1、ACI (308-213)R-13Report on Internally Cured Concrete Using Prewetted Absorptive Lightweight Aggregate Reported by ACI Committee 308 and ACI Committee 213First PrintingJune 2013Report on Internally Cured Concrete Using Prewetted Absorptive Lightweight Aggregate Copyright by the American Concrete Inst
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11、hered together in the annually revised ACI Manual of Concrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701www.concrete.orgISBN-13: 978-0-87031-821-4ISBN: 0-87031-821-7American Concrete InstituteAdvancing concre
12、te knowledgeThis report introduces the concepts of and describes the process benefit and applications for using prewetted lightweight aggre-gate to increase cement hydration in internally cured concrete. It also describes mixture proportioning and absorptive material selection and discusses the bene
13、fits relating to sustainability. The materials, processes, quality control measures, and inspections described should be tested, monitored, or performed as applicable only by individuals holding the appropriate ACI certifications or equivalent.Keywords: absorption; curing; desorption; durability; hi
14、gh-performance concrete; hydration; internal curing; internally cured concrete; lightweight aggregate; outside curing; permeability; saturated-surface-dry; shrinkage; strength; supplementary cementitious materials; water movement.ContentsCHAPteR 1IntRoDUCtIon AnD sCoPe, p. 21.1Introduction, p. 21.2S
15、cope, p. 2CHAPteR 2notAtIon AnD DeFInItIons, p. 22.1Notation, p. 22.2Definitions, p. 2CHAPteR 3PRoCess, p. 23.1General, p. 23.2Justification, p. 33.3Water movement, p. 33.4Autogenous shrinkage and self-desiccation, p. 33.5Mechanism of internal curing, p. 33.6Water movement during hydration observed
16、using X-ray microtomography, p. 4CHAPteR 4InteRnALLY CUReD ConCRete (ICC): eFFeCts, BeneFIts, AnD APPLICAtIons, p. 44.1Early-age shrinkage reduction, p. 44.2Crack reduction, p. 54.3Compressive strength, p. 54.4Overdosing prewetted lightweight aggregate (PLA), p. 64.5Flexural strength, p. 64.6Mitigat
17、ion of warping and dimensional stability, p. 64.7Modulus of elasticity, p. 64.8Permeability and resistance to deicing chemicals, p. 74.9Creep, p. 74.10Durability, p. 8ACI (308-213)R-13Report on Internally Cured Concrete Using Prewetted Absorptive Lightweight AggregateReported by ACI Committee 308 an
18、d ACI Committee 213David M. Suchorski, Chair John C. Hukey, SecretaryACI Committee 308 rosterDale P. BentzDianne CareyJennifer K. CrismanJonathan E. DongellMichael FaubelDale FisherSidney FreedmanMichael G. HernandezErik HolckCecil L. JonesFrank A. KozeliskiRonald J. KozikowskiMauricio LopezDarryl M
19、anuelSteve F. McDonaldMichael E. MurrayJohn W. RobertsPhilip A. SmithLawrence Homer TaberRichard E. Van HornJody R. WallDaniel WebberJohn B. WojakowskiACI Committee 308 Consulting Members rosterRalph C. BrunoJames N. Cornell IIBen E. EdwardsJerome H. FordR. Doug HootonDavid E. HoytJames A. LeeW. Cal
20、vin McCallWilliam S. Phelan1ACI Committee 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
21、 recommendations and who will accept 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 s
22、hall 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 documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.ACI (308-213)R-13 was adopted and published June 2013.Copyrig
23、ht 2013, 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
24、use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.CHAPteR 5BAtCHInG PRoCeDURes, p. 85.1Choice of absorptive material, p. 85.2Mixture proportioning using absorptive materials, p. 85.3Prewetting lightweight aggregate, p. 105.4Co
25、ncrete batching. mixing, transporting, placing, and finishing, p. 10CHAPteR 6sUstAInABLe ConCRete ConstRUCtIon UsInG InteRnALL CUReD ConCRete (ICC), p. 11CHAPteR 7ReFeRenCes, p. 11CHAPteR 1IntRoDUCtIon AnD sCoPe1.1IntroductionPortland-cement concrete, including mixtures with supplementary cementitio
26、us materials, does not typically develop its durability, strength, and mechanical characteris-tics without adequate curing. This report on internally cured concrete (ICC) does not presume to change the require-ment for water retention at the curing-affected zone on the concrete surface. The curing m
27、ethods listed in ACI 308R-01 should be consulted for appropriate methods to prevent or mitigate moisture loss from the concrete surface.Test trial batches should be used during initial mixture proportioning to determine and verify those concrete prop-erties required for each project.Internally cured
28、 concrete uses prewetted absorptive mate-rials that contain moisture. The absorbed moisture is released as the internal humidity of the concrete drops below 100 percent to enhance and maximize the hydration of cement.High-performance concrete typically has a low w/cm that may not supply enough water
29、 to hydrate all of the cement. Due to the reduction in permeability of high-performance concrete, even in the first 2 to 3 days, exterior water curing is limited in its ability to supply in-depth hydration to the cement as the products of hydration fill in and disconnect the capillary pore network (
30、Powers et al. 1959). In this case, the beneficial effect of external water curing is limited to the concrete surface. As a result, external water cannot penetrate the interior of the concrete to maintain a saturated capillary pore system thereby avoiding self-desiccation. One solution is to replace
31、a portion of the normalweight aggregate with absorbent materials to desorb water to the hydrating cement. The principal improvements of supplying internal water are the maintenance of a saturated cement paste, which leads to greater hydration of the cement and more complete pozzo-lanic reactions.Cha
