Slant Shear Research Articles

Factors affect the bond strength of Geopolymer repair material: Review

One of the most important construction activities worldwide is the repair and rehabilitation of damaged concrete structures. Many concrete structures are decaying, sometimes early, and need remediation to restore their protection and serviceability. As a result, in recent years the need for repair and safety has increased dramatically. This paper reviewed some studies about the potential for geopolymer to be used as a repair material and highlighted the main factors effect bond strength between GP and OPCC. The bond strength of GP was assessed using splitting tensile test and slant shear test. The results of bond strength indicated that this form of GP could be employed as a potential repair material..

Influence of substrate roughness and bonding agents on the bond strength between old and new concrete

This research aims to study factors affecting the strength of adhesion between old concrete and new concrete. Among the factors that have been studied in this research are the type of bonding material and the roughness of the surface adhesion, four types of bonding materials (EPICHOR-1768, C-Latex, SikaBond-T21, EPICHOR-500) have been selected because they are available in local markets. A wire brush is used in order to increase the roughness of sample surfaces. The pulloff and slant shear tests have been adopted to assess the bonding strength between the test the old and new concrete. 30 cylindrical samples (7 cm diameter) have been examined by pull-off test, also slant shear test was conducted on 40 samples (10 cmx10 cmx30 cm). The obtained results showed that there is an active role for the bonding material as well as the surface roughness to increase the strength of adhesion between the old and new concrete. Also, it showed that the best of these bonding materials is EPICHOR-1768 because of its significant impact in increasing the strength of the adhesion between the old and new concrete where the percentage of increase 124% in the pull-off test and 48% in slant shear test, compared to the reference sample for each test. As well, as a result of roughening the surface by brush, the strength of adhesion reaches 4% increase in the pull-off test and 23% in the slant shear test compared with the reference sample for each test, which demonstrates the importance of surface roughness to increase the bonding strength between the old and new concrete.

The influence of different bond primers on the bond strength of concrete overlays and the microstructure of the overlays transition zone

This study investigated the effect of different bond primers (BP) and the thickness of BP on bond performance. The mechanical and microstructural properties of BP were studied systematically using compressive strength, drying shrinkage, X-ray diffraction, and other methods; bond strength was evaluated using the slant shear test, and the failure modes were observed. Further, kernel density estimation was performed to qualify the crack width of the repair interface statistically characterised by analysing images obtained using the backscattered-electron method. The results indicated that when the BP was modified using silica fume, nano-silica, and Portland cement after ball milling, the modified BP pores were refined because of the combined filler, packing, and pozzolanic effects. The drying shrinkage of BP modified by an expansive agent was reduced; the BP could narrow the repair interface gap or even disappear, and the modified BP made the interfacial zone denser and improved bond strength. The results of the microscopic characterisation method of the repair interface verify the multi-scale characterisation of the new and old concrete interface.

Influence of hard segment content and soft segment length on the microphase structure and mechanical performance of polyurethane-based polymer concrete

Understanding the structure–property relationship of polyurethane (PU) binders is of critical importance in the construction engineering applications. A series of rapid room temperature-curable PU binders were prepared using polyoxypropylene glycol as the soft segments, along with polymethylene polyphenylene isocyanate and 4,4′-methylene-bis(2-chlorobenzenamine) as the hard segments. This work investigated the influence of the hard segment content (40 wt%, 45 wt%, and 50 wt%) and the soft segment molecular weight (1000 g/mol, 2000 g/mol, 3000 g/mol, and 4000 g/mol) on the microphase structure of the PU binders. Their influence on the compressive behaviors, flexural behaviors, impact strengths, and slant shear strengths of the PU-based polymer concretes was also investigated. Structural characterization revealed that increasing either the hard segment content or the larger soft segment molecular weight effectively enhanced hydrogen bonding as well as microphase separation. Our results also demonstrated that a higher hard segment content resulted in better mechanical performance and shorter pot life. In addition, the PU-based polymer concrete using 2000 g/mol polyoxypropylene glycol reached optimal mechanical performance when the hard segment was held constant. Hence, varying the hard segment content and soft segment length can be an effective method to adjust the engineering performance of PU-based polymer concrete.

