活性粉末混凝土强度影响因素研究

研究养护时间和钢纤维掺量对活性粉末混凝土抗折、抗压强度的影响,探索低成本、超高强高性能活性粉末混凝土的配制技术,旨在促进活性粉末混凝土的推广应用.     

活性粉末混凝土力学性能试验

为了研究活性粉末混凝土（RPC）的基本力学性能,在查阅各国相关文献的基础上,进行了一系列RPC力学性能试验和试验数据分析,得到了RPC的抗压强度、劈裂强度、弹性模量、泊松比、钢筋与RPC的黏结强度等数据,比较了钢筋在RPC和普通混凝土（NC）中的黏结性能,分析了RPC的应力一应变关系。结果表明：RPC的棱柱体应力一应变关系曲线接近于直线,为脆性材料;其力学性能总体上优于普通混凝土;泊松比可取为0．2,劈裂强度、弹性模量及轴心抗拉强度等可采用普通混凝土的经验公式进行计算。     

新型活性粉末混凝土的开发与性能研究

活性粉末混凝土是一种高性能的混凝土,现已开始进入实用阶段。在分析活性粉末混凝土特点的基础上,采用常规材料和一般工艺来配制活性粉末混凝土,对其性能进行测试,并探讨了它在工程方面的应用。     

大掺量矿粉活性粉末混凝土性能与微结构研究

对大掺量矿物细粉活性粉末混凝土收缩、钢纤维锈蚀、抗碳化性能、抗氯离子渗透等性能进行了试验研究,并通过孔结构和扫描电镜实验对其微结构进行分析.结果表明,大掺量矿物细粉活性粉末混凝土的早期收缩小、抗钢纤维锈蚀、抗碳化、抗氯离子渗透等性能好.孔结构试验表明,大掺量矿物细粉活性粉末混凝土的孔隙率均在5%左右,孔分布情况很均匀,主要以微小的小孔为主;水泥用量为300 kg/m3的大掺量矿物细粉活性粉末混凝土硬化体水化产物主要由不规则等粒子状的Ⅲ型C-S-H凝胶紧密堆积在一起,凝胶精细、致密,且与骨料融为一体.     

自密实活性粉末混凝土的配制研究

通过改变水胶比、硅灰、减水剂、石英粉、石英砂掺量及石英砂颗粒级配,考察了这些因素对不掺有钢纤维的活性粉末混凝土流动性及抗压强度的影响.结果表明,在石英砂颗粒级配为粗∶中∶细=1∶2∶1,水泥∶硅灰∶石英粉∶石英砂=1∶0.3∶0.37∶1.1,减水剂掺量3%时,活性粉末混凝土的流动度达到了603 mm,浆体均匀密实,符合自密实性质,其28天抗压强度为92.67 MPa.在此基础上,进行了自密实钢纤维活性粉末混凝土的试验研究,当钢纤维体积掺量为2%时,钢纤维自密实活性粉末混凝土的流动度为554 mm,符合自密实性质.28天抗压强度为104.31 MPa,劈拉强度为11.45 MPa,抗折强度为13.85 MPa.     

活性粉末混凝土基本力学性能试验研究

进行76组不同尺寸立方体试件和12组棱柱体试件的单轴受压力学性能试验，研究了活性粉末混凝土的强度标准，探讨活性粉末混凝土的基本力学性能指标(峰值应变、弹性模量、横向变形系数等)与棱柱体抗压强度之间的关系，建立了活性粉末混凝土应力一应变曲线上升段方程。     

活性粉末混凝土抗压强度尺寸效应及弹性模量研究

活性粉末混凝土(简称RPC)作为一种新型材料,拥有优异的力学性能.为了使其更好地应用于桥梁工程等工程实践当中,对RPC抗压强度的尺寸效应及弹性模量进行试验研究.对于活性粉末混凝土而言,不掺钢纤维(RPC-1)的混凝土抗压强度尺寸效应较掺钢纤维的混凝土抗压强度明显;三种尺寸的立方体块抗压强度随试块尺寸的增大而减小;100 mm×100 mm×100 mm试块的抗压强度与100 mm×100 mm×300 mm试块的轴心抗压强度非常接近,活性粉末混凝土表现出了良好的韧性;三组混凝土的弹性模量分别为44.4 GPa、41.2 GPa、41.8 GPa,试验数据显示,混凝土在1/3强度内不会出现明显的塑性变形,可看做为线弹性材料.     

