Compressive Performance of Fiber Reinforced Recycled Aggregate Concrete by Basalt Fiber Reinforced Polymer-Polyvinyl Chloride Composite Jackets

The development of recycled aggregate concrete(RAC)provides a new approach to limiting the waste of natural resources.In the present study,the mechanical properties and deformability of RACs were improved by adding basalt fibers(BFs)and using external restraints,such as a fiber-reinforced polymer(FRP)jacket or a PVC pipe.Samples were tested under axial compression.The results showed that RAC(50%replacement of aggregate)containing 0.2%BFs had the best mechanical properties.Using either BFs or PVC reinforcement had a slight effect on the loadbearing capacity and mode of failure.With different levels of BFs,the compressive strengths of the specimens reinforced with 1-layer and 3-layer basalt fiber reinforced polymer(BFRP)increased by 6.7%–10.5%and 16.5%–23.7%,respectively,and the ultimate strains increased by 48.5%–80.7%and 97.1%–141.1%,respectively.The peak stress of the 3-layer BFRP-PVC increased by 42.2%,and the ultimate strain improved by 131.3%,relative to the control.This reinforcement combined the high tensile strength of BFRP,which improved the post-peak behavior,and PVC,which enhanced the structural durability.In addition,to investigate the influence of the various constraints on compressive behavior,the stress-strain response was analyzed.Based on the analysis of experimental results,a peak stress-strain model and an amended ultimate stress-strain model were proposed.The models were verified as well;the result showed that the predictions from calculations are generally consistent with the experimental data(error within 10%).The results of this study provide a theoretical basis and reference for future applications of fiber-reinforced recycled concrete.

The Influence of Steel and Basalt Fibers on the Shear and Flexural Capacity of Reinforced Concrete Beams

To improve the shear and flexural capacity of flexural members, the steel and basalt fibers were used in model beams tested under flexure. Three series of single span free supported model beams were prepared from SFRC （steel fiber reinforced concrete） with longitudinal steel reinforcement （steel ratio of 1.2 %） and varied spacing of steel stirrups and they were tested till failure. Another three series of BFRC （basalt fiber reinforced concrete） double-span model beams with a span of 2 mm~ 1,000 mm and cross section 180 mm ~ 80 mm were tested. During the tests till to the failure the beam reactions, vertical deflections and horizontal strains in concrete were registered, to clarify the range of redistribution of bending moments and shear forces over the span of the beams. Almost all the tested model beams failed in shear, showing visible influence of steel and basalt fibers on the shear capacity of the tested beams. The tests results confirmed that steel and basalt fibers in reinforced concrete beams can partially replace （in certain cases） the traditional steel stirrups calculated for shear.

Strengthening effects of BFRP on reinforced concrete beams

Reinforced concrete （RC） beams externally bonded with basalt fiber reinforced polymer （BFRP） are experimentally investigated by using different numbers of bonding plies, transverse anchorages as well as the initial conditions of strengthened beams. The performances of the BFRP strengthening are compared with those of the carbon fiber reinforced polymer （CFRP） and the glass fiber reinforced polymer （GFRP） under the same experimental condition. Experimental results indicate that the strength and ductility of the strengthened beam with two plies of the BFRP are improved remarkably than those with one ply. The strengthening effects of the BFRP lie between those of the CFRP and the GFRP. The BFRP strengthening is little influenced by pre-cracks of concrete. Most failures are caused by interfaciai debonding induced by flexural cracks in the experiment. Clamping of Uwraps along the whole beam is less efficient than endpoint anchorage for increasing the ultimate load of the strengthened beam. Finally, the models suggested by the five guidelines for predicting the debonding strain of the CFRP are extended to the BFRP and the conservative estimates of the debonding strain of the BFRP are given as well.

Experimental study on the durability of BFRP bars embedded in concrete

This paper presents an experimental study on the alkali-resistant properties of basalt fiber reinforced polymers （BFRP） bars under a typical concrete environment. BFRP bars were embedded in concrete and exposed to different aggressive environments, including tap water, saline solution and ambient temperature environments, to study the effects of the type of solution and relative humidity （RH） on the durability of BFRP. Meanwhile, BFRP bars were directly immersed in an alkaline solution for comparison. The acceleration factor describing the relationship between the alkaline solution immersion and the moisture-saturated concrete was also obtained. Aging was accelerated with a temperature of 60 ℃. The results show that the chloridion in the saline solution does not have any harmful effects on the degradation of the concrete-encased BFRP bars. Contact with an alkaline （high pH） concrete pore-water solution is the primary reason for the degradation of the BFRP bars. The degradation rate of concrete-encased BFRP bars is accelerated when a high temperature and a high humidity are present simultaneously. The degradation rate of the BFRP bars is relatively quick at the initial stage and slows down with exposure time. Results show that the degradation of 2.18 years in moisture-saturated concrete at 60 ℃corresponds to that of one year when directly immersed in an alkaline solution （other conditions remaining the same） for the BFRP bars analyzed.

