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1.
杨娟  朋改非 《复合材料学报》2016,33(12):2931-2940
采用普通原材料制备56 d龄期抗压强度为140~160 MPa的空白组超高性能混凝土、钢纤维超高性能混凝土及混杂纤维超高性能混凝土,测定其遭受高温作用后的残余抗压强度和劈裂抗拉强度,并对100%含湿量的混凝土试块进行高温爆裂试验。此外,测定大小2种加热速率对超高性能混凝土高温爆裂行为的影响。结果表明:所配制混凝土的残余抗压强度均随着目标温度的升高呈现先增大再降低的趋势,800℃高温后的残余抗压强度约为常温强度的30%。钢纤维与混杂纤维混凝土的残余劈裂抗拉强度亦呈现先升高再降低的趋势,800℃高温后的残余劈裂抗拉强度分别为常温强度的15.1%和35.4%。空白组混凝土的残余劈裂抗拉强度随着目标温度的升高而单调下降,800℃高温后的强度值约为常温强度的20.3%。7.5℃/min加热速率下,100%含湿量的3种混凝土试块均发生了严重高温爆裂,单掺钢纤维可以改善超高性能混凝土的高温爆裂,但不能避免爆裂的发生,而混杂纤维对超高性能混凝土高温爆裂的改善效果并未显著优于钢纤维。2.5℃/min加热速率下,混杂纤维可避免部分超高性能混凝土试块发生爆裂。   相似文献   

2.
High-performance concrete (HPC) is prone to explosive spalling when exposed to fire, which may lead to failure of the concrete elements. Polypropylene fibers (PP) are often added to HPC, as upon their melting they create channels through which water vapor is evacuated, preventing the build-up of high vapor pressures. In self-compacting HPC (HPSCC), the amount of PP fibers needs to be limited in order to keep the self-compacting properties, which may reduce the fire resistance.In this paper, a novel strategy to reduce fire spalling in HPSCC is illustrated, based on adding small particles of superabsorbent polymers (SAP) during mixing. The SAP end up as empty macropores, similar to air voids, in the HPSCC matrix. The PP fibers-SAP voids system percolates at a lower fiber loading than the fibers alone, allowing maintenance of the self-compacting properties while reducing substantially the fire spalling. In particular, in this paper it is shown how addition of SAP is able to reduce fire spalling in thin-walled HPSCC slabs prestressed with carbon fibre reinforced plastic reinforcement.  相似文献   

3.
Fracture tests, especially at lower testing temperatures, have become quite popular in quantifying low-temperature cracking. However, current fracture testing analysis methods often use a single number, such as fracture energy or fracture toughness, to quantify cracking resistance. These tests do not capture both the initiation and propagation of the crack. The Resistance Curve, or R-curve, is widely applied in many fields, such as metal, polymer and composites. The R-curve considers cracking resistance as a function of crack extension, which includes initiation and propagation. In this research, three asphalt concrete mixtures, including hot mix, hot mix with reclaimed asphalt pavement (RAP) and warm mix with RAP were tested at two temperatures, three levels of ageing and two levels of moisture condition by the Semi-Circular Bend fracture test. R-curves were constructed using the data from the fracture test, and digital images were utilised to capture the crack extension. In addition to capturing the traditional fracture energy, two new parameters were explored using the R-curves: the cohesive energy and the propagation parameter energy rate. It was found that cohesive energy was always in a narrow range (approximately 500–1000 J/m2) compared to the fracture energy range (approximately 500–1700 J/m2) over all combinations of ageing and moisture conditions, which indicates that the crack initiation may not be as sensitive to temperature, ageing and moisture as fracture energy. The results of energy rate indicated that moisture and short-term ageing impact the crack propagation by reducing the resistance of crack growth. These results proved that R-curves are a potentially useful tool to quantify the cracking resistance of asphalt concrete in both crack initiation and propagation.  相似文献   

