摘要
测试了混杂聚丙烯纤维(PPF)-回收轮胎钢纤维(RTSF)增强超高性能混凝土(UHPC)高温后的抗压强度,并研究了其工作性能.结果表明:PPF体积分数达到0.9%后,可以防止UHPC发生高温爆裂;UHPC的抗压强度随着温度的升高先增大后减小,400 ℃作用后达到最大值,比20 ℃作用后提高了9.2%~19.9%;相同温度作用后,UHPC的抗压强度随着PPF体积分数的增大而降低;PPF熔化前与基体有效黏结,其与RTSF均可发挥桥连作用,PPF熔化后在基体中形成孔道,提高了UHPC的耐高温性能.
超高性能混凝土(UHPC)的致密结构使内部水蒸气难以逸
本文将PPF和RTSF混杂掺入UHPC基体,分析温度和PPF体积分数对UHPC工作性能、爆裂和抗压强度的影响,建立UHPC相对抗压强度的计算式.采用扫描电镜对UHPC的微观结构进行观测,揭示混杂PPF‑RTSF对UHPC高温后力学性能的作用机理.
P·O 42.5级普通硅酸盐水泥,密度为3 090 kg/
Fiber | Length/mm | Diameter/mm | Density/(kg· | Melting point/℃ | Strength/MPa | Elastic modulus/GPa |
---|---|---|---|---|---|---|
PPF | 12.0 | 0.03 | 910 | 165 | 486 | 4.8 |
RTSF | 3.1-15.6 | 0.22 | 7 850 | 1 535 | 2 165 | 200.0 |

图1 RTSF的长度分布图
Fig.1 Length distribution diagram of RTSF
Specimen | φPPF/% | Mix proportion/(kg· | |||||||
---|---|---|---|---|---|---|---|---|---|
Cement | Silica fume | Slag | Quartz sand | Water | Superplasticizer | RTSF | PPF | ||
SP03 | 0.3 | 799.00 | 240.00 | 120.00 | 959.00 | 209.00 | 46.34 | 157.00 | 2.73 |
SP06 | 0.6 | 799.00 | 240.00 | 120.00 | 959.00 | 209.00 | 46.34 | 157.00 | 5.46 |
SP09 | 0.9 | 799.00 | 240.00 | 120.00 | 959.00 | 209.00 | 46.34 | 157.00 | 8.19 |
SP12 | 1.2 | 799.00 | 240.00 | 120.00 | 959.00 | 209.00 | 46.34 | 157.00 | 10.92 |
SP15 | 1.5 | 799.00 | 240.00 | 120.00 | 959.00 | 209.00 | 46.34 | 157.00 | 13.65 |
首先,按配合比将石英砂、水泥、硅灰和矿粉干拌3 min;接着,加入水和减水剂,搅拌5 min;然后,加入PPF和RTSF,继续搅拌5 min至纤维分布均匀;最后,搅拌完成后将拌和物浇筑到40 mm×40 mm×160 mm的棱柱体模具中,并在振动台上振捣密实. 24 h后脱模,放入(20±2) ℃、相对湿度在95%以上的标准养护室养护至28 d.
根据GB/T 2419—2005《水泥胶砂流动度测定方法》测试UHPC的流动度.为避免升温过程中因含湿量过大导致试件爆裂,在高温试验前,将试件放入(105±5) ℃的烘箱烘干24 h.采用高温炉对烘干后的试件进行加热,设定目标温度T为20、200、400、600、800 ℃,升温速率为4 ℃/min,达到目标温度后恒温2 h,避免试件因受热不均而导致试验误差;恒温后关闭高温炉,使试件在炉内自然冷却至室温. 根据GB/T 17671—2021《水泥胶砂强度检验方法(ISO法)》,使用微机控制电液伺服万能试验机对试件进行抗压强度测试.利用泰思肯公司的Mira4扫描电镜(SEM)观测UHPC基体和纤维的形貌.
