Direct tensile strength of lightweight concrete with different specimen depths and aggregate sizes Se-Jin Choi a,1 , Keun-Hyeok Yang b,⇑ , Jae-Il Sim c,2 , Byong-Jeong Choi b,3 a Building Structure & Materials Research Department, Research Institute of Industrial Science & Technology, Incheon, Republic of Korea b Department of Plant Architectural Engineering, Kyonggi University, Kyonggi-do, Republic of Korea c Department of Architectural Engineering, Kyonggi University, Seoul, Republic of Korea highlights  This study examines the size effect in tensile strength of lightweight concrete.  The reference tensile strength for size effect model is established.  A stronger size effect with the decrease in concrete density is confirmed.  This study finds a stronger size effect in direct tension than in compression.  This study finds that the effect of aggregate size on tensile strength is negligible. article info Article history: Received 6 February 2014 Received in revised form 17 March 2014 Accepted 4 April 2014 Keywords: Lightweight concrete Size effect Direct tension Aggregate size Concrete unit weight abstract To examine the size effect in direct tension, 8 ready-mixed concrete batches classified into all-lightweight concrete (ALWC) and sand-lightweight concrete (SLWC) groups were prepared. In each group, the maximum aggregate size varied between 4 mm and 19 mm, and then the lateral depth of specimen with rectangular section ranged from 100 mm to 500 mm in each concrete batch. The size effect curves based on the basic formulas proposed by Baz ˇant (1984) [1], Kim and Eo (1990) [2], and Yang and Sim (2011) [3] were also determined using a total of 28 lightweight concrete (LWC) data of current tests and 114 normal-weight concrete (NWC) data compiled from the available literature (Carpinteri and Ferro, 1994; Hu, 2011) [4,5], though specimens with lateral depth beside 100 mm is very insufficient even in NWC. The present experimental observations and verifications by prediction models clearly showed that the size effect is more notable with the decrease of the unit weight of concrete and it is stronger in direct tension than in compression. The validity of Baz ˇant’s model (Baz ˇant, 1984) [1] is significantly dependent on the maximum aggregate size, while the models proposed by Kim and Eo (1990) [2] and Yang and Sim (2011) [3] closely predict the size effect trend observed from test data, confirming that the influence of the maximum aggregate size on the concrete tensile strength and the size effect is negligible, especially for LWC. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The tensile strength of concrete is a critical property that requires further research. Although the tensile strength of concrete is frequently neglected when evaluating the ultimate load-bearing capacity of reinforced concrete elements, it significantly affects the deflections, cracking, and shear and bonding behaviors in such elements. In particular, an accurate evaluation of the concrete tensile strength helps enhance the appearance, serviceability, and durability of concrete structural members by controlling cracks. The tensile strength of concrete has primarily been examined using splitting tension test methods because of their convenience, despite the common knowledge that a direct tension test provides more rational and reliable results [6]. As a result, the direct tensile strength of concrete has been given relatively little attention. The tensile strength of concrete is significantly affected by the strength, surface texture, and size of the aggregates used in the http://dx.doi.org/10.1016/j.conbuildmat.2014.04.055 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +82 (0)31 249 9703. E-mail addresses: csj2378@gmail.com (S.-J. Choi), yangkh@kgu.ac.kr (K.-H. Yang), jisim@kgu.ac.kr (J.-I. Sim), bjchoi@kgu.ac.kr (B.-J. Choi). 1 Tel.: +82 (0)32 200 2538. 2 Tel.: +82 (0)31 249 9843. 3 Tel.: +82 (0)31 249 9702. Construction and Building Materials 63 (2014) 132–141 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat