Investigation of Microstructural Damage in Ultrahigh‐Performance Concrete under Freezing‐Thawing Action

Abstract

This work aims to investigate the damage in ultrahigh-performance concrete (UHPC) caused by freezing-thawing action. Freezing-thawing tests were carried out on UHPCs with and without steel fibers. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray computed tomography (X-ray CT) were applied to detect the microstructure of the UHPC matrix before and after the freezing-thawing tests. The results showed that UHPC possessed very excellent freezing-thawing resistance due to its dense microstructure. After the freezing-thawing action, cracks occurred and were prone to initiate at the sand-paste interface in the UHPC matrix. MIP results also indicated that cracks appeared in the UHPC matrix after the freezing-thawing action. The number of defects that can be seen by X-ray CT increased in UHPC after the freezing-thawing action as well. The mismatch of the thermal expansion coefficients of the aggregate and the paste is considered to be the reason for the cracking at the sand-paste interface. The steel fibers in UHPC inhibited the propagation of cracks in the matrix and improved the freezing-thawing performance of UHPC.

Micro-CT-based micromechanics and numerical homogenization for effective elastic property of ultra-high performance concrete

“…Thus, the experimental results show decrease while the FE results indicate little difference. This point of view is also observed in Gu et al (2018), showing that, after 800 F-T cycles, micro-cracks at the ITZ between the fiber and matrix in UHPC were detected with SEM.…”

Evaluation of the Thermal and Shrinkage Stresses in Restrained High-Performance Concrete

“…The difference between these two methods lies in the existence of the thermal stress. The concrete and the steel have similar thermal expansion coefficients, which are both about 10–12 με/K [43]. Hence, the thermal stress was not aroused in the rebar restrained stress tests since the temperatures of the concrete and the rebar were almost the same in the tests.…”

Behaviour of green ultra-high-performance concrete beams with corrosion resistant alloy steel (MMFX) bars

“…Its modulus of rupture may reach 15 MPa, compressive strength of more than 150 MPa, and elastic modulus of about 45 GPa, with minimum long-term creep [5]. Besides, UHPC has high resistance to carbonation, chloride penetration and freeze-thaw cycles with no visible damage [6]. Also it provides excellent protection for embedded steel reinforcement [7].…”