Experimental study on behaviors of polypropylene fibrous concrete beams

Synthetic fibers made from nylon or polypropylene have gained application when loose and woven into geo textile form although no information on the matrix＇s mechanical performance is obtained so that more understanding of their structural contribution to resist cracking can be determined. This paper presents the results of an experimental investigation to determine the performance characteristics of concrete reinforced with a polypropylene structural fiber. In this investigation ＂Fiber mesh＂ brand of fibers manufactured by SL Concrete System, Tennessee, USA and marketed by M/S Millennium Building System, Inc., Bangalore, India are used. The lengths of the fibers used were 24 mm. Fiber dosages used were 0.9, 1.8, 2.7 kg/m^3. A total of three mixtures, one for each fiber dosage were made. A standard slump cone test was conducted on the fresh concrete mix with and without fibers to determine the workability of the mix. The test program included the evaluation of hardened concrete properties such as compressive, split tensile, modulus of rupture and flexural strengths. The increase in compressive strength is about 36.25%, 26.20%, and 23.75% respectively that of plain concrete. This increase in strength was directly proportional to amount of fibers present in the mix. The increase in flexural strength for Mixes I-III is about 21%, 16.6%, and 23% respectively that of plain concrete specimens. An experimental investigation was also made to study the behaviors of reinforced fibers concrete beams （with longitudinal reinforcements） under two-point loading. The deflection and crack patterns were also studied. The improvements in strength and ductility characteristics were discussed.     

钢纤维混凝土力学性能的试验研究

通过不同纤维掺量、不同养护龄期下钢纤维混凝土的力学性能试验,研究钢纤维掺量对混凝土抗压强度和抗折强度的影响。结果表明,钢纤维对混凝土抗压强度和抗折强度均有明显增强作用,掺量为1．6％时强度最大。     

高性能轻集料混凝土中各因素对早期抗压强度影响的试验研究

运用均匀试验设计法研究了水泥、粉煤灰、砂率、钢纤维和水胶比五个因素对高性能轻集料混凝土早期抗压强度的影响,找出了其中显著的影响因素。并根据试验结果,进行线性回归,给出回归方程。     

南方高温地区水泥混凝土路面早期裂缝防治研究

研究了三种外掺料对路面混凝土早期开裂性能的影响。通过理论分析, 将水泥路面的早期开裂机理归结为混凝土具有塑性收缩、自收缩和干缩等早期收缩性能; 采用室内试验分别研究了聚丙烯纤维、钢纤维和粉煤灰对混凝土早期收缩性能的改善效果。研究结果表明, 聚丙烯纤维和粉煤灰能够大幅度降低混凝土的早期收缩值, 钢纤维的改性作用则不明显。建议为全面评价不同混凝土的长期开裂性能, 应增加开裂后的疲劳和冲击试验研究。     

粉煤灰及矿粉对水泥基注浆料性能的影响

以硅酸盐和硫铝酸盐复合水泥为基材制作水泥基注浆材料,分别讨论了不同类型、不同掺量的粉煤灰和矿粉对水泥基注浆材料的流动度、容重、膨胀率、抗压抗折强度的影响。结果表明:粉煤灰能有效地增加水泥基注浆料的流动度,当粉煤灰掺量低于20%时,可以提高注浆料的塑性膨胀率,当Ⅰ级粉煤灰掺量为20%或Ⅱ级粉煤灰掺量为15%时,3 h膨胀率最高达1%;粉煤灰对注浆料的早期强度不利,但可以增强其后期强度。矿粉可以改善其流动度,随着矿粉的增加,注浆料的容重和膨胀率均呈下降趋势;矿粉对注浆料的28 d强度无显著影响,其早期强度随着矿粉的增加而下降,当S75矿粉掺量高于7%或S95矿粉掺量高于11%时,抗压抗折强度不满足规范要求。     

Preparation and Dynamic Tensile Behavior of C200 Green Reactive Powder Concrete

A new type of green reactive powder concrete (GRPC) with compressive strength of 200 MPa is prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, toughness, fracture energy and interfacial bonding strength) of GRPC specimens, cured in three different types of regimes, are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the powder binders that is composed of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume are better than the others'. The corresponding compressive strength, flexural strength and fracture energy are more than 200 MPa, and 30 000 J/ m2 respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the split Hopkinson pressure bar (SHPB) according to the spalling phenomenon. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of GRPC. With the increase of strain rate, its peak stress and relevant strain increase. The GRPC exhibits an excellent strain ratio stiffening effect under the dynamic tensile load with high strain ratio, resulting in a significant change of the fracture pattern.     

