Olivine as a reactive aggregate in lime mortars

This paper presents the first investigation into the use of olivine as an aggregate material for calcium lime mortars. Lime binders provide many advantages when compared to cement binders such as higher vapour permeability and the ability to accommodate movement. They are undergoing a resurgence in their use in the conservation of historic buildings and in combination with environmentally friendly natural materials where these attributes are particularly important. Their ability to mitigate against global warming through the sequestration of CO ₂ by carbonation is a further advantage which will bring impact. The equilibrium reaction products between non-hydraulic lime and olivine were calculated using the thermodynamic software GEMS3 Selektor. Experimental mortar mixes were modelled with varying ratios of quartz sand aggregate and olivine sand aggregate. The software predicted phase assemblage at equilibrium comprising calcite, dolomite, magnesite and quartz, with mass percentages depending on the ratio of quartz to olivine. The mortars morphological, chemical and mechanical properties were evaluated using Scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA) and compressive strength testing. Significantly, this study has shown that the use of olivine based aggregates in finely divided form can enhance carbonation, and hence the CO ₂ absorption capacity of these mortars. Dolomite formed within the mortar from the reaction of olivine aggregate with lime and carbon dioxide in the presence of moisture is attributed to the superior mechanical properties observed increasing from 0.5 to 2.5 MPa.