摘要
为改善橡胶混凝土的力学性能,以纳米SiO2为改性剂,研究了纳米SiO2增强橡胶混凝土的断裂行为,采用数字图像相关方法,分析了纳米SiO2增强橡胶混凝土断裂性能,并结合微观结构分析探讨了其增强机理.结果表明:纳米SiO2的掺入对橡胶混凝土的断裂性能和强度提高效果显著;纳米SiO2与橡胶的协同作用提高了混凝土裂缝扩展稳定性,延长了断裂过程起裂到失稳的时间;纳米SiO2对橡胶混凝土断裂性能的提升归结于其对水泥基质的改善,从而提高了混凝土的承载能力.
将废旧橡胶加工后取代天然骨料掺入混凝土,可以实现废橡胶的回收再利用,且会提升混凝土的韧性、抗冲磨性能、延性及抗疲劳性能
针对传统混凝土韧性差、易开裂的缺点,国内外学者研究了橡胶的掺入对混凝土断裂性能的影响,并在提升混凝土断裂能方面达成了共
本文采用三点弯曲切口梁,结合数字图像相关(DIC)方法,研究了纳米SiO2的掺入对橡胶混凝土断裂性能的影响,并对裂缝扩展规律进行了分析;结合扫描电镜(SEM)测试,探究了纳米SiO2对橡胶混凝土断裂性能的提升机理.
用P·I 42.5基准水泥配制普通混凝土(PC);已有研究表明橡胶颗粒体积分数为20%时橡胶混凝土拥有较理想的断裂韧度且不损失较多强
Appearance | Particle size/nm | Average particle size/nm | pH value | Solution | Specific gravity | Specific surface area/(c | Viscosity/(mPa·s) |
---|---|---|---|---|---|---|---|
Liquid | 10-80 | 30 | 7.9 | Water | 1.202 | 250 ± 30 | 3.39 |
Specimen | mW/mC | Mix proportion/(kg· | fc/MPa | ft/MPa | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Stone | Sand | Water | Cement | Rubber | Nano‑SiO2 sol | Water reducer | ||||
PC | 0.43 | 1 100.00 | 675.40 | 185.00 | 430.00 | 0 | 0 | 0.30 | 44.9 | 2.99 |
RC | 0.43 | 1 100.00 | 547.90 | 185.00 | 430.00 | 56.71 | 0 | 0.43 | 34.2 | 2.70 |
NRC | 0.43 | 1 100.00 | 547.90 | 185.00 | 430.00 | 56.71 | 43.00 | 0.52 | 39.9 | 3.21 |
根据DL/T 5332—2005《水工混凝土断裂试验规程》,用微机控制电液伺服万能试验机(50 kN),采用三点弯曲切口梁试验研究橡胶混凝土双K断裂参数和断裂能,加载速率为0.05 mm/min.试验制作3组共15个试件,试件尺寸为100 mm×100 mm×515 mm,跨高比为4,初始缝长0为40 mm.用动态采集仪系统采集试验数据,得到了完整的荷载-裂缝端开口位移(P‑CMOD)曲线和荷载-位移(P‑δ)曲线.为获取断裂试件表面全场应变数据,采用DIC‑3D系统对观测面全场应变进行观测.
断裂韧度是反映材料所能容纳应力场强度能力的特性,采用Xu
失稳断裂韧度的计算式为:
(1) |
(2) |
(3) |
式中:为P‑CMOD曲线的峰值荷载;S为试件两个支座间的跨度;L为试件长度;m为试件支座间的质量,用试件总质量按S/L比折算;g为重力加速度,取值9.81 m/
起裂韧度的计算式为:
(4) |
(5) |
(6) |
式中:为起裂荷载;f(')为与初始裂缝长度有关的几何形状因子;为初始缝高比.