活性粉末混凝土配比优化及收缩性能研究

根据紧密堆积理论,编程计算RPC所用原料粒径理论分布值,选取合理的配合比计算值,结合力学实验确定试验各原料的比例.在此基础上,采用粉煤灰取代部分水泥,矿渣取代部分石英粉,配制活性粉末混凝土,研究各配比的活性粉末混凝土工作性、热养及常温养护的收缩等性能.结果表明:水胶比0.23,粉煤灰取代水泥30%,矿渣取代石英粉50%,掺钢纤维2%的活性粉末混凝土,工作性能良好,强度合格,28 d干燥收缩不显著.该配合比的RPC成本降低,易于工程推广应用.     

活性粉末混凝土微观层面的研究进展

作为新型水泥基复合材料,活性粉末混凝土具有高强度,高韧性以及高耐久性等优异性能,在桥梁与路面工程、建筑工程、水利工程和特种结构等领域拥有广阔的应用前景.但由于组成中活性组分多,内部结构复杂,微观机理研究尚不够明确,难以为材料的宏观性能提供明确的理论依据.介绍了活性粉末混凝土的基本组成、各组分产生的反应及影响因素,总结了国内外学者对活性粉末混凝土微观形貌及孔结构等的研究成果,更进一步地提出了现阶段微观层面研究和材料本身所存在的问题,指出了发展趋势,并进行了分析和讨论.     

掺钢渣活性粉末混凝土的制备及其变形性能

进行了掺钢渣粉活性粉末混凝土配合比的正交设计试验,研究了钢纤维掺量与养护条件对掺钢渣RPC强度和体积变形的影响.结果表明:掺入总量为48%的钢渣粉、超细粉煤灰和硅灰,并以细河砂代替石英砂,同时掺入适量钢纤维,在0.18水胶比下制备了掺钢渣活性粉末混凝土(RPC200).经90℃热水养护72 h后,其抗压和抗折强度分别达152 MPa和27.9 MPa;钢纤维或热养护均有利于提高掺钢渣RPC的强度,且掺入钢纤维还能有效降低掺钢渣RPC的收缩率.     

Durability and micro-structure of reactive powder concrete

Durability of traditional reactive powder concrete (RPC) with rich cement and high volume of fly-ash reactive powder concrete (FRPC) were studied. The X-diffraction and scanning electron microscope (SEM) measurement was imployed to analyze the microstructure. The results show that both types of RPC have higher compressive strength, less volume shrinkage ratio and better carbonation-, chloride-, freezing-resistances than the conventional concrete. The results of X-diffraction indicate that they basically have C-S-H as the main composition without Ca(OH)₂ crystal and ettringite. SEM results show that hydration products of FRPC is mainly III-C-S-H which is piled up closely like densely arranged stone body and it has very compacted structure, in addition, Ca/Si ratio of C-S-H gel is lower than 1.5.     

冻融循环作用后圆钢管混凝土界面粘结性能试验研究

为研究冻融循环作用后圆钢管混凝土界面粘结滑移性能,以冻融循环次数、钢管壁厚、混凝土强度为变量,设计21个试件进行推出试验,分析冻融损伤后圆钢管混凝土柱粘结强度、荷载—滑移及钢管应变的变化规律。结果表明：经冻融循环作用后圆钢管混凝土柱的荷载—滑移曲线与未经冻融试件趋势相似,均可分为上升段、下降段、残余段;受冻融循环作用影响的圆钢管混凝土柱界面粘结性能下降,粘结强度与冻融循环次数成反比,界面滑移量总体呈上升趋势;增大套箍系数可增大试件界面粘结强度,提高圆钢管混凝土柱抗冻性能。根据试验结果,提出考虑冻融循环次数和套箍系数的圆钢管混凝土柱粘结强度计算表达式,计算结果与试验结果吻合良好。     

Behavior of high water-cement ratio concrete under biaxial compression after freeze-thaw cycles

The high water-cement ratio concrete specimens under biaxial compression that completed in a triaxial testing machine were experimentally studied. Strength and deformations of plain concrete specimens in two loading direction under biaxial compression with stress ratio of a=0, 0.25, 0.5, 0.75, 1.0 were obtained after 0, 25, 50 cycles of freeze-thaw. Influences of freeze-thaw cycles and stress ratio on the peak stress and deformation of this point were analyzed according to the experimental results, Based on the test data, the failure criterion expressed in terms of principal stress after different cycles of freeze-thaw, and the failure criterion with consideration of the influence of freeze-thaw cycle and stress ratio were proposed respectively.     

Effect of freeze-thaw cycles on bond strength between steel bars and concrete

The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.     

