Influence of curing conditions in air lime-metakaolin blended mortars – A mineralogical and mechanical study

The need to formulate mortar compositions with adequate durability and compatibility is nowadays one of the major challenges in historical buildings repair. The incorporation of pozzolanic materials as addition or replacement of lime is viewed as a solution to these challenges regarding the increase in hardening time, mechanical strength, water resistance and durability. This paper includes part of an extensive work being developed in Portugal, which has the objective of developing and characterizing lime-metakaolin mortars for conservation purposes. This paper evaluates the influence of the curing conditions, namely medium and high relative humidity (HR), lab and outdoor exposition, and direct daily contact with potable or sea water. Two air lime mortars with volumetric proportion 1/3 of binder and aggregate, with 0 and 9% metakaolin (mass % replacement of air lime) were characterized up to one year of age. The mortars evolution with curing was followed by XRD, TG-DTA, tensile and compressive strength tests. The humid and urban curing revealed the best results in terms of the pozzolanic reaction, occurring mostly at lower curing times (28 days), although carbonation reaction is dominant throughout all ages up to 1 year.