scholarly journals Pore size analyses of cement paste exposed to external sulfate attack and delayed ettringite formation

2019 ◽  
Vol 123 ◽  
pp. 105766 ◽  
Author(s):  
Yushan Gu ◽  
Renaud-Pierre Martin ◽  
Othman Omikrine Metalssi ◽  
Teddy Fen-Chong ◽  
Patrick Dangla
Keyword(s):  
Pore Size ◽  
Cement Paste ◽  
Sulfate Attack ◽  
Delayed Ettringite Formation ◽  
Ettringite Formation

scholarly journals Fractal Cracking Patterns in Concretes Exposed to Sulfate Attack

Materials ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2338 ◽  
Author(s):  
Jinwei Yao ◽  
Jiankang Chen ◽  
Chunsheng Lu
Keyword(s):  
Crack Nucleation ◽  
Fractal Dimensions ◽  
Sulfate Attack ◽  
Growth Patterns ◽  
X Ray Diffraction ◽  
Delayed Ettringite Formation ◽  
Crack Evolution ◽  
X Ray ◽  
Surface Cracking ◽  
Ettringite Formation

Sulfate attack tests were performed on concrete samples with three water-to-cement ratios, and micro-crack growth patterns on concrete surfaces were recorded. The expansive stress and crack nucleation caused by delayed ettringite formation (DEF) were studied using X-ray diffraction and scanning electron microscopy. By means of a digital image processing technology, fractal dimensions of surface cracking patterns were determined, which monotonously increase during corrosion. Moreover, it is shown that the change of fractal dimensions is directly proportional to accumulation of DEF, and therefore, a simple theoretical model could be proposed to describe the micro-crack evolution in concretes under sulfate attack.

Modelling the Swelling due to Delayed Ettringite Formation - Application to a Real Bridge

2016 ◽  
Vol 711 ◽  
pp. 722-729
Author(s):  
Othman Omikrine-Metalssi ◽  
Badreddine Kchakech ◽  
Stéphane Lavaud ◽  
Bruno Godart
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Cement Paste ◽  
Early Age ◽  
High Humidity ◽  
Delayed Ettringite Formation ◽  
Precise Control ◽  
Ettringite Formation ◽  
Structural Disorders

Delayed ettringite formation (DEF) can affect the long-term durability of concrete structures by causing cracking and expansion of the material. Consequently, mechanical properties decrease which may cause large structural disorders due to unexpected deformations and additional stresses in concrete and reinforcement. This reaction consists in ettringite crystallization within concrete after hardening is substantially complete, and in which no sulphates come from outside the cement paste. It may occur in materials that have been subjected to temperature above about 65 °C at early age and to high humidity. At this high temperature, the ettringite turns unstable while the concrete is still plastic and forms again after cooling in the hardened material, thus generating swelling due to crystallisation pressure.This article aims to present a new model for the calculation of structures affected by DEF and to study the effect of the prefabrication temperature on the development of this reaction. In this context, the elaborated model was applied to the 3D simulations of a real bridge affected by this phenomenon. The results highlight that the temperature reached in the precast beams of the studied bridge during prefabrication has a significant effect on the displacements and stresses. Therefore, more precise control of the prefabrication temperature has to be applied in order to prevent the swelling and damage to structures.

The Development of Accelerated Test Method for Internal Sulfate Attack by Delayed Ettringite Formation

2020 ◽  
Vol 987 ◽  
pp. 27-32
Author(s):  
Van Huong Nguyen ◽  
Nordine Leklou ◽  
Pierre Mounanga
Keyword(s):  
Elevated Temperature ◽  
Electrochemical Techniques ◽  
Sulfate Attack ◽  
Test Method ◽  
Delayed Ettringite Formation ◽  
Ettringite Formation ◽  
Physico Chemical ◽  
Mechanical Performances ◽  
Induced Decomposition ◽  
Internal Sulfate Attack

Delayed Ettringite Formation (DEF) is an internal sulfate attack caused by heat-induced decomposition and/or prevention of normal ettringite formed during the initial hydration of cement at elevated temperature (above about 70°C) and its re-crystallization in the hardened matrix. This reaction is a physico-chemical phenomenon inducing an expansion of the cement paste that could lead to cracking of cementitious matrix. These cracks result in a decrease in the mechanical performances and durability parameters of the material. However, the internal sulfate attack is characterized by a very slow reaction kinetics and therefore it is difficult to study it in laboratories. This research developed an accelerated method focused on mortar specimens; it is based on electrochemical techniques in order to speed the leaching of alkalis that could be accelerated the DEF.

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