新旧水泥砂浆界面粘结性能试验研究

在荷载和环境因素作用下,混凝土结构产生不同程度的劣化。为了保证结构的安全性和耐久性,需要对损伤水泥基材料进行修复。基体的含水饱和度、界面粗糙度、修补砂浆的水灰比以及试件的养护条件都会影响修补砂浆与基体间的粘结强度。选取四种含水饱和度(0%、30%、70%、100%)的旧砂浆作为基体,浇筑水灰比为0.4和0.6的新砂浆,试件密封养护28 d,剪切试验结果表明:当新砂浆水灰比为0.6,旧砂浆含水饱和度按照70%、30%、100%、0%的顺序变化时,界面的剪切强度逐渐减小;当新砂浆水灰比为0.4,旧砂浆含水饱和度按照30%、0%、70%、100%的顺序变化时,界面的剪切强度逐渐减小。同时发现,新砂浆水灰比为0.4时的界面剪切强度普遍大于水灰比为0.6的数值。通过切槽法改变旧砂浆的界面粗糙度,然后浇筑水灰比为0.6的新砂浆,试件标准养护。剪切试验结果表明:当旧砂浆界面粗糙时,界面间的剪切强度是旧砂浆光滑时的1.26倍。选取两种含水饱和度(0%、100%)的旧砂浆作为基体,浇筑水灰比为0.4和0.6的新砂浆,分别进行标准养护和密封养护,剪切试验结果表明:在旧砂浆含水饱和度和新砂浆水灰比相同的情况下,标准养护下的界面剪切强度明显大于密封养护下的界面剪切强度。     

Experimental techniques for measuring fibre/matrix interfacial bond shear strength

Experimental techniques for directly obtaining some measure of the shear strength of the interfacial bond between fibrous reinforcements and cemetitious matrices are reviewed. These techniques— essentially single- or multiple-fibre pull-out out tests — are classified according to specimen type and configuration and are then evaluated and compared using a set of criteria adapted by the author for this purpose. None of the techniques are found to satisfy completely all of the criteria, but several probably could be modified to do so. The objective of this state-of-the-art review is to provide a basis for discussion of the possible future standardization of a test technique for determining fibre/matrix interfacial bond shear strength in cementitious matrix composite specimens.     

Autogenous healing of fibre/matrix interfacial bond in fibre-reinforced mortar

Autogenous or self-healing of the interfacial bond between steel fibres and a cementitious mortar matrix has been examined experimentally using water-cured, single-fibre pull-out specimens. The test results indicate that the extent of the interfacial bond healing which occurs is greater than that observed for fractured plain mortar or concrete similarly cured.     

Bonding behavior of concrete matrix and alkali-activated mortar incorporating nano-SiO2 and polyvinyl alcohol fiber: Theoretical analysis and prediction model

As an emerging construction material, alkali-activated mortar is considered as a sustainable alternative to cementitious composites for the repairing and reinforcement of existing defective buildings. Furthermore, the bonding performance of alkali-activated mortar and concrete matrix can be promoted by adding polyvinyl alcohol (PVA) fiber and nano-SiO₂ (NS). In this study, the effects of PVA fiber and NS contents, alkali-activated mortar type, concrete strength grade, and interfacial roughness on the bonding behavior of two-interfaced shear samples were explored. Based on the experimental results, the grey relation analysis was applied to evaluate the significance of each factor on the bond properties of the alkali-activated mortar and concrete matrix. A prediction model of artificial neural network (ANN) was established considering the effects of alkali-activated mortar type, concrete strength grade, and interfacial type on the bond strength of the samples. The relevant factors affecting bond strength derived by grey relation analysis and weight contribution algorithm was compared and analyzed. Results of the two-interfaced shear test showed that the addition of PVA fiber and NS can significantly boost the bonding property of the samples, and the bond strength increases with the increase of concrete strength grade, alkali-activated mortar strength, and interfacial roughness. Grey relation analysis results indicate that the interfacial type has the most noticeable effect on the bond strength of the samples, followed by the concrete strength grades and the alkali-activated mortar types. The optimum bond strength is derived from PN-C40-III, which is alkali-activated mortar with 0.6% PVA fiber and 1.0% NS contents, concrete strength grade of C40, and interface of type III. The prediction results of the ANN indicate that the predicted values of the bond strengths of the samples are consistent with the experimental values (R = 0.982), and the importance of each factor towards the bond behavior derived by the grey relation analysis and weight contribution algorithm is ultimately consistent after normalization.     

