Initial Cracking Load Research Articles

Effects of creep recovery on the fracture properties of concrete

To study the influence of creep recovery on the fracture properties of concrete, the pre-notched specimens were firstly subjected to three-point bending (TPB) loading at 60% peak load (Pmax) over 30 days. Afterwards, the load was removed and the creep recovery tests were performed for 1, 2, 3 and 15 days, respectively. Thereafter, the quasi-static TPB tests were conducted on the creep recovery specimens. The deformation versus time curves, initial cracking load (Pini), peak load and fracture energy in the quasi-static TPB tests after creep recovery were obtained. Also, the numerical analyses were conducted by combining with the Norton-Bailey model to investigate the stress variations at the crack tip and the time-dependent behaviour of concrete. By comparing the fracture parameters for the specimens with and without undergoing creep recovery, the effects of creep recovery on the fracture characteristics of concrete were assessed. The results showed that during the creep stage, the stress relaxation generated at the crack tip due to viscoelastic characteristics of concrete enlarged the deformation. In contrast, the reversed stress would occur at the crack tip during the recovery stage, and its relaxation over the time contributed to the time-dependent deformation during the creep recovery stage. By comparing with the specimens under the quasi-static TPB loading, Pini and Pmax for the creep recovery specimens would increase, and the increments slowed down over the recovery time. However, the increases in Pini and Pmax for the creep recovery specimens could not enhance the initial and critical fracture toughnesses and these toughnesses were approximately equal to those under the quasi-static tests.

Research on the Crack Resistance and Bearing Capacity of Concrete Roadway Enhanced by Carbon Fiber Mesh and Carbon Fiber Short Cut Wire

Shotcrete support technology can play a certain role in strengthening and anti-permeability of underground roadway. However, the lack of crack resistance and bending resistance seriously affects the function of shotcrete support. In this paper, the crack resistance and bearing capacity of underground concrete shotcrete layer were improved by means of high density carbon fiber mesh (CFM) embedded in prefabricated layer and carbon fiber short cut wires (CFSC) with different content of uniform cloth, which was focused on the synergistic strengthening mechanism between CFM and CFSC. The results show that the addition of high density CFM can significantly improve the bearing capacity of concrete shotcrete layer, but the improvement of crack resistance is not obvious. The addition of CFSC (with a content of 2% and a length of 3 mm) can significantly increase the initial crack load of concrete shotcrete, thus improving the crack resistance performance, but it has no obvious effect on the bearing capacity. Adding CFM and CFSC together can further significantly enhance the bearing capacity and crack resistance of concrete shotcrete layer and give full play to the synergistic enhancement effect between the two.

A new test method for the complete load-displacement curve of concrete under mixed mode I-II fracture

A new test method for measuring the complete load-displacement curve of concrete under mixed mode I-II fracture is presented in this paper. Three-point bending beams with a multi-segment notch in the midspan were selected for this purpose. The ratio of the stress intensity factors at the notch tip between mode II and mode I, KII/KI, varied with the notch-depth ratio of the first segment and the inclination angle of the last segment. Compared with the available testing methods, it was less challenging to follow the proposed procedure to obtain the entire load vs. displacement curves for the KII/KI ratio up to 1.23. By introducing the finite element method, the entire crack propagation process was reproduced based on the crack propagation criterion for a mixed mode I-II crack in concrete. The predicted crack trajectories, the load vs. crack mouth opening/shear displacement curves, the initial cracking loads, and the peak loads were validated against the experimental results. The results agreed remarkably well.

