Numerical parametric study on the influence of location and inclination of large-scale asperities on the shear strength of concreterock interfaces of small buttress dams

When assessing the sliding stability of a concrete dam,the influence of large-scale asperities in the sliding plane is often ignored due to limitations of the analytical rigid body assessment methods provided by current dam assessment guidelines.However,these asperities can potentially improve the load capacity of a concrete dam in terms of sliding stability.Although their influence in a sliding plane has been thoroughly studied for direct shear,their influence under eccentric loading,as in the case of dams,is unknown.This paper presents the results of a parametric study that used finite element analysis(FEA)to investigate the influence of large-scale asperities on the load capacity of small buttress dams.By varying the inclination and location of an asperity located in the concrete-rock interface along with the strength of the rock foundation material,transitions between different failure modes and correlations between the load capacity and the varied parameters were observed.The results indicated that the inclination of the asperity had a significant impact on the failure mode.When the inclinationwas 30and greater,interlocking occurred between the dam and foundation and the governing failure modes were either rupture of the dam body or asperity.When the asperity inclination was significant enough to provide interlocking,the load capacity of the dam was impacted by the strength of the rock in the foundation through influencing the load capacity of the asperity.The location of the asperity along the concrete-rock interface did not affect the failure mode,except for when the asperity was located at the toe of the dam,but had an influence on the load capacity when the failure occurred by rupture of the buttress or by sliding.By accounting for a single large-scale asperity in the concrete-rock interface of the analysed dam,a horizontal load capacity increase of 30%e160%was obtained,depending on the inclination and location of the asperity and the strength of the foundation material.

The Effects of Degradation Phenomena of the Steel-Concrete Interface in Reinforced Concrete Structures

Reinforced concrete (RC) constructions are the innovation of sustainable constructions replacing masonry constructions. Despite this, the use of concrete and steel to improve the performance of structural members in service is a recurring problem due to the immediate or overtime appearance of cracks. The objective of this work was therefore to assess the damage phenomena of the steel-concrete interface in order to assess the performance of an RC structure. Samples of approximately 30 cm of reinforcement attacked by rust were taken from broken reinforced concrete columns and beams in order to determine the impact of corrosion on high adhesion steel (HA) and therefore on its ability to resist. The experimental results have shown that the corrosion degradation rates of reinforcing bars of different diameters increase as the diameter of the reinforcing bars decreases: 5% for HA12;23.75% for HA8 and 50% for HA6. Using the approach proposed by Mangat and Elgalf on the bearing capacity as a function of the progress of the corrosion phenomenon, these rates made it possible to assess the new fracture limits of corroded HA steels. For HA6 respectively HA8 and HA12, their initial limit resistances will decrease by 4/4, 3/4 and 1/4. Based on the results of this study and in order to guarantee their durability, an RC structure can be dimensioned by taking into account the effects of reinforcement corrosion.

Mode-I fracture and durability of FRP-concrete bonded interfaces

In this study, a work-of-fracture method using a three-point bend beam （3PBB） specimen, which is commonly used to determine the fracture energy of concrete, was adapted to evaluate the mode-I fracture and durability of fiber-reinforced polymer （FRP） composite-concrete bonded interfaces. Interface fracture properties were evaluated with established data reduction procedures. The proposed test method is primarily for use in evaluating the effects of freeze-thaw （F-T） and wet-dry （W-D） cycles that are the accelerated aging protocols on the mode-I fracture of carbon FRP-concrete bonded interfaces. The results of the mode-I fracture tests of F-T and W-D cycle-conditioned specimens show that both the critical load and fracture energy decrease as the number of cycles increases, and their degradation pattern has a nearly linear relationship with the number of cycles. However, compared with the effect of the F-T cycles, the critical load and fracture energy degrade at a slower rate with W-D cycles, which suggests that F-T cyclic conditioning causes more deterioration of carbon fiber-reinforced polymer （CFRP）-concrete bonded interface. After 50 and 100 conditioning cycles, scaling of concrete was observed in all the specimens subjected to F-T cycles, but not in those subjected to W-D cycles. The examination of interface fracture surfaces along the bonded interfaces with varying numbers of F-T and W-D conditioning cycles shows that （1） cohesive failure of CFRP composites is not observed in all fractured surfaces; （2） for the control specimens that have not been exposed to any conditioning cycles, the majority of interface failure is a result of cohesive fracture of concrete （peeling of concrete from the concrete substrate）, which means that the cracks mostly propagate within the concrete; and （3） as the number of F-T or W-D conditioning cycles increases, adhesive failure along the interface begins to emerge and gradually increases. It is thus concluded that the fracture properties （i.e., the critical load and fracture energy） of the bonded interface are controlled primarily by the concrete cohesive fracture before conditioning and by the adhesive interface fracture after many cycles of F-T or W-D conditioning. As demonstrated in this study, a test method using 3PBB specimens combined with a fictitious crack model and experimental conditioning protocols for durability can be used as an effective qualification method to test new hybrid material interface bonds and to evaluate durability-related effects on the interfaces.

