Search Results (212)

The preparation of new-generation concrete from recycled coarse aggregate (RA) is an effective way to realize the resource utilization of construction waste. However, loose and porous attached mortar leads to RA showing low-density, high-water absorption, and high crushing value. However, carbonation modification treatment can effectively improve the performance of RA. This paper studied the effects of carbon dioxide (CO₂) concentration, gas pressure, and moisture content on the RA physical properties (apparent density, water absorption, crushing value, and soundness) of waste concrete. The results showed that, when the (CO₂) concentration increased from 20% to 60%, the apparent density of RA after carbonation increased by 0.23–0.31%, the water absorption decreased by 0.57–0.93%, the crushing value decreased by 0.36–0.61%, and the soundness decreased by 0.47–0.85%. When the (CO₂) concentration was further increased from 60% to 80%, the apparent density of RA after carbonation was increased by 0.04–0.05%, the water absorption was improved by 0.15–0.31%, the crushing value was reduced by 0.06–0.07%, and the soundness was reduced by 0.09–0.11%. During the carbonation modification process, the performance of RA was significantly enhanced when the moisture content was 3.4% and the dissolution of hydration products was accelerated. The diffusion rate of CO₂ and the carbonation reaction rate decreased with the high moisture content of RA. As gas pressure increases to 0.01 MPa, the physical properties of RA change significantly, because gas pressure promotes the carbonation reaction between hydration products and CO₂ in attached mortar. As the gas pressure increased to 0.5 MPa, RA’s apparent density gradually increased, while its water absorption, crushing value, and stability gradually decreased. The result improved RA’s performance. SEM images show that carbonation modification of RA under different gas pressures increases CaCO₃ in attached mortar, filling the Interfacial Transition Zone (ITZ), and decreasing crack width and number. Gas pressure accelerates CO₂ diffusion and reaction with hydration products, resulting in narrower ITZ and dense mortar. Full article

Two hydrophilic copolymers containing functional groups such as carboxyl, amido, and sulfonic acid are synthesized using ammonium persulfate-catalyzed free radical polymerization in water. Aluminum sulfate is then introduced, resulting in two polymer complexes that exhibit reduced cement setting times (initial, 1.16–2.44 min; final, 2.02–3.14 min) and improved compressive (24 h, 5.81–7.25 MPa) and flexural (24 h, 2.80–2.99 MPa) strengths compared to pure aluminum sulfate-facilitated cementing (initial, 19.11 min; final, 37.05 min; compressive, 24 h, 5.51 MPa; flexural, 24 h, 2.56 MPa). Following this, ball-milled illite powder is added, and the resulting admixtures further display slightly prolonged setting times (initial, 2.35–2.99 vs. 1.16–2.44 min; final, 3.98–4.35 vs. 2.02–3.14 min), along with comparable compressive strengths (5.85–7.11 vs. 5.81–7.25 MPa) and enhanced flexural strengths (3.92–5.83 vs. 2.80–2.99 MPa). Notably, a unique adhesive pozzolanic clinker, Ca₅₄MgAl₂Si₁₆O₉₀ (54CaO·MgO·Al₂O₃·16SiO₂), emerges in the presence of illite-based admixtures, contributing to the mechanical strength development of the hydrated mortars. Although illite itself is hydrophobic, the coating of ball-milled illite powder with aluminum sulfate and copolymers facilitates its dispersion into the gaps and pores of the cement matrix during setting, thereby increasing the flexural strength. This work presents an interesting approach to utilizing illite materials in cement applications, which is significant for reducing CO₂ emissions during cement production and use. Full article

The cracks in concrete serve as pathways for aggressive agents, leading to deterioration. One approach to addressing these cracks and enhancing structures durability is the use of self-healing agents, such as bacteria used to heal cracks in cementitious matrices. Bacteria can be found in several environments, and their identification and healing viability must be evaluated prior to their use in cementitious matrices. In this study, distinct indigenous bacteria were collected from soil in industrial yards associated with the cement industry. These bacteria were identified and incorporated in cement and mortar mixtures with 18% entrained air. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed to characterize the formed products, and compressive strength testing was conducted to evaluate the mechanical properties of the mortars. The identified bacteria were of the genus Cronobacter, Citrobacter, Bacillus, and Pseudomonas, and their potential to form self-healing products was evaluated with microscopic and mineral analyses. Results showed that all bacteria could form calcite (CaCO₃) crystals, with full crack healing in some of the samples. Mechanical testing indicated increases in average compressive strength of up to 108% at 28 days with respect to a reference mortar. Full article

