Shear Properties Of Interface Research Articles

Bonded Interface Shear Performance of a Double-Layer Asphalt Mixture Based on DIC Technology

Abstract To study the effect of water and salt erosion on the bonded interface shear performance of a double-layer asphalt mixture (DLAM), an inclined shear test was conducted on a DLAM using a tack coat as the bonded interface between simulated old asphalt pavement (AC-16) and overlay (SMA-13). First, the inclined shear test of the DLAM before and after freeze–thaw (F–T) cycles was conducted. Second, the digital image correlation (DIC) technique was used to calculate the deformation field to divide the failure of the specimen into meso- and macrocracks and analyze them. According to the results of this study, the shear failure of DLAM under F–T cycles consisted of two stages. In the first stage (three cycles), the interface shear properties decreased due to ice expansion load. In the second stage (after three cycles), the interface shear performance deteriorated, and chlorine salts accelerated the interlayer failure due to the interface debonding of asphalt and aggregate under the combined action of water/salt and vehicle load. The damage factor defined on the basis of the statistical analysis of the strain field by DIC could reflect the deformation of the bonded interface in real time. The damage factor evolution curve was used to compare the interface damage degree caused by water and salt erosion. A method for judging the crack initiation area of mesocracks was proposed by DIC technology, and the correctness of the appearance position of the interface crack was verified by calculation.

Large-scale field test on the shear behavior of concrete pipe-silty soil interfaces in pipe jacking: A case study

With the rapid advancement of urbanization, research on the shear behavior of concrete pipe-silty soil interfaces in pipe jacking has a high engineering application value. In this study, a large-scale field direct shear test apparatus and the corresponding test method were designed and proposed to investigate the shear properties of the concrete-silty soil interfaces in pipe jacking. A series of in-situ direct shear tests were conducted at five normal stress levels under four interface contact conditions. The results show that the shear stress-displacement relationships of the interfaces conform to the typical elastic-plastic constitutive relations, the shear strength-normal stress relationships of the interfaces can be well fitted by the Mohr-Coulomb failure criterion, and the interface shear properties are influenced by soil properties, normal stress, lubrication conditions and stagnation time. Without lubrication, the concrete-silty soil interfaces have a shear stress-displacement curve shape similar to that of the test results obtained from indoor direct shear tests, but their ductility and shear strengths are lower. Under lubrication conditions, the paraffin wax and thixotropic slurry can both effectively diminish the interface friction angle, thereby reducing the concrete-silty clay interface friction coefficient by 62.8% and 72.2% and reducing the concrete-silty sand interface friction coefficient by 60.8% and 59.2%, respectively. Based on the macroscopic and microscopic images observed in the tests, the lubrication mechanisms of the lubricants were analysed. The research results can provide a reference for the prediction of jacking force and construction disturbance in adjacent pipe jacking projects.

Experimental and numerical study on flexural behaviors of damaged RC beams strengthened with UHPC layer using the bonding technology of post-installed reinforcing bar

Due to the outstanding mechanical and durability properties, Ultra-high performance concrete (UHPC) has been popularly used for strengthening of existing reinforced concrete (RC) beams. To improve the reliability of UHPC strengthening RC beams and enhance the effectiveness of its usage on site applications, bonding technology of post-installed reinforcing bar was proposed to connect the RC beams with UHPC layers. In this paper, a push-out test program was firstly carried out to study the shear properties of interface between UHPC and normal strength concrete (NSC) using the post-installed reinforcing bar connection technology, and to select suitable embedment length of the post-installed reinforcing bar in UHPC layer. Then, a bending test program consisted of three damaged RC beams strengthened with UHPC layers and one control RC beam was conducted to investigate the flexural behaviors of the damaged RC beams strengthened by UHPC layers using the bonding technology of post-installed reinforcing bar. Thereafter, three-dimensional FE models were developed to simulate the flexural performance of the strengthened RC beams, and the crucial parameters were investigated. The results of the present study revealed that the strengthening with reinforced UHPC layers could effectively improve the cracking and flexural performance of damaged RC beams. All the strengthened beams using the bonding technology of post-installed reinforcing bar failed in the typically flexural failure and no obvious interface cracks caused by the interface connection were observed throughout the bending test process.

