Ultimate Crack Research Articles

Influence of the Geometry of Corrosion-Fatigue Cracks on the Residual Service Life of Objects Intended for Long-Term Operation

We establish conditions for the prediction of the development of cracklike defects of semielliptic shape in a pipe wall according to the results obtained by using the experimental-numerical procedure. The relationship between the ultimate sizes of a semielliptic crack and the rate of its propagation in “metal–medium” systems is revealed. We propose a criterial dependence of the initial and ultimate crack sizes that can be used for the evaluation of hazard of the recorded defects and interpret the results of technical diagnostics of pipelines after long-term operation.

Flexural performance of hybrid polypropylene–polyolefin FRC composites

The objectives of the present study are to conduct experimental studies and determine the flexural strength and ductility of fiber-reinforced concrete (FRC) by adding two types of fibers, namely the polypropylene (PO) and polyolefin (PP) fibers in mono and hybrid forms, and assess the flexural toughness of fiber-reinforced concrete (FRC). The reinforced concrete (RC) beams of size 150 mm × 200 mm × 1000 mm were cast by adding discontinuous fibers of volume fraction (Vf) of 1% of PP (100%), PO (100%) and PP–PO (50–50%) in concrete. The flexural toughness of FRC beams with PP-1%, PO-1% and hybrid-1% (PP–PO) was evaluated from the area under the load–deflection curve and compared with control specimens (CS) (without fibers). The flexural strength and ductility were higher for FRC beam specimens reinforced with hybrid fibers (PP-Vf = 0.5% + PO-Vf = 0.5%) than beam specimens cast with mono PP fibers of Vf = 1% and PO fibers of Vf = 1%, and CS. The flexural toughness (FT) at beam deflection, L/150 (L = span length) and flexural toughness ratio (FTR) were found to be higher for FRC-hybrid PP–PO beam specimens than the specimens reinforced with PP and PO and control specimens (CS). The first-crack width and ultimate crack width of beam specimens were comparatively lesser for hybrid PP–PO than PP, PO fibers and CS.

A Study of the Impact Resistance of Rubber Concrete at Low Temperatures (−30°C)

In the present study, the impact resistance of rubber concrete at low temperatures (−30°C) was examined. The initial and ultimate crack impact times and the ductility indexes were evaluated. This study’s specimens were prepared by adding two different sizes of rubber particles (20 mesh and 50 mesh) in different ratios (0%, 5%, 10%, 15%, and 20%) at both 25°C and −30°C. The concrete specimens were evaluated using a drop hammer weight test method. The results showed that the initial and ultimate crack impact times and ductility indexes of the rubber concrete specimens had decreased at −30°C. Also, the decrease amplitudes were determined to be lower than those of the reference concrete specimens. Consideration was given in this study to the large variations in the impact values, and a two‐parameter Weibull distribution method was adopted in order to analyze the obtained experimental data. The results had demonstrated that the impact times of the rubber concrete specimens could be described using the two‐parameter Weibull distribution method results.

Performance of Self-Compacting Concrete Slab with Grinded Local Rocks

The effect of using grinded rocks of (quartzite and porcelanite) as powder of (10 and 20) % replacement by weight of cement for self-compacting concrete slabs was investigated in this study. Five slabs with 15 concrete cubes were tested experimentally at 28 days to study the compressive strength, ultimate load, ultimate deflection, ductility, crack load and steel strain. The test results show that, the compressive strength improvement when replacement of local rock powder reached to (7.3, 4.22) % for (10 and 20) % quartzite powder and (11.3, 16.1) % for (10 and 20) % porcelanite powder, respectively compared to the reference specimen. The ultimate load percentage increase for slabs with (10 and 20) % replacement of quartzite powder was 41.17% and 23.53%, while the slabs with (10 and 20) % replacement of porcelanite powder were 23.53% and 35.3% compared to the reference slab, respectively. The ultimate deflection, ductility, spread cracks and ultimate steel strain for slabs with replacement materials (quartzite and porcelanite) increased significantly compared to the reference slab. 