32、racteristics of high-performance concrete that may be improved by increased hydration from internally absorbed moisture include resistance to early-age cracking; higher strength; decreased permeability; decreased warping; dimen-sional stability; resistance to freezing-and-thawing damage, deicing che
33、micals, and chemical attacks; and creep.In the past 50 years, portland cement has become finer with higher contents of tricalcium silicate and alkalis (Bentz et al. 2008). These changes have led to generally faster hydrating cements that produce much of their strength in only a few days. Concretes m
34、ade with these cements, however, can be more prone to early-age cracking due to their increased heat of hydration and significantly increased autogenous strains and stresses that can develop when self-desiccation occurs.1.2scopeInternally cured concrete uses absorptive materials in the mixture that
35、supplement the standard curing practices by supplying moisture to the interior of the concrete (ACI 308R-01). This process adds moisture without affecting the w/cm. The moisture is desorbed for internal moisture augmentation at the time needed to further hydrate the cement. This water addition can b
36、e achieved using several materials (Jensen and Lura 2006; Kovler and Jensen 2007), including prewetted lightweight aggregate, super-absorbent particles, wood fibers, and absorbent limestone aggregate. This report will focus primarily on the use of prewetted lightweight aggregate.CHAPteR 2notAtIon An
37、D DeFInItIons2.1notationCf= cement factor (content) for concrete mixture, lb/yd3(kg/m3)CS = chemical shrinkage of cement (mass of water/mass of cement)MLWA= mass of (dry) lightweight aggregate needed per unit volume of concrete, lb/yd3(kg/m3)S = degree of saturation of aggregate (0 to 1, measured ab
38、sorption percentage divided by the absorption percentage at which desorption was measured)wic/c = the ratio of the water supplied by internal curing to the cement in the concrete mixture on a mass basisamax= maximum expected degree of hydration of cement (0 to 1); for ordinary portland cement, the m
39、aximum expected degree of hydration of cement can be assumed to be 1 for w/cm 0.36 and the value of (w/cm) divided by 0.36 for w/cm 0.42 can benefit from the use of PLFA. A substitution of lightweight fine aggregate in the amount of 100 lb/yd3(59 kg/m3), in a mixture at a w/cm of 0.43, has been show
40、n to increase the modulus of elasticity by approximately 10 percent. Note that, in some cases, lower values of the modulus of elasticity might be preferred because they generate lower tensile stresses associated with restrained shrinkage, thus reducing the risk of cracking. The designer should consi
41、der variations in the modulus of elasticity when addressing changes in tensile and compressive strength.4.8Permeability and resistance to deicing chemicalsDense, crack-free, low-permeability cement paste offers substantial resistance to deicing chemicals. Use of PLA may contribute to minimizing the
42、transport of deleterious substances from the environment into the concrete, with fewer cracks and lower cement paste permeability. Conventionally, to produce concrete with enhanced durability, low-w/cm mixtures, supplementary cementitious materials, or both, have been used with positive results. Pre
43、wetted absorptive materials have also been shown to have a positive influence. For example, a PLFA substitution of only 100 lb/yd3(59 kg/m3), which by volume is approximately 11 percent, can reduce the rapid chloride permeability test (RCPT) coulomb number by more than 25 percent (Hoff 2003).In anot
44、her study, chloride permeability of different high-performance concrete mixtures with and without PLA was investigated for more than 3 years (Thomas 2006). At 28 days, the main difference in chloride permeability among the mixtures was given by the w/cm; there were not significant differences betwee
45、n the lightweight and normal-weight aggregate mixtures. After 1 and 3 years, however, the permeability of the lightweight aggregate mixtures was approximately 45 and 30 percent, respectively, of those with normalweight aggregate. The difference in performance was attributed to the increased hydratio
46、n of the cement supplied by the PLA.4.9CreepBased on 4.1 through 4.8, the following statements can be made about the effect of partial or total replacement of normalweight aggregate by prewetted absorptive materials on creep (Lopez 2005). Using PLA can:a) Increase the compressive strength of concret
47、e; lower creep can be expected;b) Increase the internal relative humidity of concrete. Several of the proposed creep mechanisms state that creep is caused by water migration within the concrete and from concrete to the environment. If higher internal relative humidity is main-tained, a reduction in
48、creep can be expected. Depending on the creep mechanisms, the reduction will be in the drying creep portion or in both the drying and the basic creep portions;c) Decrease the permeability of cement paste. A reduced permeability reduces water loss from the concrete to the environment, which reduces d
49、rying creep;d) Increase the degree of hydration. An increase in hydration reduces the amount of unhydrated cement in the concrete. Unhydrated cement contributes to the aggregate restraining effect on creep and shrinkage (Neville et al. 1983). An increase in creep may be expected due to the rela-tive reduction in this restraining phase.Therefore, statements a), b), and c) suggest a reduction on creep whereas statement d) suggests the oppositean increase in creep. A reduction in creep, however, has been observed overall. For example, recent research