Viscoelastic micromechanical model for dynamic modulus prediction of asphalt concrete with interface effects

A viscoelastic micromechanical model is presented to predict the dynamic modulus of asphalt concrete （AC） and investigate the effect of imperfect interface between asphalt mastic and aggregates on the overall viscoelastic characteristics of AC. The linear spring layer model is introduced to simulate the interface imperfection. Based on the effective medium theory, the viscoelastic micromechanical model is developed by two equivalence processes. The present prediction is compared with available experimental data to verify the developed framework. It is found that the proposed model has the capability to predict the dynamic modulus of AC. Interface effect on the dynamic modulus of AC is discussed using the developed model. It is shown that the interfacial bonding strength has a significant influence on the global mechanical performance of AC, and that continued improvement in surface fimctionalization is necessary to realize the full potential of aggregates reinforcement.

Physicochemical Study on the Interface Zone of Concrete Exposed to Different Sulfate Solutions

This paper reports the results of the visual observations and micro-analysis of concrete core samples after 6 and 12 months of their exposure to sodium, ammonium and magnesium sulfate solutions with the same concentration of sulfate ions. XRD, SEM and EDS were used for micro-analysis of the mi-crostructure and the composition of the interface zone in the samples. The results indicate that the deterioration of concrete by different sulfate solutions could proceed differently with regard to the mechanism and the mode of damage caused. The damage of concrete exposed to sodium sulfate solution is mainly caused by the gypsum crystals formed in the interface zone, which lead to expansion and cracking. In the case of concrete immersed in magnesium sulfate solutions, a layer of brucite (magnesium hydroxide) and gypsum was produced in the interface zone, which reduces the cohesiveness of the interface zone in concrete. For the concrete immersed in ammonium sulfate solutions, the conversation of mortar to some mush mass by ammonium ions and the formation of a large of gypsum occurred in the interface zone, consequently, serious softening of hydrated cement pastes and expansion and cracking of concrete are the characteristics of the attack by ammonium sulfate solutions. Also, it is considered that using drilled concrete core as samples to evaluate the sulfate resistance of concrete is a good and accelerated method.

Performance of interface between TRC and existing concrete under a chloride dry-wet cycle environment

Textile-reinforced concrete(TRC)is suitable to repair and reinforce concrete structures in harsh environments.The performance of the interface between TRC and existing concrete is an important factor in determining the strengthening effect of TRC.In this paper,a double-sided shear test was performed to investigate the effects of the chloride dry-wet cycles on the average shear strength and slip at the interface between the TRC and existing concrete,also considering the existing concrete strength,bond length,textile layer and short-cut fiber arrangements.In addition,X-ray diffraction(XRD)technology was used to analyze the microscopic matter at the interface in the corrosive environment.The experimental results indicate that the interface performance between TRC and existing concrete would decrease with continued chloride dry-wet cycles.Compared with the specimen with a single layer of textile reinforcement,the specimens with two layers of textile with added PVA or AR-glass short-cut fibers could further improve the properties of the interface between the TRC layer and existing concrete.For the TRC with a single layer of textile,the average shear strength tended to decrease with increasing bond length.In addition,the strength grade of the existing concrete had a minor effect on the interface properties.

Influence of construction interfaces on dynamic characteristics of roller compacted concrete dams

To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams(RCCDs),mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary(VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam.However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes,combination quality of the RCC layers should be significantly ensured.

A study on dynamic shear strength on frozen soil-concrete interface

Using newly developed dynamic shearing devices, the dynamic sheafing strength of frozen soil-conerete interface was studied experimentally. By placing concrete blocks in the lower half of the shear box and frozen soil sample in the upper part, a series of dynamic shear tests on their interfaces were carried out. The obtained results are summarized and the main influencing factors are revealed.

Finite Element Analysis of Shrinkage in the Interface of Functionally Graded Concrete Segment Used in Shield Tunneling

In functionally graded materials (FGM), the problem of interface stability caused by the volume deformation is commonly regarded as the key factor for its performance. Based on test results, in terms of finite element method (FEM) this paper analyzed problems in the shrinkage of functionally graded material interface of shield concrete segment, which was designed and produced by the principle of functionally graded materials. In the analysis model, the total shrinkage of concrete was converted into the thermal shrinkage by means of the method of 'Equivalent Temperature Difference'. Consequently, the shrinkage stress of interface layer was calculated and compared with the bond strength of interface layer. The results indicated that the volume deformation of two-phase materials of functionally graded concrete (FGC) segment, which were the concrete cover and the concrete structure layer, showed better compatibility and the tension stress of interface layer, which was resulted from the shrinkage of concrete and calculated by ANSYS, was less than the bond strength of interface layer. Therefore, the interface stability of functionally graded concrete segment was good and the sliding deformation of interface layer would not generate.