Flexural behaviour of reinforced concrete beams with partial replacements of metakaolin and marble powder

Concrete is the most widely used and versatile building material which is generally used to resist compressive force. By addition of some pozzolanic materials as admixtures, the various properties of concrete can be improved. Many modern concrete mixes are modified with the addition of admixtures, which improve the micro structural properties as well as decrease the calcium hydroxide concentration by consuming it through a pozzolanic reaction. Metakaolin is a cementitious pozzolanic material highly efficient and can react rapidly with the excess calcium hydroxide resulting from OPC hydration by a pozzolanic reaction, to produce calcium silicate hydrate and calcium alumino silicate hydrates. Due to rapid growth of construction activity, the available sources of natural sand are getting exhausted. Therefore, it is necessary to replace natural sand in concrete by an alternate material either partially or completely without compromising the quality of concrete. Waste marble dust is one such material which can be used to replace sand as fine aggregate in concrete. The present study describes an experimental program conducted to investigate the flexural behaviour of Reinforced Concrete beams with metakaolin as partial replacement for cement and marble powder as partial replacement for river sand in preparation of concrete. The percentage replacement of cement by metakaolin considered in this experimental study are 0, 2, 4, 6 and 8% by weight of cement and sand by marble powder are 20, 15, 10, 5 and 0%. The mechanical properties such as compressive and split tensile strength are analysed for conventional and modified concretes, at the age of 7, 14 and 28 days. A total of five RC beams, with dimensions 150 × 200 × 1500 mm was cast and tested under four point loading. The observations made were initial crack load, ultimate failure load and deflection of the beams. The results show that metakaolin and marble powder can be used as alternate construction materials at lower percentage replacement levels.

Flexural Capacity and Behaviour of Geopolymer Concrete Beams Reinforced with Glass Fibre-Reinforced Polymer Bars

Geopolymer concrete (GPC) with Glass fibre-reinforced polymer (GFRP) bars can provide a better construction system with high sustainability, high durability, and adequate strength. Few studies deal with the combination of these materials. The present investigation obtains the flexural capacity and behaviour of GPC and ordinary Portland concrete beams reinforced with GFRP bars (GFRP-RGPC and GFRP-ROPC, respectively). Twelve beams consisting of nine GFRP-RGPC and three GFRP-ROPC beams were cast and tested by using the four-point bending test over an active span of 2000 mm. Rebar ratio, compressive strength, and concrete types were taken as the variables. Initial cracking load, ultimate load capacity, load–deflection behaviour, Load–strain curves, crack width, the number of cracks and failure modes, were studied. Experimental results of beams were compared with the proposed equations provided by ACI 440.1R-15, CSA S806-12, and parabolic stress block method. The Results showed the decrease of deflection and increase of first cracking load by increasing the compressive strength. A slight increase in the deflection of GFRP-RGPC beams and approximately the same value of ultimate load were observed. GFRP-RGPC beams also recorded a higher value of crack width compared with GFRP-ROPC beams. The parabolic stress block method predicted the flexural capacity of the beams close to the experimental results rather than ACI 440.1R-15 and CSA S806-12.

Transverse and longitudinal flexural properties of unidirectional carbon fiber composites interleaved with hierarchical Aramid pulp micro/nano-fibers

Unidirectional carbon fiber reinforced polymer (UD-CFRP) composites designed for ultimate tensile strength and stiffness along the fiber direction are vulnerable in the transverse direction. In this study, UD-CFRPs were reinforced in the transverse direction using sparsely distributed hierarchical Aramid pulp (AP) micro/nano-fibers between 2 and 8 g per square meter (gsm) per ply interface. Those AP micro/nano-fibers, a few hundred microns in length, effectively formed an ultra-thin interleaving layer around 20 μm in thickness between carbon fiber plies. Flexural properties along and perpendicular to continuous carbon fiber direction were measured under three-point-bending (3-P-B) to determine the toughening effects of AP. Flexural loads in both longitudinal and transverse directions have been enhanced by 30% and over 100% respectively from those randomly distributed AP micro/nano-fibers with diameters varied from a few hundred nanometers to 10 μm. Even slight increase in the elastic modulus of AP-toughened CFRP along the fiber direction was observed. Total fracture energy absorption, initial cracking and final fracture loads were measured and compared, indicating AP micro/nano-fibers have contributed to the high strength, high toughness and high modulus characteristics of AP-interleaved UD-CFRPs. Details on toughening mechanisms were revealed from SEM and cross-section optical microscopy examinations. Comparisons of unreinforced UD-CFRP and AP-toughened UD-CFRP showed the hierarchical AP micro/nano-fibers indeed played an important role in composite microstructure design and property optimization. The ultra-thin interleaved AP veil around 20 μm in thickness can be conveniently incorporated into pre-preg fabrication so that the extra interleaving step can be eliminated, i.e. the toughened pre-pregs can be used as normal pre-pregs in the final composite forming.