Evaluation of Bentonite Application for the Abandonment of Deep Geo-energy Wells

Hydrated bentonite is considered an alternative subsurface sealing/plugging material for deep geo-energy wells. However, the knowledge related to this application and the corresponding properties of bentonite is still lacking. This includes the mechanical properties at the interface of bentonite plugs with the adjacent materials (surrounding rock or casing steel) and the mechanical stability of plugs under downhole in-situ conditions. In this work, we performed experiments investigating the interface shear properties and shear strength of a bentonite plug under various settings for deep geo-energy applications, such as hydrocarbon and geothermal wells. The interface’s shear properties against various adjacent materials and fluid conditions were characterized. The influence of chemical exposure, the salinity of the curing fluid, fluid pH, pressure, and temperature on bentonite’s mechanical stability was evaluated in a small- and large-scale setting. The latter was performed using realistic casing sizes and placement methods, relevant for the field application. The experimental results show that the averaged shear strength of the bentonite plug interface is 13.3 kPa and 9.1 kPa when cured in freshwater and seawater, respectively. The increase in strength with increasing curing pressure, temperature, and fluid pH was characterized for the first time. The interfacial properties of cohesion and friction angle vary with different surrounding materials. They are also influenced by the saturating condition and salinity of the saturating fluid. Based on the experimental results, a bentonite plug with a minimum length of 15–43 m placed in casings of 7–5/8″ to 13–3/8″ would be sufficient to meet the necessary criteria of the Dutch regulators as an isolating material for well abandonment.

Effect of the particle size ratio on macro- and mesoscopic shear characteristics of the geogrid-reinforced rubber and sand mixture interface

As a new type of material for civil engineering projects, the rubber and sand mixture is widely used in roadbed fillers, offering environmental benefits over traditional tyre disposal methods. This study uses a large-scale direct shear apparatus to examine the interface shear properties of the geogrid-reinforced rubber and sand mixture, considering different particle size ratios (r), rubber contents, and normal stresses. Based on indoor tests, direct shear models of the mixture with different values of r are established in PFC3D, revealing the meso-mechanical mechanism of the mixture in the direct shear process. The results show that when r is greater than 1, incorporating a certain amount of rubber particles can increase the shear strength of the mixture. The r values of 15.78, 7.63, and 3.98 correspond to an optimal rubber content of 30%, 10%, and 20%, respectively. When r is less than 1, mixing rubber particles can only reduce the shear strength of the mixture. When the rubber content is low, the smaller the value of r, the greater is the thickness of the shear band. Furthermore, the normal and tangential contact forces are greater. The fabric anisotropy evolution law of the mixture is consistent with the change in the contact force distribution.

Shear Characteristics of the Interface between Recycled Concrete Aggregates and Various Geosynthetics

To investigate the interface shear characteristics between various geosynthetics and recycled concrete aggregate (RCA), 30 large-scale monotonic direct shear tests were conducted. The main work was to analyse the effect of a biaxial polypropylene geogrid, a glass fiber geogrid, a warp-knitted polyester geogrid, a woven geotextile, and geonet on the interface shear properties of RCA. The test results show that adding a biaxial polypropylene geogrid or a geonet to RCA can improve its interface shear strength. The inclusion of glass fiber geogrids, warp-knitted polyester geogrids, and woven geotextiles decrease the interface shear strength of RCA. The reinforcing RCA with geosynthetics can effectively suppress its shear dilation, and the change in internal friction angle is consistent with the change law of the material interface enhancement coefficient. Finally, the aperture size of a geogrid has a significant effect on the mechanical properties of the geogrid-RCA interface. The interface shear strength increases first and then decreases with an increase in the ratio between aperture size and median particle diameter. It is concluded that there is an optimal range of aperture ratio between a geogrid and RCA.

