Early age fracture mechanics and cracking of concrete

Crack propagation in concrete slab observed at the. Timedependent material properties were measured and the effect of restraint was tested in both ring and slab specimens. Abstractcracking in singlespan concrete bridge decks was investigated. Factors influencing durability and earlyage cracking in.

T1 influence of ultrafine fly ash on the early age response and the shrinkage cracking potential of conrete. Oct 16, 2008 new slabsonground crack when tensile stresses from restrained shrinkage exceed the concrete s strength. Due to the low hydration rate of highvolume fly ash hvfa concrete at early age. Modern high performance concretes have low water cement ratios and do often includesilica fume. The researchers used fracture mechanics to show that the needed depth of saw cut depends on the fracture strength of the concrete and that saw cut timing is much more important than saw cut depth in controlling random cracking.

Yet design is not based on fracture mechanics, even though the basic fracture mechanics theory has been available since the middle of this. The most well suited method for determination of early age fracture properties of concrete is the wedge splitting test. Early age fracture mechanics and cracking of concrete experiments and modelling ostergaard, lennart publication date. Our procedure involves the development of a thermomechanical numerical model based on the finite element method that accounts for the change in the mechanical properties of. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design. An assessment of the cracking as it relates to in situ concrete strength was performed. Microcracking of concrete behavior under multiaxial loading. Experimentally, threepoint bending tests are performed on concrete notched beams at very early age before 24 h to obtain the load crack mouth opening displacement cmod curves.

Early age sawcutting, as one form of crack induction, has been applied to concrete pavement surfaces at specific contraction joint locations. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the materials resistance to fracture in modern materials science, fracture mechanics is an important tool used to improve the. However, the fundamental mechanisms affecting the early age. Shrinkage cracking of restrained concrete slabs journal. Practical use of highstrength concrete in norway has shown that it is susceptible to cracking at early ages, and that it normally is subjected to high curing temperatures due to high cement contents. Assessment of the risk of early age thermal cracking in a. Most of the experiments and theories in fracture mechanics are formulated taking ductile materials as object of interest. The susceptibility to cracking is particularly high at the early stages of concrete, when there is plenty of water available and the material has not gained sufficient strength to resist the effect of the restraint. Prevention of thermal cracking in concrete at early ages. The longterm performance of concrete structures is affected to a large extent by the properties and behaviour of concrete at early age. This is believed principally to be the result of diffi.

Sizeindependent fracture energy of concrete at very early. A mesoscopic simulation for the earlyage shrinkage cracking. The uniaxial tension test is not suited for early age concrete, but it serves as an essential tool for comparison. Phase field simulation of earlyage fracture in cement. In this paper, the early age tensile basic creep behaviors of hsc containing fly ash fa and blast furnace slag bs were investigated by experiments, and the influences of loading age and stress level stressstrength ratio of. Applications of fracture mechanics to concrete, rock and other quasibrittle materials shah, surendra p. The possible influences on and causes of thermal cracking of concrete are discussed and cases of practical measures for avoiding cracking are detailed. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete. Early cracking of concrete pavement causes and repairs. Fracture results from a number of sources applied loading such as in the flexing of a beam and that due to punching on a slab, material shrinkage during curing of the concrete, and stress concentration related to structural geometry as in shear keys such as those in precast concrete bridge segments and from the reinforcing bar. The presence of any restraint, when concrete undergoes volume changes, results in cracking of the concrete. Joints are placed in portland cement concrete pcc pavements principal ly to prevent the development of uncontrolled, random cracking brought about by environmental forces temperature and moisture and concrete.

Again the influence of specimen sizegeometry was apparent with smaller specimens cracking at an earlier age. A number of examples for various early age cracking problems of concrete. A major problem in the concrete floor technology is early age cracking due to the socalled plastic or capillary shrinkage of the young concrete. This paper presents findings from a study directed at identifying key properties of ingredient materials that are influential on the early age cracking behavior of concrete, with an emphasis on the effects of aggregate size, aggregate morphologies, and watercement ratio wc. The research described in this paper is based on the theory of linear elastic fracture mechanics lfem using the standard threepoint notched bending beam for the doublek model.

