摘要
为了提高聚乙烯醇(PVA)纤维增强水泥基材料的力学性能,将氧化石墨烯(GO)引入PVA纤维增强水泥基材料中,探究GO掺量在0%~0.05%范围内对材料单轴拉伸性能的影响.结果表明:掺入适量的GO能够有效提高材料的单轴拉伸性能,当GO掺量为0.01%时,28 d时材料的初裂拉伸强度、极限拉伸强度和极限拉伸应变均达到最大值,与未掺GO的对照组相比分别提高了26.97%、31.28%、23.25%;适量的GO可以优化孔隙结构,减少材料内部缺陷,促进水化产物的生成,使微观结构致密化,增强纤维和基体间的界面结合力,从而改善PVA纤维增强水泥基材料的宏观性能.
传统的水泥基材料在土木工程领域中广泛应用,但其存在易开裂和韧性差等问
纳米材料也越来越多地应用于水泥基材料的改性,其对浆体微观结构的改善为解决水泥基材料的脆性问题提供了新的可能
本文主要探究引入GO后制备的PVA纤维增强水泥基材料的单轴拉伸性能,并从微观结构方面分析GO在PVA纤维增强水泥基材料中的改性机制.
胶凝材料采用炼石牌P·O 42.5普通硅酸盐水泥和Ⅱ级粉煤灰(FA),其主要化学组
Material | SiO2 | Al2O3 | Fe2O3 | CaO | MgO | SO3 | IL |
---|---|---|---|---|---|---|---|
Cement | 21.70 | 4.35 | 3.32 | 62.53 | 2.08 | 2.92 | 1.62 |
Fly ash | 45.10 | 24.20 | 3.11 | 5.60 | 2.08 | 1.78 | 3.52 |
Length/mm | Diameter/μm | Density/(g· | Tensile strength/MPa | Elastic modulus/GPa | Elongation/% |
---|---|---|---|---|---|
2.08 | 1.21 | 45.10 | 24.2 | 3.11 | 5.6 |
试验所用GO为工业级别氧化石墨烯溶液,固体质量占溶液质量的1.0%,来源于中国科学院成都有机化学有限公司.采用多功能钨丝灯扫描电镜(SEM)对GO的形貌进行表征,结果如

图1 GO的SEM图像
Fig.1 SEM image of GO

图2 GO的FTIR光谱
Fig.2 FTIR spectrum of GO

图3 GO的XPS图谱
Fig.3 XPS spectra of GO

图4 GO的XRD图谱
Fig.4 XRD pattern of GO
在本研究中,水泥与粉煤灰的质量比为72∶153,水胶比为0.30,砂胶比为0.36,纤维用量(φF,与水泥基材料的体积比)为2%.根据课题组前期的研究工
参照DL/T5150—2017《水工混凝土试验规程》,制备了尺寸为70.7 mm×70.7 mm×70.7 mm的试件,采用3 000 kN电液伺服压力试验机进行抗压强度测试.参照GB/T 17617—1999《水泥胶砂强度检测方法(ISO法)》,制备了尺寸为40 mm×40 mm×160 mm的试件,采用DYE‑300型全自动抗压抗折强度试验机进行抗折强度测试.所有试件均标准养护至规定龄期后再进行相关试验.
采用250 kN MTS疲劳试验机进行PVA纤维增强水泥基材料的单轴拉伸试验,监测了不同GO掺量的试件在拉伸状态下的应力-应变曲线.在研究PVA纤维增强水泥基材料等应变硬化材料的直接拉伸性能时,常采用哑铃型薄板试件.这种选择基于哑铃型试件具有较小的厚度,有助于减少拉力在厚度方向上的偏心影响.为了确保试验结果的科学性和可比性,参考文献[

图5 单轴拉伸性能试验哑铃型试件
Fig.5 Dumbbell type specimen for uniaxial tensile performance test (size:mm)
通过SEM观察PVA纤维增强水泥基材料破坏断面上的纤维表面形态,以评估GO对纤维与基体界面结合性能的影响.使用压汞仪(MIP)测定不同GO掺量的浆体在28 d时的孔隙结构特征.
不同GO掺量下PVA纤维增强水泥基材料的力学性能如

图6 不同GO掺量下PVA纤维增强水泥基材料的力学性能
Fig.6 Mechanical properties of PVA fiber reinforced cementitious materials with different GO dosages
在28 d时,掺0.01%GO的试件G0.01表现出多缝开裂和良好延性,如

图7 28 d试件G0.01的抗压试验破坏形态和抗折试验多缝开裂图
Fig.7 Compressive damage pattern and flexural multi‑seam cracking diagram of specimen G0.01 at 28 d

图8 不同GO掺量下PVA纤维增强水泥基材料28 d的应力-应变曲线
Fig.8 Stress‑strain curves of PVA fiber reinforced cementitious materials with different GO dosages at 28 d

图9 28 d试件G0.01的拉伸损伤形态
Fig.9 Tensile damage pattern of specimen G0.01 at 28 d

图10 不同GO掺量下PVA纤维增强水泥基材料的单轴拉伸性能
Fig.10 Uniaxial tensile properties of PVA fiber reinforced cementitious materials with different GO dosages
PVA纤维增强水泥基材料的抗拉强度主要与纤维/基体间的摩擦黏结力和化学黏结力相
28 d时PVA纤维增强水泥基材料破坏断面处纤维的微观形貌如

图11 28 d时PVA纤维增强水泥基材料破坏断面处纤维的SEM图像
Fig.11 SEM images of fibers at the section of PVA fiber reinforced cementitious materials at 28 d
Specimen | Total porosity(by volume)/% | Mode pore‑size/nm | Pore size distribution(by volume)/% | |||
---|---|---|---|---|---|---|
Harmless hole | Less harmful hole | Harmful hole | Porous hole | |||
G0 | 27.30 | 42.65 | 38.51 | 33.06 | 21.36 | 7.07 |
G0.01 | 24.89 | 33.52 | 42.17 | 37.16 | 12.01 | 8.66 |
G0.03 | 25.62 | 35.97 | 40.38 | 39.01 | 13.06 | 7.55 |
G0.05 | 28.51 | 42.19 | 35.53 | 35.76 | 21.95 | 6.76 |
适量GO的掺入还优化了孔径分布,如

图12 28 d时不同GO掺量下PVA纤维增强水泥基材料的孔径分布曲线
Fig.12 Pore size distribution curves of PVA fiber reinforced cementitious materials with different GO dosages at 28 d
(1)氧化石墨烯(GO)在PVA纤维增强水泥基材料中的应用能有效提高材料的力学性能,相对于单独采用PVA纤维增强的水泥基材料,0.01%GO的掺入使材料28 d时的初裂拉伸强度、极限拉伸强度和极限拉伸应变分别提高了26.97%、31.28%、23.25%;但GO掺量过多容易发生团聚,对PVA纤维增强水泥基材料的提升效果反而降低.
(2)从微观形貌来看,相对于单独采用PVA纤维增强的水泥基材料,掺入适量GO能够促进水化产物形成,增强水化产物与PVA纤维的黏附性,使界面结合得更紧密,增加了PVA纤维与水泥基体之间的结合强度.
(3)在PVA纤维增强水泥基材料中加入适量GO能够改善材料的孔隙率,并优化孔隙结构的分布,减少其内部缺陷,使微观结构更加致密均匀,从而改善了试件在断裂时的薄弱环节,有效提高了试件的延性.
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