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束状玄武岩纤维增强混凝土力学性能试验研究

高鹏, 储圣洁, 韦海涛, 封磊, 黄玲玲

高鹏, 储圣洁, 韦海涛, 等. 束状玄武岩纤维增强混凝土力学性能试验研究[J]. 复合材料学报, 2024, 43(0): 1-11.
引用本文: 高鹏, 储圣洁, 韦海涛, 等. 束状玄武岩纤维增强混凝土力学性能试验研究[J]. 复合材料学报, 2024, 43(0): 1-11.
GAO Peng, CHU Shengjie, WEI Haitao, et al. Experimental study on mechanical properties of bundled basalt fiber reinforced concrete[J]. Acta Materiae Compositae Sinica.
Citation: GAO Peng, CHU Shengjie, WEI Haitao, et al. Experimental study on mechanical properties of bundled basalt fiber reinforced concrete[J]. Acta Materiae Compositae Sinica.

束状玄武岩纤维增强混凝土力学性能试验研究

基金项目: 安徽省住房城乡建设科学技术计划项目(2022-YF073);安徽高校自然科学研究重点项目(2022AH051805)
详细信息
    通讯作者:

    高鹏,博士,副教授,研究方向为纤维复合材料加固混凝土结构 E-mail: owen.gp@163.com

  • 中图分类号: TU528

Experimental study on mechanical properties of bundled basalt fiber reinforced concrete

Funds: Anhui Province Housing and Urban-Rural Construction Science and Technology Programme (2022-YF073); Natural Science Research Project of Anhui Educational Committee (2022AH051805)
  • 摘要:

    为研究束状玄武岩纤维(Bundled Basalt Fiber, BBF)增强混凝土的力学性能,对不同纤维长度(12 mm、18 mm、24 mm)、体积掺量(0.1%、0.2%、0.3%)和类型(束状玄武岩、短切玄武岩和聚丙烯)的纤维增强混凝土进行立方体抗压、劈裂抗拉和断裂韧性试验,并通过扫描电镜观察了其微观结构。结果表明:BBF对混凝土抗压强度提升效果不明显;而对劈裂抗拉强度增强效果显著,在纤维长度为24 mm,体积掺量为0.2%时,抗拉强度最大提高幅度为26.65%;随纤维增强指数(Reinforcement Index, RI)增加,BBF混凝土拉压比呈升高趋势,且RI为24时,拉压比为普通混凝土(Normal Concrete, NC)的1.39倍;BBF的掺入显著提升了混凝土三点弯曲峰值荷载、起裂韧度及失稳韧度,且当掺量为0.3%,纤维长度为12 mm时,三者较NC最大提升幅度分别为53.66%、47.06%及151.03%。电镜扫描显示BBF表面附着大量水化产物,与水泥浆体粘结紧密且与基体间无明显界面过渡区,有效抑制了微裂缝扩展连通。

     

    Abstract:

    In order to study the mechanical properties of bundled basalt fiber (BBF) reinforced concrete, cube compressive strength, splitting tensile strength and fracture toughness experiments of fiber reinforced concrete with different fiber lengths (12 mm, 18 mm, 24 mm), volume fraction (0.1%, 0.2%, 0.3%) and types (bundled basalt, chopped basalt and polypropylene) were carried out. And the microstructure was observed by scanning electron microscopy. Results show that the effect of BBF on compressive strength of concrete is not obvious; when the fiber length is 24 mm and the dosage is 0.2%, the maximum increase of tensile strength is 26.65%. With the reinforcement index (RI) increases, the tension-compression ratio of BBF concrete tends to increase, and when RI gets to 24, the tension-compression ratio is 1.39 times that of NC. Incorporation of BBF generally increases three-point bending peak load, initiation toughness and unstable toughness of concrete, in which the maximum increase rate at 0.3% are 53.66%, 47.06% and 151.03%, respectively. Scanning electron microscopy shows that a large number of hydration products are attached to surface of BBF, which are closely bonded to cement paste and have no obvious interface transition zone with matrix, effectively inhibiting propagation of micro-cracks.

     

  • 玄武岩纤维是由天然玄武岩经1500℃的高温熔融后,拉制而成的具有良好力学性能的环保型纤维[1]。大量研究表明,短切玄武岩纤维(Chopped Basalt Fiber, CBF)掺入普通混凝土(Normal Concrete, NC)后,在一定掺量[2,3]与长度[4,5]范围,可显著提升其抗拉强度[6,7]、抗裂性能[8,9]与断裂韧性[10,11]。然而,CBF具有较强的吸水性[12],并在高掺量下会出现纤维结团现象[13],会对混凝土工作性能及增强效果产生不利影响[14]。而束状玄武岩纤维(BBF)是由纤维原丝经表面处理和集束成型的新型纤维,从而实现在混凝土中大直径和高掺量纤维的增强效果[15]。目前关于BBF增强混凝土的研究主要基于粗骨料粒径较小[16],或无粗骨料[17]且低水胶比[18]的高性能混凝土。Mohaghegh等[19]研究了BBF增强高性能混凝土梁的抗剪性能,发现BBF推迟了临界剪切裂缝的产生。Chen等进行了BBF增强超高性能混凝土的抗压[20]和抗弯[21]试验,结果表明小直径及高掺量的BBF对混凝土抗压强度和弯曲峰值荷载提升效果较好。崔圣爱等[22]试验研究了BBF对混凝土弯曲韧性的影响,发现弯曲韧性指标值最大提升8.39倍。但目前BBF增强普通骨料粒径范围的混凝土的力学性能研究尚不足。

    因此使用BBF、CBF及聚丙烯纤维(Polypropylene Fiber, PPF)作为增强纤维,设置纤维长度与体积掺量参数,制作了纤维混凝土试件,进行了立方体抗压、劈裂抗拉及三点弯曲断裂韧性试验。通过试验结果比较不同类型、尺寸和掺量的纤维,对增强普通骨料混凝土效果的差异;并分析BBF纤维增强效果的优越性。研究结论为BBF增强普通骨料混凝土的应用提供参考。

    试验使用海螺P·Ⅱ 52.5水泥,F类Ⅰ级粉煤灰及S95矿粉;选用细度模数为2.6的河砂;及连续级配的,粒径为5~10 mm的小石和10~25 mm的中石,比例为2∶8。

    使用普通地下水拌合,及使用江苏苏博特公司生产的减水率为19.4%的聚羧酸(Polycarboxylic Acid, PCA)水剂减水剂。

    使用江苏天龙玄武岩连续纤维股份有限公司生产的BBF纤维(图1(a))、CBF纤维(图1(b)),及常州市天怡工程纤维有限公司生产的PPF纤维(图1(c))。玄武岩纤维密度均为2.70 g/cm3,短切纤维直径为17 μm,束状纤维直径达0.2 mm,纤维原丝拉伸强度为2200 MPa,及弹性模量为80.3 GPa。PPF直径18 μm,密度为0.92 g/cm3,拉伸强度和弹性模量分别为620 MPa及6.5 GPa。

    图  1  纤维种类
    Figure  1.  Fiber types

    试验中每立方米混凝土的组成材料重量配比为(单位:kg),水泥∶水∶粉煤灰∶矿渣∶砂∶小石∶中石为236∶160∶65∶80∶734∶220∶880。

    为使纤维在混凝土中均匀分散,避免因制备导致的纤维团聚增强效果的干扰。使用干拌法来制备混凝土。制作中先将粗细骨料搅拌1 min;后均匀撒入纤维再搅拌1 min,最后加入水和PCA搅拌2 min。在24 h后将试件脱模,并在标准条件下养护28天。

    考虑纤维种类、纤维体积掺量和纤维长度三个因素,设计并制作了16组试件。每组中尺寸为100 mm×100 mm×100 mm的试件将进行28天立方体抗压和劈裂抗拉试验;尺寸为100 mm×100 mm×400 mm,底部带有开口宽度为3 mm和高度40 mm预制裂缝的缺口梁试件,将被进行三点弯曲断裂韧性试验。试件分组及设计参数见表1。其中RI是纤维增强指数(Reinforcement Index),为纤维长径比与体积掺量(%)的乘积[23]

    表  1  试件分组的设计参数
    Table  1.  Parameters of tested specimens for each group
    Specimen number Type Length/mm Dosage/% RI
    NC - - - -
    BBF0.1 L12 BBF 12 0.1 6.0
    BBF0.2 L12 BBF 12 0.2 12.0
    BBF0.3 L12 BBF 12 0.3 18.0
    BBF0.2 L18 BBF 18 0.2 18.0
    BBF0.2 L24 BBF 24 0.2 24.0
    CBF0.1 L12 CBF 12 0.1 70.6
    CBF0.2 L12 CBF 12 0.2 141.2
    CBF0.3 L12 CBF 12 0.3 211.8
    CBF0.2 L18 CBF 18 0.2 211.8
    CBF0.2 L24 CBF 24 0.2 282.4
    PPF0.1 L12 PPF 12 0.1 66.7
    PPF0.2 L12 PPF 12 0.2 133.3
    PPF0.3 L12 PPF 12 0.3 200.0
    PPF0.2 L18 PPF 18 0.2 200.0
    PPF0.2 L24 PPF 24 0.2 266.7
    Notes: FRP type include bundled basalt fiber (BBF), chopped basalt fiber (BBF) and polypropylene fiber (PPF). Dosage is defined as volume fraction. RI represent reinforcement index, which is the product of fiber aspect ratio and dosage (%).
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    在混凝土试块制备时,依照GB/T 50080-2016《普通混凝土拌合物性能试验方法标准》[24],测定了混凝土拌合物坍落度。