PPF体积分数对UHPC流动度的影响见

图2 PPF体积分数对UHPC流动度的影响
Fig.2 Effect of φPPF on flowability of UHPC
高温试验过程中,试件SP03、SP06分别在400~420、450~500 ℃发生爆裂;φPPF≥0.9%的UHPC在不同温度作用后均保持完整.高温下,水泥水化反应和火山灰反应的持续进行使UHPC基体更致
不同PPF体积分数的UHPC试件表面颜色随温度变化规律一致.随着温度的升高,试件表面颜色分别为青黑色(20 ℃)、青灰色(200 ℃)、黄褐色(400 ℃)、黄灰色(600 ℃)和灰白色(800 ℃).
高温后UHPC各组分的物理及化学变化,增大了UHPC的内部损伤,宏观表现为质量损失率增大和力学性能变

图3 UHPC的质量损失率
Fig.3 Weight loss rate of UHPC
温度对UHPC抗压强度的影响见

图4 温度对UHPC抗压强度的影响
Fig.4 Effect of temperature on compressive strength of UHPC
由
高温作用后,将UHPC抗压强度fc,T与常温下抗压强度fc之比记为相对抗压强度(fc,T/fc).Ju
(1) |
根据PPF在高温下的状态变化,将加热温度分为3个阶段进行分析:(1)阶段I(20 ℃),PPF保持固态稳定;(2)阶段Ⅱ(200 ℃),PPF为熔融状态;(3)阶段Ⅲ(400~800 ℃),PPF分子汽化逸出.不同阶段混杂PPF‑RTSF增强UHPC微观结构示意图见

图5 不同阶段混杂PPF‑RTSF增强UHPC微观结构示意图
Fig.5 Schematic demonstration of microstructure of hybrid PPF‑RTSF reinforced UHPC at different stages

图6 不同温度作用后纤维与UHPC基体界面的SEM照片
Fig.6 SEM images of interface between fiber and UHPC substrate after exposure to different temperatures
对阶段I:常温状态下UHPC微观结构较为致密(见
对阶段Ⅱ:200 ℃作用后,PPF熔化并吸附在孔道内壁周围(见
对阶段Ⅲ:400~800 ℃时,PPF完全汽化逸出形成纤维孔道(见
(1)超高性能混凝土(UHPC)的流动度随着聚丙烯纤维(PPF)体积分数的升高而降低,PPF体积分数为0.6%~1.5%的UHPC流动度比PPF体积分数为0.3%的UHPC降低了3.6%~15.0%. UHPC的质量损失率随着温度的升高而增大,各温度下不同PPF体积分数UHPC的质量损失率相近.
(2)温度从20 ℃升至800 ℃时,UHPC的抗压强度呈先增大后减小的趋势.400 ℃时UHPC的抗压强度达到最大值,比20 ℃时提高了9.2%~19.9%;400 ℃后UHPC的抗压强度急剧下降.20~400 ℃水化产物的增多使纤维和基体的黏结更紧密,400~800 ℃作用后废旧轮胎钢纤维(RTSF)与基体的黏结程度减弱,基体内孔隙和裂纹网络扩展增加了内部缺陷.
(3)PPF体积分数0.3%和0.6%的UHPC(RTSF体积分数为2.0%),在400~500 ℃发生爆裂,PPF体积分数达到0.9%可以防止UHPC高温爆裂.各个温度作用后UHPC的抗压强度随着PPF体积分数的增大而减小;高温作用后PPF熔化可以缓解UHPC高温爆裂,同时增大了内部缺陷.
(4)常温下PPF和RTSF可以在UHPC基体中发挥协同作用,有效抑制裂纹产生和发展.高温作用后RTSF良好的导热性使UHPC的温度传递更加均匀,PPF熔化后的孔道可以释放孔隙蒸汽压力,缓解爆裂损伤. 同时,高温后RTSF与基体界面黏结力逐渐减弱,RTSF周围出现的微裂纹与PPF熔化后形成的孔道相连形成网络,增大了基体的内部损伤.
