Basis for and Practical Approaches to Stress Calculations and Crack Risk Estimation in Hardening Concrete Structures – State of the Art
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www.coinweb.no SINTEF Building and Infrastructure Øyvind Bjøntegaard (Norwegian Public Roads Administration) Basis for and practical approaches to stress calculations and crack risk estimation in hardening concrete structures – State of the art COIN Project report 31 – 2011 SINTEF Building and Infrastructure Øyvind Bjøntegaard (Norwegian Public Roads Administration) Basis for and practical approaches to stress calculations and crack risk estimation in hardening concrete structures – State of the art FA 3 Technical performance SP 3.1 Crack free concrete structures COIN Project report 31 – 2011 COIN Project report no 31 Øyvind Bjøntegaard (Norwegian Public Roads Administration) Basis for and practical approaches to stress calculations and crack risk estimation in hardening concrete structures – State of the art FA 3 Technical performance SP 3.1 Crack free concrete structures Keywords: Hardening phase, curing technology, stress simulations, crack-risk assessment Photo, cover: The Norwegian Public Roads Administration (Statens vegvesen) Project no.: 3D005930 ISSN 1891–1978 (online) ISBN 978-82-536-1236-2(pdf) ISBN 978-82-536-1237-9 (printed) © Copyright SINTEF Building and Infrastructure 2011 The material in this publication is covered by the provisions of the Norwegian Copyright Act. Without any special agreement with SINTEF Building and Infrastructure, any copying and making available of the material is only allowed to the extent that this is permitted by law or allowed through an agreement with Kopinor, the Reproduction Rights Organisation for Norway. Any use contrary to legislation or an agreement may lead to a liability for damages and con- fiscation, and may be punished by fines or imprisonment. Address: Forskningsveien 3 B POBox 124 Blindern N-0314 OSLO Tel: +47 22 96 55 55 Fax: +47 22 69 94 38 and 22 96 55 08 www.sintef.no/byggforsk www.coinweb.no Cooperation partners / Consortium Concrete Innovation Centre (COIN) Aker Solutions Rescon Mapei AS Norwegian Public Roads Administration Contact: Jan-Diederik Advocaat Contact: Trond Hagerud Contact: Kjersti K. Dunham Email: [email protected] Email: [email protected] Email: [email protected] Tel: +47 67595050 Tel: +47 69972000 Tel: +47 22073940 Saint Gobain Weber SINTEF Building and Infrastructure Unicon AS Contact: Geir Norden Contact: Tor Arne Hammer Contact: Stein Tosterud Email: [email protected] Email: [email protected] Email: [email protected] Tel: +47 22887700 Tel: +47 73596856 Tel: +47 22309035 Norcem AS Skanska Norge AS Veidekke Entreprenør ASA Contact: Terje Rønning Contact: Sverre Smeplass Contact: Christine Hauck Email: [email protected] Email: [email protected] Email: [email protected] Tel: +47 35572000 Tel: +47 40013660 Tel: +47 21055000 NTNU Spenncon AS Contact: Terje Kanstad Contact: Ingrid Dahl Hovland Email: [email protected] Email: [email protected] Tel: +47 73594700 Tel: +47 67573900 Basis for and practical approaches to stress calculations and crack risk estimation in hardening concrete structures Preface This study has been carried out within COIN - Concrete Innovation Centre - one of presently 14 Centres for Research based Innovation (CRI), which is an initiative by the Research Council of Norway. The main objective for the CRIs is to enhance the capability of the business sector to innovate by focusing on long-term research based on forging close alliances between research- intensive enterprises and prominent research groups. The vision of COIN is creation of more attractive concrete buildings and constructions. Attractiveness implies aesthetics, functionality, sustainability, energy efficiency, indoor climate, industrialized construction, improved work environment, and cost efficiency during the whole service life. The primary goal is to fulfil this vision by bringing the development a major leap forward by more fundamental understanding of the mechanisms in order to develop advanced materials, efficient construction techniques and new design concepts combined with more environmentally friendly material production. The corporate partners are leading multinational companies in the cement and building industry and the aim of COIN is to increase their value creation and strengthen their research activities in Norway. Our over-all ambition is to establish COIN as the display window for concrete innovation in Europe. About 25 researchers from SINTEF (host), the Norwegian University of Science and Technology - NTNU (research partner) and industry partners, 15 - 20 PhD-students, 5 - 10 MSc-students every year and a number of international guest researchers, work on presently 5 projects: • Advanced cementing materials and admixtures • Improved construction techniques • Innovative construction concepts • Operational service life design • Energy efficiency and comfort of concrete structures COIN has presently a budget of NOK 200 mill over 8 years (from 2007), and is financed by the Research Council of Norway (approx. 