    之后进行了材料力学性能试验。依照GB /T 50081-2002《普通混凝土力学性能试验方法标准》[25],在安徽省土木工程结构与材料实验室,使用STYE-2000压力机测定28天混凝土立方体抗压和劈裂抗拉强度。参照DL/T 5332-2005《水工混凝土断裂试验规程》[26],使用STYE-300C抗压试验机,进行缺口梁三点弯曲断裂韧性试验。缺口梁试件支座间跨度300 mm,加载速率70 N/s;由YHD-50型位移计采集试件跨中挠度数据;YC 10/4型夹式引伸计采集底部预制裂缝张开口位移。并根据所测数据绘制荷载-裂缝张开口位移曲线(Load-Crack Mouth Opening Displacement,P-CMOD)。

    在材料力学性能试验完成后,制备材料样本,在合肥工业大学分析测试中心使用Gemini 500型热场发射扫描电子显微镜观察典型试件微观形貌。

    在骨料配合比相同情况下,测定不同纤维掺量及长度的纤维增强混凝土及NC的坍落度,如图2图3所示。可见掺入纤维后,混凝土坍落度普遍降低,且随掺量增加下降愈加显著。如图2中,当纤维长度保持为12 mm时,随BBF掺量由0.1%逐渐增加至0.2%和0.3%,尽管在减水剂用量略微增加情况下,纤维增强混凝土坍落度比较NC时,依然分别降低了30 mm、30 mm和180 mm。而坍落度数值与纤维长度相关性较弱。如图3中,当纤维掺量保持为0.2%,长度为18 mm时,BBF混凝土坍落度较NC最多降低了60 mm。及在纤维长24 mm和0.2%的体积掺量时,BBF混凝土所用减水剂为CBF混凝土的66.61%,而前者坍落度却比后者高出35 mm;在其他条件下的BBF混凝土坍落度也与CBF相当,且减水剂用量较低。由此可看出相比其他类型纤维,BBF吸水性较弱,对混凝土坍落度影响较小。

    图  2  不同纤维掺量试件的坍落度
    Figure  2.  Slump of specimens with different fiber dosage
    图  3  不同纤维长度试件的坍落度
    Figure  3.  Slump of specimens with different fiber length

    将养护完成的混凝土试件取出后,进行立方体抗压、劈裂抗拉及三点弯曲断裂韧性等宏观力学性能试验。不同掺量的BBF混凝土立方体受压破坏后形态如图4所示。NC破坏时由端部产生裂缝并沿纵向迅速贯通,同时横向扩展出新裂缝,并伴随底部混凝土剥落,如图4(a)所示。纤维长度保持为12 mm时,掺入0.1%的BBF时,混凝土两侧出现未贯通纵向裂缝(图4(b));当掺量为0.2%时,仅在试件一侧出现细微裂缝(图4(c));而掺量为0.3%时,试件破坏时混凝土表面基本保持完整(图4(d))。可见BBF的掺入改善了混凝土抗压破坏形态,试件中散落分布的BBF,承担了部分压剪应力,减小了微裂缝端部应力集中,抑制了宏观裂缝出现;且纤维掺量越高,阻裂性能越好。

    图  4  不同掺量BBF混凝土试件抗压破坏形态
    Figure  4.  Compressive failure modes of concrete specimens with different BBF dosage

    劈裂抗拉试验中典型试件的混凝土劈裂面如图5所示。试验中,掺入纤维会使试件在破坏时的劈裂声由清脆转为沉闷,是混凝土脆性改善的表现。在混凝土劈裂面可发现仍以集束形式存在的BBF,且主体呈现拔出破坏,如图5(a)所示;PPF则具有良好的分散性,均匀地布满整个劈裂面,如图5(b)所示。

    三点弯曲试验中的典型试件裂缝形态如图6所示。由图6(a)可见,NC切口梁试件破坏迅速,裂缝产生后沿纵向迅速贯通,形态显示较为平直。如图6(b)、6(c)和6(d)所示,掺入纤维后,试件从加载至破坏的时间相对延长,可观察到裂缝起裂、扩展和贯通的过程;且对应断裂裂缝较为曲折,呈“S”形,尤其体现BBF混凝土中(图6(b))。这是因为荷载通过纤维在微裂缝两侧混凝土间传递,改变了裂缝扩展路径[27];随荷载增加至临界值,纤维被拉断或拔出,使混凝土应力重分布[28];开裂混凝土退出工作后,裂缝继续扩展。增强纤维消耗了大量能量,显著增强了混凝土韧性;大直径的BBF纤维在其中体现的作用尤为明显。

