Experimental Evaluation of Drilling Damage on the Strength of Cores Extracted from RC Buildings

Authors: A. Masi, A. Digrisolo, G. Santarsiero

Abstract:

Concrete strength evaluated from compression tests on cores is affected by several factors causing differences from the in-situ strength at the location from which the core specimen was extracted. Among the factors, there is the damage possibly occurring during the drilling phase that generally leads to underestimate the actual in-situ strength. In order to quantify this effect, in this study two wide datasets have been examined, including: (i) about 500 core specimens extracted from Reinforced Concrete existing structures, and (ii) about 600 cube specimens taken during the construction of new structures in the framework of routine acceptance control. The two experimental datasets have been compared in terms of compression strength and specific weight values, accounting for the main factors affecting a concrete property, that is type and amount of cement, aggregates' grading, type and maximum size of aggregates, water/cement ratio, placing and curing modality, concrete age. The results show that the magnitude of the strength reduction due to drilling damage is strongly affected by the actual properties of concrete, being inversely proportional to its strength. Therefore, the application of a single value of the correction coefficient, as generally suggested in the technical literature and in structural codes, appears inappropriate. A set of values of the drilling damage coefficient is suggested as a function of the strength obtained from compressive tests on cores.

Keywords: RC Buildings, Assessment, In-situ concrete strength, Core testing, Drilling damage.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1087121

References:

[1] CEN, 2005. Eurocode 8 - Design of structures for earthquake resistance - Part 3: Assessment and retrofitting of buildings, EN 1998-3, Brussels.
[2] NTC 2008, Ministero delle Infrastrutture, DM 14 gennaio 2008, Norme tecniche per le costruzioni, Suppl. or. n.30 alla G.U. n.29 del 4/2/2008 (in Italian).
[3] EN 12504 – 1, “Testing concrete in structures – Cored specimens – Taking, examining and testing in compression”, 2000.
[4] M. Dolce, A. Masi, M. Ferrini, “Estimation of the actual in-place concrete strength in assessing existing RC structures”, Proc. of the Second International fib Congress, June 5-8, 2006, Naples, Italy.
[5] EN 13791, "Assessment of in-situ compressive strength in structures and precast concrete components", European Standard ICS 91.080.40, 2007.
[6] Concrete Society, "Concrete core testing for strength", Technical Report 11 (TR 11), 1976.
[7] American Concrete Institute (ACI),“Guide for Obtaining Cores and Interpreting Compressive Strength Results”, ACI 214.4R-10, Detroit, June 2010.
[8] G. Cestelli Guidi, G. Morelli, “Valutazione della resistenza dei calcestruzzi sulle strutture finite”, L’industria italiana del cemento, n. 3/1981, (in Italian).
[9] P. Bocca, F. Cianfrone, “Le prove non distruttive sulle costruzioni: una metodologia combinata”, L’industria italiana del cemento, n. 6/1983, (in Italian).
[10] M. Collepardi, "Il nuovo calcestruzzo (seconda edizione)", Tintoretto Ed., 2002 (in Italian).
[11] E. Donaggio, “Manuale del calcestruzzo armato”, Zanichelli Ed., 1990 (in Italian).