BFRP筋碱激发混凝土粘结性能试验研究与数值模拟

玄武岩纤维增强复合筋(BFRP筋)碱激发混凝土为海洋环境下混凝土的耐久性提供安全保障。在其中心拉拔试验的基础上,采用分离式模型,运用ABAQUS有限元软件进行粘结滑移性能数值模拟与分析。通过试验数据,得出适用于BFRP筋碱激发混凝土的粘结滑移本构模型以及碱激发混凝土的塑性损伤模型,构建了基于非线性弹簧单元的数值模型,试验结果与计算结果吻合程度较好,验证了模型的准确性。试验与模拟结果表明:粘结长度为2.5d、5d(d为BFRP筋直径)的试件均发生筋材拔出破坏,粘结长度为10d的试件均发生劈裂破坏;BFRP筋与碱激发混凝土之间的粘结应力分布并不均匀,随着粘结长度和筋材直径的增大,极限粘结强度逐渐减小;当BFRP筋直径d=12 mm,粘结长度为2.5d、5d和10d的碱激发混凝土试块极限粘结强度分别为13.92 MPa、13.56 MPa和12.60 MPa,较相同粘结长度的普通混凝土试件,其极限粘结强度分别提高6.58%、10.97%和9.76%。     

表面内嵌FRP筋混凝土粘结-滑移本构关系试验研究

通过对一组表面内嵌FRP筋混凝土试件进行拉拔试验,分析表面内嵌FRP筋混凝土的受力过程和破坏模式;研究FRP筋直径、粘结长度和FRP筋类型等因素对粘结滑移性能的影响。结果表明,试件的破坏模式表现为FRP筋与结构胶界面破坏、结构胶与混凝土界面剥离、FRP筋被拉断和结构胶劈裂四种破坏模式;内嵌BFRP筋试件的粘结应力随粘结长度的增长而增大,而内嵌GFRP筋试件的粘结应力随粘结长度的增长而减小。因FRP筋泊松比的降低和剪切滞后效应,试件的粘结应力随着FRP筋直径的增大而减小。同时,对试验结果进行处理分析,建立了一种适用于表面内嵌FRP筋混凝土粘结-滑移本构关系模型,并给出模型特征点的数学表达式,将拟合曲线与试验曲线进行对比分析。结果表明,该本构关系能够较为准确地模拟表面内嵌FRP筋混凝土的粘结滑移性能。     

BFRP侧向约束对GFRP带肋筋与混凝土粘结性能的影响

为考察BFRP侧向约束对GFRP带肋筋与混凝土粘结性能的影响,对36个GFRP筋混凝土拉拔试件进行试验研究,主要试验参数为BFRP侧向约束层数(0层、1层、2层和3层)和混凝土相对保护层厚度c/d(1.6、2.2和3.0)。试验结果表明:BFRP侧向约束使拉拔试件的破坏模式由混凝土劈裂破坏转为GFRP带肋筋的拔出破坏;试件的粘结强度和达到粘结强度所对应的滑移量、侧向约束应力会随BFRP侧向约束层数的增加而增大;相同BFRP侧向约束层数下,相对粘结强度随着c/d的增大而增大,但达到粘结强度所对应的侧向约束应力却随c/d的增大呈指数减小;相对粘结强度增加量随着达到粘结强度时侧向约束应力的增加呈对数增加。     

冻融循环下纤维再生混凝土与BFRP筋粘结强度试验研究

为了研究纤维再生混凝土和BFRP筋间的粘结强度,本文通过54个试件中心拉拔试验,研究单掺玄武岩纤维、聚丙烯纤维、混杂玄武岩-聚丙烯纤维和冻融循环对再生混凝土与BFRP筋粘结强度的影响.结果表明:单掺玄武岩或是聚丙烯纤维都会不同程度地降低粘结强度,但降低效果不显著;掺入混杂纤维时,若体积掺量小于某一临界值,可以提高粘结强度,但掺量过多时,粘结强度降低;在冻融循环条件下由于冻融次数增加,混凝土会发生二次水化作用,导致极限粘结强度得到提高.     

