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%.

Compressive and Flexural Strength of Recycled Reactive Powder Concrete Containing Finely Dispersed Local Wastes

The main objective of this experimental study is to investigate the behavior of Recycled Reactive Powder Concrete (RRPC) developed from finely dispersed local waste raw materials. In this study, RRPC was developed by utilizing local wastes (finely dispersed waste glass powder, waste fly ash and waste ceramic powder) together with Portland cement, fine sand, admixture, steel fibers and water through full replacement of silica fume as well as quartz powder for sustainable construction practice. In this study, all raw materials for making RRPC were analyzed for X-Ray Fluorescence analysis. For sustainability of local construction works, this study employed standard curing method at ambient temperatures instead of steam curing at higher temperatures. Moreover, hand mixing was used throughout the study. To evaluate the structural performances of the developed RRPC mixes, compressive and flexural strengths of RRPC were investigated experimentally and compared with the control mix. The experimental results indicated that replacing the silica fume fully by finely dispersed local waste glass powder (GP) and fly ash (FA) is a promising approach for local structural construction applications. Accordingly, a mean compressive strength of 62.9 MPa and flexural strength of 8.8 MPa were developed using 50% GP-50% FA at 28thdays standard curing. In this study, 17.56% larger compressive strength and 30.6% flexural strength improvements were observed as compared to the control mix.

Preparation of Reactive Powder Concrete Using Fly Ash and Steel Slag Powder

To decrease the cement and SF content of RPC by using ultra-fine fly ash （UFFA） and steel slag powder （SS）, the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental results indicate that the utilization of UFFA and SS in RPC is feasible and has prominent mechanical performance. The microstructure analysis （SEM and TG-DTG-DSC） demonstrated that the excellent mechanical properties of RPC containing SS and UFFA were mainly attributed to the sequential hydration filling effect of the compound system.

Mechanical Properties of Reactive Powder Concretes Produced Using Pumice Powder

We examined the applicability of the pumice aggregate on the concrete formed by considering the reactive powder concrete mixture ratios, for the rigid superstructure concrete road pavement and building construction. The natural pumice aggregate in fibrous and non-fibrous concrete samples was used in the production of concrete by fracturing in 0.1-0.6 mm dimensions in rotor mill. The concreted formed in this way is named after the pumice powder concrete(PPC). The PPC samples produced were taken 7 days as 20 ℃ standard water cure, 28 days as 20 ℃ standard cure and 9 different types of combined cures. The combined cures were applied different temperatures in different durations. PPC samples were subjected to some pressure and flexural tests at the end of the standard water and combined cures. The highest compressive and flexural strengths of PPC samples were obtained after the combined cures: 3 days in 20 ℃ as standard water curing + 2 days in 180 ℃ in drying-oven. The highest compressive strength of PPC samples without any fiber was found to be 47.27 MPa, as for the highest flexural strength, it is found to be 5.23 MPa, in the end of the study. The highest compressive strength of fibrous PPC samples was 51.12 MPa, while flexural strength was 6.57 MPa.

The Effect of Various Polynaphthalene Sulfonate Based Superplasticizers on the Workability of Reactive Powder Concrete