Model Test on Bearing Characteristics of Basalt Fiber‐Reinforced Concrete Lining

Adding fiber can improve the brittleness of plain concrete. Compared with plain concrete, basalt fiber‐reinforced concrete has the advantages of strengthening, toughening, and crack resistance. Compared with steel fiber‐reinforced concrete, basalt fiber‐reinforced concrete has better construction performance. Basalt fiber concrete is a type of inorganic material with environmental protection and high mechanical properties, which has an important mechanical advantage for controlling the deformation of the soft surrounding rock tunnel. Through the indoor model test of mechanical behavior of reinforced concrete and basalt fiber‐reinforced concrete lining, the bearing characteristics of basalt fiber‐reinforced concrete lining was studied. The results show that, compared with reinforced concrete, the initial crack load of basalt fiber‐reinforced concrete is increased by 20%; the toughness of lining structure is enhanced by adding basalt fiber, and the lining can still bear large bending moment and deformation after the initial crack appears; after the initial crack appears, the bearing characteristic curve of reinforced concrete lining rises slowly and converges rapidly; the bearing characteristic curve of basalt fiber‐reinforced concrete lining rises slowly, and there is no sign of convergence when it reaches 2 times of initial crack load. For the soft surrounding rock tunnel, it is necessary to seal the rock surface as early as possible, provide support as soon as possible, and have a certain deformation capacity. Basalt fiber‐reinforced concrete can better meet these needs.

Experimental Study on Load Bearing Characteristics of Steel Fiber Reinforced Concrete Lining in the Soft Surrounding Rock Tunnel

Tunnels in soft rock with high ground stress will encounter the problem of large deformation of surrounding rock. The study of new high‐performance tunnel lining materials is of great significance to improve the safety of tunnel excavation in soft rock with high ground stress. In this paper, the bearing characteristics of the plain concrete, the reinforced concrete, and the steel fiber reinforced concrete lining are studied by the indoor model experiment. By extracting the displacement and stress data of typical parts of lining, the bearing characteristics of the steel fiber reinforced concrete lining are analyzed and summarized. The test results show that the initial crack load and ultimate load of the steel fiber reinforced concrete lining are significantly higher than those of the other two materials, and the crack development path is more tortuous, and the number of cracks is greater. Steel fiber can improve the bearing capacity and deformation capacity of the lining structure so that the failure mode of the lining structure changes from brittle shear failure to ductile bending failure. It is concluded that steel fiber reinforced concrete can improve the toughness of lining. Because of its excellent mechanical properties, steel fiber reinforced concrete can completely replace the conventional reinforced concrete as a new lining material for soft rock tunnel. The above research results are of great significance to the design and construction of tunnel lining in the soft surrounding rock.

Design and behaviour of double skin composite beams with novel enhanced C-channels

This paper firstly developed a new type of Double Skin Composite (DSC) beams using novel enhanced C-channels (ECs). The shear behaviour of novel ECs was firstly studied through two push-out tests. Eleven full-scale DSC beams with ECs (DSCB-ECs) were tested under four-point loading to study their ultimate strength behaviours, and the studied parameters were thickness of steel faceplate, spacing of ECs, shear span, and strength of concrete core. Test results showed that all the DSCB-ECs failed in flexure-governed mode, which confirmed the effective bonding of ECs. The working mechanisms of DSCB-ECs with different parameters were reported, analysed and discussed. The load-deflection (or strain) behaviour of DSCB-ECs were also detailed reported. The effects of studied parameters on ultimate strength behaviour of DSCB-ECs have been discussed and analysed. Including the experimental studies, this paper also developed theoretical models to predict the initial stiffness, elastic stiffness, cracking, yielding, and ultimate loads of DSCB-ECs. Validations of predictions against 11 test results proved the reasonable estimations of the developed theoretical models on those stiffness and strength indexes. Finally, conclusions were given based on these tests and analysis.