This study aims to explore the dynamic response of ballastless tracks under various temperatures of the cement-emulsified asphalt (CA) mortar layer and other environmental factors. CA mortar is the key material in the ballastless track structure, exhibiting notably temperature-dependent viscoelastic properties. It can be damaged or even fail due to the continuous loads from trains. However, the dynamic behaviors of ballastless tracks considering the temperature-dependent viscoelasticity of CA mortar have been insufficiently studied. This paper captures the temperature-dependent viscoelastic characteristics of CA mortar by employing the fractional Maxwell model and applying it to finite element simulations through a Prony series. A vehicle–track–subgrade (VTS) coupled CRTS I ballastless track model, encompassing Hertz nonlinear contact and track irregularity, is established. The model is constrained symmetrically on both of the longitudinal sides, and the bottom is fixed on the infinite element boundary, which can reduce the effects of reflected waves. After the simulation outcomes in this study are validated, variations in the dynamic responses under different environmental factors are analyzed, offering a theoretical foundation for maintaining the ballastless tracks. The results show that the responses in the track subsystem will undergo significant changes as the temperature rises; a notable effect is caused by the increase in speed and fastener stiffness on the entire system; the CA mortar layer experiences the maximum stress at its edge, which makes it highly susceptible to damage in this area. The original contribution of this work is the establishment of a temperature-dependent vehicle–track–subgrade coupled model that incorporates the viscoelasticity of the CA mortar, enabling the investigation of dynamic responses in ballastless tracks. Full article

The alkali-activation of blast-furnace slags (BFSs) is a topic largely studied today. However, some types of activators, more environmentally friendly, have been less studied such as alkali-sulphate activators. In this study, the effect of four alkali-sulphate activators (Na₂SO₄, K₂SO₄, MgSO₄, CaSO₄.2H₂O) is investigated to better understand the effect of cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) and of a high content of sulphate ions (SO₄²⁻) on the hydration process of BFS and the nature of the hydrates. To reach this objective, a large experimental campaign is carried out to characterize the pore solution, the hydration products and the kinetics of the chemical reactions. As the temperature seriously affects the hydration advancement, the activation energy coefficient is also determined experimentally to compare the results as function of the equivalent time. Finally, a new method is proposed to determine the evolution of the hydration degree of BFSs, a key parameter for predicting the evolution of the hydrates through a thermodynamic modeling. The results indicate that the use of sodium sulphate results in faster hydration kinetics and shorter setting times due to a higher pH of their pore solution, leading to a larger rate of C-A-S-H type gel precipitation from the initial setting time to the long term and a higher hydration advancement. These hydration products are characterized by a higher content of Na⁺ and a denser rim around the surface of anhydrous particles. The effect of K₂SO₄, MgSO₄ and CaSO₄.2H₂O on the BFS activation efficiency is limited compared to Na₂SO₄ due to their lower rate of C-S-H type gel evolution at early age. It is directly related to the pH of the pore solution and the effect of cations on the nature of hydrates. However, the compressive fis research study, a large strength beyond 28 days is more significant for mortars activated with Na₂SO₄ and MgSO₄, satisfying the strength requirement of the repaired mortars (R2 and R3) due to the larger contents of C-(N)-A-S-H/M-S-H-type gels, ettringite and hydrotalcite. Full article

Cement–asphalt (CA) mortar voids in earth’s structure are prone to inducing abnormal vibrations in vehicle and track systems and are more difficult to recognize. In this paper, a vehicle–ballastless track coupling model considering cement–asphalt mortar voids is established and the accuracy of the model is verified. There are two main novel results: (1) The displacement of the track slab in the ballastless track structure is more sensitive to the void length. Voids can lead to blocked vibration transmission between the ballastless track slab and concrete base. (2) The wheel–rail vibration acceleration is particularly sensitive to voids in cement–asphalt mortar, making the bogie pendant acceleration a key indicator for detecting such voids through amplitude changes. Additionally, the train body pendant acceleration provides valuable feedback on the cyclic characteristics associated with single-point damage in the cement–asphalt mortar, thereby enhancing the accuracy of dynamic inspections for vehicles. In the sensitivity ordering of the identification indexes of voids, the bogie’s vertical acceleration in high-speed trains > the nodding acceleration of the bogie > the vehicle’s vertical acceleration. Adaptive suspension parameters can be designed to accommodate changes in track stiffness. Full article

