Impact Resistance of Reactive Powder Concrete

The impact behaviour of three types of reactive powder concretes （RPC） was studied using the split Hopkinson press bar （SHPB） testing method. These RPC were prepared with steel fiber volume fraction of 0%, 3%, and 4%, respectively. The stress-strain relationship, strain rate sensitivity threshold value, dynamic strength increase factor, modulus of elasticity and failure pattern of these RPC specimens subjected to impact load were investigated. From the tests, the strain rate sensitivity threshold value of 50 s-1 was obtained. The experimental results showed that when the strain rate increased from the threshold value to 95 s-1, the maximum stress of RPC increased by about 20% and the modulus of elasticity of RPC increased by about 30%. The failure pattern of RPC specimens with steel fiber reinforcement was very different from that of the RPC matrix specimen when subjected to impact loading. Under similar impact loading rate, cracks developed in the steel fiber reinforced RPC specimens, whilst the RPC matrix specimens were broken into small pieces.

EXPERIMENTAL AND NUMERICAL STUDIES ON DYNAMIC COMPRESSIVE BEHAVIOR OF REACTIVE POWDER CONCRETES

Split Hopkinson pressure bar （SHPB） technique is used to determine the dynamic strength of reactive powder concretes （RPCs） with different steel-fiber contents. Two types of pulse shapers with different thicknesses are considered to reduce the high-frequency-oscillation effect and achieve a nearly constant strain rate over a certain deformation range. It is known that the compressive strength of concrete-like materials is hydrostatic-stress-dependent, and the apparent dynamic strength enhancement comes from both the effects of the hydrostatic stress and strain rate. In order to differentiate them, numerical method is used to calculate the contribution of the hydrostatic stress, and then the genuine strain-rate effect on dynamic compressive strength of RPCs is determined. In addition, the effect of steel-fibers on dynamic strength and failure mode of RPCs is discussed.

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.

Shaped charge penetration into high-and ultrahigh-strength Steel-Fiber reactive powder concrete targets

Experiments on shaped charge penetration into high and ultrahigh strength steel-fiber reactive powder concrete(RPC) targets were performed in this paper.Results show that the variation of penetration depth and crater diameter with concrete strength is different from that of shaped charge penetration into normal strength concrete(NSC).The crater diameter of RPC is smaller than that of NSC penetrated by the shaped charge.The jet particles are strongly disturbed and hardly reach the crater bottom because they pass through the narrow channel formed by jet penetration into the RPC.The effects of radial drift velocity and gap effects of jet particles for a shaped charge penetration into RFC target are discussed.Moreover,a theoretical model is presented to describe the penetration of shaped charge into RPC target.As the concrete strength increases,the penetration resistance increases and the entrance crater diameter decreases.Given the drift velocity and narrow crater channel,the low-velocity jet particles can hardly reach the crater bottom to increase the penetration depth.Moreover,the narrow channel has a stronger interference to the jet particles with increasing concrete strength;hence,the gap effects must be considered.The drift velocity and gap effects,which are the same as penetration resistance,also have significant effects during the process of shaped charge penetration into ultrahigh-strength concrete,The crater profiles are calculated through a theoretical model,and the results are in good agreement with the experiments.

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.

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%.

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.

Strength and Toughness of Steel Fibre Reinforced Reactive Powder Concrete Under Blast Loading

The blast resistance of structures used in buildings needs to be investigated due to the increased threat of a terrorist attack. The damage done by Composition B or Powergel to steel fibre reinforced reactive powder concrete （SFRPC） panels and ordinary reinforced concrete （RC） panels of equivalent static flexural strength is compared. A 0. 5 kg charge was detonated at a distance of 0. 1 m from the 1. 3 m × 1. 0 m × 0. 1 m （thick） panels, which were simply supported and spaning 1.3 m. Dynamic displacement measurements, high-speed video recording and visual examination of the panels for spall and breach were undertaken. The SFRPC panels withstood the bare charge blast better than the reinforced ordinary concrete panels. Neither type of panel was breached using a O. 5 kg charge, The RC panel exhibited more spalling when Composition B was used. Under successive Composition B loading conditions, the RC panel was breached. In comparison the SFRPC panel was not breached. Exposure to fragmenting charge loading conditions confirmed these performance differences between the SFRPC panel and the reinforced ordinary concrete panel.