Interactions between Superplasticizer and Release Agents at the Concrete/Formwork Interface

Improving the knowledge of rheological and tribological characteristics of fresh concrete is important to contribute to the progress of construction sites and the final quality of the work. The objective of this study is to identify the effect of a superplasticizer based on polycarboxylic ether on the tribological behavior of fresh concrete at the concrete/formwork and concrete/oil/formwork interfaces. Friction tests on fresh concrete were carried out using a plan/plan tribometer. In order to study the behavior of the superplasticizer close to the formwork, three concretes with 30% of paste and different dosage of superplasticizer were formulated. The results show that the increase of the dosage of superplasticizer reduces the friction stress. The properties of the superplasticizer generate a deflocculating action of concrete grains and lead to a stabilisation of the soap-oil micellae present in the vicinity of the formwork. Thus, the efficiency of superplasticizer depends on the quantity of fines, on the quantity of soap formed and so, on the release agent formulation.

Freeze-Thaw Effect on Coarse Sand Coated Interface between FRP and Concrete

This paper examines the effect of freezing and thawing on the coarse sand coating chosen to achieve the composition of FRP and concrete in FRP-concrete composite deck. Push-out test specimens with dimensions of 100 × 100 × 450 mm were subjected to repeated freeze-thaw cycles under wet conditions ranging from -18℃± 2℃ to 4℃ ± 2℃. The failure strength of the interface and the deformation of FRP at failure exhibited by the specimens that experienced 300 freezing-thawing cycles showed a difference of merely 5% compared to those of the specimens that were not subjected to freeze-thaw. This indicates that coarse sand coating is not affected by freezing-thawing cycles and the FRP-concrete composite deck owns sufficient applicability in terms of durability against freezing-thawing.

Investigation on Fracture Behavior of FRP-Concrete Interface under Direct Shear

In this study, the authors reviewed and compared the existing researches on debonding performance of FRP-Concrete Interface under direct shear firstly. Following that, two determinants of the debonding ultimate bearing capacity of FRP-Concrete Interface under pure shear are introduced into this study, namely fracture-resisting force at the undamaged area and friction stress transferred along the already debonded surface. The authors deduced the formulae on fracture energy for FRP-Concrete Interface and obtained the values for fracture energy and friction stress at FRP-Concrete Interface based on the experimental results of eight specimens of FRP-Concrete Interface. On the basis of theoretical frame mentioned above, the authors concluded that the friction-resisting stress transferred along the deteriorated bi-material interface is independent of length of FRP bonded onto concrete substrates and concrete strength, but it relies on the tension rigidity （i.e., the layers of the bonding FRP, it is found that the friction stress declines substantially while the layers of FRP increases bonded to concrete substrate）. On the contrary, cohesive fracture energy is dependent on length of FRP bonded to concrete substrate and the tension stiffness of bi-material interface. In addition, the percentage of the fracture-resisting force in the ultimate debonding load at the interface decreases with the bonding length of FRP increasing, but increases with the increase of the layers of the FRP.

Study on Interface mechanical behavior of steel tube reinforced concrete composite pile

Currently for the steel tube reinforced concrete composite pile research, although predecessors make a comprehensive research on the composite pile beating performance, design technology, but there are still many problems have not been solved, such as the steel tube reinforced concrete pile composite interracial force learn performance research is still in the initial stage. In this paper, we mainly discuss the research methods of several interface mechanical properties and propose the possibility of studying the mechanical properties of the steel tube reinforced concrete composite pile by using the principle of ultrasonic speckle.

Effects of freeze-thaw cycles on fracture behavior of epoxy asphalt concrete

According to the winter temperature of Peking,the freeze-thaw（FT） condition in laboratory was determined.Seven groups of epoxy asphalt concrete（EAC） specimen were exposed to different FT cycles.The flexural modulus and fracture energy（G_F） of EAC exposed to different FT cycles were obtained through the 3-point bending test.Meanwhile,the plane strain fracture toughness（K_（IC）） of EAC was obtained through numerical simulation.The results show that the flexural modulus of the FT conditioned EAC samples decreases with the increase of FT cycles.The FT damage of flexural modulus is 60%after 30 FT cycles.Nevertheless,with the increase of FT cycles,the G_F and K_（IC） of EAC decrease first and then increase after 15 FT cycles.

