Thermal analysis and calorimetric methods in the characterisation of polymorphs and solvates

Mortars and concretes employed in ancient structures concern composite materials which have exhibited excellent durability through time. They were used as lining materials in cisterns, wells, aqueducts, shafts and duct drains, as supporting materials for pavements and mosaics, as plasters on external and internal walls, as supporting materials for frescoes and as joint mortars on masonry structures. They were comprised of various binding materials (or mix of them) and natural or artificial aggregates, along with natural or artificial pozzolanic additions, primarily of volcanic origin, that improved their performance and prolonged their longevity. Moreover, various types of organic substances were employed to increase plasticity and regulate setting rates, while fibrous materials were commonly used to obtain greater strengths or to avoid cracks due to the shrinkage during setting. The comprehension of the production procedures employed and of the physico-chemical and mechanical characteristics of such composite materials can be achieved by integrating properly the results of various analyses. Data obtained from tests performed on a large number of historic composites sampled from ancient structures in the Mediterranean Basin permitted the identification of physico-chemical and mechanical characteristics of the most typical mortars encountered in ancient structures.

Composite materials in ancient structures

Awareness of the need for compatible materials for the preservation of the architectural heritage has resulted in the revival of lime-based mortar technology and applications. However, knowledge of...

Lime Mortars for the Conservation of Historic Buildings

In this research, restoration mortars with analogous chemical composition of binders, aggregates and mineral additions, as they derive from the study of historic mortars, were evaluated regarding the strength development and the lime reaction, up to 15 months of curing. For this purpose several mixtures were tested in laboratory regarding their chemical and mechanical characteristics. The obtained results show that most of them present a slow rate of chemical and mechanical evolution, with the exception of hydraulic lime mortar and mortar with lime putty–natural pozzolanic addition. The best mechanical behavior was observed in mortars with lime powder and lime powder–artificial pozzolanic addition. These materials present also a low ratio of compressive to flexural strength ( f c / f f ). Further investigations on these materials would determine the time where their chemical and mechanical characteristics become stable. Only at that time, it would be possible to compare the compatibility characteristics of the restoration mortars with those employed in the past.

Strength development and lime reaction in mortars for repairing historic masonries

http://digital.csic.es/bitstream/10261/97254/1/2010%20Polymer%20Kinetic%20model%20for%20thermal%20dehydrochlorination%20of%20poly%28vinyl%20chloride%29.pdf

Kinetic model for thermal dehydrochlorination of poly(vinyl chloride)

Following previous work on the measurement of meaningful activation energies and the application of Constant Rate Thermal Analysis (CRTA) to the determination of kinetic parameters [1, 2], here we further examine sources of error in determining activation energies and go on to consider the form of the alpha function and the value ofA. Using theoretical arguments based on transition state theory, we conclude that allowing significant pressures of product gas to appear in the reaction environment will lead to very high values for apparent activation energies. We note that, although this is observed in practice for calcium carbonate, it in no way invalidates the application of the Arrhenius equation to solid state decomposition reactions, provided care is taken to avoid this type of distortion of experimental results. We attempt to determine the alpha function for the decomposition of calcium carbonate using data gathered from a variety of different types of temperature programme and reaction conditions. We find that the apparent alpha function depends on the method adopted and the experimental conditions used. We propose an explanation of why this occurs and tentatively introduce a new way of looking at the development of a reaction interface for this type of reaction. We review the literature and conclude that, while significant variations for the activation energy for the decomposition of calcium carbonate exist, a critical appraisal leads to good agreement amongst values that follow good experimental practice and reliable methods of data reduction. The apparent divergence of results can be explained in the light of the theoretical arguments advanced and the easily understood sources of experimental error.

The measurement of meaningful kinetic parameters for solid state decomposition reactions

Thermal analytical investigation of unaltered Ca(OH)2 in dated mortars and plasters

The production of an active solid by thermal decomposition of some precursor material usually an oxysalt is only one way of producing such a material. The activity of any solid resides at the surface albeit some of the surface may be internal or in the decomposition process a reaction interface. The peculiar property of any solid phase is that to describe it properly one must cite the pre-history of the material, and it can be shown that the pre-history of any solid phase is mainly that of altering the surface and textural properties. This fact influences the application of thermodynamic and kinetics to processes involving the solid phase. This becomes more evident in the case of active solids where a larger proportion of chemical species than usual resides at or near the surface. This is evidenced by the existence of many or more active solids in an amorphous phase and the possible co-existence of different types of solid phase. In this review, the usefulness of normal solid phase structural determination is discussed and the manner in which thermal analysis can be used to determine thermodynamic and kinetic parameters.

Thermodynamic, kinetic and surface texture factors in the production of active solids by thermal decomposition

The use of thermal analysis in studying ancient mortars in English cathedrals is explained. Thermal analysis can be used to investigate both mortar and stone in dated structures. Analysis of ancient mortars show that though recarbonated, they remain soft, yielding to structural deformations. The use of hard (cement mortar) in modern renovation can result in micro-cracking in the stone and subsequent chemical attack from the atmosphere. Contrary to the literature, data developed in the present study suggests that most medieval mortars have reached a near total state of recarbonation.

D. Dollimore

Papers

The measurement of meaningful kinetic parameters for solid state decomposition reactions

Thermal analytical investigation of unaltered Ca(OH)2 in dated mortars and plasters

Thermodynamic, kinetic and surface texture factors in the production of active solids by thermal decomposition

Thermal analytical investigation of ancient mortars from gothic churches