Deterioration and REPAir of above Ground Concrete Water Tanks in Ontario, Canada

Ontario Ministry Of The Environment

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• Publié par: ketok
• Nombre de lectures: 84
• Langue: English
• Poids de l'ouvrage: 5 Mo

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'^u/^y ,h/i^ù^ ^^/U.^ DETERIORATION AND REPAIR OF ABOVE GROUND CONCRETE WATERTANKS ONTARIO, CANADAIN REPORT TO ONTARIO MINISTRYOF THE ENVIRONMENT AssociatesColder September,1987 W.M. Slater & Associates Inc.DETERIORATION AND REPAIR OF ABOVE GROUND CONCRETE WATER TANKS IN ONTARIO, CANADA AUTHORS R. GRIEVE W.M. SLATER Colder Associates W.M. Slater & Associates Inc. L. ROTHENBURG Colder Associates(i) APPLIED RESEARCH GROUP MEMBERS -G. Aldworth MacLaren Engineers -T.I. Campbell Queen's University -R. Grieve Colder Associates -K. MacKenzie Dalhousie Materials -W. Pery W. Pery Engineering (Deceased) -L. Rothenburg Colder Associates -W.M. Slater W.M. Slater & Associates Inc. (Chairman) -R. Staton MacLaren Engineers -R. Crawford Ministry of the Environment -P. Rostern- of the -M. Toza Ministry of the -O. Wigle of the Environment REPORTS PREPARED UNDER THE APPLIED RESEARCH PROGRAMME FOR THE MINISTRY OF THE ENVIRONMENT Evaluation of Waterproof Coatings for Concrete \\ater Tanks. Mackenzie, K., (Dalhousie Materials), Slater, W.M.,(W.M. Slater & Associates Inc.) and McCrenerc, P., (Knox Martin Kretch) (Editing). Preliminary, 1985. Freeze Protection for Above Ground Concrete Uater Tanks in Cold Regions. Aldworth, C, Staton, R., (MacLaren Engineers), and Slater,W.M., (W.M. Slater & Associates Inc.). Preliminary, 1985. Temperature Monitoring, Ontario Concrete Water Tanks. Crieve, R. (Colder .Associates). May, 1984 and February, 1986. Ice Loading in Elevated Water Tanks. Campbell, T.I. and Kong, W.L., (Queen's LTnivcrsity). .April, 1986.(ii) FOREWORD concrete tank service lives to, say, fifty years was not carried out. This report began as a study of the problems associated with the The objective of the study was to be deterioration of some of the 53 above directed towards seeking rehabilitation ground concrete water storage tanks solutions for existing structures in order achieve life expectancybuilt in Ontario during the period 1956 to a of at least funded 25 more years. The appliedto 1980. It was initiated and by research Environment (MOE) programme, therefore, wasthe Ministry of the focussed water tank mainly in the direction of repair, ratheras part of the concrete programme which was than on basic concrete research.rehabilitation it's Project Engineeringsupervised by In spite of the emphasis in theBranch study to seek remedial solutions to the various Concrete tanks are structurally problems associated with the rapid straightforward systems but, being deterioration and failure of concrete exposed to severe environmental water tanks in Ontario, a study of the conditions, appear to suffer a rate of mechanisms which caused some of the deterioration which has greatly reduced observed rapid failures was considered to the expected life of the structures. The be most important in seeking repair damage ranges from heavy surface solutions. Numerous field observations spalling and cracking to delamination of apparently unique and hitherto and eventual failure of the structure. unreported and undocumented types of The study showed that the prime factors failure in reinforced and prestressed identified as determining the rate of concrete water tanks, required some concrete structure deterioration were the attempt findto a scientific explanation number of freeze-thaw cycles, for the causes of the problems. temperature amplitudes and frequencies, concrete permeability, hydrostatic The mechanisms of concrete dilation and pressure, location, the effect of steel delaminations, as well as the effect of reinforcement embedments, and internal internal ice, air entrainment, thermal ice formations. differential strains and strain rates, and other deterioration factors are described construction wellSince defects, as as in the report, but no laboratory or proof the prime factors listed above, have havea tests been carried out to date. dominant affect on the accelerated rate of deterioration of concrete water tanks Since the various factors and in Ontario, remedial solutions such as mechanisms may act concurrently, and repair of joints and honeycombing, have not been described in technical applying waterproof coatings, insulation, literature, it is recommended in the and replacement by steel tanks, were report that basic research be carried out proposed. in these areas in the future to try to the deteriorationquantify identified. The was limited addressingstudy to already established problems existing in A brief section in the report gives the the 53 pre-1981 structures. Many of the principal results of the temperature concrete tanks had site specific monitoring of three concrete tanks, one problems, so basic research into such uninsulated and two insulated, from areas, for example, as the design of three separate locations in central, special concrete mixes to improve new south-west, and north-west Ontario.