The effect of natural pozzolan on delayed ettringite formation of the heat-cured mortars

Nguyen, Van-Huong; Leklou, Nordine; Aubert, Jean‐Emmanuel; Mounanga, Pierre

doi:10.1016/j.conbuildmat.2013.07.016

Cited by 53 publications

(26 citation statements)

References 16 publications

(22 reference statements)

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“…A series of experiments [36][37][38] have studied the macroscopic expansion along with measurement of Young's modulus loss over months of samples subjected to DEF. In these experiments, the macroscopic stress Σ = 0 so that the isotropic macroscopic expansion E = E DEF 1 is linked to the DEF pressure in cement paste p = 3k p ε f by (4) as E DEF = (b hom /3k hom )p. The potential energy is then only function of the two state variables (p,d) and the damage driving force simplifies to The mortar follows a reversible poroelastic evolution until the DEF pressure reaches a first value such that F d = F c .…”

Section: Application To Damage Induced By Defmentioning

confidence: 99%

Micromechanical modelling of damage induced by delayedettringite formation in concrete

et al. 2020

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A multi-scale poromechanical model of damage induced by Delayed Ettringite Formation (DEF) as a consequence of progression of micro-cracks at the fine aggregate scale is developed. The aim is to link the DEF-induced expansion at both the microscopic and macroscopic scales to the loss of stiffness of the mortar and the increase of its diffusion coefficient. At the microscopic scale, mortar is assumed to be constituted of three phases: cement paste, sand and micro-cracks. Damage is assumed to be driven by a free expansion of cement paste due to ettringite crystallization pressures in small capillary pores, at a lower scale. The corresponding homogenised poroelastic properties are estimated along with the diffusion coefficient by resorting either to a Mori-Tanaka scheme or to a self-consistent scheme, as a function of paste and aggregate properties as well as on the density of micro-cracks. The latter is assumed to be an evolving internal variable in order to model DEF-induced damage in the mortar. As the DEF-induced expansive free strain in the cement paste is restrained by the sand particles, internal stresses arise in the mortar. The corresponding free energy can be partially released by an increase in the micro-cracks density by analogy with the energy restitution rate of linear elastic fracture mechanics. The role of the damage criterion adopted on the thermodynamic force associated with micro-cracks density increase is investigated.

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Section: Application To Damage Induced By Defmentioning

confidence: 99%

Micromechanical modelling of damage induced by delayedettringite formation in concrete

et al. 2020

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“…Gathering eqs. (14), (19) and (20) yields the average of the strain concentration tensor in the sand:…”

Section: Problem (P')mentioning

confidence: 99%

“…Five mortar formulations results subjected to DEF are compared to the model results. Four formulations have been prepared by Nguyen, who studied mineral additions impact on DEF [3,20]. A last formulation was prepared recently (Normalized CEM I (Y)) for additional results comparison.…”

Section: Experimental Set Upmentioning

confidence: 99%

“…Two brass studs, one on the upper and one the lower square surface of the prisms are used to measure the specimen expansion. After molding, the prisms are placed at 20 • C for 2 hours and cured in an oven at maximum 80 • C for over 149 hours in order to simulate heat exposure in precast concrete elements [20]. After heat treatment, specimens are placed in plastic boxes filled with deionized water at 20 • C. Water is frequently changed in order to enhance alkali lixiviation which accelerates ettringite formation.…”

Section: Experimental Set Upmentioning

confidence: 99%

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Micromechanical modelling of damage induced by delayed ettringite formation

Yammine¹

2019

Proceedings of the 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures

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Delayed ettringite formation (DEF) is a pathology that induces concrete swelling and cracking. Factors contributing to DEF have been identified experimentally, but on the modelling side the link between DEF-induced expansion and the evolution of concrete and mortar physical properties has been less studied. A multi-scale poromechanical model is introduced which features a description of DEF induced mortar damage by progression of microcracking. The model considers mortar as a three phases material that is constituted of cement paste, sand and micro-cracks. The Mori-Tanaka scheme is used to homogenise the poroelastic properties of the mortar. The loading parameters are a macroscopic strain and an expansive free strain induced by DEF in cement paste. Damage progression by micro cracking is accounted for by a Griffith-like energy criterion. The model allows to link the DEF-induced expansion at both the microscopic and macroscopic scales to the loss of stiffness of the mortar. A comparison of the model to experimental data on mortars formulated with CEM I cement and natural silica sand is carried out.