Alkali-activated fly ash foams for narrow-trench reinstatement

Unlike with traditional earthfill, materials used in the reinstatement of narrow-trenching must satisfy certain engineering properties. Otherwise, the ongoing traffic and environ- mental condition will damage the trench, degrade the road pavement and damage the service-lines that were installed. This report identifies eight mixtures using Fly Ash as the alumino-silicate precursor to prepare alkali-activated foams, cast to densities between 600 and 1100 kg/m3. These systems were examined for their mechanical performance, dimensional stability, and bond with the asphalt substrate. The hardened foams were first tested for their strength, modulus of elasticity, and Poisson's ratio. This was followed by evaluating their drying shrinkage and their coefficient of thermal expansion. Lastly, these mixtures were cast against asphalt concrete to assess both slant shear and flexural bond strength. The test outcomes were used to rank the mixtures with an analytical hierarchy process. The results show that the mixtures at the median density (800 kg/m3) offer the most promise and substantial benefit accrues from fibre reinforcement.

Evaluation of interfacial strength between hydrating cement paste and epoxy coating

The objective of this work is to determine the interfacial strength between cement paste and epoxy, coated at the different instant of time during the hydration. The factors influencing the magnitude of interfacial adhesive strength were also studied. To pursue this, the interfacial adhesive strength between cement paste and epoxy coated at different days of hydration was determined by performing macro-mechanical experiments such as slant shear and pull-off adhesion test. The various instant of hydration when epoxy was coated are 2, 7, 14, 21, and 28 days from the point of initiation of hydration. The possible influencing factors considered were water-cement ratio, curing time, and thickness of the coating. Results of macro-mechanical tests show that the average interfacial adhesive strength between cement paste and the epoxy coating was in the same range, irrespective of the instant of coating. Although the higher surface energy and work of adhesion should result in a higher interfacial strength for epoxy coated on 2nd day, the measured value of interfacial strength, however, did not show such. One of the possible reasons why interfacial strength of epoxy coated on the 2nd day is similar to 28th day coating in spite of higher surface energy and work of adhesion, is the presence of the larger amount of surface water during the earlier days. The effect of this excess water balances out the contributory effect of the physical interactions and mechanical interlocking. From the parametric study, it was observed that the factors considered in the present study play a major role, particularly when coated during the early days of hydration.

A Study on bond strength of normal concrete to high volume fly ash concrete

Now-a-days the deterioration of concrete is further current due to numerous reasons like improper bonding, corrosion of steel, inferior quality of materials any as improper accomplishment. The deterioration of concrete finishes up in reduction in helpful strength of concrete therefore necessitates the adoption of correct repairing ways in which some repairing/strengthening techniques of concrete structures frequently involve adding new concrete to associate existing concrete 0.5. The bond performance between the existent and repair concretes plays a awfully important role on the powerfulness of this strengthening strategy. Surface treatments like wire - brushing, sandblasting, water spouting, chipping, etc., unit typically adopted. The Bond strength at the interface depends on roughness of the substrate that successively depends on Cohesion and Friction at the interface.at intervals the gift study previous concrete substrates every at 450 angles with vertical and in addition the ash concrete as overlaid material were unreal to live the shear the parameters of the investigation embrace 1) totally utterly completely different grades of concrete substrate (M30 & M60) 2) Roughness condition at the interface (Smooth (as cast) &Rough (chipped indentations)) 3) The overlaid concrete with different percentages of cement replacement with ash (0%, twenty fifth and 50%) 4) Varying percentages of steel reinforcement resisting the shear at the interface (4 No’s of 4mm military intelligence (0.502%) and four No’s of 6mm military intelligence. The specimen adopted is additionally a customary prism size of 400mm X 100mm X 100mm.The take a look at conducted is ‘Slant Shear test’ as per SB 6319 zero.5 5.From shear tests it totally was found that the bond strength between the 2 interfaces was accumulated for twenty fifth ash content in overlaid concrete and reduced for five hundredth ash content in overlaid concrete all the same the roughness of the substrate. However, the magnitude of increase in bond strength relied on the roughness of the substrate. further the presence of Steel reinforcement (Substrate with no treatment for the roughness at the interface) accumulated the bond strength at the interface. From the determined Bond strength at the interface it's tried to estimate the planning constant of Cohesion and magnificence constant of Friction at the interface between the normal concrete and the fly ash overlaid concrete

Laboratory evaluation of interfacial mechanical properties in geogrid-reinforced bituminous layers

In this study, the mechanical properties of composite bituminous structures with geogrid products, used as an interlayer between different types of bituminous mixtures, at a constant temperature, were examined. A twofold experimental program based on new approaches was selected. A new configuration of the 3-Point Bending Test (3-PBT) was adopted to capture the J-integral and crack resistance property defined by crack resistance index (CRI) at the interface against bottom-up crack propagation. The bonding quality at the interface was also defined through a new index named coefficient of interface bonding (CIB), which was measured via a modified version of the slant shear device. The results derived from this research revealed that reinforcement of the interface, with varying degree of surface texture, by geogrid products significantly enhances the fracture toughness of the whole system in terms of the J-integral, which could be properly connected to the combined functions of bonding quality and crack resistance indices defined at the interface.