参考文献
朋改非, 杨娟, 石云兴, 等. 超高性能混凝土抗高温爆裂性能试验研究[J]. 建筑材料学报, 2017, 20(2):229‑233. [百度学术]
PENG Gaifei, YANG Juan, SHI Yunxing, et al. Explosive spalling resistance of ultrahigh performance concrete[J]. Journal of Building Materials, 2017, 20(2):229‑233.(in Chinese) [百度学术]
LI Y, ZHANG D. Effect of lateral restraint and inclusion of polypropylene and steel fibers on spalling behavior, pore pressure, and thermal stress in ultra‑high‑performance concrete (UHPC) at elevated temperature[J]. Construction and Building Materials, 2021, 271:121879. [百度学术]
BANERJI S, KODUR V, SOLHMIRZAEI R. Experimental behavior of ultra high performance fiber reinforced concrete beams under fire conditions[J]. Engineering Structures, 2020, 208:110316. [百度学术]
QIN H, YANG J C, YAN K, et al. Experimental research on the spalling behaviour of ultra‑high performance concrete under fire conditions[J]. Construction and Building Materials, 2021, 303:124464. [百度学术]
JU Y, WANG L, LIU H B, et al. An experimental investigation of the thermal spalling of polypropylene‑fibered reactive powder concrete exposed to elevated temperatures[J]. Science Bulletin, 2015, 60(23):2022‑2040. [百度学术]
郑文忠, 李海艳, 王英. 高温后不同聚丙烯纤维掺量活性粉末混凝土力学性能试验研究[J]. 建筑结构学报, 2012, 33(9):119‑126. [百度学术]
ZHENG Wenzhong, LI Haiyan, WANG Ying. Mechanical properties of reactive powder concrete with different dosage of polypropylene fiber after high temperature[J]. Journal of Building Structures, 2012, 33(9):119‑126. (in Chinese) [百度学术]
LI Y, TAN K H, YANG E H. Synergistic effects of hybrid polypropylene and steel fibers on explosive spalling prevention of ultra‑high performance concrete at elevated temperature[J]. Cement and Concrete Composites, 2019, 96:174‑181. [百度学术]
JANG H S, SO H S, SO S Y. The properties of reactive powder concrete using PP fiber and pozzolanic materials at elevated temperature[J]. Journal of Building Engineering, 2016, 8:225‑230. [百度学术]
KAHANJI C, ALI F, NADJAI A, et al. Effect of curing temperature on the behaviour of UHPFRC at elevated temperatures[J]. Construction and Building Materials, 2018, 182:670‑681. [百度学术]
FOŘT J, TRNÍK A, ČÍTEK D, et al. Residual mechanical properties of hybrid fiber reinforced HPC exposed to high temperatures[J]. Key Engineering Materials, 2016, 722:52‑58. [百度学术]
LI H Y, LIU G. Tensile properties of hybrid fiber‑reinforced reactive powder concrete after exposure to elevated temperatures[J]. International Journal of Concrete Structures and Materials, 2016, 10(1):29‑37. [百度学术]
ZHENG W Z, LI H Y, WANG Y. Compressive behaviour of hybrid fiber‑reinforced reactive powder concrete after high temperature[J]. Materials and Design, 2012, 41:403‑409. [百度学术]
MAO Z H, ZHANG J C, LUO Z Z, et al. Behavior evaluation of hybrid fibre‑reinforced reactive powder concrete after elevated temperatures[J]. Construction and Building Materials, 2021, 306:124917. [百度学术]