    图  5  典型试件劈裂面
    Figure  5.  Splitting surface of typical specimens
    图  6  三点弯曲试验的典型试件裂缝形态
    Figure  6.  Crack morphology of typical specimens in three-point bending test

    经过三点弯曲断裂韧性试验后的典型试件的混凝土断裂面孔隙分布情况如图7所示。其中图7(a)为NC断面,可看出试件内部有较多大的气孔(使用红圈标识);由图7(b)可见,BBF掺入明显改善了混凝土内部孔隙结构,孔隙数量和直径大幅减小;在PPF混凝土试件断面也有相似现象,如图7(c)所示。这是由于纤维掺入后,破坏了混凝土的原生孔隙结构,使之充满水泥浆[29];同时纤维形成的连体结构也能承担一部分混凝土温差及干缩变形产生的应力[30],抑制孔隙的扩展与连通。

    图  7  三点弯曲试验的典型试件断裂面
    Figure  7.  Fracture surface of typical specimens in three-point bending test

    对纤维掺量为0.1%、0.2%及0.3%和长度为12 mm、18 mm及24 mm的BBF、CBF及PPF混凝土进行了28天立方体抗压强度测试,结果分别见图8图9。由图8可见纤维掺量提高对混凝土抗压强度提升不明显。图9中,随纤维长度增加,混凝土抗压强度均逐渐降低。纤维掺量在0.2%,长度为18 mm时,BBF、CBF及PPF混凝土抗压强度相较12 mm时降幅分别为12.26%、12.95%及8.51%。因为过长的纤维,搅拌时难以分散、易交叉重叠[31],增加混凝土内部缺陷,导致混凝土抗压强度降低。

    图  8  不同纤维掺量试件的立方体抗压强度
    Figure  8.  Compressive strength of specimens with different fiber dosage

    对掺量为0.1%、0.2%及0.3%和纤维长度为12 mm、18 mm及24 mm的BBF、CBF及PPF混凝土进行了28天劈裂抗拉强度测试,结果分别见图10图11。由图10可知,相同试验条件下,BBF混凝土劈裂抗拉强度均高于PPF混凝土。因为PPF较低的抗拉强度,拉断或拔出时耗能远低于BBF。当纤维长度保持12 mm时,随纤维掺量由0.1%增加至0.2%及0.3%,BBF混凝土劈裂抗拉强度较NC分别提升了10.29%、13.46%及9.50%,呈现先升高后降低趋势。而CBF及PPF混凝土劈裂抗拉强度则随掺量增加呈现相反趋势,前者随掺量增加逐渐降低,后者逐渐升高。这是因为试验混凝土骨料粒径较大,只有BBF具有较大直径及较高的抗拉强度,能够显著分布在试件劈裂面而消耗大量能量;PPF虽然分散性较好,但抗拉强度较低,因此较高掺量时,才能够通过劈裂面较多数量的PPF拉断消耗足够能量;而由于高掺量的CBF易产生纤维结团[32],负面作用超过了纤维增强效果。

    图  9  不同纤维长度试件的立方体抗压强度
    Figure  9.  Compressive strength of specimens with different fiber length
    图  10  不同纤维掺量试件的劈裂抗拉强度
    Figure  10.  Split tensile strength of specimens with different fiber dosage
    图  11  不同纤维长度试件的劈裂抗拉强度
    Figure  11.  Split tensile strength of specimens with different fiber length

    图11,当纤维掺量保持为0.2%时,BBF、CBF及PPF混凝土劈裂抗拉强度分别在纤维长度为24 mm、18 mm及12 mm时达到峰值,较NC增幅分别为26.65%、15.04%及−2.64%。在坍落度研究中发现BBF、CBF及PPF吸水性逐渐增强,较强的吸水性使得水化反应难以产生充足的水泥浆包裹纤维;而此时若纤维长度过长,更易产生交叉重叠,形成薄弱区,显著影响混凝土劈裂抗拉强度。因此吸水性较弱的BBF随长度增加,混凝土劈裂抗拉强度总体呈上升趋势,长度为24 mm时达到最大值。因为随纤维长度增加,形成的有效纤维网格结构增多[33],既而增加纤维拔出或拉断时消耗的能量,提高劈裂抗拉强度。