Impact of shear connectors on the behaviours of box-girders with corrugated webs

The impact of different shear connectors (perfobond leisten (PBL) shear connectors and stud shear connectors) on the mechanical performances of prestressed concrete (PSC) composite box-girders with corrugated steel webs was studied. Mechanical properties were researched by conducting experiments on two specimens with PBL shear connectors or stud shear connectors; these properties included the ultimate bearing capacity, the flexural stiffness, crack resistance and the efficiency of prestressing of the girder. The test results showed that, compared with the stud shear connectors, PBL shear connectors greatly improved the ultimate bearing capacity, flexural stiffness and crack resistance of PSC composite box-girders with corrugated steel webs. However, regarding the efficiency of prestressing, the PBL shear connectors did not perform as well as the stud shear connectors.

The effect of fiber orientation on the post-cracking behavior of steel fiber reinforced concrete under bending and uniaxial tensile tests

The present paper deals with an experimental study on the post-cracking tensile behavior of Steel Fiber Reinforced Concrete (SFRC). In this regard, a broad experimental campaign based on Uniaxial Tensile Tests (UTTs) on notched cylinders as well as three point bending tests (3 PBTs) on notched beams was carried out.Based on the experimental results, the benefits offered by the addition of fiber in the post-cracking behavior was deeply studied: fibers increase the toughness of concrete and the ultimate crack width.The uniaxial post-cracking tensile laws of SFRCs were directly obtained by UTTs and indirectly retrieved by 3 PBTs by performing an inverse analysis procedure. In the latter case the fracture energy was generally higher. It was proven that there is a strongly dependency of the SFRC post-cracking performance with the fiber distribution and orientation that was measured by means of image-analysis technique.

Crack Width and Load-Carrying Capacity of RC Elements Strengthened with FRP

The present study focuses on a prediction of crack width and load-carrying capacity of flexural reinforced concrete (RC) elements strengthened with fibre-reinforced polymer (FRP) reinforcements. Most studies on cracking phenomena of FRP-strengthened RC structures are directed to empirical corrections of crack-spacing formula given by design norms. Contrary to the design norms, a crack model presented in this paper is based on fracture mechanics of solids and is applied for direct calculation of flexural crack parameters. At the ultimate stage of crack propagation, the load-carrying capacity of the element is achieved; therefore, it is assumed that the load-carrying capacity can be estimated according to the ultimate crack depth (directly measuring concrete’s compressive zone height). An experimental program is presented to verify the accuracy of the proposed model, taking into account anchorage and initial strain effects. The proposed analytical crack model can be used for more precise predictions of flexural crack propagation and load-carrying capacity.

DUCTILITY RESPONSE OF HYBRID FIBRE REINFORCED CONCRETE BEAMS

Abstract: The effect of fibre content on the Strength and ductility behaviour of hybrid fibre reinforced concrete (HFRC) beams having different fibre volume fractions was investigated. The parameters of this investigation included service load, ultimate load, service load deflection, ultimate load deflection, crack width, deflection ductility and energy ductility. The fibre volume fraction (Vf) ranged from 0.0 to 2.0 percent. Steel and polyolefin fibres were combined in different proportions and their impact on the above parameters was studied. The ductile response of hybrid fibre reinforced concrete beams was compared with that of control beam. The test results show that addition of 2.0 percent by volume of hybrid fibres improve the strength and ductility appreciably. Empirical expressions for predicting the strength and ductility of hybrid fibre reinforced concrete (HFRC) are proposed based on regression analysis. A close agreement has been obtained between the predicted and experimental results.

DUCTILITY RESPONSE OF HYBRID FIBRE REINFORCED CONCRETE BEAMS

Abstract: The effect of fibre content on the Strength and ductility behaviour of hybrid fibre reinforced concrete (HFRC) beams having different fibre volume fractions was investigated. The parameters of this investigation included service load, ultimate load, service load deflection, ultimate load deflection, crack width, deflection ductility and energy ductility. The fibre volume fraction (Vf) ranged from 0.0 to 2.0 percent. Steel and polyolefin fibres were combined in different proportions and their impact on the above parameters was studied. The ductile response of hybrid fibre reinforced concrete beams was compared with that of control beam. The test results show that addition of 2.0 percent by volume of hybrid fibres improve the strength and ductility appreciably. Empirical expressions for predicting the strength and ductility of hybrid fibre reinforced concrete (HFRC) are proposed based on regression analysis. A close agreement has been obtained between the predicted and experimental results.

