Development of artificial hydraulic lime

Introduction. Lime mortars used for the restoration of historical buildings are characterized by low resistance during operation. The durability of lime solutions can be increased by using hydraulic lime as a binder. However, the share of hydraulic lime in the lime binder production structure is only 19.8%. Given the low volume of production of natural hydraulic lime, it is promising to develop a formulation of artificial hydraulic lime. Materials and methods. To develop the formulation of artificial hydraulic lime, grade 2 slaked lime (pushonka) with an activity of 64% was used, as well as grade 2 air lime with an activity of 84% (GOST 9179-18). The technology for producing artificial hydraulic lime consisted of mixing slaked lime with pozzolan additives, as well as mixing air lime with pozzolan additives during the quenching process. When developing the formulation of the plaster mortar, quartz sand from various deposits was used as a fine filler. The optimal type of sand was selected based on the strength criterion of calcareous composites and sand activity, characterized by the value of free surface energy. Results. It has been established that the most effective is the addition of metakaolin. The compressive strength of the solution at the age of 28 days of hardening is 2.1 MPa when using second-grade quicklime. Increasing the dosage of metakaolin to 40% by weight of lime increases the compressive strength to 2.7–3.1 MPa. Pozzolan additives silica, dehydrated clay, diatomite at a dosage of 10% by weight of lime do not provide the required compressive strength of at least 2.0 MPa. The introduction of Portland cement in the formulation in an amount of 25% by weight of lime contributes to a significant increase in compressive strength, amounting to 2.9–4.0 MPa, depending on the type of additive and type of lime, as well as the technology of binder preparation. The porosity of calcareous stone based on artificial hydraulic lime was determined, amounting to 48–51%, while a decrease in the volume of closed pores was observed. Solutions based on artificial hydraulic lime provide sufficient adhesion strength to the brick substrate, amounting to 0.4–0.55 MPa/kg. It has been established that the use of methakaolin in the amount of 40–50% of the mass of air lime makes it possible to obtain artificial hydraulic lime. The developed compositions of artificial hydraulic lime are proposed to be used for the restoration of buildings of historical buildings, as well as finishing newly erected facilities. Conclusion. It has been established that the use of aerial quicklime in the preparation of artificial hydraulic lime promotes a more durable lime composite structure. The porosity of limestone based on artificial hydraulic lime is lower than that of limestone based on aerial lime, and for limestone based on cement-based compositions, it is lower than that of limestone based on hydraulic lime. HL artificial hydraulic lime and plaster mortar formulations based on it have been developed for the restoration of cultural heritage sites and the finishing of new buildings.