Natural hydraulic lime versus cement for blended lime mortars for restoration works

•Comparative study of blended lime-cement and blended lime-hydraulic lime mortars.•Pore structure of mortars has implications on water transport and mechanical properties and overall compatibility.•Properties of blended lime mortars were more affected by cement than by natural hydraulic lime.•Strength did not improve when natural hydraulic lime or cement contents up to 25% were added.•The blended lime mortar with 50% natural hydraulic lime was the most promising mix to be used as repair mortar. The paper analyses the potential of blended lime-cement mortars to substitute blended lime-natural hydraulic lime mortars as repair mortars in restoration works, since the availability of natural hydraulic lime is reduced in many countries, unlike cement. The study focuses on the pore structure of both types of blended mortars and its implications on their water transport properties, initial mechanical strength and overall incompatibility risk. The influence of binder type and composition and of binder/aggregate ratio on pore structure was discussed. Cement altered more markedly the mechanical and water transport properties of blended mortars than hydraulic lime, with consequences on compatibility. Considering the properties evaluated, blended lime-cement mortars can be used but cement content should be higher than 25% (of total binder mass), so that there is a strength increase at early age, and lower than 50%, in order to not significantly affect compatibility. Nevertheless, the blended lime mortar with 50% natural hydraulic lime presented the highest potential for restoration.