The relationship between substrate roughness parameters and bond strength of ultra high-performance fiber concrete

The bonding that exists between the old concrete and the new concrete depends largely on the quality of substrate surface preparation. The accurate representation of substrate surface roughness can help determine very precisely the correct bonding behavior. In this work, an experimental investigation was carried out to quantify the normal concrete (NC) substrate roughness parameters and evaluate their relationship with the bonding performance of ultra high-performance fiber concrete (UHPFC), used as a repair material. The bond strength was quantified based on the results of the pull-off test, splitting cylinder tensile test, and the slant shear test. Three types of NC substrate surface preparation were used: as-cast (without surface preparation) as reference, wire-brushed, and sand-blasted (SB); the roughness of which was determined using an optical three-dimensional (3D) surface metrology device (Alicona Infinite Focus). It was observed from the result of the pull-off test that failure occurred in the substrate, even though adequate substrate surface roughness was provided. Moreover, analysis of the splitting cylinder tensile and slant shear test results showed that the substrate surface preparation method had a significant influence in bonding strength between UHPFC and the NC substrate. The composite UHPFC/NC substrate having a SB surface behaved closely as a monolithic structure under splitting and slant shear tests. An excellent correlation (R ²?>?85%) was obtained between the substrate roughness parameters and the results of the splitting cylinder tensile and slant shear tests.     

新老混凝土修补界面过渡区微细观结构改善方法的研究

针对新老混凝土修补界面薄弱过渡区的特点，提出改善方法，既选用适量浓度HCl和时间酸洗老混凝土界面，以显著提高老混凝土界面的微细观糙度，并不过度损务界面；在水泥净浆界面剂中加入粉灰和砂，以大幅度减少过渡区的收缩和粗大晶体含量，对比实验结果表明，以上两项措施，使老混凝土比表面积显著增加，过渡区微细观结构显著改善，粘结强度显著增高。     

A way for improving interfacial transition zone between concrete substrate and repair materials

An attempt to modify the repair interfacial transition zone by introducing fly ash into a primer between concrete substrate and repair materials was proposed. A comparison test was carried out for five different bond interfaces coated with five kinds of primers, namely neat cement paste, expansive paste, cement mortar, water-dispersible epoxy resin, and fly ash-modified mortar. The test results showed that the fly ash-modified primer made the microstructure of the repaired interface zone more dense and uniform. As a result, the splitting bond strength of the interface coated with the fly ash-modified primer was significantly higher than those coated with the other kinds of primers.     

Molecular simulations of deformation and failure in bonds formed by glassy polymer adhesives

The mechanical behavior of glassy polymer bonds is examined with molecular dynamics simulations. We show that the interfacial strength of the bond in mode I (tensile) and mode II (shear) fracture is strongly influenced by the coupling between the adhesive and adherends as well as by the roughness of the substrate surface. Failure occurs at the substrate (interfacial failure) when the interaction is weak, and in the bulk (cohesive failure) when the interaction is strong. The transition from interfacial to cohesive failure under mode I loading is nearly unaffected by roughness, while roughness leads to a dramatic increase in interfacial strength under mode II loading. Stress mixity is another crucial parameter that determines whether the polymer fails through shear deformation or through cavitation and crazing. By varying the geometry of the adhesive bond, we illustrate different limiting behaviors of a rupturing film.     

UHPC与普通混凝土试件界面黏结抗冻性能试验研究

超高性能混凝土(UHPC)因为其较高的强度和优良的耐久性被认为是极具潜力的结构修补用材料之一。同时,UHPC与普通混凝土(NC)之间的界面黏结性能,是影响UHPC在混凝土加固修复工程中应用可靠性的关键因素。针对严寒环境,本试验对超高性能混凝土与普通混凝土(以下简称UHPC-NC)黏结试件开展－60 ℃的冻融循环试验,分析冻融循环后试件的宏观形态变化、质量变化率。通过黏结强度试验,获得界面的黏结强度以及相应的界面破坏模式。试验主要分析－60 ℃冻融循环对UHPC-NC试件界面黏结性能的影响,以及界面的不同处理方式(钢丝刷刷毛、高压水射流冲毛及劈裂)对抗－60 ℃冻融循环作用的影响,同时,对冻融作用下UHPC-NC试件的界面损伤机理进行初步探索。试验结果表明:－60 ℃冻融循环对UHPC-NC试件黏结强度有较大影响,劈裂组试件的界面黏结强度在经历10次、15次、20次冻融循环后分别下降为界面黏结基准强度的72.94%、55.62%及44.33%,界面黏结强度呈现先急速下降再缓慢下降的趋势;界面粗糙度越高,界面的剩余黏结强度越大,经历20次冻融循环后,劈裂组试件的剩余黏结强度为高压水射流冲毛试件的2.03倍。     