Shear Behaviour of Rock–Tailings Backfill Interface: Effect of Cementation, Rock Type, and Rock Surface Roughness

Determination of interface shear behaviour is critical for the design of many geotechnical structures, including cemented paste backfill structures. However, the shear characteristics of the CPB–rock interface is not fully understood. No studies have been conducted to assess the impact of the characteristics of rock (e.g., type of rock, rock surface roughness), cementation and the coupled effects of surface roughness and degree of cementation on the shear characteristics of the interface between rock and tailings backfill. This paper presents new findings of research conducted to investigate the effect of different types of rock, rock surface roughness and degree of cementation as well as the coupled effects of these factors on the shear properties and behaviour of the interface between cemented paste backfill (CPB) and rock. The results show that roughness and the interaction between roughness and degree of cement hydration have a significant effect on the shear characteristics of a CPB–rock interface. For a certain degree of cementation, the roughness can increase the shear strength due to the increased size of the interlocking structure. The interface samples with roughness, especially those sheared at high normal stress, tend to experience two peak shear stresses during the shear test. Moreover, the shear strength, shear dilation, and adhesion of the interface also increase with degree of cementation. However, according to the revised Barton’s equation, the effective friction angle of interface with roughness experiences a decreasing tendency with degree of cementation, despite the increasing tendency of the friction angle of the smooth interface. In other words, the interface asperity contributes more to the evolution of adhesion, and the contribution of friction angle to the shear strength is partially offset. It is also found that the rock type (considered in this study) has limited effects on the interface shear properties. The failure of the interface between CPB and rock is because of the existence of the interfacial transition zone, which is characterized by high porosity. These new findings have practical importance to the design of the underground CPB structures.

A coupled chemo-elastic cohesive zone model for backfill-rock interface

Abstract To date, only a very few number of models are available to study the shear characteristics of the backfill-rock interface, and none of them have incorporated the effect of the interactions between sulphate ions and cement hydration on the interface shear behaviour. Therefore, a coupled chemo-elastic cohesive zone model (CZM) has been developed to simulate the shear characteristics of the cemented paste backfill (CPB)-rock interface that contains sulphate ions at the early ages. To quantitatively address the influence of sulphate on binder hydration at the early ages, the concept of equivalent chemical age is proposed and integrated into a binder hydration model. Besides, the interface shear properties, fracture toughness as well as shear stiffness are expressed as a function of the equivalent chemical age. By implementing the developed model in COMSOL Multiphysics, the results of the numerical simulation are found to agree with the experimental results. The validated results confirm the capability of the developed model to describe the shear characteristics of the interface that contains sulphate ions. The developed model will contribute to improving the assessment of the shear behaviour of the CPB-rock interface in the field, thus leading to a more economical design of safe CPB structures.

Investigation of interface shear properties and mechanical model between ECC and concrete

This paper reveals an investigation of the influences of ECC mixture construction method (i.e., common casting and spraying ECC), ECC strength grade, interface roughness of concrete substrate, and polyvinyl alcohol (PVA) fiber type on shear properties of ECC-to-concrete interface. The test results show that two failure modes of interface shear failure and ECC failure were observed. The roughness degree of concrete substrate had a strong effect on the failure mode, while ECC strength grade, ECC mixture construction method, and PVA fiber type had almost no influence on the failure mode. The shear load-slip curves of all specimens were basically similar. Compared to the casting ECC, the spraying ECC had an obvious decreasing effect on interface shear strength. The ECC strength grade and roughness degree of concrete substrate had a significant influence on interface shear strength, and higher ECC compressive strength and coarser interface could cause higher interface shear strength. On the contrary, PVA fiber type had a slight influence on interface shear strength. Based on the micro-bonding mechanism and test results of shear load-slip curves, a shear strength mechanical model and a shear stress-slip model of ECC-to-concrete interface were proposed to predict interface shear strength and shear stress-slip curve, respectively.