    拉压比(劈裂抗拉强度与立方体抗压强度的比值)是反映混凝土韧性的指标之一,混凝土的高拉压比与高韧性正相关。而纤维增强指数RI能综合考虑纤维长度、直径及掺量水平参数,反映纤维增强混凝土力学性能受到的影响。由于CBF较强的吸水性,纤维结团作用显著,试验数据不理想,因此仅采用PPF作为对比,下同。当BBF的RI为24,及PPF的RI为267时,混凝土拉压比均达到峰值,较NC分别提升了39.06%及14.02%。且BBF与PPF混凝土拉压比随RI增加先小幅上升后降低,而后又出现大幅上升趋势(图12(a)和12(b))。因为RI较低时,纤维掺量及长度水平较低,增韧作用有限;当RI增大时,由于掺量或长度增加,对混凝土内部造成一定缺陷,影响增韧效果,拉压比表现为小幅降低;当RI继续增大,纤维桥接作用及拉断拔出耗能作用显著提升,占主导地位,表现为拉压比数值迅速升高。总体来看,掺入BBF及PPF均提升了混凝土拉压比,且BBF混凝土拉压比数值随RI变化尤为显著。

    图  12  RI对BBF及PPF纤维增强混凝土拉压比影响
    Figure  12.  Effect of reinforcement index on tension-compression ratio of BBF and PPF reinforced concrete

    通过混凝土缺口梁三点弯曲断裂韧性试验,绘制了表征裂缝扩展过程的P-CMOD曲线如图13图14。因试验仪器限制,NC的P-CMOD曲线在达到峰值荷载Pmax前均为线性升高,峰值荷载后荷载迅速降低,体现准脆性特征。两种纤维混凝土的P-CMOD曲线则存在较明显的线性上升(弹性未裂)、曲线上升(裂缝稳定扩展)及下降段(裂缝失稳扩展)。因为纤维掺入能延缓微裂缝相互贯通形成细观裂缝。同时BBF由于较大的直径和较高的抗拉强度,能在一定程度上阻止细观裂缝进一步发展为宏观裂缝,表现为曲线下降段相对NC较为平缓。由图13(a)可知,当BBF长度为12 mm时,随纤维掺量由0.1%逐渐增加至0.2%及0.3%,混凝土峰值荷载较NC分别提升了19.15%、28.37%及53.66%;且在0.3%掺量时峰值荷载及其对应的开口位移Vc均达到最大值,分别为6.50 kN和0.45 mm。由图13(b)可知,PPF长度为12 mm时,当掺量由0.1%增加至0.3%时,混凝土峰值荷载由4.51 kN增加至5.40 kN;峰值荷载对应的开口位移由0.26 mm增加至0.33 mm;在0.3%掺量时,峰值荷载和其对应的开口位移较NC分别最大提升了27.66%及120.00%。因为随纤维掺量增加,乱向分布的纤维密度增加,纤维有效间距减小,对微裂缝和细观裂缝的扩展抑制作用增强,吸收能量增多;表现为BBF及PPF混凝土峰值荷载及开口位移逐渐提高。同时BBF由于较大的直径及较高的抗拉强度,相同条件下,其峰值荷载显著高于PPF混凝土。

    图  13  不同掺量BBF及PPF混凝土典型试件P-CMOD曲线
    Figure  13.  P-CMOD curve of typical BBF and PPF concrete specimens with different fiber dosage
    图  14  不同纤维长度BBF及PPF混凝土典型试件P-CMOD曲线
    Figure  14.  P-CMOD curve of typical BBF and PPF concrete specimens with different fiber length

    图14(a),当BBF掺量为0.2%时,随纤维长度由12 mm增加至18 mm和24 mm,混凝土峰值荷载较NC增幅分别为28.37%、30.73%及29.31%;图14(b)中,PPF掺量为0.2%时,随纤维长度由12 mm增加至24 mm,混凝土峰值荷载较NC增幅分别为9.22%、15.60%及12.29%。BBF及PPF混凝土峰值荷载均在纤维长度为18 mm时达到最大值,分别为5.53 kN及4.89 kN。可见纤维长度增加对混凝土三点弯曲峰值荷载影响不大,相同条件下PPF混凝土峰值荷载显著低于BBF混凝土。

    由P-CMOD曲线中直线与曲线段的交点纵坐标可确定起裂荷载Pini[34],但若试验中部分曲线的起裂荷载不明显,将起裂荷载取为峰值荷载Pmax的0.7倍[35]。试验中试件支座间跨度S为0.3 m;试件长度L为0.4 m、厚度t及高度h均为0.1 m;初始裂缝长度a0为0.04 m;刀口薄钢板厚度为0.001 m。再根据DL/T 5332-2005《水工混凝土断裂试验规程》[26]中的混凝土缺口梁断裂韧度公式,计算得到起裂韧度KQ IC及失稳韧度KS IC。起裂荷载及峰值荷载对应的裂缝张开口位移分别用ViniVc表示。相关计算结果列于表2

