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1、ACI 308R-01 became effective August 14, 2001. Copyright 2001, 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,
2、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, designing, ex
3、ecuting, 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 re- sponsibility for the application of the material it contains. The American Concrete Ins
4、titute disclaims any and all re- sponsibility 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 con- tract documents. If items found in this document are de- sired by the Architect/Engineer to be a p
5、art of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer. 308R-1 Guide to Curing Concrete ACI 308R-01 The term “curing” is frequently used to describe the process by which hydraulic-cement concrete matures and develops hardened propertie
6、s over time as a result of the continued hydration of the cement in the presence of sufficient water and heat. While all concrete cures to varying levels of maturity with time, the rate at which this development takes place depends on the natural environment surrounding the concrete, and the measure
7、s taken to modify this environment by limiting the loss of water, heat, or both, from the concrete, or by externally providing moisture and heat. The word “curing” is also used to describe the action taken to maintain moisture and temperature conditions in a freshly placed cementitious mixture to al
8、low hydraulic-cement hydration and, if applicable, pozzolanic reactions to occur so that the potential properties of the mixture may develop. Current curing techniques are presented; commonly accepted methods, procedures, and materials are described. Methods are given for curing pavements and other
9、slabs on ground, for structures and buildings, and for mass concrete. Curing methods for several specific categories of cement-based products are discussed in this document. Curing measures, in general, are specified in ACI 308.1. Curing measures directed toward the maintenance of satis- factory con
10、crete temperature under specific environmental conditions are addressed in greater detail by Committees 305 and 306 on Hot and Cold Weather Concreting, respectively, and by ACI Committees 301 and 318. Keywords: cold weather; concrete; curing; curing compound; hot weather con- struction; mass concret
11、e; reinforced concrete; sealer; shotcrete; slab-on-ground. CONTENTS Chapter 1Introduction, p. 308R-2 1.1Introduction 1.2Definition of curing 1.3Curing and the hydration of portland cement 1.3.1Hydration of portland cement 1.3.2The need for curing 1.3.3Moisture control and temperature control 1.4When
12、 deliberate curing procedures are required 1.4.1Natural conditions 1.4.2Sequence and timing of curing steps for unformed surfaces 1.4.3When curing is required for formed surfaces 1.4.4When curing is required: cold and hot weather 1.4.5Duration of curing 1.5The curing-affected zone 1.6Concrete proper
13、ties influenced by curing Reported by ACI Committee 308 Don BrognaGene D. Hill, Jr. Aimee Pergalsky Joseph Cabrera Edward P. HolubWilliam S. Phelan James N. Cornell IIR. Doug Hooton Robert E. Price Ronald L. Dilly Kenneth C. Hover* Larry R. Roberts Jonathan E. DongellJohn C. HukeyPhillip Smith Ben E
14、. EdwardsFrank A. KozeliskiLuke M. Snell Derek FirthJames A. LeeJoel Tucker Jerome H. FordDaryl ManuelPatrick M. Watson Sid FreedmanBryant MatherJohn B. Wojakowski Gilbert J. HaddadCalvin W. McCall Samuel B. HelmsH. Celik Ozyildirim Steven H. Gebler Chairman Cecil L. Jones Secretary * Chair of docum
15、ent subcommittee Deceased 308R-2ACI COMMITTEE REPORT Chapter 2Curing methods and materials, p. 308R-12 2.1Scope 2.2Use of water for curing concrete 2.3Initial curing methods 2.3.1Fogging 2.3.2Liquid-applied evaporation reducers 2.4Final curing measures 2.4.1Final curing measures based on the applica
16、tion of water 2.4.2Final curing methods based on moisture retention 2.5Termination of curing measures 2.6Cold-weather protection and curing 2.6.1Protection against rapid drying in cold weather 2.6.2Protection against frost damage 2.6.3Rate of concrete strength development in cold weather 2.6.4Remova
17、l of cold-weather protection 2.7Hot-weather protection and curing 2.8Accelerated curing 2.9Minimum curing requirements 2.9.1General 2.9.2Factors influencing required duration of curing Chapter 3Curing for different types of construction, p. 308R-19 3.1Pavements and other slabs on ground 3.1.1General
