Compressive strength classes and performance classes of ultra-high-performance concrete (2)

Figure: Leutbecher/Riedel

Fig. 8: Determination of the post-cracking tensile strength of UHPFRC by means of direct or indirect methods: direct tensile test on unnotched (a), dog-bone-shaped (b), notched specimen (c); typical stress-crack opening or stress-strain relationship of UHPFRC (d); 3-point bending test on notched beam (e); 4-point bending test on unnotched beam (f)

Figure: Leutbecher/Riedel

Fig. 9: Load-deflection curves of 3-point tests acc. to DIN EN 14651 (left) and of 4-point tests acc. to DAfStb Guideline “Steel Fibre Reinforced Concrete” (right) for UHPFRC of Series 1 from [23] (see chapter 3.2)

Figure: Leutbecher/Riedel

Fig. 10: 3-point bending test acc. to DIN EN 14651: a) test specimen (gray: side from which the mould was filled; dimensions in mm); b) detail of the notch and measuring CMOD

Figure: Leutbecher/Riedel

Fig. 11: Direct tensile test: a) geometry and location of the tensile specimens cut from beams (gray: side from which the mould was filled; dimensions in mm); b) tensile specimen with instrumentation [23]

Figure: Leutbecher/Riedel

Fig. 12: Load-deflection curves of 3-point tests acc. to DIN EN 14651 for UHPFRC of Series 3 (left) and 4 (right) from [23]

Figure: Leutbecher/Riedel

Fig. 13: Mean values of axial post-cracking tensile strength determined in direct tensile tests and of residual tensile strengths f_Rm,j determined in 3-point bending tests acc. to DIN EN 14651 as well as ratios f_cftm/f_Rm,j

Figure: Leutbecher/Riedel

Torsten Leutbecher

(detailed vita see BFT 09/2020
p. 54)

(ausführliche Vita siehe BFT 09/2020 S. 54)

Philipp Riedel

(detailed vita see BFT 09/2020
p. 54)

(ausführliche Vita siehe BFT 09/2020 S. 54)

At present, a national technical approval or an approval on a case-by-case basis is required for structural applications of concretes >C100/115 as well as steel-fiber-reinforced concretes >C50/60. This holds true likewise to the application of ultra-high-performance concrete (UHPC), which is not yet regulated in Germany. Please read the second part here (References, vitae see part 1).

3 Classification of UHPFRC in tension

3.1 Parameters and test method

The axial post-cracking tensile strength (notation: f_cft) is the most important material parameter of ultra-high-performance fiber-reinforced concrete (UHPFRC) in tension. It is defined as the maximum nominal concrete tensile stress under axial tension which can be carried by the action of fibers in the cracked state. It therefore corresponds to the maximum value of the stress-crack opening or stress-strain curve in the post-cracking range (Fig. 8d).

Several methods have become established for the determination of the axial...