Deterioration mechanism of sulfate attack on concrete under freeze-thaw cycles

The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses such as SEM, XRD and TGA measurements were performed on the selected samples after freeze-thaw cycles. The corrosion products of the concrete were distinguished and quantitatively compared by the thermal analysis. Besides, the damage mechanism considering the dynamic modulus of elastically of concrete under the coupling effect was also investigated. The experimental results show that, under the action of freeze-thaw cycles and sulfate attack, the main attack products in concrete are ettringite and gypsum. The corrosion products exposed to MgSO4 solution are more than those to Na2SO4 solution. Furthermore, the content of gypsum in concrete is less than that of ettringite in test, and some of gypsum can be observed only after a certain corrosion extent. It is also shown that MgSO4 solution has a promoting effect to the damage of concrete under freeze-thaw cycles. Whereas for Na：SO4 solution, the damage of concrete has restrained before 300 freeze-thaw cycles, but the sulfate attack accelerates the deterioration process in its further test period.     

高温后RPC立方体抗压强度退化规律研究

为摸清活性粉末混凝土(RPC)的高温爆裂情况及高温后立方体抗压强度的退化规律,对300个70.7 mm×70.7 mm×70.7 mm的RPC立方体试件和120个40 mm×40 mm×160 mm的RPC棱柱体试件进行高温试验与高温后抗压试验,考察纤维种类、纤维掺量、温度、尺寸效应等因素对RPC立方体抗压强度及受压破坏特征的影响。结果表明：单掺钢纤维体积率为2%或单掺聚丙烯纤维体积率为0.3%时可以有效防止RPC发生爆裂;钢纤维可以有效提高RPC高温后立方体抗压强度并改善其受压破坏特征,聚丙烯纤维对抗压强度有不利影响． 高温后RPC立方体抗压强度随经历温度的升高呈先增大后减小的变化规律,通过回归分析,建立了RPC立方体抗压强度随温度变化的计算公式．     

活性粉末混凝土预制管组合柱抗震性能试验研究

活性粉末混凝土预制管组合柱（Concrete-filled RPC tube,简称CFRT）将活性粉末混凝土（Reactive Powder Concrete,简称RPC）的力学性能和箍筋的约束效应有效结合了起来,是一种基于超高性能水泥基套管的新型约束组合柱。对4个CFRT柱和1个箍筋约束混凝土柱开展了恒定轴力下的低周反复荷载试验,获取了组合柱的破坏形态、滞回曲线和钢筋的应变等数据,并对相关抗震指标及试验参数进行了分析。结果表明：CFRT柱在低周反复荷载作用下表现出典型的弯曲破坏特征,在RPC管表面出现大量细而密的裂缝,但没有明显的剥落现象;CFRT柱的滞回曲线较饱满,其抗震性能显著优于普通箍筋约束混凝土柱;在试验条件下,CFRT柱的极限侧移率在0.042~0.075之间,高于中国抗震设计规范关于罕遇地震下结构柱极限塑性侧移率不低于0.02的要求;从抗震性能来看,在RPC管内部填充高强混凝土,对于CFRT是可以接受的组合方式。     

活性粉末混凝土柱抗震性能试验

为了考察活性粉末混凝土柱类构件的抗震性能,开展了18根活性粉末混凝土柱的拟静力试验,研究了轴压比、纵筋配筋率、配箍率和钢纤维体积含量4个因素对活性粉末混凝土柱破坏形态、滞回特性、骨架曲线、刚度、承载力及延性的影响规律.研究表明:活性粉末混凝土柱的承载力随着轴压比的增大而提高,但其延性随着轴压比的增大有下降的趋势;试件柱的承载力及位移延性系数随着纵筋配筋率的增大而显著增大;配箍率的提高一定程度上改善了荷载达到峰值后阶段的滞回特性,骨架曲线的下降段变得较为平缓;钢纤维掺量的增加,改善了试件柱的破坏进程,一定程度上提高了试件柱的延性及耗能能力.     

Size effect on compressive strength of reactive powder concrete

In this paper the coefficient and law of the size effect of RPC were studied through experiments and theoretical analysis. The size-effect coefficients for the compressive strength of RPC are deduced through experiments. They indicate that RPC without fiber behaves quite the same as normal or high strength concrete. The size effect on compressive strength is more prominent in RPC containing fiber. Bazant's size effect formula of compressive strength applies to RPC. A formula is given to predict the compressive strength of cubic RPC specimens 100 mm on a side where the fiber dosage ranges from 0-2%.