A new way to increase the long-term bond strength of new-to-old concrete by the use of fly ash

The short-term and long-term bond strengths of new-to-old concrete were experimentally investigated with an emphasis on the influence of new concretes and binders. These new concretes included ordinary Portland cement concrete, expansive concrete and high-volume fly ash concrete, while the binders included pure cement paste (C-binder), expansive binder (E-binder) and fly ash mortar (F-binder). The results showed that the short-term bond strength of all specimens with fly ash concrete was lower than that with ordinary Portland cement concrete, which in turn was lower than that with expansive concrete. The bond strength of the specimens with F-binder was the lowest at the age of 7 days. However, the long-term bond strength of all specimens with added fly ash was the highest and strength losses were observed in the specimens repaired with expansive concrete or E-binder at the age of 3 years. The microstructure of the transition zone with F-binder was also studied by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) at the ages of 28 days and 1 year, respectively.     

Compatibility of silorane composite repaired with methacrylate-based restorative systems

The aim of this study was to evaluate the repair bond strength of silorane composites using either the silorane or methacrylate-based restorative systems. Expired silorane composite was used as the substrate material in all experimental groups. Silorane blocks (5?×?5?×?4?mm) were fabricated and stored at 37?°C for 24?h. Six experimental groups were developed according to the repair: I-silorane composite (no intermediary); II-P90 Bond/Silorane; III-P90 Adhesive System (primer/bond)/silorane; IV-P90 bond/Scotchbond Universal/methacrylate composite (Filtek P60); V-Scotchbond Universal/methacrylate; and VI-silane/Adper Single Bond 2/methacrylate. The repaired blocks were stored for 24?h at 37?°C, and then sectioned, yielding stick-shaped specimens (0.5?mm²) that were tested in tensile (0.5?mm/min). The results were analyzed using ANOVA/Tukey test (α?=?0.05). The interfacial micromorphology and nanoleakage were also analyzed under SEM. Scotchbond Universal/methacrylate composite, either associated with the P90 bond or not, exhibited similar bond strength to that of P90 Adhesive System/silorane composite. Scotchbond Universal either associated with the P90 Bond or not to repair the silorane allowed no pre-testing failures. The worst scenarios were repairing the silorane with no intermediary (G-I) or combination silane/Adper Single Bond 2/methacrylate composite (G-VI) that presented significantly lower bond strengths and higher incidences of pre-failure testing. The importance of the silane was not confirmed. Characteristic micromorphology and no signs of nanoleakage were identified in all experimental groups. The silane-containing, phosphorylated methacrylate-based adhesive associated with a methacrylate composite was proven to reliably repair the expired composite in a similar way to that of the application of dedicated silorane adhesive.     

混凝土修复中水分交换对水泥水化、微观结构和界面黏结强度的影响(英文)

修复材料浇注到旧混凝土上后,在毛细作用驱动下修复材料和旧混凝土之间存在水分交换。此过程会引起修复材料中水含量的变化,从而影响修复材料的水化过程和微观结构以及界面的黏结强度。研究了修复材料和旧混凝土之间水分交换对修复材料的水化程度、孔隙率和黏结强度的影响。结果表明:饱和的旧混凝土可以为修复材料提供更多的水,促进了修复材料的水化。当旧混凝土不饱和时,不饱和的旧混凝土从修复材料里吸取大量的水分,导致修复材料水灰比降低。因此,修复材料的水化程度和孔隙率也降低了。同时,降低的水灰比提高了界面的黏结强度。     

Effects of styrene–acrylic emulsion on bond performance and interface microstructure of repair mortar of ternary cementitious system

This study investigates the effects of styrene–acrylic emulsion (SAE) as a modifier and interfacial agent on the interfacial bond performance of ordinary Portland cement–aluminate cement–gypsum (PAG) repair mortar. The hydration products and interfacial microstructure are analyzed via x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The results demonstrate that the addition of SAE can effectively enhance the tensile bond strength and flexural bond strength of the PAG repair mortar, and the optimal addition amount of SAE is 10 wt%. The tensile and flexural bond strengths of the PAG repair mortar with SAE interfacial agent at 40% concentration are 1.38 and 1.34 times than those of the mortar without the interfacial agent, respectively. XPS and FTIR analyses reveal that the carboxyl groups in SAE and Ca²⁺ generated from cement hydration form Ca²⁺–carboxyl complexes. The SEM and XRD analyses indicate that SAE can alter the distribution and size of crystals at the bond interface and considerably reduce the thickness of the bond interface; however, SAE cannot change the type of hydration products at the bond interface.     

