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Keywords: efflorescence, laitance, concrete, degradation, moisture transport, chemical reactions.

Summary

The paper is concerned with efflorescence and laitance in concrete. Although presence of these phenomena in concrete elements is not fatal for their mechanical properties, such as material strength etc., it can still cause serious problems resulting from impairing their aesthetic value arising in non-negligible financial loses.

The main reasons for efflorescence creation are discussed together with common ways for their removal, reduction and/or remediation. A number of recent publications dealing with the problem of efflorescence are referred to. Thus, the paper provides a solid base of references for further studies in the area of efflorescence in concrete.

The second part of the paper develops a finite element model for analysis of moisture transport in concrete structures. First, a full model containing water convection and water vapour convection and diffusion parts of moisture transport is developed. The model also comprises gas transport and heat transport, (as water vapour properties strongly depend on temperature).

Thereafter, this model is simplified for the purpose of evaluation of concrete predisposition to a possible efflorescence creation. This (second) model comprises only convection transport, because efflorescence is typically caused by salts dissolved in water. Hence, the convection transport (based on Darcy's equations) is the most important phenomenon in fighting the problem of efflorescence and laitance in concrete.

As for constitutive equations, the presented model relies on laboratory measurements. This approach was chosen due to the fact that existing material models would account only with difficulty for special admixtures that are added to concrete in order to reduce moisture transport, (e.g. hydrophobic admixtures). Each material curve, such as hydraulic permeability, saturation etc. is defined as a product of several multi-linear functions.

The model developed for moisture transport in concrete is implemented in the ATENA software, including a special material model allowing direct input for measured hydraulic conductivities and capacities. The two models presented are now available in the CCPolluteTransport [1] and CCStructuresTransport [2] engineering modules.

Finally, the latter module is used to carry out a sample analysis of water infiltration in a ceramic brick and the results are compared with those from Reference [3].

References

1: L. Jendele, "ATENA Pollutant Transport Module - Theory", Edited PIT, Prague, Czech Republic, 2004.
2: V. Cervenka, J. Cervenka, L. Jendele, "Atena Program Documentation, Part 1 Theory", Cervenka Consulting, Prague, Czech Republic, 2000-2007.
3: S. Roels, "Modelling Unsatutrated Moisture Transport in Heterogenous Limestone", Thesis, Departement Burgerlijke Bouwkunde, Laboratorium Bouwfysica, Katholieke University, Leuven, Belgium, 215, 2000.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 93 PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: Paper 270 Multi-Scale Modelling of Concrete Degradation such as Efflorescence and Laitance L. Jendele¹, I. Smid² and J. Cervenka¹ ¹Cervenka Consulting, Prague, Czech Republic ²Prague Institute of Technology, Czech Republic doi:10.4203/ccp.93.270 purchase the full-text of this paper Full Bibliographic Reference for this paper L. Jendele, I. Smid, J. Cervenka, "Multi-Scale Modelling of Concrete Degradation such as Efflorescence and Laitance", in , (Editors), "Proceedings of the Tenth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 270, 2010. doi:10.4203/ccp.93.270 Keywords: efflorescence, laitance, concrete, degradation, moisture transport, chemical reactions. Summary The paper is concerned with efflorescence and laitance in concrete. Although presence of these phenomena in concrete elements is not fatal for their mechanical properties, such as material strength etc., it can still cause serious problems resulting from impairing their aesthetic value arising in non-negligible financial loses. The main reasons for efflorescence creation are discussed together with common ways for their removal, reduction and/or remediation. A number of recent publications dealing with the problem of efflorescence are referred to. Thus, the paper provides a solid base of references for further studies in the area of efflorescence in concrete. The second part of the paper develops a finite element model for analysis of moisture transport in concrete structures. First, a full model containing water convection and water vapour convection and diffusion parts of moisture transport is developed. The model also comprises gas transport and heat transport, (as water vapour properties strongly depend on temperature). Thereafter, this model is simplified for the purpose of evaluation of concrete predisposition to a possible efflorescence creation. This (second) model comprises only convection transport, because efflorescence is typically caused by salts dissolved in water. Hence, the convection transport (based on Darcy's equations) is the most important phenomenon in fighting the problem of efflorescence and laitance in concrete. As for constitutive equations, the presented model relies on laboratory measurements. This approach was chosen due to the fact that existing material models would account only with difficulty for special admixtures that are added to concrete in order to reduce moisture transport, (e.g. hydrophobic admixtures). Each material curve, such as hydraulic permeability, saturation etc. is defined as a product of several multi-linear functions. The model developed for moisture transport in concrete is implemented in the ATENA software, including a special material model allowing direct input for measured hydraulic conductivities and capacities. The two models presented are now available in the CCPolluteTransport [1] and CCStructuresTransport [2] engineering modules. Finally, the latter module is used to carry out a sample analysis of water infiltration in a ceramic brick and the results are compared with those from Reference [3]. References 1 L. Jendele, "ATENA Pollutant Transport Module - Theory", Edited PIT, Prague, Czech Republic, 2004. 2 V. Cervenka, J. Cervenka, L. Jendele, "Atena Program Documentation, Part 1 Theory", Cervenka Consulting, Prague, Czech Republic, 2000-2007. 3 S. Roels, "Modelling Unsatutrated Moisture Transport in Heterogenous Limestone", Thesis, Departement Burgerlijke Bouwkunde, Laboratorium Bouwfysica, Katholieke University, Leuven, Belgium, 215, 2000. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £145 +P&P)
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