Innovative composite materials as reinforcing interlayer systems for asphalt pavements: an experimental study

Interlayers for asphalt reinforcement are considered an effective option to enhance pavement service life. In this regard, innovative factory-made composite materials can be designed as interlayer systems able to combine reinforcing and stress-relieving properties. This can be accomplished by embedding grids or fabrics in bituminous membranes. Given this background, this study considered dynamic flexural properties and interface shear strength of asphalt systems reinforced with different composite membranes obtained by changing the embedded reinforcement and/or the bituminous compound. Results clearly rank the studied materials showing enhanced fatigue response of reinforced asphalt layers. However, interface shear properties strongly suggest proper design and adequate selection of the installation depth.

Experimental Study on Shear Properties of Interface between Clay and Cement Paste

According to the typical clay in Changzhou, the shear properties of interface between cement paste and clay were studied through changing water content of clay and water cement ratio of cement paste. Rules of shear strength, internal friction angle and cohesion of contact surface between cement paste and clay changing with water content were researched. The results show that when the water cement ratio and clay moisture content remain unchanged, the shear stress increases with the increase of normal stress. After reaching a peak value, the shear stress begins to decrease. When water cement ratio and normal stress remain unchanged, the shear stress decreases with the increase of water content. When the water cement ratio is constant, the internal friction angle decreases with the increase of water content. When the water cement ratio is 0.4 and 0.45, the cohesion decreases with the increase of water content. When the water cement ratio is above 0.5, the cohesion increases first and then decreases with the water content. 17% is the optimum moisture content, at this time, the cohesion is the greatest.

Effect of tack coat dosage and temperature on the interface shear properties of asphalt layers bonded with emulsified asphalt binders

The shear strength of the interface of asphalt concrete structure has a great influence on the mechanical properties and durability of asphalt pavement. This paper describes the experimental design and analysis of the shear properties of the interface between asphalt layers. A self-designed device was employed to measure the direct shear strength of the interface with the aid of the Universal Test Machine (UTM-100). The effect of temperature, dosage of tack coat and type of tack coat on the shear properties of the interface were studied through laboratory testing. Two types of emulsified asphalt binders, namely PC-3 and HV, were selected as the tack coats. The property was evaluated in three tack coat dosages (0.25Kg/m2, 0.5Kg/m2 and 0.75Kg/m2 based on residual binder) and at four test temperatures (−10°C, 0°C, 25°C and 50°C). Hence, a total number of 72 composite specimens made of AC-13 and AC-20 were subjected to the shear test to evaluate the interface shear characteristics in terms of interface shear strength, the shear failure displacement and the coefficient of interface bonding at the initial stage of shear. The results showed that the shear strength at the interface decreases gradually with increasing temperature. The least failure shear displacement of all specimens was observed at the highest temperature of 50°C. Moreover, the results indicated that the brittleness at low temperatures, the flowability at intermediate temperatures, and the viscosity at high temperatures of tack binder have the most significant effects on the shear property of the interface of asphalt pavement.

Effects of low-frequency pulsed wave ultrasound on the shear properties of the interface of vancomycin-loaded acrylic bone cement-stem