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.

Corrosion Behavior of Steel Fibers in Reactive Powder Concrete with High Volume of Mineral Admixtures

The corrosion behavior and the effects of temperature on critical chloride content (Ccrit) of steel fibers in RPC were analyzed by a pH meter, ion chromatography, mercury intrusion porosimetry (MIP), and electrochemical techniques. It was found that the suspension pH value, the chloride binding capacity, and the total porosity of RPC were lower than those of high-performance concrete (HPC). The pore structure of RPC mainly consisted of gel pores. The Ccrit values of steel fibers in RPC and HPC at 20 ℃ were 1% and 2%, respectively. When the temperature reached 50 ℃, the Ccrit value of steel fibers in HPC decreased significantly, whereas it remained unchanged in RPC. The corrosion rate of corroded fibers in both RPC and HPC started to decrease with the rise in temperature.

Analysis on plastic properties of reactive powder concrete continuous beams reinforced with GFRP bars

To study the plastic properties of reactive powder concrete continuous beams reinforced with GFRP bars,the calculation programs for moment redistribution coefficients are prepared by using nonlinear analysis methods such as moment-curvature,conjugate beam method and so on. By comparing the test results of existed FRP bars reinforced concrete continuous beams with simulation results,the accuracy of the calculation program is verified. Then 18 simulated GFRP bars reinforced reactive powder concrete continuous beams are selected whose change parameters are reinforcement ratio of mid-span and middle support. Through the nonlinear analysis of simulated beams,moment redistribution coefficients under mid-span concentrated loads,one-third point loads and uniformly distributed loads are obtained respectively. Thus the formula of moment redistribution coefficients is obtained by fitting moment redistribution coefficients and factors. The results show that the reactive powder concrete continuous beams reinforced with GFRP bars have good plastic properties.

Surface Morphology of Reactive Powder Concrete Containing Soil

Recent studies have revealed that concrete can be used as a media to contain As （arsenic） removed from drinking water. Concrete, which is a composite material, has been effective in solidifying hazardous wastes and contaminated soils. A research project was conducted to study the effects of uncontaminated soil and arsenic contaminated soil on the microstructure of concrete to qualitatively define the mechanisms of the encapsulation of soils containing inorganic material such as arsenic by application of solidification/stabilization technique. This research paper focused on studying the surface morphology of RPC （reactive powder concrete） containing soil.

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.

Investigating the influence of gamma ray energies and steel fiber on attenuation properties of reactive powder concrete

The effect of gamma ray energies and volume ratio of micro steel fiber(1 and 1.5%) on attenuation properties of reactive powder concrete(70 MPa compressive strength) was investigated. Different characteristics have been considered such as linear attenuation coefficient,mass attenuation coefficient, and half-value thickness.Sodium iodide crystal with a gamma ray spectrometer and collimated beam of gamma ray has been implemented to perform the experimental test. Three sources(Cs-137, Co-60, and Bi-207) with energies of(0.662, 1.17 1.33, 0.569,and 1.063) MeV were adopted in the test. The results obtained indicated that mass attenuation coefficient is proportioned inversely with gamma ray energies and directly with a volume ratio of micro steel fiber. The linear attenuation coefficient and half-value thickness of the tested samples have been calculated and discussed. The obtained results showed that increasing the volume ratio of steel fiber has modified the adequacy of the reactive powder concrete as a shielding element since it increases the density and reduces the half-value thickness.

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.

