ACI 364.5T-2010 Importance of Modulus of Elasticity in Surface Repair Materials.pdf

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1、1Importance of modulus of elastIcIty In surface repaIr materIalsKeywords: compatibility; cracking; creep; elastic modulus; load-carrying; repair; strain; stress; tension.QuestionHow important is the modulus of elasticity as a property of surface repair materials?AnswerThe modulus of elasticity is a

2、very important property. For structural repairs, the elastic modulus should be similar to that of the substrate concrete, whereas in the case of nonstructural repairs, a lower elastic modulus may be beneficial.Discussionnullncrete repairs may be broadly classified as structural nulload-carryingnulla

3、nd nonstructural nullrotective andnullr cosmeticnull The load-carrying capacity and stress distribution must be considered in the case of structural repairs where replacement of deteriorated load-bearing concrete is renullired. The repair material may be subnullcted to tension, compression, andnullr

4、 shear forces. nullet, even with enullivalent or higher modulus repair material, perma -nent loads will not be shared unless the enullsting member is unloaded prior to repair. nullfferent approaches may be renullired for the design and analysis of such repairs. null should be emphasinulld, however,

5、that a structural repair must also protect the underlying concrete and reinforcing steel from deterioration and corrosion. The modulus of elasticity is a measure of the stiffness of a material.nullnullnullmaterial with a higher modulus of elasticity is more rigid than a lower modulus material, which

6、 is more nullnullble. The modulus of elasticity is the constant of proportionality between the applied stress and the strain within the linear stress-strain range of the material. null corresponds to the slope of the straight line portion of a graph of stressnullversus strain.nullThe term elasticity

7、 refers to the reversible character of the dimensional change nulls a spring would recover if compressed or stretchednull The modulus of elasticity of repair materials is typically measured using nullTnullnullnull or nullTnullnullnull test methods. nullditional information regarding the modulus of e

8、lasticity testing and its significance is included in nullnullnullnullnull.The modulus of elasticity of a repair material with respect to that of the substrate partially determines the relative loads resisted by the new repair and the remaining substrate materials. nulle important consideration for

9、proper material selection is dimensional compatibility between the substrate and repair.nullnullnull a material of lower modulus than the substrate is selected, the repair is unable to carry as much load as the original concrete, but it is helpful in reducing stresses induced by volume changes in th

10、e material or surrounding concrete. nullnversely, if a higher modulus material than the substrate is selected, not only will the repair carry more load relative to the substrate, but the thermal- and shrinkage-induced stresses may also be concentrated in the repair materialnull situation that can le

11、ad to cracking or debonding of the repair.To have good resistance to cracking nullhigh tensile strain capacitynull, the repair material for protective repairs should be nullenulltensible.null nullt should have a low modulus of elasticity, low shrinkage values, and high creep. nullt should be remembe

12、red, however, when developing such enulltensible materials for protective repairs, that some factors that reduce shrinkage, such as relatively low water-cement ratio nullwnullcnull or stiffer aggregates, have been observed to decrease creep or relanullation and increase the modulus of elasticity at

13、the same time, thus offering little or no benefit to the tensile strain capacity nullTnullnullnull. nulln addition, good bond strength of the repair material to the base concrete is critical to the success of the repair; however, increasing the bond strength of repair materials typically increases t

14、heir modulus of elasticity and decreases their Tnullnull. nullften, a compromise must be reached between high bond strength and low modulus of elasticity.nullmphasis should be placed, therefore, on modifying these parameters that produce a net increase in Tnullnull. nullne such potentially favorable

15、 parameter is the aggregate fraction. nullontrary to what is generally nullnullress is intensity of force per unit area nullsi nullnullnull.nullnullrain is displacement per unit length nulln.nulln. nullmnullmnull.ACI 364.5T-10TechNoteAmerican Concrete Institute Copyrighted Materialnullnull.concrete.

16、org2 IMPORTANCE OF MODULUS OF ELASTICITY IN SURFACE REPAIR MATERIALS (ACI 364.5T-10)reported in the case of compressive creep, it has been observed that increasing the amount of aggregate in the repair material causes the tensile creep of the repair concrete to increase.nullnullecause shrinkage is r

17、educed when the aggregate content is increased, a proper repair minullture for cosmeticnullprotective repairs should have the lowest possible cement paste content that is compatible with serviceability and the placement renulluirements. nullepair material with well-detailed reinforcement that is pin

18、ned into the enullisting substrate will distribute cracks and prevent localinulled wide cracks.nullhen materials with differing moduli act monolithically, the difference in stiffness may lead to distress under enullternally applied loads, depending on the induced stress field with respect to the str

19、ucture layout. For enullmple, when the enullernal load is essentially perpendicular to the bond line nulleft view in Fig. null, as in the case of pavement overlay on a highly rigid foundation, a difference in modulus of elasticity between the repair material and the substrate does not significantly

20、affect the overall mechanical behavior of the structure. nullnversely, in repairs where the service load stresses are parallel to the bond line, the deformation of the lower modulus material causes the load to be transferred to the higher modulus material, which may then become overstressed and frac

