ABSTRACT

This article focuses on the development of a new pore pressure measurement technique. The study lies under a most general context of understanding the concrete behavior under ballistic impacts. The gradient of saturation of a massive concrete structure changes from fully saturated state in its core to almost zero near its skin. Since structures might be subjected to an impact, concrete exhibits high triaxial compressive stresses and its behavior is highly influenced by the state of water saturation in the material itself. Many static and dynamic tests have been developed for determining the behavior of concrete under confined conditions for both dry and wet conditions. Vu et al.[1] conducted static triaxial tests at high confinement pressure on dry and wet ordinary concrete and showed that as the degree of saturation increases, a decrease in the volumetric strains as well as in the shear strength is observed. Forquin et al. [2] studied as well the influence of free water presence in a micro-concrete passively confined tested under dynamic loading. At high or intermediate strain rates, the author observed a continuous increase of strength with pressure in dried specimens and a quasi-nil strength enhancement in water-saturated specimens.

A new experimental technique was developed to measure the pore pressure into concrete while subjected to high hydrostatic confinement pressure generated by the ‘Giga' press. Normally, specimen of 14cm length and 7cm diameter are tested within the press. In the new concept, the specimen length was reduced to 8cm and a water collect steel cap of 6 cm is incorporated. The cap has micro-holes on its upper face, so that, when the specimen is loaded the interstitial pore pressure in the concrete is transmitted to the cap where a cylindrical sensor equipped with a circular gage is placed. The pore pressure is then calculated by measuring the deformation of the gage. Before doing tests on concrete, sensor calibration must be done. The test consists in applying a known confining pressure generated by the fluid of the press and allows measuring the deformation of the sensor. A relation then is established between pressure and deformation and can be used to calculate the pore pressure in concrete specimens.

First, numerical simulations using FEM software (Abaqus) are performed to obtain the optimal sensor geometry. Then, the experimental set-up and results on a saturated ordinary concrete specimen are presented.

REFERENCES

[1] Vu, X.H., Malecot, Y., Daudeville, L., Buzaud, E., 2009. Experimental analysis of concrete behavior under high confinement: eeffect of the saturation ratio. International Journal of Solids and Structures. 2009, Vol. 46, pp. 1105-1120.

 [2] Forquin, P., Safa, K., Gray, G., 2010. Influence of free water on the quasi-static and dynamic strength of concrete in confined compression tests. Cement and Concrete Research. 2010, Vol.40, pp. 321-33