Performance of Crumb Rubber Incorporated Ferro Geopolymer Panels under Flexure

This research work presents the overview of geopolymer mortar application into the ferro cement panel with the incorporation of crumb rubber and Nano fly ash. The geopolymer mortar is prepared by using industrial wastes as a base material such as fly ash and ground granulated blast furnace slag (GGBFS) which generally helps to reduce the level of CO2 emission. Also, the recycled tyre crumb rubber is utilized as a sustainable innovative construction material which is used a partial substitution for sand upto 5% for enhancing the ductility without any strength degradation. These reduces land fill problems and ground water quality degradation problems. Crumb rubber has the ideal capacity to absorb energy from static and other kind of loads. The geopolymer binder preparation is done by utilizing material such as fly ash, GGBFS, alkaline liquid made of NaOH and Na2SiO3 , Nano fly ash. The Nano fly ash is used as an additive which helps in increasing the strength and durability of the element by its pore filling capability. This project aims to enhance the strength of fly ash based geopolymer mortar with the help of GGBFS incorporation. The molarity of alkaline activator, solution to binder ratio and silicate to hydroxide ratio is fixed as 12, 0.4 and 1.5 throughout the process. The mortar cubes and panels were heat cured under hot air oven at 80ᵒ C for 48 hours. The mechanical behavior of geopolymer mortar is assessed by compressive strength test water absorption test. The panel is made of high strength geopolymer mortar and expanded metal mesh with chicken mesh for obtaining higher energy absorption capacity with good deforming ability and less crack pronouncement. The investigation involves finding the initial crack load, ultimate failure load and residual flexural strength ratio. The results show that the tyre inclusion enhances the flexural strength of the ferro geopolymer panel by means of its ductile enhancing capacity

Laser-assisted cyclic chipless splitting for hard-to-cut thick wall tubes and fatigue fracture mechanism analysis

High-quality precision cropping of hard-to-cut thick wall tubes is urgently needed as the first process for precision forming of tubular parts. Due to the deficiencies of large cutting load and waste of chips and coolants in the present cutting methods, a laser-assisted cyclic chipless splitting (LACCS) method is developed, which prefabricates circumferential crack with large stress concentration by laser, and exerts cyclic rotary load at a low amplitude simultaneously to split the tube. The theoretical laser crack depth and critical loads are derivated for fatigue crack propagation and instant rupture, respectively, and an XFEM model based on cohesive damage criterion is established to reveal the fracture mode based on stress intensity factors. Finally, section quality and microfracture mechanism are investigated by experimental tests with different initial crack depths and load control curves. The results show that critical fatigue splitting load and instant rupture load gradually drop with crack depth at a decreasing rate; for crack depth of 0.7 mm, the critical loads are 0.67% and 34.36%, respectively, of that in the traditional cutting method. The type I crack is the primary fracture mode in this LACCS process, and the stress intensity factor KI varies as a cosine curve with peak amplitude of 436.09 MPa(m)1/2. Step-reduction frequency load can smoothly transite the crack propagation to final rupture, and obtains high-quality sections in 16–32 s, with outer roundness error of 0.6%, flatness error of 0.2–0.3 mm and final rupture area of 0.25–1.19 mm2. The fractographies typically show laser affected zone, cracks propagation zone and final rupture zone. Micro-cracks initiate from the tangency points on the laser notch curve with maximal stress change rate, and the ductile striations propagate with growth rate of 3.3–5.1 μm/cycle. Final rupture zone forms under shear stress, featured by quasi-parabolic dimples involving microvoid coalescence.