A superplasticizer is a type of chemical admixture used to alter the workability(viscosity)of fresh concrete.The workability of fresh concrete is often of particular importance when the water-to-cement(w/c)ratio is low and a particular workability is desired.Reactive Powder Concrete(RPC)is a high-strength concrete formulated to provide compressive strengths exceeding 130MPa and made of primarily powders.RPC materials typically have a very low w/c,which requires the use of a chemical admixture in order to create a material that is easier to place,handle and consolidate.Superplasticizer are commonly used for this purpose.Superplasticizers are developed from different formulations,the most common being Polycarboxylate Ether(PCE),Polymelamine Sulfonate(PMS),and Polynaphthalene Sulfonate(PNS).This study investigates the effect of various PNS based superplasticizers on the rheological performance and mechanical(compressive strength)performance of a RPC mixture.Six distinctive types of PNS based superplasticizers were used;three of various compositional strengths(high,medium,low range)from a local provider,and three of the same compositional strengths(high,medium,low)from a leading manufacturer.The properties investigated were the individual superplasticizers’viscosity,the concrete workability,determined through a mortar spread test,the concrete viscosity,and the compressive strength of the hardened RPC mixtures measured at 7,14,and 28 days.Two separate RPC mixtures were prepared,which contained two different water-to-cementitious ratios,which consequently increases the dosage of superplasticizer needed,from 34.8L/m3 to 44.7L/m3.The results show that the name brand high range composition produced the overall highest spread,lowest viscosity,and a highest compressive performance.However,the local provider outperformed the name brand in the mid and low range compositions.Lastly,the rheology assessment also confirmed that the name brand high range,and RPC fabricated with the name brand high range,developed the lowest viscosities.

基于堆积密实度的固废活性粉末混凝土配合比设计方法

采用固废掺合料(粉煤灰、矿渣和玻璃粉)进行了活性粉末混凝土(RPC)制备及性能研究,研究了固废种类、掺量和掺入方式对RPC堆积密实度、工作性能、力学性能和微观结构的影响,提出了固废RPC强度模型。结果表明:粉煤灰、矿渣和玻璃粉的替代水泥量分别为15%、10%~15%和20%时,RPC强度更具有优势,工作性能和微观性能更好;固废合理的掺入可使立方体抗压强度最高提高25.8%,而且随着堆积密实度的增大,固废RPC立方体抗压强度先提高后稍有降低;结合鲍罗米公式和密度堆积模型,考虑影响RPC性能的主要因素,提出了固废掺合料RPC配合比的设计方法,为RPC的工程应用提供依据。

早强型钢渣基胶凝材料的制备及其水化机理研究

钢渣是炼钢过程中产生的主要废弃物,具有用途单一、产生量大、污染环境等特点。本文使用钢渣微粉、42.5普通硅酸盐水泥分别与增强剂Ⅰ、增强剂Ⅱ混合制备早强型钢渣基胶凝材料,通过测定原料化学成分、矿物组成,测试胶凝材料的力学性能,分析其热稳定性、微观形貌来揭示胶凝材料的水化机理。研究结果表明:胶凝材料的早期抗压强度大幅提高,后期抗压强度良好;这是因为增强剂能促进Ca(OH)2消耗并提高水化反应速率,Ca(OH)2水解出的OH-能促进钢渣微粉中玻璃体溶出硅酸盐,与Ca^(2+)生成C-S-H凝胶;增强剂含有的硫酸盐能与胶凝材料生成钙矾石AFt,并填充于凝胶孔隙中,增强了材料的密实度。早强型钢渣基胶凝材料的最优配比为钢渣微粉125 g、增强剂Ⅱ用量10 g。研究成果为早强型钢渣基胶凝材料的制备提供了新思路,也可为钢渣综合利用研究提供借鉴。

钢渣粉与硅灰复掺水泥基材料的流变、早期水化热与强度

为缓解大量存在且利用率很低的钢渣处理难题,将其研磨成微粉置换水泥,并掺入硅灰形成一种兼顾力学性能、绿色低碳水泥基材料。基于不同配比的复掺水泥基材料体系的流变行为、早期水化热、强度与吸水率试验研究,主要结果如下:钢渣粉颗粒微形貌棱角与片状较少,替代15%水泥时可有效改善基体稠度,略微降低强度,并显著降低早期水化放热(降幅8.8%),有利于控制早期温度裂缝。复掺硅灰可有效降低材料塑性黏度与泵送压力,对需要长距离泵送的大体积混凝土或高性能混凝土,硅灰掺量可控制在5%以内。且硅灰空间填充效应与火山灰反应会增强材料密实性,显著提高强度。综上,复掺15%钢渣粉和5%硅灰的水泥基材料,不仅可以改善泵送性能,提升强度和耐久性,还能降低早期水化放热量,具有良好的工程应用前景。

