ACI 308R-2016 Guide to External Curing of Concrete.pdf

1、Guide to External Curing of ConcreteReported by ACI Committee 308ACI 308R-16First PrintingMay 2016ISBN: 978-1-942727-87-3Guide to External Curing of ConcreteCopyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material may not be reproduced or copied, in whol

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10、r information: ACI documents are available in print, by download, on CD-ROM, through electronic subscription, or reprint and may be obtained by contacting ACI.Most ACI standards and committee reports are gathered together in the annually revised ACI Manual of Concrete Practice (MCP).American Concret

11、e Institute38800 Country Club DriveFarmington Hills, MI 48331Phone: +1.248.848.3700Fax: +1.248.848.3701www.concrete.orgThis guide reviews and describes practices, procedures, materials, and monitoring methods for the external curing of concrete and provides guidance for specifying curing procedures.

12、 Current curing techniques are presented and commonly accep ted methods, proce-dures, and materials are described. Methods are given for curing structures and buildings, pavements and other slabs-on-ground, and for mass concrete. Curing methods for several specific catego-ries of cement-based produc

13、ts are discussed in this document.The materials, processes, quality control measures, and inspec-tions described in this document should be tested, monitored, or performed as applicable only by individuals holding the appro-priate ACI certifications or equivalent.Keywords: cold weather construction;

14、 curing compound; hot weather construction; mass concrete; reinforced concrete; sealer; shotcrete; slabs-on-ground.CONTENTSCHAPTER 1INTRODUCTION, p. 21.1Introduction, p. 21.2Curing, p. 21.3Curing and hydration of portland cement, p. 21.4Deliberate curing procedures, p. 51.5Curing-affected zone, p. 1

15、01.6Concrete properties influenced by curing, p. 111.7Effects of elevated temperature, p. 121.8Sustainability, p. 14CHAPTER 2DEFINITIONS, p. 15CHAPTER 3CURING METHODS AND MATERIALS, p. 153.1Scope, p. 153.2Use of water for curing concrete, p. 153.3Initial curing methods, p. 153.4Final curing measures

16、, p. 163.5Termination of curing measures, p. 203.6Cold-weather protection and curing, p. 203.7Hot-weather protection and curing, p. 21David M. Suchorski, Chair Erik Holck, Vice Chair Lawrence Homer Taber*, SecretaryACI 308R-16Guide to External Curing of ConcreteReported by ACI Committee 308ACI Commi

17、ttee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document 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

18、responsibility for the application of the material it contains. 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 document

19、s. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.ACI 308R-16 supersedes ACI 308R-01 and was adopted and published May 2016.Copyright 2016, American

20、 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 knowle

21、dge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.Voting MembersDale P. BentzDianne CareyJennifer K. CrismanJonathan E. DongellMichael FaubelDale FisherSidney FreedmanMichael G. HernandezJohn C. HukeyCecil L. JonesFrank A. KozeliskiRonald L. K

22、ozikowski Jr.Mauricio LopezDarryl ManuelSteven F. McDonaldMike MurrayJohn W. RobertsPhilip A. SmithRichard E. Van HornJody R. WallDaniel WebberJohn B. Wojakowski*Chair of document subcommittee.Consulting MembersRalph C. BrunoJames N. Cornell IIBen E. EdwardsJerome H. FordR. Doug Hooton David E. Hoyt

23、13.8Accelerated curing, p. 213.9Minimum curing requirements, p. 213.10Temperature limits during curing, p. 22CHAPTER 4CURING FOR DIFFERENT TYPES OF CONSTRUCTION, p. 234.1Pavements and other slabs on ground, p. 234.2Buildings, bridges, and other structures, p. 234.3Mass concrete, p. 244.4Curing color

24、ed concrete floors and slabs, p. 254.5Specialty constructions, p. 25CHAPTER 5MONITORING CURING AND CURING EFFECTIVENESS, p. 255.1General, p. 255.2Evaluating environmental conditions, p. 255.3Means to verify application of curing, p. 285.4Impact of curing procedures on immediate environ-ment, p. 285.

25、5Impact of curing procedures on moisture and temperature within concrete, p. 295.6Maturity method, p. 295.7Assessing curing effectiveness, p. 29CHAPTER 6REFERENCES, p. 30Authored references, p. 31CHAPTER 1INTRODUCTION1.1IntroductionThe principles and practices of external curing are appli-cable to a

26、ll types of concrete construction. This document does not fully address curing for specialty concrete and special construction techniques (refer to 4.5), nor does it fully address internally cured concrete. For additional information on internally cured concrete using preconditioned absorp-tive ligh

27、tweight aggregates, refer to ACI (308-213)R. Curing measures, in general, are specified in ACI 308.1. Curing measures directed toward the maintenance of satisfactory concrete temperature under specific environmental condi-tions are addressed in greater detail in ACI 305R, ACI 306R, ACI 301, and ACI

28、318.The fundamental principles of external curing remain the same as in the past; however, new research and methods of curing are presented herein. Topics such as internal curing, curing at elevated temperatures, sustainability, curing of moisture-sensitive flooring, sensors for mass concrete curing

29、, and new curing monitoring techniques have been added or enhanced in this document.1.2CuringCuring is an action taken to maintain moisture and temperature conditions in a freshly placed cementitious mixture to allow hydraulic cement hydration and, if pozzo-lans are used, pozzolanic reactions to occ