Characterization and optimization of hardened properties of self-consolidating concrete incorporating recycled steel, industrial steel, polypropylene and hybrid fibers

Abstract This paper presents an experimental/analytical investigation to examine the feasibility of hybrid fibers in self-consolidating concrete containing different fiber types (industrial steel fiber, recycled steel fibers, and Polypropylene fiber), contents (0.5%, 0.75%, 1%, 1.5% in Vol.), and combinations (as single and blended fibers). Fresh and hardened properties of the fiber reinforced self-consolidating concrete were assessed, considering total fiber volume fraction of 1.5%. The fresh state properties were assessed in terms of flow slump diameter and T500. Moreover, the hardened state properties of specimens were characterized by using the ultrasonic pulse velocity, the compressive strength, the splitting tensile strength, the flexural strength, and the impact resistance. Then, a statistical method based two-parameter Weibull and an optimization procedure were executed on the collected experimental results. The results showed an enhancement of mechanical properties and impact resistance in self-consolidating concrete by the addition of fiber, which was significantly governed by fiber type, content, and combination. Moreover, the optimization procedure revealed that the best performance in terms of maximum mechanical properties and impact resistance, as well as the minimum cost, was achieved in the mixture reinforced with 1.5% recycled steel fiber (Rst1.5) as mono-fiber and the mixture reinforced with 1% industrial steel fiber and 0.5% recycled steel fiber (St1Rst0.5) as hybrid fiber. In addition, the statistical study showed that the two-parameter Weibull could be adopted to analyze the distribution of the first crack (FC) and ultimate crack (UC) impact resistance.

FINITE ELEMENT ANALYSIS OF DEEP BEAM UNDER DIRECT AND INDIRECT LOAD

This research study the effect of exist of opening in web of deep beam loaded directly and indirectly and the behavior of reinforced concrete deep beams without with and without web reinforcement, the opening size and shear span ratio (a/d) was constant. Nonlinear analysis using the finite element method with ANSYS software release 12.0 program was used to predict the ultimate load capacity and crack propagation for reinforced concrete deep beams with openings. The adopted beam models depend on experimental test program of reinforced concrete deep beam with and without openings and the finite element analysis result showed a good agreement with small amount of deference in ultimate beam capacity with (ANSYS) analysis and it was completely efficient to simulate the behavior of reinforced concrete deep beams. The mid-span deflection at ultimate applied load and inclined cracked were highly compatible with experimental results. The model with opening in the shear span shows a reduction in the load-carrying capacity of beam and adding the vertical stirrup has improve the capacity of ultimate beam load.

Carrageenan-based superabsorbent biopolymers mitigate autogenous shrinkage in ordinary portland cement

We report the synthesis and characterization of biobased superabsorbent copolymers from κ-carrageenan and poly(acrylic acid) that mitigate autogenous shrinkage in ordinary portland cement paste. Synthesized via free radical graft polymerization, the biobased superabsorbent polymers (SAPs) were characterized with regard to their thermochemical properties and swelling behavior in both aqueous and ionic solutions. The biobased SAPs were incorporated into cement paste to investigate their ability to mitigate autogenous shrinkage cracking in high-performance concrete. Results demonstrate that the biobased SAPs absorb up to 438 and 94 [g/g] (by mass) in aqueous and ionic solutions, respectively, after 24 h. Furthermore, the biobased SAPs were successful in mitigating shrinkage in low water-to-cement ratio pastes. While the control paste exhibited negative strain and ultimate shrinkage cracking, the samples containing biobased SAP experienced net-positive expansion during cement hydration.

Experimental and Theoretical Behavior of Reinforced Concrete Two Way Slabs Strengthened by Steel Fiber Ferrocement Layers at Tension Zone

An experimental and analytical behavior of strengthened reinforced concrete two way slabs by steel fiber ferrocement layers ,this study included testing 14 simply supported two way slabs, which include 1 control slab, 13 strengthened slabs. In the strengthened slabs the effect of the ferrocement layers with; steel fiber content in the ferrocement mortar of (0.25,0.5,0.75.1.1.25%), thickness of ferrocement layers, the compressive strength for ferrocement mortar and wire mesh layers number of ferrocement was investigated. The mid span deflection at ultimate load and cracks pattern were discussed. All the reinforced concrete slab specimens were designed of the same dimensions and reinforced identically to fail in flexure. Simply supported conditions for all slabs has bean tested under central concentrated load. The experimental results show that; the ultimate loads and mid span deflection of strengthened reinforced concrete slabs were more effected by using the steel fiber on the ferrocement mortar, increasing the thickness of ferrocement and the compressive strength of ferrocement. Three-dimensional nonlinear finite element analysis has been used to conduct the analytical investigation, ANSYS (Version 16.0) computer program was used in this study. The analytical result from modeling in ANSYS program exhibited a good agreement with experimental results.

