1、 1 ACI 364.15T-18TechNoteSignificance of the Shrinkage-compenSating and nonShrink LabeLS on packaged repair materiaLSKeywords: cracking; expansion; nonshrink; packaged; prestress; repair material; restraint; shrinkage-compensating; tensile stress.QuestionWhat does it mean when a packaged repair mate
2、rial is labeled as shrinkage-compensating or nonshrink?AnswerThe terms shrinkage-compensating and nonshrink are both intended to describe materials that exhibit no or little net contraction as a result of shrinkage. In practice, however, these terms are of limited use in the selec-tion of repair mat
3、erials without supporting test data on time-dependent volume changes.DiscussionMany proprietary repair materials are described as shrinkage-compensating or nonshrink. In most cases, the manufacturers data sheets do not explain the meaning of such terms. Given the restraint conditions typi-cally prov
4、ided by the concrete substrate, accurate expansion and shrinkage data are essential for selection of shrinkage-compensating or nonshrink materials that will provide durable repairs. This Technote provides clarifications on the actual significance of the labels shrinkage-compensating or nonshrink fou
5、nd in technical data sheets.Moisture loss is unavoidable in cement-based materials as soon as they are exposed to a relative humidity less than 100 percent. This moisture loss results in drying shrinkage and volume changes within the material. In addition to shrinkage that occurs due to drying, the
6、hydration reactions will cause some unavoidable chemical shrinkage. Consequently, significant efforts have been made to counteract shrinkage and its undesirable effects, such as tensile stresses and cracking. Expansive cements were first introduced more than half a century ago to produce so-called s
7、hrinkage-compensating concretes. Shrinkage-compensating is defined by the ACI CT as:A characteristic of grout, mortar, or concrete made using an expansive cement in which volume increases after setting and, if properly elastically restrained, induces compressive stresses which are intended to approx
8、imately offset the tendency of drying shrinkage to induce tensile stresses.In these materials, a chemical agent added to the cement reacts during curing to produce an expan-sive compound, resulting in a net volume increase of the material. The dosage of expansive agent has to be selected such that t
9、he initial expansion will offset subsequent shrinkage, as depicted in Fig. 1.The shrinkage-compensation process for repair materials is similar to that for shrinkage-compensating concretes. The latter are often made with Type K cement (ASTM C845/C845M) and sometimes with the use of other types of ex
10、pansive agents added during the mixing operations, generally calcium sulfoaluminate-Fig. 1Typical length change behavior of shrinkage-compensating and portland cement concretes (adapted from ACI 223R).American Concrete Institute Copyrighted Material www.concrete.org2 SHRINKAGE-COMPENSATING AND NONSH
11、RINK LABELS ON PACKAGED REPAIR MATERIALS (ACI 364.15T-18)based (CSA) or lime-based (CaO). The various proprietary shrinkage-compensating repair materials available can differ significantly in composition, especially when it comes to the nature of the expansive compound. In addition to the aforementi
12、oned CSA-based and CaO-based agents, other additives such as gas-liberating agents (nitrogen, hydrogen, and oxygen, for example) and diols (dihydric alcohols) are also used. Some dual-action materials even contain two forms of expansive agents; for instance, one agent that produces a gas to countera
13、ct shrinkage occurring while the material is still in a plastic state, and another that leads to the formation of a compound that produces expansion in the hardened state.The term nonshrink is often, if not always, used in place of the probably more suitable expression shrinkage-compensating. Hydrau
14、lic-cement nonshrink grout is defined in ASTM C125 as:A hydraulic-cement grout that produces a volume that, when hardened under stipulated test condi-tions, is greater than or equal to the original installed volume, often used as a transfer medium between load-bearing members.There will be some shri
15、nkage as long as cementitious materials are part of the system; thus, strictly speaking, a cement-based material cannot be nonshrinking. The term is used by many manufacturers, however, to describe the shrinkage-compensating behavior of their materials. It is also used in ASTM C1107/C1107M for packa
16、ged dry, hydraulic-cement grouts. The important thing to know is that when a prepackaged material is labeled as nonshrink, it means that during the life of the material, under given environmental conditions, the dimen-sional balance (expansion minus shrinkage) is supposed to remain positive; there s