将传统夹式引伸计(E)和DIC得到的混凝土P‑CMOD曲线进行对比,结果见

图1 混凝土的P‑CMOD曲线和P‑δ曲线
Fig.1 P‑CMOD and P‑δ curves of concretes
采用DIC对数字图像分析区域的全场位移进行监测,探究纳米SiO2的引入对橡胶混凝土断裂过程区(FPZ)裂缝扩展演化规律的影响.橡胶混凝土各加载阶段示意图见

图2 橡胶混凝土各加载阶段示意图
Fig.2 Schematic diagram of each loading stage of rubber concrete
试件PC、RC和NRC的裂缝发展图见

图3 试件PC、RC和NRC断裂过程区裂缝发展图
Fig.3 Crack propagation in FPZ of specimen PC, RC and NRC
将CMOD随时间的变化规律进行了定量分析.试件PC在480 s起裂,在80 s内失去承载能力,最大裂缝开口位移为0.74 mm,呈现出明显的脆性.试件RC和NRC分别在432、415 s开始稳定扩展,并分别在864、900 s开始失稳扩展,从起裂到失稳扩展分别持续432、485 s,此后在低载下裂缝继续扩展.与试件RC相比,试件NRC在保持较好变形能力的同时还拥有较高的承载能力.
根据P‑CMOD曲线和P‑δ曲线提供的参数,由式(

图4 试件的起裂韧度和失稳韧度
Fig.4 Crack initiation toughness and instability toughness of specimens
试件的断裂能和延性指数见

图5 试件的断裂能和延性指数
Fig.5 Comparison of fracture energy of of specimens
综上,以橡胶颗粒等体积取代20%砂时,混凝土的抗压强度、起裂韧度与峰值荷载都会受到不同程度的削弱,再掺入水泥质量3%的纳米SiO2,试件NRC的各项断裂性能指标皆高于试件RC.这是由于在纳米SiO2与橡胶颗粒综合作用下,混凝土具有更好的变形和承载能力.
纳米SiO2改性水泥基材料的增强主要从填充效应、火山灰效应、晶核效应及界面调控4个方面来解

图6 28 d龄期试件RC和NRC水化产物的SEM照片
Fig.6 SEM images of hydration products of specimen RC and NRC at 28 d
混凝土ITZ微观结构形态的SEM照片见

图7 混凝土ITZ微观结构形态的SEM照片
Fig.7 SEM images of microstructure and morphology of ITZ in concretes
有研究表明混凝土边界及尺寸效应、粗骨料最大粒径及分布等因素与断裂韧度相关,而在材料几何尺寸固定的情况下,断裂韧度的提高和强度密不可
(9) |
纳米SiO2对橡胶混凝土起裂韧度的提升归结于其对承载能力的提高,在已知抗压强度的情况下,可较准确地预测起裂韧度值.而失稳韧度是由材料承载能力和变形能力共同决定的指标,断裂过程区的变形和黏聚力均为非线性分
(1)纳米SiO2能提高橡胶混凝土的起裂韧度、失稳韧度和断裂能.掺入纳米SiO2后,橡胶混凝土断裂过程中的起裂荷载与峰值荷载分别提高了11.9%、8.0%,起裂韧度、失稳韧度和断裂能分别提高了10.7%、9.3%、5.2%.
(2)纳米SiO2通过改善橡胶混凝土强度对起裂韧度进行提升,并通过填充效应、火山灰效应、晶核效应及界面调控改善水泥基体与界面的微观结构和强度.回归分析结果表明,随着混凝土抗压强度的增大,其起裂韧度呈线性增大趋势.
(3)纳米SiO2对橡胶混凝土断裂性能的提升可以从承载能力和变形能力两方面进行解释.纳米SiO2的掺入弥补了因橡胶界面薄弱而造成的起裂韧性和峰值荷载的降低.通过提高橡胶混凝土裂缝扩展过程的黏聚力和变形能力,提高了其失稳韧度和断裂能,延缓裂缝扩展失稳时间,使试件维持更加平稳的劣化失稳状态.
