Experimental applications of mortars with pozzolanic additions: Characterization and performance evaluation

https://doi.org/10.1016/j.conbuildmat.2007.12.003Get rights and content

Abstract

Old fortresses near the coast of Lisbon have been originally rendered with very durable lime mortars, sometimes showing pozzolanic reactions (Silva A. Caracterização de argamassas antigas – casos paradigmáticos (in Portuguese). Lisbon: LNEC; October 2002. Cadernos Edifı´cios, No. 2. p. 87–101; Pinto J, Silva A. Lime mortars with pozzolans. The S. Julião da Barra and Ericeira case studies (in Portuguese). In: 3rd ENCORE, Encontro sobre Conservação e Reabilitação de Edifı´cios. Lisbon: LNEC; May 2003), but their very severe environmental conditions – salty atmosphere and sea water close to foundations and walls, mechanical action of the waves, hot sun and temperature variations, strong wind – and also some lack of knowledge concerning maintenance and conservation techniques, produced the deterioration of these renders and the need for their substitution.

The best options were thought to be lime mortars with pozzolanic additions.

Because of the lack of experience with modern pozzolanic mortars on sea environment, it was decided to carry out experimental applications on one of the Fortresses’ walls of renders with different pozzolanic additives and of some comparison mortars with known performance. Tests were carried out in situ and in laboratory and one of the formulations was chosen for application as a substitution render of the Fortress’s walls.

Introduction

Whenever possible, conservation strategies are always the best option to consider when degradation affects ancient renders: treatment with biocide, small repairs, fulfilment of lacunae, cracks repair, consolidation to restore loss of cohesion or loss of adhesion [27].

Nevertheless, if defects are severe – generalised desegregation or large detachments – it may be necessary to substitute old renders, partially or completely. In those cases it is essential to choose mortars presenting good compatibility with the background and enough durability concerning the environment.

Old fortresses near the coast of Lisbon have been originally rendered with very durable lime mortars, sometimes showing pozzolanic reactions [19], [21], but their very severe environmental conditions – salty atmosphere and sea water close to foundations and walls, mechanical action of the waves, hot sun and temperature variations, strong wind – and also some lack of knowledge concerning maintenance and conservation techniques, produced the deterioration of these renders and the need for their substitution.

To choose substitution renders for these constructions is a challenging situation, because a very good durability in moist, salty, aggressive environment is necessary and this implies resistance to water, meaning some hydraulicity. On the other hand, cement mortars and highly hydraulic lime mortars are known to be incompatible with old masonry [3], [11], [23], [26], [33]. Lime–cement mortars have been used in a similar case, apparently with acceptable results for the last ten years [24], but there are well based opinions [10], [17], [23], [29] sustaining that cement must be avoided whenever possible, because it favours salt damage due to its content on alkaline ions. Thus the best options in this case were thought to be lime mortars with pozzolanic additions.

Because of the lack of experience with modern pozzolanic mortars on sea environment, it was decided to carry out experimental applications on one of the Fortresses’ walls of renders with different pozzolanic additives and of some comparison mortars with known performance. An experimental program was carried out, both on mortars prepared in laboratory and on the panels applied in situ, to verify the compatibility of the solutions with the existent materials and their performance in the aggressive conditions.

The substitution mortar was chosen considering the tests results, the observations accomplished and the first application trials in work.

Section snippets

Render compositions

The render solutions to test in situ were chosen taking into account the following aspects:

  • Compatibility with the old masonry from the physical, mechanical, chemical and aesthetic points of view was a fundamental issue [2], [4], [12], [18], [26].

  • Physical compatibility concerning the water behaviour was considered particularly important because of the exposure to sea water and salts.

  • Materials available in the market and technology accessible to common construction workers.

The option was by

Selected in situ tests

The tests performed on the panels (Fig. 7) to evaluate the behaviour and characteristics of the applied renders included: (i) sphere impact; (ii) controlled penetration; (iii) adhesion to background; (iv) evaluation of the water content; (v) water permeability under low pressure (with Karsten tubes); (vi) carbonation; and (vii) salt identification with colorimetric identifiers.

