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Vector II slab was tested on a natural scale (a slab with a dimension of 6.30 × 6.30 m) and a strip 6.30 m long and 1.20 m wide. The Vector II slab is built by precast panel 60 cm wide, 4 cm thick and 14-20 cm thick concrete overtopping on the construction site. The main purpose of the slab tests on a natural scale was to observe the “faulting” effect and temporary deflections. During the tests, the displacements in the area of the panel joints in the middle of the slab span were recorded. The maximum difference in displacement between adjacent panels of the slab model was 0.16 mm, and the vertical displacement was 1.9 mm. The strip model had no cracks that could indicate a interface cracks between the precast element and the concrete overlay. After completion of the field tests, the load was left on the slab model to verify long-term effects.

Concrete structures have been widely used for many years to resist impact loads. Steel–concrete composite structures may be considered efficient structures in the emerging modern construction field. Hence, the main objective of this research was to study the impact behavior of steel concrete composite slabs with different shear connectors and compare them with conventional slabs. Seven specimens of dimensions 500 × 500 × 50 mm were cast, which included plain cement concrete slabs, two reinforced cement concrete slabs with steel mesh and steel rebars as reinforcement, and four steel-concrete composite slabs with four different shear connectors: stud, tee, angle, and channel connectors. The composite action was achieved using a steel decking sheet welded with connectors on which the concrete layer was poured at the top. The test setup was fabricated with slots provided for specimens with simply supported end conditions and a mild steel drop weight. The specimens were impacted at the center of the span by dropping a steel mass from a free fall height of 1 m. The number of blows corresponding to the initial cracking and ultimate failure stages was recorded. The parameters that were used to compare the specimens were the impact energy absorbed, crack pattern, crack width, and increase in impact energy from the first blow to the last blow. The experimental results were very close to the analytical results obtained using ANSYS. The experimental and analytical results showed that the composite slabs with channel connectors performed better than the others, and it was proven that the composite slabs performed better under impact loading than conventional slabs.

Degradation and disintegration of concrete depend on the formation of cracks and micro cracks intensively. With increase loading, micro cracks are linked together and form cracks. To solve the problem and to provide the homogenous condition, a series of thin fibers having been spread through the volume of concrete are used in the several last decades and they are called as fibers. In the study, the steel fibers integrated in the different percentages of weight have been investigated. The performance of fibers has been studied how to increase compressive strength, tensile strength, and bending strength. To survey compressive strength, tensile strength, and bending strength in the produced concrete, three plans of mixtures including the different percentages of the steel fibers have been examined. The results show that compressive strength in the concrete reinforced with steel fibers relies mainly on the quality of mortar. The added steel fibers cause the inconsiderable changes in the compressive strength of concrete. The results demonstrate that the concrete reinforced with steel fibers increase tensile strength considerably. The more the volume of steel fibers is, the more tensile strength is. Pozzolanic materials used in the specimens reinforced in steel fibers improve tensile strength. To investigate bending strength of the specimens reinforced with steel fibers, the study has used 4-point loading system. Generally, steel fibers used in the concrete increase bending strength of the concrete. The results indicate the increased steel fibers enhance bending strength in three plans of mixtures. Among the specimen reinforced with steel fibres, the most mechanical properties are related to the plans including 1, 1.5, and 2 percentages of dramix hooked steel fibers in the study. To examine crack pattern of the matrix tensile specimen reinforced with the different percentages of fibers, parameters such as the number of cracks, width of cracks, and distance between them are investigated.

Nowadays plastic is closely linked to the way of our life. The annual consumption of plastics has been increasing gradually. The inadequate disposal of plastic has been resulted in major environmental problems due to the shortage of space for landfilling and low biodegradability. The reuse of plastic wastes as construction materials provides a remarkable future market for waste recycling. This work aims to study the possibility of Evolon ® plastic non-woven sheets in concrete mixtures. For this purpose, an experimental study was conducted to investigate some properties of the ordinary concrete wrapped by non-woven PET plastic sheets. Samples with five various configurations; reference, 1-layer, 2-sides, 3-sides, and full wrapped were considered and prepared. The compressive, flexural, and split tensile strengths and ultrasonic pulse velocity (UPV) were measured. The outcomes of the study highlight that the compressive strength was improved for the wrapped samples, particularly for the cylindrical specimens. In addition, split tensile and flexural strengths of the wrapped samples improved significantly compared to the reference ones at each strengthened configuration. Moreover, it was observed that reference samples were damaged to many parts after mechanical testing, while wrapped specimens were taken by the applied configurations and were not separated into many small fragments. Therefore, non-woven fabrics are recommended to improve certain properties of the concrete.