The purpose of the study was to determine the mechanical and ecotoxicological properties of mortars with differently shaped recycled PET plastics as a partial natural aggregate replacement and assess its environmental impact. Different methods were used for determining mechanical properties, while ecotoxicity tests with two types of plants were performed for the assessment of the ecotoxicological potential of mortars. Results of strength tests revealed that PET in mortars increased 28-day compressive strength by up to 3% and decreased flexural strength by up to 14% compared to conventional mortar. Ultrasonic pulse velocity and dynamic modulus of elasticity were lower in PET mortars, while XRD and SEM-EDS showed fewer hydration products in PET mortars. Duckweed ecotoxicity test results revealed that frond growth inhibition values in PETS and conventional mortar leachate (100 g L⁻¹) were around 50%, while root growth inhibition values did not exceed 40%. Mustard seed germination test results revealed root growth inhibition values in both mortar leachates were lower than 20%. Ecotoxicity tests showed that conventional and PET mortar were non-toxic to duckweed in aquatic environments and non-toxic to mustard seeds in terrestrial environments. Characterization of mortar leachates showed a significant increase in chloride, Ca, Si, and Ba content as potential causes for growth inhibition of both plants. Plastic waste reduction due to the potential use of PET in mortars confirmed that plastic waste could be completely eliminated and the global consumption of primary natural resources for concrete production reduced up to 4%. Such an approach could increase mortar sustainability. Full article

The effects of high-temperature modified phosphogypsum (HPG), incorporated at contents of 40%, 50%, and 60%, on the compressive strength and elastic modulus of mortar and concrete were investigated. Additionally, the influence of graded granulated blast furnace slag powder (GGBS), quicklime, and silica fume on the mechanical properties of HPG-based mortar (HPGM) and HPG-based concrete (HPGC) was discussed. Moreover, the microstructure of HPGM was analyzed using scanning electron microscopy (SEM). A two-dimensional mesoscale model of HPGC was developed to predict how variations in HPG content, coarse aggregate characteristics, and interfacial transition zone (ITZ) characteristics influence the compressive strength and elastic modulus of HPGC. The experimental results showed that high volumes of HPG weakened the mechanical properties of HPGM and HPGC, while appropriate amounts of mineral admixtures offset the negative effects caused by calcium hydroxide (Ca(OH)₂) crystals and impurities within the system. The simulation results indicated that the maximum deviation between the mesoscale model prediction and experimental data was only 8.38%, which verified the accuracy of the mesoscale model prediction. The compressive strength of HPGC initially decreased and subsequently increased with the rise in the modulus and content of coarse aggregate, whereas it declined with higher HPG dosage and increased ITZ thickness. In contrast, the elastic modulus of HPGC showed a gradual increase with rising coarse aggregate content and improved ITZ mechanical properties, while it decreased as HPG content and ITZ thickness increased. Full article

To understand the mechanical behavior of CRTS (China Railway Track System) II cement emulsified asphalt mortar (CA mortar), this study tested the compressive strength and flexural strength of CA mortar at different ages under varying water-to-cement ratios and dosages of water-reducing agent. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) results, the hydration products and microstructure of CA mortar at different ages were analyzed. The main conclusions are as follows. As the water-to-cement ratio increases, the compressive strength and flexural strength of CA mortar generally exhibit a decreasing trend. The strength increases rapidly in the early stages, with the 7-day compressive strength reaching over 80% of the 28-day compressive strength, and the 7-day flexural strength reaching over 93% of the 28-day flexural strength. As the dosage of water-reducing agent increases, both the compressive strength and flexural strength of CA mortar first increase and then decrease, with a reasonable range of water-reducing agent dosage being between 0.2% and 1.0%, and 0.5% is most appropriate. The hydration reaction of CA mortar is nearly complete at 3 days, with the increase in ages, the cement hydration slows down due to the coating action of asphalt, and the strength no longer changes greatly. Hydration products are mainly Ettringite, which is the main source of strength of CA mortar. After the emulsified asphalt breaks, it adsorbs onto the hydration products and sand surfaces, gradually forming a continuous phase, which enhances the structural toughness of the CA mortar. Full article