Flexural Experimental Study on Continuous Reinforced Concrete Beams Strengthened with Basalt Fiber Reinforced Polymer/Plastic

This paper discusses a new fibrous composite known as continuous basalt fiber reinforced polymer /plastic(BFRP).Compared with other fiber reinforced polymer/plastic,BFRP has many advantages,such as ductility,high thermal resistance,corrosion resistance and economic cost.To test mechanical properties and failure modes of flexural members strengthened with BFRP,flexural experiment is conducted on four two-span T-section continuous beams strengthened with BFRP and one un-strengthened comparative beam.The experimental result shows that the strengthened beams perform remarkably in terms of yield strength,ultimate strength and ductility.BFRP has good prospects in retrofitting and strengthening of concrete structures which require good ductility and corrosion resistance.

Structural performance of a façade precast concrete sandwich panel enabled by a bar-type basalt fiber-reinforced polymer connector

In this study,a novel diagonally inserted bar-type basalt fiber reinforced polymer(BFRP)connector was proposed,aiming to achieve both construction convenience and partially composite behavior in precast concrete sandwich panels(PCSPs).First,pull-out tests were conducted to evaluate the anchoring performance of the connector in concrete after exposure to different temperatures.Thereafter,direct shear tests were conducted to investigate the shear performance of the connector.After the test on the individual performance of the connector,five façade PCSP specimens with the bar-type BFRP connector were fabricated,and the out-of-plane flexural performance was tested under a uniformly distributed load.The investigating parameters included the panel length,opening condition,and boundary condition.The results obtained in this study primarily indicated that 1)the bar-type BFRP connector can achieve a reliable anchorage system in concrete;2)the bar-type BFRP connector can offer sufficient stiffness and capacity to achieve a partially composite PCSP;3)the boundary condition of the panel considerably influenced the out-of-plane flexural performance and composite action of the investigated façade PCSP.

Deformation Damage and Energy Evolution of Basalt Fiber Reinforced Concrete under the Triaxial Compression

To explore the law of energy evolution and the change of damage before and after specimen failure,the conventional triaxial compression tests(5,10,15,20,and 30 MPa)of basalt fiber reinforced concrete(BFRC)with different fiber volume fractions(0,0.2%and 0.4%)were carried out by MTS816 rock testing system,and the cyclic loading and unloading tests of BFRC with a fiber content of 0.2%were carried out.The experimental results show that the peak strength and strain of BFRC increase with the increase of confining pressure.Tensile failure occurs under low confining pressure,and shear failure occurs under high confining pressure.The best volume fraction of fiber is 0.2%.Under different confining pressures,the input energy,elastic energy,plastic properties,and dissipated energy of the samples first increase and then decrease to a stable level.The elastic energy and dissipated energy reach the maximum near the peak stress,while the input energy and plastic properties reach the maximum at the peak.At the same time,the damage increases continuously with the input of load under different confining pressures,indicating that the failure of the specimen is a process of energy accumulation.

低温下玄武岩纤维混凝土劈拉强度尺寸效应试验

为研究极端低温作用下结构尺寸和纤维体积分数对玄武岩纤维混凝土劈拉强度的定量影响规律和作用机制,设计了4种尺寸(边长分别为70、100、150和200 mm)、4种纤维体积分数(分数范围0%~0.5%)的玄武岩纤维混凝土立方体试块在常温和低温下(温度范围20~-90℃)进行了静态劈拉破坏试验。试验结果表明:不同类型混凝土的劈拉强度均随温度降低而线性增大(最大增幅接近130%),呈现出显著的低温增强效应;玄武岩纤维的掺入能略微强化混凝土劈拉强度的低温增强效应。不同纤维体积分数玄武岩纤维混凝土的劈拉强度均呈现出一定的纤维增强效应,并且随体积分数增加而增强;极端低温作用下玄武岩纤维的主导破坏模式由拔出破坏转变为拉断破坏,导致纤维增强效应随温度下降而变强。劈拉强度的尺寸效应随温度下降而更明显,但玄武岩纤维的掺入能减弱尺寸效应(最大削弱程度达25.8%)。本文研究能为玄武岩纤维混凝土材料在极端低温环境下的大规模工程结构应用提供有效参考。