Cracks that occur in rigid pavements include longitudinal cracks, transverse cracks, and corner cracks. The relatively large crack width not only spoils the aesthetics of the concrete structural elements but can also lead to structural failure. This study aims to determine the crack width of a rigid pavement concrete slab located above the subgrade which is considered a beam on an elastic foundation, so that a minimum rigid pavement concrete slab thickness can be recommended. The specimen will be observed at various thicknesses to obtain the optimum thickness. The load used is a centralized monotonous load, which represents the load of the truck vehicle. The research limitation is using a test object in the form of a concrete plate measuring 2000x600 mm which is placed on the ground with CBR=6 %. The quality of reinforced concrete slabs is fc'=40 MPa and fy=440.31 MPa. The thickness of the concrete slab varies between 100 mm, 150 mm, and 200 mm. The slab placed on the ground is then given a central loading in the form of a centralized monotonic load. The loading range starts from a load of 2–180 kN with a load interval of 2 kN. The experimental results show that the rigid pavement slab has a bending failure so that the crack pattern that occurs begins with the first crack on the underside of the slab. The crack pattern in terms of slab thickness variation has a similar pattern. The initial crack width on the slab is 0.04 mm. The thicker the slab smaller the crack width at the same load. Based on the maximum allowable crack width=0.3 mm. For loads between (80–100) kN (Road Class I, II, and III), a minimum thickness of rigid pavement slabs (70–80) mm is recommended. For loads between (130–140) kN, the minimum thickness of the rigid pavement slab (105–115) mm is recommended

Crack width variation along the concrete cover depth has been studied from the past for better understanding of the cracking phenomenon in reinforced concrete (RC) structures. Previous studies have highlighted important cracking behaviors like internal cracks. The behavior of ‘slip’ between the reinforcement and concrete and the formation of a nonuniform crack face along the concrete cover depth are still not very clearly understood. An experimental program has been conducted to study the crack width variation along the cover depth in concrete prisms reinforced with a central ribbed bar and smooth bar, by varying the concrete cover depths. Both in specimens with smooth bars (SS) and specimens with ribbed bars (SR), crack width is larger on the concrete surface than at the steel bar surface. The crack width at the reinforcement is considerably larger in the SS than in the SR. In the SR, the crack width increases from the reinforcement along the cover depth bi-linearly, while, in the SS, it increases linearly. For the SR, the aforementioned behavior is due to the occurrence of internal cracks. In the SS, significant slip has been identified at the reinforcement and concrete interface, whereas negligible slip has been observed in the SR. A surface crack width calculation model has been developed, considering both the strain difference and the effect of the nonuniform crack face along the concrete cover depth. Its predictions showed good agreement with the experimental surface crack widths from the conducted study and with the results from the experiments in literature.

Composites made with inorganic matrix, namely fabric reinforced cementitious mortar (FRCM) composites are becoming widespread as strengthening materials for existing masonry structures. These composites are made of a dry grid of fibres embedded in an inorganic matrix. FRCMs can be considered a valid alternative to traditional organic composites such as fibre reinforced polymers (FRPs) because of their better compatibility with the masonry support. This work presents an experimental study for the tensile characterization of a basalt fabric reinforced cementitious mortar (BFRCM) composite. Tensile tests were carried out on coupons reinforced with one, two or three layers of grid to investigate the influence of the reinforcement on the load–strain and stress–strain response of the composite. The basalt grid and cementitious mortar matrix were also tested in order to compare the mechanical properties of the constituent materials to the response of the composite. The digital image correlation (DIC) technique was used to check in-plane and out-of-plane bending effect, to measure the crack opening and to analyse the crack pattern evolution and failure modes.