Concrete, as the most widely used construction material globally, is prone to cracking under the influence of external factors such as mechanical loads, temperature fluctuations, chemical corrosion, and freeze–thaw cycles. Traditional concrete crack repair methods, such as epoxy resins and polymer mortars, often suffer from a limited permeability, poor compatibility with substrates, and insufficient long-term durability. Microbial biogrouting technology, leveraging microbial-induced calcium carbonate precipitation (MICP), has emerged as a promising alternative for crack sealing. This study aimed to explore the potential of Bacillus pasteurii for repairing concrete cracks to enhance compressive strength and permeability performance post-repair. Experiments were conducted to evaluate the bacterial growth cycle and urease activity under varying concentrations of Ca²⁺. The results indicated that the optimal time for crack repair occurred 24–36 h after bacterial cultivation. Additionally, the study revealed an inhibitory effect of high calcium ion concentrations on urease activity, with the optimal concentration identified as 1 mol/L. Compressive strength and water absorption tests were performed on repaired concrete specimens. The compressive strength of specimens with cracks of varying dimensions improved by 4.01–11.4% post-repair, with the highest improvement observed for specimens with 1 mm wide and 10 mm deep cracks, reaching an increase of 11.4%. In the water absorption tests conducted over 24 h, the average mass water absorption rate decreased by 31.36% for specimens with 0.5 mm cracks, 29.06% for 1 mm cracks, 27.9% for 2 mm cracks, and 28.2% for 3 mm cracks. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed the formation of dense calcium carbonate precipitates, with the SEM–EDS results identifying calcite and vaterite as the predominant self-healing products. This study underscores the potential of MICP-based microbial biogrouting as a sustainable and effective solution for enhancing the mechanical and durability properties of repaired concrete. Full article

Civil briquette furnace slag (FS), as a type of industrial solid waste, is not currently being recycled as a resource by the building materials industry. This study focuses on the potential of FS in the formulation of alkali-activated materials (AAMs) compared with calcium carbide slag (CS). This study encompasses three distinct AAM systems: alkali-activated fly ash alone (AAFA), fly ash–slag powder blends (AAFB), and slag powder alone (AABS). Electrical conductivity, fluidity, drying shrinkage, and flexural and compressive strengths were also assessed. Advanced characterization techniques, including SEM-EDS, XRD, FTIR, and TG-DSC, were utilized to examine the morphology, mineralogy, and reaction products. Despite the chemical similarity between FS and CS, FS exhibits limited active chemical components (SiO₂, Al₂O₃, CaO, and MgO) and primarily functions as a physical filler, and thus lacks the chemical binding properties of CS. FS has a positive effect on the long-term compressive strength of the AABS system but not on the AAFA and AAFB systems. The NaOH-activated SP mortar sample with 20% FS reaches a compressive strength of 29.8 MPa at 360 days. The binding strength in AAMs incorporating FS is predominantly attributed to the gel formation within the alkali-activated matrix. This research offers valuable insights into the strategic use and substitution of CS, FS, and other silico–aluminon additives within the context of AAMs development. Full article

Recently, numerous studies have been carried out with natural fibers in cementitious composites, due to the viability of using this type of fiber as a substitute for synthetic fibers. In this field of study, the present research aims to evaluate the feasibility of using corn straw fiber for the production of innovative cementitious composites. Mortars with a composition of 1:1:6:1.55 (cement/lime/sand/water) containing 0, 2.5 and 5% corn straw fiber were produced. The corn straw fibers were treated with three different alkaline products: sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂). The compositions were evaluated by means of compressive strength, water absorption, density and porosity and consistency tests. Characterization tests were also carried out on the natural fibers subjected to the different treatments, where it was observed that chemical characterization revealed an increase in crystalline cellulose from 59.03% to 63.50% (NaOH), 62.41% (KOH) and 60.40% (Ca(OH)₂), which enhances fiber strength. In the mortars, it was observed that the water absorption results were reduced when the alkaline treatments were used, reducing from 15.95% (composition without fibers) to 6.34% and 6.61% in the compositions with 2.5% and 5.0% of fibers treated with KOH, for example. The effects were also positive in the compositions with fibers treated in NaOH, where the water absorption values were 7.59% and 7.88% for the compositions containing 2.5% and 5.0% of treated fiber, respectively. Alkaline treatments also promote an increase in compressive strength when comparing the results of mortars with natural fibers and fibers treated with NaOH, for example. The result for mortars containing 5.0% untreated fibers was 0.22 MPa, while for the composition containing 5.0% fibers treated with NaOH, it was 3.79 MPa, an increase of more than 15x. This behavior is justified by the effect of the treatment, which, in addition to removing impurities from natural fibers, such as sugar, increases the crystalline cellulose content and the adhesion between fiber and matrix. Based on the results obtained, it is possible to conclude that (i) the treatment with NaOH increases the crystallinity and tensile strength of the fibers, promoting good properties for innovative cementitious composites; (ii) the treatment with KOH degrades the cellulose structure of the fiber, reducing the crystallinity and tensile strength; this promotes greater adhesion of the fiber to the matrix, reducing porosity and water absorption, but promotes a reduction in compressive strength when compared to composites with 2.5% natural fiber; and (iii) the treatment with Ca(OH)₂ presents a reduction in water absorption and porosity, due to the impregnation of calcium in the fiber that improves the adhesion between fiber and matrix. Full article