矿渣-地聚合物混凝土的制备、特性及机理研究

本文利用矿渣粉取代部分偏高岭土来配制地聚合物基体,以强度为指标寻求最佳地聚合物配比;同时为优化养护制度,采用了标准养护、蒸汽养护、压蒸养护三种养护制度,从中选出最有利于发挥胶凝材料活性的养护制度;实验结果表明,在矿渣粉掺量为50％,80℃蒸养8h时抗压和抗折强度达到最优,分别为75.2MPa、10.1MPa。之后,将粗集料加入到这种最优的矿渣-地聚合物基体中制成混凝土。     

玄武岩纤维长径比对混凝土力学性能的影响

研究了玄武岩纤维长径比对混凝土立方体抗压强度、劈裂抗拉强度及抗折强度的影响。结果发现:玄武岩纤维的掺入有利于提高混凝土强度,但纤维长径比不同,对强度的改变程度不同。玄武岩纤维对混凝土立方体抗压强度提升幅度最小,最高为8.1%,较适宜纤维长径比在800:1~1200:1之间;对混凝土的劈裂抗拉强度提升幅度最大,最高为23.8%,对混凝土的抗折强度提升幅度居中,最高为15.8%,最优纤维长径比均在1200:1~1600:1之间。为提高混凝土强度,长径比相对较大的纤维应适当降低纤维体积率,长径比相对较小的纤维可适当增加纤维体积率,但不宜超过0.15%。     

Replacing stirrups of self-compacting concrete beams with steel fibers

Based on the investigation of fiber influence on workability of self-compacting concrete (SCC), tests were carried out on two series of SCC rectangular simply supported beams, which were made of hooked steel fibers reinforced concrete with or without stirrups, subjected to four-point symmetrically placed vertical loads. The major test variables are steel fiber contents and stirrup ratios. The results indicate that the ultimate load significantly increases with the increase of fiber content; the addition of ...     

One and two dimensional chloride ion diffusion of fly ash concrete under flexural stress

A preloading frame is firstly designed to accurately apply external flexural stress to concrete specimens. Then a method is developed to measure one and two dimensional (1D and 2D) chloride ion concentrations at different distances from the surface of concrete under flexural stress. Using this method and the preloading frame, 1D and 2D stress-diffusion is systematically investigated for fly ash concretes made with different fly ash contents (0%, 10%, 20%, 40%, and 60%), and water to binder ratios (0.3, 0.35, and 0.4). The stress accelerating effect on 1D and 2D chloride ion diffusion is also quantitatively analyzed through a comparison between stress-diffusion and nonstress-diffusion. A diffusion accelerating effect caused by external flexural stress can clearly be observed through the comparison. In order to quantify the stress accelerating effect, a stress accelerating factor is proposed in this paper. The relationship between stress accelerating factor and external stress-to-ultimate stress ratio is given as an exponential function. Finally, the process of the initiation, prorogation, and distribution of microcracks on the tensile face of specimen is observed in-situ by using a small-sized loading frame and scanning electron microscope (SEM). The above research provides an insight into chloride attack on the edge reinforcing bars of concrete structures under flexural stress, such as large-span beam and board in the field of civil engineering.     