(iii) main objective of the monitoring The report discusses the variousThe methods measure the thermal repairprogramme was to used to different types of history of an uninsulated tank, and by concrete tanks and gives comparison, measure the effectiveness of recommendations for assessment and insulation systems developed as possible analysis of repair systems. engineering solutions to the concrete tank deterioration problem by reducing Although corrosion of metals is not a both the number and temperature serious problem in concrete water tanks, amplitude characteristics of freeze-thaw some corrosion of tendons and other cycles on the tank walls. The detailed metallic components has occurred. The graphical data is presented in a separate report gives examples of this type of report prepared for the MOE by Colder deterioration, and the remedial methods Associates in February 1986, entitled used in the rehabilitation programme. "Temperature Monitoring, Ontario Concrete Water Tanks". Useful Interim guidelines have been prepared information such as the number and for the design and construction of new frequency of freeze-thaw cycles, concrete water tanks in Ontario based solar and on thedifferences between exposed experience gained during the shaded quadrants, temperature rehabilitation programme, and from the differentials and rate of temperature applied research carried out. The change, temperature external to and guidelines recommend that internal the concrete walls, has been waterproofingwithin etc. and external insulation be reported and plotted in that report. used as the primary protection against Full analysis of this data and its general the deterioration of above ground aspects is not within the scope of this concrete water tanks in Ontario. report. The main conclusion of the report is that, without adequate protection of permeable concrete from direct contact with water and elimination of cyclic freezing in the tank wall, above ground concrete water tanks will continue to deteriorate rapidly.(iv) ACKNOWLEDGEMENTS described in this report is the result of the efforts of many individualsThe work who assisted with various tasks from tank inspection and testing through to review and drafting of the report. The members of the Applied Research Group wish to acknowledge the help, encouragement, and support offered by the following Ministry of the Environment personnel: L. Benoit, R.K. Brown, R.G. Crawford, J.C.F. MacDonald (retired), Wright.W.C. Ramsden, P. Rostern, M. Toza, O. Wigle, and T. and the Ministry also wish to thank persons from the Ministry ofThe authors Transportation and Communications, Ontario Hydro and from various consulting engineering firms who reviewed draft reports, and offered their advice. In addition they wish to thank and acknowledge Wyllie and Ufnal and Knox Martin Kretch for the use of some of their inspection and photographic data. A special thanks to the typing, drafting and office staff of Golder Associates. In Philomena D'Souza, Mike Wright, Jim Alexander, and Vic Milligan whoparticular greatly assisted in the production of this report.(V) TABLE OF CONTENTS 1.0 INTRODUCTION 1.1 General 1.2 Description 1.3 Applied Research 1.4 Rehabilitation Programme 1.5 Above Ground Water Tank Types 1.6 Performance Rating DETERIORATIONOFABOVEGROUNDCONCRETEWATERTANKS 2-2.0 -General 22.1 -Observations2.2 2 -External Wall Delamination 22.2.1 - .1 Post-Tensioned Unbonded (PTU) 2 - .2 Bonded (PTB) 2 .3 Wire Wound Gunite 2-1Protected (G) 2-2.4 Reinforced Concrete Standpipes (RC) .5 Conclusions 2-5 2.2.2 Internal Wall Delamination 2-5 2.2.3 Localized Spalling 2-6 2.2.4 Jack-Rod Spalls 2-7 2.2.5 Cover Coat Shrinkage and Cracking 2-8 2.2.6 Quality of Concrete in Water Tanks 2-9 2.2.7 Summary of Observations 2 -10 MONITORING 3-13.0 TEMPERATURE 3-13.1 General Instrumentation 3-13.2 Temperature 3-23.3 Test Results 3-43.4 Freezing in Concrete 3-43.5 Seasonal Wall Conditions 3-53.5.1 Thermal Conductivities - 3-53.5.2 Autumn Winter Condition - 3-53.5.3 Winter Spring 3-63.5.4 Insulated Tank Winter Profile 3-63.6 Daily Thermal Cycle 3-73.7 Critical Ambient Temperatures 4.0 INVESTIGATION OF THE FREEZE-THAW FAILURE 4-1MECHANISM IN CONCRETE 4-14.1 General 4-2Review4.2 Literature Affecting the Freeze-Thaw Durability Of4.3 Some Factors 4-2Concrete 4-3Concrete in Water Tanks4.3.1 Saturation of 4-3and Evaporation4.3.2 Hydrostatic Pressure(vi) Table of Contents (contd) 4-44.3.3 Air Voids 4-4Affect of Prestress on Permeability4.3.4 4-5of Freezing Temperature on Concrete4.4 Action 4-9Summary4.4.1 4-9Standard Freeze-Thaw Tests4.5 4-10of Re-Saturating Dilated Concrete4.6 Rate Induced Expansion .... 4-114.7 Stresses in Concrete Due to Frost -12in Tank Walls 44.7.1 Tensile Stresses -14Tensile Stress Accumulation 44.7.2 Model of -17of Stresses 44.7.3 Distribution -1844.7.4 Summary 4-194.8 Spot Saturation 4-20Jack-Rod Spalls4.8.1 4-21Hydraulic Pressure "Sandwich"4.9 -224.10 Conclusions and Recommendations 4 REPAIR AND REHABILITATION OF CONCRETE WATER TANKS5.0 -ONTARIO 5IN -General 55.1 -5.2 Design of Repairs 5 -5.2.1General 5 -5.2.2 Structural Evalua