玄武岩纤维棒聚合物混凝土的弯曲韧性

研究了玄武岩纤维棒(BFB)的纤维增强指数I_(R)对玄武岩纤维棒聚合物混凝土(BFB-PC)韧性指标T_((2(n-1)))(n)的影响,通过分形理论探究了T_((2(n-1)))(n)与裂缝形貌的关系,并建立了弯曲韧性计算模型.结果表明:当IR=90.0时,BFB对BFB-PC的增韧效果最优,此时BFB-PC的弯曲韧性比未掺BFB时提升了8.39倍;BFB的增韧阈值为IR=37.5和IR=90.0;当IR相同时,与未掺聚合物的混凝土相比,聚灰比为0.06的BFB-PC T_((2(n-1)))(n)更高;IR越大裂缝形貌越复杂,T(2(n-1))(n)与裂缝分形维数呈二次函数关系;本文提出的弯曲韧性计算模型准确描述了BFB对PC梁的增韧作用,其试验值与理论值的相对误差小于15.00%.

BFRP筋回收轮胎钢纤维混凝土黏结性能分析

对玄武岩纤维增强复合材料(BFRP)筋在回收轮胎钢纤维(RTSF)混凝土中的黏结性能进行了试验和分析研究.对不同RTSF体积掺量、BFRP筋直径和嵌入长度的试件进行了拉拔试验,研究其对黏结破坏模式、黏结滑移响应和黏结强度的影响,并提出了BFRP筋RTSF混凝土的黏结滑移理论模型.结果表明:BFRP筋RTSF混凝土黏结破坏类型包括拔出破坏、劈裂破坏以及拔出且劈裂破坏;BFRP筋直径对黏结破坏模式无显著影响,而RTSF体积掺量、BFRP筋直径和嵌入长度均对黏结强度有较大影响,且RTSF体积掺量与极限黏结强度呈正相关,BFRP筋直径和嵌入长度对其影响与之相反;当RTSF体积掺量从0增大至1.5%时,其极限黏结强度最大可提高约23.87%.与已有模型相比,所提出的黏结滑移理论模型对BFRP筋RTSF混凝土的黏结滑移曲线具有更高的拟合精度.

冻融循环下玄武岩纤维混凝土冲击力学性能预测模型

冻融循环下纤维混凝土的劣化规律是寒区服役混凝土工程安全性和耐久性评价的重要依据,现有服役混凝土工程的安全性和耐久性评价的研究具有工作量大、成本高、周期长等特点,构建基于机器学习的高精度力学性能预测模型已成为本领域研究热点。为探究冻融循环后玄武岩纤维混凝土冲击力学性能的高精度预测模型,采用SHPB装置对冻融循环后BFRC开展动态冲击压缩力学性能试验,并构建机器学习-Optuna混合预测模型,对60组以玄武岩纤维体积掺量、冻融循环次数、动荷载冲击速度为影响因素建立的动态峰值应力样本数据集进行预测。结果表明:k近邻、Lasso、多层感知机、极度梯度提升树和随机森林5种经典机器学习模型的预测准确度均较高,说明机器学习算法对于冻融循环后BFRC动态力学性能预测具有良好的预测效果,其中随机森林算法为最优预测算法;RF-Optuna混合预测模型显示出0.9754的拟合优度,具有良好的预测精度;非数据集工况预测表明,该混合模型对于各影响因素均具有良好泛化能力。研究成果可为冻融循环条件下BFRC动态力学性能的快捷精准预测提供参考。

