This research presents an experimental study behaviour of high strength concrete, for
evaluation of stress - strain curve and derivation of factors of equivalent compressive
stress block, we depend it in design of high strength concrete elements.
For this purpose, number of cylinders specimens with strength 60 MPa were prepared
and tested in compression, then curve was obtained.
The results showed the possibility of producing high strength concrete from local
materials and with strengths are highest than those were obtained, the resulting diagrams of
curve are shown to be essentially linearly elastic up to failure with a steeper declining
portion of the stress - strain diagram, which agree with the results of global researches, the
failure was almost sudden and rapid with increasing strength which shows that the highstrength
concrete less ductile than normal concrete at the failure. Curve of high strength
concrete differs from that normal concrete, this affects on the properties of rectangular
equivalent stress block which requires modifications on the factors led to optimum represent
for it and with evaluation of curve of the tested specimens, the diagram takes a
trapezoidal shape ( ), its value at the top is and the depth of the compressive
block is and we found and ( is average compression/cylinder
compressive strength of concrete, is ratio of the active depth that defined location of
compression force center), when concrete strength increases up , the diagram
shape will be closer to triangular than trapezoidal and then curve takes the shape of triangle its
value at the top is and the depth is and with replacing triangular diagram to rectangle.