The article demonstrates the effectiveness of the mechanochemical activation of a cement-ash binder by increasing the specific surface area of the ash and introducing a sodium fluorosilicate additive (Na₂SiF₆). It has been experimentally proved that the introduction of a Na₂SiF₆ additive makes it possible to increase the degree of cement hydration, as well as the intensity of free CaO binding when heating the cement-ash binder in the range of 500 °C to 800 °C. Mechanochemical activation prevents a decrease in the strength of the preheated cement-ash binder. During cyclic heating and cooling of slag mortars based on the activated cement-ash binder, an improvement in the set of basic properties was observed: compressive strength, flexural strength, water absorption, dynamic modulus of elasticity, and conditional elongation. Experimental design was carried out to obtain experimental–statistical models of mortar properties based on composition, heating temperature, and number of heating–cooling cycles. These models made it possible to develop quantitative relationships for predicting mortar properties at elevated temperatures and to rank the factors in order of importance. The optimal values for the dosage of fly ash, sodium silicofluoride additive, and the binder’s specific surface area were established. It was demonstrated that the activator has a positive effect on the thermal deformation of mortars. Full article

Water-stable proteins may offer a new field of applications in smart materials for buildings and infrastructures where hydraulic reactions are involved. In this study, cement mortars modified through water-soluble silk fibroin (SF) are proposed. Water-soluble SF obtained by redissolving SF films in phosphate buffer solution (PBS) showed the formation of a gel with the $\beta$ sheet features of silk II. Electrical measurements of SF indicate that calcium ions are primarily involved in the conductivity mechanism. By exploiting the water solubility properties of silk II and Ca²⁺ ion transport phenomena as well as their trapping effect on water molecules, SF provides piezoresistive and piezocapacitive properties to cement mortars, thus enabling self-sensing of mechanical strain, which is quite attractive in structural health monitoring applications. The SF/cement-based composite introduces a capacitive gauge factor which surpasses the traditional resistive gauge factor reported in the literature by threefold. Cyclic voltammetry measurements demonstrated that the SF/cement mortars possessed memcapacitive behavior for positive potentials near +5 V, which was attributed to an interfacial charge build-up modulated by the SF concentration and the working electrode. Electrical square-biphasic excitation combined with cyclic compressive loads revealed memristive behavior during the unloading stages. These findings, along with the availability and sustainability of SF, pave the way for the design of novel multifunctional materials, particularly for applications in masonry and concrete structures. Full article

Coal-fired power plants are a main source of energy in Poland. In the rapidly growing demand for the reduction of CO₂ emission in the energy industry, the use of biomass for energy purposes has increased significantly. The combustion of biomass results in the generation of fly ash, with higher levels of CaO, K₂O, P₂O₅, in contrast to the fly ash derived from the combustion of coal. The aim of this study was to examine the influence of phosphate compounds on fly ash-based geopolymer mortars. Geopolymers were made by mixing two types of fly ash—one from the combustion of wood biomass and the second from the combustion of coal in a heat and power station. Basic activators (NaOH and Na₂SiO₃) were used for the alkali activation. The maximum level of tetraphosphorus decaoxide addition was established at 5% of the total mass of the aluminosilicate precursors mass. The results showed that the phosphate oxide concentration within the specimens demonstrated a positive correlation with flexural and compressive strength across all temporal intervals (7, 28, and 56 days). The porosity, however, for samples with a 5% addition of P₄O₁₀, increased more than twofold in comparison to reference samples (from 4.26% to 9.98%). Full article