were investigated. The results showed that the CS specimens, subjected to wet–dry corrosion, behaved in a more brittle manner and appeared massive CFRP and adhesive rupturing coincided with the failure. As the wet–dry cycle increasing, the yield strength and ultimate strength of CS strengthened specimens decreased signifi - cantly, while the stiff ness before and beyond yield strength degraded slightly. Furthermore, the yield strength and ultimate strength of double-sided specimens subjected to wet–dry cycles were higher than those of one-sided specimens. Finally, analytical formulas considering wet–dry corrosion were proposed to predict elastic modulus, yield strength, tangent modulus, ultimate strength of CS specimens subjected to wet–dry cycles, respectively. The calculated results were in good agreement with experimental values.

Hysteretic behavior of rapid self-sealing of cracks in cementitious materials incorporating superabsorbent polymers

Hong, Geuntae,Song, Chiwon,Park, Jangsoon,Choi, Seongcheol Elsevier 2019 Construction and Building Materials Vol.195 No.-

<P><B>Abstract</B></P> <P>In this study, the hysteresis in the swelling behavior of spherical superabsorbent polymers (SAPs) on rapid self-sealing of cracks in cementitious materials under wet/dry cycles was evaluated experimentally. The results from an experiment using the tea-bag method showed that the absorption capacity of SAPs was lower in a cement pore solution compared to that in distilled water. As the SAP particles repeatedly swelled/deswelled, their absorption capacity increased until 3–cycle and then gradually decreased. The water-flow test results showed that the mean reduction ratios in water runoff through cracks for the cracked specimens containing spherical SAP particles were 0.278 and 0.367 for SAP dosages of 0.5% and 1.0% in 1–cycle, respectively. As the wet/dry cycles were repeated, however, the ratios gradually increased and converged to about 1.75 times and 1.99 times those of 1–cycle, respectively. A non-linear regression analysis was performed on the measured reduction ratios in flow rates per cycle. The modification factors for the volume fraction of a crack sealed by the swollen spherical SAP particles gradually increased and then converged with the repeated wet/dry cycles, and they were approximately 1.0259–1.0599 and 1.0657–1.0943 for the S–0.5 and S–1.0 specimens after 4–cycle, respectively. In conclusion, the experimental results indicated that SAPs can repeatedly exhibit rapid crack self-sealing performance in cementitious materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We studied hysteresis in superabsorbent polymer swelling behavior. </LI> <LI> This was studied to realize rapid crack self-sealing. </LI> <LI> Swelling behavior varied with swelling/deswelling under wet/dry cyclic conditions. </LI> <LI> Reduction in flow rates measured every cycle was compared with predicted values. </LI> <LI> The polymer repeatedly revealed rapid crack self-sealing performance. </LI> </UL> </P>

Investigation on Mechanical and AE Characteristics of Yellow Sandstone Undergoing Wetting-Drying Cycles

Yaoyao Meng,Hongwen Jing,Qian Yin,Xiaowei Gu 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.11

The cyclic wetting-drying phenomenon is a complicated physical and chemical process. This kind of process will weaken the properties of rock to some extent. Some fundamental physical parameters of sandstone were first tested to study the weakening influence of wetting-drying cycles on the physical characteristics. Then, the water weakening effect on the mechanical and acoustic emission (AE) characteristics of rock on account of wetting-drying cycles was experimentally studied. Laboratory test results showed that when the number of cycles increased from 0 to 25, the density, P-wave velocity, uniaxial compressive strength (UCS), (elastic modulus (E)) and total AE counts of the rock specimens continuously decreased. However, the water absorption would increase as the number of cycles increased. The functional relationships between the total AE counts and the mechanical parameters (UCS and E) of sandstone after each cyclic number were established based on the test results. In addition, the chemical components and microstructure variations of rock undergoing wetting-drying cycles were examined. From the results, it can be concluded that microcrack growth and expansion inside the rocks undergoing wetting-drying cycles are the main reasons for the attenuation of the rock properties. Moreover, with increasing loading rate, the UCS, E and total AE counts of sandstone after each cyclic number would increase.

