scholarly journals Micromechanical modelling of damage induced by delayedettringite formation in concrete

2020 ◽  
Vol 322 ◽  
pp. 01037
Author(s):  
Alexandre Yammine ◽  
François Bignonnet ◽  
Nordine Leklou ◽  
Marta Choinska
Keyword(s):  
Diffusion Coefficient ◽  
Cement Paste ◽  
Internal Variable ◽  
Thermodynamic Force ◽  
Internal Stresses ◽  
Fine Aggregate ◽  
Free Expansion ◽  
Linear Elastic ◽  
Ettringite Formation ◽  
Micro Cracks

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.

scholarly journals Reliability as a Key Driver for a Sustainable Design of Adaptive Load-Bearing Structures

2022 ◽  
Vol 14 (2) ◽  
pp. 895
Author(s):  
Dshamil Efinger ◽  
Andreas Ostertag ◽  
Martin Dazer ◽  
David Borschewski ◽  
Stefan Albrecht ◽  
...  
Keyword(s):  
Environmental Sustainability ◽  
Construction Materials ◽  
Internal Stresses ◽  
Elastic Model ◽  
Load Spectrum ◽  
Operating Life ◽  
Load Bearing ◽  
Linear Elastic ◽  
High Rise ◽  
Bearing Structure

The consumption of construction materials and the pollution caused by their production can be reduced by the use of reliable adaptive load-bearing structures. Adaptive load-bearing structures are able to adapt to different load cases by specifically manipulating internal stresses using actuators installed in the structure. One main aspect of quality is reliability. A verification of reliability, and thus the safety of conventional structures, was a design issue. When it comes to adaptive load-bearing structures, the material savings reduce the stiffness of the structure, whereby integrated actuators with sensors and a control take over the stiffening. This article explains why the conventional design process is not sufficient for adaptive load-bearing structures and proposes a method for demonstrating improved reliability and environmental sustainability. For this purpose, an exemplary adaptive load-bearing structure is introduced. A linear elastic model, simulating tension in the elements of the adaptive load-bearing structure, supports the analysis. By means of a representative local load-spectrum, the operating life is estimated based on Woehler curves given by the Eurocode for the critical notches. Environmental sustainability is increased by including reliability and sustainability in design. For an exemplary high-rise adaptive load-bearing structure, this increase is more than 50%.

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 Effect of basalt powder addition on properties of mortar

2019 ◽  
Vol 262 ◽  
pp. 06002 ◽  
Author(s):  
Magdalena Dobiszewska ◽  
Waldemar Pichór ◽  
Paulina Szołdra
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Beneficial Effect ◽  
Cement Paste ◽  
Cement Hydration ◽  
Asphalt Mixture ◽  
Partial Replacement ◽  
Fine Aggregate ◽  
Freeze Resistance ◽  
Powder Addition

The study evaluates the use of waste basalt powder as a replacement of cement to enhance hydration of cement and mortar properties. The basalt powder is a waste resulting from preparation of aggregate used in asphalt mixture production. Previous studies have shown that analysed waste used as a fine aggregate replacement has a beneficial effect on some properties of mortar and concrete, i.e. compressive strength, flexural strength and freeze resistance. The present study shows the results of the research concerning the modification of cement paste and mortar with basalt powder. The modification consists in adding the powder waste as a partial replacement of cement. The percentages of basalt powder in this research are 0-40% and 0-20% by mass of cement in the pastes and mortars respectively. The experiments were carried out to determine the influence of basalt powder on cement hydration, as well as compressive and flexural strength. Results indicate that addition of basalt powder as a replacement of cement leads to deterioration of compressive strength. The flexural strength of mortar is improved in some cases. Waste basalt powder only slightly influences the cement hydration.

Changes of Pore Structures in Hardened Cement Paste Subjected to Flexural Loading and Wet-Dry Cycles in Seawater

2011 ◽  
Vol 374-377 ◽  
pp. 1930-1933
Author(s):  
Wu Man Zhang ◽  
Wei Sun ◽  
Jin Yang Jiang
Keyword(s):  
Cement Paste ◽  
Mercury Intrusion Porosimetry ◽  
Coupling Effect ◽  
Great Influence ◽  
Hardened Cement ◽  
Hardened Cement Paste ◽  
Pore Structures ◽  
Flexural Loading ◽  
Micro Cracks ◽  
Simulated Seawater

The coupling effect of flexural loading and environmental factors has great influence on the pore structures in hardened cement paste. In this paper, Mercury intrusion porosimetry (MIP) and field emission scanning electron microscope (SEM) were used to analyze and observe the changes of pore structures in hardened cement paste subjected to flexural loading and wet-dry cycles in simulated seawater. The results show that the porosity greatly increases when the flexural loading level is raised from 0 f (the ultimate flexural loading capacity) to 0.8 f. Micro-cracks are observed and the connectivity, width and density of micro-cracks increase with the increment of flexural loading. The peaks position of pore size shifts toward greater micro-pores when the flexural loading was raised from 0 f to 0.8 f. The flexural loading and simulated seawater accelerate the degradation of pore structures.

