ACI-365.1R-2000.pdf

ACI 365.1R-00 became effective January 10, 2000. Copyright 2000, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc- tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in planning, de- signing, executing, and inspecting construction. This docu- ment is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it con- tains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract docu- ments, they shall be restated in mandatory language for in- corporation by the Architect/Engineer. 365.1R-1 Service-Life PredictionState-of-the-Art Report ACI 365.1R-00 This report presents current information on the service-life prediction of new and existing concrete structures. This information is important to both the owner and the design professional. Important factors controlling the service life of concrete and methodologies for evaluating the condition of the existing concrete structures, including definitions of key physical prop- erties, are also presented. Techniques for predicting the service life of con- crete and the relationship between economics and the service life of structures are discussed. The examples provided discuss which service-life techniques are applied to concrete structures or structural components. Finally, needed developments are identified. Keywords: construction; corrosion; design; durability; rehabilitation; repair; service life. CONTENTS Chapter 1Introduction, p. 365.1R-2 1.1Background 1.2Scope 1.3Document use Chapter 2Environment, design, and construction considerations, p. 365.1R-3 2.1Introduction 2.2Environmental considerations 2.3Design and structural loading considerations 2.4Interaction of structural load and environmental effects 2.5Construction-related considerations Chapter 3In-service inspection, condition assessment, and remaining service life, p. 365.1R-11 3.1Introduction 3.2Evaluation of reinforced concrete aging or degrada- tion effects 3.3Condition, structural, and service-life assessments 3.4Inspection and maintenance Chapter 4Methods for predicting the service life of concrete, p. 365.1R-17 4.1Introduction 4.2Approaches for predicting service life of new concrete 4.3Prediction of remaining service life 4.4Predictions based on extrapolations 4.5Summary Chapter 5Economic considerations, p. 365.1R-24 5.1Introduction 5.2Economic analysis methods 5.3Economic issues involving service life of concrete structures Reported by ACI Committee 365 S. L. Amey* M. GeikerD. G. Manning J. P. Archibald C. J. HookhamP. K. Mukherjee N. R. BuenfeldW. J. IrwinJ. Pommersheim P. D. Cady* A. KehnemuiM. D. Thomas C. W. Dolan R. E. Weyers* *Report chapter coordinators Deceased Report coordinator James R. Clifton* Chairman Dan J. Naus* Secretary 365.1R-2ACI COMMITTEE REPORT Chapter 6Examples of service-life techniques, p. 365.1R-27 6.1Example IRelationship of amount of steel corro- sion to time of concrete spalling 6.2Example IIComparison of competing degradation mechanisms to calculate remaining life 6.3Example IIIUtilization of multiple input to calcu- late the life of a structure 6.4Example IVWhen to repair, when to rehabilitate 6.5Example VUtilization of reaction rate to calculate the life of a sewer pipe 6.6Example VIEstimating service life and mainte- nance demands of a diaphragm wall exposed to sa- line groundwater 6.7Example VIIApplication of time-dependent reli- ability concepts to a concrete slab and low-rise shear wall Chapter 7Ongoing work and needed developments, p. 365.1R-36 7.1Introduction 7.2Designing for durability Chapter 8References, p. 365.1R-37 8.1Referenced standards and reports 8.2Cited references CHAPTER 1INTRODUCTION 1.1Background Service-life concepts for buildings and structures date back to when early builders found that certain materials and designs lasted longer than others (Davey 1961). Throughout history, service-life predictions of structures, equipment, and other components were generally qualitative and empirical. The understanding of the mechanisms and kinetics of many degradation processes of concrete has formed a basis for making quantitative predictions of the service life of struc- tures and components made of concrete. In addition to actual or potential structural collapse, many other factors can gov- ern the service life of a concrete structure. For example, ex- cessive operating costs can lead to a structures replacement. This document reports on these service-life factors, for both new and existing concrete structures and components. The terms “durability” and “service life” are often errone- ously interchanged. The distinction between the two terms is evident when their definitions, as given in ASTM E 632, are compared: Durability is the capability of maintaining the serviceabil- ity of a product, component, assembly, or construction over a specified time. Serviceability is viewed as the capacity of the above to perform the function(s) for which they are de- signed and constructed. Service life (of building component or material) is the pe- riod of time after installation (or in the case of concrete, placement) during which all the properties exceed the mini- mum acceptable values when routinely maintained. Three types of service life have been defined (Sommerville 1986). Technical service life is the time in service until a defined un- acceptable state is reached, such as spalling of concrete, safety level below acceptable, or failure of elements. Functional ser- vice life is the time in service until the structure no longer ful- fills the functional requirements or becomes obsolete due to change in functional requirements, such as the needs for in- creased clearance, higher axle and wheel loads, or road wid- ening. Economic service life is the time in service until replacement of the structure (or part of it) is economically more advantageous than keeping it in service. Service-life methodologies have application both in the design stage of a structurewhere certain parameters are established, such as selection of water-cementitious materi- als ratios (w/cm), concrete cover, and admixturesand in the operation phase where inspection and maintenance strategies can be developed in support of life-cycle cost analyses. Service-life design includes the architectural and structural design, selection and design of materials, mainte- nance plans, and quality assurance and quality control plans for a future structure (CEB/RILEM 1986). Based on mixture proportioning, including selection of concrete constituents, known material properties, expected service environment, structural detailing (such as concrete cover), construction methods, projected loading history, and the definition of end- of-life, the service life can be predicted and concrete with a rea- sonable assurance of meeting the design service life can be specified (Jubb 1992, Clifton and Knab 1989). The acceptance of advanced materials, such as high-performance concrete, can depend on life-cycle cost analyses that consider predictions of their increased service life. Methodologies are being developed