Evaluation of the Behaviour of Lime and Cement Based Mortars Exposed at Elevated Temperatures

Abstract

Exposure to fire and elevated temperatures is diachronically a significant decay factor, influencing the stability of structures. Cement and lime-based mortars have a different behavior when exposed at elevated temperatures, usually testified by the post-fire preservation state of historic and contemporary constructions. In this paper, the correlation of their properties is envisaged, in order to identify the key elements of their performance. To this direction, five compositions of cement and lime based mortars were manufactured and tested, after their exposure at 200oC, 400oC, 600oC, 800oC and 1000oC. The binders used concerned CEM I42.5Ν (C), hydrated lime (L) and natural pozzolan (P), while the systems applied regarded C, C:L (1:1), L, L:P (1:1) and L:P:C (1:0.8:0.2) (parts per weight). The aggregates used were natural of siliceous origin and their gradation varied from 0-4mm to 0-8mm. The B/A ratio was 1/2 by weight and the W/B ratio was adjusted in order to maintain workability around 15±1cm. The physico-mechanical properties of the specimens, were recorded before and after their exposure at the selected temperatures. From the evaluation of the results, it was concluded that the mortars’ behavior was different at the early temperature rate (up to 600oC) according to their type, whereas the results were more comparable at the extreme temperature level. Generally it was observed that although the initial strength of the lime-based mortars was low (1-4MPa), they presented a more stable and efficient performance at the elevated temperatures, rendering them probably more resistant at the first stages of fire actions. Cement- based mortars seemed to present a better performance at the highest temperatures of 800oC and 1000oC.

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References

[1] Lea F. and Stradling R. The resistance to fire of concrete and reinforced concrete. Engineering (1922) 114:395R-396R.

[2] Georgali B. and Tsakiridis P.E. Microstructure of fire-damaged concrete. A case study. Cement Concrete Comp (2005) 27:255-59.

[3] Chan Y.N., Peng G.F. and Anson M. Residual strength and pore structure of high- strength concrete and normal strength concrete after expose to high temperature. Cement Concrete Comp (1999) 21:23-27.

[4] Ingham J.P. Application of petrographic examination techniques to the assessment of fire-damaged concrete and masonry structures. Mater Charact (2009) 60:700-9.

[5] Khoury G.A. Effect of fire on concrete and concrete structures. Prog Struct Eng Mat (2000) 2:429-47.

[6] Chung H.W. and Law K.S. Assessing fire damage of concrete by the ultrasonic pulse technique. Cement Concrete Aggr (1985) 7:84-8.

[7] Pachta V., Triantafyllaki S. and Stefanidou M. Performance of lime-based mortars at elevated temperatures. Constr and Build Mat (2018) 189:576-84.

[8] Krzemien K. and Hager I. Post-fire assessment of mechanical properties of concrete with the use of the impact-echo method. Constr Build Mater (2015) 96:155-63.

[9] Stefanidou M. and Pachta V. Influence of perlite and aerogel addition on the performance of cement-based mortars at elevated temperatures. In: Int. Conf. SBE19, Sustainability in the built environment for climate change mitigation (2019).

[10] RILEM TC 129 MHT. Test methods for mechanical properties of concrete at high temperatures and RILEM TC HTC. Mechanical concrete properties at high temperature- modelling and applications; Part 1: Introduction. Mater Struct (2007) 40:841-53

[11] RILEM TC 200-HTC. Recommendation of RILEM TC 200-HTC: mechanical concrete properties at high temperatures - modeling and applications Part 1: Introduction - General presentation. Materials and Structures (2007) 40:841-53.

[12] EN 1991-1-2 2002. Eurocode 1: Actions on structures - Part 1-2: General actions - Actions on structures exposed to fire. European Committee for Standardization (Brussels).

[13] EN 1992 2004. Eurocode 2: Design of concrete structures - Part 1-2: General rules - Structural fire design European Committee for Standardization (Brussels).

[14] ISO 834-11 2014. Fire resistance tests - Elements of building construction - Part 11: Specific requirements for the assessment of fire protection to structural steel elements. International Standards Organization.

[15] BS 476-3 2004. Fire tests on building materials and structures. Classification an method of test for external fire exposure to roofs. British Standards Institute (London).

[16] Russo S. and Sciarretta F. Masonry exposed to high temperatures: Mechanical behaviour and properties - An overview. Fire Safety Journal (2013) 55:69-86.

[17] Pachta V., Triantafyllaki S. and Stefanidou M., The impact of elevated temperatures at the properties of lime-based mortars. In: J.I. Alvarez et al. (Eds): 5th Historic Mortars Conference, HMC 2019, RILEM Proceedings, PRO 130 (2019), pp. 1156-1165.