This paper aims to experimentally and numerically investigate the flexural behavior of laced reinforced concrete moderately deep beams. The study focuses on the influence of the lacing angle (30, 45, and 60°) and the ratio of the tension reinforcement (0.33, 1.13, and 2.01%). Six beams were fabricated, with a cross-sectional width of 150 mm and a depth of 240 mm, and 1530 mm in length. In five specimens, lacings were employed as shear reinforcement instead of the conventional stirrups. A reference beam was fabricated with conventional vertical stirrups. All beam specimens were subjected to the four-point bending up to failure with effective and shear spans of 1400 and 400 mm, respectively. Compared to the reference beam, laced beams experienced significant stiffness enhancements of up to 43.7%. However, the improvement in the ultimate load did not exceed 10%. The recorded strains in lacings clearly signify the efficiency of lacings in resisting the longitudinal and diagonal tension stresses induced along the flexural and shear spans. Moreover, a nonlinear finite element analysis was performed using ABAQUS, based on which parametric studies were conducted. Parametric studies showed that the ductility was significantly increased with the increase of lacings bar diameter, while the ultimate load capacity was only slightly enhanced.

International audience; In the last few decades, premature deterioration of reinforced concrete (RC) structures has become a serious problem because of severe environmental actions, overloading, design faults, and materials deficiencies. Therefore, repair and strengthening of RC elements in existing structures are very important to extend their service life. There are numerous methods for retrofitting and strengthening of RC structural components such as; steel plate bonding, external pre-stressing, section enlargement, fiber-reinforced polymer (FRP) wrapping, and so on. Although these modifications can successfully improve the load-bearing capacity of the beams, they are still prone to corrosion damage resulting in failure of the strengthened elements. Therefore, many researchers used cementitious materials due to its low-cost, corrosion resistance, and resulted in the improvement of the tensile and fatigue behaviors. Different types of cementitious materials such as; fiber-reinforced concrete (FRC), high performance concrete (HPC), high strength concrete (HSC), ultra-high performance concrete (UHPC), steel fiber-reinforced high strength lightweight self-compacting concrete (SHLSCC), fabrics reinforced cementitious material (FRCM) and so on have been used to strengthen structural elements. This paper summarized previously published research papers concerning the structural behaviors of RC beams strengthened by different cementitious materials. Shear behaviors, flexural characteristics, torsional properties, deflection, cracking propagation, and twisting angle of the strengthened beams are explained in the present paper. Finally, proper methods are proposed for strengthening RC beams under various loading conditions.

Geogrid is as one of the component materials classified under the geosynthetics used for soil stabilizing and reinforcement. Due to its higher strength-to-weight ratio, ease of handling, and comparatively low costs, geogrid has been gradually explored for possible use in concrete reinforcement. This research aims to assess the feasibility of using geogrids as a possible reinforcement for high-strength self-compacted concrete slabs to provide additional tensile strength and ductility. To enhance the bond between geogrid layers and the cement matrix, two types of geogrid surface modification methods are introduced. Gluing sand to the geogrid surface as a physical surface modification method and immersion in polycarboxylate as a chemical surface modification method are investigated. The effect of geogrid type (uniaxial, biaxial and triaxial) and the number of layers is also introduced. The test results show that the chemical treatment increased the ultimate flexural loading capacity of the tested slab by about 8.5% for one geogrid layer and 13% for two geogrid layers compared to untreated specimens. This work was extended to add two geogrid layers in addition to the slab&rsquo, s steel reinforcement. The results show that adding geogrid decreased the ultimate flexural loading capacity but significantly increased the slab ductility.

Aim of the paper is the evaluation of the bond transfer mechanism and the following cracking behavior for concrete elements reinforced with Glass Fiber Reinforced Polymer (GFRP) bars. At the scope, an experimental survey has been developed on nine 3000 mm long tie-specimens with square cross-section of 150 mm × 150 mm, reinforced with a 4000 mm long GFRP reinforcing bar embedded in the centerline. Besides the reference element, reinforced with conventional steel rebar with diameter equal to 16 mm, nine GFRP bars with the same equivalent diameter and different surface treatments (smooth, sand-coated and helical fiber wrapped surfaces) were taken into account. The specimens were subjected to tensile force and the obtained results have shown how the different surface coating may affect the bond behavior at the concrete – GFRP interface, and the following crack pattern.

Contraction of soil during desiccation gives rise to polygon-patterned cracking. This phenomenon was investigated by continuous full-strain measurements on soil sample surfaces using digital image correlation techniques. The results show that desiccation cracking was of the mode I variety and can be reliably predicted through strain field analyses: the observed cracking was restricted mostly to high stretching domains. The observed high stretching stems from either external restraint or internal flaws of the shrinking soil. The cracks redistribute the stress in their vicinity and lead neighboring cracks to intersect them mostly orthogonally. As desiccation proceeds, the surface strain field ceases to provide useful information for predicting crack locations. Further analysis indicates that although drying occurs from exposed material surfaces, late-generation cracks actually initiate in the subsurface and express themselves subsequently at the surface. These observations offer insights into the intrinsic mechanisms of drying-induced crack growth in soils.