The dependence of interfacial shear strength on matrix and interphase properties

Experiments were conducted to determine the dependence of the interfacial shear strength on the bulk material matrix properties using model compounds based on epoxy/amine chemistry. AS4, carbon fibers were used as the subject for these measurements with both a difunctional epoxy (DGEBA) system as well as a tetrafunctional epoxy (MY720) system. Amine curing agents were carefully chosen to produce matrices which produced a range of matrix properties from brittle, elastic to ductile, plastic. The fiber-matrix interfacial chemistry was constant throughout this study by always using a stoichiometric amount of curing agent. The results indicate that, for both the difunctional as well as the tetrafunctional epoxy system, the interfacial shear strength (as determined by the fragmentation test) decreases nonlinearly with decreasing modulus of the matrix. Linear elastic analysis yields a nearly linear relationship, for both systems, between the interfacial shear strength and the product of strain to final break and the square root of the matrix shear modulus. A linear relationship is also found between the difference in test temperature and glass transition temperature of the cured matrix and the interfacial shear strength. Additionally, the failure mode is seen to remain interfacial as the ductility of the matrix changes.     

涂层对速凝3D打印水泥砂浆力学性能的影响

3D打印砂浆普遍存在层间界面粘结较弱、抗折强度较低的问题,而膨胀水泥浆涂层涂覆于砂浆表面可产生表层压应力,进而提升其抗折强度,作为界面剂涂覆于层间可同时增强其界面粘结强度。本文通过将硫铝酸盐水泥与膨胀剂混合而成的涂层涂覆于速凝3D打印砂浆的表面与层间,研究了该涂层对不掺纤维及掺0.5%(体积分数)玄武岩纤维3D打印砂浆试件力学性能的影响规律。结果表明,涂覆层间涂层对无纤维与掺纤维速凝3D打印砂浆的层间界面粘结强度提升率分别为21.4%、12.2%,同时对其抗压强度也有一定提升作用。仅涂覆表面涂层与仅涂覆层间涂层对3D打印砂浆的抗折强度提升效果相当;同时涂覆表面及层间涂层对3D打印砂浆的抗折强度提升效果最显著,与无纤维、掺纤维的无涂层试件相比,提升率最高分别可达44.2%、23.2%。涂层对于无纤维3D打印试件层间粘结强度及抗折强度的提升效果优于掺纤维试件。     

不同龄期钢纤维增强水泥砂浆纤维拉拔试验与模拟研究

钢纤维增强水泥基复合材料作为一种多相复合材料,其增强增韧效果的发挥依赖于钢纤维与基体之间的界面粘结性能。通过开展不同龄期的钢纤维增强水泥基复合材料单根纤维拉拔试验及数值模拟研究,分析了龄期对钢纤维增强水泥砂浆界面粘结性能的影响,建立了不同龄期的单根纤维拉拔细观模型,通过将模拟结果与试验结果进行对比验证模型的有效性。根据所建立的细观模型分别对不同龄期钢纤维增强水泥砂浆纤维-基体间的界面粘结作用机理及纤维-基体间粘结表面在纤维拔出过程中的应力变化进行了分析。结果表明:所建立细观模型模拟得到的纤维最大拉拔力及荷载-滑移曲线与试验结果吻合较好,钢纤维的最大拉拔力及钢纤维-水泥砂浆基体的界面粘结强度均随着龄期的增加而增加;在7 d龄期内界面粘结强度的增长速度较快,7 d龄期后增长速度放缓;随着龄期的增加,不同龄期段的界面粘结强度的增长率逐渐减小并趋于稳定。采用拟合得到的粘结表面材料参数能够有效模拟各龄期下单根钢纤维从水泥砂浆中的拔出过程。     

Effect of interfacial weight loss by silver migration on the pullout strength of a silver wire embedded in an adhesive matrix

In this study an effort is made to correlate interfacial weight loss, by migration, from the surface of a silver wire embedded in an adhesive matrix, to bond strength between the silver wire and the adhesive matrix. Comparative studies are also performed using an aluminum an wire in place of silver to accurately assess the effect of interfacial weight loss by silver migration. The results of the pullout tests on silver migrated specimens are compared with pullout tests on silver-wire specimens, which were immersed in water for 2 h but without silver migration. Pullout tests are performed in both wet, and dry conditions of the bonded specimens. It is determined that the pullout strength of bonded silver-wire specimens in wet condition decreases by as much as 86%, subsequent to silver migration. The loss of bond strength for silver-migrated specimens tested in dry condition varies between 23% and 4%, depending on the embedded length used.     

