In this work, the effect of multi-walled carbon nanotubes (MWCNT1, MWCNT2, and MWCNT3) with different outer diameters and specific surface areas on the mechanical and electrical properties of cement mortar have been investigated. Various concentrations of MWCNTs were used (0.05, 0.10, and 0.15%), the effective dispersion of which was carried out by an Ultrasonic machine (for 40 min with 160 W power and a 24 kHz frequency) using a surfactant. Composites have been processed with a biosilica content of 10% by weight of cement and without it. Compressive strength tests were carried out on days 7 and 28 of curing. The 7-day compressive strength of samples prepared without biosilica increased compared to the result of the control sample (6.4% for MWCNT1, 7.4% for MWCNT2, and 10.8% for MWCNT3), as did those using biosilica (6.7% in the case of MWCNT1, 29.2% for MWCNT2, and 2.1% for MWCNT3). Compressive strength tests of 28-day specimens yielded the following results: 21.7% for MWCNT1, 3.8% for MWCNT2, and 4.2% for MWCNT3 in the absence of biosilica and 8.5%, 12.6%, and 6.3% with biosilica, respectively. The maximum increase in compressive strength was observed in the composites treated with a 0.1% MWCNT concentration, while in the case of 0.05 and 0.15% concentrations, the compressive strengths were relatively low. The MWCNT-reinforced cement matrix obtained electrical properties due to the high electrical conductivity of these particles. The effect of MWCNT concentrations of 0.05, 0.10, and 0.15 wt% on the electrical properties of cement mortar, especially the bulk electrical resistivity and piezoresistive characteristics of cement mortar, was studied in this work. At a concentration of 0.05%, the lowest value of resistivity was obtained, and then it started to increase. The obtained results show that all investigated specimens have piezoresistive properties and that the measurements led to a deviation in fractional change in resistivity.

This study examines the influence of pyrolysis temperature on the physicochemical characteristics of malt-derived biochar (BC) and its effect on the performance of cement mortars. Malt biomass, a by-product of the brewing industry, was subjected to pyrolysis at 300 °C and 500 °C, followed by high-energy ball milling to produce nanoscale biochar. Characterization using FTIR, Raman spectroscopy, XRD, BET, SEM, and XRF revealed that BC500 possessed higher graphitic ordering, larger specific surface area (110 m₂/g), and smaller pore size compared to BC300, which exhibited greater hydrophobicity. Incorporation of BC500 into cement mortars at 0.25–1.0 wt.%, with and without superplasticizer, resulted in up to a 20.6% increase in compressive strength and a significant reduction in water absorption. These enhancements are attributed to the internal curing effect of biochar, its refined pore structure, and improved interfacial bonding with hydration products. The findings demonstrate that optimized malt biochar serves as a sustainable additive that improves the mechanical performance and durability of cementitious materials while advancing circular economy principles through the valorization of industrial malt waste and the mitigation of the environmental impact of cement production.

The growing demand for sustainable construction materials has intensified efforts to reduce the environmental impact of Portland cement. This study investigates the effect of partial substitution of cement with metakaolin (MK, 5–15 wt.%) and biosilica (BS, 5 wt.%) on the physical, mechanical, and microstructural properties of cementitious mortars. The influence of a polycarboxylate ether-based superplasticizer (Mf) and ultrasonic treatment (ULT) was also evaluated. The mortars were characterized through setting time, density, water absorption, flexural and compressive strength tests, as well as FTIR and SEM analyses. Water absorption decreased from 12.21% to 9.8%, indicating improved pore refinement and densification. Flexural strength of all modified mortars exceeded that of the control mix: from 10.0% to 89.9% at 7 days, and from 4.7% to 50.4% at 28 days. The compressive strength improved markedly with MK and BS incorporation, from 20.8% to 51.3% at 7 days and from 9.7% to 35.2% at 28 days compared to the control sample. FTIR and SEM results confirmed enhanced pozzolanic activity and formation of C–S–H gel. The synergistic use of MK, BS, and Mf—especially with ultrasonic dispersion—yielded denser, stronger, and more sustainable cementitious composites.

This study examined the effects of basalt microfibers and amorphous-structured bentonite clay on the properties of complex mortar mixtures composed of cement and quicklime, utilizing locally sourced raw materials. Bentonite clay was subjected to thermal treatments at 400, 600, and 1000°C, and a technogenic pozzolanic additive was incorporated to investigate its influence on mortar performance. Optimal results were observed for the clay treated at 600°C, which was subsequently used in the mortar formulations. The primary objective was to assess the effects of varying basalt microfiber dosages (0.5%, 1%, and 2%) and thermally treated bentonite clay concentrations (5%, 15%, and 25%) on the chemical composition, physico-mechanical properties, and structural development of the resulting multi-component systems. Advanced analytical techniques, including SEM/EDS, XRD, FTIR, XRF, DLS, and thermochemical analyses (TG/DTG, TG/DSC, and TG/MS), were used to evaluate the mineralogical composition, particle size distribution, microstructure, and thermal behavior. The findings show that the combined use of basalt microfibers and thermally treated bentonite clay significantly enhanced the mechanical strength and structural formation of the mortars. This study provides novel insights into the synergistic effects of these components, offering a promising approach for enhancing mortar performance using locally sourced materials.