External sulfate attack is a progressive degradation process that may cause expansion, cracking, loss of binder cohesion and increased permeability in cementitious materials. Crystallization pressure theory has often been referred to as the most likely mechanism. However, thus far the stress causing the expansion has not been quantified. In this study, small cement paste pipes with a wall thickness of 2.5 mm were prepared and immersed in sodium sulfate solutions with SO42− ion concentrations of 1.5 g/L and 30 g/L. Three types of longitudinal restraints were applied on the specimens before exposure, which were created by a spring, a thin or a thicker stainless steel bar that was centered in the hollow specimens in order to facilitate the non-, low- or high-restraint condition. The free expansion, restrained expansion and generated stress were quantified. The pore size distribution, sulfur distribution and crack pattern were periodically analyzed during the sulfate immersion tests up to 420 days. The generated stresses were found to be as high as 13.1 MPa in high sulfate solution and 8.3 MPa in low sulfate solution under high-restraint condition after 420-day immersion. For the unrestrained specimens immersed in low sulfate solution, an almost uniform sulfur distribution along the diffusion direction was found at 189-day immersion. However, for the unrestrained specimens immersed in high sulfate solution, a layer or several layers of mainly gypsum were formed subparallel to the exposed surface from 133-day immersion.

Three partially pre-stressed interior beam-column sub-assemblages (SI) and two partially pre-stressed exterior beam-column sub-assemblages (SE) made of reactive powder concrete as test specimens were numerically modeled using a finite element program. The objective of this study was to investigate the behavior of the SI and SE numerical models. The numerical model inputs were: material data, details of test specimen dimensions, and test specimen reinforcements. The numerical models were subjected to the same loads as those applied experimentally. The numerical modeling results were hysteretic and backbone curves and stress distribution contours. The numerical model outputs showed good similarity with the experimental results. The stress distribution contours of the numerical models correlated with the crack patterns in the joint zone of the test specimens. The behavior of the SI numerical models differed from the SE numerical models due to various stresses on the beam plastic joints and the joint zones.

This study presents the performance of a combined finite-discrete element method for prediction of the structural response of reinforced concrete beams under impact loading. A combination of finite and discrete element methods enables the modelling of the concrete and the reinforcement before the concrete cracking, as well as a discontinuous nature of the concrete caused by fracture and fragmentation under high impact loading. Discretisation of the concrete with triangular finite elements is coupled with one-dimensional reinforcing bars embedded inside the concrete finite elements. The cracking in the concrete activates the joint elements used to simulate the non-linear behaviour of both concrete and reinforcement. Numerical analysis based on experimental test data has been carried out to simulate the main features of the reinforced concrete beams impacted by free-falling drop-weights. A high level of accuracy was demonstrated in various comparisons between the experimental tests and the analysis results, including peak displacement, crack pattern, damage level and failure modes of reinforced concrete beams.

This study aims to investigate the effects of corrosion distribution, specifically non-uniform and localized corrosion, on cracks propagation in concrete. Different corrosion distributions along rebar length were simulated using a sodium chloride pond with various sizes set on the concrete cover, and a direct current was applied to accelerate the corrosion process. The test results showed that the crack pattern is more influenced by corrosion distribution than by concrete cover thickness. The cracking mechanism was analyzed using the Rigid Body Spring Method with a corrosion-expansion model, which utilized a set of experimental data relating to corrosion distribution. The crack patterns are simulated reasonably well. The analysis also indicated that the internal crack pattern is closely related to concrete surface deformation.

This paper presents the experimental study of concrete beams in bending, externally strengthened with Textile Reinforced Cementitious materials (TRC) with varying contact area with the concrete. In order to study the pure influence of the TRC on the concrete substrate, only non-internally-reinforced concrete beams are considered. The crack pattern evolution is monitored with Digital Image Correlation, and the influence of the contact width between the concrete substrate and the external reinforcement is investigated. The results show that the TRC reinforcement has an important crack bridging capacity, and consequently that its application over the full beam width is beneficial for the loadbearing capacity and the limitation of the crack widths of the concrete beam.

