Design and evaluation of restoration mortars for historic masonry using traditional materials and production techniques
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Design and evaluation of restoration mortars for historic masonry using traditional materials and production techniques Antonia Moropoulou, Asterios Bakolas, Petros Moundoulas, Eleni Aggelakopoulou, Sofia Anagnostopoulou Section of Materials Science and Engineering, Department of Chemical Engineering, National Technical University of Athens, 9 Iroon Polytechniou St., Zografou, Athens, Greece ABSTRACT Cement based mortars used for historic masonry restoration presented unsatisfactory results, due to their chemical and physico-mechanical incompatibility to original buildings. In the present research, several syntheses of restoration mortars are produced using traditional techniques and materials such as binders (aerial and natural hydraulic lime), pozzolanic additives (natural and artificial pozzolanas) and aggregates (sand and crushed brick). The technical characteristics of the mortars were determined using mechanical tests (compressive and flexural) and mercury intrusion porosimetry measurements at the time of 1, 3, 9, 15 months of curing. Water absorption measurements were performed at the time of 9 and 15 months curing, in order to evaluate mortars microstructural characteristics, their rate of water absorption and the total percentage of absorbed water. The aerial lime - artificial pozzolana mortar presented the best mechanical and microstructural performance. Hydraulic mortars acquired the maximum of the mechanical strength in 1 month, lime - pozzolana mortars in 3 months while aerial lime mortars continue to gain mechanical strength even in 15 months curing. Furthermore, the use of ceramic aggregates produces lightweight and elastic mortars, compatible to historic ones. INTRODUCTION Most commonly used binder for mortars production was lime. Greeks and Romans used lime, either as pure binder to get aerial mortar, or mixed with pozzolana (natural or artificial), for the manufacturing of hydraulic mortars [1]. The aggregates were of calcite or quartz and, in many cases, ceramic fragments or other lightweight aggregates were mixed with the conventional aggregates to produce lightweight and elastic mortars. Through the centuries, the historic mortars have been proved to be compatible with the historic building materials and long lasting under severe mechanical and environmental loads. On the other hand, the current mortars used for restoration works in historic masonries are based on cement and polymer materials. Because of their incompatible mechanical, microstructural and physico-chemical characteristics compared to historic structural materials, negative results have been observed in historic masonries restored with these types of mortars [2,3]. Furthermore, it was observed that even the use of «traditional» type of raw materials does not assure the production of compatible restoration mortars, since their industrial production processes have changed a lot through the last decades. Thus, the current aerial and hydraulic lime as well as the artificial pozzolana and the brick fragments do not present the same II2.
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