18、 3.1.2Curing procedures 3.1.3Duration of curing 3.2Buildings, bridges, and other structures 3.2.1General 3.2.2Curing procedures 3.2.3Duration of curing 3.3Mass concrete 3.3.1General 3.3.2Methods and duration of curing 3.3.3Form removal and curing formed surfaces 3.4Curing colored concrete floors and
19、 slabs 3.5Other constructions Chapter 4Monitoring curing and curing effectiveness, p. 308R-22 4.1General 4.2Evaluating the environmental conditions in which the concrete is placed 4.2.1Estimating evaporation rate 4.3Means to verify the application of curing 4.4Quantitative measures of the impact of
20、curing proce- dures on the immediate environment 4.5Quantitative measures of the impact of curing proce- dures on moisture and temperature 4.6Maturity method 4.7Measuring physical properties of concrete affected by temperature and moisture control to assess curing effectiveness Chapter 5References,
21、p. 308R-26 5.1Referenced standards and reports 5.2Cited references CHAPTER 1INTRODUCTION 1.1Introduction This guide reviews and describes the state of the art for curing concrete and provides guidance for specifying curing procedures. Curing practices, procedures, materials, and monitoring methods a
22、re described. Although the principles and practices of curing discussed in this guide are applica- ble to all types of concrete construction, this document does not specifically address high-temperature or high-pressure accelerated curing. 1.2Definition of curing The term “curing” is frequently used
23、 to describe the process by which hydraulic-cement concrete matures and develops hardened properties over time as a result of the continued hy- dration of the cement in the presence of sufficient water and heat. While all concrete cures to varying levels of maturity with time, the rate at which this
24、 development takes place de- pends on the natural environment surrounding the concrete and on the measures taken to modify this environment by limiting the loss of water, heat, or both, from the concrete, or by externally providing moisture and heat. The term “cur- ing” is also used to describe the
25、action taken to maintain moisture and temperature conditions in a freshly placed ce- mentitious mixture to allow hydraulic-cement hydration and, if applicable, pozzolanic reactions to occur so that the poten- tial properties of the mixture may develop (ACI 116R and ASTM C 125). (A mixture is properl
26、y proportioned and ad- equately cured when the potential properties of the mixture are achieved and equal or exceed the desired properties of the concrete.) The curing period is defined as the time period beginning at placing, through consolidation and finishing, and extending until the desired conc
27、rete properties have de- veloped. The objectives of curing are to prevent the loss of moisture from concrete and, when needed, supply additional moisture and maintain a favorable concrete temperature for a sufficient period of time. Proper curing allows the cemen- titious material within the concret
28、e to properly hydrate. Hy- dration refers to the chemical and physical changes that take place when portland cement reacts with water or participates in a pozzolanic reaction. Both at depth and near the surface, curing has a significant influence on the properties of hard- ened concrete, such as str
29、ength, permeability, abrasion resis- tance, volume stability, and resistance to freezing and thawing, and deicing chemicals. 1.3Curing and the hydration of portland cement 1.3.1 Hydration of portland cementPortland cement concrete is a composite material in which aggregates are bound in a porous mat
30、rix 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. Similar products are formed from the reactions between cement, water, and other cementitious materials. The cement-water reaction incl
31、udes both chemical and physical processes that are collectively known as the hydra- tion of the cement (Taylor 1997).1 As the hydration process continues, the strength of the interparticle bonding increases, GUIDE TO CURING CONCRETE308R-3 and the interparticle porosity decreases. Figure 1.1 shows pa
32、rticles of unhydrated portland cement observed through a scanning electron microscope. In contrast to Fig. 1.1, Fig. 1.2 shows the development of hydration products and interparticle bonding in partially hydrated cement. Figure 1.3 shows a single particle of partially hydrated portland cement. The s
33、urface of the particle is covered with the products of hydra- tion in 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 the gel products as they are bein
