703 research outputs found
Effect of freeze-thaw cycles on shear resistance of reinforced concrete beams strengthened with UHPFRC
No full textUltra-high performance fiber-reinforced concrete (UHPFRC) has emerged as one of the promising materials for strengthening of concrete structures. For the strengthening application of UHPFRC, one of the primary concerns is to evaluate the degradation of bond behavior and structural re-sponse of strengthened elements under harsh environmental conditions. Therefore, an experi-mental program has been carried out to investigate the interfacial behavior between UHPFRC and normal concrete, as well as the shear performance of UHPFRC-concrete hybrid beams subjected to combined freeze-thaw cycles and mechanical load. In this study, two groups of shear-deficient reinforced concrete beams were first strengthened by UHPFRC precast panels using epoxy resin. Then, the specimens subjected to 0 and 30 freeze-thaw cycles were loaded to failure under three-point bending. The results indicate that the utilization of epoxy resin is an effective bonding tech-nique to ensure the integral performance of the composite beams and the shear capacity is greatly enhanced with the application of UHPFRC. In addition, it is observed that the effect of applied freeze-thaw regime on the UHPFRC-concrete interfacial bond strength and shear resistance of unstrengthened and strengthened beams is negligible.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Concrete Structure
Experimental and numerical studies on failure behaviours of sandstones subject to freeze-thaw cycles
Get PDFThe freeze-thaw induced damage of rock affects the durability and serviceability of geo-structures, especially those constructed in the regions frequently impacted by climatic changes. A series of laboratory tests including P-wave velocity tests, freeze-thaw tests, uniaxial compression strength (UCS) tests and Brazilian tensile strength (BTS) tests are conducted to investigate the physical-mechanical properties and failure behaviours of Tasmanian sandstones subjected to various freeze-thaw cycles. It is observed that the P-wave velocity, BTS and UCS of the sandstone decrease as the number of freeze-thaw cycles increases, in which the decreasing rate from 0 to 20 freeze-thaw cycles was more pronounced than that from 20 to 40 and 40 to 60 freeze-thaw cycles. Moreover, it is found that the main failure mode of the sandstone changes from axial splitting to shearing along a single plane in the UCS tests and from central smooth fractures to a central zigzag fracture in the BTS tests with the number of freeze-thaw cycles increasing. Three-dimensional (3D) numerical modellings are then conducted using a self-developed 3D hybrid finite-discrete element method (HFDEM) parallelized on the basis of general-purpose graphic processing units (GPGPU) to further investigate the failure mechanisms of Tasmanian sandstones subjected to various freeze-thaw cycles in the UCS and BTS tests. The 3D numerical modellings agree very well with the experimental observations that the physical-mechanical parameters of the sandstone degrade with the increasing number of the freeze-thaw cycles. Moreover, the 3D numerical modellings reveal the deterioration and failure mechanisms of sandstones subjected to various freeze-thaw cycles. For the sandstone specimens without subjecting to freeze-thaw cycles, axial splitting is the main failure pattern while tensile and mixed-mode damages are the dominant failure mechanism in the UCS tests. For the sandstone subjecting to various freeze-thaw cycles, the increasing number of freeze-thaw cycles causes the macroscopic cracks to propagate, interact and coalesce in the shear behaviour resulting in the final shear fracture pattern in the UCS test. The 3D numerical modellings of the BTS test show that, although, for both the models with and without subjecting to freezing and thawing cycles, a central fracture is the eventual failure pattern, the failure surface becomes more zigzag as the number of freeze-thaw cycles increases
Vulnerability of the north Alaska Highway to permafrost thaw: Design options and climate change adaptation
Get PDFThe Alaska Highway between Burwash Landing and the Yukon/Alaska border is underlain by extensive discontinuous, warm and frequently ice-rich permafrost. The disturbance caused by construction of the road and climate warming has already led to the thawing of permafrost, which has had an impact on the road. Some sections of the highway have experienced longitudinal cracking, embankment failure, differential settlement and even complete collapse. In order to better understand these issues, the Yukon Government Department of Highways and Public Works (HPW) has partnered with the Northern Climate ExChange in a four-year project (2012-2016) to assess permafrost sensitivity to thaw under the northern 200 km of the Alaska Highway. Since its construction, this section of highway has been affected by permafrost thaw. In the context of current and anticipated climate change, permafrost temperature is warming and is expected to continue to rise (SNAP 2014). Faster and more extensive permafrost thaw will result in an increase of frequency and magnitude of the damage sustained by the highway.articleFinal article published