Micromechanics prediction of the transverse tensilc strength of carobn fiber/epoxy composites: The influence of the matrix and interface

Currently, there is great interest in understanding and improving the bond between the fibers and matrix in high performcance composite materials. In many recently developed systems, fiber surface treatments have been developed to improve poor bonding. These treatments are often evaluated by measureing their effect on a composite property sensitive to the interfacial bond strength, typically the composite shear strength. This paper presents an evaluation of the influence of the matrix and interface properties on the transverse tensile strength. These effects were quantified by compring transverse flexural experimental data with results from a finite element micromechanics model. The results indicate that the transverse tensile strength is significantly more dependent upon sizing than is the shear strength. Finally, the transvere flexure test appears to provide an additional and complementary test for evaluating interface bond characteristics.     

Effect of biochemical treatment on the adhesion of poly-p-amidobenzimidazole fibre

In order to improve the interaction between the reinforcement and the matrix binder, fibre surface modification with micro-organisms is proposed. Enzymatic hydrolysis of surface macromolecules in aramid fibres leads to the formation of carboxyl groups. If an aqueous solution containing polyvinyl alcohol is the nutrient for the micro-organisms, hydrolysis is followed by the grafting of alcohol molecules onto the fibre surface through etherification. The fibre strength does not deteriorate, but the morphology and the chemical nature of the surface undergo alterations. As a result, wetting by molten thermoplastics is improved. The three-fibre method was used to investigate the adhesion between poly-p-amidobenzimidazole fibres (unmodified and modified) and thermoplastic matrices (polysulphone and polycarbonate). The biochemical treatment almost doubled the bond strength. Examination of the modified fibres, separated from the matrices, by scanning electron microscopy indicated the presence of a diffuse interphase between the fibre and the matrix. In the case of untreated fibres, the adhesional contact failed through interfacial shear; however, with modified fibres both were observed: interfacial shear and cohesive failure in the fibre. Thus, biochemical modification seems to be a simple method for fibre treatment to promote the compatibility of fibres and matrices, and to increase the composite strength.     

Influence of the roughness of aggregate surface on the interface bond strength

An experimental investigation on the bond strength of the interface between mortar and aggregate is reported. Composite compact specimens were used for applying Mode I and Mode II loading effects. The influence of the type of mortar and type of aggregate and its roughness on the bond strength of the interface has been studied. It has been observed that the bond strength of the interface in tension is significantly low, though the mortars exhibited higher strength. The highest tensile bond strength values have been observed with rough concrete surface with M-13 mortar. The bond strength of the interface in Mode I load depends on the type of aggregate surface and its roughness, and the type of mortar. The bond strength of the interface between mortar M-13 cast against rough concrete in direct tension seems to be about one third of the strength of the mortar. However, it is about 1/20th to 1/10th with the mortar M-12 in sandwiched composite specimens. The bond strength of the interface in shear (Mode II) significantly increases as the roughness and the phase angle of the aggregate surface increase. The strength of mortar on the interface bond strength has been very significant. The sandwiched composite specimens show relatively low bond strength in Mode I loading. The behavior of the interface in both Mode I and Mode II loading effects has been brittle, indicating catastrophic failure.     