Mechanical Properties and Microcosmic Properties of Self-Compacting Concrete Modified by Compound Admixtures

It has become a research hotspot to explore raw material substitutes of concrete.It is important to research the mechanical properties of self-compacting concrete(SCC)with slag powder(SP)and rubber particle(RP)replacing cement and coarse aggregate,respectively.12 kinds of composite modified self-compacting concrete(CMSCC)specimens were prepared by using 10%,20%and 30%SP and 30%,40%,50%and 60%RP.The rheological properties,mechanical properties and microstructure of the CMSCC were investigated.Results indicate that the workability,compressive strength,splitting tensile strength and flexural strength of CMSCC prepared by 20%SP and less than 40%RP are improved.In order to maximize the utilization of waste materials,20%SP and 40%RP can be used as the optimal ratio of the combined modifier.The microstructure shows that the addition of proper amount of SP is conducive to the formation of increasingly more uniform C-S-H gel.C-SH gel can fill the internal pores of the sample and enhance the adhesion between the aggregate,thus improving the mechanical properties of CMSCC.RP has a rougher surface and lower density and stiffness,which inhibits the workability and mechanical properties of CMSCC.The above research results have important theoretical and practical significance for the selection of raw materials of self-compacting concrete and the rational use of industrial wastes.

Properties of Fresh and Hardened Self-compacting Concrete Produced by Using Locally Available Materials

Self-compacting concrete （SCC） is defined so that no vibration is necessary for the compaction. The main criteria of producing SCC have to satisfy the following characteristics [1, 2, 3]： （1） Ability to flow into and completely fill complex forms under its own weight; （2） Ability to pass through and bond to congested reinforcements; （3） High resistance to aggregate segregation. Self-compacting concrete presents a significant sign in improving the product quality and efficiency of the building industry. It also enhances the working conditions and the quality and appearance of concrete. Japan has been used self-compacting concrete in bridge, building and tunnel construction since the early 1990s. In the last decade, SCC has been produced a high potential for greater acceptance and wider applications in highway bridge construction in the Europe and U.S.. However, till now, there is no application of SCC in the construction industry in Egypt. Therefore, the main objective of this research is to produce SCC by using the locally available materials in our region such as basalt, gravel, sand, limestone powder and silica fume. Experimental programme was designed to characterize the properties of fresh and hardened SCC. It comprises different concrete mixes thbricated with different types and percentages of constituent materials. Three full-scale reinforced concrete beams were fabricated from the SCC mixes and tested under flexure. For the purpose of comparison, an extra RC beam was made of conventional normal concrete to serve as a reference beam. This study, in general, demonstrated that the applications of SCC in construction industry oiler products with enhanced characteristics as well as could be economical.

Stress-strain relationship for reactive powder concrete with recycled powder under uniaxial compression

The recycled powder(RP)from construction wastes can be used to partially replace cement in the preparation of reactive powder concrete.In this paper,reactive powder concrete mixtures with RP partially replacing cement,and natural sand instead of quartz,are developed.Standard curing is used,instead of steam curing that is normally requested by standard for reactive powder concrete.The influences of RP replacement ratio(0%,10%,20%,30%),silica fume proportion(10%,15%,20%),and steel fiber proportion(0%,1%,2%)are investigated.The effects of RP,silica fume,and steel fiber proportion on compressive strength,elastic modulus,and relative absorption energy are analyzed,and theoretical models for compressive strength,elastic modulus,and relative absorption energy are established.A constitutive model for the uniaxial compressive stress-strain relationship of reactive powder concrete with RP is developed.With the increase of RP replacement ratio from 0% to 30%,the compressive strength decreases by 42% and elastic modulus decreases by 24%.

Failure Patterns and Energy Analysis of Shaft Lining Concrete in Simulated Deep Underground Environments

The failure patterns and energy evolution of three types of shaft lining concrete subjected to static and dynamic loading were reported.The energy and damage characteristics of concrete were determined by means of a uniaxial hydraulic servo machine,acoustic emission (AE) equipment,a split Hopkinson pressure bar (SHPB) and an ultrasonic wave analyser.The experimental results indicate that the confluence of multiple cracks forms a penetrating cross section in normal high-strength concrete (NHSC) under the condition of static loading,while the elastic energy that surges out at failure can cause tremendous damage when subjected to dynamic loading.A single crack was split into multiple propagation directions due to the presence of fibres in steel fibre-reinforced concrete (SFRC);adding fibre to concrete should be an effective way to dissipate energy.The non-steam-cured reactive powder concrete (NSC-RPC) designed in this paper can store and dissipate more energy than normal concrete,as NSC-RPC exhibits a strong ability to resist impact.Applying NSC-RPC to the long-service material of a shaft lining structure in deep underground engineering is quite effective.

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.