Interfacial Bond Properties between Normal Strength Concrete and Epoxy Resin Concrete

It is necessary to pay attention to the bonding strength of the interface between precast normal strength concrete (NSC) and cast‐in‐place epoxy resin concrete (EMR) when using EMR as a repair or filling material or an overlay in bridges’ rehabilitation. However, the performances of epoxy concrete are different due to differential mix ratios; thus, the bonding properties between various epoxy resin concrete and cement concrete are not completely the same. This article investigated the interfacial bond properties between NSC and ERC by direct tensile, push‐out, and slant shear test with specimens of special size and structure and observed the interfacial bond strength and corresponding failure modes. The minimum bond strength under direct tension was 0.72 MPa, while the minimum bond strength was 1.71 MPa and 3.19 MPa for the push‐out test and slant shear test, respectively. Results indicated that the slant shear test specimens with an inclination angle of 45° are not suitable for the slant shear test due to higher compressive stress. Furthermore, the cohesion and friction coefficient of interface bond strength were calculated inversely in accordance with the results obtained from the corresponding direct tensile and slant shear tests. The minimum cohesion value was 1.71 MPa, and the minimum friction coefficient value was 0.46.

Experimental study of the interfacial bond strength between cementitious grout and normal concrete substrate

The interfacial bond strength between cementitious grout and normal concrete substrate was experimentally investigated by conducting slant shear tests and splitting tensile tests. The effects of concrete substrate strength, surface roughness, and type of cementitious grout on the bond strength of cementitious grout and normal concrete were discussed in detail. The results showed that, for composite specimens, the effects of concrete substrate strength on the slant shear bond strength were more obvious than those on the splitting tensile bond strength. Specifically, with an increase in the normal concrete substrate strength, the slant shear bond strength showed an increasing trend for composite specimens with a surface roughness of 0.25 mm, and it exhibited no significant trend for slant shear composite specimens with a lower surface roughness (0, 0.06, and 0.13 mm) and splitting tensile composite specimens. With an increase in surface roughness, the slant shear bond strength and splitting tensile bond strength presented different degrees of increase within a certain limit. In addition, a comparison of specimens with different types of cementitious grout indicated that the interfacial bond strength of specimens prepared using CGM-270 overlays was the highest. The relationship between slant shear strength and splitting tensile bond strength was analysed, and a linear correlation between the slant shear bond strength and splitting tensile bond strength was established. Thereafter, empirical models of the slant shear bond strength and splitting tensile bond strength between cementitious grout and normal concrete were proposed.

Effect of high temperature on the mechanical properties of basalt fibre self-compacting concrete as an overlay material

Basalt fibres are modern inorganic concrete fibres, fabricated by melting the basalt rock. These fibres exhibited remarkable resistance to elevated temperatures in comparison with other manufactured fibres. Thus, when the impact of fire is the main consideration, basalt fibres are favoured in the construction of concrete buildings. In this study, the effects of basalt fibres on the workability of fresh self-compacting concrete (SCC) were measured using slump flow, J-ring flow, V-funnel flow and L-box height ratio. The properties of hardened concrete such as compressive strength, splitting strength, modulus of elasticity, flexural strength, and Poisson’s ratio were examined at temperatures between 25 °C and 500 °C. Also, the bond strength between the basalt fibre SCC as an overlay material and a normal concrete substrate was analysed at elevated temperatures. The interfacial surface between the concrete parts of the hybrid samples was roughened in different ways to determine the best roughening mode, which induced high slant shear strength of concrete under fire. The experimental results revealed that increasing the temperature up to 500 °C reduced the tensile and compressive strengths of SCC by over 20%. The optimum slant shear strength of hybrid concrete under fire was achieved by roughening the interfacial surface through the sandblasting method.