4.
超高性能混凝土的火灾高温性能研究综述   总被引:1,自引:0,他引:1  
朋改非  牛旭婧  成铠 《材料导报》2017,31(23):17-23
超高性能混凝土(Ultra-high-performance concrete,UHPC),以其突出的优点如超高强度与超高耐久性等,符合可持续发展战略,是混凝土科技发展的主要方向之一。近年来,UHPC的火灾高温性能吸引了广泛关注。由文献综述可知,高温会引发UHPC的爆裂和力学强度变化。爆裂主要由蒸汽压机理控制,蒸汽来源于内部游离水,高的内部湿含量往往导致剧烈的高温爆裂,有效的抑制措施是掺加聚合物纤维如聚丙烯(Polypropylene,PP)纤维。关于钢纤维对UHPC抗高温爆裂性的影响,还存在争议。高温作用后UHPC的残余强度在常温至300℃或400℃范围内有所增长,而在更高的温度下则为单调下降。残余强度增长是高温促进混凝土内部的一系列化学变化所引起。最新研究发现,组合养护是有效改善UHPC火灾高温性能的新方法,可避免爆裂发生。  相似文献   

5.
为进一步提高在海洋浪溅区等严重氯盐腐蚀环境下混凝土结构的耐久性,采用以配筋超高性能混凝土(UHPC)用作免拆模板加素填芯混凝土的技术思路,通过轴压实验研究了配筋UHPC用作免拆模板对短柱轴压力学性能的影响。结果表明,与破坏时海工混凝土柱出现大量的混凝土剥落和钢筋裸露不同,UHPC免拆模板柱的整体性良好,表面的UHPC仅出现少量剥落且钢筋不外露。同时,在等截面和相同配筋的情况下,UHPC免拆模板方柱和圆柱的开裂荷载明显高于高强海工混凝土方柱和圆柱的极限荷载,且分别达到其自身极限荷载的93%和88%。考虑到混凝土对钢筋的有效保护是影响海工混凝土结构耐久性的重要因素,配筋UHPC用作免拆模板这一思路在提高柱体的极限承载力、延性、刚度的同时还可以提高结构的开裂荷载、抗裂性能,有效地提高结构耐久性,适用于沿海工程。其中圆柱的力学性能提高幅度要远高于方柱,从配筋UHPC免拆模板的使用效果和施工便利性考虑,优选UHPC免拆模板圆柱。  相似文献   

6.
为提高纤维增强聚合物复合材料(FRP)筋混凝土梁抗裂性能,改善其脆性破坏特征,将玻璃纤维增强聚合物复合材料(GFRP)筋与橡胶集料混凝土共同应用于梁构件中。采用ABAQUS对GFRP筋橡胶集料混凝土梁的受弯性能进行有限元模拟及参数分析,探究了橡胶掺量、GFRP筋配筋率、混凝土强度等级及截面高度对梁受弯性能的影响。结果表明:增加混凝土中橡胶颗粒的掺量可提高梁的开裂荷载,当橡胶掺量为15%时,开裂荷载提高了29%;增加配筋率可提高梁的开裂荷载和承载力,当受拉筋直径由10 mm增加至18 mm时,橡胶掺量为10%的GFRP筋橡胶混凝土梁开裂荷载提高了约15%,承载力提高了约85%,但配筋率增加至一定数值后,其影响不再明显;提高橡胶混凝土强度等级,可提高梁的开裂荷载及承载力,当橡胶混凝土强度等级由C25提高至C40时,开裂荷载提了高约53.7%,承载力提高了约23%;为更好地满足正常使用极限状态,GFRP筋橡胶混凝土梁的截面高度宜适当增加。   相似文献   

