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The cement industry could potentially consume large amounts of solid industrial waste in order to improve its sustainability. The suitability of selected quarry and mine waste as secondary raw materials (SRM) was examined for the sustainable production of cement following the concept of a circular economy. The chemical, mineralogical, and radiological characterization of SRM was conducted in this study. Its potential use in low-carbon and low-energy belite-sulfoaluminate cement was investigated by incorporating the examined SRM into cement clinker. Various characterization methods were used to characterize the cement, including X-ray powder diffraction (XRD), thermal analysis (DTA/TG), and isothermal calorimetry. Depending on the chemical composition of the waste, lower or higher amounts were allowed to be incorporated into the raw clinker mixture for a targeted clinker phase composition. Among the samples, differences were observed in the phase composition of synthesized clinkers, which slightly influenced the reactivity of the cement but did not significantly change the compressive strength of the final product.

This paper aims to evaluate the effect of replacement of aggregate by recycled one on fracture response of selected composites. These are hemp fibre reinforced cement-based composites. Four different mixtures were prepared: in reference one, the only natural aggregate was used whereas in the other three mixtures, the natural aggregate was replaced by recycled one in the amount of 10, 25 and 50 %, respectively. All mixtures contained hemp fibres with a length of 10 mm in the dosage of 1 % by volume. In order to determine the selected mechanical fracture characteristics of the investigated composites, three-point bending fracture tests were carried out on prismatic specimens with nominal dimensions 40 × 40 × 160 mm3 provided with an initial notch. During the whole course of the testing, the loading process was governed by a constant displacement increment of 0.02 mm/min. The vertical displacement (midspan deflection) was measured using the inductive sensor mounted on a special measurement frame placed on the specimens. The fracture tests were terminated when the midspan deflection reached 0.5 mm. The mechanical fracture parameters were obtained through a direct evaluation of the fracture test data via the effective crack model and the work-of-fracture method. The paper shows that composites with a higher dosage of recycled aggregate (25 and 50 wt%) achieve similar values of mechanical fracture properties, so this replacement can be recommended.

The physical and mechanical properties of hemp-fibre-reinforced alkali-activated (AA) mortars under accelerated carbonation were evaluated. Two matrices of different physical and chemical properties, i.e., a low Ca-containing and less dense one with fly ash (FA) and a high Ca-containing and denser one with FA and granulated blast furnace slag (GBFS), were reinforced with fibres (10 mm, 0.5 vol% and 1.0 vol%). Under accelerated carbonation, due to the pore refinement resulting from alkali and alkaline earth salt precipitation, AA hemp fibre mortars markedly (20%) decreased their water absorption. FA-based hemp mortars increased significantly their compressive and flexural strength (40% and 34%, respectively), whereas in the denser FA/GBFS matrix (due to the hindered CO2 penetration, i.e., lower chemical reaction between CO2 and pore solution and gel products), only a slight variation (±10%) occurred. Under accelerated carbonation, embrittlement of the fibre/matrix interface and of the whole composite occurred, accompanied by increased stiffness, decreased deformation capacity and loss of the energy absorption capacity under flexure. FA-based matrices exhibited more pronounced embrittlement than the denser FA/GBFS matrices. A combination of FA/GBFS-based mortar reinforced with 0.5 vol% fibre dosage ensured an optimal fibre/matrix interface and stress transfer, mitigating the embrittlement of the material under accelerated carbonation.