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logo LGC logo LGC__TSTM_rupture logo lgc__concrete_1 Early age properties of concrete in tension for numerical modeling
Contact Stéphanie Staquet, Brice Delsaute  
Keywords Early age, creep, relaxation, tension, setting time, restrained shrinkage  
Dr Max Hendriks, TU Delft, Delft, Netherlands

Claude Boulay, IFSTTAR, Paris, France

Dr Stefano Dal Pont, IFSTTAR, Paris, France

Dr Jean-Michel Torrenti, IFSTTAR, Paris, France
Description of the research project The construction of massive elements in reinforced concrete such as bridge-deck, bridge-pier, dam or all elements in concrete built in different phases can be subject to cracking. Health of mature concrete is largely influenced by early age cares to prevent cracking processes. Restrained deformations, by re-bars or other stiff environment, are often the origin of cracks. Even if they are not always applied in field applications, remedies are known to prevent cracking processes. Realistic simulations, based on numeric and experimental approaches, can bring a precious help to diagnose cracking risks.

Shrinkage and thermal strains in restrained conditions induce tensile stress in concrete. Cracking appeared when stresses exceed the tensile strength. In concrete, the shrinkage induced stresses (Figure 1) are reduced by the creep and the relaxation phenomena. Moreover, time has two effects. The first is an increase of the tensile strength which decreases the risk of cracking. The second is an increase of the stiffness of the material.

early age_evol

Figure 1 - cracking for restrained shrinkage

A good knowledge of the early age behavior and the restrained conditions of concrete is important to limit cracking risk. For this purpose, several tests has to be carried out for the shrinkage including the thermal deformation, the autogenous deformation, the drying shrinkage, the Young's modulus, the creep, the relaxation and finally the restriction degree. Monitoring the evolution of an early age set of parameters on samples is necessary to simulate the early age behaviour of structures. The difficulty lies in the fact that this monitoring must be automatic because the setting and the hardening processes durations of the concrete take place over a period counted in hours or days. In this research, specific devices for early age concrete are used: TSTM (Temperature Stress Testing Machine), BTJADE and FreshCon (Figure 2).

TSTM essaiBTJADEFreshCon  

Figure 2 - TSTM, BTJADE and FreshCon

Selected publications [1]Boulay C., Crespini M., Staquet S., Carette J., Delsaute B.: "Monitoring of the creep and the relaxation behavior of concrete since setting time, part 1: compression.", CFRAC (International Conference on Computational Modeling of Fracture and Failure of Materials and Structures), Barcelone, Juin 2011.

[2]Delsaute B., Carette J., Staquet S., Boulay C., Crespini M.: "Monitoring of the creep and the relaxation behaviour of concrete since setting time, part 2: tension.", CFRAC, Barcelone, juin 2011.

[3]Delsaute B., Carette J., Staquet S.: "Monitoring of the creep and the relaxation behavior of concrete since setting time: complementary results on the CEOS concrete", Concrack 2 (Control of Cracking in R.C. structure), Paris, Juin 2011.