Mija H. Hubler

Comprehensive Database for Concrete Creep and Shrinkage: Analysis and Recommendations for Testing and Recording

The first large worldwide database of creep and shrinkage tests was assembled at Northwestern University (NU) in 1978. It was expanded as the RILEM database in 1992 and further in 2008. A major expansion, completely restructured and verified, named the NU Database, is now presented. The number of the test curves of creep and drying shrinkage is more than doubled and over 400 test curves of autogenous shrinkage are added. The database covers longer measurement periods and encompasses the effects of admixtures in modern concrete mixtures. The database contains roughly 1400 creep and 1800 shrinkage curves, of which approximately 800 creep and 1050 shrinkage curves contain admixtures. Their analysis shows significant influence of admixtures on the creep and shrinkage behavior. The mixture proportions, testing conditions, and specimen geometries are documented in greater detail, and information on the admixture contents and aggregate types is included. The new database makes it possible to calibrate and verify improved creep and shrinkage prediction models. Additionally, the statistics of the mixture parameters, strength distributions, and scatter of the compliance curves have been extracted for applications in reliability engineering and probabilistic performance assessment. Data analysis brings to light various recommendations for testing and recording, and suggests corrections of various oversights distorting the reported data. These recommendations would make future test data more useful, consistent, complete, and reliable. The NU database is now available for free download at www. civil.northwestern.edu/people/bazant/ as well as at www.baunat.boku.ac.at/creep.html.

Microtexture Analysis of Gas Shale by XRM Imaging

AbstractAlthough it is generally agreed that microscale material structural features of gas shale dictate their mechanical and transport properties, which are key for efficient resource extraction,...

Size-Effect Law for Scratch Tests of Axisymmetric Shape

AbstractThis paper presents a theoretical and experimental framework for the application of size-effect analysis to microscratch testing as a means to quantify the fracture properties and internal friction of materials at the microscale. The energetic size-effect law (SEL) for microscratch tests is developed for a general monomeric probe shape in terms of an intrinsic size function. The fundamental idea of the proposed approach is to rescale the scratch response to that of the flat punch, a conjecture that allows one to compare the SEL for different probe geometries, and thus solve for the asymptotic fracture toughness and effective process zone length from scratch tests done on homogenous (acetal homopolymer resin and polycarbonate resin) and inhomogeneous materials (mica ceramic and gas shale). As a material of current interest for controlled fracture studies, two samples of gas shale cored from the Marcellus and Eagle Ford formations are tested and analyzed to quantify all material properties that may ...

Water Sorption Hysteresis in Cement Nano Slits

An important feature of the water sorption in cement has been the pronounced hysteresis. The hysteresis in capillary pores has been explained by so-called «ink-bottles» theory and/or the meniscus theory. In contrast, the hysteresis in gel pores (nanopores) received little attention. This paper investigated the sorption hysteresis in cement slits via atomistic simulations. Tobermorite 11 was adopted to represent the cement atomistic structures. In order to create the surface for adsorption, the Wollastonite chains in Tobermorite 11 were removed and the dangling bonds were saturated with hydrogen atoms. Charges were balanced to be neutral for the whole simulation cell. The sorption isotherms were calculated using the Sorption module in Material Studio (a commercial software for MD simulations), which calculates adsorption isotherms for water in the pores from a series of fixed pressure simulations. Three Tobermorite11 slits of widths H = 10 A, 20 A and 30 A were studied. The temperature was kept at 298 K. The results for all three slits showed significant and slit-size-dependent hysteresis sorption-desorption loops. The hysteresis shrinks when the width of the slits decreases. The role of Coulomb interaction in the hysteresis, as well as the water molecular density within the slits, were discussed. The results on sorption hysteresis in nano slits can be used to revise/refine the existing water hysteresis models for cement and concrete. This paper provides the pathway towards a better understanding of creep and drying shrinkage of ordinary Portland cement on the nanoscale.