7.
Concrete is a poor conductor of heat, but can suffer considerable damage when exposed to fire. Unraveling the heating history of concrete is important to forensic research or to determine whether a fire-exposed concrete structure and its components are still structurally sound. Assessment of fire-damage concrete structures usually starts with visual observation of color change, cracking and spalling. On heating, a change in color from normal to pink is often observed and this is useful since it coincides with the onset of significant loss of concrete strength. This paper presents results of cores strength, as well as, optical microscopy investigations of fire-damaged concrete. Samples were taken from concrete that had been exposed to fire. Optical microscopy has focused on microstructure of cement paste, aggregates, microvoids and cracks, as well as, on quantification the crack patterns found in heated concrete samples. The physical condition of concrete sample in combination with the microscopic examination, enable a petrographer to make a reasonable estimation of the minimum exposure temperature and its relative impact to the depth of damage in concrete.  相似文献   

8.
This paper deals with modelling of plain concrete in tension. The aim is to improve the accuracy of the numerical analyses for projectile and fragment impacts on concrete. A bi-linear crack softening law and a strain rate-dependent law are implemented in the hydrocode AUTODYN. Parametric studies are made, and numerical analyses are compared with experiments conducted and with experiments found in the literature. The depth of penetration is mainly dependent on the compressive strength of the concrete. However, to correctly model spalling, cracking and scabbing in concrete, the tensile strength, fracture energy, and strain rate in tension are very important. It is shown that the accuracy of the results in the numerical analyses of concrete subjected to projectile and fragment impacts was improved, when using a bi-linear softening law and the modified strain rate dependency for tension.  相似文献   

9.
R-curves caused by crack face interactions are important for the strength assessment of components with small cracks. Whereas an influence of the initial crack length on the R-curve is well understood on the basis of fracture mechanics, it will be shown here that also the type of the crack affects the crack growth resistance. For a given crack-bridging relation it can be shown that 3-dimensional cracks as circular internal cracks and semi-circular surface cracks must exhibit a lower R-curve than obtainable from 2-dimensional edge cracks.  相似文献   

10.
Fly ash based geopolymer is an emerging alternative binder to cement for making concrete. The cracking, spalling and residual strength behaviours of geopolymer concrete were studied in order to understand its fire endurance, which is essential for its use as a building material. Fly ash based geopolymer and ordinary portland cement (OPC) concrete cylinder specimens were exposed to fires at different temperatures up to 1000 °C, with a heating rate of that given in the International Standards Organization (ISO) 834 standard. Compressive strength of the concretes varied in the range of 39–58 MPa. After the fire exposures, the geopolymer concrete specimens were found to suffer less damage in terms of cracking than the OPC concrete specimens. The OPC concrete cylinders suffered severe spalling for 800 and 1000 °C exposures, while there was no spalling in the geopolymer concrete specimens. The geopolymer concrete specimens generally retained higher strength than the OPC concrete specimens. The Scanning Electron Microscope (SEM) images of geopolymer concrete showed continued densification of the microstructure with the increase of fire temperature. The strength loss in the geopolymer concrete specimens was mainly because of the difference between the thermal expansions of geopolymer matrix and the aggregates.  相似文献   

11.
考虑混凝土强度、工程水泥基复合材料(ECC)强度和横向高强钢绞线配筋率等因素,研究新型复合材料“高强钢绞线网/ECC约束素混凝土”(以下简称HSE约束素混凝土)的受压性能。HSE约束素混凝土轴心受压试验显示,达到最大荷载的30%左右时,约束层ECC出现约为0.01 mm的竖向裂缝;约为最大荷载的85%时,表面最大裂缝宽度约为0.07 mm;达到最大荷载时,最大裂缝宽度仅为0.20 mm;说明该新型复合材料具有很好的裂缝分散和控制能力。之后荷载缓慢下降至最大荷载75%左右,第一根横向钢绞线断裂;达到破坏时裂而不碎,约束层和核心混凝土未发生黏结破坏,完整性良好。HSE约束素混凝土与素混凝土相比,其开裂应力提高了88%~116%;轴心抗压强度提高了21%~49%、轴心压应变增加了约45%;极限压应变提高了106%~175%。ECC强度和混凝土强度及横向钢绞线配筋率的提高,均增大其开裂和最大荷载及极限压应变。   相似文献   

