摘要
采用不同尺寸的EPS颗粒预制混凝土的初始孔隙率及初始孔径尺寸,系统开展4种初始孔隙率和5种初始孔径尺寸下混凝土的轴心抗压强度和弹性模量试验研究,并基于数值统计原理分析含初始缺陷混凝土力学性能的影响规律.结果表明:混凝土的轴心抗压强度和弹性模量降幅随初始孔隙率的增加呈近似线性上升趋势,混凝土的轴心抗压强度降幅随着初始孔径尺寸的增加呈近似对数上升趋势.同时考虑初始孔隙率和初始孔径尺寸的影响,混凝土在初始小孔径、高孔隙率下的损伤度低于其在初始大孔径、低孔隙率下的损伤度.相较初始孔径尺寸,初始孔隙率对混凝土轴心抗压强度和弹性模量的损伤更为显著.
混凝土为典型的非均质多孔材料.受施工方法、振捣工艺、养护条件和环境温湿度等众多因素的影响,混凝土不可避免地存在初始孔隙缺
鉴于此,本文通过控制EPS颗粒掺量及颗粒直径,预制了含4种初始孔隙率及5种初始孔径尺寸的混凝土,系统研究了其轴心抗压强度及弹性模量的演化规律.同时采用数值统计原理,分析了含初始孔隙缺陷混凝土的力学性能变化规律.
粗骨料采用5~20 mm、20~40 mm的二级配石灰岩碎石;细骨料采用人工砂,两者物理性能指标见表
Apparent density/ (kg· | Mud content (by mass)/% | Water absorption (by mass)/% | Crushing value(by mass)/% | Needle content(by mass)/% |
---|---|---|---|---|
2 790 | 0.30 | 0.21 | 6.20 | 2.00 |
Fineness modulus | Apparent density/(kg· | Solidity/% | Dry water absorption(by mass)/% |
---|---|---|---|
2.61 | 2 790 | 1.0 | 1.20 |
EPS particle size/mm | 0.3-0.6 | 1.0-2.0 | 3.0-5.0 | 6.0-8.0 | 8.0-10.0 |
---|---|---|---|---|---|
Apparent density/(kg· | 45.0 | 28.0 | 16.0 | 15.0 | 27.0 |

图1 EPS颗粒和含EPS颗粒混凝土拌和物外观
Fig.1 Appearance of EPS particles and concrete mixture containing EPS particles
EPS particle size/mm | Porosity(by volume)/% | mW/mC | Amount of concrete material/(kg· | |||||
---|---|---|---|---|---|---|---|---|
Water | Cement | Sand | Limestone | EPS | ||||
5-20 mm | 20-40 mm | |||||||
0 | 0.57 | 165.00 | 290.00 | 842.00 | 582.00 | 582.00 | 0 | |
0.3-0.6 | 1 | 834.00 | 573.50 | 573.50 | 0.45 | |||
4 | 810.00 | 548.00 | 548.00 | 1.80 | ||||
7 | 786.00 | 522.50 | 522.50 | 3.15 | ||||
10 | 762.00 | 497.00 | 497.00 | 4.50 | ||||
1.0-2.0 | 1 | 0.57 | 165.00 | 290.00 | 834.00 | 573.50 | 573.50 | 0.28 |
4 | 810.00 | 548.00 | 548.00 | 1.12 | ||||
7 | 786.00 | 522.50 | 522.50 | 1.96 | ||||
10 | 762.00 | 497.00 | 497.00 | 2.80 | ||||
3.0-5.0 | 1 | 0.57 | 165.00 | 290.00 | 834.00 | 573.50 | 573.50 | 0.16 |
4 | 810.00 | 548.00 | 548.00 | 0.64 | ||||
7 | 786.00 | 522.50 | 522.50 | 1.12 | ||||
10 | 762.00 | 497.00 | 497.00 | 1.60 | ||||
6.0-8.0 | 1 | 0.57 | 165.00 | 290.00 | 834.00 | 573.50 | 573.50 | 0.15 |
4 | 810.00 | 548.00 | 548.00 | 0.60 | ||||
7 | 786.00 | 522.50 | 522.50 | 1.05 | ||||
10 | 762.00 | 497.00 | 497.00 | 1.50 | ||||
8.0-10.0 | 1 | 0.57 | 165.00 | 290.00 | 834.00 | 573.50 | 573.50 | 0.27 |
4 | 810.00 | 548.00 | 548.00 | 1.08 | ||||
7 | 786.00 | 522.50 | 522.50 | 1.89 | ||||
10 | 762.00 | 497.00 | 497.00 | 2.70 |
由于混凝土振动台的振动频率较高,若直接采用振动台进行振捣,EPS颗粒会严重上浮,导致混凝土的预制孔隙不均匀.因此,首先将EPS颗粒、水泥及骨料干拌30 s,再加水继续拌和至180 s;然后将拌和物装入模具,采用人工振捣方式进行振捣,为保证不同组数之间的EPS颗粒均匀程度、密实程度一致,将每个试件分3层装入试模,且每层均人工振捣40次;最后采用振动台振动5 s,24 h后拆模,自然养护至标准龄期后开展相关试验.由于EPS颗粒质量较轻,称量时使用精度为0.000 1 g的电子天平.
