摘要
以天然水硬性石灰和偏高岭土为复合胶凝材料,掺加聚乙烯醇(PVA)纤维、聚乙烯(PE)纤维或玄武岩(BF)纤维,制备了高延性天然水硬性石灰基材料,并研究了其抗压、轴拉力学性能、裂缝控制能力和纤维增强增韧机理. 结果表明:PVA、PE纤维与石英砂或石灰石砂组合均可使水硬性石灰表现出优异的应变硬化和饱和多缝开裂特征,显著提高材料的拉伸强度和极限拉伸应变;PE纤维和石灰石砂组合使材料极限拉伸应变提高至5.604%,PVA纤维和石英砂及石灰石砂组合使材料极限拉伸应变提高至4.000%以上;PVA、PE纤维均可将裂缝宽度控制在100 μm以下,材料在获取超高变形能力的同时具备良好的裂缝控制能力.
中国现存大量古代建筑和岩石质文物因受自然侵蚀和人为破坏已出现不同程度的损坏,选择使用恰当的现代修复材料是建筑遗产保护的核心问题之
与传统的纤维增强水泥基材料不同,高延性水泥基复合材料(ECC)材料可实现突出的高延性和微裂缝控制功能,能够有效克服水泥基材料的脆性并极大改善其耐久性,现已应用于结构加强、裂缝修补等领
本文在天然水硬性石灰-偏高岭土复合胶凝材料体系中掺入适量优选的纤维和特细骨料,制备高延性天然水硬性石灰材料,研究不同纤维和骨料种类及其组合对材料力学性能和裂缝控制能力的影响,并通过微观结构分析揭示其内在增强增韧机理.开发的新材料可提升水硬性石灰体系的服役性能,拓展其在古建筑修复和新型墙体加固工程中的应用.
天然水硬性石灰为法国Saint‑Astier公司生产的NHL5型石灰(NHL5),外观呈浅灰色,其矿物成分包括硅酸二钙(C2S)、Ca(OH)2、CaCO3和少量SiO2晶体;偏高岭土为内蒙古超牌新材料公司生产的白色粉末状高活性偏高岭土,其主要化学成分为SiO2和Al2O3,是典型的非晶态物质. 胶凝材料的化学组成(质量分数,文中涉及的组成、比值等除特殊说明外均为质量分数或质量比)见
Binder | CaO | SiO2 | Fe2O3 | Al2O3 | MgO | K2O | SO3 | Na2O | Other |
---|---|---|---|---|---|---|---|---|---|
NHL5 | 77.07 | 18.00 | 0.64 | 1.87 | 1.22 | 0.24 | 0.56 | 0.07 | 0.23 |
Metakaolin | 0.38 | 57.65 | 1.12 | 38.81 | 0.21 | 0.54 | 0.02 | 0.06 | 1.21 |

图1 胶凝材料的XRD图谱
Fig.1 XRD patterns of binders
Fiber | Density/(g·c | Tensile strength/MPa | Elastic modulus/GPa | Diameter/mm | Length/mm | Melting temperature/℃ |
---|---|---|---|---|---|---|
PVA | 1.30 | 1 620 | 42.8 | 0.039 | 12 | 243 |
BF | 2.75 | 2 130 | 78.0 | 0.017 | 12 | 1 500 |
PE | 0.97 | 3 000 | 116.0 | 0.024 | 12 | 144 |

图2 细骨料的光学显微镜照片
Fig.2 Optical microscope images of fine aggregates
设置水胶比为0.55,砂胶比为0.40,胶凝材料m(NHL5)∶m(偏高岭土)=0.70∶0.30,纤维体积掺量为1.7%.以胶凝材料的质量计,水的用量为55%,试件的配合比见
Specimen | Sand | Fiber | ||||
---|---|---|---|---|---|---|
Quartz sand | Limestone sand | PVA | BF | PE | ||
QS‑PVA | 40 | 0 | 2.4 | 0 | 0 | |
CS‑PVA | 0 | 40 | 2.4 | 0 | 0 | |
QS‑BF | 40 | 0 | 0 | 5.3 | 0 | |
CS‑BF | 0 | 40 | 0 | 5.3 | 0 | |
QS‑PE | 40 | 0 | 0 | 0 | 1.8 | |
CS‑PE | 0 | 40 | 0 | 0 | 1.8 | |
QS0 | 40 | 0 | 0 | 0 | 0 | |
CS0 | 0 | 40 | 0 | 0 | 0 |
试件的搅拌成型与养护步骤如下:(1)细骨料预湿.将细骨料投入搅拌机后加入总拌和水的8%,搅拌1 min, 使其充分润湿以提高表观黏聚
采用40 mm×40 mm×40 mm的立方体试件,每组制备3个试件,结果取平均值.抗压试验在YAW4306型MTS电液伺服试验机上进行,采用位移加载模式,加载速率为0.5 mm/min.加载过程中计算机实时采集加载时间、荷载和承压板位移等数据.
试件加载破坏过程的试验现象为:加载初期,试件表面无明显变化;当荷载增加至约峰值荷载的80%时,表面开始出现微裂缝;随着荷载的继续增大,微裂缝延伸扩展,并伴随新裂纹产生;当加载至峰值荷载附近时,裂缝贯穿试件;此后,荷载随变形增大而下降,裂缝继续扩展,试件横向变形明显增大.
试件的受压破坏形态见