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“…Whereas the replacement of cement with 8 % of silica fume does not make it possible to control long-term expansion due to the crystallization of delayed ettringite, although the onset of expansion is delayed [19,20]. Papers [21,22] note a significant influence over the expansion of the high specific surface of pozzolan. It is expedient to study the efficacy of pozzolan, which contains active Al 2 O 3 , in terms of control over the crystallization of secondary ettringite, whose mechanism and the conditions for formation differ from the mechanism and conditions for a delayed ettringite formation [1].…”

Section: Literature Review and Problem Statementmentioning

confidence: 99%

Improving the resistance of concrete for sleepers to the formation of delayed and secondary ettringite, the alkali-silica reaction, and electric corrosion

Troyan

Sova²

2019

EEJET

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Представлено результати дослiдження впливу добавок модифiкаторiв на корозiйну стiйкiсть бетону для залiзобе тонних шпал за критерiями електричного опору, стiйко стi до лужної корозiї та корозiї внаслiдок кристалiзацiї запiзнiлого та вторинного еттрингiту. Наведенi дослiджен ня було виконано в рамках вирiшення проблеми передчасно го руйнування залiзобетонних шпал, внаслiдок прогресуючо го трiщиноутворення на стадiї термообробки та подальшої експлуатацiї. Встановлено, що введення до складу бето ну шпал пуцоланових добавок, що мiстять в своєму складi активний Al 2 O 3 , дозволяє мiнiмiзувати ризик корозiї, що обумовлена реакцiєю кремнезему заповнювачiв з лугами та корозiї внаслiдок кристалiзацiї запiзнiлого та вторинно го еттрингiту. Висока ефективнiсть щодо названих видiв корозiї пуцоланових добавок, якi вмiщують активний Al 2 O 3 , пояснюється зв'язуванням лугiв в нерозчиннi лужнi гiдроалю мосилiкати, що сприяють ущiльненню системи зi зниженням вмiсту iонiв Na + /K + в розчинi. Зниження вмiсту в поровому розчинi лугiв обумовлює блокування реакцiї «луг-кремнiєва кислота» та пiдвищення температури стабiльностi еттрiн гiту до бiльш високих значень. Це знижує потенцiйну кiль кiсть циклiв утворення вторинного еттрiнгiту та iмовiр нiсть утворення запiзнiлого еттрiнгiту. Альтернативний механiзм дiї активного Al 2 O 3 пуцолан полягає у зв'язуван нi iонiв SO 4 2та Ca 2+ з порового розчину у низкосульфатнi форми гiдросульфоалюмiнатiв кальцiю, що виключає крис талiзацiю запiзнiлого та вторинного еттрiнгiту. Зниження витрати цементу та води за рахунок викори стання добавокпластифiкаторiв дозволяє пiдвищити пито мий електричний опiр модифiкованого бетону шпал вище рiвня контрольного складу без добавок. Одержанi результа ти надають можливiсть забезпечення проектної довговiч ностi бетону залiзобетонних шпал шляхом їх комплексної модифiкацiї пластифiкаторами та активними мiнеральни ми добавками, що мiстять активний Al 2 O 3 Ключовi слова: реакцiя «луг-кремнiєва кислота», за пiзнiлий еттрингiт, вторинний еттрiнгiт, електричний опiр, метакаолiн, зола виносу, мiкрокремнезем, пластифiкатор

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The effect of natural pozzolan on delayed ettringite formation of the heat-cured mortars

Cited by 53 publications

References 16 publications

Micromechanical modelling of damage induced by delayedettringite formation in concrete

Micromechanical modelling of damage induced by delayedettringite formation in concrete

Micromechanical modelling of damage induced by delayed ettringite formation

Improving the resistance of concrete for sleepers to the formation of delayed and secondary ettringite, the alkali-silica reaction, and electric corrosion

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