玄武岩纤维对混凝土抗冻性能的影响

为研究玄武岩纤维掺量对混凝土抗冻性能的影响及作用机理,开展了快速冻融试验和微观孔隙试验,研究了4种不同玄武岩纤维体积掺量(0、0.1%、0.2%、0.3%)混凝土冻融循环过程中的外观、质量损失率、相对动弹性模量、抗压强度、抗折强度、冲击弹性波波速损失率及气泡特征参数的变化规律,并通过灰熵分析法对玄武岩纤维改善混凝土性能的微观机理进行了研究。结果表明:混凝土各项性能随着冻融循环次数的增加而逐渐降低;掺加玄武岩纤维能够提高混凝土抗冻性能且存在最优掺量;玄武岩纤维混凝土宏观性能的改变与气孔比表面积、含气量、弦长>200 nm气孔频率等微观孔隙参数之间呈一定的相关性;玄武岩纤维掺量为0.2%时对混凝土抗冻性能的改善效果最佳。

玄武岩纤维沙漠砂钢筋混凝土梁受弯性能试验研究

通过试验对沙漠砂部分代替普通砂的可行性进行探讨,研究沙漠砂和玄武岩纤维的掺入对混凝土试块和钢筋混凝土梁性能的影响。对普通砂混凝土梁、沙漠砂混凝土梁、玄武岩纤维普通砂混凝土梁、玄武岩纤维沙漠砂混凝土梁进行了受弯性能试验,得出了试验梁的荷载-挠度曲线、裂缝分布和破坏模式。之后,利用现有理论公式,计算混凝土试块的劈裂抗拉强度、轴心抗压强度、弹性模量和试验梁的屈服弯矩、极限弯矩。结果表明:天然沙漠砂部分代替普通砂是可行的;沙漠砂和玄武岩纤维的掺入没有使混凝土试块和钢筋混凝土梁的性能发生本质性改变;沙漠砂和玄武岩纤维掺入后,混凝土试块和钢筋混凝土梁的计算准则仍旧适用。

玄武岩纤维混凝土抗硫酸盐侵蚀性能研究

为探究掺玄武岩纤维混凝土抗硫酸盐侵蚀性能,在混凝土试件中分别掺入体积掺量为0、0.1%、0.2%、0.3%的玄武岩纤维,以试件的外观、质量损失率和抗压强度为主要评价指标,进行了不同侵蚀环境下玄武岩纤维混凝土的抗硫酸盐侵蚀性能试验研究。研究结果表明:体积掺量为0.2%的试件在质量损失率、抗压强度方面表现最佳,而体积掺量为0.1%的试件抗折强度增幅最大;干湿循环条件下试件的外观、质量和抗压强度波动幅度较自然侵蚀环境下更大,且干湿周期越短侵蚀程度越严重;试件的微观结构分析发现,侵蚀前混凝土试件内部因水泥水化作用,存在少量C-S-H(水化硅酸钙)、Ca(OH)_(2)等水化产物,掺入玄武岩纤维后使混凝土内部黏结十分紧密,试件内部裂缝发育较缓,减少了侵蚀产物的生成,一定程度上提高了混凝土的力学性能。

SiO_(2)/KH560改性玄武岩纤维混凝土力学性能研究

为了研究硅烷偶联剂(KH560)和纳米SiO_(2)协同KH560改性玄武岩纤维(BF)对混凝土力学性能的影响,本文采用KH560对BF进行表面改性,制得KH560-BF,并采用纳米SiO_(2)和KH560改性BF制得SiO_(2)-KH560-BF。通过正交试验筛选出高强度改性纤维,研究了纳米SiO_(2)分散液、润滑剂和KH560三者的质量分数对SiO_(2)-KH560-BF的丝束强度影响。采用SEM和EDS对改性混凝土的7和28 d的力学性能进行评估,并对混凝土的微观结构进行表征。结果表明,SiO_(2)-KH560-BF的最佳上浆剂成分为纳米SiO_(2)分散液1.6%、润滑剂0.4%和KH5600.5%,且三个因素的影响程度从大到小依次为纳米二氧化硅分散液、KH560、润滑剂。与KH560-BF相比,SiO_(2)-KH560-BF纤维丝束强度提高了8.62%,拉伸强度提高了4.41%,Si含量提升了24.9%,并且从SEM照片中可以看出SiO_(2)-KH560-BF团状堆积比KH560-BF少。掺入适量SiO_(2)-KH560-BF的混凝土7和28 d抗压、劈裂抗拉和轴心抗压强度提升效果均高于掺入KH560-BF的混凝土。