This includes the methods to monitor setting and hardening, as well as the development of strength and engineering properties. Recently, the early age ultimate drying shrinkage of cementbased mortars was investigated through the use of the equivalent systems. The susceptibility of structural concrete to earlyage cracking depends on. The fiber contents applied ranged from zero to 3 kgm3 it could clearly be shown that this type of fiber reinforcement significantly restricts early age cracking. Finite tensile strength size is much larger than steel. When a subbase contracts from a reduction in temperature, it may induce reflective cracks in the overlying concrete at an early age. When we describe the cracking mechanisms, it is important to differentiate between the mode of crack initiation and how this occurs at the microscopic level, and the subsequent paths of propagation and the eventual macroscopic crack pattern at the engineering level. Determination of the stress fields and crack widths based on. Specifically, this investigation departs from the following points of inquiry. Feb 14, 2019 considering the importance of the crack width in the durability of concrete members, assessing the risk of early age thermal cracking is crucial.

Identification of earlyage cracking in concrete bridge decks. This paper presents a general procedure based on fracture mechanics models in order to analyze the level of cracking and structural safety in reinforced concrete elements at early ages, depending. The purpose of this study is to experimentally investigate, at early ages, the fracture characteristics of concrete such as critical crack tip opening displacement, critical stress intensity factor, fracture energy, and bilinear softening curve based on the concepts of the effectiveelastic crack model and the cohesive crack model. Restrained shrinkage experiments were developed and shrinkage cracking was shown to be sizegeometry dependent, even though shrinkage strains and residual stress levels were comparable. Fracture characteristics of concrete at early ages. Experimental chemomechanics of earlyage fracture properties. A practical equation for elastic modulus of concrete. Baiant, elsevier applied science, london, 1140 reprinting of s25. Crack propagation in concrete at very early ages uq espace.

Prevention of thermal cracking in concrete at early ages r. When the crack opens, the stress is not assumed to fall to zero at once. In this paper, simple yet sufficiently rigorous theoretical analyses of crack propagation in early age concrete slabs, based on combined geotechnical engineering and fracture mechanics models, are presented. This webinar focuses on the assessment of the risk. Earlyage cracking analysis of a hvfa concrete structure based. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete. Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. Factors influencing durability and earlyage cracking in high. The purpose of this study is to experimentally investigate, at early ages, the fracture characteristics of concrete such as critical crack tip opening displacement, critical stress intensity factor, fracture energy, and bilinear softening curve based on the concepts of the effectiveelastic crack model and the cohesive crack. The crack is assumed to propagate when the stress reaches the tensile strength. When implemented in finite element method, the node is separated into two nodes. Lattice modeling of earlyage behavior of structural concrete ncbi. Fracture mechanics analysis for saw cutting requirements of concrete pavements. Department of civil engineering, technical university.

The age of cracking was measured, as was the development of a moisture gradient. Sawcut depth considerations for jointed concrete pavement. Fracture mechanics analysis for saw cutting requirements of. Early age cracking in a heterogeneous concrete structure at the mesoscopic scale we now consider the microstructural effects on the early age behavior of the concrete materials. Effects of specimen size on assessment of shrinkage cracking of. A mechanics based approach to the determination of sawcut depth and spacing requirements by fracture mechanics analysis is presented. Sep 01, 2015 read experimental chemo mechanics of early age fracture properties of cement paste, cement and concrete research on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. The bond strength between the cement paste and dirty, dusty or extremely hard coarse aggregate also may be low at an early age, which could also contribute to cracking around coarse particles. Crack propagation in concrete at very early ages core. In ac companying tests, early age shrinkage strains and fracture mechanics properties were determined. This clearly demonstrates that, despite the successful.