Effects of Microwave Processing on Fiber-matrix Adhesion in Composites

Experiments have been done using a single mode (TE₁₁₁, 2.45 GHz) cylindrial microwave cavity with single fiber composite specimens. After obtaining a cure cycle with microwaves to match that achieved with a conventional thermal cure cycle as measured by tensile tests, dynamic mechanical analysis and differential scanning calorimetry, quantitative measurements of interfacial shear strength and physical properties have been carried out and compared with the results from conventional thermally-cured systems. Under the conditions studied for single fiber specimens, the fiber-matrix interfacial shear strength decreases slightly in both glass-epoxy and aramid-epoxy cases as comapared with thermally-cured specimens. Graphite fiber-epoxy adhesion, on the other hand, increases significantly in these single fiber studies in microwave processed specimens as indicated by an increase in the interfacial shear strength. The failure mode changes from interfacial (thermal curing) to matrix failure.     

The Interfacial Bond Strength in Glass Fibre-Polyester Resin Composite Systems Part 2. The Effect of Surface Treatment

The effect of surface treatments on the bond strength in glass fibre-polyester resin composites has been investigated using single fibre interfacial shear strength specimens and the short beam shear test for interlaminar shear strength.

A range of bond strengths was obtained by using, either alone or in combination, the various components of the size formulation which is normally applied to the fibres, so that the interaction between the glass surface and the polyester ranged from Van de Waal forces through hydrogen bonding to covalent bonding, the bond strength increasing in that order.

The relative contribution to bond strength of mechanical bonding due to thermo-mechanical mismatch between the two components and of chemical bonding or physical interaction between the three phases, glass-surface treatment-resin, has been evaluated and found to be one third and two thirds respectively.     

The Temperature Dependence of Interfacial Shear Strength for Various Polymeric Matrices Reinforced with Carbon Fibers

The influence of temperature on the interfacial shear strength between epoxy thermoset matrices and surface treated, carbon AS4 as well as with surface treated and sized AS4-C carbon fibers was investigated. The thermoset matrices all consisted of DGEBA epoxy resin cured with different amine curing agents resulting in matrices with a range of behavior from brittle, elastic to ductile, plastic. For all systems, the results indicate that the interfacial shear strength (ISS) decreases with increasing temperature and as the T_g of the matrix is approached, a large corresponding decrease in the interfacial shear strength is seen. Moreover, the AS4-C (epoxy sized) system revealed a distinct decrease in interfacial shear strength at temperatures lower than the bulk matrix T_g indicating the formation of an interphase layer of composition different from the bulk matrix. Linear superposition methods were used to generate a master curve for the different matrix materials reinforced with the AS4 fibers. These results allow the prediction of ISS at any temperature.     

Effect of α-methyl styrene on curing behaviour and interfacial properties of glass fibre-reinforced vinyl ester resins

The curing behaviour of bismethacryloyl derivative of diglycidyl ether of bisphenol A (vinyl ester VE resin) containing styrene and α-methyl styrene (MS) as reactive diluents was studied. Delayed curing was observed in samples containing increasing proportions of MS. Interfacial shear stress of untreated as well as γ-methacryloyloxy-propyl trimethoxy silane (MTS) treated, glass fibre-reinforced VE resin composites were measured by single fibre technique. In comparison to untreated glass fibres, a 30 – 50% increase in interfacial shear stress was observed in composites based on MTS treated glass fibres. Addition of up to 5 wt.-% MS to VE resin did not affect the interfacial shear strength (ILSS). This behaviour was observed by using ILSS measurement of both glass fabric-reinforced composites as well as single fibre specimens. Further increase in MS to 15 wt.-% resulted in an increase in ILSS and bending stiffness as well as flexural strength.     

Effects of Microwave Processing on Fiber-matrix Adhesion in Composites

Experiments have been done using a single mode (TE₁₁₁, 2.45 GHz) cylindrial microwave cavity with single fiber composite specimens. After obtaining a cure cycle with microwaves to match that achieved with a conventional thermal cure cycle as measured by tensile tests, dynamic mechanical analysis and differential scanning calorimetry, quantitative measurements of interfacial shear strength and physical properties have been carried out and compared with the results from conventional thermally-cured systems. Under the conditions studied for single fiber specimens, the fiber-matrix interfacial shear strength decreases slightly in both glass-epoxy and aramid-epoxy cases as comapared with thermally-cured specimens. Graphite fiber-epoxy adhesion, on the other hand, increases significantly in these single fiber studies in microwave processed specimens as indicated by an increase in the interfacial shear strength. The failure mode changes from interfacial (thermal curing) to matrix failure.     

