Self-Desiccation and Its Importance in Concrete Technology
Total Page：16
File Type：pdf, Size：1020Kb
LUND INSTITUTE OF TECHNOLOGY LUND UNIVERSITY Division of Building Materials SELF-DESICCATION AND ITS IMPORTANCE IN CONCRETE TECHNOLOGY Editors: B Persson, D Bentz and L-O Nilsson Proceedings of the Fourth International Research Seminar, Gaithersburg, Maryland, USA, June, 2005 Report TVBM-3126 ISRN LUTVDG/TVBM--05/3126--SE(1-270) ISSN 0348-7911 TVBM ISBN 91-631-7102-3 Lund Institute of Technology Telephone: 46-46-2227415 Division of Building Materials Telefax: 46-46-2224427 Box 118 www.byggnadsmaterial.lth.se SE-221 00 Lund, Sweden PREFACE This is the fourth Research Seminar on Self-Desiccation in Concrete organized by the Building Materials Division of Lund University. The three previous seminars were held in 19971, 19992, and 2002.3 While the fourth seminar has a change in locale to the National Institute of Standards and Technology (NIST), it is hoped that the enthusiasm of the participants and the high technical quality of the presentations that have characterized the first three seminars will be maintained. RILEM TC 196-ICC has defined self-desiccation as “the reduction in internal relative humidity of a sealed system when empty pores are generated. This occurs when chemical shrinkage takes place at the stage where the paste matrix has developed a self- supportive skeleton, and the chemical shrinkage is larger than the autogenous shrinkage.” While self-desiccation will thus occur in any concrete cured under sealed conditions, its effects are quite dependent on the sizes of the generated empty pores. These pore sizes in turn are dependent on the initial water-to-binder ratio (w/b), the particle size distributions of the binder components, and their achieved degree of hydration. The continuing trends towards finer cements and much lower w/b have significantly reduced the capillary pore “diameters” (spacing) in the paste component of the fresh concrete, and have often resulted in materials and structures where the effects of self-desiccation are all to visible as early-age cracking. Many strategies for minimizing the detrimental effects of self-desiccation (mainly the high internal stresses and strains that may lead to early-age cracking), such as internal curing, rely on providing a “sacrificial” set of larger water-filled pores within the concrete microstructure that will empty first while the smaller pores in the hydrating binder paste will remain saturated. It must be kept in mind that the effects of self-desiccation are not always detrimental, as exemplified by the benefits offered by self-desiccation in terms of an earlier RH reduction for flooring applications and an increased resistance to frost damage. As this volume of proceedings contains contributions from authors representing nine different countries, it is obvious that the high level of international interest and ongoing research on this topic exhibited in the first three seminars is continuing. The understanding of the mechanisms by which self-desiccation occurs is now on a strong scientific foundation, and thus the research in this area is rapidly advancing from a basic to an applied phase, from the research laboratory to the field, and from concrete researchers to concrete practitioners. It is hoped that this volume will contribute both strength and durability to this technology transfer. Gaithersburg, MD USA, May 2005 Dale Bentz 1 Persson, B., Fagerlund, G. (Eds.), Self-Desiccation and Its Importance in Concrete Technology, Report TVBM-3075, Div. Building Materials, Lund Institute of Technology, Lund University, Lund, 255 pp. (1997). 2 Persson, B., Fagerlund, G. (Eds.), Self-Desiccation and Its Importance in Concrete Technology, Report TVBM-3085, Div. Building Materials, Lund Institute of Technology, Lund University, Lund, 171 pp. (1999). 3 Persson, B., Fagerlund, G. (Eds.), Self-Desiccation and Its Importance in Concrete Technology, Report TVBM-3104, Div. Building Materials, Lund Institute of Technology, Lund University, Lund, 250 pp. (2002). Lund University, Lund, Sweden Photo: Madeleine Persson, 2005. ii TABLES OF CONTENTS PAGE Part I - Basic topics J.-H. Moon, F. Rajabipour, B. Pease, and J. Weiss 1 AUTOGENOUS SHRINKAGE, RESIDUAL STRESS, AND CRACKING IN CEMENTITIOUS COMPOSITES: THE INFLUENCE OF INTERNAL AND EXTERNAL RESTRAINT V. Baroghel-Bouny and P. Mounanga 21 EFFECTS OF SELF-DESICCATION ON AUTOGENOUS DEFORMATIONS, MICROSTRUCTURE AND LONG-TERM HYGRAL BEHAVIOUR L.-O. Nilsson and K. Mjörnell 49 A MACRO-MODEL FOR SELF-DESICCATION IN HIGH PERFORMANCE CONCRETE T. Noguchi, P. Sun-Gyu, and I. Maruyama 67 MECHANICAL PROPERTIES OF HIGH-PERFORMANCE CONCRETE WITH EXPANSIVE ADDITIVE AND SHRINKAGE REDUCING ADMIXTURE UNDER SIMULATED COMPLETELY-RESTRAINED CONDITION AT EARLY AGE .C.Z Grasley, D.A. Lange, A.J. Brinks, and M.D. D’Ambrosia 78 MODELING AUTOGENOUS SHRINKAGE OF CONCRETE ACCOUNTING FOR CREEP CAUSED BY AGGREGATE RESTRAINT B. Persson 95 ON THE TEMPERATURE EFFECT ON SELF-DESICCATION OF CONCRETE S. Miyazawa and E.