Flexural behavior of self-compacting concrete beams strengthened with steel fiber reinforcement

Steel fiber self-compacting concrete (SFSCC) is an innovative material that can flow underneath its own weight in the fresh state, thus eliminating any need for mechanical vibration and complexity of the formwork, and which employs the benefits of steel fiber addition in the hardened state. Hence, this study evaluated the performance of a self-compacting concrete (SCC) under the effect of filler addition and then investigated the effect of steel fiber (SF) addition on flexural behavior, splitting tensile strength, compressive strength, and modulus of elasticity. Fourteen reinforced concrete beams were tested under monotonic loads: two sets of six SCCs (with and without SFs) and two normal concretes (NCs). Ultimate capacity, deflection, crack pattern, and mode of failure were recorded. The present experimental and theoretical results were compared in accordance with ACI 318 codes to assess the applicability of the aforementioned methods to predict the flexural strength of SCC specimens. The results of the tests carried out on fresh concretes indicate excellent deformability without blocking. Moreover, the flexural strength in beams increases with increasing concrete compressive strength, longitudinal steel reinforcement ratio, and SF amount.

Behaviour of hybrid fibre reinforced concrete beams strengthened with GFRP laminates

This study aims to investigate the flexural behaviour of glass fibre reinforced polymer (GFRP) laminated hybrid fibre reinforced concrete (HFRC) beams. The flexural and ductility performance of GFRP laminated HFRC beams having different proportions of polyolefin and steel fibres with 1.0% of total volume fraction were investigated. The parameters of this investigation included: load and deflection at first crack, yield, and ultimate stages, ductility and crack width. A total of seven beams of 150x250 mm in cross-section were tested in the laboratory over an effective span of 2800 mm. One reinforced concrete (RC) beam without any internal or external GFRP was taken as the reference beam. Of the remaining six beams, one beam was strengthened with GFRP, one beam with 100% steel fibres was strengthened with GFRP and four beams, each with different volume proportions of polyolefin and steel fibres (20:80, 30:70, 40:60, 50:50) were strengthened with GFRP. All the above beams were tested until failure. The experimental results show that a fibre volume proportion of 40:60 (polyolefin-steel) has significantly improved the overall performance of the tested beams.

Nonlinear analysis of contemporary and historic masonry vaulted elements externally strengthened by FRP

This paper addresses numerical modeling and nonlinear analysis of unreinforced masonry walls and vaults externally strengthened using fiber reinforced polymers (FRP). The aim of the research is to provide a simple method for design of strengthening interventions for masonry arched structures while considering the nonlinear behavior. Several brick masonry walls and vaults externally strengthened by FRP which have been previously tested experimentally are modeled using finite elements. Numerical modeling and nonlinear analysis are performed using commercial software. Description of the modeling, material characterization and solution parameters are given. The obtained numerical results demonstrate that externally applied FRP strengthening increased the ultimate capacity of the walls and vaults and improved their failure mode. The numerical results are in good agreement with the experimentally obtained ultimate failure load, maximum displacement and crack pattern; which demonstrates the capability of the proposed modeling scheme to simulate efficiently the actual behavior of FRP-strengthened masonry elements. Application is made on a historic masonry dome and the numerical analysis managed to explain its structural behavior before and after strengthening. The modeling approach may thus be regarded a practical and valid tool for design of strengthening interventions for contemporary or historic unreinforced masonry elements using externally bonded FRP.