Effects of Freeze-thaw History on Bearing Capacity of Granular Base Course Materials
No full textAbstractWe used a newly developed freeze–thaw California bearing ratio (CBR) test apparatus to investigate the effects of freeze–thaw history on the bearing capacity characteristics of granular base course material. It was found that CBR was reduced by freeze-thaw under all water content conditions. Taking the example of C-40, which is frequently used as a base course material, freeze–thaw cycles reduced CBR to about 0.6 times its initial value. We found volume expansion in even non-frost susceptible C-40, and therefore investigated changes in particle pore water due to freeze–thaw cycles. We found that freezing causes particle pore water to be dislocated to particle surfaces, thereby causing interparticle friction and altering the void structure
Effect evaluation of freeze-thaw on resilient modulus of unsaturated granular base course material in pavement
Get PDFThis study examines the effects of freeze-thaw and water content on the resilient deformation characteristics of subbase course materials to evaluate the mechanical behavior of granular base in cold regions. A series of resilient modulus tests on subbase course materials under various water contents were conducted using a newly developed test apparatus. Besides, the test results were compared with the results of freeze-thaw CBR tests and the long-term field measurement at a model pavement structure including FWD tests. As the results, it was revealed that the resilient deformation characteristics of unbound granular base materials (UGBMs) deteriorate due to freeze-thaw and increment of the water content in thawing season. This indicates that the freeze-thaw of granular base has a strong influence on the fatigue life of pavement structures
Influence of freeze-thaw action on hydraulic behavior of unsaturated volcanic coarse-grained soils
Get PDFThis study aims to evaluate the effects of freeze-thaw action on the water retention-permeability characteristics of volcanic coarse-grained soils under unsaturated conditions, in order to examine the hydraulic behavior of volcanic soil during the snow-melting season. In this study, a series of water retention, permeability, and slaking tests on three types of crushable volcanic coarse- grained soils, differing in their degrees of particle crushability, were performed under various degrees of saturation and various freeze-thaw histories, while comparing the test results with those of non-crushable sand. Based on the experimental results, the effects of freeze-thaw action on the water retentivity, permeability, and particle breakage were examined. The test results indicated that freeze-thaw action has strong influence on the hydraulic behavior of crushable volcanic coarse-grained soils under unsaturated conditions, even if the soil is a non-frost- susceptible geomaterial
Improving freeze-thaw resistance of alkali-activated slag by admixtures
No full textAlkali-activated material (AAM) is one of the most attractive alternatives to ordinary Portland cement (OPC). Recently, more and more research interests are devoted to durability performance. In cold areas, freeze-thaw resistance is a crucial durability factor for concrete. However, the understanding of the freeze-thaw resistance of AAMs is minimal. Accordingly, the subject of this thesis is drawn forth. The main aim of this study was to investigate the effects and mechanisms of using admixtures (SAP and AEA) to improve the freeze-thaw resistance of alkali-activated slag (AAS). Regarding the general properties, such as workability and mechanical properties, it was found that the influence of adding SAP or AEA is acceptable. Then, the air-void systems created by SAP and AEA were reconstructed and characterized by the micro-CT scan. It was found that both SAP and AEA successfully entrained air voids into AASM, while the characteristics of the resultant air-void system were quite different. Further analysis on the surface condition of AASM undergoing 28-day sealed curing or preconditioning procedures in the CDF test, and the ASTM C672 test revealed that AASM shows a considerable surface microcracking potential. Samples sealed for 28 days showed a considerable extent of microcracking due to autogenous shrinkage. Samples that underwent 14-day drying after 7/14 days’ curing showed significant microcracking due to autogenous shrinkage and drying shrinkage. With the addition of SAP, the cracking caused by autogenous shrinkage was minimized, but the cracking caused by drying was only slightly reduced. With the addition of AEA, there was only a minor improvement in surface integrity. The freeze-thaw resistance of AASM with or without the addition of SAP or AEA was investigated in the form of surface scaling damage by a modified CDF test. Plain AASM showed poor surface scaling resistance mainly attributed to the pre-existing surface microcracking. The addition of SAP and AEA successfully improved the surface scaling resistance of AASM. The improvement was more significant by adding SAP due to the