Experimental study of the interlaminar fracture of composite materials in mode III by MSCB test

This paper focuses on the study of interlaminar fracture of composite materials in mode III using the Modified Split Cantilever Beam (MSCB) test. MSCB test is applied to investigate the dependency of the mode III energy release rate on geometric parameters (specimen width, and thickness), initial crack length, loading condition and crack front material layup. A non perforated release film is introduced to create delamination at the mid-plane of the tested specimens. Three sets of samples (a total of 56 samples) are fabricated and tested from Unidirectional Glass fibers. The length of the specimens is 154 mm. The first set of tests is conducted for three different widths (35 mm, 20 mm, 12 mm) to select the most appropriate width that leads to a crack initiation prior to specimen failure. The remaining sets of tests are conducted with different loading conditions, different thickness, different initial crack length, and different lay up orientations at the crack front (0/0, +45/−45, 0/45, and 0/90). Results show that both width selection and load configuration are of extreme importance for the success of the test. The energy release rate (GIIIc) increases with increasing thickness and width. The stacking orientation at the crack front shows minor influence on GIIIc.

Characteristics of Flexural Behavior of Reinforced Concrete Member Substituted Heavyweight Waste Glass as Fine Aggregate

The progress of civilization has been led to the increase of industrial products, the amount of waste is increasing, and its disposal has become a problem. And, the huge amount of expended concrete has led to the dissipation of natural aggregate. To deal with these problems, many researches have been executed to use a variety of industrial waste as aggregate in concrete materials. So, in this paper, the flexural behavior with substitution ratio of heavyweight waste glass were compared and evaluated in reinforced concrete members. From the results, initial cracking load, yielding load and flexural rigidity less affected by substitution ratio of heavyweight waste glass. However, the ductility of the RC member was significantly affected when all of the fine aggregate is replaced by the heavyweight waste glass.

Experimental study on shear resistance of reactive powder concrete beams without stirrups

The tests results of 18 longitudinally reinforced reactive powder concrete (RPC) beams without stirrups and subjected to combined flexural and shear are presented in this paper. The main test variables were the ratio of the shear span-to-effective depth (a/d), the ratio of the longitudinal reinforcement (ρw), the percentage of steel fibers volume fractions (Vf) and the percentage of silica fume (SF) powder. The findings of this paper reveal that addition of steel fibers into the RPC mixture does not considerably affect the initial diagonal cracking load but it influences the ultimate load capacity. For all tested fibrous RPC beams, the ratio of the ultimate shear force to diagonal cracking force (Vu∕Vcr) have an average ratio of about 2.5. The shear design equations recommended by the (ACI 318-14) code, (CSA A23.3-04) code, (NZS 3101-06) code and (BS 8110-97) code have been modified to predict the ultimate shear strength of RPC beams without stirrups. The suggested equations gave satisfied predictions for the shear strength of the tested RPC beams with coefficients of variation (COV) ranging from 0.09049 to 0.1817.