Fibre reinforced concrete (FRC) has been widely used in industrial pavements and non-structural elements such as pipes, culverts, tunnels, and precast elements. The strengthening effect of fibres in the concrete matrix is achieved primarily due to the bridging effect of fibres at the crack interfaces. The workability of the concrete was reduced on addition of high percentages of steel fibres. The optimum percentage of addition of steel fibres varies with its aspect ratio. For this study, 1% addition of steel has resulted to be the optimum percentage for both Hooked and Crimped Steel Fibres and was added to the beam specimens. The fibres restrain efficiently the cracks and take up residual stresses beyond the cracking. In this sense, diagonal cracks are effectively stitched up by fibres crossing it. The failure of beams within the shear failure range changed from shear to flexure in the presence of sufficient steel fibre quantity. The shear strength is increased with the addition of steel fibres and had exceeded the enhancement obtained with the transverse reinforcement. However, such increase is not directly in proportion with the quantity of fibres used. Considering all the clarification made in the present experimental investigation, it is concluded that 1% of crimped steel fibres with an aspect ratio of 50 is the best type of steel fibres for replacement of transverse stirrups in high strength concrete beams when compared to the steel fibres with hooked ends., {"references":["Julia Sauer, Jan Lingemann, Dipl.-Ing., Oliver Fischer, and Konrad Zilch, \"Shear Capacity of Steel Fiber Reinforced Concrete Beams without Stirrups\", 3rd fib International Congress – 2010.","Mohamed Zakaria, Tamon Ueda, Zhimin Wu and Liang Meng, Experimental Investigation on Shear Crack Behaviour in Reinforced Concrete beams with Shear Reinforcement, Journal of Advanced Concrete Technology, Vol. 7, No.1 February 2009, PP. 79-96.","Thomas, J., and Ramaswamy, A., Mechanical Properties of Steel Fiber reinforced Concrete., ASCE Journal of Materials in Civil Engineering,19(5) 2007, PP. 385-392.","Antonie E .Naaman, Engineered Steel Fibers with Optimal Properties for Reinforcement of Cement Composites, Journal of Advanced Concrete Technology, vol.1, No.3, PP 241-252","D. H. Lim, B. H. Oh, Experimental and theoretical investigation on the shear of steel fibre reinforced concrete beams, Eng. Struct. 21 (1999) 37–44.","M. Hamrat, B. Boulekbache, M. Chemrouk, S. Amziane, Shear behaviour of RC beams without stirrups made of normal strength and high strength concretes, Adv. Struct. Eng. 13 (1) (2010) 29–41.","M. K. Johnson, J. A. Ramirez, Minimum shear reinforcement in beams with higher strength concrete, ACI Struct. J. 86 (4) (1989) 376–382.","P. Casanova, P. Rossi, Analysis and design of steel fibre reinforced concrete beams, ACI Struct. J. 94 (5) (1997) 595–602.","R. Narayanan, I. Y. S. Darwish, Use of steel fibres as shear reinforcement, ACI Struct. J. 84 (3) (1987) 216–227.\n[10]\tR. S. Pendyala, P. Mendis, Experimental study on shear strength of high strength concrete beams, ACI Struct. J. 97 (4) (2000) 564–571.\n[11]\tS. Furlan Jr., J.B. de Hanai, Shear behaviour of fibre reinforced concrete beams, Cement Concr. Compos. 19 (1997) 359–366.\n[12]\tS. Shin, S. H. Ghosh, J. Moreno, Flexural ductility of ultra-high strength concrete members, ACI Struct. J. 8 (4) (1989) 394–400."]}

Strain controlled fatigue tests have been performed on two types of heavily filled epoxy corrosion protection coating sprayed onto a 6 mm steel substrate. Fatigue cycling was performed at R ratios of 0 and −1. The two coatings differed in their formulation and the major differences in mechanical performance were in their static strain to first crack development and their fracture toughness, where Coating A was significantly tougher than coating B. During strain cycling coating crack development was monitored using optical observations and surface replicas. It was found that in both coatings surface crack development began soon after the onset of cycling and proceeded via growth of surface channelling cracks and multiple initiation of new cracks. Detailed studies were made of crack development morphology and its relation to coating type and to the applied strain range. A definition of coating life as the first appearance of a 2 mm surface crack length was used. This represented the end of the life where the coating protected the substrate. Before this life was achieved, crack growth rates of single cracks were invariant with crack length. After this point further crack growth, multiple cracking and crack to crack interactions took place. Cracking in this region could be characterised with a new total crack length parameter shown to be strongly dependent on applied strain range.