17、hould be no net contraction resulting from drying (Fig. 1). It does not mean that there will be no volume changes.Because the induced expansion and shrinkage are generally not synchronous, the effectiveness of a shrinkage-compensating system is dependent on restraint during the expansive process to
18、produce a compressive prestress that will decrease with subsequent shrinkage. In new construction, a minimal amount of reinforcement is used to provide this restraint, as recommended in ACI 223R. There is no such provision for repair materials, and it certainly requires some attention, especially in
19、 the case of bonded surface repairs without reinforcement where the restraint is provided by simple interface bond with the substrate and, depending on the configuration of the repair (partial-depth versus overlay work), by abutment to the vertical edges.Information on the dimensional behavior of sh
20、rinkage-compensating or nonshrink repair materials is generally insufficient or absent from the manufacturers data sheets. This lack of information is due, in part, to the absence of explicit standardized test procedures and specifications for shrinkage-compensating materials. ASTM C1107/C1107M requ
21、ires that the height change of moist-cured hardened hydraulic-cement grout be within the range of 0 to +0.3 percent when tested in accordance with ASTM C1090/C1090M. In the case of rapid-hardening cementi-tious materials for concrete repairs (ASTM C928/C928M), many of which are also claimed to be sh
22、rinkage-compensating, the maximum allowable increase in length change is 0.15 percent after 28 days in water and the maximum allowable decrease is 0.15 percent after 28 days in air. This range for maximum allowable expansion and contraction is so permissive that most materials fall between the limit
23、s. Also, there are no requirements for rate of volume change for rapid-hardening cementitious repair materials. The rate of volume change is impor-tant in repairs and is addressed for other types of materials in ASTM C845/C845M and C1107/C1107M.As illustrated in the following examples, which are exc
24、erpts from actual data sheets downloaded from two different manufacturers websites, the information provided to the customer can be quite confusing (see the commentary provided at the bottom of each example).American Concrete Institute Copyrighted Material www.concrete.orgSHRINKAGE-COMPENSATING AND
25、NONSHRINK LABELS ON PACKAGED REPAIR MATERIALS (ACI 364.15T-18) 3Example 1: Material ADescription: One component, polymer-modified, fast-setting, nonshrink repair mortar with fiber and corro-sion inhibitor.Use: Rapid structural and cosmetic repairs to any vertical or overhead concrete; fills holes, s
26、palls, cracks, or honeycombs on vertical or horizontal concrete; restores disintegrated surfaces of old concrete and masonry, cornices, lintels, sills, handrails.Properties:28-day shrinkage/50 percent relative humidity (ASTM C490/C490M): 0.10 percent.28-day expansion/50 percent relative humidity (AS
27、TM C490/C490M): 0.03 percent.Curing: Repaired areas should be kept damp for 20 to 30 minutes or cured with a water-based curing compound.ASTM C490/C490M is the standard practice for the use of the apparatus to determine length change in a variety of ASTM test methods. It is not a sufficient referenc
28、e for data reporting, as neither the curing time and duration, the demolding time, or the storage conditions are specified. How can a material be classified as nonshrink when the reported shrinkage at 28 days is more than three times the reported expansion value at the same age? Besides, how are the
29、se 28-day shrinkage and expansion values determined from the same experiment? Is the volume change complete at 28 days?Example 2: Material BDescription: One-component, shrinkage-compensated, micro-concrete designed for large-volume repairs, including structural elements, typically in applications fr
30、om 2 in. (51 mm) to full depth.Use: Large volume structural repairs; repair or replacement of spandrel beams, columns, balcony edges, partial or full-depth placements of structural concrete elements, parking garages, water and wastewater tanks, tunnels, dams, bridges, and marine structures.Propertie
31、s:28-day shrinkage/50 percent relative humidity (ASTM C157/C157M): 0.0350 percent.21-day shrinkage/50 percent relative humidity (ASTM C157/C157M modified): 0.0611 percent.Curing: Repair mortar should be cured immediately after the formwork is stripped in accordance with good concrete practices; refe
