As Ultra-High Performance Concrete (UHPC) technology continues to advance, there is an increasing need for innovative methods to characterize and assess its unique material properties properly. Sometimes conventional testing techniques used for conventional concrete and FRCs are inaccurate for UHPC, leading to potential discrepancies in the performance assessment of the material. This session will focus on novel approaches tailored specifically for UHPC characterization, highlighting advancements that address the current challenges and improve testing accuracy. Experts from national and international research groups, material suppliers, and industry professionals will present the latest methods for UHPC testing of mechanical properties such as compression and tension, fresh properties, and durability. The session aims to provide essential insights into UHPC material characterization, contribute to design practices, and ultimately improve the longevity and reliability of UHPC applications.
Learning Objectives:
(1) Evaluate the strengths and limitations of existing and emerging test methods for UHPC conformance and quality control;
(2) Compare different approaches for qualifying UHPC tensile behavior, including direct tension, flexural back-analysis, and wedge-splitting methods;
(3) Interpret experimental findings on UHPC mechanical properties to inform material specifications and performance standards;
(4) Recognize how new test frameworks can enhance reliability, repeatability, and standardization in UHPC characterization.
This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.
Towards a UHPC Material Conformance Framework for UHPC
Presented By: Rafic Helou
Affiliation: FHWA-TFHRC
Description: With the publication of the Guide Specification for the Structural Design with Ultra-High Performance Concrete (UHPC) by the American Association of State and Highway Transportation Officials (AASHTO), the need for material conformance guidance has become critical to enable the widespread and consistent use of UHPC in structural engineering. To address this need, the Federal Highway Administration (FHWA) has embarked on an effort, in coordination with AASHTO, to develop the needed UHPC material conformance guidance. This framework consists of two key sections: the first outlines the required testing procedures to qualify UHPC compression and tensile parameters, while the second defines the acceptance phase, ensuring that UHPC supplied during production remains consistent with the qualified material. A recently completed testing program at the FHWA Turner-Fairbank Highway Research Center has established a comprehensive set of compression, tension, and flexure test results for various UHPC mixtures, providing critical data to support the experimental validation of the proposed conformance framework. While the AASHTO T 397 uniaxial tension test method has been confirmed as a reliable approach for qualifying UHPC tensile properties for structural design using prismatic specimens, the program identified a new flexural test method that uses the same specimens, providing a practical solution for assessing tensile behavior during production and acceptance. Building on prior approaches and utilizing simplified equipment, this method is currently being refined in collaboration with AASHTO to establish it as a standardized testing protocol. This presentation will provide an overview of the proposed UHPC material conformance framework, demonstrate its implementation, and highlight the evolved flexural test method proposed for UHPC acceptance.
Evaluation of Test Methods for Characterization of UHPC Mechanical Properties, and for Pre-qualification and Quality Control of UHPC Materials
Presented By: Angel Perez Irizarry
Affiliation: Wiss, Janney, Elstner Associates Inc.
Description: As applications of UHPC continue to advance, there is an increasing need for new test methods to
characterize its unique material properties since conventional testing techniques used for conventional concrete and fiber reinforced concrete may not be suitable for UHPC. The recently published AASHTO Guide Specifications For Structural Design With UHPC requires that the tensile properties of UHPC used for structural design be determined following AASHTO T397-22: Uniaxial Tensile Response of Ultra-High Performance Concrete. AASHTO T397 is therefore the benchmark for the pre-qualification process of UHPC mixtures to be used for design per the AASHTO Guide Specifications. However, AASHTO T397 is a complex test requiring specialized testing equipment and meticulous sample preparation and test protocol. Furthermore, the likelihood of crack localization within the gauge length and thus obtaining a complete stress-strain response is typically between 50 and 70%. Given these challenges, AASHTO T397 is not a practical or cost-effective test for routine quality control and acceptance of UHPC. This presentation
summarizes the results of an experimental study aimed to: 1) quantify the variability of AASHTO T397, ASTM C1609, and the double-punch test to better understand the potential of these test methods to be used for routine QC of UHPC and ensure compliance with the pre-qualified tensile performance of UHPC; and 2) evaluate the tensile stress-strain response and the flexural response of a UHPC mixture with the goal of investigating the adequacy of defining minimum flexural performance (load-deflection curves) for routine QC testing of UHPC. Test results for samples cast from a single UHPC batch and tested by a single operator will be presented. Results from published data are included to develop correlations between flexure and tensile response of various UHPC mixtures and illustrate a potential approach to defining acceptance criteria based on the ASTM C1609 flexural test for
Development of Alternative Test for Characterization of Ultra-High Performance Fiber Reinforced Concrete in Tension
Presented By: Zoi Ralli
Affiliation: CTLGroup
Description: This paper presents a new, robust, and easy to conduct testing method for UHPFRC material characterization in tension, including the cracking and ultimate tensile strength, elastic modulus, tensile ductility and strain energy capacity. The proposed test setup that is a modification of the Brazilian Splitting Test, designed to alleviate such ambiguities as observed in the BST, takes advantage of easily accessible compression testing equipment that most labs have and uses a strut & tie model. The proposed test setup is evaluated by comparing the tension stress-strain response results with those obtained from direct tension tests for a variety of commercial UHPFRC premixes. Results demonstrate excellent agreement with the direct tension testing with lower dispersion in the response, showing the potential of the test to be used for material characterization but also quality control testing.
