Investigation on degradation of micromechanical properties of interfacial transition zone of ultra-high performance concrete under freeze-thaw cycles

The Ultra High Performance Concrete (UHPC) is a very promising material suitable for application in special structures. However, the knowledge of performance of this relatively new material is rather limited. The exceptional mechanical properties of UHPC allow for a modification of the design rules, which are applicable in ordinary or high strength concrete. This paper deals in more detail with impact of thermal stress on bond properties between prestressing strands and UHPC and an influence of high temperature to final material properties of different UHPC mixtures. Specimens in the first experimental part were subjected to the cycling freeze-thaw testing. The relationship between bond behavior of both type of material (UHPC and ordinary concrete) and effect of cycling freeze-thaw tests was investigated. The second part of experimental work was focused on mechanical properties of UHPC exposure to the high temperature (Tmax = 200°C to Tmax = 1000°C). Tested mechanical properties were compressive and flexural strengths, the fracture properties will be presented in the next paper. The obtained experimental data serve as a basis for further systematic experimental verification and more accurate information about the significantly higher material properties of UHP(FR)C and its behavior in extreme conditions.

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The Influence on High-Temperature Mechanical Properties of Hybrid-Fiber-Reinforced High-Performance Concrete and Microscopic Analysis

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.226-228.1709 ◽

2012 ◽

Vol 226-228 ◽

pp. 1709-1713

Author(s):

Lan Yan ◽

Y.M. Xing ◽

Ji Jun Li

Keyword(s):

Mechanical Properties ◽

High Temperature ◽

Transition Zone ◽

High Performance ◽

Room Temperature ◽

Steel Fiber ◽

High Performance Concrete ◽

Interfacial Transition Zone ◽

Hybrid Fiber ◽

High Temperature Mechanical Properties

This paper investigated the high temperature mechanical properties of the hybrid fiber reinforced high performance concrete (HFHPC) and normal concrete (NC) .After being subjected to different elevated heating temperatures, two kinds of concretes have been tested for the compressive strength, splitting tensile strength and flexural strength of test specimen at room temperature and 200 °C,400 °C,600 °C,800 °C.Microstructure changes of concrete were also observed by using Scanning Electron Microscopy (SEM) after high temperature. The results show that the hybrid fiber can significantly increase mechanical properties of the concrete at room temperature and high temperature. SEM and XRD analysis shows that there is a permeable diffusion layer in the steel fiber surface because of solid state reaction in the Interfacial Transition Zone of steel fiber and concrete. This permeable diffusion layer is white, bright, serrated and mainly consist of FeSi2 and the complex hydrated calcium silicate. The compounds of this layer change the Interfacial Transition Zone structure, enhance bonding capacity of the steel fiber and matrix, and increase the high temperature mechanical properties of concrete.

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Fire-Damage or Freeze-Thaw of Strengthening Concrete Using Ultra High Performance Concrete

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.79-82.2047 ◽

2009 ◽

Vol 79-82 ◽

pp. 2047-2050 ◽

Cited By ~ 9

Author(s):

Min Gin Lee ◽

Yi Shuo Huang

Keyword(s):

High Temperature ◽

High Performance ◽

High Performance Concrete ◽

Fire Damage ◽

Ultra High Performance Concrete ◽

Freeze Thaw ◽

Concrete Members ◽

Repair Materials ◽

Environmental Durability ◽

Temperature Exposure

There are some reinforced concrete structures exposed to severe environmental conditions might require maintenance or strengthening. Many of these severe circumstances are the result of extreme climate conditions such as low temperature, freeze–thaw action, fire attack, and exposure to deicing salts. Because of this, the environmental durability of both the repair materials and methods used in rehabilitation applications are of utmost importance. A small fire can reach 250°C, while a common blaze can easily produce temperatures of around 800°C. In major conflagrations the temperature can even reach 1100°C. At this level, the heat affects most materials, provoking the spontaneous combustion of some of them and affecting the resistance of others. However, very little research has been performed in evaluating the environmental durability of strengthening materials for concrete members. Very little work has been done on the effects of freeze–thaw cycling on bonding and repair materials. In this study, ultra high performance concrete (UHPC) was used to investigate the effect of strengthening concrete members by fire-damage test or freeze-thaw test. The results show that the mechanical properties of UHPC possess high strength, toughness, and freeze-thaw resistance. The CFRP (carbon fiber reinforced plates) wrapping specimens exposed at 300 °C showed totally failure with the deterioration of the adhesive. The UHPC with bonding 10 mm thickness specimens exposed at 400 °C and duration of 1 hour still in good shape. The UHPC with 1-cm or 2-cm thickness on strengthening concrete members could be obtained specific retrofit effects. The performance of UHPC specimens is better than those of CFRP wrapping specimens during high temperature exposure. The results of slant shear tests show that the bond strength of PC/PC, UHPC/PC and UHPC/UHPC decreased significantly after 600 freeze–thaw cycles or high temperature exposure.

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

International Journal of Damage Mechanics ◽

10.1177/1056789519848475 ◽

2019 ◽

Vol 29 (1) ◽

pp. 45-66 ◽

Cited By ~ 3

Author(s):

Qi Luo ◽

Dongxu Liu ◽

Pizhong Qiao ◽

Zhidong Zhou ◽

Yanlin Zhao ◽

...

Keyword(s):

Elastic Properties ◽

Representative Volume Element ◽

High Performance ◽

High Performance Concrete ◽

Volume Element ◽

Image Resolution ◽

Micro Ct ◽

Ultra High Performance Concrete ◽

Freeze Thaw ◽

Representative Volume

A computational homogenization model using microstructures obtained from X-ray micro-CT is developed to estimate the porosity-based elastic properties of ultra-high performance concrete under freeze–thaw action. The model is transformed directly from micro-CT which is capable of reflecting realistic distribution of porosity and heterogeneities inside the ultra-high performance concrete. Factors are taken into consideration, including the determination of representative volume element, the position and numbers of representative volume element cubes, fiber orientation, image resolution, applied filter, and pore distribution. The relationship between the material internal structure and freeze–thaw resistance is studied at micro-scale. The volume-averaged homogenization approach is applied to calculate the effective properties of the ultra-high performance concrete which are compared with experimental data. It is demonstrated that the proposed model provides an effective tool to evaluate the elastic properties of the ultra-high performance concrete based on microstructural characterization data.

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