40 %), industrial partners (approx 45 %) and by SINTEF Building and Infrastructure and NTNU (in all approx 15 %). For more information, see www.coinweb.no Tor Arne Hammer Centre Manager 3 Basis for and practical approaches to stress calculations and crack risk estimation in hardening concrete structures Summary Temperature- and stress simulation programs are used to calculate the cracking tendency of hardening concrete structures. If cracking is likely to occur, the simulations can be used to find the necessary countermeasures to avoid cracking. The subject area is often denoted stress-based curing technology, or advanced curing technology. The “technology” can also be used in the production planning with regard to for more traditional curing technology considerations, such as how to avoid freezing of fresh concrete, determination of temperature gradients, earliest time of form removal, earliest time of post-tensioning, etc. The report is an introduction to the understanding of advanced curing technology. The governing properties and mechanisms behind stress development and cracking tendency of hardening concrete structures are dealt with, and illustrated by experimental examples. Propositions on how to approach simulations with experiments and data implementation are presented, showing materials models and strategies that reflects Norwegian traditions. The presented approaches should however have rather general validity since the choice of a given materials model is often of secondary importance as long as good experimental data is available. Simplified calculation methods are presented to illustrate the interplay between the different concrete properties. Simulation programs based on the finite-elements method are discussed briefly. The main scope here is to give a basis for the understanding of such programs. The content is based on experience and knowledge from various national and international projects (with Norwegian participation) during the last two decades, in addition to a more general literature study. Acknowledgements The proof reading of the report, pieces of advice and comments by Erik J. Sellevold are greatly appreciated. Appreciated is also the contribution from Steinar Helland on chapter 2, and for the pictures in chapter 1. 4 Basis for and practical approaches to stress calculations and crack risk estimation in hardening concrete structures Table of contents PREFACE ................................................................................................................................................. 3 SUMMARY .............................................................................................................................................. 4 TABLE OF CONTENTS ........................................................................................................................ 5 1 INTRODUCTION ........................................................................................................................ 7 2 CURING TECHNOLOGY - HISTORICAL REVIEW .......................................................... 9 2.1 DAMS ......................................................................................................................................... 9 2.2 EXTERNAL RESTRAINT AND STRESS-MEASUREMENTS ............................................................ 10 2.3 STRUCTURAL BEHAVIOUR ....................................................................................................... 12 2.4 COMPUTER-BASED CURING TECHNOLOGY .............................................................................. 13 2.5 THERMAL DILATION AND AUTOGENOUS SHRINKAGE .............................................................. 15 2.6 CONFERENCES AND RESEARCH PROJECTS ............................................................................... 16 2.7 NORWEGIAN DEVELOPMENTS ................................................................................................. 17 3 THE HARDENING PHASE AND DEFINITION OF T0 ...................................................... 21 4 INTERNAL AND EXTERNAL RESTRAINT ....................................................................... 23 5 STRESS DEVELOPMENT AND “CRACK INDEX” .......................................................... 28 6 MATURITY TIME – THE “STATE PARAMETER” .......................................................... 30 7 THE DRIVING FORCES TO STRESS GENERATION ..................................................... 33 7.1 GENERAL ................................................................................................................................