养护制度对活性粉末混凝土承载力的影响研究

为了研究活性粉末混凝土在不同养护制度条件下对承载能力的影响,制作了30个活性粉末混凝土试块和2根HRB500级钢筋活性粉末混凝土简支梁,进行抗压、抗折和抗弯承载力研究试验,分析试块与试验梁的承载力大小随温度的变化情况,利用扫描电镜研究了在不同养护制度下活性粉末混凝土内部结构变化。研究结果表明:(1)当试件养护温度在[常温~180℃]范围内,活性粉末混凝土(RPC)质量损失很小;(2)当温度低于180℃时,随着温度升高,水泥水化反应加剧,RPC微观结构得到改善,抗压强度提高;(3)当温度达到设定值后,继续保持设定温度养护较非恒定温养护的抗压强度高;(4)当养护温度达到180℃时,RPC基体中仍存在未水化颗粒,由此可以假定养护温度仍可以提高。

Mesomechanism of steel fiber reinforcement and toughening of reactive powder concrete

Reactive powder concrete (RPC) is a novel cement-based composite material with ultra-high strength. Embedding a certain amount of short steel fibers in the matrix can improve the RPC’s toughness and overcome the disadvantage of high brittle- ness. In this paper, a number of direct uniaxial tension tests have been carried out with ‘8-shape’ RPC200 specimens. The bond-slip process, mesoscopic structural variation and mechanical characteristics of a fiber pullout of the matrix have been investigated using the real-time SEM loading system and CCD observation tech- niques. The influence of the volume of embedded short steel fibers in matrix on the mesoscopic morphology of attachments on the surface of a pulled individual fiber, the initial cracking force, the ultimate pullout force, interfacial bond strength and the pullout rupture energy have been analyzed. A general formulation relating these quantities to the volume of fibers in matrix has been proposed. The components comprising the interfacial bond strength have been outlined. In addition, the con- tribution that fibers make to enhance and toughen the reactive powder concrete has been discussed. It is shown that there exists an optimal threshold of fiber volume ρv, opt =1.5% at which the bond performance of a fiber pullout of RPC be- haves best.

Experimental study of dynamic mechanical properties of reactive powder concrete under high-strain-rate impacts

The dynamic mechanical properties of reactive powder concrete subjected to compressive impacts with high strain rates ranging from 10 to 1.1×102 s-1 were investigated by means of SHPB (split-Hopkinson-pressure-bar) tests of the cylindrical specimens with five different steel fiber volumetric fractions.The properties of wave stress transmission,failure,strength,and energy consumption of RPC with varied fiber volumes and impact strain rates were analyzed.The influences of impact strain rates and fiber volumes on those properties were characterized as well.The general forms of the dynamic stress-strain relationships of RPC were modeled based on the experimental data.The investigations indicate that for the plain RPC the stress response is greater than the strain response,showing strong brittle performance.The RPC with a certain volume of fibers sustains higher strain rate impact and exhibits better deformability as compared with the plain RPC.With a constant fiber fraction,the peak compressive strength,corresponding peak strain and the residual strain of the fiber-reinforced RPC rise by varying amounts when the impact strain rate increases,with the residual strain demonstrating the greatest increment.Elevating the fiber content makes trivial contribution to improving the residual deformability of RPC when the impact strain rate is constant.The tests also show that the fiber content affects the peak compressive strength and the peak deformability of RPC in a different manner.With a constant impact strain rate and the fiber fraction less than 1.75%,the peak compressive strength rises with an increasing fiber volume.The peak compressive strength tends to decrease as the fiber volume exceeds 1.75%.The corresponding peak strain,however,incessantly rises with the increasing fiber volume.The total energy Edisp that RPC consumed during the period from the beginning of impacts to the time of residual strains elevates with the fiber volume increment as long as the fiber fraction is not larger than 2%.It turns to decrease if the fiber volume exceeds 2%.The added fibers make various contributions to enhancing the capability of RPC to consume energy at different loading stages.If the fiber fraction is not larger than 2%,the added fibers make more contribution to enhancing the energy consumption ability of RPC in the period before the peak strain than in the period after the peak strain.The impact strain rate,however,distinctively affects the total energy that RPC consumed and the energy consumed in the different loading periods.The higher the impact strain rate,the more the energy consumed in the stages and therefore the higher the dynamic impact toughness.The empirical relationships of the peak compressive strength,corresponding peak strain,residual strain,total consumed energy and the energy consumed in the varied periods with the impact strain rate and the fiber fraction are derived.Four generalized forms of the dynamic impact stress-strain responses of RPC are formulated by normalizing stresses and strains as the generalized coordinates and by taking account of the influences of impact strain rates and fiber volumetric fractions.