Combined with the extended finite element method xfem, another subroutine for early age cracking analysis in the mechanical field was then developed. Microstructural mechanisms of early age cracking behavior of. Early age fracture properties of microstructurallydesigned. Finiteelement modeling of deformation and cracking in early. He is actively involved in research on cement and concrete materials specifically focused on early age property development, cracking, transport in concrete, and concrete durability. International journal of rock mechanics and mining sciences 45 6, 831847, 2008. Pdf earlyage cracking analysis of a hvfa concrete structure.

Earlyage cracking analysis of a hvfa concrete structure. Nonlinear fracture mechanics and plasticity of the split. Earlyage fracture mechanics and cracking of concrete. The influence of early age crack on concrete cover was studied in this paper. Cracking at early age of a massive reinforced concrete structure. This is recognized as a serious limitation for engineers to design materials and structures against early age concrete cracking, and provides enough motivation for this experimental chemo mechanics investigation of early age fracture properties of cement paste. But if we compare the salient features in lefm with results derived from the testing of concrete. Also early age high strength cements are often applied and. This improved understanding would form a solid basis for more effective control of early age cracking in concrete. Other conferences cover the subject of fracture mechanics, but rarely focused on its application to concrete and concrete structures. In this work, improvement of crack resistance against thermal stress and shrinkage of the mass concrete at an early age were studied using a hybrid fiber reinforced concrete frc. The mechanical part uses b3b4 model for concrete creep and shrinkage with isotropic damage model for cracking, able to predict a crack width.

This paper provides an explanation for this geometry dependence through the use of fracture mechanics. Cracks in concrete increase the permeability of concrete, the section where cracking occurs should be treated as getting thinner. A finite elementbased methodology for the thermomechanical. Fracture energy of concrete at early ages springerlink. A novel method for tensile testing of very earlyage concrete. Fracture toughness and microstructure of concrete at early ages zongjin li 1, xianyu jin 2 and chen lin 2 1 dept. Thermomechanical simulations of earlyage concrete cracking with.

A novel method for tensile testing of very early age concrete duy nguyen. Concrete cracking age in rings is determined by comparing the g and the. The formation and propagation mechanism of the early age cover crack, and cover crack depth were two main topics, which were discussed mainly based on the dual boundary element method. Microstructural mechanisms of early age cracking behavior. By combining this model with continuum mechanics, damage mechanics, and fracture mechanics, a relatively complete system for concrete mesoscopic mechanics analysis was established to simulate the process of early age shrinkage cracking in hpc. Linear elastic fracture mechanics yields reliable results in the field of ductile materials like steel. This paper reports the experimental results involving the application of the size effect law to early age concrete for determining the material fracture parameters k sub if and c sub f. It is examined whether the degree of hydration can be used as the parameter for the description of the softening behaviour of early age concrete submitted to tensile forces. A mechanicsbased approach to the determination of sawcut depth and spacing requirements by fracture mechanics analysis is presented. Early age fracture behavior of hybrid fiberreinforced concrete controlling and mitigating cracks in concrete is one of the main problems in construction engineering. Settlement cracks settlement of the subgrade and subbase can cause the cracking of the concrete pavement. Influence of ultrafine fly ash on the early age response and. Influence of mineral admixture on earlyage concrete cracking. In this model, the value of initial fracture toughness and unstable fracture toughness are taken as the two key parameters to analyze the fracture process of concrete.

The split cylinder test is subjected to an analysis combining nonlinear fracture mechanics and plasticity. Many conferences include discussions of damage, cracking and fracture of concrete, but mostly outside the context of fracture mechanics. Fracture mechanics of concrete and concrete structures. They found that the early saw cuts, while shallower, promote joint activation because the tensile stress development. This type of early age cracking occurs during the first few days of the slabs life and is. This powerful technique can therefore be used to investigate several hydrationdependent properties such as drying shrinkage, creeprelaxation, early age cracking, and transport properties at early age.