-i. Tazawa 125 PREDICTION MODEL FOR AUTOGENOUS SHRINKAGE OF CONCRETE WITH DIFFERENT TYPE OF CEMENT Part II - Consequences M. Suzuki, M. Tanimura, and R. Sato 139 THE EFFECT OF AUTOGENOUS SHRINKAGE ON FLEXURAL CRACKING BEHAVIOR OF REINFORCED HSC BEAMS AND IMPROVEMENT BY USING LOW-SHRINKAGE HSC iii M.-C. Han and C.-G. Han 153 THE EFFECT OF SPECIMEN SIZE ON THE SHRINKAGE PROPERTIES OF HIGH PERFORMANCE CONCRETE P. Lura, Y. Guang, K. Tanaka, and O.M. Jensen 165 MICROCRACK DETECTION IN HIGH-PERFORMANCE CEMENTITIOUS MATERIALS M. Qin and B. Ni 179 MOISTURE DISTRIBUTION IN CEMENT PASTE CONSIDERING SELF- DESICCATION Part III - Utilization D. P. Bentz 189 CAPITALIZING ON SELF-DESICCATION FOR AUTOGENOUS DISTRIBUTION OF CHEMICAL ADMIXTURES J.W. Roberts 197 CURRENT AND FUTURE TRENDS IN THE APPLICATION OF INTERNAL CURING OF CONCRETE H. Lam and R. D. Hooton 210 EFFECTS OF INTERNAL CURING METHODS ON RESTRAINED SHRINKAGE AND PERMEABILITY B.J. Mohr, L. Premenko, H. Nanko, and K.E. Kurtis 229 EXAMINATION OF WOOD-DERIVED POWDERS AND FIBERS FOR INTERNAL CURING OF CEMENT-BASED MATERIALS M. Tanimura, Y. Mitani, and R. Sato 245 AN INVESTIGATION OF PREDICTION MODEL FOR AUTOGENOUS SHRINKAGE/EXPANSION STRAIN OF LOW-SHRINKAGE HSC I. Maruyama and R. Sato 264 A TRIAL OF REDUCING AUTOGENOUS SHRINKAGE BY RECYCLED AGGREGATE iv AUTOGENOUS SHRINKAGE, RESIDUAL STRESS, AND CRACKING IN CEMENTITIOUS COMPOSITES: THE INFLUENCE OF INTERNAL AND EXTERNAL RESTRAINT J.-H. Moon, F. Rajabipour, B. Pease, and J. Weiss Purdue University, West Lafayette, Indiana, USA Abstract The premise of this paper is that low water-to-cement ratio (w/c), higher strength concrete may undergo substantial volume changes, especially at early ages (< 24 hours), and the prevention of these volume changes can lead to invisible micro-cracking as well as visible through-cracking. This paper compares the predicted response of concrete undergoing autogenous shrinkage using two different models. The first model considers the concrete as a homogeneous material with effective elastic properties. The second model considers the concrete as a heterogeneous two-phase composite. The paper begins with an overview of common effective elastic property computations. These effective properties are then used to compute residual stresses when external restraint is provided. Heterogeneous system simulations were performed to quantify the effect of both internal and external restraint on shrinkage. Internal restraint may be caused by aggregate particles while the structure surrounding the concrete composite may produce external restraint. These simulations considered a series of ‘model systems’ ranging from a single aggregate particle, to an assembly of hexagonal unit cells containing aggregate particles, to a more realistic system consisting of various sizes and shapes of aggregate particles. The finite element analysis (FEA) simulations illustrate how localized stresses develop, how effective equivalent properties can be determined for heterogeneous composites, and how localized stresses can lead to cracking. 1. Research approach and motivation This paper provides an overview of a research program that is currently being conducted at Purdue University. The objective of the overall program is to develop procedures to enable information from sensors placed in a concrete structure or pavement to be utilized efficiently as real-time feedback for updating performance simulation models [1]. While this project has many facets, one aspect of this work is to better understand how an embedded stress sensor may be used to quantify residual stresses in concrete. Toward this end, a series of preliminary computations have been performed to better understand the residual stresses that develop in a heterogeneous composite system when one phase (the paste phase) shrinks and the other phase (the aggregate phase) does not. Subsequent computations have been performed to investigate stresses that develop when both phases experience differential movement, though they will not be discussed in this paper. 1 The overall research program is being conducted to try to resolve a few key questions that need to be answered to enable residual stress sensors to be used more efficiently in concrete. This paper describes work to address the following potential concerns: x Numerous researchers and engineers frequently simplify concrete by assuming it behaves like a homogeneous material by using ‘effective material properties’. While this is commonly done, the impact of simplifications made to implement ‘effective material properties’ remain unclear, especially as these