construction and demolition waste; lime; metakaolin; compatibility; historic buildings

In view of the current need to reduce CO2 emissions during the production process of construction materials, in addition to the reuse of construction and demolition waste (CDW) in these materials in order to reduce the environmental impact generated by their improper disposal in nature, it’s necessary to create new alternatives for sustainable materials that gradually replace those that cause greater damage to the environment, which must meet performance, durability and compatibility criteria. In order to contribute to this demand, the present research aimed to explore the properties of pastes composed of lime with metakaolin and construction and demolition waste in order to enable a future application of this new product in the production of mortars for the restoration of historical constructions and other applications, contributing to the reduction of CO2 emissions on the planet and the inappropriate disposal of construction and demolition waste in the environment. Bearing in mind that compatibility isone of the most relevant criteria when carrying out the conservation and restoration of historic constructions, four mixtures were compared throughout the research, one being a reference (50% lime and 50% metakaolin) and three containing mass replacements of lime with metakaolin (MK) by 10, 20 and 30% of CDW. All pastes were produced with W/B = 0,8 and comparative analysis between mixtures containing CDW and the reference occurred in anhydrous, fresh and hardened states. In the anhydrous state, the materials and mixtures were characterized in terms of their physical, chemical and mineralogical properties. In the fresh state, the mini-slump and rheology tests were performed. In the hardened state, the following tests were performed at 14, 28, 56 and 90 days: x-ray diffraction (XRD); differential thermal analysis (DTA) combined with thermogravimetry (TG); infrared spectroscopy (IR); compressive strength; and mass variation over the 90 days. The results indicate a slight physical chemical and mineralogical modification between the pastes containing 10% CDW and the reference one, which may be an indication of compatibility and enable the use of conservation and restoration materials containing proportions of CDW in historic constructions carried out with lime and pozzolans. Furthermore, according to a mechanical performance criterion, specifically compressive strength, all mixes containing CDW meet compatibility requirements for use as mortar for restoring historic constructions. Consequently, some mixtures obtained suitable results with those recommended for use in historic heritage conservation and restoration works. Thus, they may be the subject of further research that evaluates other compatibility parameters not analyzed in this study, enabling a better comparison between original historic mortars and the mortars containing the addition of construction and demolition waste.