32、r to ACI 308.1.Without a description of the modifications to the ASTM C157/C157M method or proper reference, the reported 21-day shrinkage data is meaningless. Additionally, no expansion data is reported.What was the curing regimen used in determining the shrinkage data reported and, in such conditi
33、ons, what level of shrinkage compensation was achieved?In addition to the general lack of information regarding the dimensional behavior of shrinkage-compensating repair materials, the discrepancy found in the information disclosed in data sheets from one manufacturer to the other makes the comparis
34、on between different products very difficult. Conformity with either ACI 364.3R or ICRI No. 320.3R in the preparation of repair material data sheets would contribute to elimination of these shortcomings.According to ACI 546.3R:When testing shrinkage-compensating materials, it is critical that the de
35、molding time, curing condi-tions, and comparator reading schedule are understood when interpreting the test results. For example, if the initial measurement is recorded while the material is still expanding, the ultimate drying shrinkage appears less than it actually is; the net length change (expan
36、sion less shrinkage) during the test, therefore, should be used as the value for drying shrinkage.American Concrete Institute Copyrighted Material www.concrete.org4 SHRINKAGE-COMPENSATING AND NONSHRINK LABELS ON PACKAGED REPAIR MATERIALS (ACI 364.15T-18)The length change data should be determined an
37、d reported in accordance with ASTM C157/C157M, as modi-fied by the instructions and curing provisions provided in ACI 364.3R.In practice, without adequately referenced test data on the actual time-dependent volume changes the mate-rials undergo during and after curing, the designations shrinkage-com
38、pensating and nonshrink are of limited significance in the selection of repair materials. In the absence of appropriate information, the specifier should consult the manufacturer to determine the suitability of a given material in a given situation.More information on the expansion-shrinkage sequenc
39、e, the development of tensile stress, and the achieve-ment of crack prevention can be found in ACI 223R.SummaryAll cementitious materials undergo some drying shrinkage when exposed in an environment where relative humidity is below 100 percent. The labels shrinkage-compensating and nonshrink found i
40、n the technical data sheet of some prepackaged repair materials mean that they are formulated to exhibit no resulting net contrac-tion upon drying, owing to a chemical expansion process taking place in the early stages of curing. Proper selec-tion and use of such repair materials requires the knowle
41、dge of adequately referenced test data on the actual time-dependent volume changes the material undergoes during and after curing.ReferencesAmerican Concrete InstituteACI CT-16ACI Concrete TerminologyACI 223R-10Guide for the Use of Shrinkage-Compensating ConcreteACI 308.1-11Specification for Curing
42、ConcreteACI 364.3R-09Guide for Cementitious Repair Material Data SheetACI 546.3R-14Guide to Materials Selection for Concrete RepairASTM InternationalASTM C125-16Standard Terminology Relating to Concrete and Concrete AggregatesASTM C157/C157M-08(2014)Standard Test Method for Length Change of Hardened
43、 Hydraulic-Cement, Mortar, and ConcreteASTM C490/C490M-17Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and ConcreteASTM C845/C845M-12Standard Specification for Expansive Hydraulic CementASTM C928/C928M-13Standard Specification for Pac
44、kaged, Dry, Rapid-Hardening Cementitious Materials for Concrete RepairsASTM C1090/C1090M-15Standard Test Method for Measuring Changes in Height of Cylindrical Specimens of Hydraulic-Cement GroutASTM C1107/C1107M-14aStandard Specification for Packaged Dry, Hydraulic-Cement Grout (Nonshrink)Internatio
45、nal Concrete Repair InstituteICRI No. 320.3R-2012Guideline for Inorganic Repair Material Data Sheet ProtocolAmerican Concrete Institute Copyrighted Material www.concrete.orgSHRINKAGE-COMPENSATING AND NONSHRINK LABELS ON PACKAGED REPAIR MATERIALS (ACI 364.15T-18) 5Reported by ACI Committee 364Ashok M
46、. Kakade, Chair Paul E. Gaudette, SecretaryRandal M. Beard Liying Jiang Consulting MembersBenoit Bissonnette Keith E. Kesner Robert V. GeveckerRyan Alexander Carris John S. Lund Stephen A. JohansonLarry D. Church Marjorie M. Lynch Emory L. KempBruce A. Collins Surendra K. Manjrekar Howard H. Newlon
47、Jr.Timothy R. W. Gillespie James E. McDonald Weilan SongFred R. Goodwin Jay H. Paul Dela TharmabalaPawan R. Gupta Murat B. Seyidoglu Robert TracyAnn Harrer K. Nam Shiu Alexander M. VaysburdJohn L. Hausfeld Kyle D. Stanish William F. WescottRobert L. Henry David A. VanOckerCharles J. Hookham David W. Whitmore