试验采用尺寸为ϕ150×300 mm的圆柱体试件,设置21个试验组,其中包含未预制初始孔隙的标准对照组.每个试验组共6块试件,3块用于测定轴心抗压强度,另外3块用于测定弹性模量.混凝土的轴心抗压强度和弹性模量按照SL/T 352—2020《水工混凝土试验规程》进行测试.弹性模量采用应变片法,试验前首先在试件左右两侧对称粘贴应变片;然后将试件放入加载平台,同时将应变片与数据采集装置连接,待正式试验开始前,先对试件进行3次预加载,再以0.5 MPa/s的间隔分步加载,并记录每步加载所对应的应变值,直至加载压力超过40%破坏荷载后停止;最后以0.3 MPa/s的恒定速率加载至试件破坏.
将混凝土预制的目标初始孔隙率定义为EPS颗粒表观体积与混凝土体积的百分比.以未预制初始孔隙混凝土与不同预制初始孔隙混凝土的轴心抗压强度差值及弹性模量差值占未预制孔隙混凝土的百分比,作为含不同初始孔隙混凝土轴心抗压强度及弹性模量的降幅,其变化曲线如

图2 不同初始孔径尺寸下混凝土轴心抗压强度及弹性模量降幅与初始孔隙率的关系
Fig.2 Relationship between reduction of axial compressive strength and elastic modulus of concretes and initial porosity under different initial pore sizes
由
不同初始孔隙率下混凝土轴心抗压强度及弹性模量降幅与初始孔径尺寸的关系如

图3 不同初始孔隙率下混凝土轴心抗压强度及弹性模量降幅与初始孔径尺寸的关系
Fig.3 Relationship between reduction of axial compressive strength and elastic modulus of concretes and initial pore size under different initial porosities
由
由
为进一步分析初始孔隙率与初始孔径尺寸的综合影响规律,取不同预制初始孔隙率混凝土的轴心抗压强度、弹性模量与未预制孔隙混凝土的轴心抗压强度、弹性模量之差,与未预制孔隙混凝土的比值作为混凝土的轴心抗压强度损伤度、弹性模量损伤度.以初始孔径尺寸为X轴,初始孔隙率为Y轴,再分别以混凝土的轴心抗压强度损伤度及弹性模量损伤度为Z轴,绘制混凝土的轴心抗压损伤和弹性模量损伤曲面,如

图4 混凝土的轴心抗压强度损伤和弹性模量损伤曲面
Fig.4 Surface diagram of axial compressive strength damage and elastic modulus damage of concretes
由
利用数理统计原理,采用双因素方差分析法对不同预制初始孔隙下混凝土的轴心抗压强度损伤度和弹性模量损伤度进行分析.以不同初始孔隙率(因素A)和初始孔径尺寸(因素B)这两个因素对混凝土轴心抗压强度和弹性模量的影响效应显著性进行分析.假设两因素之间无交互影响,则双因素方差数学模型见
(1) |
式中:为双因素影响效应();为总均值; 为因素A各变量的主效应;为因素B各变量的主效应;为随机误差;为因素A的变量个数;为因素B的变量个数.
统计检验假设为:
(2) |
(3) |
式中:分别为因素A、因素B的原假设;分别为因素A、因素B的备假设.
在检验假设下,若因素A的组间差异性大于显著性水平λ的组间差异性,则拒绝假设,即因素A具有显著影响,反之亦然.因素B同理.