Digital Image Correlation (DIC) is a full-field contactless optical method for measuring displacements in experimental testing, based on the correlation of the digital images taken during test execution. It is used in several fields of experimental solid mechanics, but its potential application to the characterization of composite reinforcements has not been fully investigated yet. In this paper DIC is used in tensile and bond tests on composite reinforcements comprising different textiles and matrices. Results obtained by two DIC software programs are validated by comparison with displacement and strain transducers. DIC provides additional information on damage pattern (crack location and width) and composite-to-substrate load transfer mechanism (effective bond length and local stress concentrations). It also offers the advantageous possibility of selecting several measurement points after the test, overcoming some drawbacks of traditional transducers. On the other hand, since only on the outer surface of the specimen is monitored, no information is directly available on the textile embedded in the matrix. The combination of DIC and traditional sensors in laboratory testing allows improving the understanding of the mechanical behaviour of composite reinforcements and the identification of their fundamental properties.

International audience; Surface cracking or heat-checking is investigated at a microscopic scale on a hot work tool steel (X38CrMoV5) tested under thermal fatigue. Thermal fatigue tests are periodically interrupted to observe the surface of the specimens by scanning electron microscopy (SEM). A non destructive and semiautomatic method is developed to assess and evaluate the two-dimensional crack pattern initiated on the oxide scale layer formed on the specimen surface. The crack pattern is characterized by image analysis in terms of density, morphological and topological features. This technique allows to determine the number of cycles to initiate the microscopic heat-checking and to follow its evolution.

The paper is concerned with numerical modeling of corrosion of steel reinforcement in the reinforced concrete. The cracking response of the reinforced concrete beams due to the corrosion effect of the steel reinforcement and due to the load effects was analyzed. The effect of corrosion was simulated by the nonlinear numerical analysis with the FEM program using the 3D model.

Primary load-bearing glass constructions are often subjected to relatively important in-plane loads, transferred through so-called point-fixed connections. The according in-plane load introduction, structural resistance and failure mechanisms have been studied abundantly for axial tensile loading cases, but are relatively unknown for axial compression, in particular when buckling of the compressed component cannot occur. Consequently, stress distributions, resistance and failure mechanisms of small glass specimens subjected to locally introduced axial compression are investigated and presented in this contribution using a coupled experimental and numerical approach. The stress distributions and observed fracture patterns demonstrated that the major failure mechanism was splitting tension: the glass fractured due to high tensile stresses following the compressive stresses. However, the maximal principal tensile stresses at the crack origin were significantly lower compared to the axial tensile loading case. In addition, and in contradiction to the tensile loading case, significant maximal principal compressive stresses were found at the crack origin, leading to the conclusion that the axially compressed glass panels failed due to a complex stress state and not simply to tensile stresses, as is generally assumed in glass design. © 2009 Elsevier Ltd. All rights reserved.

Seven full-scale steel fiber reinforced self-consolidating concrete (SFRSCC) beams were tested to study the effects of macro steel fibers on the flexural behavior of reinforced self-consolidating concrete beams. The major test variables are fiber contents and longitudinal reinforcement ratios. The ultimate load, midspan deflections, steel reinforcement strains, crack width and crack spacing were investigated. The enhanced ultimate flexural capacity and reduced midspan deflection due to the addition of steel fibers were observed. With the increasing of fiber contents, the strain in longitudinal reinforcement, crack width and crack spacing decreased significantly. The possibility of using steel fibers for partial replacement of the conventional longitudinal reinforcement is estimated, which is meaningful for extending the structural application of SFRSCC. A method incorporating fiber contribution to the post-cracking tensile strength of concrete in the flexural analysis of SFRSCC beam is also suggested. Comparisons are made between the suggested model and the fib Model Code 2010 model with experimental data. The results showed that the suggested model can estimate ultimate flexural capacity accurately., National Natural Science Foundation of China: Grants: 51078058 and 51121005.