参考文献
刘艳荣, 葛树奎, 韩瑜. 废旧轮胎橡胶粉改性水泥基材料研究概况[J]. 材料导报, 2014, 28(增刊2):422‑426. [百度学术]
LIU Yanrong, GE Shukui, HAN Yu. Research progress of scrap rubber powder of waste tires modified cement‑based composites[J]. Materials Reports, 2014, 28(Suppl 2):422‑426.(in Chinese) [百度学术]
JASSIM T A, ZHUANG B, IBRAHIM A M, et al. Using wasted rubber material for reducing loads and energy dispersal in building industries:State of the art[C]//IOP Conference Series:Materials Science and Engineering. Diyala: IOP Publishing, 2021, 1076(1):012114. [百度学术]
杨荣周, 徐颖, 郑强强, 等. 分级等荷循环受压下橡胶水泥砂浆的疲劳损伤演化[J]. 建筑材料学报, 2021, 24(5):961‑969. [百度学术]
YANG Rongzhou, XU Ying, ZHENG Qiangqiang, et al. Fatigue and damage evolution characteristics of rubber cement mortar under graded constant load cyclic compression[J]. Journal of Building Materials, 2021, 24(5):961‑969.(in Chinese) [百度学术]
WANG J, GUO Z Y, YUAN Q, et al. Effects of ages on the ITZ microstructure of crumb rubber concrete[J]. Construction and Building Materials, 2020, 254:119329. [百度学术]
朱星曈, 耿欧, 朱思远. 废轮胎橡胶混凝土界面过渡区特征试验研究[J]. 硅酸盐通报, 2021, 40(2):573‑578. [百度学术]
ZHU Xingtong, GENG Ou, ZHU Siyuan. Study on the characteristics of rubber concrete interface transition zone of waste tire[J].Bulletin of the Chinese Ceramic Society, 2021, 40(2):573‑578.(in Chinese) [百度学术]
ELDIN N N, SENOUCI A B. Rubber‑tire particles as concrete aggregate[J]. Journal of Materials in Civil Engineering, 1993, 5(4):478‑496. [百度学术]
GHALY A M, CAHILL IV J D. Correlation of strength, rubber content, and water to cement ratio in rubberized concrete[J]. Canadian Journal of Civil Engineering, 2005, 32(6):1075‑1081. [百度学术]
胡艳丽,高培伟, 李富荣, 等. 不同取代率的橡胶混凝土力学性能试验研究[J]. 建筑材料学报, 2020, 23(1):85‑92. [百度学术]
HU Yanli, GAO Peiwei, LI Furong, et al. Experimental study on the mechanical properties of rubber concrete with different substitution rates [J]. Journal of Building Materials, 2020, 23(1):85‑92.(in Chinese) [百度学术]
THOMAS B S, GUPTA R C, KALLA P, et al. Strength, abrasion and permeation characteristics of cement concrete containing discarded rubber fine aggregates[J]. Construction and Building Materials, 2014, 59:204‑212. [百度学术]
CHEN C Y, LEE M T. Application of crumb rubber in cement‑matrix composite [J]. Materials, 2019, 12(3):529. [百度学术]
GAO Y T, WANG B, LIU C J, et al. Experimental investigation on static compressive toughness of steel fiber rubber concrete[J]. Reviews on Advanced Materials Science, 2022, 61(1):576‑586. [百度学术]
HE L, MA Y, LIU Q T, et al. Surface modification of crumb rubber and its influence on the mechanical properties of rubber‑cement concrete[J]. Construction and Building Materials, 2016, 120:403‑407. [百度学术]
LI G Y, WANG Z K, LEUNG C K Y, et al. Properties of rubberized concrete modified by using silane coupling agent and carboxylated SBR[J]. Journal of Cleaner Production, 2016, 112:797‑807. [百度学术]