Index | Difference source | Degree of freedom | Mean square | F value | Significance coefficient(P) | Correlation coefficient( |
---|---|---|---|---|---|---|
Axial compressive strength | Porosity (factor A) | 3 | 0.065 | 175.290 | 0.000 1 | 0.982 |
Pore size(factor B) | 4 | 0.012 | 32.938 | 0.000 1 | ||
Elastic modulus | Porosity (factor A) | 3 | 0.031 | 145.630 | 0.000 1 | 0.976 |
Pore size(factor B) | 4 | 0.003 | 14.262 | 0.000 1 |
由
采用多元线性回归对试验数据进行拟合,可得到初始孔隙率与初始孔径尺寸对混凝土轴心抗压强度损伤度及弹性模量损伤度的拟合函数,分别见式(
(5) |
(6) |
式中:为混凝土的轴心抗压强度损伤度;为混凝土的弹性模量损伤度;为混凝土的初始孔隙率;为混凝土的初始孔径尺寸.
Index | Mean absolute error (SMAE) | Mean square error (SMSE) | Root mean square error (SRMSE) | Correlation coefficient ( |
---|---|---|---|---|
Axial compressive strength | 0.026 00 | 0.001 10 | 0.033 00 | 0.912 |
Elastic modulus | 0.013 00 | 0.000 26 | 0.016 00 | 0.951 |
由
(1)在相同初始孔径尺寸条件下,混凝土的轴心抗压强度及弹性模量降幅均随着初始孔隙率的增大呈近似线性上升趋势;在相同初始孔隙率条件下,混凝土的轴心抗压强度及弹性模量降幅均随初始孔径尺寸的增大而上升,轴心抗压强度呈对数上升趋势,弹性模量则呈线性上升趋势,且混凝土轴心抗压强度对初始孔径尺寸为0.3~2.0 mm的孔隙敏感性更为显著.
(2)同时考虑初始孔径尺寸和初始孔隙率的影响,混凝土在初始小孔径、高孔隙率下的损伤度低于初始大孔径、低孔隙率下的损伤度.混凝土的初始孔隙率及初始孔径尺寸均对含初始孔隙缺陷混凝土的力学性能存在影响.而相较初始孔径尺寸,初始孔隙率对混凝土轴心抗压强度和弹性模量的损伤影响更为显著.
(3)相同初始孔隙率及初始孔径尺寸下,混凝土轴心抗压强度较弹性模量对初始空隙缺陷具有更加显著的敏感性.初始孔径尺寸越大,孔隙数量就越少,因此对含初始孔隙缺陷混凝土的力学性能进行评价时,应综合考虑初始孔隙率和初始孔径尺寸对混凝土强度及弹性模量的耦合影响.
参考文献
孙浩然, 邹春霞, 薛慧君, 等. 模袋混凝土干湿-冻融侵蚀孔结构的分形特征[J]. 建筑材料学报, 2022, 25(2):124‑130. [百度学术]
SUN Haoran, ZOU Chunxia, XUN Huijun, et al. Fractal characteristics of dry‑wet and freeze‑thaw erosion pore structure of mold‑bag concrete[J]. Journal of Building Materials, 2022, 25(2):124‑130.(in Chinese) [百度学术]
LIAO L, WU S Q, HAO R Q, et al. The compressive strength and damage mechanisms of pervious concrete based on 2D mesoscale pore characteristics[J]. Construction and Building Materials, 2023, 386:131561. [百度学术]
WANG W J, SU C, FU D. Automatic detection of defects in concrete structures based on deep learning[J]. Structures, 2022, 43:192‑199. [百度学术]
HOU S D, DUAN Z H, YE T H, et al. Mechanical properties and pore structure of 3D printed mortar with recycled powder[J]. Construction and Building Materials, 2023,394:132068. [百度学术]
孙浩凯, 高阳, 郑新雨, 等. 基于图像统计的带预制缺陷混凝土破坏机理[J]. 建筑材料学报, 2021, 24(6):1154‑1162. [百度学术]
SUN Haokai, GAO Yang, ZHENG Xinyu, et al. Failure mechanism of precast defective concrete based on image statistics[J]. Journal of Building Materials, 2021, 24(6):1154‑1162. (in Chinese) [百度学术]
陈正, 陈犇, 逄子超, 等. 青藏高原环境下混凝土结构密实性超声无损检测研究[J]. 工程力学, 2023, 40(6):1‑8. [百度学术]
CHEN Zheng, CHEN Ben, PANG Zichao, et al. Ultrasonic non‑destructive testing of concrete structures compactness under circumstances of Qinghai‑Tibet Plateau[J]. Engineering Mechanics, 2023, 40(6):1‑8.(in Chinese) [百度学术]
邵化建, 李宗利, 肖帅鹏, 等. 干湿循环作用下混凝土力学性能及微观结构研究[J]. 硅酸盐通报, 2021, 40(9):2948‑2955. [百度学术]