These tests have been presented in previous work [13], [15], [25], [29] or in bibliography and they are very briefly

Test results

The results of laboratory tests are summarized in Table 3. The in situ test results are synthesised in Table 4, Table 5 and Graphics 1 and 2.

Mechanical behaviour

In what concerns the mechanical resistance at 6 weeks it is observed that, amongst the renders with lime and pozzolanic materials, the panel with silica fume is the most deformable and the most susceptible to penetration, comparable with the air lime–hydraulic lime panel. The highest behaviour seems to belong to the air lime–Cabo Verde pozzolan panel,

Selection of the final render and application

For the selection of the substitution mortar to use some factors were took in consideration:

  • The results of the in situ tests on the panels, especially those on 14 weeks. Actually, the hardening of lime mortars and even of lime–pozzolan mortars, is slow and results at 4 weeks are not representative. Naturally, they have to be high enough to resist to actions during the first period. Lime–Cabo Verde pozzolan panel had the best results, but lime–metakaolin had results almost as good at 14 weeks.

Conclusions

The work carried out showed the importance of in situ applications and in situ tests to evaluate the performance of lime-based mortars for ancient buildings. Actually, the results obtained in laboratory tests can be misleading, because the curing conditions and the application techniques play a fundamental part in the final characteristics of lime mortars.

The use of comparative materials with known behaviour is also important because the in situ tests results have not a direct correspondence

Acknowledgements

The authors wish to thank LNEC technicians Bento Sabala, Dora Santos and Ana Francisco their collaboration in carrying out of the tests. Also the good collaboration of the application enterprise in fulfilling the application and materials specifications was a precious help. Finally, we wish to thank the Fundação para a Ciência e Tecnology (Portuguese Foundation for Science and Technology) for the financial contribution to this work, within the scope of Research Projects “Conservação de rebocos

References (33)

  • J. Lanas et al.

    Masonry repair lime-based mortars: factors affecting the mechanical behaviour

    Cement Concr Res

    (2003)
  • P. Maravelaki-kalaitzaki et al.

    Physico-chemical study of Cretan ancient mortars

    Cement Concr

    (2003)
  • Association Française De Ormalisation (AFNOR). Mesure du Module d’élasticité dynamique. Paris: AFNOR; avril 1975, NF...
  • Binda L, Fontana A, Frigerio G. Mechanical behaviour of brick masonries derived from unit and mortar characteristics....
  • E. Borrelli

    Conservation of architectural heritage, historic structures and materials salts

    (1999)
  • Bromlet Philippe, Martinet Giles, Martin François. Approach for compatible mortars for restoration purposes: stone...
  • European Committee of Standardization (CEN)

    Methods of test for mortar for masonry – Part 3: determination of consistence of fresh mortar (by flow table)

    (1999)
  • European Committee of Standardization (CEN)

    Methods of test for mortar for masonry – Part 11: determination of flexural and compressive strength of hardened mortar

    (1999)
  • European Committee of Standardization (CEN)

    Methods of test for mortar for masonry – Part 12: determination of the adhesive strength of hardened rendering and plastering mortars on substrates

    (2000)
  • European Committee of Standardization (CEN)

    Methods of test for mortar for masonry – Part 18: determination of water absorption coefficient due to capillary action of hardened rendering mortar

    (2002)
  • Fragata A, Paiva H, Velosa AL, Veiga MR, Ferreira VM. Application of crushed glass residues in mortars. To be presented...
  • Gonçalves T. Salt crystallization in plastered or rendered walls. Ph.D. Thesis, Lisbon: IST-LNEC; February...
  • Magalhães AC, Veiga MR, Carvalho F. Diagnosis of anomalies of wall renderings. Experimental techniques for in situ...
  • Magalhães AC, Veiga MR. Estudo comparativo de possı´veis soluções de argamassas para revestimentos de paredes de...
  • Magalhães A, Veiga MR. Comparison of in situ mechanical tests on masonry mortars: sphere impact and controlled...
  • G. Massari et al.

    Damp buildings. Old and new

    (1993)
  • Cited by (101)

    View all citing articles on Scopus
    View full text