1、1Evaluation and MiniMization of Bruising (Microcracking) in concrEtE rEpairKeywords: bond strength; bruising; microcracking; pull-off test; repair, surface preparation.IntroductionBruising (microcracking) induced in a concrete substrate during the concrete removal or surface preparation process prio
2、r to repair is detrimental to the bond between the repair material and the substrate. Preventing or minimizing bruising and its effect on bond is an important requirement for a successful repair.Questionsnullat is nullruising,nullhow is it evaluated, and how can it be minimizednullAnswernullncrete r
3、epair pronullcts commonlnullinvolve the removal of unsound concrete and replacement with new material. nulle concrete removal process can damage the substrate surface, resulting in varnullng degrees of microcracks and fractures, commonlnullreferred to as nullruisingnull(nullg. null. nullbruised surf
4、ace is a surface lanullr weakened bnullinterconnected microcracks.nullncrete can be removed using a varietnullof methods such as chipping hammers, milling, abrasive blasting, and hnullrodemolition. nullmoval of unsound and sound concrete subnullcts the concrete substrate to a wide range of impact an
5、d dnullamic loads, and the resulting bruising will depend on the method used and the qualitnullof the concrete. nullhe depth of the bruised lanuller varies, but is usuallnull supernullcial (tnullpical depth of the order of nullnullnull in. nullnull mmnull. nullere are no criteria nullt for the degre
6、e of bruising that reduces service life.Pull-off testing of the repair snulltem (surface repair and substrate) can be conducted to determine the bond strength.nullnullBruising translates into a weakened concrete surface lanullr and will result in lower recorded pull-off strengths,nullnullwith failur
7、es occurring predominantlnullin the substrate. nulle incidence, severitnull, and depth of bruising can be identinulld bnullmicroscopic enullmination (such as petrographic enullmination using nullnull nullnullnullmethods) of the concrete. nullcroscopic enullmination can further be used to assess reme
8、dial actions taken to eliminate bruising of the concrete. nullo identifnullbruising, a polished surface needs to be magninulld null to nullnulltimes, depending on the width of the cracks (nullg. null.Bruising can be minimized bnullselecting the appropriate concrete removal equipment and techniques f
9、or the given repair application,nulland avoiding whenever possible those that are known to induce signinullant micro -Fig. 1Optical microscope images of concrete core cross sections exhibiting bruising below the surface.6ACI 364.7T-02(11)TechNoteAmerican Concrete Institute Copyrighted nullterianulln
10、ullnull.concrete.org2 EVALUATION AND MINIMIZATION OF BRUISING (MICROCRACKING) IN CONCRETE REPAIR (ACI 364.7T-02)cracking. nulle latter techniques include scabblers, scarinullrs, bush hammers, or pneumatic hammers, especiallnullthose equipped with wide chisel tools. Bruising problems can be prevented
11、 bnullusing methods such as abrasive shotblasting, water-blasting, or hnullrodemolition.nullere the use of more damaging methods is required to increase production rate or reduce costs, the damage can be mitigated somewhat bnullabrasive shot- or water-blasting as a nullal preparation step. null brui
12、sing is detected, the depth and enullent of the damage to the substrate should be assessed and mitigated. null some cases, the damage manullgo benullnd surface bruising and can enullend into the concrete. nullplacing the commonlnullused sand in abrasive blasting with alternative materials such as si
13、ntered slag, nullnt silicon carbide, or aluminum onullde can reduce damage. nulle use of lightweight pneumatic-chipping hammers equipped with sharp, pointed tools can also limit the enullent of bruising, but manullmake concrete removal more time consuming.Referencesnull nullnullnullmmittee nullnull
14、nullse of nullonull nullmpounds with nullncrete (nullnullnullnull-null),nullnullerican nullncrete nullstitute, nullrmington nulllls, null, nullnull, null pp.null nullnull, nulluide for nulling null-nulltu nullensile Pull-nullf nullests to nullaluate Bond of nullncrete nullrface nullterials (nullnull
15、 nullnullnullnullnull) nullormerlnullnull. nullnullnull,nullnullternational nullncrete nullpair nullstitute, nullsemont, null, nullnull, null pp.null nullnull nullnullnullnull, nulltandard nullest nullthod for nullensile nullrength of nullncrete nullrfaces and the Bond nullrength or nullensile nullr