A Direct Comparison of the Fragmentation Test and the Microbond Pull-out Test for Determining the Interfacial Shear Strength

Experiments were conducted to compare the fragmentation test with the microbond pull-out test for determining the interfacial shear strength between carbon AS4 fibers and a thermoset matrix consisting of a Di-Glycidyl Ether of Bisphenol A (DGEBA) resin cured with a diamine (meta-phenylenediamine, m-PDA) curing agent. The results indicate that, for the microbond test, diffusion of the rather volatile m-PDA curing agent at early stages of cure leads to low values of interfacial shear strengths when compared with results obtained for the same system with the fragmentation test.

With the microbond test, a distinct relationship between the glass transition temperature of the droplets and their size is noticed. Smaller (< 150 μm) droplets have very low Tg's and are incompletely cured. While changing to a modified curing cycle and/or using a m-PDA-rich curing environment alleviates the diffusion problem, the interfacial shear strength values are still not in good agreement with the fragmentation test results. Microbond data from another system consisting of DGEBA resin cured with a different, less volatile dimaine curing agent indicates that diffusion of the curing agent becomes less severe as the volatility of the curing agent decreases and the corresponding microbond interfacial shear strengths agree better with fragmentation test results.     

Experimental Investigation of Aluminum/Epoxy Interfacial Properties in Shear and Tension

This paper presents the results of comprehensive testing to characterize the effect of several different surface treatments on shear and tensile bond strength between 7075-T6 aluminum and two epoxy systems: EPON 815/V40 and EPON 828/Z. A rod pull-out test was used to determine interfacial shear strength, modeled after similar tests on reinforced concrete. The tensile bond strength was characterized using a tension test fixture designed in this study. Overall, the interfacial shear strengths were higher than the tension strengths. Surface knurling gave the highest interfacial shear strength, representing a 72% increase over untreated specimens. Phosphoric acid anodization (PAA) was also quite effective in shear. In tension, the highest strength was obtained from specimens treated with the PAA process along with a silane coupling agent. These specimens showed an increase in interfacial tensile strength by a factor of 5.6.     

The Interfacial Bond Strength in Glass Fibre-Polyester Resin Composite Systems

The interfacial bond strength in glass fibre-polyester resin composites has been investigated using various experimental techniques. These included blocks of resin containing fibre (in which, depending on the geometry of the specimen, failure occurs in either a shear or tensile mode) the pullout of a fibre from a disc of resin and a short beam shear test for interlaminar shear strength determination.

Low power optical microscopy and optical retardation measurements of stress induced birefringence were used to detect the difference between intact and debonded fibre resin interfaces. The shear modulus and shear strength of the resin were obtained from torsion tests on cylindrical rods of the resin.

The single fibre shear debonding specimen and the short beam shear test are shown to be the most viable test methods but interpretation of the results is complicated by the various modes of failure possible and by the different stress states which exist in the area of the specimen where debonding starts. Stress concentration factors obtained by finite element analysis and photoelastic analysis have been applied to the results from these tests and the corrected interfacial bond strengths are in close agreement.

The real interfacial bond strengths of well bonded glass-fibre polyester resin systems is shown to be of the order of 70 MN m^-2.     

The Interfacial Bond Strength in Glass Fibre-Polyester Resin Composite Systems

The interfacial bond strength in glass fibre-polyester resin composites has been investigated using various experimental techniques. These included blocks of resin containing fibre (in which, depending on the geometry of the specimen, failure occurs in either a shear or tensile mode) the pullout of a fibre from a disc of resin and a short beam shear test for interlaminar shear strength determination.

Low power optical microscopy and optical retardation measurements of stress induced birefringence were used to detect the difference between intact and debonded fibre resin interfaces. The shear modulus and shear strength of the resin were obtained from torsion tests on cylindrical rods of the resin.

The single fibre shear debonding specimen and the short beam shear test are shown to be the most viable test methods but interpretation of the results is complicated by the various modes of failure possible and by the different stress states which exist in the area of the specimen where debonding starts. Stress concentration factors obtained by finite element analysis and photoelastic analysis have been applied to the results from these tests and the corrected interfacial bond strengths are in close agreement.

The real interfacial bond strengths of well bonded glass-fibre polyester resin systems is shown to be of the order of 70 MN m^?2.