Objective: To investigate the effects of low-frequency pulsed wave ultrasound on the shear properties of interface of the vancomycin -loaded acrylic bone cement-stem. Methods: The interfaces of 1% vancomycin-loaded acrylic bone cement-stem specimences were successfully manufactured and randomly divided into three groups: the control group, 450 mW/cm(2) ultrasound group and 1 200 mW/cm(2) ultrasound group, each group consisted of eight samples.Two ultrasound groups were exposed to a local ultrasonic field for 7 d, then immersed in PBS for 23 d, and the control groups were immersed in PBS for 30 d. After curing in air for 24 h, the shear strength of the stem-cement interface was determined by push-out test.The specimens were then photographed using SEM and analysed using Image-Pro Plus 6.0 to determine the porosity at the stem-cement interface. Results: The mean shear strength of stem-cement interface additionally decreased by 9% (P>0.05) and 17% (P<0.05) in 450 mW/cm(2) ultrasound group and 1 200 mW/cm(2) group respectively comparing with the control group, but no significant difference was found between the two ultrasound groups.The porosity at the stem-cement interface additionally increased by 44% (P>0.05) and 110% (P<0.05) in 450 mW/cm(2) ultrasound group and 1 200 mW/cm(2) group respectively comparing with the control group, furthermore.The porosity in 1 200 mW/cm(2) ultrasound group increased by 46% (P<0.05) comparing with the 450 mW/cm(2) group. There are much more fluid penetration along the stem-cement interface in ultrasound group . Conclusion: Low-frequency pulsed wave ultrasound signifiantly enhanced porosity and fluid penetration interface, and reduced the interface shear strength and initial stability.

Interface shear properties of geosynthetics and construction and demolition waste from large-scale direct shear tests

In recent years environmental sustainability has demanded a progressive increase of waste recycling in general and waste value-added utilisation in the construction industry in particular. As regards the application of construction and demolition wastes (C&amp;DW) in geotechnical works, it has been noticed that the use of recycled aggregates is found mostly in road construction. Value-added utilisation of C&amp;DW in geosynthetic-reinforced structures is almost an unexplored field. This paper presents the results of physical, mechanical and environmental characterisation of recycled C&amp;DW, as well as the direct shear behaviour of three recycled C&amp;DW–geosynthetic interfaces. The C&amp;DW material was collected from a recycling plant and came from the demolition of single-family houses and the cleaning of land with illegal deposits of C&amp;DW. Two geogrids and one geocomposite reinforcement (high- strength geotextile) were used to assess the behaviour of C&amp;DW–geosynthetic interfaces. The environmental characterisation of the C&amp;DW, carried out through leaching tests, did not show environmental concerns. Direct shear test results have demonstrated that properly selected and compacted C&amp;DW can exhibit shear strength similar to natural soils. The coefficients of interaction achieved for C&amp;DW–geosynthetic interfaces compare well with those reported in the literature for soil–geosynthetic interfaces under similar conditions, which supports the feasibility of using these recycled materials as backfill in geosynthetic-reinforced structures.

Interface shear properties of geosynthetics and construction and demolition waste from large-scale direct shear tests

Interface shear properties of geosynthetics and construction and demolition waste from large-scale direct shear tests

Laboratory evaluation of the effect of low-temperature application of warm-mix asphalts on interface shear strength

A potential drawback, not yet investigated, of low application temperatures of asphalt mixes could be a reduced interface shear strength. Such low temperatures could be due to improper construction as well as to the use of warm mix asphalt (WMA) technology. In this sense, this paper illustrates an experimental laboratory research aimed at characterizing interface shear properties of double-layered asphalt systems. The upper layer of the specimens (WMA or hot mix asphalt control mix) was mixed and compacted at different temperatures in order to simulate different application conditions. A plain bitumen and a polymer modified binder were used for the asphalt mixes whereas an organic (wax) additive was selected as warm modifier. Experimental data were also compared with the stress field of a typical flexible pavement calculated through a layered elastic theory (LET) model. The research study mainly showed that interface shear strength sensibly decreases for low application temperatures of the upper layer (below 140°C) regardless of bitumen type and presence of the warm additive. However, the use of polymer modified bitumen as binder for the upper layer asphalt concrete leads to noticeably higher interface shear strength at any test temperature reducing the risk of delamination.