Performance evaluation of open-graded epoxy asphalt concrete with two nominal maximum aggregate sizes

Open-graded friction course(OGFC) is applied to pavement surfaces to increase driving safety under wet conditions, and recently, to reduce tire/pavement noise. The durability of OGFC, however, has been a concern since conventional OGFC mixes last typically less than ten years before major maintenance or rehabilitation is needed. This work investigates a new open-graded asphalt mixture that uses epoxy asphalt as binder to improve mix durability. One type of epoxy asphalt that has been successfully applied to dense-graded asphalt concrete for bridge deck paving was selected. A procedure of compacting the mix into slab specimens was developed and a series of laboratory tests were conducted to evaluate the performance of the new mix, including Cantabro loss, permeability, friction, shear strength, and wheel rutting tests. Results show superior overall performance of the open-graded epoxy asphalt mix compared to conventional open-graded asphalt mix. There are also preliminary indications that the OGFC mix with 4.75-mm NMAS gradation can improve the resistance performance to raveling, while the OGFC mix with 9.5-mm NMAS gradation can improve the performance of surface friction at a high slip speed.

Microstructure Model of the Interfacial Zone Between Fresh and Old Concrete

A new model of repaired concrete which divides the bonding interface into a penetrating layer,a strongly-affected layer and a weakly-affected layer was put forward.The model is mainly based on the observation of the microstructure of interface between fresh and old (3 months to 60 years) concretes by using scanning electron microscopy.Then,the mechanism of the microstructure formed was analyzed.Finally,the relationship between the micro-structure and macro-mechanical performance of the interface was discussed.

Behavior of Corrosion-Repaired Concrete Beams Reinforced by Epoxy Mortar

The performance of concrete beams repaired with epoxy mortar was investigated by constructing twelve beam specimens.All the beam specimens were subjected to a constant current for accelerated corrosion.Six specimens were corroded without subsequent reparation as a control group,and the other six beam specimens were corroded and repaired utilizing epoxy mortar.All specimens were tested to failure.During test process,we focused on the failure pattern of beam specimens,structural cracks,mid-deflections,bearing capacity,and probed into the influence of corrosion degree and repair of epoxy mortar on the performance of beam specimens.It was observed that corrosion-repaired beams in the loading test were in a bending failure pattern.It is obvious that cracking loads and bending stiffness of repaired beams and corrosion-repaired beams were larger than those of unrepaired beams and secondly-corroded beams.When the mass loss of main steel bars was smaller than 10%,the bearing capacity of the repaired beams was similar to that of the unrepaired beams.When the mass loss of main steel bars was larger than 10%,the bearing capacity of the repaired beams increased significantly compared with that of the unrepaired beams.

Performance of Epoxy-Repaired Corroded Reinforced Concrete Beams

Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated corrosion with the constant current,beam specimens are repaired with epoxy mortar and the flexural test of beams is investigated.Then the behaviors of repaired corroded reinforced concrete beams are evaluated.The experimental results show that cracking and ultimate loads of corroded RC beams are enhanced after being repaired.And the strain distributions measured across sections of beam specimens still obey the assumption of plane section.After being repaired,the number of cracks decreases and the crack spacing increases.

Study on the Pulsed Flashover Characteristics of Solid-Solid Interface in Electrical Devices Poured by Epoxy Resin

In electrical devices poured by epoxy resin, there are a lot of interfaces between epoxy resin and other solid dielectrics, i.e. solid-solid interfaces. Experiments were carried out to study the flashover characteristics of two typical solid-solid interfaces （epoxy-ceramic and epoxy~ PMMA） under steep high-voltage impulse for different electrode systems （coaxial electrodes and finger electrodes） and different types of epoxy resin （neat epoxy resin, polyether modified epoxy resin and polyurethane modified epoxy resin）. Results showed that, the flashover of solid-solid interface is similar to the breakdown of solid dielectric, and there are unrecoverable carbonated tracks after flashover. Under the same distance of electrodes, the electric stress of coaxial electrodes is lower than that of finger electrodes; and after the flashover, there are more severe breakdown and larger enhanced surface conductivity at interface for coaxial electrodes, as compared with the case of finger electrode. The dielectric properties are also discussed.

Modelling the Rheological Properties of Epoxy Asphalt Concrete

This paper presents an investigation into modelling the rheological properties of epoxy asphalt concrete( EAC) by using the Huet-Sayegh model. Complex modulus tests were conducted on EAC specimens at various temperature and loading frequency conditions. Dynamic modulus and phase angles obtained from the complex modulus tests were used in the construction of the Huet-Sayegh model. The dynamic modulus master curve was developed by the Huet-Sayegh model as well as the Burgers model for comparison purpose. The results showed that EAC exhibits typical rheological behavior whose dynamic modulus decreases with the increase of temperature while increases with the increase of frequency,and phase angles increase with the decrease of frequencies and the increase of temperatures. The Huet-Sayegh model predicts the dynamic modulus master curve of EAC very well and much better than the Burgers model over a wide range of frequencies.