ORIGINAL ARTICLE Regression models to predict SCC pressure exerted on formworks containing vertical and transverse reinforcing bars Joseph J. Assaad . Pierre Matar Received: 4 January 2018 / Accepted: 26 April 2018 Ó RILEM 2018 Abstract The use of self-consolidating concrete (SCC) containing recycled concrete aggregate (RCA) considerably increased in sustainable structural applications and civil engineering works. However, current literature and construction practices are not clear regarding the influence of RCA additions and presence of steel reinforcement on formwork pressure exerted by the plastic concrete. This paper reports experimental data obtained from 32 SCC mixtures possessing different stability levels and cast in 1.6-m high formwork containing various combinations of vertical and transverse steel bars. Test results have shown that mixtures incorporating recycled aggre- gates exhibited reduced initial maximum pressure, given the higher RCA surface roughness that promotes internal friction and material build-up at rest. The decrease in pressure was particularly accentuated in presence of steel bars, suggesting that the reinforce- ment cage confines the plastic concrete and carries part of its load. The transverse steel was around 1.5-times more influential than vertical steel in reducing the formwork pressure. The rates of pressure drop over time were not altered because of steel, implying that pressure decay is governed by the concrete intrinsic properties such as thixotropy, RCA friction, and cement hydration. Special emphasis was placed to develop regression models and examine suitability of existing ones to predict lateral pressure of RCA- modified SCC cast in formworks containing reinforc- ing bars. Keywords Self-consolidating concrete Á Formwork pressure Á Reinforcement Á Recycled aggregates Á Thixotropy 1 Introduction The prediction of lateral pressure developed by self- consolidating concrete (SCC) on vertical formworks is complex, given the interplay of large number of influencing factors including material composition, placement conditions (such as ambient temperature and casting rate), form characteristics (such as width and material type), and presence of reinforcing bars [1–6]. Currently, it is agreed that the rate at which concrete builds-up its internal structure (i.e., thixo- tropy) is affected by material composition, which in its turn, directly influences the development of lateral pressure. Higher thixotropy can be achieved by reducing free mixing water, increasing binder content, J. J. Assaad (&) Faculty of Engineering, Balamand University, Balamand Al Kurah, Lebanon e-mail: Joseph.Assaad@balamand.edu.lb P. Matar Department of Civil Engineering, Faculty of Engineering, Lebanese University, Roumieh, Lebanon e-mail: pmatar@ul.edu.lb Materials and Structures (2018)51:62 https://doi.org/10.1617/s11527-018-1188-x