Strength Characteristics

The compressive and the tensile strength which may be achieved by UHPC depend strongly on the concrete composition, in particular with regard to the type and amount of binders and the fine aggregates (micro — fillers) as well as the type and duration of curing. If ordinary curing, at room temperature of 20°C, is applied a maximum com­pressive strength of UHPC of approximately 200 MPa can be achieved. If the curing temperature is increased to 100°C, the strength will reach approximately 250 MPa. A further increase of the curing temperature to 250°C is accompanied by a strength gain to almost 400 MPa. A compressive strength value of approximately 800 MPa may be achieved, if mechanical pressure is applied in addition.

Similarly to ordinary fibre reinforced concrete, the addition of fibres (mostly steel fibres) causes a small improvement of the compressive strength of UHPC, but may significantly affect the strain capacity of the concrete. The investigations on the effect of the volume content of fibres of up to 6% by volume, point to an optimum fibre content of approximately 2.5%.

The uniaxial tensile strength and the flexural tensile strength of UHPC reach values ranging approximately from 10 to 60 MPa. When special binders and tech­niques are applied, a tensile strength of 150 MPa may be attained. It should be noted that, unlike the compression characteristics, the tensile strength of UHPC may be doubled when fibres (1.5-3.0% by volume) are added to the mix. This may be attrib­uted to a large extent to the reduction of the brittleness of non-reinforced UHPC, where minor flaws and cracks may tremendously reduce the tensile strength.

Concerning the fracture energy and the characteristic length of UHPC, the avail­able knowledge is still very insufficient. It appears that for UHPC made without fibres these values are somewhat lower than for high strength concrete. Of course, the addi­tion of fibres may increase the fracture energy up to a factor of approximately 100.

Updated: 23 августа, 2015 — 10:09 дп