Dynamic Behavior of Concrete: Experimental Aspects - Dynamic Behavior of Concrete and Seismic Engineering - page 33

1.5. Synthesis of the experimental data on concrete and associated materials
1.5.1. Data on cement paste mortar and concrete
1.5.1.1. Looking for a consistent interpretation
When analyzing experimental results, the multiplicity of experimental data,
obtained under different stress conditions, and the difficulty in interpreting them
with frequent necessary re-calculation and transient analysis, coupled with the
variety of observation scales used makes a clear presentation of the characteristics of
concrete's dynamic behavior rather difficult.
We propose an interpretation based on Rossi's initial ideas [ROS 91],
highlighted by many experimental programmes, the validity range of which is being
discussed. The underlying idea is essentially linked to the fact that cement materials
that have had evaporable water removed do not show any evolution of strength
when stressed at rates ranging from 10 -6 to 10 s -1 [TOU 95a]. This fact has been
verified on mortar and concrete, in both traction and compression ([DAR 95], [HAR
90], [ROS 92b], [TOU 95a]), within a domain where the quasi-static interpretation
of the test results is valid and thus allows a “conventional” interpretation of the
behavior of the material.
We can infer from this that the “sensitivity” of the concrete material to stress rate
is (within the considered domain) linked to the presence of free water inside the
porous material [TOU 99a]. This fact makes the control of its hydration state crucial
when its properties are being identified at high speeds, which is rather difficult to
implement. Part of the variability of the results observed in literature can be
explained by partial drying of specimens ([COW 66], [KAP 80]), in addition to self-
stresses linked to drying, which are superimposed to the initial mechanical state of
test bodies, the influence of which is all the more important due to their small size.