Underground Coal Gasification (UCG) is considered to be a clean coal technology primarily intended to utilize deep underground (>300 m) coal deposits. In this process, a mixture of reactant gases like air/oxygen and steam are injected directly to an ignited portion of underground coal seam. UCG involves complex interactions of different processes like drying, pyrolysis, chemical reactions and spalling. Spalling is detachment of small coal particles from the coal seam due to interconnection of cracks developed in it. It plays an important role by offering higher surface area to give improved performance. The mechanism of spalling and its characterization are not well understood. Furthermore, there are no well established experimental techniques to measure the spalling rates. This paper studies spalling behavior of a lignite coal, which is characterized by high moisture and volatile matter, and suggests a possible underlying mechanism. The rate of spalling was measured using an experimental setup under the UCG-like conditions. In this setup, a reacting coal block was attached to a load cell and suspended in a UCG-like environment. When the experiments were repeated under similar conditions with different blocks of same coal, it was found that there were variations in the rates of spalling. This might be due to the heterogeneity in coal blocks in the form of originally present fissures or weak regions. A UCG process model was used to explain these experimental results and also to investigate the effect of spalling rate on product gas calorific value. We believe that spalling happens due to formation and extension of cracks. Hence a microscopic crack pattern on a heated coal monolith was examined in different stages of heating to understand the mechanism of spalling. It is concluded that cracks are first formed during the initial stage of drying due to the capillary stresses developed due to removal of moisture from the pores and were further extended due to shrinkage of coal during pyrolysis. The detachment of coal particles happens due to horizontal linking of vertical cracks, which might result out of either horizontal cracks, if any, or available fissures and weak regions or relatively weak interlayer bonding at the bedding planes. (C) 2015 Elsevier Ltd. All rights reserved.

Micro cracks occurring in concrete around tensile rebar is well known latent damage phenomenon. These micro cracks develop, and can be detected after reaching the surface of the concrete. Detection of these cracks before they are fully formed is preferable, but observing the whole crack structure is difficult. Another problem is repairing micro cracks under the concrete surface. The autogenous ability of bond cracks along rebar was evaluated using the air permeability test. Air permeability coefficients were measured before and after tensile loading, and experimental air permeability coefficients became larger near cracks along rebar as a result of tensile loading. Recuring for 28 days after tensile loading made the air permeability coefficients smaller, but this restriction only occurred during water recuring. Observation of crack patterns helped the understanding of change in the air permeability coefficients. Several small cracks along rebar were observed after tensile loading, and most cracks along rebar were not found after water recuring. On the other hand, the crack pattern did not change after air recuring. These results indicate that bond cracks along rebar can be closed by autogenous healing, and cause the air permeability coefficients.

Refined non-linear static or dynamic analyses of reinforced concrete structures require the knowledge of the actual force-displacement or bending moment-rotation curves of each structural member, which depend on the crack widths and on the crack pattern, and after all on the slip between concrete and reinforcing steel. For this reason the definition of improved local models taking into account all these local aspects is a fundamental prerequisite for advanced assessment of r.c. structures. A numerical procedure which allows to predict the relative displacement between steel reinforcement and the surrounding concrete in a reinforced concrete element, once assigned the stress in the naked steel bar and the bond-slip law is discussed. The method provides as final outcomes the sequence of crack openings and the individual crack widths, regardless of the particular bond-slip correlation adopted. The proposed procedure is implemented referring to two relevant experimental case studies, demonstrating that it is able to predict satisfactorily actual strain fields and slips along the investigated reinforced concrete elements.

This paper describes the results of experimental testing of glass fiber reinforced plastic (GFRP) composite beam strengthened reinforced concrete (RC) slabs with two symmetrical openings. Specimens, one-half scale, have been designed and fabricated to reflect the most common RC bathroom slab used in school buildings. The specimen had dimensions of 2000 mm (width) × 150 mm (thickness) × 3000 mm (length) were used with the two openings of 300 mm × 400 mm. The aim of this study is to investigate the most effective strengthening method using GFRP composite beams in slabs with openings for enhancing the load-carrying capacity and stiffness. Test results showed that the strengthened slabs seems to increase the load-carrying capacity by 29%, 21% and 12% over that of the control specimen for diagonal, parallel and surround strengthening respectively. Furthermore, test results showed that the diagonal-strengthened system is one of the most effective methods for strengthening an RC slab with openings in terms of load-carrying capacity, stiffness and crack patterns.