The Effect of Cutting Openings on the Behavior of Two-way Solid Loaded Slabs

It is often necessary to cut openings in existing two-way reinforced concrete slabs due to late design requirements. Those openings should be studied extensively; as they pose a break in the continuity of the reinforcing bars hence; they weaken the slabs and reduce their load carrying capacity. The purpose of this research is to investigate the behavior of two-way RC beamed slabs with openings introduced after casting. The method of cutting the slab under service loading and the strengthening methods' efficiency are the main parameters. Ten square reinforced concrete two-way beamed slabs were prepared to be tested experimentally. They were divided into two cases: (case A), and (case B). Case A consisted of: five slabs cast with a square 300 mm side opening in the mid-span of the slabs, and case B was composed of: five slabs with no openings.For (case A), the five slabs were divided into: a control two-way slab with an opening in the mid-span; which was not strengthened, three two-way slabs each with an opening in the mid-span; they were strengthened internally using extra reinforcing steel bars around the opening; which had different development length, and finally, a slab with a mid-span opening strengthened with externally bonded Carbon Fiber Reinforcing Polymer (EB-CFRP) laminates at the tension side. Whereas, (case B's) five slabs were: a square control slab, it was examined till failure to evaluate the slabs' capacity, and four two-way squared reinforced concrete slabs with no openings, they were tested following a certain sequence. It was as follows; the four two-way squared reinforced concrete slabs were loaded till the initial cracking load as that of the control slab. Then, the strengthening was installed, and the opening was cut at the mid-span. The loading continued till failure occurred. The strengthening was carried out using Near Surface Mounted Technique (NSM) and EB CFRP. Strength, deflection and energy dissipation were calculated, and compared for both groups.The experimental results were verified numerically using Yield Line Theory.

Investigations on the FPZ evolution of concrete after sustained loading by means of the DIC technique

The three-point bending (TPB) specimens were first subjected to two levels of sustained loading, i.e., 30% peak load and the initial cracking load over 115 days. Then, they were moved out from the loading frames and tested under TPB loading until failure. The digital image correlation (DIC) technique was utilized to investigate the fracture process in concrete after sustained loading. According to the variations of the crack opening displacement from the experimental observations, the crack propagation lengths and the crack widths with respect to different loading points were derived, which provides the information on the evolution of the fracture process zone (FPZ) in concrete after sustained loading. The results indicated that, compared with the tested results from the aging specimens in the static TPB tests, the low sustained loading did not show obvious effects on the FPZ evolution. However, under the high sustained loading, the crack initiated during the loading duration, resulting in a longer critical crack propagation length. In addition, the decrease in the FPZ length for the specimens under the high sustained loading is more significant at the post-peak load stage, resulting in the increase in brittleness of concrete. Finally, a test method for determining the crack propagation length using clip gauges was proposed, which is more convenient in lab. The crack propagation lengths tested using clip gauges fairly well agreed with those by means of the DIC and verified the proposed measure method in this study.

Effect of steel fibers on the flexural behavior of RC beams with very low reinforcement ratios

This study aims to investigate the implications of hooked-end steel fibers on the flexural performance of reinforced concrete (RC) beams with very low reinforcement ratios. For this, four different fiber volume fractions, vf, of 0.25%, 0.50%, 0.75%, and 1.00%, were incorporated into the concrete mixture and plain concrete without fibers was considered as a control specimen. Four reinforcement ratios of 0.178%, 0.267%, 0.317%, and 0.406%, which are 44%, 66%, 78%, and 100% of the minimum reinforcement ratio, ρmin, were also adopted to evaluate the steel fiber effect on the flexural behavior of RC beams with various very low reinforcement ratios. The test results indicated that the overall flexural performance of RC beams, in terms of flexural strength, deflection capacity, post-cracking flexural stiffness, and cracking behavior, was improved by increasing the reinforcement ratio up to ρmin. Higher initial cracking and yield loads, post-cracking stiffness, and better cracking performance of RC beams were also obtained by including steel fibers. However, the enhancement of ultimate load carrying capacity by steel fibers was relatively minor, and the ductility index and flexural strength margin, used to guarantee a ductile failure mode, deteriorated with the inclusion of steel fibers. The lower reinforcement ratios and higher fiber volume fractions clearly led to lower ductility indices. Therefore, it was concluded that longitudinal steel rebar could not be replaced with discontinuous steel fibers at moderate volume fractions, vf ≤ 1.0%, in terms of ultimate load carrying capacity, ductility, and flexural strength margin. Lastly, analytical results considering material models for steel fiber-reinforced concrete (SFRC), given by the RILEM recommendation, generally overestimated the flexural capacities of reinforced SFRC beams, and the inaccuracy increased with increasing fiber contents.