SHAO Huajian, LI Zongli, XIAO Shuaipeng, et al. Mechanical properties and microstructure of concrete under drying⁃wetting cycles[J]. Bulletin of the Chinese Ceramic Society, 2021, 40(9):2948‑2955. (in Chinese) [百度学术]
MOHAN M K, RAHUL A V, VAN STAPPEN JEROEN F, et al. Assessment of pore structure characteristics and tortuosity of 3D printed concrete using mercury intrusion porosimetry and X‑ray tomography[J]. Cement and Concrete Composites,2023,140:105104. [百度学术]
LIAN S S, MENG T, ZHAO Y X, et al. Experimental and theoretical analyses of chloride transport in recycled concrete subjected to a cyclic drying‑wetting environment[J]. Structures, 2023, 52(6):1020‑1034. [百度学术]
郭嘉, 高嵩, 班顺莉, 等. 再生混凝土单轴受压下多重界面过渡区的破坏机理研究[J]. 硅酸盐通报, 2022, 41(10):3445‑3457. [百度学术]
GUO Jia, GAO Song, BAN Shunli, et al. Failure mechanism of multi‑interfacial transition zones of recycled concrete under uniaxial compression[J]. Bulletin of the Chinese Ceramic Society, 2022, 41(10):3445‑3457. (in Chinese) [百度学术]
LIU L, HE Z, CAI X H, et al. Application of low‑field NMR to the pore structure of concrete[J]. Applied Magnetic Resonance, 2021, 52(9):15‑31. [百度学术]
LIANG C F, YOU J K, GU F, et al. Enhancing the elastic modulus of concrete prepared with recycled coarse aggregates of different quality by chemical modifications[J]. Construction and Building Materials, 2022,360:129590. [百度学术]
郭玉柱, 陈徐东, 宁英杰, 等. 基于X‑CT的蒸养大掺量矿物掺合料砂浆孔结构[J].建筑材料学报,2022,25(9):885‑892. [百度学术]
GUO Yuzhu, CHEN Xudong, NING Yingjie, et al. Pore structure of steam cured high volume mineral admixture mortar based on X‑CT technology[J]. Journal of Building Materials, 2022, 25(9):885‑892. (in Chinese) [百度学术]
杜向琴, 张臻, 娄宗科, 等. 基于CT图像的细观混凝土孔隙缺陷研究[J]. 建筑材料学报, 2020, 23(3):603‑610. [百度学术]
DU Xiangqin, ZHANG Zhen, LOU Zongke, et al. Research of pore defects in mesoscopic concrete based on CT images[J]. Journal of Building Materials, 2020, 23(3):603‑610. (in Chinese) [百度学术]
董健苗, 曹嘉威, 李洋洋, 等 . EPS水泥基复合材料界面改性试验研究[J]. 建筑材料学报, 2019, 22(6):917‑921. [百度学术]
DONG Jianmiao, CAO Jiawei, LI Yangyang, et al. Interfacial modification of EPS cement based composite materials[J]. Journal of Building Materials, 2019, 22(6):917‑921.(in Chinese) [百度学术]
ZHANG G H, YANG Z D, YAN Y Z, et al. Experimental and theoretical prediction model research on concrete elastic modulus influenced by aggregate gradation and porosity[J]. Sustainability, 2021, 13(4):1811. [百度学术]
BABAVALIAN A, RANJBARAN A H, SHAHBEYK S. Uniaxial and triaxial failure strength of fiber reinforced EPS concrete[J]. Construction and Building Materials, 2020, 247:118617. [百度学术]
LI Y L, MA H, WEN L F, et al. Influence of pore size distribution on concrete cracking with different AEA content and curing age using acoustic emission and low‑field NMR[J]. Journal of Building Engineering, 2022, 58:105059. [百度学术]