Experimental study on shear behavior of prestressed reactive powder concrete I-girders

As a new generation of concrete,RPC(Reactive Powder Concrete)has attracted great research attention for its ultra-high strength and high durability.In the present paper,experimental results from tests on eight prestressed RPC I-section girders failing in shear are reported herein.The beams with RPC of 120 MPa in compression were designed to assess the ability to carry shear stress in thin webbed prestressed beams with stirrups.The test variables were the level of prestressing,shear span-depth ratio(a/d)and stirrup ratio.Shear deformation,shear capacity and crack pattern were experimentally investigated in detail.With regard to the shear resistance of the test beams,the predictions from three standards(AFGC,JSCE and SIA)on the design of UHPC structures were compared with the experimental result suggesting that the experimental strength is almost always higher than predicted.RPC,as a new concrete,was different from normal concrete and fiber reinforced concrete.Further study should be needed to develop an analytical method and computation model for shear strength of RPC beams.

早高强单层喷锚衬砌在隧道支护中的应用研究

本文以某隧道斜井为工程依托,对早高强单层喷锚衬砌材料组成及其在斜井中的施作效果进行分析。研究结果表明:早高强单层喷锚衬砌中超微粉复合掺合料的最优混合掺量为30%,联合新型纳米晶胶聚合物应用而使得抗压强度提升15.4%;纳米晶胶聚合物喷射混凝土具有回弹率低、抗渗性能好、强度高等优异特性,其中回弹率为3.4%,28d抗渗性能> P12,6h抗压强度为7.1MPa。本文提出的早高强单层喷锚衬砌施工工艺及工艺参数具有较好的控制效果。

养护温度与脱硫石膏掺量对RPC性能的影响

以普通硅酸盐水泥、脱硫石膏、矿渣等制备了活性粉末混凝土(RPC),研究了养护温度(20、45、70℃)和脱硫石膏掺量(2%~7%)对RPC强度和膨胀率的影响,并进行了XRD和SEM分析。结果表明:当养护温度为20℃时,随着脱硫石膏掺量的增加,试件的28 d抗折与抗压强度均先增大后减小;当养护温度为45℃时,随着脱硫石膏掺量的增加,试件的28 d抗折强度增大,28 d抗压强度先增大后减小;当养护温度为70℃时,试件的28 d抗折与抗压强度均增大;当脱硫石膏掺量相同时,随着养护温度的提高,试件的28 d抗折与抗压强度基本呈增大趋势;脱硫石膏掺量越高,试件的膨胀率越大;养护温度越高,试件趋于稳定时的膨胀率越低;在RPC中掺入适量石膏,并辅以适宜的养护温度,可有效加快水泥和矿渣的水化进程,生成钙矾石,进而改善RPC的强度和膨胀性能。

活性粉末混凝土盖板抗弯承载力与无损检测参数的相关性试验

为了有效预测实际工程中活性粉末混凝土(RPC)盖板开裂强度与破坏强度,收集了27块实际工程中使用的RPC盖板,测试其表面硬度、表面回弹值、超声波波速、剪压值、名义开裂强度、名义破坏强度。线性拟合了不同检测参数与名义破坏强度、名义开裂强度之间的关系。结果表明:砂浆型回弹仪测得的RPC盖板表面回弹值与名义破坏强度线性相关性较强,相关系数为0.82。实际工程中推荐使用砂浆型回弹仪测试RPC盖板表面回弹值,预测其抗弯承载力。

