1、 1 ACI 506.6T-17TechNoteVisual shotcrete core Quality eValuationKeywords: cores; encapsulation; visual evaluation; reinforcing bars; voids.During shotcrete construction, owners, architects, engineers, and contractors want to verify the quality of shotcrete being placed. Shotcrete cores are normally
2、extracted from shotcrete sample panels or when needed from as-placed shotcrete for evaluation of shotcrete quality (ACI 506.4R). In addition to the routine tests such as compressive strength or other material quality tests required by project specification, visual examination of shotcrete cores by a
3、n experienced licensed design professional (LDP) is an important tool for evaluation of shotcrete quality.The contractor should demonstrate that shotcrete material can be placed in a manner that accomplishes intimate contact between the shotcrete and the reinforcing steel to accomplish the design re
4、quirements of the project. Visual examination can reveal imperfections, including voids, sand lenses, delaminations, and degree of reinforcing steel encapsulation. Visual evaluation of core quality will be dependent on the LDPs experience and knowledge. Visual evaluation is intended to detect qualit
5、y issues on the surface of the core and should be conducted on a group of no less than three coresnot dependent on a single core that may not be representa-tive of the entire area sampled (ACI 506.4R).To provide guidance for visual evaluation of cores, Table 1 lists quantitative criteria for each ca
6、tegory of core quality an LDP can refer to during the core evaluation. This TechNote should be considered a reference document by the LDP to provide a reasonable evaluation of shotcrete quality. These are intended to be general guidelines, and the LDPs professional judgment should be used to ascerta
7、in the demonstrated quality of the cores. Whether the demonstrated quality is adequate for the intended purpose of the in-place shotcrete is the subject of ACI 506.4R.Visual core evaluation is not an exact science; it requires professional judgment from the LDP. This visual evaluation process should
8、 employ Table 1 and a written description in this document to provide guidance. When needed, other aspects linked to the placement of shotcrete may be helpful for evaluating overall quality of shotcrete placement (for example, the inspection of the back of the shotcrete panel for rebound or overspra
9、y entrapment or other visible imperfections not necessarily found on the surface of the cores).There are four categories of visual evaluation of core quality. Each category of quality is clearly discussed and quantified in Table 1 based on two criteria. It is important to understand that each catego
10、ry is not only a function of the imperfections found, but also intimately linked to the complexity of the reinforcement layout. Factors including size of the reinforcement, spacing, laps, layers, reinforcement location within a cross section, and other types of placement obstacles may affect the per
11、formance of shotcrete placement.Categories are as follows:a) Very GoodIn a lightly reinforced structure, cores show few local imperfections and complete encap-sulation of the reinforcement. As reinforcement complexity increases, localized imperfections (which are not repeated in the same core) behin
12、d the reinforcement may be found with void areas not more than 25 percent of the area of the largest-diameter reinforcement considered or with bonded encapsulation exceeding 90 percent of the circumference of the reinforcement. There should not be any sand lenses or delamination. Scattered voids up
13、to 1/4 in. (6.4 mm) diameter should be ignored.b) GoodIn a lightly reinforced structure, cores show small local imperfections. As reinforcement complexity increases, localized imperfections (which are not repeated in the same core) behind the reinforcement may be found with void areas not more than
14、30 percent of area of the largest-diameter reinforcement considered or with bonded encapsulation exceeding 80 percent of the circumference of the reinforcement.American Concrete Institute Copyrighted Material www.concrete.org2 VISUAL SHOTCRETE CORE QUALITY EVALUATION (ACI 506.6T-17)The longest linea
