6 Aug 2014 | 13:39
By Manaswini Acharya

Background


Damage due to ingress and retention of moisture in building materials plays a significant role in limiting the life of the building. When renovation or rehabilitation work is taken up in an old structure it is important to investigate the moisture ingress properties of used building materials in the old structure as well as those in respect of restoration materials. Compatibility of new and old materials is desirable in principle. When compatible materials with identical moisture holding capacity and thermal expansion properties are used in repair works, the combination acts well against hydration and humidification alleviating concerns of deterioration with advance of time.

[1,2,3,4]

DVS© techniques, developed by Surface Measurement Systems Ltd. (an ISO 9001:2008 certified company), was used to 
determine the hygroscopic properties of new and old materials to establish their suitability or otherwise for use in the renovation work.

The Materials, Methodology and Inference

Abbey Mill

Abbey Mill before and during flooding

The studies have been performed on building materials: Abbey Mill old brick, Millbarh stone, Abbey Mill new brick, Abbey Mill Mortar, Millbarh Mortar, Millbarh Timber, and Odda chapel. The samples were kindly made available by UCL for studies. The samples were processed on a DVS automated moisture sorption instrument at 25 ºC for obtaining change in mass and isotherm plots.
 It was seen that the ultimate uptake at 95% RH is as follows: 1.2%, 1.5%, 1.6%, 3.5%, 11.7%, 22.9%, and 24.7% for Abbey Mill Old brick, Millibarh stone, Abbey Mill New brick, Abbey Mill Mortar, Millibarh Mortar, Millbarh Timber, and Odda Chappel, respectively [See graph below].

Water Vapor Sorption Isotherms

Water vapor sorption isotherms showing the ultimate uptake for the samples at 25 ºC

Water absorption properties are useful indicators of durability. High water absorption leads to excessive moisture in the building materials and in turn promotes biological growth processes like fungi, algae and bacteria, all detrimental to durability. There is also likelihood of reduction in thermal insulation rendered by materials with rise in moisture content as thermal conductivity of damp materials are much higher. Needless to say that  it is important to  choose materials exhibiting low water absorption capacity and high strength.
In the findings of current study, the materials with high water uptake like Abbey Mill Mortar, Millibarh Mortar, Millibarh timber and Odda chappel do not appear to be very good restoration building materials because of the cited reasons. On the other hand the percentage of water uptake is low and similar for Abbey Mill New brick, Abbey Mill old brick, and Millbarh stone. Therefore it may  be inferred that Abbey Mill old brick, Abbey Mill new brick and Millbarh stone are better choice as building materials for renovation works.

The DVS technology by SMS

The introduction of Dynamic Vapour Sorption (DVS) in 1994 revolutionised the field of gravimetric moisture sorption measurement. This cutting edge technology precisely measures hygroscopic properties of materials for various uses. The above Investigation on suitable restoration materials made use of DVS instrumentation developed by Surface Measurement Systems (SMS) Ltd ,the world leaders in Dynamic Vapor Sorption and Inverse Gas Chromatography.

Conclusion

The negative effects of presence of moisture in building materials and structures are well documented. In this study, the results of experimental investigation assessing the suitability of materials for rehabilitation of buildings related to their moisture characteristics are presented. The DVS experiments using SMS developed technology renders valuable information for choice of compatible building materials for durable reconstruction like Abbey Mill new brick, Abbey Mill old brick and Millbarh stone.

References

[1] Assessment of the unsaturated water transport properties of an old concrete: Determination of the pore-interaction factor. Stéphane Poyet, Sébastien Charles, Nicolas Honoré, Valérie L’hostis, Cement and Concrete Research 41 (2011) 1015–1023[2] A sorption balance study of water vapour sorption on anhydrous cement minerals and cement constituents E. Dubina, L. Wadsö, J. Plank Cement and Concrete Research 41 (2011) 1196–1204[3] Method for simultaneous determination of sorption isotherms and diffusivity of cement-based materials. Anders Anderberg, Lars Wadsö Cement and Concrete Research 38 (2008) 89–94[4] Investigation of the Effectiveness of Siloxane Hydrophobic Injection for Renovation of Damp Brick Masonry. Z. Pavlík, M. Keppert, M. Pavlíková, R. Černý World Academy of Science, Engineering and Technology Vol:6 2012-01-28

About the author:

The author Ms Manaswini Acharya holds a dual Masters degree (MS and M.Tech) in Advanced Chemistry. She has in-depth expertise across a spectrum of products like DVS and IGC. She currently a Senior Scientist at SMS and has proficiency on the products science & instrumentation. She also holds the position of the Head of Quality.

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