Shrinkage effect on stress intensity factors of concrete pavements at early age. A study analyzed the effect of several concrete mixture proportions and constituents on the early age fracture properties and their effect on saw cut timing and depth for concrete pavements with several slab geometries. The last section of the chapter is dedicated to understanding the causes and significance of nonstructural cracks, which are an offshoot of the early age behaviour of concrete. Early age fracture mechanics and cracking of concrete dtu orbit. This paper presents findings from a study directed at identifying key properties of ingredient materials that are influential on the early age cracking behavior of concrete, with an emphasis on the. Prediction of earlyage shrinkage cracking in concrete. Failure ot concrete structures typically involves stable growth of large cracking zones and the formation of large fractures before the maximum load is reached. This book presents models and methods to determine thermal stresses and cracking risks in concrete. Workshop on fracture mechanics for concrete pavements. Results exhibit favorable comparison between theoretical modeling and experimental observations. Fracture mechanics of earlyage concrete request pdf. This paper deals with the analysis of fracture characteristics of concrete at very early ages. In current study, experimental investigations have been conducted on concrete at early age.

This clearly demonstrates that, despite the successful application of fracture mechanics to study the fracture behavior of mature concrete, its application to the cracking of very early age concrete i. This paper presents a general procedure based on fracture mechanics models in order to analyze the level of cracking and structural safety in reinforced concrete elements at early ages, depending on the stripping time. Proper control of early age cracking risk in concrete as well as optimisation of relevant processes in precast industry requires an adequate knowledge of tensile and fracture properties of. The blowups usually occur at joints or cracks in the pavement and the concrete at the blowup appear to be weak or deteriorated at that point. The tension setup developed in the present study worked very well for obtaining the fracture energy of concrete at early age. The fictitious crack model is applied for the analysis of splitting tensile fracture, and the mohrcoulomb yield criterion is adopted for modelling the compressive crushingsliding failure. Due to the adopted small specimen size, very fast servo system, and stiff testing frame, a stable experiment and a complete softening curve were obtained, even for concrete specimens with an age as early as 24 h.

With the development of nonlinear fracture mechanics nlfm of concrete, which took fracture process zone fpz of concrete into consideration, rilem had tentatively. Concrete mechanical behavior at early age is characterized by the. However, the experimental investigation and the modelling of the early age concrete after crack initiation has occurred, is scarce. New slabsonground crack when tensile stresses from restrained shrinkage exceed the concrete s strength. Ab the goal of this investigation was to better understand and predict early age shrinkage cracking in restrained concrete structures. He received his phd in civil engineering from the university of california at berkeley, berkeley, ca. However, the underlying mechanism of this form of crack propagation has remained largely unexplained, with very limited literature available. For this method a fast and simple method for interpretation and inverse analysis has been developed and calibrated versus the.

After cracking, the stress at the node is calculated by the fracture energy curve. A computerautomated fracture mechanics model was used to successfully predict the age at first cracking. Experiments were performed on both normal and high strength concrete with 0, 1, and 2% shrinking reducing admixture. Early age tensile basic creep behavioral characteristics. For this method a fast and simple method for interpretation and inverse analysis has been. Microstructural mechanisms of early age cracking behavior of concrete. This contribution focuses on the evolution of the fracture energy of concrete at early ages.

A general approach for numerically simulating this type of behavior is presented. Fracture mechanics analysis for saw cutting requirements. Earlyage concrete cover crack and its effects on concrete. Tensile creep is an important parameter to evaluate cracking probability of highstrength concrete hsc structure, and the mineral admixtures have great effect on it. Additionally, the double power law dpl model was used to depict early age deformations of concrete in the mechanical field. Early age fracture mechanics and cracking of concrete. The driving forces of crackcausing stresses for earlyage concrete casts are. An important new report from the rilem technical committee 119. The main nonlinear phenomena that govern the deformational behavior of early. Computational models for fracture fracture mechanics for structural concrete. Determination of fracture energy of early age concrete. Portland cement concrete is a relatively brittle material and as a result, its mechanical behavior is critically influenced by crack propagation. A fracture mechanics modeling approach was developed to predict the behavior of a variety of restrained concrete specimens.