BFRP筋与分级粒径河砂ECC粘结滑移性能试验研究

通过玄武岩纤维增强复合材料(BFRP)筋/高延性水泥基复合材料(ECC)的中心拉拔试验,分析了分级粒径ECC和BFRP筋表面形式及直径对BFRP筋/ECC粘结性能及粘结-滑移曲线的影响。结果表明,BFRP筋/ECC的破坏模式分为BFRP筋拔出破坏和BFRP筋拉伸破坏。选取BFRP筋/ECC粘结-滑移曲线中的残余波浪段各峰值应力点,采用拟合直线斜率的绝对值|k|表征ECC对BFRP筋横肋的磨损程度,当|k|值≥0.144时,BFRP筋横肋会被完全磨损,当|k|值＜0.144时,BFRP筋横肋会被磨损至与填充其凹陷的ECC齐平。BFRP筋/ECC的平均粘结强度随骨料粒径的变化并不显著,分级粒径ECC可使BFRP筋/ECC的平均粘结强度提高3.2%~9.6%,采用骨料粒径为0.15~0.3 mm的BFRP筋/ECC粘结性能最优。BFRP筋的直径越大,BFRP筋/ECC的平均粘结强度越小,BFRP筋直径为12 mm的BFRP筋/ECC平均粘结强度与BFRP筋直径为8 mm、10 mm的BFRP筋/ECC相比降低分别约8.2%、4.4%。采用浅螺纹BFRP筋的BFRP筋/ECC,平均粘结强度下降83.7%,但其整体粘结应力变化较为平稳,对ECC和BFRP筋的损伤程度均最小。减小BFRP筋直径、ECC骨料粒径,或BFRP筋/ECC自由端处BFRP筋的肋深,有助于提高BFRP筋/ECC的粘结性能及稳定性。     

玄武岩纤维增强塑料筋混凝土黏结性能的梁式试验研究

设计制作了14个玄武岩纤维增强塑料筋（BFRP筋）混凝土梁式试件和2个钢筋混凝土梁式试件,通过梁式试验分析了影响BFRP筋混凝土黏结性能的主要因素。结果表明,（1）BFRP筋的受力过程可分为微滑移段、正常滑移段、加速滑移段和下降段;（2）当BFRP筋的锚固长度相同时,随着混凝土强度的提高,黏结强度随之增大;（3）当混凝土强度相同时,随着BFRP筋锚固长度的增加,黏结强度明显减小,并且试件的破坏模式也发生了改变;（4）BFRP筋直径的大小对黏结强度的影响不明显;（5）当筋直径、锚固长度和混凝土强度相同时,BFRP筋混凝土的黏结强度与钢筋混凝土基本相当;（6）BFRP筋的外形对BFRP筋混凝土的黏结性能有着较大的影响。     

温度对芳纶复合材料与混凝土抗剪切粘结强度影响的试验研究

用21个试件,测定了芳纶复合材料(AFRP)与混凝土之间的抗剪粘结强度,通过改变温度,研究了温度对AFRP与混凝土间抗剪切粘结强度的影响。研究表明:在-40～60℃之间的温度段内,其抗剪切粘结强度变化较小,破坏形态均为混凝土试块的破坏;而当温度达70℃时,抗剪切粘结强度降低程度非常大,且破坏形态发展为树脂与混凝土粘结层的破坏。     

GFRP筋与混凝土粘结性能试验研究

基于40个试件的试验,对GFRP筋试件和钢筋试件的粘结破坏进行了研究。试验结果表明,拔出端存在明显的应力集中现象;两种试件的破坏粘结强度接近,仅与混凝土的极限拉应力有关;破坏过程中GFRP试件比钢筋试件表现出了更好的延性。本文提出了筋材的混凝土保护层临界厚度确定公式,考虑了影响临界厚度的主要因素:即筋材粘结强度、混凝土单轴抗拉强度和筋材直径,建议GFRP筋混凝土保护层厚度不能简单采用钢筋混凝土的,即应通过试验提出合理的取值。     

型钢与地聚合物混凝土粘结滑移性能研究

为了研究型钢与地聚合物混凝土之间的粘结滑移规律,对9个型钢地聚合物混凝土柱试件进行推出试验,研究地聚合物混凝土抗压强度、型钢的保护层厚度、型钢的锚固长度以及配箍率四个参数对型钢地聚合物混凝土试件荷载-滑移曲线、破坏形态以及粘结滑移性能的影响。结果表明:试件的荷载-滑移曲线具有相同的发展趋势,可将其划分为无滑移段、荷载上升段、荷载下降段和水平残余段四个阶段;试件的破坏模式为混凝土劈裂破坏,劈裂裂缝从加载端型钢翼缘产生,并向自由端发展;随着地聚合物混凝土抗压强度、型钢的保护层厚度和配箍率的提高,试件的特征粘结强度呈上升趋势;与普通水泥型钢混凝土不同,型钢的锚固长度增大也会使试件的特征粘结强度提高。根据试验结果,建立了特征粘结强度的计算公式,提出了型钢地聚合物混凝土的粘结-滑移本构模型,采用该模型计算得到的型钢地聚合物混凝土粘结-滑移曲线与试验曲线吻合度较高。     