34、g formed (Powers and Brownyard 1947; Powers 1948). The rate 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 successively lower relative humidity (RH), the rate of cement hydration dropped signif- icant
35、ly. Cement in equilibrium with air at 80% RH hydrated at only 10% the rate as companion specimens in a 100% RH curing environment. Therefore, curing procedures ensure that sufficient water is available to the cement to sustain the rate and degree of hydration necessary to achieve the desired concret
36、e properties 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 con- ditions of hydration. A mass fraction of between 0.21 to 0.28 of chemically bound water is r
37、equired to hydrate a unit mass of cement (Powers and Brownyard 1947; Copeland, Kantro, and Verbeck 1960; Mills 1966). An average value is approx- imately 0.25 (Kosmatka and Panarese 1988; Powers 1948). As seen in Fig. 1.2 and 1.3, the gel that surrounds the hy- drated cement particles is a porous, r
38、andomly 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 service, e
39、ven under dry ambient conditions, as its removal at atmospheric pressure requires heating the hardened cement paste to 105 C (221 F) (Neville 1996). The amount of gel water adsorbed onto the expanding surface of the hydration products and into the gel pores is “about equal to the amount that is (che
40、mically) combined with the cement” (Powers 1948). The amount of gel water has been calculated more precisely to be a mass fraction of about 0.20 of the mass of hydrated cement (Powers 1948; Powers and Brownyard 1947; Cook 1992; Taylor 1997). Both the hydrate water and physically adsorbed gel water a
41、re distinct in the microstructure of the hardened cement paste, yet both are required concurrently as portland cement cures. Neville (1996) writes that continued hydration of the cement is possible “only when sufficient water is available both for the chemical reactions and for the filling of the ge
42、l pores being formed.” The amount of water consumed in the hy- dration of portland cement is the sum of the water incorporated physically onto the gel surfaces plus the water incorporated Fig 1.1Unhydrated particles of portland cementmagni- fication 2000 (photo credit Fig. 1.1-1.3, Eric Soroos). Fig
43、 1.2Multiple particles of partially hydrated portland cementmagnification 4000. Fig 1.3Close-up of a single particle of hydrated cement magnification 11,000. 1 “In cement chemistry the term hydration denotes the totality of the changes that occur when an anhydrous cement, or one of its constituent p
44、hases, is mixed with water” (Taylor 1997). 308R-4ACI COMMITTEE REPORT chemically into the hydrate products themselves. (Neville 1996; Powers and Brownyard 1947; Mindess and Young 1981; Taylor 1997.) Because hydration can proceed only in saturated space, the total water requirement for cement hy- dra
45、tion is “about 0.44 g of water per gram of cement,2 plus the curing water that must be added to keep (the capillary pores of) the paste saturated” (Powers 1948). As long as suf- ficient water is available to form the hydration products, fill the interlayer gel spaces and ensure that the reaction sit
46、es re- main water-filled, the cement will continue to hydrate until all of the available pore space is filled with hydration prod- ucts or until all of the cement has hydrated. The key to the development of both strength and durability in concrete, however, is not so much the degree to which the cem
47、ent has hydrated but the degree to which the pores be- tween the cement particles have been filled with hydration products (Powers and Brownyard 1947, Powers 1948). This is evident from the microperspective seen in Fig. 1.2 and from the macrobehavior illustrated in Fig. 1.4 and 1.5, in which it can
48、be seen that the continued pore-filling accompa- nying sustained moist-curing leads to a denser, stronger, less-permeable concrete. The degree to which the pores are filled, however, depends not only on the degree to which the cement has hydrated, but also on the initial volume of pores in the paste
49、, thus the combined importance of the availability of curing water and the initial water-cement ratio (w/c). The pore volume between cement particles seen in Fig. 1.2 (darker areas of the photograph) was originally occupied in the fresh paste by the mixing water. As the volume of mixing water decreases relative to the volume of the cement, the ini- tial porosity of the paste decreases as well. For this reason, pastes with lower w/c have a lower initial porosity, requiring a reduced degree of hydration to achieve