16、ength of nullncrete nullpair and nullerlanullnullterials bnullnullrect nullension (Pull-off nullthod),nullnullnull nullterna -tional, nullest nullnshohocken, Pnull nullnull, nullpp.null nullnull, nulluide for nulllecting and nullecifnullng nullterials for nullpair of nullncrete nullrfaces (nullnull
17、nullnullnull-nullnull) nullormerlnullnull. nullnullnull,nullnullternational nullncrete nullpair nullstitute, nullsemont, null, nullnull, null pp.null nullrinkel, null null, nullreparing Bridge nullcks for nullerlanull,null Concrete Repair Digest, null. null null. null nullnull, pp. nullnullnullnulln
18、ull Bissonnette, B.; nullurard, null; nullanullburd, null null; and Bnullair, null, nulloncrete nullmoval nullechniquesnullnullnullence on nullsidual nullacking and Bond nullrength,nullConcrete International, null. null, null. null, nullc. nullnull, pp. null-null.null nullnull nullnull-null, nulltan
19、dard Practice for Petrographic nullamination of nullrdened nullncrete,nullnullnull nullterna-tional, nullest nullnshohocken, Pnull nullnull, null pp.null nullarner, null; Bhunulln, null; nulloak, null. null; nullndo, null; and nullrinkel, null, nullurface Preparation for nullerlanull,null Concrete I
20、nternational, null. null, null. null nullnullnullnull, pp. null-null.Referenced Standards and Reportsnullnullnullmmittee nullnull nullnull, nulloncrete nullpair nullide (nullnullnullnull-null),nullnullerican nullncrete nullstitute, nullrmington nulllls, null, null pp.nullndo, null null, nullnull, nu
21、lln-Place Bond nullesting and nullrface Preparation of nullncrete,null Concrete International, null. null, null. null nullr., pp. null-null.nullnull, nullnull, nulluide for nulllecting and nullecifnullng nullncrete nullrface Preparation for nullalers, nullatings, and Polnuller nullerlanull (nullnull
22、 nullnullnullnullnull) nullormerlnullnull. nullnullnull,nullnullternational nullncrete nullpair nullstitute, nullsemont, null, null pp.nullilfwerbrand, null., nullnullnullnull, nullnullmproving nulloncrete Bond in nullepaired Bridge nullecks,null Concrete International, null. nullnull, nullo. null,
23、nullept., pp. null-null.EVALUATION AND MINIMIZATION OF BRUISING (MICROCRACKING) IN CONCRETE REPAIR (ACI 364.7T-02) 3American Concrete Institute Copyrighted nullterianullnullnull.concrete.orgReported by ACI Committee 364nulled null nullodwinnullairnullnullrie null nullnullchnullcretarnullnullndall nu
24、ll BeardBenoit Bissonnettenullristopher null Brownnulluglas Burkenullnulln nullenullnder nullrrisBruce null nullllinsBrian nulle nullpeBoris nullagunsknullPeter null nullmonsPaul null nulludettenullimothnullnull null. nullllespienullreh B. nullegorianPawan null nullptanullmes null nullnullnaldnullil
25、liam null nullshnullnullnull Paulnull nullm nulliunullomas null nullencernullhn null nullannernullalernullnullokarnullvid null nullannullkernullenullnder null nullanullburdnullrt null. von nullnullnullmes nullarnernullvid null. nullitmorenullhn null nullusfeldnulln nullffronnullbert null nullnrnulln
26、ulll null nullndonullarles null nullokhamnullhok null nullkadenullmes null nullspernullornullnull nullmpnullith null nullsnernullick null nullrsonnullhn null nullndPritpal null nullngatnullrendra null nullnnullekarConsulting membersnullbert null. nullveckernullephen null nullhansonnullward null null
27、wlon null.nulleilan nullngnullla nullarmabalanullbert nullracnullnullilliam null. nullescottnullnullnull nullechnullotes are intended for reference for the design and construction of concrete structures. nullhis document is intended for the use of individuals who are competent to evaluate the signif
28、icance and limitations of its content and who will accept responsibilitnullfor the application of the information it contains. nullhe nullmerican nulloncrete nullnstitute disclaims annull and all responsibilitnull for the accuracnull of the content and shall not be liable for annull loss or damage a
29、rising therefrom. nulleference to this document shall not be made in contract documents.nullnullnullnullnull-null was adopted and published nullril nullnull.nullpnullight nullnullnull, nullerican nullncrete nullstitute.nullll rights reserved including the rights of reproduction and use in annull for
30、m or bnull annull means, including the making of copies bnull annull photo process, or bnull electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in annullknowledge or retrieval snulltem or device, unless permission in writing is obtained from the copnullight proprietors.For additional copies, please contact: American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 4833null nullone: null8null48nullnull0, Fanull 348null48nullnullnull nullnullnullconcretenullorg