12.
Spalling concrete was simulated in the laboratory by utilizing pullout test methods generally used for the determination ofin situ concrete strength. The cracking patterns displayed by pullout test specimens typify the damage of concrete by spalling. All specimens were damaged by pullout testing, repaired with epoxy mortar and subjected to a second pullout test at a later time. The test programme showed that the overriding factor which governs successful repairs to concrete is the soundness of the repair plane.  相似文献   

13.
In conventional analysis and design procedures of reinforced concrete structures, the ability of concrete to resist tension is neglected. Under cyclic loading, the tension-softening behavior of concrete influences its residual strength and subsequent crack propagation. The stability and the residual strength of a cracked reinforced concrete member under fatigue loading, depends on a number of factors such as, reinforcement ratio, specimen size, grade of concrete, fracture properties, and on the tension-softening behavior of concrete. In this work, a method is proposed to assess the residual strength of reinforced concrete beams subjected to cyclic loading. The crack extension resistance based approach is used for determining the condition for unstable crack propagation. The effect of reinforcement is modeled as a closing force counteracting the effect of crack opening produced by the external moment. The effect of percentage reinforcement and specimen size on the failure of reinforced beams is studied. Finally, the residual strength of the beams are computed by including the softening behavior of concrete.  相似文献   

14.
A new and simple method to study the change in crack resistance during the process of crack growth in ceramic materials has been developed. The method is based on using the chevron-notched short-bar test which is generally accepted as a convenient method for measuring fracture toughness. The simple modification described here allows one to measure fracture toughness using the assumption that fracture toughness changes in the process of crack growth (presence of crack resistance curve, or R-curve). This method presents many advantages, especially the long stable crack growth under mode I fracture specimen and plane strain, small specimen size and no need of pre-cracking for measuring R-curve behaviour in ceramic materials.  相似文献   

15.
高性能混凝土抗裂性能研究   总被引:3,自引:0,他引:3  
该文对高性能混凝土的抗裂性能进行了系统的研究,主要包括:高性能混凝土收缩与抗裂性能的试验方法,研制出一种测试混凝土抗裂性能的诱导开裂试验方法,该方法避免了混凝土裂缝出现位置的随机性以及混凝土塑性沉降引起的材料不均匀等带来的测试结果不准确,同时研制出一种多点、实时、自动监测混凝土试件开裂时间的系统,可应用于测试混凝土早期的裂缝出现时间;进行了大量自生收缩试验和干燥收缩试验,对影响高性能混凝土自生收缩和干燥收缩的因素进行了深入的研究,提出了减少收缩变形的混凝土原材料选用和粉煤灰及矿渣单掺与多掺的最佳掺量,提出了高性能混凝土自生收缩和干燥收缩计算模型;采用平板诱导开裂法和圆环测试系统进行了大量的抗裂性能试验,深入研究了混凝土原材料特别是粉煤灰及矿渣影响高性能混凝土抗裂性能的规律,提出了实现高抗裂性能的混凝土原材料选用和粉煤灰及矿渣单掺与多掺的最佳掺量;研究成果成功地应用于实际工程中,取得了显著的技术和经济效益。  相似文献   

