钢纤维对再生混凝土抗冲击性能的影响

为研究不同再生骨料取代率、钢纤维掺量和纤维类型对再生混凝土(RAC)抗冲击性能的影响,采用自由落锤冲击试验装置,对其进行抗冲击试验.利用两参数Weibull分布函数模型对试件抗冲击初裂次数和破坏冲击次数的概率分布规律,进行了拟合检验和失效概率预测分析;并以抗冲击延性比、抗裂性能定量评价了钢纤维再生混凝土(SFRAC)的...     

碳纤维混杂纤维混凝土抗冲击性能研究

对比美国混凝土学会的混凝土落锤冲击试验装置,自行设计了混凝土落锤弯曲冲击试验装置,进行了不同几何尺寸及弹性模量的碳纤维、钢纤维和聚丙烯纤维混凝土的抗冲击力学性能试验研究。分析比较了不同纤维几何尺寸和弹性模量、种类和掺量对混杂纤维混凝土抗冲击性能的影响和增强机理。本文通过定义混杂效应系数,可定量评价混凝土抗冲击力学性能的正混杂效应。研究表明纤维可以明显提高混凝土的抗冲击强度,其中碳纤维混杂纤维混凝土的提高幅度更为显著。     

混杂纤维增强再生砖骨料混凝土增强机制与抗压性能计算方法

通过钢-聚烯烃混杂纤维增强再生砖骨料混凝土（HF/RBAC）的抗压与弹性模量试验,研究了再生砖骨料（RBA）取代率、混杂纤维掺量、纤维种类对混凝土抗压强度和弹性模量的影响。根据RBA的XRD图谱、X-CT图像、RBA火山灰活性成分与水泥水化产物反应原理及能量平衡原理,分析了HF/RBAC的破坏机制和纤维增强机制。研究表明,当RBA全取代天然骨料（NA）时,HF/RBAC立方体抗压强度、轴心抗压强度和弹性模量分别降低了36.72%、24.95%和43.53%。当钢-聚烯烃混杂纤维体积掺量为1.5%时,HF/RBAC立方体抗压强度、轴心抗压强度和弹性模量分别增加了20.51%、30.33%和35.84%。最后,提出了考虑RBA压碎指标和取代率、纤维种类和掺量等因素影响的HF/RBAC抗压强度和弹性模量的计算方法。     

钢筋与结构型合成纤维对混凝土抗冲击性能混杂效应的分析

为了研究钢筋与结构型合成纤维混杂后对混凝土抗冲击性能的影响,采用改进的自由落球冲击试验装置,对素混凝土、钢筋混凝土、结构型合成纤维增强混凝土以及钢筋-结构型合成纤维混杂增强的混凝土试件的抗冲击性能进行了试验研究,分析了钢筋、结构型合成纤维以及钢筋与结构型合成纤维混杂后对混凝土抗冲击性能的影响及其增强机理。同时,利用Weibull分布理论分析了试件初裂冲击次数和破坏冲击次数的分布规律。研究表明:结构型合成纤维可以提高混凝土抗冲击性能;对于提高混凝土的抗冲击性能,钢筋与结构型合成纤维表现出显著的正混杂效应;两参数Weibull分布能较好的描述钢筋-结构型合成纤维混凝土抗冲击次数的分布特征。     

低温下玄武岩纤维混凝土的抗冲击性能

采用直径15μm的两种长度的玄武岩纤维,制成不同纤维体积掺量的玄武岩纤维混凝土。对其进行抗冲击试验,分析玄武岩纤维混凝土在低温环境下的抗冲击性能。结果表明:玄武岩纤维能够提高混凝土在低温环境下的抗冲击次数。对试验结果进行统计分析和失效概率预测,结果表明:威布尔分布可以有效地对基于U形试件的玄武岩纤维混凝土抗冲击性能进行统计分析。以玄武岩纤维混凝土在冲击试验中的初裂和终裂次数的自然对数来评价其抗冲击性能,则在相同的失效概率情况下,玄武岩纤维混凝土的抗冲击性能与玄武岩纤维的掺量近似呈线性关系。且在相同的失效概率和玄武岩纤维掺量的条件下,18mm长纤维对混凝土的抗冲击性能的改善作用优于6mm短纤维。     

C—P混杂纤维增强混凝土弯曲疲劳性能的试验研究

本文对Ｃ－Ｐ混杂纤维增强混凝土（ＨｙｂｒｉｄＦｉｂｅｒＲｅｉｎｆｏｒｃｅｄＣｏｎｃｒｅｔｅ－ＨＦＲＣ）的弯曲疲劳性能进行了试验研究，揭示了疲劳寿命，疲劳强度随纤维掺量的变化规律，建立了Ｃ－ＰＨＦＲＣ材料的疲劳方程，研究表明，混杂纤维的加入可以大大改善混型土材料的弯曲疲劳性能。     

混杂纤维增强混凝土材料的力学性能和耐久性能研究

采用聚丙烯纤维和碳纤维掺杂的方法制备了单纤维和混杂纤维增强混凝土材料.利用电子万能试验机对单纤维和混杂纤维增强混凝土材料样品进行了抗弯强度和劈裂抗拉强度试验;采用扫描电子显微镜(SEM)对样品的拉伸断口形貌进行了观察;采用NEL扩散试验测试了样品的氯离子扩散系数.结果表明,混杂纤维增强混凝土材料HFRC-B的抗弯性能、...     