    表2知,掺入BBF后混凝土的起裂韧度及失稳韧度均得到明显提升,且与纤维掺量呈正相关关系。当BBF长度为12 mm时,随掺量由0.1%增加至0.2%和0.3%,起裂韧度由0.82提升至0.93和1.00;及失稳韧度由1.53提升至1.89和2.51;且0.3%掺量时,BBF混凝土的起裂韧度及失稳韧度均达到峰值,较NC分别提高了47.06%及151.03%。BBF对混凝土失稳韧度提升效果尤为显著,表现出其在阻止宏观裂缝失稳扩展方面的良好效果。与掺量因素相比,BBF纤维长度水平对混凝土起裂韧度及失稳韧度影响相对较小。当BBF掺量为0.2%,长度为24 mm时,混凝土起裂韧度及失稳韧度较NC最大增幅分别为41.18%及102.06%。而与BBF相比,PPF对混凝土韧性指标提升效果有限。在掺量为0.2%,长度为24 mm时,PPF混凝土起裂韧度较NC最高增幅仅为25.00%。

    表  2  双K断裂参数
    Table  2.  Double K parameters
    Specimen
    number
    Crack initial load (Pini)/kN Opening displacement corresponding to cracking load (Vini)/μm Quality of specimens between supports (m)/kg Peak load (Pmax)/kN Critical value of crack opening displacement
    (Vc) / μm
    Initiation toughness
    (KQIC)/(MPa·m1/2)
    Unstable toughness
    (KSIC)/(MPa·m1/2)
    NC 3.27 30 7.395 4.23 150 0.68 1.94
    BBF0.1 L12 3.98 50 7.373 5.04 370 0.82 2.96
    BBF0.2 L12 4.60 50 7.335 5.43 430 0.93 3.67
    BBF0.3 L12 4.98 40 7.275 6.50 450 1.00 4.87
    BBF0.2 L18 3.94 30 7.328 5.53 220 0.81 3.00
    BBF0.2 L24 4.72 50 7.335 5.47 460 0.96 3.92
    PPF0.1 L12 3.45 30 7.425 4.51 260 0.68 2.90
    PPF0.2 L12 [3.23] / 7.245 4.62 260 0.67 /
    PPF0.3 L12 [3.78] / 7.155 5.40 330 0.78 /
    PPF0.2 L18 [3.42] / 7.178 4.89 160 0.71 /
    PPF0.2 L24 4.18 390 7.208 4.75 680 0.85 1.28
    Note: The crack initiation load data with “[ ]” indicates that is calculated as 0.7 times peak load. And “m” is defined as the quality of specimens between supports, which is calculated as the specimens quality multiplied the ratio of supports span S to specimen length L.
    下载: 导出CSV 
    | 显示表格

    在混凝土宏观力学性能试验完成后,制备典型试件的材料样本,进行微观形貌测试。图15(a)为NC基体放大2000倍的电镜照片,可见其内部存在大量微裂缝,它们会在外荷载作用下相互连通并扩展形成宏观裂缝,直至造成混凝土构件破坏。图15(b)为0.3%掺量和长度12 mm的BBF混凝土切片影像,可见集束纤维形式存在的BBF有效抑制了两侧裂缝的连通。结合0.3%掺量和长度12 mm的PPF混凝土照片,如图15(c),可知BBF及PPF均存在拔出破坏和拉断破坏。且PPF拉断为主要破坏方式,因为其纤维抗拉强度较低;而BBF由于有较高的抗拉强度和较大直径,拉断破坏时所需能量显著高于PPF。且PPF表面较为光滑,与混凝土基体粘结较弱。而BBF表面具有大量羟基,吸收周围水分子后会形成氢键;随水化反应进行,BBF表面会覆盖较多水化胶凝产物[36],如图15(d)。同时BBF与基体之间没有明显界面过渡区[27],纤维与基体之间有良好的粘结。较强的粘结力不仅利于传递应力,也能增加纤维被拔出时消耗的能量,从而提升对混凝土的增强效果。

    图  15  典型试件微观形貌
    Figure  15.  Microscopic morphology of typical specimens

    通过设计纤维体积掺量和纤维长度参数,进行了不同类型纤维增强的普通骨料粒径下的混凝土的立方体抗压、劈裂抗拉及断裂韧性等力学性能试验和电镜扫描微观测试,结果显示束状玄武岩纤维(BBF)对普通混凝土抗压和劈裂抗拉强度提升效果显著优于聚丙烯纤维混凝土(PPF)和短切玄武岩纤维混凝土(CBF)。具体结论如下:

    (1) BBF对混凝土抗压强度影响较小;但改善了混凝土抗压破坏形态。随BBF体积掺量从0.1%增加到0.3%,增强混凝土的裂缝数量明显降低及宽度减小;而随纤维长度从12 mm增加到24 mm,混凝土抗压强度提高受到明显抑制作用;

