Nelli Muradyan

This study examines iron-based graphene nanoplatelets (Fe-GNPs), synthesized through a modified ferrocene pyrolysis route, as hybrid nano-additives for cement mortars. The nanomaterial was characterized by scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, and thermogravimetric analysis, confirming a graphitic carbon network decorated with crystalline α-Fe nanoparticles. Mortars containing 0.001, 0.01, 0.05, and 0.1 wt.% Fe-GNPs, with and without surfactant-assisted ultrasonication, were tested in flexure and compression after 7 and 28 days of curing. The results showed a clear concentration-dependent response, with 0.01 wt.% yielding the highest strength gains. At 28 days, this dosage increased flexural strength by 14.5% without surfactant and by 21.2% with surfactant, while compressive strength rose by 17.8% and 22.5%, respectively, relative to the control mortar. Higher dosages reduced the reinforcing effect, mainly because agglomeration limited efficient stress transfer and matrix densification. The findings indicate that Fe-GNPs synthesized by a continuous atmospheric-pressure route are promising hybrid nano-additives for improving the mechanical performance of cement mortars, provided that dosage and dispersion are carefully controlled.

This study aims to develop high-performance road pavement concrete capable of withstanding increasing traffic loads while ensuring long service life and reduced maintenance needs. The research focuses on enhancing the mechanical characteristics of fine-grained concrete used in the outer pavement layer through the incorporation of complex additives and dispersed reinforcement. The methodology involved modifying the concrete matrix using the superplasticizer Melflux 5581F, microsilica MK-85, and varying percentages of basalt fibers introduced through different preparation techniques. Mechanical testing, including compressive and flexural strength evaluations, was performed on 40×40×160 mm specimens cured under standard conditions and tested at 7 and 28 days. The analysis showed that Melflux 5581F significantly enhanced strength without increasing cement content, while MK-85 further improved compressive and flexural strengths by up to 50.59% and 46.28%, respectively. The addition of basalt fibers increased flexural strength, with optimal formulations achieving 89.49 MPa in compressive strength and 11.14 MPa in flexural strength. These findings demonstrate that the combined use of chemical, mineral, and fiber additives, together with appropriate technological approaches, substantially improves the performance of road concrete. The proposed modified concrete exhibits enhanced durability, offering a promising solution for extending pavement service life and reducing repair frequency.

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 explores the potential use of volcanic tuff mining waste in geopolymer mortar formulations, aiming to enhance recycling and promote sustainable construction. Two filler-to-binder ratios (70/30 and 65/35) were developed using a geopolymer binder composed of tuff waste, dolomite powder, and sodium silicate. The mortars were subjected to heat treatments at 200, 350, 500, and 650°C for 8.5 hours. Compared to natural tuff (reference sample), water absorption decreased from 16.8% to 7.7%, with the lowest absorption observed in the 65/35 composition. Flexural strengths increased by 0.97% to 117.1%, and compressive strengths improved by 17.8% to 97.1%, reaching their maximum at 500°C; at 650°C, strengths declined due to water evaporation, shrinkage, and microcrack formation. Softening coefficients increased by over 10%, indicating enhanced resistance to water-induced softening. The study demonstrates that incorporating dolomite powder improves water resistance, while tuff waste serves effectively as both filler and binder component. Moreover, geopolymer mortars produce significantly lower CO₂ emissions (0.133 t/m³) compared to ordinary Portland cement mortars (0.415 t/m³), highlighting their environmental advantage. These results underscore the potential of tuff-based geopolymer mortars for sustainable construction applications.

In recent years, there has been extensive research on the mechanical and physical properties of composite cement-based building materials containing nanosized carbon particles, particularly multi-walled carbon nanotubes (MWCNTs), owing to their mechanical and physical advantages. This study investigated the effect of purified multi-walled carbon nanotubes (MWCNTs) with different aspect ratios on the compressive strength of cement-based concrete. This study aimed to enhance the mechanical properties of the composites by optimizing the MWCNT dosage and type. The novelty of this study lies in comparing three MWCNT types (TNM2, TNM3, and TNM7) with aspect ratios ranging from ~250 to ~4347. Concrete samples with 0–0.2 wt.% MWCNTs by the weight of cement were tested after 7 days of curing. The results show that the compressive strength increased by 9.41% (TNM2 at 0.2%), 2.80% (TNM3 at 0.05%), and 12.13% (TNM7 at 0.05%). High-aspect-ratio MWCNTs showed consistent improvement with increasing content, whereas low-aspect-ratio MWCNTs peaked at 0.05%. This effect is attributed to the nanotube dispersion, reinforcement efficiency, and porosity control. A standardized ultrasonic dispersion technique was used to ensure the homogenous distribution of nanotubes in the cement matrix. These findings support the development of nano-engineered concrete with improved early strength for structural and precast construction applications.

