Revista Română de Materiale / Romanian Journal of Materials 2015, 45 (1), 55 – 58 55 METODE EXPERIMENTALE PENTRU DETERMINAREA VALORILOR NOMINALE ALE DEFORMAŢIEI DIN CONTRACŢIA BETONULUI EXPERIMENTAL METHOD FOR DETERMINING THE NOMINAL VALUES OF CONCRETE SHRINKAGE STRAINS DAN GEORGESCU ∗ , RADU PASCU, RADU GAVRILESCU, TIBERIU PASCU Universitatea Tehnică de Construcţii Bucureşti, B-dul Lacul Tei, nr. 124, CP 020396, Bucureşti, România The shrinkage deformations may lead to concrete cracking with adverse effects on structural reliability, durability and aspect of the reinforced concrete elements and structures. For preventing and mitigation of shrinkage effects measures must be taken in structural design in determining the composition and in concreting. The paper presents theoretical, practical and experimental aspects related to shrinkage strains calculation, pointing out the differences between the values computed using the provisions of SR EN 1992-1-1 -„Design of concrete structures” and measured values. Due to these differences we consider that a new approach for computing the shrinkage deformations is needed. This need is emphasized by the large number of cases in our country of cracked structural elements short time after the concrete was cast. Deformaţiile împiedicate din contracţia betonului pot provoca fisurarea acestuia, cu efecte negative asupra siguranţei structurale, durabilităţii şi aspectului elementelor şi structurilor din beton armat. Pentru prevenirea şi limitarea efectelor fenomenului de contracţie trebuie luate măsuri corespunzătoare la proiectarea, la stabilirea compoziţiei şi la punerea în operă a betonului. Articolul prezintă aspecte teoretice, practice şi experimentale privind calculul deformaţiilor din contracţie şi evidenţiază diferenţele constatate între rezultatele obţinute. Datorită acestor diferenţe, între valorile obţinute experimental şi cele recomandate în SR EN 1992-1-1 „Proiectarea structurilor din beton armat”, este necesară o nouă abordare a modului de calcul al deformaţiilor din contracţie. Acest aspect este în concordanţă cu realitatea din ţară, unde, în ultima perioadă, au apărut numeroase cazuri de fisurare ale elementelor de construcţie după punerea în operă a betonului. Keywords: Concrete, Shrinkage, Test methods 1. Introduction The concrete shrinkage is a type of deformation characteristic for this material. Known from the beginning of the concrete history it is still a problem with significant implications on reliability and durability of RC buildings. Shrinkage, after hardening of concrete in open air (RH%<100%), is the decrease with time of concrete volume. In saturated environment (RH%=100%) the converse of shrinkage is produced (swellage) which denotes volumetric increase due to moisture gain in the hardened concrete (Fig.1). Because in most cases concrete is not in saturated environment and shrinkage results in concrete cracking, this is the aspect that matters in structural engineering. Drying shrinkage is a long term process, fast after the concrete hardening and progressively attenuated with time. Troxell`s experiments quoted by Neville [1] shows that at 28 days the shrinkage strain is about 40% of the strain at 20 years and at 1 year is about 80% of the same strain (Fig.2). Fig. 1 – Shrinkage and swelling of concrete [1]. The main cause of shrinkage is the loss of adsorbed water in the pores which results in reducing the distances between the solid parts. The phenomenon in only partially reversible probably because of hydrated calcium silicate gels hardening (C-S-H). ∗ Autor corespondent/Corresponding author, E-mail: danpaulgeorgescu@yahoo.com