Evaluating Applicability of ASTM C 928 Approach in Assessing Adequacy of Patch Repair of Bridge Piers

Severe environmental conditions in many parts of Iran could adversely affect infrastructures, especially bridge piers. This research evaluates the efficiency of fiber-reinforced polymer-modified self-compacting concrete in patch repair of bridge piers. The efficiency of this material for repair has been verified using ASTM C 928 and a novel testing method (patch test) that uses a cylindrical compression test simulating indirect force transfer from old (existing) concrete to new (patch repaired) concrete. To investigate the efficiency of self-compacting concrete in patch repair and derive the correlation between bond strength and patch strength, two sets of specimens have been included in the experimental program. These include 24 and 27 specimens which are prepared for patch and slant shear tests, respectively. Test results show significant improvement in strength due to use of polymer modified and fiber reinforced self-compacting concrete in slant shear tests, where strength enhancement as much as 50% (compared to undamaged specimens) was observed. Meanwhile, in the patch tests, repaired specimens are only able to barely exceed the original strength of undamaged specimens. In the slant shear tests, the use of polymer is very effective in increasing bond strength and using fibers reduces observed variation in the strength of repaired specimens. Considering force path in the patch repair and regardless of materials used for repair, the results show that judging the efficiency of the repair method based on the slant shear test, as proposed by ASTM C 928, in the case of patch repaired elements could be misleading.

Effect of interfacial surface preparation technique on bond characteristics of both NSC-UHPFRC and NSC-NSC composites

Ultra-high performance fiber reinforced concrete (UHPFRC) reveals superior mechanical properties that make it suitable for the strengthening/rehabilitation of normal strength concrete (NSC) structures. This paper investigates the effects of the interfacial surface preparation's methods on the bond performance for both the NSC-UHPFRC and the NSC-NSC composites. The interfacial bond characteristics of five surface preparation methods were studied, i.e., the fair face, the wire brushed surface, the use of the colloidal glue and the x-wrap epoxy on both the fair face and the wire brushed surfaces in addition to the drilled holes and grooves with different areas by using the slant shear, the splitting tensile and the direct shear bond tests. The results indicated that the overall interfacial performances of the NSC-UHPFRC composites were better than their NSC-NSC counterparts because the viscous UHPFRC material can fill the pores and the concaves on the NSC surface causing shear connectors able to enhance the bond performance. The bond strengths of the fair face composites could not achieve the acceptable minimum requirements specified by the ACI 546-06 in contrast to the wire brushed specimens. The area of the drilled holes and grooves had a significant effect on the bond performance and the failure patterns of the tested composites. The recorded splitting tensile bond strength level of the drilled holes and grooves composites categorized as an “Excellent” bonding. The cohesion and the friction parameters of the all tested composites with the proposed interfacial preparations methods achieved the acceptable limits specified by the AASHTO (2010).

Bond Strength Between Concrete Substrate and Reinforced Polyester Composites

The bond strength of polymer composite to the concrete surface is a critical aspect of bridge and parking structures. In this study, the bond strength between concrete and polyester composites reinforced by silica-based materials of different sizes was investigated. Waste marble dust/silica fume particles were applied alone or combined with nano-silica into polymer composite to enhance the bond strength. Slant shear and splitting tensile test results showed that the bond strength of reinforced polyesters is higher in comparison with the neat polyester composites. The combination of waste marble dust with nano-silica and single nano-silica achieved the highest bond strength. In addition, it was observed that the addition of nano-silica and marble dust to the polymer composites showed a high load corresponding to low deformation in comparison with the other groups.

Interface role in composite RC beams with a light-weight concrete core and an ultra high-durability concrete skin

This present paper describes an experimental study focused on the influence of the interface strength, between the lightweight aggregate concrete (LWAC) and the ultra-high durability concrete (UHDC), on the structural behavior of composite beams. The beams were produced with a new concept which consists of using an UHDC layer only in the cover, being the core produced with LWAC. The great benefit of using this ‘superskin’ is to apply UHDC only where it is greatly needed for durability purpose and not in the total cross section of the structural members, avoiding high cement consumption, which is important to reduce the environmental impact associated to cement production.Thirteen different beams were tested until bending – or shear – controlled failure, varying the type of interface between the LWAC core and the UHDC cover: i) smooth; b) rough; c) with steel connectors; and d) indented. Several slant shear tests (SST) were performed to evaluate the longitudinal shear strength of the LWAC-UHDC interfaces. The main goals of this study were: 1) to analyze if composite beams’ behavior is monolithic under load increasing, in both flexural an shear tests, i.e., to check for possible slip of the outer layer; 2) to evaluate the influence of the interface roughness and of UHDC cover on structural performance, and finally 3) to evaluate which is the most proper interface to produce this type of composite beams. The results show that the superskin greatly enhances the structural behavior of the beams and that an appropriate roughness is necessary at the interface between the two concretes, to make the proposed solution viable and reliable.