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 work presents the types of waste of Armenian volcanic aluminosilicate tuff rocks extraction, as a component of the raw material of non-cement, artificial stone materials, the technical possibilities of their use, and the results of experiments for meeting the indicators of physical and mechanical characteristics of natural stone. Preliminary orientational experimental studies have specified the proportions of the raw materials in the compositions, the connections between the preparation of mixtures, the compaction of samples, and the shortest possible heat treatment regimes at temperatures up to 200 °C. Non-cement artificial stones were developed using tuff waste, with filler–composite binder ratios of 75/25 and 70/30, and a water/solid mass ratio of 0.10-to-0.12%. After 9 h of heat treatment, the density, water absorption, and compressive strength of non-cement artificial stone materials were determined. The results showed that these materials outperformed natural stone materials from the same deposits, in terms of the same physical and mechanical characteristics. The use of tuff waste resulted in increased densities, from 10.5 to 39%, decreased water absorption by 2 to 2.5 times, and increased compressive strength of non-cement artificial stone materials, from 15 to 30% compared to natural tuff stones. X-ray diffraction and SEM image studies were also carried out for the obtained non-cement artificial stones. The novelty in the developed technology of obtaining stone materials primarily revolves around the mixture preparation technology by using tuff waste materials and low-temperature heat treatment.

This study investigated how the water–cement ratio and silica fume concentration affect the compressive strength of cement mortars. This comprehensive study delved into the intricate interplay between water–cement ratio and silica fume concentration, examining their influence on cement-based mortars’ compressive strength and water absorption characteristics. The silica fume concentration was investigated, ranging from 5% to 15% of the cement weight. The investigation employed two distinct mixing techniques, mixing cement and silica fume, before extracting appropriate samples; alternatively, a magnetic stirrer was used to prepare samples by dissolving silica fume in water. The cement mortars were also prepared with three different water–cement ratios: 0.44, 0.47, and 0.5. The interesting findings of compressive tests illuminated a consistent trend across all curing days and mixing methods—a reduction in the water–cement ratio corresponded with a notable increase in compressive strength. However, it is essential to note that the influence of the mixing method on the compressive strength of cement-based mortars is based on the water–cement ratio. The results show that by using the suggested technological method, it was observed that samples prepared with water–cement ratios (W/C) of 0.47 and 0.44 exhibited higher compressive strengths compared to those prepared using the well-known standard mixing method. The compressive test results underscored that the water–cement ratio reduction consistently enhanced the compressive strength in every combination of curing days and mixing techniques. Furthermore, this reduction in the water–cement ratio was correlated with a decrease in water absorption of the mortar. Conversely, the water–cement ratio itself played a pivotal role in defining how the mixing technique affected the compressive strength and water absorption of cement-based mortars. This multifaceted exploration underscores the nuanced relationships between key variables, emphasizing the need for a comprehensive understanding of the intricate factors influencing the mechanical and absorptive properties of cement-based materials.

This article touches upon the development of dispersed-reinforced concrete components and the improvement of their physical and mechanical properties. They can be used in road and defense structures, bridges, and takeoff and landing zones. Multifunctional micro-reinforced fine-grained concrete compositions have been developed based on basalt fiber, where the limit of compression strength varies from 65.6 to 78.35 MPa, flexural strength from 6.4 to 9.1 MPa, and water permeability from 3.7 to 1.8%. Among the compositions of micro-reinforced concrete with basalt fiber, the best strength result was recorded in the case of 2% basalt fiber and 10% microsilica, with compression and flexural strengths of 78.35 and 9.1 MPa, respectively. The best water absorption result of 1.8% was obtained only with basalt fiber concrete when the fiber content was increased to 3.2%. As a result, the water absorption was reduced by 62% compared to the initial concrete. The increases in flexural and compression strengths were 42.19% and 13.8%, respectively.