International audience; Laboratory tests were conducted to investigate the effect of wetting-drying (W-D) cycles on the initiation and evolution of cracks in clay layer. Four identical slurry specimens were prepared and subjected to five subsequent W-D cycles. The water evaporation, surface cracks evolution and structure evolution during the W-D cycles were monitored. The effect of W-D cycles on the geometric characteristics of crack patterns was analyzed by image processing. The results show that the desiccation and cracking behaviour was significantly affected by the applied W-D cycles: the measured cracking water content c, surface crack ratio Rsc and final thickness hf of the specimen increased significantly in the first three W-D cycles and then tended to reach equilibrium; the formed crack patterns after the second W-D cycle were more irregular than that after the first W-D cycle; the increase of surface cracks was accompanied by the decrease of pore volume shrinkage during drying. In addition, it was found that the applied W-D cycles resulted in significant rearrangement of specimen structure: the initially homogeneous and non-aggregated structure was converted to a clear aggregated-structure with obvious inter-aggregate pores after the second W-D cycle; the specimen volume generally increased with increasing cycles due to the aggregation and increased porosity. The image analysis results show that the geometric characteristics of crack pattern were significantly influenced by the W-D cycles, but this influence was reduced after the third cycle. This is consistent with the observations over the experiment, and indicates that the image processing can be used for quantitatively analyzing the W-D cycle dependence of clay desiccation cracking behaviour.

An experimental study was conducted to investigate the effect of web opening dimension on the behavior of reinforced concrete hybrid deep T-beam subjected to pure torsion. Four reinforced concrete hybrid deep T-beams were tested under pure torsion, where the three beams with different dimension of circular web opening and the other beam without opening as a reference beam. The testing program and experimental results are presented. The results show that dimension of circular web opening with diameter more than 100 mm significantly reduces the cracking and ultimate torque. It is also shown that the angle of crack inclination with respect to the longitudinal axis of the beam increases with the increase of web opening dimension. Abstrak . Suatu studi eksperimental telah dilakukan untuk meneliti pengaruh dimensi bukaan pada perilaku balok tinggi-T hybrid beton bertulang yang dikenai torsi murni. Empat balok diuji dibawah beban torsi murni, dimana tiga balok mempunyai dimensi bukaan yang berbeda dan satu balok tanpa bukaan sebagai tolok ukur. Program pengujian dan hasil-hasilnya disajikan dalam makalah ini. Hasil pengujian memperlihatkan bahwa dimensi bukaan dengan diameter lebih dari 100 mm secara signifikan mengurangi kekuatan torsi pada saat retak dan saat maksimum. Hasil eksperimental juga menunjukkan bahwa sudut kemiringan retak terhadap sumbu memanjang balok meningkat dengan meningkatnya dimensi bukaan.

Analytical study on cracking behavior of concrete due to rebar corrosion in the cases of multi-rebar specimens with various rebar spacings, of specimens with locally corroded rebar and specimens with pitting corrosion rebar was carried out. Three-dimensional Rigid-Body-Spring-Method (RBSM) with three phase material corrosion expansion model was applied to simulate crack initiation, internal cracking patterns and crack width propagation. It was confirmed that rebar spacing, ratio of local corrosion length and rebar length and pitting corrosion pattern played important roles in the cracking behavior.

Previous studies concluded that inclusions highly influence the initial cracking and propagation of the surrounding mortar. This initial cracking and propagation further affects the specimen's compression strength. It was also shown that the ratio of the inclusion area with respect to the mortar and the inclusion configuration determine the stress levels where cracking starts. The stress concentrations were especially pronounced for the inclusions with sharp angles in the line of loading. This paper evaluates the influence of the inclusion-to-mortar area ratio and the inclusion angle to the micro-crack behaviour and compression strength of a single-inclusion mortar specimen. Visual observations to the specimen's behaviours under increasing load were accessed, and the STRAND7 software was utilized to study the stress distributions and concentrations of the mortar area adjacent to the interface between the aggregate and mortar.

In this paper, we present a finite element approach to fracture modeling for brittle or quasi-brittle materials and its application to thermal shock crack simulations. The proposed fracture model is constructed on the basis of the conventional maximal principal stress criterion for uniform tensile loads and the Griffith-Irwin criterion for crack propagation prediction. Consequently, the proposed fracture criterion can be used to predict both the crack initiation and the crack growth. By using the proposed model, we carried out detailed numerical simulations on cracking process of ceramic materials subjected to thermal shock loading. The random aspect of strength and toughness of the material was considered by generating stochastically their spatial distribution. The comparison with the experimental results shows that the periodic and hierarchical structure of the crack pattern is faithfully reproduced by the numerical simulations.