预制与后浇混凝土粘结的劈拉性能试验研究

通过对预制与后浇混凝土粘结的劈拉试验研究,分析了后浇混凝土的浇筑方式、粘结面粗糙度及温度对混凝土粘结劈拉性能的影响规律。结果表明：同种工况条件下,水平向浇筑混凝土粘结劈拉强度明显大于竖直向浇筑粘结劈拉强度,粘结劈拉强度随粘结面的粗糙度的增加而显著增大,随温度的升高而急剧下降,到300℃时,比常温下降了50％。为阐明混凝土粘结劈拉机理提供详实的数据支撑,并为装配式混凝土结构发展提供参考。     

化学溶液预处理再生粗骨料对再生混凝土改性的影响

为研究不同浓度的硅酸钠溶液和硅烷溶液复合改性再生粗骨料对再生混凝土力学与变形性能及微观结构的影响,通过立方体抗压强度试验研究复合改性对再生混凝土力学性能的影响,同时基于数字图像相关(DIC)方法研究复合改性对再生混凝土变形性能的影响,并借助扫描电子显微镜(SEM)和能谱仪(EDS)微观测试方法分析改性再生混凝土内部微观结构。结果表明:质量分数为5%的硅酸钠溶液和质量分数为10%的硅烷溶液改性后的再生粗骨料24 h吸水率降幅最大,由其制成的再生混凝土28 d抗压强度显著提高,较未改性再生混凝土提高了35.80%;硅酸钠溶液和硅烷溶液复合改性再生粗骨料可有效减小再生混凝土的变形,应力较大时,可阻止应力过度集中,使再生混凝土整体变形性能较好;此外,还可以改善再生粗骨料表面疏松结构和粗糙程度,加强骨料与砂浆界面过渡区(ITZ)性能,但对于新、旧砂浆ITZ性能的改善不明显。     

Adhesion of Different Concrete Repair Systems Exposed to Different Environments

This article presents the results of experiments conducted to assess the effects of aging under dry laboratory conditions, underwater storage, cyclic freeze-thaw, and temperature changes on the adhesion between the repair and the substrate concrete. The repair systems considered for these studies included ordinary sand/cement (S/C) mortar, with and without bonding agents, two polymer modified cementitious mortars, and two resinous mortars. The specimens were concrete slabs of 600 × 300 × 100 mm dimensions with saw cut face 600 × 300 mm on which a repair layer of 20 mm had been applied. In order to eliminate the effects of surface texture and surface strength of the concrete on the adhesion of repair systems, repair applied surfaces were all saw cut surfaces of concrete with 28-day design compressive strength of 65 MPa. Tensile bond strengths of these specimens were measured using a direct tensile test (pull-off) method. The results indicated that the tensile bond strengths of different repair systems under dry laboratory conditions, and stored underwater, ranged from 1.51 to 5.27 Mpa. Exposure to 300 cycles of freeze-thaw and to 200 cycles of temperature changes resulted in 6 to 100 percent reduction in their tensile bond strengths.     

Adhesion of Different Concrete Repair Systems Exposed to Different Environments

This article presents the results of experiments conducted to assess the effects of aging under dry laboratory conditions, underwater storage, cyclic freeze-thaw, and temperature changes on the adhesion between the repair and the substrate concrete. The repair systems considered for these studies included ordinary sand/cement (S/C) mortar, with and without bonding agents, two polymer modified cementitious mortars, and two resinous mortars. The specimens were concrete slabs of 600 × 300 × 100 mm dimensions with saw cut face 600 × 300 mm on which a repair layer of 20 mm had been applied. In order to eliminate the effects of surface texture and surface strength of the concrete on the adhesion of repair systems, repair applied surfaces were all saw cut surfaces of concrete with 28-day design compressive strength of 65 MPa. Tensile bond strengths of these specimens were measured using a direct tensile test (pull-off) method. The results indicated that the tensile bond strengths of different repair systems under dry laboratory conditions, and stored underwater, ranged from 1.51 to 5.27 Mpa. Exposure to 300 cycles of freeze-thaw and to 200 cycles of temperature changes resulted in 6 to 100 percent reduction in their tensile bond strengths.     