Bridging Classical FRC and AASHTO T-397: A Consistent Path to Reporting the Effective Cracking and Localization Strengths for Strain-Hardening UHPC
Presented By: Manuel Bermudez
Affiliation: National Cheng Kung University
Description: A recently published shear database revealed that only 30 percent of UHPC beam studies report tensile properties at all, and those reports include only the peak tensile strength, omitting the cracking strength that controls strain-hardening behavior. The gap between visual first-crack practices inherited from classical fiber-reinforced concrete (FRC) and UHPC standards for structural applications hinders data consistency and slows acceptance, particularly for non-proprietary mixes. This study advocates adopting the effective cracking strength and localization strength defined in AASHTO T-397, turning a subjective first-crack sighting into a repeatable load-strain point. A concise example demonstrates how the AASHTO T-397 method captures the onset of uniform microcracking without visual judgment. Consistently reporting the effective cracking and localization strengths will streamline database compilation, improve cross-study comparisons, and guide engineers in adjusting fiber volume, aspect ratio, and bond characteristics to develop UHPC mixes that meet strain-hardening requirements.
Identifying the Tensile Constitutive Law of UHPC: Double Edge Wedge Splitting Test Compared to Direct Tensile Test and Flexural Test Back Analysis
Presented By: Liberato Ferrara
Affiliation: Politecnico di Milano
Description: The need of more environmentally and economically sustainable structures pushes ahead the formulation of new advanced cementitious materials which, on the one side, can reduce the carbon footprint in the production phase, and, on the other side, can significantly improve the structural durability thus resulting into a longer service life with reduced maintenance. In a design perspective, this makes it necessary to develop an effective approach for identifying the main parameters describing the overall behaviour in tension. In the present study, starting from the results of 4-Point Bending Tests (4PBT) and direct tensile tests, performed on specimens extracted from same larger cast slab structure, a combined experimental/numerical identification procedure has been implemented in order to evaluate the effective material behaviour in direct tension in terms of stress-strain law. It has been also investigated the role of different types of fibre and cement on the overall tensile response and post-crack localization behaviour. Moreover an experimental methodology named Double Edge Wedge Splitting test, which through indirect testing identifies straightforward the tensile constitutive law, s thoroughly validated, employing specimens obtained from undamaged portions of the specimens previously tested in bending, so to have a clear identification of the material, also allowing to assess the role of fibre orientation and through thickness distribution in the test specimens.
The issue of the stability of the performance of the material over time even in aggressive conditions is discussed.
Influence of Size, Casting, and Support Conditions on the Flexural Response of UHPC Beams
Presented By: Kay Wille
Affiliation: University of Connecticut
Description: The flexural behavior of fiber-reinforced concretes (FRCs) is commonly assessed through standardized beam tests under three- or four-point loading. However, significant variability in results can arise from differences in specimen size, casting method, and support conditions. This presentation highlights findings from a comprehensive experimental program evaluating these parameters for UHPC. Equivalent bending strengths ranging from 10 MPa (1.4 ksi) to 29 MPa (4.2 ksi) were obtained using the same mixture design, depending on test setup. Finite element analyses further revealed that high-friction supports, modeled with a shear friction coefficient of 0.4, increased apparent bending strength by approximately 30% compared to roller-like supports. Results also emphasize the need for clearer guidance on casting methods when testing highly workable FRC mixtures. The study underscores the importance of test parameter selection in achieving reliable and comparable assessments of UHPC flexural performance.