DONG Q, HUANG B S, SHU X. Rubber modified concrete improved by chemically active coating and silane coupling agent[J]. Construction and Building Materials, 2013, 48:116‑123. [百度学术]
KHAN K, AHMAD W, AMIN M N, et al. Nano‑silica‑modified concrete:A bibliographic analysis and comprehensive review of material properties[J]. Nanomaterials, 2022, 12(12):1989. [百度学术]
KIM B J, LEE G W, CHOI Y C. Hydration and mechanical properties of high‑volume fly ash concrete with nano‑silica and silica fume[J]. Materials, 2022, 15(19):6599. [百度学术]
ZHAO J B, ZHANG B F, XIE J H, et al. Effects of nano‑SiO2 modification on rubberised mortar and concrete with recycled coarse aggregates[J]. Nanotechnology Reviews, 2022, 11(1):473‑496. [百度学术]
XU J, WANG B B, ZUO J Q. Modification effects of nanosilica on the interfacial transition zone in concrete:A multiscale approach [J]. Cement and Concrete Composite, 2017, 81:1‑10. [百度学术]
徐晶, 王彬彬, 赵思晨. 纳米改性混凝土界面过渡区的多尺度表征[J]. 建筑材料学报, 2017, 20(1):7‑11. [百度学术]
XU Jing, WANG Binbin, ZHAO Sichen. Multi‑scale characterization of interfacial transition zone in nano‑modified concrete[J]. Journal of Building Materials, 2017, 20(1):7‑11.(in Chinese) [百度学术]
FANG J, ZHAO L, SHI J C. Frost resistance and pore structure of concrete incorporated with rubber aggregates and nano‑SiO2[J]. Materials, 2021, 14(5):1170. [百度学术]
ZHANG P, WAN J Y, WANG K J, et al. Influence of nano‑SiO2 on properties of fresh and hardened high performance concrete:A state‑of‑the‑art review[J]. Construction and Building Materials, 2017, 148:648‑658. [百度学术]
GRINYS A, SIVILEVIČIUS H, PUPEIKIS D, et al. Fracture of concrete containing crumb rubber[J]. Journal of Civil Engineering and Management, 2013, 19(3):447‑455. [百度学术]
REDA TAHA M M, EL‑DIEB A S, ABD EL‑WAHAB M A,et al. Mechanical, fracture, and microstructural investigations of rubber concrete[J]. Journal of Materials in Civil Engineering, 2008, 20(10):640‑649. [百度学术]
曹国瑞, 王娟, 卿龙邦, 等. 橡胶混凝土断裂性能试验研究[J]. 土木建筑与环境工程, 2018, 40(6):91‑97. [百度学术]
CAO Guorui, WANG Juan, QING Longbang, et al. Experiment study on the fracture characteristics of crumb rubber concrete[J]. Journal of Civil and Environmental Engineering, 2018, 40(6):91‑97.(in Chinese) [百度学术]
WANG J,GUO Z X, ZHANG P, et al. Fracture properties of rubberized concrete under different temperature and humidity conditions based on digital image correlation technique[J]. Journal of Cleaner Production, 2020, 276:124106. [百度学术]
刘妙燕, 陆俊, 明攀. 三点弯曲下橡胶混凝土的断裂性能[J]. 水利水运工程学报, 2021(3):31‑40. [百度学术]
LIU Miaoyan, LU Jun, MING Pan. Fracture properties of rubber concrete under three‑point bending[J]. Hydro‑Science and Engineering, 2021(3):31‑40.(in Chinese) [百度学术]
薛刚, 董亚杰, 衣笑, 等. 橡胶粒径及掺量对混凝土断裂韧性的影响[J]. 混凝土, 2022(2):99‑101, 106. [百度学术]
XUE Gang, DONG Yajie, YI Xiao, et al. Influence of rubber particle size and content on fracture toughness of concrete[J]. Concrete, 2022(2):99‑101, 106.(in Chinese) [百度学术]