钢纤维改性橡胶混凝土与变形钢筋的粘结性能

本试验共设计制作4组钢纤维(钢纤维体积率分别为0%、0.5%、1.0%、1.5%)改性橡胶混凝土粘结试件,采用中心拉拔试验的方法,系统研究了钢纤维体积率的变化对粘结破坏形态、初始粘结强度、极限粘结强度以及粘结滑移曲线的影响规律。研究结果表明:随着钢纤维体积率的增大,与橡胶混凝土相比,初始粘结强度分别提高了5.37%、8.35%、0.89%,极限粘结强度分别提高了9.44%、16.49%、12.91%。适量掺入钢纤维可以显著改善粘结试件的破坏形态。上升段、下降段以及残余段共同组成钢纤维改性橡胶混凝土的粘结滑移曲线,且粘结滑移曲线的饱满程度以及上升段斜率随着钢纤维体积率的增加而增加。基于试验结果,建立了钢纤维改性橡胶混凝土与变形钢筋的粘结滑移本构方程,该方程能为其在结构设计中提供一定的参考。     

One-year bonding performance of one-bottle etch-and-rinse adhesives to dentin at different moisture conditions

Abstract

This study aimed to investigate the one-year bond strengths to dentin of one-bottle etch-and-rinse adhesive systems applied under different moisture conditions. Class V cavities were prepared in bovine incisors and randomly allocated (n?=?8) according to the type of adhesive system used – SB (Adper? Single Bond 2); PB (Prime & Bond 2.1); and XPB (XP Bond) – and the moisture condition kept in the cavity – moist, over-wet, and over-dry. Filtek? Z250 was used for teeth restoration. Specimens for microtensile bond strength (µTBS) test were obtained and stored in water for 24?h or 1?year, and submitted to mechanical testing. Data were analyzed using t-tests, ANOVA and the Holm–Sidak post hoc test (α?=?0.05). Weibull analysis was used to verify the reliability of specimens. The type of adhesive and the moisture condition of the substrate affected the µTBS. At 24?h, SB performed better under the moist and over-wet conditions. At 1?year, SB, PB, and XPB showed the greatest percentage reduction at the moist (～38%), over-wet (100%), and over-dry (100%) conditions, respectively. The reliability of adhesives was affected by the variable factors tested. In conclusion, the solvent composition of adhesives and the moisture condition of the substrate play an important role in the bond strength and bonding stability of resin-based restorations, as well as on the reliability of the adhesive interfaces over time.     

Effect of adhesive type and composite viscosity on the dentin bond strength

Objectives: Evaluate the influence of composite resins viscosity and type of cure of the adhesive systems on the bond strength of composite resins submitted to artificial aging.

Methods: Dentin specimens (n = 240) were divided into 2 groups: Group GC: GrandioSO, and Group GF: GrandioSO Heavy Flow. These groups were subdivided into 6: FM: Futurabond M – light cured, FDCC: Futurabond Dual Cure – chemical cured, FDCL: Futurabond Dual Cure – light cured, CS3: Clearfil S3 – light cured, CDCC: Clearfil Dual Cure – chemical cured, and CDCL: Clearfil Dual Cure – light cured. Resin blocks were build up on the dentin surface. Half of samples on each group were cut to obtain resin/dentin sticks (1 × 1 mm). The other half was first submitted to thermomechanical aging. The dentin/resin sticks were submitted to microtensile bond strength test and the results were analyzed using three-way ANOVA and Tukey’s test (α = 5%).