Surface characteristics and adhesion performance of black oxide coated copper substrates with epoxy resins

Black oxide is a conversion coating applied onto the copper substrate to improve its interfacial adhesion with polymeric adhesives. A comprehensive study is made to characterize the black oxide coating using various characterization techniques, including SEM, XPS, AFM, XRD, Auger electron spectroscopy, TEM, D-SIMS, RBS and contact angle measurements. It was found that the oxide coating consisted of cupric and cuprous oxide layers from the top surface to inside. The cuprous oxide layer was formed on the copper crystal surface, on which densely-packed fibrillar cupric oxide grew continuously until saturation. The cupric oxide had a fibrillar structure with high roughness at the nanoscopic scale, whereas the cuprous oxide was rather flat and granular. There was a continuous change in oxide composition with no distinct boundary between the two oxide layers. The bond strength between the epoxy resin and the oxide coated copper substrate increased rapidly at a low level of oxide thickness, and became saturated at thicknesses greater than about 800 nm. There were similar dependences of bond strength on surface roughness, oxide thickness especially of cupric oxide and surface energy, reflecting the importance of these surface characteristics in controlling the interfacial adhesion.     

Effects of Cyclic Loading,Freeze-Thaw and Temperature Changes on Shear Bond Strengths of Different Concrete Repair Systems

An experimental study was performed to evaluate the residual shear bond strengths between different cementitious and resinous repair materials and substrate concrete after being subjected to cyclic loading, freeze-thaw, and temperature changes. In this paper, techniques and results of test methods that induce shear along the repair/concrete interface are discussed. In addition to the effect of surface preparation on the strength of the old concrete surface, which proved the saw cut surface as the most suitable substrate concrete for shear bond strength assessment, by means of cylindrical shear and friction-transfer methods, the effects of cyclic loading, freeze-thaw, and temperature changes on the shear bond strengths of six different repair systems are illustrated. Analysis of the results indicated that: in order to avoid fatigue failure, the maximum safe stress level to be applied should be between 20 to 40% of the original shear bond strength of the repair system, and the critical stress level differs for different repair materials; 300 freeze-thaw cycles can reduce the shear bond strength of a resin mortar by up to about 80%; and 200 cycles, of temperature changes can reduce the original shear bond strength of a cementitious mortar by up to about 90%.     

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.     

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.     

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.     

Degradation of concrete by flue gases from coal combustion

The effect of flue gases from coal combustion on the concrete shell of a power plant stack was analyzed and the damage to the concrete was evaluated. The compressive and tensile strengths of concrete were determined by rebound hammer test and pull-off test on the site. Samples of concrete taken from various zones of the stack shell were analyzed in detail. The examination techniques used included chemical analysis, water suspension analyses, XRD, thermal analysis, SEM and EDS. It was found that the flue gases and the acid condensate, acted very aggressively at an elevated temperature and caused severe degradation of the inside surface zone of the concrete shell. The binding material in this zone was converted into sulfur-bearing compounds. Gypsum was identified as the dominant compound in the degraded zone of concrete in the upper parts, while anhydrite in the lower parts of the stack. Carbonated zone was located below the clearly delimitated sulfated zone of the concrete. The aggressive environment in the stack did not affect the internal zones in the concrete.     

基于细观尺度的再生混凝土性能研究综述

基于当前国内外学者对再生混凝土性能试验的结果,研究骨料、砂浆、界面过渡区等细观参数对再生混凝土宏观性能影响.在骨料方面,骨料分布的均匀程度高、颗粒级配较好、大中型骨料颗粒数越多的再生混凝土在抗拉、抗压、抗折强度及弹性模量等方面都会有所提高;在砂浆方面,随着新、老砂浆的强度提高,再生混凝土力学性能更好,老砂浆厚度越高,再生混凝土内部氯离子浓度越大;在界面过渡区方面,随着新、老界面过渡区弹性模量的提高,再生混凝土的性能表现地越好,界面过渡区厚度越大,氯离子扩散系数越大.