Abstract
The classic Schmidt hammer (SH) and the Equotip hardness tester (EHT) are the widely used nondestructive (NDT) instruments for measuring surface dynamic hardness (rebound hardness) of materials. In previous studies, both instruments have been used individually to establish empirical models for uniaxial compressive strength (UCS) evaluation of rock materials. However, no specific research seems to have been undertaken to investigate their relative UCS prediction effectiveness when performed on the same rock samples. In this study, we evaluated the relative UCS prediction performance of these two NDT instruments by performing laboratory tests on core specimens of some selected rock materials used as masonry and building stones. The correlations of Schmidt hammer rebound hardness (SHR) and Equotip hardness (HLB) to UCS were determined by using regression analyses and test statistics. Also, the variability of each test method was evaluated by employing variance analyses. The results indicated that the established UCS prediction models for both NDT methods were significant in the statistical sense (p value <0.05), with the EHT method showing somewhat better prediction accuracy (R2 = 0.87; accuracy ratio = 0.60) compared to the SH method (R2 = 0.84; accuracy ratio = 0.78). Data scatter graphs showed increasing standard deviation in UCS for increasing rebound indices. An average conversion factor (k) of 15.7 was derived in the zero-intercept regression model HLB = k ⋅ SHR, which may be used in practice as a guide to translate the measured hardness values from one instrument to another. For improved UCS prediction accuracy, an attempt was made to evaluate the potential use of a newly proposed combined NDT method involving the simultaneous use of SH and EHT test results. With this kind of approach, a relatively better prediction accuracy was achieved (R2 = 0.89; accuracy ratio = 0.52) compared to the use of the SH and EHT methods individually.
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References
Alvarez Grima M, Babuska R (1999) Fuzzy model for the prediction of unconfined compressive strength of rock samples. Int J Rock Mech Min Sci 36:339–349
Aoki H, Matsukura Y (2008) Estimating the unconfined compressive strength of intact rocks from Equotip hardness. Bull Eng Geol Environ 67:23–29
Asiri Y, Corkum A, El Naggar H (2016) Leeb hardness test for UCS estimation of sandstone. 69th Geo Vancouver conference, Vancouver, October 2016
ASTM (2000) Standard test method for determination of rock hardness by rebound hammer method. D 5873–00
ASTM A956 (2012) Standard test method for Leeb hardness testing of steel products. 15 November 2012
Aydin A (2009) ISRM suggested method for determination of the Schmidt hammer rebound hardness: revised version. Int J Rock Mech Min Sci 46:627–634
Breccolotti M, Bonfigli MF, Materazzi AL (2013) Influence of carbonation depth on concrete strength evaluation carried out using the SonReb method. NDT E Int 59:96–104
Breysse D (2012) Nondestructive evaluation of concrete strength: an historical review and a new perspective by combining NDT methods. Constr Build Mater 33:139–163
Craeye B, Van De Laar H, Van Der Eick J, Gijbels W, Lauriks L (2017) On-site strength assessment of limestone based concrete slabs by combining non-destructive techniques. J Build Eng 13:216–223
Das B (1973) Rebound strength of the coal series. Fuel 52:118–120
Deere DU, Miller RP (1966) Engineering classification and index properties for intact rock. Air Force Weapons Laboratory Technical Report, AFWL-TR65–116, Kirtland Air Base, New Mexico, p 309
Günes Yılmaz N (2013) The influence of testing procedures on uniaxial compressive strength prediction of carbonate rocks from Equotip hardness tester (EHT) and proposal of a new testing methodology: hybrid dynamic hardness (HDH). Rock Mech Rock Eng 46:95–106
Gunsallus K, Kulhawy FH (1984) A comparative evaluation of rock strength measures. Int J Rock Mech Min Sci Geomech Abstr 21:233–248
Hack R, Huisman M (2002) Estimating the intact strength of a rock mass by simple means. Proceedings of 9th congress of the international association for engineering geology and the environment. Durban, South Africa, 16–20 September, pp 1971–1977
Hack HRGK, Hıngıra J, Verwaal W (1993) Determination of discontinuity wall strength by Equotip and ball rebound tests. Int J Rock Mech Min Sci Geomech Abstr 30:151–155
Hussain A, Akhtar S (2017) Review of non-destructive tests for evaluation of historic masonry and concrete structures. Arab J Sci Eng 42:925–940
ISRM (2007) The complete ISRM suggested methods for rock characterization, testing and monitoring: 1974–2006. In: Ulusay R, Hudson JA (eds) Suggested methods prepared by the ISRM commission on testing methods. Compilation arranged by the ISRM Turkish National Group, Ankara
ISRM (2014) The ISRM suggested methods for rock characterization, testing and monitoring: 2007–2014. In: Ulusay R (ed) Suggested methods prepared by the commission on testing methods. International Society for Rock Mechanics, Springer, Heidelberg, p 293
Mann L (1970) Applied engineering statistics for practicing engineers. Barnes & Noble Inc., New York, p 175
Meulenkamp F, Alvarez Grima M (1999) Application of neural networks for the prediction of the unconfined compressive strength (UCS) from Equotip hardness. Int J Rock Mech Min Sci Geomech Abstr 36:29–39
Mol L, Viles HA (2012) The role of rock surface hardness and internal moisture in tafoni development in sandstone. Earth Surf Process Landf 37:301–314
Proceq SA (2007) Equotip 3 portable hardness tester, operating instructions. Proceq, Schwerzenbach, Switzerland
Szilagyi K, Borosnyoi A (2009) 50 years of experience with the Schmidt rebound hammer. Concr Struct 10:46–55
Szilagyi K, Borosnyoi A, Zsigovics I (2011) Rebound surface hardness of concrete: introduction of an empirical constitutive model. Constr Build Mater 25:2480–2487
Tofallis C (2015) A better measure of relative prediction accuracy for model selection and model estimation. J Oper Res Soc 66:1352–1362
Vasanelli E, Calia A, Colangiuli D, Micelli F, Aiello MA (2016) Assessing the reliability of non-destructive and moderately invasive techniques for the evaluation of compressive strength of stone masonry units. Constr Build Mater 124:575–581
Viles H, Goudie A, Grab S, Lalley J (2011) The use of the Schmidt hammer and Equotip for rock hardness assessment in geomorphology and heritage science: a comparative analysis. Earth Surf Process Landf 36:320–333
Wang H, Lin H, Cao P (2017) Correlation of UCS rating with Schmidt hammer surface hardness for rock mass classification. Rock Mech Rock Eng 50:195–203
Wilhelm K, Viles H, Burke O (2016) Low impact surface hardness testing (Equotip) on porous surfaces – advances in methodology with implications for rock weathering and stone deterioration research. Earth Surf Process Landf 41:1027–1038
Yilmaz I, Sendir H (2002) Correlation of Schmidt hardness with unconfined compressive strength and Young’s modulus in gypsum from Sivas (Turkey). Eng Geol 66:221–219
Acknowledgements
The authors sincerely thank Prof. Dr. A. Bahadır Yavuz (Dokuz Eylül University, Geological Engineering Department) for generously providing the rock samples used in the experimental campaign. Sincere thanks are also given to Prof. Dr. Yaşar Kibici (formerly with Dumlupınar University, Geological Engineering Department) for his help in the petrographic descriptions of the samples.
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Yilmaz, N.G., Goktan, R.M. Comparison and combination of two NDT methods with implications for compressive strength evaluation of selected masonry and building stones. Bull Eng Geol Environ 78, 4493–4503 (2019). https://doi.org/10.1007/s10064-018-1382-7
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DOI: https://doi.org/10.1007/s10064-018-1382-7