Influence of Initial Damage Degree on the Degradation of Concrete Under Sulfate Attack and Wetting–Drying Cycles

Yujing Lv,Wenhua Zhang,Fan Wu,Huang Li,Yunsheng Zhang,Guodong Xu 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.5

The previous researches on the degradation process of concrete under sulfate attack mainly focus on non-damaged concrete. It may lead to an excessive evaluation of the durability of the structure, which is detrimental to the safety of the structure. In this paper, three different damage degrees of concrete specimens with non-damaged (D0) and initial damage of 10% (D₁) and 20% (D₂) were prefabricated and subjected to sulfate attack and wetting–drying cycles. With the increase of sulfate attack cycles (0, 30, 60, 90, 120, 150 cycles), the changes in mass loss, relative dynamic modulus of elasticity, and the stress–strain curve were studied. The results show that the mass of the D0 specimen had been increasing continuously before 150 sulfate attack cycles. The mass of D₁ and D₂ had been increasing before 60 cycles, and decreasing after 60 cycles. At 150 cycles, the mass loss of D0, D₁, D₂ were − 1.054%, 0.29% and 3.20%, respectively. The relative dynamic modulus of elasticity (RDME) of D0 specimen increases continuously before 90 sulfate attack cycles. After 90 cycles, the RDME gradually decreases. However, for D₁ and D₂ specimens, the RDME began to decrease after 30 cycles. The damage degree has an obvious influence on the compressive strength and elastic modulus. For the D0 specimen, the compressive strength and elastic modulus increased continuously before 90 cycles and decreased after 90 cycles. The compressive strength and elastic modulus of D₁ and D₂ specimens began to decrease after 30 cycles. The stress–strain curves of concrete with different initial damage degrees were established, and the fitting results were good. Finally, based on the analysis of experimental data, the degradation mechanism of concrete with initial damage under the sulfate wetting–drying cycle was discussed.

Stability and Micro-mechanisms of Lignin-improved Soil in a Drying-wetting Environment

Gaoqiang Wang,Xianghui Kong,Yanhao Zhang,Quanman Zhao,Xiao Feng 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.8

To evaluate the long-term service performance of subgrade with high-liquid-limit soil improved by lignin, a drying-wetting cycle test was carried out for the improved soil with 3% lignin content, and comparison was made with quicklime-improved soil with the same properties in terms of pH, unconfined compressive strength (UCS), appearance, and volume stability. Using a scanning electron microscope (SEM), the microscopic characteristics of the lignin-improved soil were analyzed qualitatively and quantitatively. By analyzing the evolution law of the soil microstructure and pores under the action of drying-wetting cycles, the strength degradation mechanism of the improved soil was discussed at the microscopic level. The test results showed that the soil pH value of the lignin-improved soil was more beneficial to the ecological environment compared with that of the quicklime-improved soil. Furthermore, the stability of the lignin-improved soil was better than that of the quicklime-improved soil due to strength loss and increased volume expansion rate caused by the drying-wetting cycles. In terms of the microstructure, the cementing materials enhanced the agglomeration of the soil by wrapping grains and filling pores. Under the action of drying and wetting, the number of pores inside the soil increased, and the soil structure loosened. Under drying and wetting conditions, the strength degradation of the lignin-improved soil was the result of the interaction of pore development and cementing materials dissolution.

Effects of Soaking and Cyclic Wet-dry Actions on Shear Strength of an Artificially Mixed Sand

Jun-Jie Wang,Yong-Feng Zhou,Xiao Wu,Hui-Ping Zhang 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.4

This study focuses on the effects of soaking action and wetting-drying cycles on the shear strength of a sandstone-mudstone mixture. This mixture is constantly used as a filler in earth structures along bank of harbor or in a large reservoir. Two-type direct shear tests in laboratory, Soaking Direct Shear Test (SDST) and Wetting-Drying Direct Shear Test (WDDST), were carried out. The experimental data indicate that the shear strength is reduced by the soaking action and wetting-drying cycles. While the period of soaking time (t) increased from 24 to 392 hours, the values of initial angle of shearing resistance (φ0) and reducing angle of shearing resistance (φd) reduced from 45.17° to 40.26° and from 19.68° to 12.28°, respectively, along logarithmic curves. With increment of the number of wetting-drying cycles (N) from 1 to 30, the values of φ0 and φd reduced from 40.99° to 38.84° and from 8.76° to 7.58°, respectively, along logarithmic curves. During the soaking action or wetting-drying cycles, the inevitably lessening of the stiffness of soil particle would happen, and hence the shear strength of mixture is decreased. With increment of t or N value, the rates of effects isinstantly reducing.