Comparative study on the properties of three hydraulic lime mortar systems: Natural hydraulic lime mortar, cement-aerial lime-based mortar and slag-aerial lime-based mortar

To evaluate the differences of properties between natural and artificial hydraulic lime mortars, the macro and micro properties of natural hydraulic lime (NHL2 and NHL5) mortars, white Portland cement-aerial lime-based (CL15 and CL25) mortars and slag-aerial lime-based (SL20 and SL40) mortars were studied through the examination of their physical and mechanical properties, environmental resistance properties, hardening mechanism and microstructure of lime mortars or pastes. The results show that the NHL mortars have preferable fluidity compared to the artificial CL and SL mortars, while the mechanical properties of artificial CL and SL mortars are advantageous compared to those of NHL mortar. In terms of environmental resistance, the water resistance of SL mortar is best, closely followed by the CL mortar, and the NHL mortar is relatively weak; moreover, CL mortar shows the best sulphate resistance, and SL mortar has the best alkali resistance. The hydration reaction (or pozzolanic reaction) and carbonization reaction could occur in the three kinds of hydraulic lime pastes, and the hydration reaction of the NHL and CL pastes mainly occur in the early stage of paste hardening (before 28 days), while the pozzolanic reaction of the SL paste reach a high degree at early hardening stage (28 days) and still maintains a certain reaction rate in the later period. The carbonation reaction process of the three kinds of lime pastes continues to the later period of the hardening, and the carbonation rate of SL pastes in the later stage would be obviously enhanced; furthermore, the carbonation degree of NHL paste is obviously higher than that of the CL and SL pastes. The different hydration-hardening process and mechanism of the three lime pastes lead to differences in the morphology and pore structure among them. There are more large-size pores in NHL5 paste (the pore volume in the range of pore diameter greater than 200 nm reaches 63.13%), while the pore size of the SL paste is relatively small (the pore volume in the range of pore diameter less than 100 nm reaches 44.15%). The porosity during the 180 days curing period was as follows: SL40 (27.32%) < CL25 (29.65%) < NHL5 (33.09%).