玄武岩纤维增强聚合物筋混凝土循环拉拔试验及预测模型

为探究动荷载下玄武岩纤维增强聚合物(BFRP)筋与混凝土的黏结行为,开展了BFRP筋混凝土正反向循环拉拔试验,对其黏结动力性能进行分析。结果表明,从黏结应力⁃滑移关系曲线揭示,循环荷载下BFRP筋与混凝土黏结行为经历4个阶段的受力特征:弹性阶段、裂缝扩展阶段、裂缝闭合阶段和摩擦阶段;随BFRP聚合物筋直径的增大,降低了BFRP筋⁃混凝土界面的黏结强度;随循环次数的增加,BFRP筋与混凝土的黏结强度减小,黏结强度对应的滑移量增加,剪切滞回面积减小,耗能能力降低;基于试验结果,提出了适用于计算循环荷载下BFRP筋与混凝土黏结性能的预测模型,从而为BFRP筋混凝土抗震和疲劳行为奠定试验和理论基础。

BFRP模壳不排水加固RC墩柱恢复力模型

为研究玄武岩纤维增强聚合物(basalt fiber reinforced polymer, BFRP)模壳不排水加固钢筋混凝土(reinforced concrete, RC)墩柱抗震恢复力模型,在拟静力试验基础上,采用OpenSees有限元软件对模壳加固墩柱进行数值分析,主要研究参数为填充层混凝土强度、模壳厚度、加固高度、轴压比。研究表明:填充层混凝土强度等级越高,墩柱抗震性能有所增强,但C40以上的填充层混凝土强度等级墩柱的抗震性能较为接近;模壳加固厚度较大墩柱的抗震性能优于厚度较小墩柱;当模壳加固高度较高时,墩柱的抗震性能较好,当加固高度大于2~3倍原墩柱塑性铰高度时,抗震性能提升效果趋于稳定;轴压比越大,墩柱的刚度退化较快,不利延性发展。后通过数据回归分析,建立了BFRP模壳加固RC墩柱恢复力模型,对比可知,恢复力模型与试验曲线拟合较好,能有效反映加固墩柱的滞回性能,可为此类结构的抗震性能分析提供参考。

氯盐-硫酸盐内外源耦合作用下现浇玄武岩纤维混凝土耐腐蚀试验

将不同体积掺量(0、0.1%、0.3%、0.5%)的短切玄武岩纤维和拌和水质量3%的NaCl试剂掺入混凝土中,开展不同浓度(0、3%、5%、10%)Na2SO4溶液全浸泡下现浇玄武岩纤维混凝土的耐腐蚀试验,探究强盐渍土环境中现浇玄武岩纤维混凝土的抗盐蚀性能。研究结果表明:(1)内掺氯盐后,现浇混凝土中水泥早期的水化速率明显加快,但过快的水化使得混凝土后期强度增长速率放缓,导致试件的宏观耐久性能比基准组试件的差;(2)玄武岩纤维的桥接作用延缓了现浇混凝土内部微裂缝的生成和扩展进程,提升了试件抵抗氯盐-硫酸盐内外源耦合侵蚀的能力;(3)玄武岩纤维掺量为0.3%试件组的立方体抗压强度和抗折强度均比其他掺量试件组的高,其相对动弹性模量变化最为平缓,质量损失率最小,腐蚀产物最少,抵抗氯盐-硫酸盐内外源耦合侵蚀的能力最强。研究成果可为强盐渍土地区现浇玄武岩纤维混凝土的工程应用提供参考依据。

硫酸盐环境下BFFC侵蚀试验及强度预测模型

开展不同纤维掺量的玄武岩纤维增强泡沫混凝土(BFFC)在硫酸盐环境下的侵蚀试验,探究BFFC的破坏形式、无侧限抗压强度、质量及微观结构的演变特性。根据试验结果提出不同纤维掺量及硫酸盐循环侵蚀次数下BFFC无侧限抗压强度的预测模型。研究结果表明:纤维体积掺量为0.18%、0.36%、0.48%、0.60%的BFFC无侧限抗压强度分别比无纤维掺入的混凝土抗压强度提高了58%、85%、88%、94%,BFFC合理纤维掺量约为0.36%;在质量分数为10%的硫酸盐溶液中,BFFC试件进行干湿循环试验的侵蚀稳定时间约为15 h;BFFC无侧限抗压强度和质量随着侵蚀循环次数增加均表现为先增长后衰减的趋势;纤维体积掺量为0、0.18%、0.36%、0.48%、0.60%的BFFC试块经过30次循环时的质量损失至原始质量的55%、60%、70%、72%、80%,其强度降低至初始强度的35%、40%、42%、48%、50%。