Results: ANOVA showed significant influence for adhesive (p = 0.0000) and aging (p = 0.0001). No significant influence of the composite viscosity on bond strength was observed (ANOVA: p = 0.0861). For adhesive, the results of Tukey’s test (MPa) were CDCC: 13.44 (±5.13)a; FM: 14,01 (±2.71)a; CDCL: 14.51 (±4.98)a; FDCC: 18.66 (±7.13)b; CS3: 18.80 (±6.50)b; FDCL: 19.18 (±7.39)b. For aging: AGED: 14.99 (±6.32)a; NOT AGED: 17.87 (±5.97)b.

Conclusion: Composite resin viscosities did not influence on the bond strength. Type of cure of the adhesives had influence on the bond strength. Thermomechanical aging decreased the bond strength.     

Performance of protein-based wood bioadhesives and development of small-scale test method for characterizing properties of adhesive-bonded wood specimens

A small-scale test method to measure the tensile strength of adhesive-bonded wood strip specimens was developed by simple modification of commercially available binder clips. As bioadhesives, soy protein concentrate (SPC) and gelatin resins were prepared and were evaluated for shear and tensile bond strengths of bamboo and maple wood-bonded specimens. Titebond-II (TB-II), a commercially available wood glue was also tested to compare its bonding property to SPC and gelatin-based bioadhesives. TB-II glue showed the highest shear and tensile bond strengths with both bamboo and maple wood strips. Hot-pressing increased the shear and tensile bond strengths of SPC resin with wood specimens by 500% while the increase for gelatin resins was up to 200%. Roughness profile and surface properties were also characterized with an optical interferometric profiler and a scanning electron microscope. The results indicated that rougher surface significantly increased the bond strengths in both shear and tensile modes.     

基于BP神经网络的HPFL加固层与混凝土粘结强度预测

根据HPFL加固层和加固混凝土构件之间的243个正拉粘结强度试验测试和24个剪切粘结强度试验测试,将影响二者粘结强度的主要因素,如抹灰龄期、加固界面粗糙度、混凝土和砂浆强度、修补方位等作为特征参数,建立了预测HPFL加固层与混凝土粘结强度的BP人工神经网络模型.采用训练好的BP神经网络对HPFL加固层与混凝土粘结强度进行了预测,并与实测值进行了对比.正拉粘结强度预测值与试验值之比的平均值为1.056,标准差为0.057;剪切粘结强度预测值与试验值之比的平均值为0.988,标准差为0.127.结果表明:预测值与试验值符合良好,利用BP神经网络对HPFL加固层与混凝土粘结强度进行预测是可行的.     

Ultrasonic analysis of nonlinear response and strength of adhesive bonds

A theoretical investigation has been carried out to obtain information on the adhesive bond strength from ultrasonic test results. It is postulated that failure of an adhesive bond is preceded by nonlinear behavior in thin boundary layers at the interfaces of the adhesive and the adherends. The nonlinear adhesive bond behavior is represented by a relation between tractions and gross displacement increments across the adhesive layer. Intertia of the adhesive layer is taken into account, and the effect of a nonlinear adhesive response on the reflection and transmission of longitudinal waves is investigated for the case of normal incidence. A procedure is presented to obtain the nonlinear relation from reflected wave results. As an alternative to a completely nonlinear analysis, the case of prestressing the adhesive layer in the nonlinear range and superimposing a small ultrasonic disturbance has been considered, but the inertia of the adhesive is neglected for this case. For this case, the propagation of interface waves and horizontally polarized plate waves is discussed. Finally, for the nonlinear case the generation of higher harmonics has been investigated, and it has been shown that certain nonlinear parameters can be obtained from the spectrum of higher harmonics.     

矿渣掺量对胶砂和混凝土强度的影响

本文研究了矿渣掺量对胶砂强度、混凝土强度和混凝土与钢筋的粘结强度的影响.在水泥胶砂或粉煤灰-水泥胶砂中,用矿渣取代部分水泥后,胶砂3d强度会降低,且随取代量增加,胶砂3d强度逐渐降低.在水泥胶砂或粉煤灰-水泥胶砂中,当矿渣取代水泥量≤55％时胶砂28 d强度会增加,但矿渣取代水泥量至60％时胶砂28 d强度会下降.在水泥混凝土或粉煤灰-水泥混凝土中,当矿渣取代水泥量≦50％时混凝土28 d强度及其与钢筋的粘结强度会提高,但矿渣取代水泥量≥60％时混凝士强度和粘结强度会降低.     