Influence of sustained loading on fracture properties of concrete

To investigate the effects of sustained loading on the fracture properties of concrete, basic creep and three-point bending (TPB) tests were conducted on the pre-notched beams. The specimens were first subjected to two sustained loading levels, i.e. 30% peak load and the initial cracking load over 115 days. Then, they were moved out from the loading frames and tested under TPB loading until failure. The critical crack propagation length (Δac), the peak load (Pmax) and the fracture energy (Gf) were measured in the tests, and the unstable fracture toughness (KICun) was calculated accordingly. Furthermore, based on the load-displacement curves obtained in the TPB tests, the energy dissipation was derived using the modified J-integral method. By enforcing balance between the energy dissipated and the energy caused by the fictitious cohesive force acting on the fracture process zone, the tension-softening constitutive laws under the two sustained loading levels were established and also simplified as bilinear forms for practical applications. Finally, the effects of sustained loading on the fracture properties were examined by comparing with the tested results from the aging specimens in the static TPB tests. The test results indicate that low sustained loading had no effects on all fracture properties of concrete investigated in this study, while under high sustained loading, Δac and KICun increased and Gf and Pmax almost remained unchanged. Meanwhile, a smaller free-stress crack opening displacement was obtained under the high sustained loading level, which indicates a shorter FPZ length formed, resulting in the increase in brittleness of concrete.

Hybrid Effects of Stirrup Ratio and Steel Fibers on Shear Behaviour of Self-Compacting Concrete

Abstract Shear cracking behaviour of fibrous self-compacting concrete of normal and high strength grade (M30 and M70) is presented here. Two stirrup diameters (6mm ∅ and 8 mm ∅) with a constant steel fiber content of 38 kg/m3 (0.5% by volume of concrete) were selected for the present study. The size of the beam was fixed at 100x200x1200mm. The clear span of the beam 1100mm, was maintained throughout the study. A total of 16 shear-deficient beams were tested under three point loading. Two stirrup spacing (180mm and 360 mm) are used for the shear span-to-depth ratio (a/d = 2). Investigation indicates that initial cracking load and ultimate load increased as the area of shear reinforcement increased by increasing the diameter of stirrup. It was also noted that the failure mode was modified from brittle shear failure to flexural-shear failure in the presence of fibers. The mechanical behaviour of SFRSCC was improved due to the combined effect of stirrups and steel fibers. The stiffness, toughness, and deflection of the beams increased when compared to SCC beams without fibers. The experimental results were compared with existing models available in literature, and the correlation is satisfactory.

Experimental Study and Shear Strength Prediction for Reactive Powder Concrete Beams

Eighteen reactive powder concrete (RPC) beams subjected to monotonic loading were tested to quantify the effect of a novel cementitious matrix materials on the shear behavior of longitudinally reinforced RPC beams without web reinforcement. The main test variables were the ratio of the shear span-to- effective depth (a/d), the ratio of the longitudinal reinforcement (ρw), the percentage of steel fibers volume fractions (Vf) and the percentage of silica fume powder (SF). A massive experimental program was implemented with monitoring the concrete strain, the deflection and the cracking width and pattern for each RPC beam during the test at all the stages of the loading until failure. The findings of this paper showed that the addition of micro steel fibers (Lf/Df = 13/0.2) into the RPC mixture did not dramatically influence the initial diagonal cracking load whereas it improved the ultimate load capacity, ductility and absorbed energy. The shear design equations proposed by Ashour et al. and Bunni for high strength fiber reinforced concrete (HSFRC) beams have been modified in this paper to predict the shear strength of slender RPC beams without web reinforcement and with a/d ≥ 2.5. The predictions of the modified equations are compared with Equations of Shine et al., Kwak et al. and Khuntia et al. Both of the modified equations in this paper gave satisfied predictions for the shear strength of the tested RPC beams with COV of 7.9% and 10%.