Abstract. The properties of the hardened concrete depend on the selected raw materials: size and amount of the particles of coarse aggregate, as well as on the ratio of other components. Particular countries use various methodologies for the selection of concrete composition to select the components of the concrete mixture. However, the properties of the concrete, selected by using any methodology for the selection of the concrete composition and hardened by following the defined conditions, must satisfy the values of certain necessary characteristics. The results of the implemented research indicate that the most optimal solution is to use the coarse aggregate of multi-fractional or discontinuous fractional composition. The optimal composition of the concrete must be selected to ensure that the binding material is not overdosed. Yet, all components must be selected in such a way, that the required properties of the final product are retained after concrete mixture hardens. When catalyst waste materials from the reactor of the catalytic cracking (15%) are used for the lightweight concrete, the density of the expanded-clay lightweight concrete investigated and compressive strength increases even for the higher water/cement ratio, more heat is dissipated during the hydration of the cement and this exothermic effect occurs several hours earlier.
The paper production is developed throughout the world, therefore, more paper sludge waste (PSw) is accumulating. The aim of this work was to determine the properties of PSw burned at 900 °C and its impact on physical–mechanical properties of cementitious matrix and evaluate its usage/utilization possibilities in cementitious materials. For the implementation of the aim, cement-based specimens were prepared and their –mechanical properties were determined. Specimens from five compositions were formed, with 2.5%, 5%, 7.5%, and 10% of the cement by weight replaced with PSw. When 5% of the cement was replaced with PSw, the compressive strength increased by approximately 7%, although density and ultrasound velocity slightly decreased (up to 1.5%). When 7.5% PSw was added, the compressive strength of the specimens decreased. To summarize, it can be stated that up to 5% PSw may be utilized/used for the preparation of cementitious mixtures. The usage of the waste allows environment conservation, reduced amount of cement in mixtures, and improvement of properties of cementitious materials.
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