16.
钢纤维类型对超高性能混凝土高温爆裂性能的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
杨娟  朋改非 《复合材料学报》2018,35(6):1599-1608
为了探寻可以有效改善超高性能混凝土(Ultra-high-performance concrete,UHPC)抗火性能的钢纤维类型,本文试验测定了不同类型钢纤维(3种普通钢纤维和2种来自于废旧轮胎的再生钢纤维)增韧UHPC及空白组混凝土的从常温至800℃高温爆裂行为和断裂能。结果显示,未掺入任何钢纤维的空白组UHPC试件全都发生了严重高温爆裂,钢纤维可以显著减轻其高温爆裂但却不能避免爆裂的发生,而掺入端钩型普通工业钢纤维(长度为35 mm,直径为0.55 mm)的UHPC呈现出最优的抗高温爆裂性能,其次是掺入未附着橡胶颗粒(RSF)的再生钢纤维(RSFR)增韧UHPC。可见,钢纤维自身性能特征显著影响了钢纤维增韧UHPC的高温爆裂,相同掺量情况下混凝土单位体积内分布密度较大的钢纤维或者分布密度较小但可以显著增加混凝土断裂韧性(断裂能)的钢纤维比较适合应用于具有较高抗火要求的UHPC结构中。  相似文献   

17.
Early-age cracking of high performance concrete (HPC) structures, in particular bridge decks, results in additional maintenance costs, burden on serviceability, and reduced long-term performance and durability. The causes behind cracking in HPC are well known and documented in the existing literature. However, appropriate shrinkage limits and standard laboratory/field tests are not clearly established in either the technical literature or in specifications. The purpose of this research was to provide shrinkage threshold limits for specifications which allow proper criteria to ensure crack-free or highly cracking-resistant HPC. The restrained ring test (ASTM C1581) was used to identify the cracking potential of 14 different HPC mixtures. By comparing free shrinkage (ASTM C157, 75 × 75 × 285 mm specimen) and restrained shrinkage tests results, a free shrinkage limit of 450 microstrain at 28 days was proposed to ensure satisfactory cracking resistance.  相似文献   

18.
This research investigates and evaluates the results of coconut shell concrete beams subjected to torsion and compared with conventional concrete beams. Eight beams, four with coconut shell concrete and four with conventional concrete were fabricated and tested. Study includes the general cracking characteristics, pre cracking behavior and analysis, post cracking behavior and analysis, minimum torsional reinforcement, torsional reinforcement, ductility, crack width and stiffness. It was observed that the torsional behavior of coconut shell concrete is comparable to that of conventional concrete. Compare to ACI prediction, equation suggested by Macgregor is more conservative in calculating cracking torsional resistance. But for the calculation of ultimate torque strength ACI prediction is more conservative compared to the equation suggested by Macgregor. Indian standard is also conservative in this regard, but it was under estimated compared to ACI and Macgregor equations. Minimum torsional reinforcement in beams is necessary to ensure that the beam do not fail at cracking. Compared to conventional concrete specimens, coconut shell concrete specimens have more ductility. Crack width at initial cracking torque for both conventional and coconut shell concrete with corresponding reinforcement ratios is almost similar.  相似文献   

19.
具有微孔洞结构陶瓷材料热冲击实验研究   总被引:2,自引:0,他引:2  
对微孔洞体积含量分别为5%(密实材料),10%,20%和30%(微孔洞结构材料)的四种氧化铝陶瓷材料通过水冷却的实验法进行了热冲击实验。实验结果表明无论从裂纹的起始模式,还是裂纹扩展程度,都表明具有微孔洞结构的陶瓷材料比其对应的密实材料有着较好的抗热冲击性能。  相似文献   

20.
A two-dimensional theoretical model is proposed for investigation of the fracture processes and assessing residual contact durability of solids subjected to cyclic contact. The model is based on the step-by-step calculation of fatigue crack propagation paths in the contact region which includes the criteria of local fracture of materials under complex stress–strain state, characteristics of fatigue crack growth resistance of materials and also presupposes the possible change of fracture mechanisms (transversal shear – normal opening fracture mechanisms). Within the frames of the model the peculiarities of formation of such typical contact fatigue damages like pits, spalls, squat (“dark spot”) and cracking (“checks”) in rolling bodies and edge cracks growth in the elements of fretting couples under conditions of sliding/sticking between them are investigated. Examples of assessing the life time by damages formation (pitting and spalling) in the contact region are presented.  相似文献   

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