effect of improving surface integrity. Based on the SAP mixtures, a good correlation was found between the SAP air-void system and the resultant surface scaling resistance. The final cumulative surface scaling generally decreased with higher entrained air content, denser air voids distribution, and smaller air voids size. A preliminary logarithm model was developed for the relationship between the reduction in surface scaling and the equivalent water/binder ratio and the air-void system. Finally, upscaling tests on the concrete scale also found that the addition of SAP improved the surface scaling resistance of AASC.Overall, in this study, the freeze-thaw resistance of AAS was successfully improved by the SAP and AEA. The effects of adding SAP/AEA and the related factors on the selected properties of AASM were revealed. The mechanisms behind these observations were also understood and generated a series of further research possibilities. It is hoped that these findings and observations can give some guidance to the industrial applications of AAS and some inspiration to the scientific community.Civil Engineering | Structural Engineerin
One- and two-dimensional finite element modelling of thaw consolidation
Get PDFCoupled thermo-hydro-mechanical finite element (FE) modelling of thaw consolidation is presented. One-dimensional FE analyses are performed for thaw consolidation of a soil column due to self-weight and with a combination of self-weight and surcharge, with the linear and nonlinear void ratio–effective stress–hydraulic conductivity relationships of thawed soil. The nonlinear behaviour of thawed soil is modelled using a modified Drucker–Prager Cap model, while the hydraulic conductivity is varied with the void ratio. Finally, two-dimensional FE modelling of thaw consolidation around a warm pipeline buried in permafrost is performed. The rapid reduction of the void ratio with consolidation, especially at the low-stress level, results in a wide variation of hydraulic conductivity within the thawed zone. The significantly large hydraulic conductivity of soil elements along the curved thaw front, as compared to that of thaw consolidated soil, causes the flow of water along the thaw front, instead of a vertical flow, as assumed in previous 1-D thaw consolidation modelling of buried pipelines.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Estimating Thaw Settlement of Coarse-Grained Permafrost Sediments
Get PDFThaw settlement, a frequently reported issue for infrastructure built on permafrost, contributes to high maintenance costs, reduced life cycles, and compromised serviceability of infrastructure. This paper presents a new method to estimate the thaw settlement in coarse-grained permafrost sediments, crucial for northern infrastructure planning. Utilizing available test results from the Canadian Arctic, an overview of the existing data for coarse-grained permafrost sediments is presented. The proposed method uses input parameters derived from particle size distribution to estimate the minimum void ratio of thawed sediments. The minimum void ratio is then used to infer the thawed void ratio, enabling the calculation of thaw strain. The effectiveness of the approach is confirmed by validating predicted thaw strains against measured values for over 60 permafrost samples. A comparison with existing empirical methods shows improved accuracy and reduced bias, further supporting the applicability of the approach. Additionally, an average thawed void ratio assigned to seven groups of granular soils proved valuable for predicting thaw strain when only visual descriptions of sediments are available. Tailored for granular materials and utilizing easily obtainable index properties, this approach provides a reliable and cost-effective method for predicting thaw settlement, benefiting engineers and planners in infrastructure development.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Volume change behaviour and microstructure of stabilized loess under cyclic freeze-thaw conditions
Get PDFFreeze-thaw action is considered to be one of the most destructive actions that can induce significant damage in stabilized subgrades in seasonally frozen loess areas. Laboratory tests include frost heave-thaw shrinkage and microstructure change during freeze-thaw cycles were conducted to evaluate the volume change rate of loess stabilized with cement, lime, and fly ash under the impact of cyclic freeze-thaw conditions. The loess specimens collapsed after eight freeze-thaw cycles (192h), but most stabilized loess specimens had no visible damage after all freeze-thaw cycles were completed. All of the stabilized loess samples underwent a much smaller volume change than the loess alone after the freeze-thaw cycles. Although surface porosity and equivalent diameter of stabilized loess samples increased, the stabilized loess can retain its microstructure during freeze-thaw cycles when the cement content was less than 6%. To ensure freeze-thaw resistance of stabilized loess subgrades, the mix proportions of the three additives was recommended to be 4 to 5% cement, 6% lime, and 10% fly ash.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
- …