钢纤维形状对高性能混凝土性能的影响

试验研究了6种长径比较小且直径较粗的钢纤维(SF)(短直形、长直线形、圆弧形、闭合三角形、闭合矩形、闭合圆环形)对高性能混凝土性能的影响。通过改变SF体积分数从而改变其形成的环域个数和面积,探究二者对混凝土流动性、抗拉及抗折强度的影响,并通过研究破坏界面分析混凝土破坏形式和机制。结果表明:闭合区域个数及纤维的环域面积对混凝土流动起主要影响;闭合SF中圆环形SF对混凝土抗折及抗压强度的提升效果优于其他形状的闭合SF。短直形SF与圆环形SF混杂试验中,圆环形SF体积分数为1vol%、短直形SF体积分数为0.5vol%时,SF/混凝土抗压强度和抗折强度提升的综合效果最佳。      

混杂比对碳纤维-玄武岩纤维混杂增强环氧树脂基复合材料弯曲性能的影响

将玄武岩纤维置于混杂铺层的压缩侧,研究了碳纤维-玄武岩纤维混杂增强环氧树脂基复合材料的弯曲性能及混杂比对其弯曲性能的影响。通过对试样进行三点弯曲试验得到了材料的弯曲性能,并通过扫描电子显微镜观察材料的失效模式。与纯碳纤维增强环氧树脂基复合材料相比,当混杂比为16.7%和33.3%时,混杂复合材料的弯曲强度明显提升,弯曲强度分别提高12.4%和15.2%,但是其弯曲模量随着混杂比的提升而降低。混杂后的材料及玄武岩纤维增强环氧树脂基复合材料的失效位移都高于碳纤维增强环氧树脂基复合材料,断裂韧性明显提升。从侧面观察可以发现不同铺层在压缩侧、拉伸侧和中间层有不同的失效形式。      

钢纤维橡胶再生混凝土的抗冻性试验

为使废弃混凝土和再生橡胶在北方地区混凝土工程中得以应用,采用正交试验法研究再生粗骨料掺量、再生粗骨料强化方式、钢纤维掺量与橡胶掺量对钢纤维橡胶再生混凝土(C45)立方体抗压强度和抗冻性的影响规律。利用扫描电镜和螺旋CT扫描技术研究了钢纤维橡胶再生混凝土的宏观和细观结构及其对抗冻性能的影响机理。结果表明:橡胶颗粒掺量是影响再生混凝土含气量、抗压强度和相对动弹模量的重要因素,再生粗骨料掺量是影响相对动弹模量和强度损失率的次要因素,钢纤维掺量对混凝土抗压强度增强作用较小,粗骨料强化方式对混凝土性能影响不大;橡胶颗粒与砂浆界面的裂缝宽度在5~55μm之间,二者之间的相容性较差;当橡胶颗粒掺量(与砂的体积比)大于20%后,随橡胶颗粒掺量增大,混凝土内部孔洞数目增多,钢纤维橡胶再生混凝土抗压强度降低、抗冻性减弱。     

Effect of recycled coarse aggregate on damage of recycled concrete

This study evaluates the possibility of measuring the damage of the recycled concrete. In this way, two conventional concretes with a w/c ratio of 0.55 and 0.65 were designed. Based on them, six recycled concretes with different percentages of replacement of natural coarse aggregates with recycled coarse aggregate (20, 50 and 100%) were obtained. To take into account the high absorption capacity of the recycled aggregates, before using them they were pre-wetted for 10 min. The results concluded that scalar damage mechanics (based on the variations of the elastic modulus) and volumetric strains curves can be use to quantify the damage of the recycled concrete. The results from both approaches indicated that the damage to concrete depended on the percentage of replacement, increasing with higher replacement percentages. Additionally, values of the damage, that are quantified using the critical stress and according to the scalar damage mechanics, are given.     

不同预浸骨料-PVA纤维对再生混凝土力学性能的影响

为研究纳米SiO2溶液和水泥净浆改性再生粗骨料后,掺入聚乙烯醇(Polyvinyl alcohol,PVA)纤维再生混凝土的基本力学性能和动态力学性能,分别对不同浓度的纳米SiO2溶液和不同水灰比的水泥净浆进行再生骨料浸泡预试验,选定浓度为2wt％的纳米SiO2溶液和水灰比为0.5的水泥净浆,对改性后再生混凝土的力学性...     

Behaviour of recycled aggregate concrete filled stainless steel stub columns

Past research indicates that recycled aggregate concrete (RAC) could be successfully used in concrete-filled steel tubular (CFST) columns. Their yielded performance is almost as good as that of the traditional CFST columns. In addition, as a comparatively new construction material, stainless steel can be used to replace carbon steel for enhancing the durability and ductility of CFST columns. With an aim to combine the advantages of both RAC and stainless steel, RAC is proposed in this paper to be used as a filling material for stainless steel tubes. A test program is introduced in this paper to investigate the behaviour of RAC-filled stainless steel stub columns. For comparison purposes, reference specimens with carbon steel tubes are also tested. In the end, finite element analysis is conducted to simulate the current test results and those reported in the literature.     

