Issue 24

Y. Petrov et alii, Frattura ed Integrità Strutturale, 24 (2013) 112-118; DOI: 10.3221/IGF-ESIS.24.12 117 S TRENGTH OF DRY AND SATURATED CONCRETE n the paper [5] the influence of relative humidity of concrete subjected to a large range of stress rate was analyzed and discussed. The Hopkinson Bar Bundle (HBB) was realized to study the high loading rate tensile properties of plain concrete cubes. The experiments were carried out on concrete cured at three different curing conditions (drying at 50 ˚C; 20 ˚C - 50% RH; and saturated) and tested at three strain rates. The results showed that level of free water inside the concrete has an important influence on the carrying capacity of concrete. 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 2 4 6 8 10 dry concrete 50% RH curing concrete saturated cocrete calculation for dry concrete calculation for 50% RH curing concrete calculation for saturated cocrete Maximum Stress (MPa) Strain Rate (1/s) Figure 5 : Strain rate effect on maximum tensile stress of concrete with three different curing states. Black squares are the experimental values for dry concrete [5]; black line is predictions of Eq. (2) for dry concrete; red triangles are the experimental values for 50% RH curing concrete [5]; and red dash line is predictions of Eq. (2) for 50% RH curing concrete; blue circles are the experimental values for saturated concrete [5]; blue dash-dot line is predictions of Eq. (2) for saturated concrete. Dry concrete 50% RH curing concrete Saturated concrete σ c , MPa 3.3 3.5 3 τ, μs 12 22 44 Table 2 : Parameters of concrete at different curing conditions. The results of experiments (points) and the prediction of these results by Eq. (2) (curves) are shown in Fig. 5. The calculations were performed on the basis of the parameters in Table 2. It is clearly seen that the saturated concrete has a lower static strength (limit stress in statics) of the three materials, but one has a higher dynamic strength (the incubation time of fracture). Humidity increases the carrying capacity of concrete at high strain rates and vice versa in statics. C ONCLUSIONS n this paper, we have analyzed the "effect of substitution" of load-carrying capacity of materials at different strain (stress) rate. The substitution effect means that in spite of the fact that static strength of one material is smaller than that of another one, its dynamic strength measured in terms of incubation time can be essentially higher. The analysis was conducted based on the incubation time approach, which allows one to separate static strength (limit stress in statics) and dynamic strength (the incubation time of fracture). As the incubation time is a material parameter, I I