Damage in prestressed concrete structures due to creep and shrinkage of concrete

This chapter focuses on polymer/metal interfaces. Attention is given to two common aspects of tremendous practical interest, namely, surface roughness andmoisture. Debonding of polymer/metal interfaces often involves both interfacial and cohesive failure. Since the cohesive strength of polymers is usually much greater than the polymer/metal interfacial strength, cohesive failure near the interface is usually desired to enhance the interfacial adhesion. Roughened surfaces generally produce more cohesive failure and, therefore, are used commonly in practice to obtain better adhesion. In this chapter, a fracture mechanics model is developed that can be used to quantitatively predict the amount of cohesive failure once the surface roughness data are given. Moisture, on the other hand, tends to degrade the interfacial strength. To quantify such degradation, a systematic and multidisciplinary study is conducted to better understand the fundamental science of moistureinduced degradation of interfacial adhesion. The approach is comprised of both experimental and modeling components of analysis and addresses some of the key issues needed to advance the understanding of the effect of moisture on interfacial adhesion.Many materials exhibit a discontinuous and inhomogeneous nature on various spatial scales that can lead to complex mechanical behaviors difficult to reproduce with continuum-based models. “Among these complex phenomena is damage evolution with nucleation, propagation, interaction, and coalescence A. Rinaldi (*) Materials Technical Unit, ENEA, C.R. Casaccia, Rome, Italy Center for Mathematics and Mechanics of Complex System (MEMOCS), University of L‘Aquila, Cisterna di Latina (LT) Italy e-mail: antonio.rinaldi@enea.it S. Mastilovic Faculty of Construction Management, Union–Nikola Tesla University, Belgrade, Serbia e-mail: smastilovic@fgm.edu.rs # Springer Science+Business Media New York 2015 G. Z. Voyiadjis (ed.), Handbook of Damage Mechanics, DOI 10.1007/978-1-4614-5589-9_22 305 of cracks that can result in a plethora of macroscale deformation forms.” Discontinua-based models are computational methods that represent material as an assemblage of distinct elements interacting with one another. The mesoscale methods of computational mechanics of discontinua presented in this our two essays can be, arguably, divided into three broad and intervening categories: spring network (lattice) models, discrete/distinct-element methods (DEM), and particle models. The distinct-element computational methods such as molecular dynamics and smoothed-particle hydrodynamics are outside the scope of the present overview. The objective of this chapter is to briefly survey the spring network models and their main applications. The discrete-based models have been extensively applied in the last decade to three-dimensional configurations. However, since the scope of this article is limited to two-dimensional (2D) models for practical purposes, these important advances are ignored. Likewise, one-dimensional (1D) fiber bundle models are also excluded from this account.The theory of concrete creep and shrinkage has not been regarded as part of what has been understood as damage mechanics. However, these inelastic phenomena do result in significant damages to structures, including not only distributed cracking, which is damage in classical sense, but also damage in the form of excessive deflection which puts the structure out of service. It is for this reason that a chapter on creep and shrinkage is included in this handbook. The theory of creep and shrinkage of concrete has become a vast field. In what follows, only a rather brief exposition of this subject will be included. The emphasis will be on the topics of wide recent interest, triggered by the revelation of practical problems that have been synthesized into a coherent picture only during the last few years. The creep effects are particularly important for super-tall buildings and prestressed concrete structures, because of their slenderness and high flexibility, and are paramount for nuclear reactor containments and vessels. At high-temperature exposure, as in fire in tunnels or tall buildings or in postulated nuclear reactor accidents, creep is very large and plays a major role.The first € price and the £ and

Theory of cyclic creep of concrete based on Paris law for fatigue growth of subcritical microcracks

price are net prices, subject to local VAT. Prices indicated with * include VAT for books; the €(D) includes 7% for Germany, the €(A) includes 10% for Austria. Prices indicated with ** include VAT for electronic products; 19% for Germany, 20% for Austria. All prices exclusive of carriage charges. Prices and other details are subject to change without notice. All errors and omissions excepted. G.Z. Voyiadjis (Ed.) Handbook of Damage MechanicsPolymer matrix composites (PMCs) are playing rapidly increasing roles in future military and civilian industries. Damage tolerance analysis is an integral part of PMC structural design. Considerable research efforts have been invested to establish predictive capabilities, but thus far highfidelity strength and durability prediction capabilities are yet to be established. Advanced numerical methods that can explicitly resolve the multiple-damage processes and their nonlinear coupling at various scales are highly desired. This paper first reviews the recent development of advanced numerical methods, including eXtended Finite Element Method (X-FEM), phantom node methods (PNM), and the Augmented Finite Element Method (A-FEM), in handling the multiple-damage coupling in composites. The capability of these methods in representing various composite damage modes explicitly with embedded nonlinear fracture models (such as cohesive zone models) makes them excellent candidates for high-fidelity failure analyses of composites. The detailed formulation of A-FEM and its implementation to a popular commercial software package (ABAQUS) as a userdefined element has been given. Successful simulations of composites at various scales using the framework of A-FEM are presented and the numerical and material issues associated with these high-fidelity analyses are discussed. Through the numerical predictions and the direct comparisons to experimental results, it has been demonstrated that high-fidelity failure analyses can be achieved with the A-FEM through careful calibration of nonlinear material properties and cohesive fracture parameters and with proper considerations of the different length scales within which these damage processes operate.