Absence of correlation of hydrogen bond donor ability with acid strength and catalytic activity of acid catalysts

Two liquids, acetic acid and hexafluoroisopropanol (HFIP), and two solids, silica gel and polymethacrylic acid (PMA), were compared for hydrogen bond donor ability, acid strength, and catalytic activity in typical acid‐catalyzed reactions, inversion of sugar and cleavage of acetone dimethyl ketal. In each pair, the weaker acid (HFIP and silica gel, respectively) was much the stronger hydrogen bond donor, but was totally devoid of catalytic activity, which the poor hydrogen bond donor but stronger acids (acetic and methacrylic acid, respectively) exhibited. A strong hydrogen bond donor (e.g., HFIP) enhances, however, the catalytic activity of the acid catalyst (AcOH). Thus, hydrogen bond donor ability is not a measure of acid strength. A correlation of the two properties is possible only when each group (acids and bases) involved in the comparison consists of very close structural relatives. Such a correlation cannot be extrapolated to any other case. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-efficiency self-repairing polyurethane based on synergy of disulfide bonds and graded hydrogen bonds

Designing an elastomer that possesses both mechanical strength and self-healing properties is a challenging. In this study, a polyurethane elastomer (PUSTP) was successfully synthesized, featuring disulfide bonds along the main chain and graded intermolecular hydrogen bonds. The results demonstrated that the mechanical properties of the polyurethane elastomer improved with an increase in the number of disulfide bonds increased. Specifically, when the molar ratio of disulfide bonds to IPDA was 5:5, the tensile strength of the composite elastomeric film was 5.22 MPa, with an elongation of 1820.26%. Furthermore, the material exhibited robust thermal stability after undergoing repair at 70°C for 12 h, the mechanical strength of the polyurethane membrane remained unchanged, showing outstanding self-healing capabilities. Additionally, the polyurethane film served as the substrate material for crafting self-healing conductive devices, which maintained excellent electrical conductivity even after damage repair. This flexible material, combining impressive mechanical recovery capabilities with electrical performance, holds significant promise for a wide array of applications.     

Interfacial integrity of low-shrinkage composite restorations related to the filling technique and consistency

Purpose: To evaluate the influence of filling techniques and consistency of low-shrinkage composites on the bond strength and internal gap formation in Class I bonded restorations. Two low-shrinkage restorative systems (N’Durance/Septodont and Filtek Silorane/3M ESPE) were used to restore Class I preparations. Bulk increment, two oblique increments or two horizontal increments were performed and Filtek Z350XT was used as a control. Each increment was photoactivated for 40?s and the restored teeth were then stored for 24?h at 37?°C before being longitudinally sectioned and the internal margins of the restorations dyed with 1% acid-red propylene glycol solution for 20?s. The specimens were water rinsed and digital images were recorded for the internal gap formation (%) analysis. Stick-shaped specimens were also tested in tension to evaluate the bond strength. Comparative consistency of unset composites was also performed. N’Durance exhibited the highest incidence of internal gaps amongst all the filling techniques. Filtek Silorane showed no significant difference of internal gap formation in comparison with Filtek Z350XT, regardless of the filling technique. Filtek Z350XT exhibited the highest bond strength and N’Durance the lowest when horizontally applied; bond strength of Filtek Silorane was not influenced by the filling technique. Both Filtek Z350XT and N’Durance presented lower consistency. Low-shrinkage composites seem to present equivalent or inferior bond strength and internal gap formation when compared to the methacrylate composite. The quality of the Class I preparation is dependent on the material and filling techniques.     

Effect of hot-etching treatment on shear bond strength of zirconia to resin cement

ABSTRACT

The purpose of this study was to evaluate the effect of hot-etching surface treatment on the shear bond strength between zirconia ceramics and resin cement. Ceramic cylinders were divided randomly into 10 groups (n?=?10) according to different surface treatments (blank control; airborne particle abrasion; hot-etching for 10?min; hot-etching for 30?min; hot-etching for 60?min) and whether or not performed thermal cycling fatigue test. Flat enamel surfaces, were prepared from human permanent incisors and were bonded to the zirconia discs. All specimens were subjected to shear bond strength test by a universal testing machine. All data were statistically analysed using one-way analysis of variance and multiple comparison least significant difference tests (α?=?0.05). Hot-etching for 60?min treatment produced higher bond strengths than the other treatment. Surface treatment of zirconia with a hot-etching solution might enhance surface roughness and bond strength between zirconia and resin cement.