Effects of characteristics of fly ash on the properties of geopolymer

The properties of two types of fly ash geopolymers made from class F fly ashes produced in wet bottom and dry bottom boilers were investigated in the present study. The source material used in the geopolymer concrete was activated with sodium hydroxide and sodium silicate solution. The results revealed that the geopolymer produced with wet bottom boiler fly ash(CZ-FA)hardened quickly, and had higher early-age strength and lower shrinkage than the geopolymer produced with dry bottom boiler fly ash(SX-FA). The compressive strength of the two geopolymers made from CZ-FA and SX-FA was 45 MPa and 15 MPa respectively when cured at 60 ℃ and delayed for 14 d. However, after 90 days' delay, the compressive strength of both the samples is almost the same, up to 80 MPa. Nearly 20% volume shrinkage of the samples made from SX-FA was much higher than that made from CZ-FA, which was almost zero. XRD, SEM/EDS and FT-IR were used to analyze the main reason of the differences.     

超细钢铁渣粉对水泥基材料的力学性能影响

以超细钢铁渣粉(以下简称“超细钢渣”) 为主要掺合料制备胶凝材料,通过XRF、粒径分析、XRD分析和力学性能测试,探究超细钢渣对水泥基材料的力学性能影响。结果表明:通过机械研磨制备出的超细钢渣,其矿相成分硅酸三钙、硅酸二钙和莫来石特征峰强度最强,复掺的超细钢渣活性指数也满足国家标准。随着超细钢渣掺量增加,3 d 抗压和抗折强度均出现逐渐降低的趋势,但在外掺m (超细钢渣) ∶ m (超细矿渣)= 2:3、w复合粉=30%时,其28 d 抗压和抗折强度达到峰值,分别为8.9、53.8 MPa。超细钢渣在不同龄期水化反应程度不同,早期水化反应较低,强度较差;后期水化程度较高,且优于同标准水泥。     

粉煤灰、矿渣掺量对混凝土强度的影响

配制了一批不同龄期的C30矿渣粉煤灰混凝土,进行全面系统的试验研究与对比分析.研究了粉煤灰、矿渣和减水剂对混凝土强度性能的影响.试验结果表明:C30矿渣粉煤灰混凝土的矿渣最佳掺量为20%～30%;掺入减水剂后,更使混凝土的孔隙率减小、界面改善、泌水性降低并易于施工;同时,混凝土的抗压强度得到明显提高.     

Carbon steel slag as cementitious material for self-consolidating concrete

This study deals with the recycling of carbon steel slag （CSS） to produce self-consolidating concrete （SCC）. Since the chemical composition of CSS is similar to that of Portland cement or blast furnace slag （BFS）, it is expected to behave similarly. In the current study, the pozzolanic activity index of CSS is examined. Furthermore, the use of CSS as a pozzolanic material to partially replace Portland cement in the production of SCC is tested. We designed concrete mixtures with different water-to- cementitious material ratios （w/cm） keeping water and superplasticizer （SP） contents constant. Results showed that the design and performance of all the concrete mixtures used in this investigation were comparable to those of SCC and high performance con- crete （HPC）. However, compared to ordinary plain concrete （OPC）, the additional CSS content increases the setting time. In the CSS mixtures set for 90 d, compressive strengths of 86%, 134% and 121% were attained as compared to the control concrete; the corresponding w/cm ratios were 0.28, 0.32 and 0.40, respectively. Verifying the soundness of the SCC for meeting the criteria for HPC, the ultrasonic pulse velocity （UPV） of CSS was found to be comparable to that of ordinary concrete. In conclusion, the recycling of CSS can be advantageously employed in the production of SCC.     