图3 试件的受压破坏形态
Fig.3 Compression failure modes of specimens
试件7、28 d抗压强度f28 d、f28 d及其比值(f7 d/f28 d)见

图4 各组试件的抗压强度及其比值
Fig.4 Compressive strength and its ratio of specimens
试件的拉伸应力-应变曲线见

图5 试件的拉伸应力-应变曲线
Fig.5 Tensile stress‑strain curves of specimen
已有研究表
由
Specimen | σfc/MPa | εfc/% | Et/GPa | σt/MPa | εt/% |
---|---|---|---|---|---|
QS‑PVA | 1.409 | 0.026 | 5.443 | 1.994 | 4.197 |
CS‑PVA | 1.267 | 0.032 | 3.857 | 1.744 | 4.407 |
QS‑BF | 0.960 | 0.017 | 5.433 | 1.787 | 0.028 |
CS‑BF | 0.798 | 0.016 | 4.710 | 1.517 | 0.033 |
QS‑PE | 1.133 | 0.019 | 5.731 | 1.530 | 3.433 |
CS‑PE | 0.886 | 0.032 | 3.942 | 1.913 | 5.604 |
通常,高延性水硬性石灰材料的破坏裂缝主要从有害缺陷处开始扩展,纤维在缺陷处起到桥接作用,使应力重分布,从而改善应力集中程度,延缓裂缝张开,对石灰基材料起到增强增韧的作用. 裂缝间距体现了裂缝密度及多缝开裂的饱和程度,裂缝间距越小代表裂缝密度越大,多缝开裂的饱和程度越高,延性越好.
试件的开裂形态图见

图6 试件的开裂形态图
Fig.6 Crack morphology diagrams of specimens

图7 试件的平均裂纹间距和宽度
Fig.7 Mean crack spacing and width of specimens
试件拉伸断面的SEM照片见

图8 试件拉伸断面的SEM照片
Fig.8 SEM images of tensile crack plane of specimens
(1)使用PVA、PE和BF纤维以及石英砂(QS)、石灰石砂(CS)掺入天然水硬性石灰-偏高岭土复合胶凝材料中,制备出具有应变硬化和微裂纹控制功能的高延性天然水硬性石灰基材料,为水硬性石灰体系的性能提升及其在古建筑修复和新型墙体加固工程中的延伸应用提供了新的选择.
(2)水硬性石灰基材表现为脆性破坏特征,而纤维的加入可显著提高其抗压韧性. 掺PVA、PE纤维试件的破坏完整性较好,PVA纤维使QS基材28 d抗压强度降低18.9%,使CS基材降低16.9%;PE纤维使QS基材28 d抗压强度降低14.6%,使CS基材降低16.9%.掺BF纤维试件出现表面碎块剥离现象,BF纤维使QS基材28 d抗压强度降低42.8%,使CS基材降低39.7%.
(3)PVA、PE纤维与QS和CS组合均可显著提高材料的抗拉强度、延性和裂缝控制能力,出现饱和多缝开裂并将裂缝宽度控制在100 μm以内. 试件CS‑PE整体抗拉性能最优,抗拉强度达1.913 MPa,极限拉伸应变达5.604%. 试件QS‑PVA和CS‑PVA具有相似的抗拉强度,极限拉伸应变均达4.000%以上. 相同掺量下BF纤维组试件均为单缝开裂,在提高石灰延性方面没有贡献.
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