矿物掺合料对活性粉末混凝土海工应用分析研究

研究以抗压强度和抗氯离子渗透性为主要指标,分析了不同掺量硅灰、粉煤灰、矿渣粉等活性矿物掺合料对活性粉末混凝土(RPC)的海工应用影响。试验显示,单掺硅灰、复掺硅灰和粉煤灰、复掺硅灰和矿渣粉对大掺量矿物细粉RPC的抗压强度和抗氯离子渗透性具有较好的作用,以粉煤灰取代部分水泥、硅灰,既能取得较好的耐久性能,抗压强度损失随之减少,同时还可进一步降低工程应用成本,故其具有一定的工程借鉴意义。

水养护温度对活性粉末混凝土强度及水化硅酸钙结构的影响研究

活性粉末混凝土(RPC)水化产物的主体是水化硅酸钙(C-S-H),但其易受温度影响,具有复杂多变的特点。本文分析了水养护温度对RPC的28d强度的影响规律,并利用^(29)Si核磁共振(NMR)技术研究了水养护温度对RPC浆体水泥水化程度、C-S-H凝胶Si原子结构特征、硅氧链平均分子链长(MCL)及Al[4]/Si等微结构参数的影响规律,探明了活性粉末混凝土C-S-H硅氧四面体聚合机制。结果表明:随着水养护温度的升高,RPC的抗压、抗折强度逐渐增大,折压比先增大后降低,其水化程度、硅氧链平均分子链长、Al[4]/Si逐渐增大;当水养护温度≥50℃时,硅灰的火山灰反应加剧,进一步提高了RPC内部水泥水化程度、C-S-H平均分子链长及Al[4]/Si。

200MPa级活性粉末混凝土试验研究

根据加拿大舍布鲁克人行桥采用的活性粉末混凝土配制,研制了适合我国原材料的200MPa级活性粉末混凝土,抗压强度为168.6MPa,抗折强度为21.6MPa。该活性粉末混凝土具有优越的力学性能和耐久性能。由该材料制备的桥梁人行道构件已通过铁道部专家鉴定,拟用于青藏铁路桥梁的实际工程中。

活性粉末混凝土抗拉性能研究

通过不同钢纤维含量活性粉末混凝土的拉伸性能试验,测定活性粉末混凝土的劈裂抗拉强度、轴心抗拉强度及轴心受拉应力-应变全曲线。研究钢纤维体积率对活性粉末混凝土劈裂抗拉强度、轴心抗拉强度的影响规律。研究表明,随着钢纤维掺量的增加,活性粉末混凝土的劈裂抗拉强度、轴心抗拉强度呈线性增大规律;给出活性粉末混凝土轴心抗拉强度和劈裂抗拉强度的关系;提出活性粉末混凝土轴心受拉应力-应变全曲线的数学模型,并根据试验结果确定模型参数。研究成果可为活性粉末混凝土在结构中的应用提供依据。

150～200MPa超高性能混凝土的配制

在分析活性粉末混凝土特点的基础上 ,研究了利用常规材料和普通工艺制备 15 0～ 2 0 0MPa超高性能混凝土的可行性。研究结果表明 ,在不剔除粗集料的情况下 ,采用极低水胶比 ,配制出最高抗压强度达到 170 3MPa的超高性能混凝土 ,混凝土拌合物的坍落度可以达到 2 4 5mm ,扩展度达到 5 6 3mm。研究认为 ,为充分发挥混凝土成本低廉的优势 ,配制超高性能混凝土最佳的技术路径并不是剔除粗集料 ,而是如何去解决混凝土中由于粗集料所带来的缺陷问题。