Bond behavior of self-compacting mortar containing construction and demolition waste under elevated temperatures

The aim of the current study is to provide useful data and information on the compatibility between self-compacting mortar (SCM) mixes containing recycled powder (RP) from construction and demolition waste (C&DW) and parent concrete under temperatures in excess of the current. For this purpose, four SCM mixes were prepared with replacement ratios of 0%, 10%, 20% and 30% RP, according to the EFNARC specifications. The compatibility was measured at 28-day curing age via slant shear test on composite cylindrical samples (half SCM/half concrete) cured in water curing tank and then held at different levels of elevated temperature: 200 °C, 400 °C and 600 °C for a duration of 2 h. The results of fresh mortar and also hardened unit weight, compressive strength and water absorption were assessed. The study concluded that the partial replacement of the cement with RP decreased both dry unit weight and compressive strength and increased water absorption of SCMs. In addition, the obtained data of slant shear test showed that mortars containing up to 20% RP exhibited sufficient adhesion with the concrete substrate (compatible mortar) at elevated temperatures (200–400 °C) during 2 h. Beyond 400 °C, only composites containing up to 10% RP could withstand this temperature.

Investigation of over-nonlocal damage and interface cohesive models for simulating structural behaviors of composite UHPC-NC members

In this paper, a finite element (FE) modeling method is proposed to predict the structural behaviors of composite members of ultrahigh-performance concrete (UHPC) and normal concrete (NC). This FE modeling method integrates: (i) over-nonlocal gradient-enhanced damage model for UHPC and NC, capable of circumventing strong mesh dependency of the classical continuum damage model and spurious damage growth of the standard gradient-enhanced damage model; and (ii) the irreversible viscosity-regularized cohesive zone formulation to describe UHPC-NC interfacial behaviors. Linearization of relative governing equations is presented and the framework is realized on general FE platform ABAQUS through user subroutines UEL and UMAT. Three UHPC-NC composite specimens were prepared to validate the versatility of the numerical method. Improved slant shear test was accompanied to realistically quantify the UHPC-NC bond strength. The height of UHPC substrate governed the overall behaviors and leaded to complete different failure patterns. It is validated that incorporating the material properties and bond behaviors in this paper predicts the composite specimens’ behaviors in an accurate and efficient way.

Comparison of bond strength analysis on the interfacial layer of old and new concrete using latex, epoxy and glycoluril

Though other methods were updated for repairing a concrete structure, improving the bond strength of the interfacial layer with effective additives is still the remarkably outstanding technique since it highly improves the structure without any compromise with the quality and strength parameters. The primary reason for the investigation is to compare the market available materials like epoxy and latex with polymer based binding material named glycoluril by slant shear test in both compression and tension. In this comparative study, epoxy bonding depicts higher bond strength in compression than the latex bonding, whereas 3% of glycoluril bonding in the interfacial layer provided for 1cm thick in the interfacial layer were noted to improve the tensile bond strength between the old and new concrete layers which turns to be effective in the repair works of bottom of the slab/beam where tension is more.

Bond Strength and Flexural Capacity of Normal Concrete Beams Strengthened with No-Slump High-Strength, High-Ductility Concrete.

This study investigates the flexural behavior of normal-strength concrete (NSC) beams that were strengthened with no-slump, high-strength, high-ductility concrete (NSHSDC). A set of slant shear tests was performed to investigate the initial performance of the NSC substrate strengthened with NSHSDC. Slant shear tests considered two types of roughness of interface and five angles of the interface between NSC and NSHSDC. The test results showed that except for specimens with a 75° interface angle, the specimens with high roughness were conformed to the properties (14–21 MPa for 28 days) of the ACI Committee 546 recommendation. For flexural strength tests, NSC beams strengthened with an NSHSDC jacket on the top and bottom sides, three sides, and four sides resulted in strength increments of about 8%, 29%, and 40%, respectively, compared to the beams without NSHSDC jacket. Therefore, the use of NSHSDC is an effective method to improve the performance of NSC beams and is recommended for strengthening reinforced concrete members.

Methodology for brick/mortar interface strength characterization at high temperature

The interface between bricks and mortar is often the weakest part of masonry structures. For refractory linings, the interface strength must be measured at high temperature. Adapted slant shear tests and a new dedicated tensile test set up are proposed here for this purpose. To test the ability of the proposed method, it was applied on two representative brick/mortar couples from room temperature up to 1450 °C. Slant shear tests were conducted to measure ultimate compression and shear stresses and to identify temperature dependent parameters of the Mohr-Coulomb failure criterion. Tensile tests were performed to identify the tensile cut-off. Depending on the brick/mortar couples, the failure can appear at the interface or in the mortar. Cohesion and tensile strength decrease sharply over 900 °C.