21、ture nullight view in Fig. null.nullhen the moduli of the repair and of the substrate differ significantly, environmental loads nullthat is, drying shrinkage and thermal deformationsnull can also generate internal stresses such that cracking and, ultimately, debonding could occur. nulloreover, shrin

22、kage or thermal enullpansion and contraction can cause distress if the modulus of the repair material is too high to permit deformation without enullcessive stress at the bond line. nullt is important to consider shrinkage compatibility and thermal compatibility nullcoefficient of thermal enullpansi

23、onnull when selecting repair materials. nullefer to nullnullnull nullnullnull.nullnull for information regarding these parameters. nullore compliant nulllower modulusnull repair material will reduce stresses due to shrinkage and thermal incompatibility, but may not be acceptable for structural repai

24、rs.Summarynullrface repairs must be dimensionally and mechanically compatible with the enullsting concrete substrate to miniminull cracking and ensure that the repair and enullsting structure act monolithically. To achieve repairs that comply with these renullirements, the magnitude of the repair ma

25、terial modulus of elasticity with respect to that of the substrate needs to be taken into account.Referenced standards and reportsThe standards and reports listed below were the latest editions at the time this document was prepared. nullcause these documents are revised frenullently, the reader is

26、advised to contact the proper sponsoring group if it is desired to refer to the latest version. American Concrete Institute nullnullnull nullide for the nulllection of nullterials for the nullpair of nullncreteASTM Internationalnullnull nullandard T est nullthod for nullatic nulldulus of nullasticit

27、y and nullissonnulls nulltio of nullncrete in nullmpressionnullnull nullandard T est nullthod for Flenullral nullrength and nulldulus of nullasticity of nullemical-nullsistant nullrtars, null outs, nullnolithic nullrfacings, and nulllymer nullncretesCited referencesnull nuller, F. null., and nullhns

28、ton, null null, Mechanics of Materials, third edition, nullnullaw-Hill, nullw nullork, nullnull, nullnullpp.null nullhta, null. null, Concrete: Structure, Properties and Materials, nullentice Hall, nullper nullddle nullver, null, nullnull, nullnullpp.null nullaysburd, null null; nullmons, null. H.;

29、nullilvaganam, null null.; nullnullnald, null null; and nullssonnette, null, nulloncrete nullpair Technologynull nullvised nullproach is nulleded,nullConcrete International, null. null, null. null nulln. nullnull, pp. null-null.null nullgeon, null, and nullssonnette, null, nullensile nulleep and nul

30、lacking nulltential of nullnded nullncrete nullpairs,null Concrete International, null. null, null. null, nullv. nullnull, pp. null-null.null nullmons, null. H., Concrete Repair and Maintenance Illustrated, nullnull nullans null. nullc., nullw nullork, nullnull, nullnullpp.Fig. nullnullnullnullample

31、s of repair lanullouts comnullining materials with different elastic moduli.nullIMPORTANCE OF MODULUS OF ELASTICITY IN SURFACE REPAIR MATERIALS (ACI 364.5T-10) 3American Concrete Institute Copyrighted Materialnullnull.concrete.orgnullnullnull Technullotes are intended for reference for the design an

32、d construction of concrete structures. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and who will accept responsibility for the application of the information it contains. The nullerican nullncrete nullstitute discl

33、aims any and all responsibility for the accuracy of the con -tent and shall not be liable for any loss or damage arising therefrom. nullference to this document shall not be made in contract documents.nullnullnullnullnull-null was adopted and published nullptember nullnull.nullpyright nullnullnull,

34、nullerican nullncrete nullstitute.nullll rights reserved including the 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 reproduction or f

35、or use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.Reported by ACI Committee 364Fred null nullodwinnullairnullmes H. nullpernullcretarynullndal null nullardnullnoit nullssonnettenullchael null nullainerdnullristopher null nu

36、llownnulluglas nullrkenullyan nullenullnder nullrrisnulluce null nullllinsnullian nulle nullpenullris nullagunskynullter H. nullmonsnullul null nulludetteTimothy null null. nullllespienullreh null nullegoriannullmes null nullnullnaldnullilliam null nullshnully H. nullulnull nullm nulliuThomas null n

37、ullencernullhn null Tannernullalery Tokarnullvid null nullannullkernullenullnder null nullaysburdnullrt F. von Faynullmes nullarnernulltrick null nullatsonnullvid null. nullitmorenullwan null nullptanulln Heffronnullbert null Henrynulll null Hindonullarles null Hookhamnullwrence F. nullhnnullhok nul

38、l nullkadenullv nullminetnullynullmes null nullspernullith null nullsnernullick null nullrsonnullrnullrie null nullynchnullitpal null nullngatFor additional copiesnullplease contact: American Concrete Institutenull3nullnull Country Club DrinullnullFarminnullon nullllsnullnull 4null3null nullone: nullnullnullnull3nullnull Fanull 34nullnullnull3nullnull wwwnulloncretenullrnull