    (2) BBF对混凝土劈裂抗拉强度提升显著。随掺量增加呈现先升后降的趋势;随长度增加总体呈升高趋势。当BBF掺量为0.2%,纤维长度为24 mm时,混凝土劈裂抗拉强度较NC增幅最大达26.65%。掺入BBF显著提高了混凝土拉压比,随RI增大总体呈升高趋势,且RI为24时拉压比较NC最大提升了39.06%;

    (3) BBF掺入延长了混凝土三点弯曲裂缝扩展路径;使得混凝土内部孔隙数量和孔径减小。当纤维长度为12 mm时,随BBF掺量由0.1%增加至0.3%,混凝土三点弯曲峰值荷载、起裂韧度及失稳韧度均显著提高;且0.3%掺量时,BBF混凝土的三者指标数值较NC最大增幅分别为53.66%、47.06%及151.03%;

    (4)微观测试表明BBF表面覆盖大量水化胶凝产物,使得其与基体粘结紧密。且其仍以集束形式分布于混凝土中,有效抑制了两侧裂缝扩展连通。

  • 图  1   纤维种类

    Figure  1.   Fiber types

    图  2   不同纤维掺量试件的坍落度

    Figure  2.   Slump of specimens with different fiber dosage

    图  3   不同纤维长度试件的坍落度

    Figure  3.   Slump of specimens with different fiber length

    图  4   不同掺量BBF混凝土试件抗压破坏形态

    Figure  4.   Compressive failure modes of concrete specimens with different BBF dosage

    图  5   典型试件劈裂面

    Figure  5.   Splitting surface of typical specimens

    图  6   三点弯曲试验的典型试件裂缝形态

    Figure  6.   Crack morphology of typical specimens in three-point bending test

    图  7   三点弯曲试验的典型试件断裂面

    Figure  7.   Fracture surface of typical specimens in three-point bending test

    图  8   不同纤维掺量试件的立方体抗压强度

    Figure  8.   Compressive strength of specimens with different fiber dosage

    图  9   不同纤维长度试件的立方体抗压强度

    Figure  9.   Compressive strength of specimens with different fiber length

    图  10   不同纤维掺量试件的劈裂抗拉强度

    Figure  10.   Split tensile strength of specimens with different fiber dosage

    图  11   不同纤维长度试件的劈裂抗拉强度

    Figure  11.   Split tensile strength of specimens with different fiber length

    图  12   RI对BBF及PPF纤维增强混凝土拉压比影响

    Figure  12.   Effect of reinforcement index on tension-compression ratio of BBF and PPF reinforced concrete

    图  13   不同掺量BBF及PPF混凝土典型试件P-CMOD曲线

    Figure  13.   P-CMOD curve of typical BBF and PPF concrete specimens with different fiber dosage

    图  14   不同纤维长度BBF及PPF混凝土典型试件P-CMOD曲线

    Figure  14.   P-CMOD curve of typical BBF and PPF concrete specimens with different fiber length

    图  15   典型试件微观形貌

    Figure  15.   Microscopic morphology of typical specimens

    表  1   试件分组的设计参数

    Table  1   Parameters of tested specimens for each group

    Specimen number Type Length/mm Dosage/% RI
    NC - - - -
    BBF0.1 L12 BBF 12 0.1 6.0
    BBF0.2 L12 BBF 12 0.2 12.0
    BBF0.3 L12 BBF 12 0.3 18.0
    BBF0.2 L18 BBF 18 0.2 18.0
    BBF0.2 L24 BBF 24 0.2 24.0
    CBF0.1 L12 CBF 12 0.1 70.6
    CBF0.2 L12 CBF 12 0.2 141.2
    CBF0.3 L12 CBF 12 0.3 211.8
    CBF0.2 L18 CBF 18 0.2 211.8
    CBF0.2 L24 CBF 24 0.2 282.4
    PPF0.1 L12 PPF 12 0.1 66.7
    PPF0.2 L12 PPF 12 0.2 133.3
    PPF0.3 L12 PPF 12 0.3 200.0
    PPF0.2 L18 PPF 18 0.2 200.0
    PPF0.2 L24 PPF 24 0.2 266.7
    Notes: FRP type include bundled basalt fiber (BBF), chopped basalt fiber (BBF) and polypropylene fiber (PPF). Dosage is defined as volume fraction. RI represent reinforcement index, which is the product of fiber aspect ratio and dosage (%).
    下载: 导出CSV