玄武岩纤维对再生混凝土抗碳化性能的影响

采用快速碳化的方法研究了玄武岩纤维(BF)掺量和再生粗骨料(RCA)取代率对再生混凝土(RAC)抗碳化性能的影响,实测了3天、7天、14天、28天的碳化深度,对随碳化天数的增加,碳化深度与BF掺量、RCA取代率之间的关系进行了分析.结果表明,RAC的碳化与天然混凝土(NAC)类似,其碳化深度均随碳化天数的增加而增加,随...     

Effect of carbonation of modeled recycled coarse aggregate on the mechanical properties of modeled recycled aggregate concrete

The modeled recycled aggregate concrete (MRAC) which is an idealized model for the real recycled aggregate concrete (RAC) was used in this study. The MRCAs prepared with two types of old mortars were modified by an accelerated carbonation process. The effects of carbonation of MRCA on the micro-hardness of MRCA and the mechanical properties of MRAC were investigated. The results indicated that the micro-hardness of the old interfacial transition zone (ITZ) and the old mortar in the carbonated MRCAs was higher than that in the uncarbonated MRCAs, and the enhancement of the old ITZ was more significant than that of the old mortar. The compressive strength and modulus of MRACs increased when the carbonated MRCAs were utilized, and the improvement was more significant for MRAC prepared with a higher w/c. In addition, a numerical study was carried out and it showed that the improvement in strength by carbonation treatment was less obvious when the difference between the new and old mortar was larger.     

Bond behaviour between recycled aggregate concrete and deformed steel bars

The results of thirty pullout tests carried out on 8 and 10 mm diameter deformed steel bars concentrically embedded in recycled aggregate concrete designed using equivalent mix proportions with coarse recycled concrete aggregate (RCA) replacement percentages of 0, 25, 50, 75 and 100 % are reported towards investigation of bond behaviour of RCA concrete. Bond strengths of the natural aggregate concrete and the RCA concrete was found to be comparable, particularly for the 10 mm rebars, and the RCA replacement percentage had an insignificant effect on peak bond stress values. However, for both the bar sizes, when the measured bond strengths were normalized with the respective compressive strengths, then the normalized bond strengths so obtained across all the RCA replacement percentages were higher for the RCA concrete compared to the natural coarse aggregate concrete. Further, higher normalized bond strength values were obtained for the 8 mm rebars compared to the 10 mm bars. An empirical bond stress versus slip relationship between RCA concrete and deformed steel bars has been proposed on the basis of regression analysis of the experimental data and it is conservatively suggested that anchorage lengths of 8 and 10 mm diameter deformed bars in RCA concrete may be taken the same as in natural aggregate concrete.     

再生钢纤维增韧超高性能混凝土的力学性能

采用来自于废旧轮胎的两种再生钢纤维制备含粗骨料的超高性能混凝土,并测定其抗压强度、劈裂抗拉强度、断裂能和静弹性模量等力学性能,空白组及普通钢纤维增韧超高性能混凝土作对比性能试验。结果显示,未附着橡胶颗粒的再生钢纤维使超高性能混凝土的抗压强度略微下降,降低幅度为3.91%,其余各类型钢纤维均有利于提高超高性能混凝土的力学性能;而附着橡胶颗粒的再生钢纤维显著提高了超高性能混凝土的断裂能,约为普通钢纤维增韧超高性能混凝土的4倍。此外,再生钢纤维对超高性能混凝土的劈裂抗拉强度和静弹性模量的提高效果均优于普通钢纤维。再生钢纤维,尤其是附着橡胶颗粒的再生钢纤维,可以作为一种增韧材料替代普通钢纤维应用到超高性能混凝土工程结构中。      

Durability of recycled aggregate concrete prepared with carbonated recycled concrete aggregates

The mechanical properties of recycled aggregate concrete (RAC) incorporating carbonated recycled concrete aggregates (RCAs) have previously been reported. However, the durability of RAC prepared with carbonated RCAs remains to be accessed. In this study, the durability properties of RAC prepared with non-carbonated RCAs and carbonated RCAs, in terms of deformation (drying shrinkage), water absorption and permeability (bulk electrical conductivity, gas and chloride ion permeability), are presented. The experimental results indicated that: (i) the incorporation of the carbonated RCAs in RAC not only helped to reduce the water absorption of RAC, but also reduced its permeability; (ii) when 100% carbonated NRCAs was used, the improvement extent of impermeability was 15.1%, 36.4% and 42.4% for bulk electrical conductivity, chloride ion permeability and gas permeability, respectively. Comparing the results of the mechanical and durability properties, the CO₂ curing treatment of RCAs had a greater beneficial impact on the durability properties of the RAC; and (iii) there was a good correlation between the water absorption of RAC and its permeability indicators. The water absorption value of RAC may be used as a criterion of the durability of RAC.