Evaluation of mortar mix designs for the conservation of the Acropolis monuments

Abstract

The present study focuses on the evaluation of the physical-mechanical characteristics of restoration mortars, designed for the conservation works of the Acropolis monuments in Athens, Greece. The mortars were prepared with different mixing ratios of hydrated lime/metakaolin, natural hydraulic lime/metakaolin, hydrated lime/cement and cement/natural pozzolan, using aggregates of different nature and grain size distribution. The mortars were evaluated till 24 months of curing. The mechanical characteristics were studied through mechanical strength tests in different curing times to determine the flexural and compressive strength and through ultrasonic pulse velocity measurements to determine the dynamic modulus of elasticity. The physical and moisture transfer properties were estimated through laboratory methods (apparent density, porosity accessible to water, total water absorption and water absorption coefficient by capillary). In addition, the durability of the mortars was tested through accelerated ageing tests in salt cycles. The results of the study showed that the hydrated lime/cement mixtures did not meet the desired criteria and therefore are not considered appropriate for application. On the contrary, the addition of metakaolin to hydrated lime mortars in certain quantities led to improved mechanical properties, while providing satisfactory hygrometric properties and sufficient resistance to the action of soluble salts, rendering these mix designs suitable for use in conservation interventions on the Acropolis monuments.