Microstructure-based modeling of the diffusivity of cement paste with micro-cracks

2013 ◽  
Vol 38 ◽  
pp. 1107-1116 ◽  
Author(s):  
Lin Liu ◽  
Huisu Chen ◽  
Wei Sun ◽  
Guang Ye
Keyword(s):  
Cement Paste ◽  
Micro Cracks

Influence of Stone Dust in Manufactured Sand on Resisting Chloride Penetration in Marine Concretes

2012 ◽  
Vol 174-177 ◽  
pp. 1419-1423
Author(s):  
Jian Bo Xiong ◽  
Peng Ping Li ◽  
Sheng Nian Wang
Keyword(s):  
Diffusion Coefficient ◽  
Pore Structure ◽  
Binding Capacity ◽  
Chloride Penetration ◽  
Dust Content ◽  
Chloride Diffusion ◽  
Fine Aggregate ◽  
Chloride Diffusion Coefficient ◽  
Manufactured Sand ◽  
Stone Dust

In China, manufactured sand has been widely used as fine aggregate in concrete. Therefore, it is necessary to investigate the effect of manufactured sand on durability of concrete. This research studies the influence of stone dust content in manufactured sand on resisting chloride penetration in marine concrete by strength and other physical mechanical tests, XRD, TGA and pore structure analysis. Test results have shown that the chloride diffusion coefficient increased with increasing the stone dust content in manufactured sand when the stone dust content increasing from 3% to 13%. The stone dust in fine aggregate was participated in hydration procedure of cementitious, which will promote the hydration degree of cementitious and increase the chloride binding capacity of hydration product. The influence of stone dust in fine aggregate on chloride diffusion coefficient were the combined effects of concrete pore structure and cementitious hydration products, and the porosity and pore size distribution were the main factors that influence the changes of diffusion coefficient.

Diffusion of Multi-Ionic Species in Recycled Aggregate Concrete

2011 ◽  
Vol 477 ◽  
pp. 56-64 ◽  
Author(s):  
Nattapong Damrongwiriyanupap ◽  
Yu Chang Liang ◽  
Yun Ping Xi
Keyword(s):  
Diffusion Coefficient ◽  
Cement Paste ◽  
Recycled Aggregate Concrete ◽  
Phase Model ◽  
Recycled Aggregate ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Aggregate Concrete ◽  
Multi Scale ◽  
Multi Phase

In recent years, recycled aggregate concrete has been used in reinforced concrete structures. Concrete structures exposed to chloride environment often encountera premature deterioration due to corrosion of steel reinforcement. In order to avoid unplanned maintenances or repairs, it is necessary to develop a reliable prediction model for the chloride diffusion in concrete. The basic formulation of the transport theory will be presented first and then its application to Recycled Aggregate Concrete (RAC) will follow. Chloride diffusion in RAC is different from the diffusion in regular concrete, because the material parameters of RAC such as chloride diffusion coefficient are different from those of regular concrete. In this paper, a multi-scale and multi-phase model will be developed to characterize theinternal structure of the recycled aggregate with a layer of residual cement paste on the surface of natural aggregate and another layer of surface treatment material on the surface of the residual cement paste. The multi-scale and multi-phase model will also be used to characterize the chloride diffusion coefficient of RAC. The numerical analysis of the diffusion equations is performed by using finite element method.

scholarly journals Effect of Main Factors on Fracture Mode of Mortar, A Graphical Study

2017 ◽  
Vol 3 (10) ◽  
pp. 897 ◽  
Author(s):  
Sahar Mahdinia ◽  
Hamid Eskandari-Naddaf ◽  
Rasoul Shadnia
Keyword(s):  
Cement Paste ◽  
Fracture Mode ◽  
Cement Mortar ◽  
Fine Aggregate ◽  
Stress Strain ◽  
Related Factors ◽  
Fracture Angle ◽  
Concrete Properties ◽  
Main Factors ◽  
Cement Strength

One of the most effective ways to identify the concrete properties is to understand further about the cement mortar, which is a mixture of cement paste and fine aggregate. In order to identify the behavior of cement mortar, all required materials including cement, fine aggregate, water as well as the different ratios of each material should beinvestigated. The main objective of this research is to study the effectiveness of main parameters of mortar on the fracture mode and related factors. Specifically 26 mixing designs of flexural mortar with three cement strength classes (32.5, 42.5 and 52.5 MPa), three water to cement (W/C) ratios (0.25, 0.3 and 0.35) and three sand to cement (S/C) ratios (2.5, 2.75 and 3) were first prepared. The prepared samples were then tested using a stress-strain apparatus. Some pictures were finally taken from the fracture surfaces to investigate the mode and angle of fractures. The results indicated that any change in the main parameters of mortar changes the fracture mode and the fracture angle.

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