ISA M N, PILAKOUTAS K, GUADAGNINI M, et al. Mechanical performance of affordable and eco‑efficient ultra‑high performance concrete (UHPC) containing recycled tyre steel fibres[J]. Construction and Building Materials, 2020, 255:119272. [百度学术]
杨娟, 朋改非, 税国双. 再生钢纤维增韧超高性能混凝土的力学性能[J]. 复合材料学报, 2019, 36(8):1949‑1956. [百度学术]
YANG Juan, PENG Gaifei, SHUI Guoshuang. Mechanical properties of recycled steel fiber reinforced ultra‑high‑performance concrete[J]. Acta Materiae Compositae Sinica, 2019, 36(8):1949‑1956. (in Chinese) [百度学术]
侯永强, 尹升华, 赵国亮, 等. 聚丙烯纤维增强尾砂胶结充填体力学及流动性能研究[J]. 材料导报, 2021, 35(19):19030‑19035. [百度学术]
HOU Yongqiang, YIN Shenghua, ZHAO Guoliang, et al. Study on the mechanical and flow properties of polypropylene fiber reinforced cemented tailings backfill[J]. Materials Reports, 2021, 35(19):19030‑19035. (in Chinese) [百度学术]
ZHONG H, ZHANG M Z. Experimental study on engineering properties of concrete reinforced with hybrid recycled tyre steel and polypropylene fibres[J]. Journal of Cleaner Production, 2020, 259:120914. [百度学术]
朋改非, 杨娟, 石云兴. 超高性能混凝土高温后残余力学性能试验研究[J]. 土木工程学报, 2017, 50(4):73‑79. [百度学术]
PENG Gaifei, YANG Juan, SHI Yunxing. Experimental study on residual mechanical properties of ultra‑high performance concrete exposed to high temperature[J]. China Civil Engineering Journal, 2017, 50(4):73‑79. (in Chinese) [百度学术]
龚建清, 邓国旗, 单波. 活性粉末混凝土高温后超声研究及微观分析[J]. 湖南大学学报(自然科学版), 2018, 45(1):68‑76. [百度学术]
GONG Jianqing, DENG Guoqi, SHAN Bo. Ultrasonic test and microscopic analysis of reactive powder concrete exposed to high temperature[J]. Journal of Hunan University(Natural Science), 2018, 45(1):68‑76. (in Chinese) [百度学术]
何越骁, 黄维蓉, 郭江川, 等. 共聚甲醛纤维超高性能混凝土高温后残余力学性能[J]. 硅酸盐学报, 2022, 50(3):839‑848. [百度学术]
HE Yuexiao, HUANG Weirong, GUO Jiangchuan, et al. Residual mechanical properties of ultra‑high performance concrete doped with copolymer formaldehyde fiber exposed to high temperature[J]. Journal of the Chinese Ceramic Society, 2022, 50(3):839‑848. (in Chinese) [百度学术]
杜咏, 严奥宇, 戚洪辉. 纤维增强超高强混凝土防高温爆裂研究[J]. 建筑材料学报, 2021, 24(1):216‑223. [百度学术]
DU Yong, YAN Aoyu, QI Honghui. Spalling prevention of fibre reinforced ultra‑high strength concrete (FRUHSC) subject to high temperature[J]. Journal of Building Materials, 2021, 24(1):216‑223. (in Chinese) [百度学术]
袁明, 吴晓娟, 颜东煌, 等. 加载速率对钢纤维与超高性能混凝土黏结性能的影响[J]. 长安大学学报(自然科学版), 2022, 42(5):62‑72. [百度学术]
YUAN Ming, WU Xiaojuan, YAN Donghuang, et al. Effect of loading rate on bond properties of steel fiber and ultra‑high performance concrete[J]. Journal of Chang’an University (Natural Science), 2022, 42(5):62‑72. (in Chinese) [百度学术]
SULTAN H K, ALYASERI I. Effects of elevated temperatures on mechanical properties of reactive powder concrete elements[J]. Construction and Building Materials, 2020, 261:120555. [百度学术]
HIREMATH P N, YARAGAL S C. Performance evaluation of reactive powder concrete with polypropylene fibers at elevated temperatures[J]. Construction and Building Materials, 2018, 169:499‑512. [百度学术]