Prediction of reinforced concrete strength by ultrasonic velocities Nevbahar Sabbağ, Osman Uyanık ⁎ Suleyman Demirel University, Faculty of Engineering, Department of Geophysical Engineering, West Campus, 32260 Çünür, Isparta, Turkey abstract article info Article history: Received 25 October 2016 Received in revised form 6 March 2017 Accepted 8 April 2017 Available online 09 April 2017 This study was aimed to determine the strength of the reinforced concrete and to reveal the reinforcement effect on the concrete strength by Ultrasonic P and S wave velocities. Studies were conducted with prepared 9 different concrete designs of showing low, medium and high strength features. 4 kinds of cubic samples which unrein- forced and including 10, 14 or 20 mm diameter reinforcement were prepared for these designs. Studies were car- ried out on total 324 samples including 9 samples for each design of these 4 kinds. The prepared samples of these designs were subjected to water curing. On some days of the 90-day period, P and S wave measurements were repeated to reveal the changes in seismic velocities of samples depending on whether reinforced or unreinforced of samples and diameter of reinforcement. Besides, comparisons were done by performing uniaxial compressive strength test with crushing of 3 samples on 7th, 28th and 90th days. As a result of studies and evaluations, it was seen that values of seismic velocities and uniaxial compressive strength increased depending on reinforcement and diameter of reinforcement in low strength concretes. However, while the seismic velocities were not mark- edly affected from reinforcement or reinforcement diameter in high strength concrete, uniaxial compressive strength values were negatively affected. © 2017 Elsevier B.V. All rights reserved. Keywords: Reinforced concrete Rebar Ultrasonic Compressional (P) and shear (S) wave velocities Uniaxial compressive strength Concrete strength Time 1. Introduction Destructive, semi-destructive and non-destructive methods can be used for determination of concrete strength in existing reinforced con- crete structures. Taking core samples from these structures and subject- ed to the uniaxial compression test are processes that cause damage to the structure. So as to minimize the damage Ultrasonic method is pre- ferred as it provides fewer sampling which is a non-destructive method. In this method, concrete strength can be determined with evaluation of velocity results that are obtained by measuring travel time of P and S waves of known size concrete sample in the laboratory or in-situ con- crete structure. Unreinforced samples are used for acquiring uniaxial compressive strength of core samples obtained from the existing struc- ture. However, the obtained core strength should be converted to stan- dard sample strength. While these transformations are occurred, the effects of reinforcement on the concrete strength are usually ignored or later added to the calculations. As is known, the reinforcement can both improve and reduce the concrete strength. Especially in old con- structions or constructions of non-protected against to the humidity, re- inforcements give way to decrease in concrete strength due to being exposed to corrosion. Additionally, concrete strength can be decreased in case of establishing bad bond between concrete and reinforcement. The concrete protects the rebar in the reinforced concrete. If con- crete has poor quality, that is, to say if it has voids and permeability, it cannot protect reinforcement. It has become certain that a close rela- tionship between seismic loads and fissuring that occurs due to rein- forcement corrosion in the concrete appears. Cheesman (1949), Jones (1949) and Whitehurst (1951) are perhaps the first people to apply ul- trasonic wave transmission experiments in the process of initial set of concrete. Jones (1949) has stated that measurement results of wave ve- locity on concrete after setting process has dramatically increased and the increase rate has remarkably decreased after one-day cure period. Furthermore, the relationship between P wave velocity and concrete strength was quite similar in the measurements made on two different concrete mixtures. It was also revealed that quantity of cement and coarse aggregate are a quiet effective factor. AI-Chlabi et al. (1986) described a method and a design for a digital tester suitable for concrete strength test by employing ultrasonic users. This shows that the experimental data demonstrates moderate accuracy figure in such device. In their study, Martin and Forde (1995) have taken non-destructively the P wave measurements in order to determine the properties of concrete. While concrete is kept in curing pool, wave ve- locity and concrete compressive strength increase in conducted study on cubic samples. Furthermore, concrete velocities were higher in con- crete of made with mortar of excess percentage aggregate. 150 m/s ve- locity difference was observed in the same age concrete mixture. Demirboğa et al. (2004) have investigated the relationship between Journal of Applied Geophysics 141 (2017) 13–23 Abbreviations: Ø, Reinforcement diameter (mm); UCS, Uniaxial compressive strength; W, Weight; V, Volume; w, Water content; V P , P wave velocity; V S , S wave velocity; t p , Transient time of P wave; t s , Transient time of S wave; T, Time (day); D1,…, D9, Type of concrete design; RMSE, Root mean square error. ⁎ Corresponding author. E-mail address: osmanuyanik@sdu.edu.tr (O. Uyanık). http://dx.doi.org/10.1016/j.jappgeo.2017.04.005 0926-9851/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Applied Geophysics journal homepage: www.elsevier.com/locate/jappgeo