that predict the service life of existing concrete structures. To predict the service life of existing concrete structures, information is required on the present condition of concrete, rates of degradation, past and future loading, and definition of the end-of-life (Clifton 1991). Based on remaining life predictions, economic deci- sions can be made on whether or not a structure should be repaired, rehabilitated, or replaced. Repair and rehabilitation are often used interchangeably. The first step of each of these processes should be to address the cause of degradation. The distinction between rehabilita- tion and repair is that rehabilitation includes the process of modifying a structure to a desired useful condition, whereas repair does not change the structural function. To predict the service life of concrete structures or ele- ments, end-of-life should be defined. For example, end-of- life can be defined as: Structural safety is unacceptable due to material degra- dation or exceeding the design load-carrying capacity; Severe material degradation, such as corrosion of steel reinforcement initiated when diffusing chloride ions attain the threshold corrosion concentration at the reinforcement depth; Maintenance requirements exceed available resource limits; Aesthetics become unacceptable; or Functional capacity of the structure is no longer suffi- cient for a demand, such as a football stadium with a deficient seating capacity. 365.1R-3 SERVICE-LIFE PREDICTIONSTATE-OF-THE-ART REPORT Essentially all decisions concerning the definition of end- of-life are combined with human safety and economic con- siderations. In most cases, the condition, appearance, or ca- pacity of a structure can be upgraded to an acceptable level; however, costs associated with the upgrade can be prohibi- tive. Guidance on making such decisions is included in this report. 1.2Scope This report begins with an overview of important factors controlling the service life of concrete, including past and current design of structures; concrete materials issues; field practices involved with placing, consolidating, and curing of concrete; and in-service stresses induced by degradation processes and mechanical loads. Methodologies used to evaluate the structural condition of concrete structures and the condition and properties of in-service concrete materials are presented. Methods are reviewed for predicting the ser- vice life of concrete, including comparative methods, use of accelerated aging (degradation) tests, application of mathe- matical modeling and simulation, and application of reliabil- ity and stochastic concepts. This is followed by a discussion of relationships between economics and the life of struc- tures, such as when it is more economical to replace a struc- ture than to repair or rehabilitate. Examples are described in which service-life techniques are applicable to concrete structures or structural components. Finally, needed devel- opments to improve the reliability of service-life predictions are presented. 1.3Document use This document can assist in applying available methods and tools to predict service life of existing structures and provide actions that can be taken at the design or construc- tion stage to increase service life of new structures. CHAPTER 2ENVIRONMENT, DESIGN, AND CONSTRUCTION CONSIDERATIONS 2.1Introduction Reinforced concrete structures have been and continue to be designed in accordance with national or international con- sensus codes and standards such as ACI 318, Eurocode 2, and Comité Euro International du Béton (1993). The codes are de- veloped and based on knowledge acquired in research and testing laboratories, and supplemented by field experience. Although present design procedures for concrete are domi- nated by analytical determinations based on strength princi- ples, designs are increasingly being refined to address durability requirements (for example, resistance to chloride ingress and improved freezing-and-thawing resistance). In- herent with design calculations and construction documents developed in conformance with these codes is a certain level of durability, such as requirements for concrete cover to pro- tect embedded steel reinforcement under aggressive environ- mental conditions. Although the vast majority of reinforced concrete structures have met and continue to meet their func- tional and performance requirements, numerous examples can be cited where structures, such as pavements and bridges, have not exhibited the desired durability or service life. In ad- dition to material selection and proportioning to meet con- crete strength requirements, a conscious effort needs to be made to design and detail pavements and bridges for long- term durability (Sommerville 1986). A more holistic ap- proach is necessary for designing concrete structures based on service-life considerations. This chapter addresses envi- ronmental and structural loading considerations, as well as their interaction, and design and construction influences on the service life of structures. 2.2Environmental considerations Design of reinforced concrete structures to ensure adequate durability is a complicated process. Service life depends on structural design and detailing, mixture proportioning, concrete production and placement, construction methods, and mainte- nance. Also, changes in use, loading, and environment are im- portant. Because water or some other fluid is involved in almost every form of concrete degradation, concrete perme- ability is important. The process of chemical and physical deterioration of con- crete with time or reduction in durability is generally depen- dent on the presence and transport of deleterious substances through concrete,* and the magnitude, frequency, and effect of applied loads. Figure 2.1 (CEB 1992) presents the relationship between the concepts of concrete durability and performance. The figure shows that the combined transportation of heat, moisture, and chemicals, both within the concrete and in ex- change with the surrounding environment, and the parameters controlling the transport mechanisms constitute the principal elements of durability. The rate, extent, and effect of fluid transport are largely dependent on the concrete pore structure (size and distribution), presence of cracks, and microclimate at the concrete surface. The primary mode of transport in un- cracked concrete is through the bulk cement paste pore struc- ture and the transition zone (interfacial region between the particles of coarse aggregate and hydrated cement paste). The physical-chemical phenomena associated with fluid move- ment through porous solids is controlled by the solids perme- ability (penetrability). Although the coefficient of permeability of concrete depends primarily on the w/cm and maximum aggregate size, it is also influenced by age, consol- idation, curing temperature, drying, and the addition of chem- ical or mineral admixtures. Concrete is generally more permeable than cement paste due to the pr