Impact of pozzolanic and inert powders on the microstructure and thermal chemistry of cement mortars

The aim of this work is the investigation of the microstructure of two types of white, high-workability cement mortars: type 1 (Am) with a relatively high content of marble powder (Binder:Aggregate = 1:2) containing fine particles, and type 2 (Mz) with a high content of marble powder (Binder + Pozzolan:Aggregate = 0.9 + 0.1:2) and up to 10 wt% clinoptilolite as a pozzolan from the white cement content. The density of the composites’ structures at 1, 28, and 120 days of water curing was evaluated by measurements of their physical-mechanical properties - density, compressive strength, and porosity. Crystal microstructure and sample morphology were investigated with mercury intrusion porosimetry (MIP), X-ray powder diffraction analysis (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermal analysis (TG/DTG-DSC). The conducted studies established that a high content of fines makes the structure denser. The formed structure has open porosity, which allows for the transportation of water, with slow continuous hydration resulting in the growth of crystals and the formation of various products, especially with the addition of clinoptilolite. The formation of cement hydrated minerals (CSH and CASH) such as ettringite, hillebrandite, yugawaralite, wairakite, hibschite, together with hemi- and mono-carboaluminate, etc., has been proven. The composition of the cement mortar with a high content of marble powder and up to 10 wt% clinoptilolite has the potential for further improvement of the process of hydration by forming a greater variety of calcium silicate hydroxyl phases. Despite the complexity of the reactions in the hydration of mortars, a generalized scheme of the reactions describing the main steps of the process is presented in correlation with the specified experimental conditions. The results allow for the development of sustainable building material strategies using waste and natural materials to reduce resource dependence and energy for production. Widespread adoption of sustainable building materials is seen as one of the most promising approaches to increasing the efficiency of the construction sector in a sustainable way and ensuring continued economic growth and a circular economy.