    表  2   双K断裂参数

    Table  2   Double K parameters

    Specimen
    number
    Crack initial load (Pini)/kN Opening displacement corresponding to cracking load (Vini)/μm Quality of specimens between supports (m)/kg Peak load (Pmax)/kN Critical value of crack opening displacement
    (Vc) / μm
    Initiation toughness
    (KQIC)/(MPa·m1/2)
    Unstable toughness
    (KSIC)/(MPa·m1/2)
    NC 3.27 30 7.395 4.23 150 0.68 1.94
    BBF0.1 L12 3.98 50 7.373 5.04 370 0.82 2.96
    BBF0.2 L12 4.60 50 7.335 5.43 430 0.93 3.67
    BBF0.3 L12 4.98 40 7.275 6.50 450 1.00 4.87
    BBF0.2 L18 3.94 30 7.328 5.53 220 0.81 3.00
    BBF0.2 L24 4.72 50 7.335 5.47 460 0.96 3.92
    PPF0.1 L12 3.45 30 7.425 4.51 260 0.68 2.90
    PPF0.2 L12 [3.23] / 7.245 4.62 260 0.67 /
    PPF0.3 L12 [3.78] / 7.155 5.40 330 0.78 /
    PPF0.2 L18 [3.42] / 7.178 4.89 160 0.71 /
    PPF0.2 L24 4.18 390 7.208 4.75 680 0.85 1.28
    Note: The crack initiation load data with “[ ]” indicates that is calculated as 0.7 times peak load. And “m” is defined as the quality of specimens between supports, which is calculated as the specimens quality multiplied the ratio of supports span S to specimen length L.
    下载: 导出CSV
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  • 目的 

    目前对束状玄武岩纤维(Bundled Basalt Fiber, BBF)增强混凝土力学性能研究主要基于粗骨料粒径较小或不掺加粗骨料的高性能混凝土。使用最大粗骨料粒径25 mm的普通混凝土(Normal Concrete, NC)作为BBF增强混凝土,研究BBF增强NC的基本力学性能及微观机理并与短切玄武岩纤维(Chopped Basalt Fiber, CBF)及聚丙烯纤维(Polypropylene Fiber, PPF)对比,凸显BBF作为增强纤维的优越性。

    方法 

    对不同体积掺量(0.1%、0.2%及0.3%)及纤维长度(12 mm、18 mm及24 mm)的BBF、CBF及PPF进行了拌合物坍落度、立方体抗压强度、劈裂抗拉强度及三点弯曲断裂韧性试验。宏观力学性能试验完成后,制作材料样本,使用Gemini 500型热场发射扫描电子显微镜观察典型试件微观形貌,分析微观机理。

    结果 

    随BBF掺量增加,混凝土坍落度显著降低。BBF掺量为0.3%时,混凝土坍落度与NC相比降低了180 mm。纤维长度则对混凝土坍落度影响相对较小。随纤维长度由12 mm增加到24 mm,混凝土坍落度较NC分别降低了30 mm、60 mm和20 mm。与其他纤维类型相比,BBF对混凝土坍落度影响较小。BBF对混凝土抗压强度提升不显著。且随纤维长度增加,混凝土抗压强度显著降低。BBF由12 mm增加至18 mm时混凝土抗压强度降幅最大。但BBF显著改善了混凝土抗压破坏形态,随BBF掺量增加,混凝土表面裂缝数量明显减少及宽度减小。掺加BBF,混凝土劈裂抗拉强度显著提升,随BBF掺量增加先升高后降低;随纤维长度增加总体呈升高趋势。与其他掺量水平相比,0.2%掺量时,BBF混凝土劈裂抗拉强度最高,较NC提升了13.5%;与其他纤维长度相比,24mm时,劈裂抗拉强度较NC最大提升了26.6%。BBF的掺入,明显延长了三点弯曲断裂韧性试验试件由加载至破坏的时间;延长了预制裂缝扩展路径;且显著提升了混凝土峰值荷载、起裂韧度及失稳韧度。0.3%掺量时,BBF混凝土峰值荷载、起裂韧度及失稳韧度较NC分别提升了53.66%、47.06%及151.03%。电镜扫描照片显示BBF表面覆盖大量水化产物,且在混凝土中仍以集束形式存在,有效抑制了两侧裂缝的扩展连通。

    结论 

    BBF对混凝土增强效果显著优于CBF及PPF。BBF对混凝土抗压强度提升影响不大,但能明显改善抗压破坏形态;BBF对混凝土劈裂抗拉强度及三点弯曲峰值荷载提升效果显著。BBF由于表面羟基,与水分子结合形成氢键,随水化反应进行吸附较多水化产物,使得纤维与基体无明显界面过渡区,与基体粘结力较强,纤维增强效果较好。

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出版历程
  • 收稿日期:  2024-09-05
  • 修回日期:  2024-11-04
  • 录用日期:  2024-11-14
  • 网络出版日期:  2024-12-01

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