15、r dimension of exposed voids created by sand lenses and delamination (excluding any voids touching the reinforcing bar) should be less than 10 percent of the longest dimension of the observed specimen. Scattered voids up to 3/8 in. (9.5 mm) diameter should be ignored.c) SatisfactoryImperfections app
16、ear on a regular basis in the samples with large localized imperfections present. As reinforcement complexity increases, localized imperfections without repetition behind the rein-forcement may be found with void areas not more than 35 percent of area of the largest-diameter reinforce-ment considere
17、d or with bonded encapsulation exceeding 70 percent of the circumference of the reinforcement. The longest linear dimension of exposed voids created by sand lenses and delamination (excluding any voids touching the reinforcing bar) should be less than 20 percent of the longest dimension of the obser
18、ved specimen. Scattered voids up to 3/8 in. (9.5 mm) diameter should be ignored.d) PoorImperfections are found throughout the samples or areas of the sample and show a high complexity of imperfections. As reinforcement complexity increases, localized imperfections without repetition behind the reinf
19、orcement may be found with void areas more than 35 percent of area of the largest-diameter reinforcement considered or with bonded encapsulation of less than 70 percent of the circumference of the reinforcement. The longest linear dimension of exposed voids created by sand lenses and delamination (e
20、xcluding any voids touching the reinforcing bar) represents more than 20 percent of the longest dimension of the observed.Shotcrete core quality evaluation tableTable 1 is primarily based on the degree of encapsulation of the reinforcing steel, and secondarily on the size and location of voids. Core
21、s are categorized as outlined in Table 1. The intent is that for a specific core evalua-tion, both Criteria a and b should be satisfied. The LDP may modify quality assurance procedures or criteria as needed based on project-specific needs. Sketches combining both Criteria a and b in Table 1 are pres
22、ented in Fig. 1.Table 1Core evaluation categoryCriteria Very good Good Satisfactory PooraEncapsulation of reinforcing steel as a percentage of the circumference of the reinforcement (any individual reinforcement cross section or total of all reinforcements in the core)*Greater than 90 percentGreater
23、 than 80 percentGreater than 70 percentLess than or equal to 70 percentbMaximum sizeof any void touching the reinforcement, as a percentage of the cross section of that reinforcementLess than 25 percentLess than 30 percentLess than 35 percentGreater or equal to 35 percent*When reinforcements are not
24、 centered in the core, an attempt should be made to determine the approximate length of the reinforcements edge contact with shotcrete.Measured as approximate area of any voids touching the reinforcing steel on the cylindrical surface of the core.Notes: Sand lenses should be measured as voids. Occas
25、ional scattered voids up to 1/4 in. (6.4 mm) diameter should be ignored.ReferencesACI Committee 506, 1994, “Guide for the Evaluation of Shotcrete (ACI 506.4R-94),” American Concrete Institute, Farmington Hills, MI, 12 pp.American Concrete Institute Copyrighted Material www.concrete.orgVISUAL SHOTCRE
26、TE CORE QUALITY EVALUATION (ACI 506.6T-17) 3Fig. 1Visual representation of Criteria (a and b) of Table 1. (Note: 1 in. = 25.4 mm)American Concrete Institute Copyrighted Material www.concrete.org4 VISUAL SHOTCRETE CORE QUALITY EVALUATION (ACI 506.6T-17)Reported by ACI Committee 506Marc Jolin, Chair J
27、ames A. Ragland, SecretaryJon B. Ardahl Ryan E. Poole Consulting MembersLars F. Balck Simon Reny Jean-Francois DufourMichael Ballou Raymond C. Schallom III Richard A. KadenLouis-Samuel Bolduc W. L. Snow Sr. Dudley R. MorganChris D. Breeds Jason P. South H. Celik OzyildirimWern-Ping Nick Chen Lawrence J. Totten Harvey W. ParkerScott R. Cumming Marcus H. von der Hofen Philip T. SeabrookWilliam T. Drakeley Jr. Curtis White George YoggyCharles S. Hanskat Peter T. YenWarren L. Harrison Ezgi YurdakulThomas Hennings Lihe ZhangMark R. Lukkarila Chris M. ZyndaJeffrey L. Novak