Study on high temperature collapse detection technology of reinforced concrete columns strengthened with angle steel

Reinforced concrete column strengthened with angle steel has strong high temperature resistance. Through the quantitative analysis and testing of the high temperature collapse of concrete column, the formula design of reinforced concrete column is improved to enhance the high temperature collapse performance of concrete column. Reinforced concrete columns high temperature collapse technology strengthened by angle steel based on bilinear elastic hysteretic model is proposed and equivalent linear recursive analysis method is used to calculate the restoring force model of concrete column. Experimental results show that the method can be used to calculate the ultimate crack depth and fracture toughness reliability of concrete column and detect high temperature collapse of reinforced concrete columns. It can be effectively combined with regular field nondestructive testing and long-term strain monitoring to achieve high temperature collapse of concrete column detection.

On low-velocity impact response of SIFCON slabs under drop hammer impact loading

The response of thin slabs of Slurry-Infiltrated Fibrous Concrete (SIFCON) with and without reinforcement under low velocity impacts is explored via drop-hammer impact experiments. For comparison purpose, plain cement concrete (PCC) and reinforced cement concrete (RCC) slabs were also cast and tested. To produce SIFCON slabs made with binary cementitious materials, the pre-determined concrete mixtures were designed with 15% of silica fume, 30% of blast furnace as a partial substitute of cement along with a constant 10% of hooked end steel fibres by volume fraction. The replication of a low-velocity impact on slab was achieved by dropping a steel ball (weighing 4.5 kg), with fall height of 457 mm, via the utilization of a self-fabricated drop-hammer impact test device. The parameters like first crack and ultimate failure energy absorption capacity, ultimate crack resistance, crack resistance ratio, ductility indices, and failure pattern were examined. The test results reported that the incorporation of binary blends of silica fume and slag in SIFCON matrix shows better performance in terms of strength and durability characteristics.

Short-term behaviour of reinforced and steel fibre–reinforced concrete composite slabs with steel decking under negative bending moment

An experimental study was conducted on reinforced and steel fibre–reinforced concrete composite slabs with steel decking under negative bending moment to quantify the ultimate behaviour, loading capacity and crack width under short-term loading. Eight full-scale slab specimens were cast with different types and amounts of reinforcement in the concrete (e.g. mesh, steel fibre or normal reinforcing bars) but with the same type of steel decking. Each slab was simply supported and tested in four-point bending under increasing load until failure. The deflections at mid-span and under the applied point loads were monitored together with the end interface slip. The crack widths were obtained for each slab for different levels of applied load. It was found that the end slip was quite negligible and complete interaction on the steel decking–concrete slab interface existed at service loads and ultimate limit states. Compared to the slab with 20 kg/m3 steel fibre, the application of steel fibre in excess of 60 kg/m3 increased the rotational capacity and ultimate load by 60% and 80%, respectively. Moreover, the higher dosage of steel fibres resulted in improved crack control, as for the same level of applied load, the crack width was often reduced by 75%. However, the slabs with conventional high-strength ductile reinforcements had the greatest ultimate load and rotational capacity and exhibited the best degree of crack control with finer and more distributed cracks.

3‐D mesoscale simulation of crack‐permeability coupling in the Brazilian splitting test

SummaryIn this paper, mesoscale hydromechanical simulations are performed to study (1) fracture features and (2) crack‐gas permeability coupling evolution in the context of the tensile splitting test. The mesostructure is based on a 2‐phase 3‐D representation of heterogeneous materials, such as concrete, where stiff aggregates are embedded into a mortar matrix. To take into account these heterogeneities without any mesh adaptation, a weak discontinuity is introduced into the strain field. In addition, a strong discontinuity is also added to take into account microcracking. This mechanical model is cast into the framework of the enhanced finite element method. Concerning the coupling with gas permeability, a double‐porosity method is used to simulate the flow through the cracks and the porosity. The apparent gas permeability is afterwards evaluated by a homogenization method. On the basis of finite element simulations, influence of aggregate size on ultimate crack opening, macroscopic ultimate tensile stress, total dissipated energy, and gas permeability evolution is numerically investigated. Furthermore, gas permeability evolution is also compared with experimental results from the literature. In addition, in the spirit of a sequential multiscale approach, macroscale gas permeability equations are identified from the hydromechanical results coming from the mesoscale computations. These equations lead to a relation between macroscale gas permeability evolution and crack opening. Besides, we show how the aggregate size influences the percolation threshold and that after this threshold, a cubic relation between macroscale gas permeability and crack opening is obtained.