30、ur so that the potential properties of the mixture may develop. A mixture is properly proportioned and adequately cured when the properties of the in-place concrete equal or exceed the design properties of the concrete. The curing period begins at placing and continues until the desired concrete pro

31、per-ties have developed. The objectives of curing are to prevent the loss of moisture from concrete and maintain a favorable concrete temperature for a sufficient period of time. Proper curing allows the cementitious material within the concrete to properly hydrate. Hydration is the chemical reactio

32、n that leads to changes that take place when portland cement reacts with water. Both at depth and near the surface, curing has a significant influence on the properties of hardened concrete, such as strength, permeability, abrasion resistance, volume stability, propensity for early-age cracking, and

33、 resistance to freezing and thawing and deicing chemicals.The term “curing” has also been used in a more general sense to describe the process by which hydraulic cementi-tious concrete matures and develops hardened proper-ties over time as a result of the continued hydration of the cementitious mate

34、rials in the presence of sufficient water and heat. While all concrete hydrates to varying levels of matu-rity with time, the rate and extent to which this development takes place depends on the natural environment surrounding the concrete and on the measures taken to modify this envi-ronment by lim

35、iting the loss of water, heat, or both, from the concrete; externally providing moisture and heat; or incor-porating special materials in the mixture design.1.3Curing and hydration of portland cement1.3.1 Hydration of portland cementPortland-cement concrete is a composite material in which aggregate

36、s are bound in a porous matrix of hardened cement paste. At the microscale, the hardened paste is held together by bonds that develop between the products of the reaction of cement with water and mechanically interlocks the aggregate. Similar products are formed from the reactions between cement, ot

37、her cementitious materials, and water.The cement-water reaction includes both chemical and physical processes that are collectively known as the hydra-tion of the cement (Taylor 1997). As the hydration process continues, the strength of the interparticle bonding increases, Fig. 1.3.1aUnhydrated part

38、icles of portland cementmagnification 2000 (Soroos 1994).American Concrete Institute Copyrighted Material www.concrete.org2 GUIDE TO EXTERNAL CURING OF CONCRETE (ACI 308R-16)and the interparticle porosity decreases. Figure 1.3.1a shows particles of unhydrated portland cement observed through a scann

39、ing electron microscope. In contrast, Fig. 1.3.1b shows the development of hydration products and interparticle bonding in partially hydrated cement. Figure 1.3.1c shows a single particle of partially hydrated portland cement. The surface of the particle is covered with the products of hydra-tion in

40、 a densely packed, randomly oriented mass known as the cement gel. In hydration, water is required for the chemical formation of the gel products and for filling the micropores that develop between and within the gel prod-ucts as they are being formed (Powers and Brownyard 1947; Powers 1948). The ra

41、te and extent of hydration depend on the availability of water. Parrott and Killoh (1984) found that as cement paste comes to equilibrium with air at succes-sively lower relative humidity (RH), the rate of cement hydration dropped significantly. Cement in equilibrium with air at 80 percent RH hydrat

42、ed at only 10 percent the rate of companion specimens in a 100 percent RH curing environ-ment. Snyder and Bentz (2004) observed that exposure to 90 percent or less RH is sufficient to suspend hydration at early ages. Therefore, curing procedures ensure that sufficient water is available to the cemen

43、t to sustain the rate and degree of hydration necessary to achieve the desired concrete prop-erties at the required time.The water consumed in the formation of the gel products is known as the chemically bound water, or hydrate water, and its amount varies with cement composition and the condi-tions

44、 of hydration. A mass fraction of between 0.21 to 0.28 of chemically bound water is required to completely hydrate a unit mass of cement depending on its phase composition (Powers and Brownyard 1947; Copeland et al. 1960; Mills 1966). An average value is approximately 0.25 (Kosmatka and Panarese 198

45、8; Powers 1948). Coefficients for chemi-cally bound water for the various clinker mineral phases are available in Molina (1992) and range between 0.21 for dical-cium silicate to 0.4 for tricalcium aluminate.As seen in Fig. 1.3.1b and 1.3.1c, the gel that surrounds the hydrated cement particles is a

46、porous, randomly oriented mass. Besides the hydrate water, additional water is adsorbed onto the surfaces and in the interlayer spaces of the layered gel structure during the hydration process. This is known as physically bound water, or gel water. Gel water is typically present in all concrete in s

47、ervice, even under dry ambient conditions, as its removal at atmospheric pres-sure requires heating the hardened cement paste to 221F (105C) (Neville 1996). The amount of gel water adsorbed onto the expanding surface of the hydration products and into the gel pores is approximately equal to the amou

48、nt that is chemically combined with the cement (Powers 1948). The amount of gel water has been calculated more precisely to be a mass fraction of approximately 0.20 for a unit mass of cement (Powers 1948; Powers and Brownyard 1947; Cook 1992; Taylor 1997).Both the hydrate water and physically adsorb

49、ed gel water are distinct in the microstructure of the hardened cement paste, yet both are required concurrently as portland cement hydrates. Continued hydration of the cement is possible only when sufficient water is available both for the chemical reactions and for the filling of the gel pores being formed (Neville 1996). The amount of water consumed in the hydra-tion of portland cement is the sum of the water incorporated physically onto the gel surfaces plus the water incorporated chemically into the hydrate products themselves (Nevill