Experimental investigation of EPS geofoam seismic buffers using shaking table tests

The paper reports the results of six shaking table tests using reduced-scale model walls constructed with expanded polystyrene (EPS) panels to reduce dynamic earth loads due to base shaking. The results are compared with a nominal identical rigid (control) wall constructed without a seismic buffer. The test results show that dynamic load attenuation increased with decreasing geofoam stiffness. The test with the highest buffer stiffness resulted in a 15% reduction in dynamic load and the test with lowest stiffness resulted in a 40% reduction in dynamic load compared with the control wall. The results of these experiments provide proof of the concept that EPS panels placed against rigid walls can act as seismic buffers to attenuate dynamic loads due to ground shaking (e.g. earthquake). Additional quantitative data related to load–deformation–time response, back-calculated elastic modulus values for the EPS seismic buffer configurations, dynamic interface shear properties, acceleration amplification in the backfill soil and post-excitation stress relaxation-creep behaviour are also reported.

Geomembrane–geotextile interface shear properties as determined by inclined board and direct shear box tests

Geomembrane–geotextile interface shear strength parameters were measured using inclined board (tilting table), standard size (60 mm×60 mm) and large-scale (300 mm×300 mm) direct shear box tests. Smooth and rough HDPE, PVC geomembranes and nonwoven needle-punched geotextiles were used in the experiments. Inclined board tests were conducted under a normal stress range of about 5–50 kPa on variable size interface areas. In direct shear tests the applied normal stresses were about 25–300 kPa and 110–400 kPa in the small and large size tests, respectively. The interface friction angle and adhesion intercept values obtained by fitting a straight line through the plots of interface shear strength versus the normal stress were compared for different tests. It has been found that inclined board test results produce envelopes with relatively small adhesion values for both smooth and rough HDPE geomembrane–geotextile interfaces. The size of the interface does not appear to be a significant factor. For smooth geomembranes direct shear and inclined board tests give comparable interface friction angle and adhesion values. For rough geomembranes, however, the direct shear adhesion values are markedly higher and friction angle values are a few degrees higher when compared to the inclined board test results.

Geosynthetic Interface Behavior Under Dynamic Loading

The seismic stability of earth slopes, embankments, and landfills that incorporate geosynthetics has been receiving increased attention in geotechnical engineering practice. In the analysis of such structures, the dynamic interface shear properties play important role. The authors have been conducting research to understand the dynamic response of various geosynthetic-geosynthetic and geosynthetic-soil interfaces. This paper presents an overview of the research including: a description of the shaking table facility and the experimental setup developed; typical test results and discussions; and a description of a constitutive model for a geosynthetic-geosynthetic interface that can be used in wave propagation analysis of soil and landfill liner systems that incorporate geosynthetics.

Interface shear properties and toughness of NiAl/Mo laminates

Mechanical properties at the interface between NiAl intermetallic and Mo ductile phase in sandwich laminates have been studied under a variety of stress states involving primarily shear. A shear/compression test for laminates of NiAl/Mo/NiAl has been used in which a double-notched specimen with cut-through metal interlayer is loaded to failure in compression. Because of the large elastic mismatch between NiAl and Mo, a primarily shear loading generates a significant amount of normal stress in this test. Interface shear response and toughness obtained using this technique are compared for NiAl/Mo laminates with interfacial segregant, Cr, Re and C layers fabricated by high temperature diffusion bonding. A microstructural investigation of the interfacial reaction zone and the shear failure path is conducted to identify failure mechanisms. Failure strength and related interfacial toughness is examined using an FEM model of local stress state close to the notch in the bimaterial shear/compression specimen geometry. A trend of increasing bond strength with reducing notch spacing is identified and analyzed in terms of local stress state, the onset of microyielding and crack shielding. Thus, a new fracture stress locus has been developed for bimaterial interfaces. Residual stress due to CTE thermal expansion mismatch is measured and the contribution of thermal residual stress to the failure behavior of the laminate is explored. The combined effect of stress concentration at crack tip, residual stress and slip discontinuity across interface have been used to explain the apparently brittle loading response and easy debonding of Mo fibers in eutectic NiAl/Mo alloys.