张鹏, 李清富, 朱海堂, 等. 纳米SiO2和钢纤维增强混凝土的断裂韧度[J]. 建筑材料学报, 2017, 20(3):366‑372. [百度学术]
ZHANG Peng, LI Qingfu, ZHU Haitang, et al. Fracture toughness of nano‑SiO2 and steel fiber reinforced concrete [J]. Journal of Building Materials, 2017, 20(3):366‑372.(in Chinese) [百度学术]
罗素蓉,林倩,李炜源,等. 纳米材料改性再生骨料混凝土断裂性能[J].建筑材料学报, 2022, 25(11):1151‑1159. [百度学术]
LUO Surong, LIN Qian, LI Weiyuan, et al. Improvement of fracture performance of recycled aggregate concrete by nanomaterials [J]. Journal of Building Materials, 2022, 25(11):1151‑1159.(in Chinese) [百度学术]
XU S L, REINHARDT H W. Determination of double‑K criterion for crack propagation in quasi‑brittle fracture, part II:Analytical evaluating and practical measuring methods for three‑point bending notched beams[J]. International Journal of Fracture, 1999, 98(2):151‑177. [百度学术]
ANON. Determination of the fracture energy of mortar and concrete by means of three‑point bend tests on notched beams[J]. Materials and Structures, 1985, 18(4):287‑290. [百度学术]
THOMAS B S, GUPTA R C, KALLA P, et al. Strength, abrasion and permeation characteristics of cement concrete containing discarded rubber fine aggregates[J]. Construction and Building Materials, 2014, 59:204‑212. [百度学术]
张廷毅, 高丹盈, 郑光和, 等. 三点弯曲下混凝土断裂韧度及影响因素[J]. 水利学报, 2013, 44(5):601‑607. [百度学术]
ZHANG Tingyi, GAO Danying, ZHENG Guanghe, et al. Fracture toughness of concrete and influencing factors under three‑point bending[J]. Journal of Hydraulic Engineering, 2013, 44(5):601‑607.(in Chinese) [百度学术]
管俊峰, 胡晓智, 王玉锁, 等. 用边界效应理论考虑断裂韧性和拉伸强度对破坏的影响[J]. 水利学报, 2016, 47(10):1298‑1306. [百度学术]
GUAN Junfeng, HU Xiaozhi, WANG Yusuo, et al. The effects of fracture toughness and tensile strength on destruction are considered by boundary effect theory[J]. Journal of Hydraulic Engineering, 2016, 47(10):1298‑1306.(in Chinese) [百度学术]
管俊峰, 王强, HU Xiaozhi, 等. 考虑骨料尺寸的混凝土岩石边界效应断裂模型[J]. 工程力学, 2017, 34(12):22‑30. [百度学术]
GUAN Junfeng, WANG Qiang, HU Xiaozhi, et al. Boundary effect fracture model for concrete and granite considering aggregate size[J]. Engineering Mechanics, 2017, 34(12):22‑30.(in Chinese) [百度学术]
管俊峰, 姚贤华, 白卫峰, 等. 水泥砂浆断裂韧度与强度的边界与尺寸效应[J]. 建筑材料学报, 2018, 21(4):556‑560,575. [百度学术]
GUAN Junfeng, YAO Xianhua, BAI Weifeng, et al. Boundary and size effect of fracture toughness and strength of mortar[J]. Journal of Building Materials, 2018, 21(4):556‑560,575.(in Chinese) [百度学术]
张新慧, 王学志, 张晓飞, 等. 不同强度对碾压混凝土试件双K断裂参数的影响[J]. 城市建设理论研究(电子版), 2018(23):89‑91. [百度学术]
ZHANG Xinhui, WANG Xuezhi, ZHANG Xiaofei, et al. Influence of different strength on double K fracture parameters of RCC[J]. Theoretical Research in Urban Construction, 2018(23):89‑91.(in Chinese) [百度学术]
胡少伟, 范向前, 陆俊. 强度等级对混凝土双K断裂参数的影响[J]. 水电能源科学, 2012, 30(9):77‑81. [百度学术]
HU Shaowei, FAN Xiangqian, LU Jun. Influence of strength grade on double‑K fracture parameters of concrete[J]. Water Resources and Power, 2012, 30(9):77‑81.(in Chinese) [百度学术]