Background and test methods

Classification of ultra-high-performance concrete

The DAfStb Guideline on “Ultra-High-Performance Concrete” will significantly expand the range of structural concretes compared to DIN EN 206. Compressive strength and axial post-cracking tensile strength are key strength parameters of ultra-high-performance fiber-reinforced concrete (UHPFRC). Based on these parameters, UHPFRC is classified into concrete strength classes and performance classes.

The compressive strength test is carried out in accordance with DIN EN 12390-3, where UHPFRC test specimens of different shapes and sizes show compressive strength ratios deviating from that of normal-strength and high-strength concrete. These ratios also essentially depend on the fiber volume fraction and the fiber orientation relative to the direction of compression. The flatness and parallelism of the loaded surfaces have a greater influence on the results of compressive strength tests on UHPFRC than in the case of normal-strength and high-strength concrete. The highest compressive strengths with low scattering are obtained by grinding even the loaded surfaces of the cubes. Because of the overall higher standard deviation, the compressive strength conformity criteria were adjusted for UHPFRC.

The axial post-cracking tensile strength 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 is determined not directly but by means of a bending test. Contrary to the DAfStb Guideline on “Steel-Fiber-Reinforced Concrete”, the bending test is performed in accordance with DIN EN 14651 as a 3-point test on a notched beam. Taking into account the non-linear stress distribution occurring in the cracked state, the basic value of the axial post-cracking tensile strength is derived from the residual flexural tensile strength at a small crack mouth opening displacement. Based on this value, the tested UHPFRC is assigned to a performance class.

Related articles:

Issue 2020-10

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

3 Classification of UHPFRC in tension 3.1 Parameters and test method The axial post-cracking tensile strength (notation: fcft) is the most important material parameter of ultra-high-performance...

Issue 2018-02 Joining precast elements and semi-precast elements

UHPFRC composite joints

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is a cementitious high-perfor­mance material which, through an optimized grain structure and added steel fibers, achieves a compressive...

Issue 2018-02 Part 2: Design and construction

The new DAfStb Guideline on UHPC

The design and construction part of the DAfStb Guideline on UHPC replicates the structure of EN 1992-1-1. The verification methods are based on the design principles for reinforced and prestressed...

Issue 2020-02 Robustness of reinforced concrete columns

Enhanced design rules on compression members using high-strength and ultra-high performance concretes

The robust design of supporting structures is the basis for every structural design. Damages caused by unplanned loads must be limited to a reasonable extent in order to prevent abrupt failure or...

Issue 2018-02 Current investigations of high-tensile concrete

Carbon-fiber reinforcement combined with the orientation effect of 3D pressure

Attempts have long been made to replace conventional steel reinforcement with suitable alternative materials. In this context, cost-effectiveness has been given special priority. At Augsburg...