Flexural fatigue strength of steel fibrous concrete containing mixed steel fibres

INTRODUCTION A number of experimental fatigue studies were conducted on plain concrete as well as on steel fibre reinforced concrete (SFRC) beams of different sizes under different loading conditions. Murdock and Kesler (1958) investigated the effect of stress ratio on the fatigue strength of plain concrete. Batson et al.(1972) reported fatigue strength of 74% and 83% of the first crack static flexural strength at 2 million cycles of complete reversed and not-reversed loads respectively…     

Strengthening an in-service reinforcement concrete bridge with prestressed CFRP bars

Carbon fiber reinforced polymer(CFRP)bars were prestressed for the structural strengthening of 8 T-shaped rein-forced concrete (RC)beams of a 21-year-old bridge in China.The ultimate bearing capacity of the existing bridge after retrofit was discussed on the basis of concrete structures theory.The flexural strengths of RC beams strengthened with CFRP bars were controlled by the failure of concrete in compression and a prestressing method was applied in the retrofit.The field construction processes of strengthening with CFRP bars-including grouting cracks,cutting groove,grouting epoxy and embedding CFRP bars,surface treating,banding with the U-type CFRP sheets,releasing external prestressed steel tendons-were introduced in detail.In order to evaluate the effectiveness of this strengthening method,field tests using vehicles as live load were applied before and after the retrofit.The test results of deflection and concrete strain of the T-shaped beams with and without strengthening show that the capacity of the repaired bridge,including the bending strength and stiffness,is enhanced.The measurements of crack width also indicate that this strengthening method can enhance the durability of bridges.Therefore,the proposed strengthening technology is feasible and effective.     

"三掺"技术配置高强低热补偿收缩混凝土的试验研究

通过试验手段阐述粉煤灰、减水剂和膨胀剂三类外掺料分别在大体积混凝土施工中的作用和共同掺入后的试验效果.以此指导"三掺"技术配置低热补偿收缩混凝土在大体积混凝土的施工应用.     

不同掺量钢纤维对钢纤维增强混凝土抗压强度的研究

通过在混凝土中掺入不同的钢纤维试验掺量,研究不同掺量钢纤维对混凝土早期和后期抗压强度的影响,对影响的原因进行了初步分析。     

耐碱玻纤混凝土抗折强度测定及不确定度评定

为了测定耐碱玻璃纤维混凝土的抗折强度并分析其不确定度及纤维体积率对混凝土抗折强度的影响,选择耐碱玻璃纤维体积率为0%0,.6%,0.8%,1.0%的100 mm×100 mm×400 mm混凝土抗折试件进行试验。试验在MTS810材料试验机上进行,通过三分点加载测定其抗折强度,分析混凝土抗折强度试验中影响试验结果不确定的因素和来源,并按照JJF 1059-1999标准的要求,对合理玻璃纤维掺量试件的抗折强度的不确定度进行分析和评定。结果表明:耐碱玻璃纤维的掺入改变了混凝土抗折破坏形式,不同纤维体积率的混凝土抗折强度较普通混凝土依次提高了18.87%,21.64%,23.24%。综合考虑各方面因素确定耐碱玻璃纤维混凝土合理玻璃纤维掺量为0.6%;通过对试件抗折强度测定的不确定度评定,表明数学模型中自由度及测量的重复性是引入测量结果不确定度的主要因素;建议在进行同类试验时,试件尺寸应尽量大,从而可增大跨距,以减小剪力对测量结果的影响。     

Strengthening an in-service reinforcement concrete bridge with prestressed CFRP bar

Carbon fiber reinforced polymer （CFRP） bars were prestressed for the structural strengthening of 8 T-shaped reinforced concrete （RC） beams of a 21-year-old bridge in China. The ultimate bearing capacity of the existing bridge after retrofit was discussed on the basis of concrete structures theory. The flexural strengths of RC beams strengthened with CFRP bars were controlled by the failure of concrete in compression and a prestressing method was applied in the retrofit. The field construction processes of strengthening with CFRP bars including grouting cracks, cutting groove, grouting epoxy and embedding CFRP bars, surface treating, banding with the U-type CFRP sheets, releasing external prestressed steel tendons-were introduced in detail. In order to evaluate the effectiveness of this strengthening method, field tests using vehicles as live load were applied before and after the retrofit. The test results of deflection and concrete strain of the T-shaped beams with and without strengthening show that the capacity of the repaired bridge, including the bending strength and stiffness, is enhanced. The measurements of crack width also indicate that this strengthening method can enhance the durability of bridges. Therefore, the proposed strengthening technology is feasible and effective.