PSI - Issue 22

2

Elise Zgheib – Wassim Raphael / Structural Integrity Procedia 00 (2019) 000 – 000

26 © 2019 The Authors. Published by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the First International Symposium on Risk and Safety of Complex Structures and Components organizers Elise Zgheib et al. / Procedia Structural Integrity 22 (2019) 25–32

Keywords: Concrete creep, Eurocode 2, admixtures, silica fume, Bayesian methods, linearization

1. Introduction An important evolution in the construction field is noticed nowadays. New high-rise buildings, bridges and dams are taking place all over the world where concrete has been used as a primary material. With the evolution in the construction field, an improvement in the performance of concrete material became necessary, (Restuccia (2017), Babu and Thenmozhi (2018)). This entails the incorporation of admixtures and additives to the mix composition which improves its properties and performance, (Jacob et al. (2018), Collepardi (1998) and Gopala Krishna Sastry et al. (2018)). These additions affect also concrete deformations especially the creep, (Zgheib et al. (2018)) defined as the time-dependent deformations which reduce the volume of concrete with the impact of external load applied to the concrete element. Since creep deformations have an important impact on long-term integrity and stability of structures, (Raphael et al. (2018)), an accurate prediction of these deformations is needed, (Su et al. (2017), Raphael et al. (2005), Zgheib et al. (2017)). But design codes do not consider admixtures effects’ while predicting concrete creep, therefore, multiple studies were undertaken in this field. In their study, Choi et al. (2015) have proposed a model for the creep phenomenon of hardened cement mixed with expansive additives. Also, Gong et al. (2016), in their study, have proposed a creep model for a concrete member subjected to axial compression and suffering from sulfate attack. In model B4, the effect of admixture type and percentage is taken into consideration by adding scaling factors to p2, p3, p4 and p5 parameters, (B ažant et al. (2015) and Hubler et al. (2015a)). As for the Eurocode 2 (EC2), it does not consider the effect of admixtures on creep of concrete, therefore, this study aims at updating it by considering the admixtures’ effects , specifically, the silica fume (SF). To study the impact of silica fume on creep predictions, a large experimental database coming from international laboratories and research centers is applied to evaluate the Eurocode 2 model, (Hubler et al. (2015b)), by comparing the predicted creep compliance to the experimental measurements using CEB statistical methods. An inaccurate estimation of Eurocode 2 creep compliance for concrete with silica fume is noted. To overcome this difference, a calibration of the Eurocode 2 model is proposed by implementing correction coefficient that takes the effect and percentage of silica fume into consideration. Using this correction coefficient will help to predict accurately creep deformations at the design stage for concrete with admixtures and hence, the long term deflection. Therefore, the required measurements and precautions can be applied to avoid excessive deflections after construction. This correction coefficient is identified by applying the Bayesian Linear Regression method.

Nomenclature J (t, t 0 ) compliance function

E cm28 modulus of elasticity of concrete at 28 days after casting E cm (t 0 ) modulus of elasticity of concrete at the loading age t 0 Φ (t, t 0 ) creep coefficient

Obs X ij experimental measurements Cal X ij Eurocode 2 creep predictions n total number of tests M CEB CEB mean deviation F CEB CEB mean square error E M i average gap of the i N

number of measurements for each test

th experiment

correction coefficient added when the percentage of silica fume is considered

t 0

age of concrete at loading