Search Results (71)

Polycarboxylate superplasticizer (PCE) is an important part of improving the overall performance of concrete. However, its synthetic raw materials are overly dependent on petrochemical products, and it also causes problems such as environmental pollution. With the development of the building material industry, the demand for petrochemical resources required for synthetic water-reducing agents will increase rapidly. Therefore, there is an urgent need to transition the synthetic raw materials of PCE from petrochemicals to biomass materials to reduce the consumption of nonrenewable resources as well as the burden on the environment. Biomass materials are inexpensive, readily available and renewable. Utilizing biomass resources to develop good-performing water-reducing agents can reduce the consumption of fossil resources. This is conducive to carbon emission reduction in the concrete material industry. In addition, it promotes the high-value utilization of biomass resources. Therefore, in this study, a biomass polyether monomer, acryloyl hydroxyethyl cellulose (AHEC), was synthesized from cellulose via the reaction route of ethylene oxide (EO) etherification and acrylic acid (AA) esterification. Biomass polycarboxylate superplasticizers (PCE-Cs) were synthesized through free radical polymerization by substituting AHEC for a portion of the frequently utilized polyether monomer isopentenyl polyoxyethylene ether (TPEG). This study primarily focused on the properties of PCE-Cs in relation to cement. The findings of this study indicated that the synthesized PCE-C5 at a dosing of 0.4% (expressed as mass fraction of cement) when the AHEC substitution ratio was 5% achieved good water reduction properties and significant delays. With the same fluidity, PCE-C5 could enhance the mechanical strength of cement mortar by 30% to 40%. This study utilized green and low-carbon biomass resources to develop synthetic raw materials for water-reducing agents, which exhibited effective water-reducing performance and enhanced the utilization rate of biomass resources, demonstrating significant application value. Full article

Electrochemical treatment by means of direct current (DC) is usually used as a measure for steel rebar corrosion protection, e.g., cathodic protection (CP), electrochemical chloride extraction (ECE), and re-alkalization (RA). However, the passage of an electrical charge through the pore system of concrete or mortar, coupled with the migration of ions, concentration changes, and resulting phase changes, may alter its chloride penetration resistance and, subsequently, the time until rebar corrosion activation. Porosity changes in hardened Portland cement mortar were studied by means of mercury intrusion porosimetry (MIP) and electrochemical impedance spectroscopy (EIS), and alterations in the mortar surface phase composition were observed by means of X-ray diffraction (XRD). In order to innovatively investigate the impact of DC treatment on the properties of the mortar–electrolyte interface, the cathode-facing mortar surface and the anode-facing mortar surface were analyzed separately. The corrosion of steel coupons embedded in DC-treated hardened mortar was monitored by means of the free corrosion potential (E_oc) and polarization resistance (R_p). The results showed that the DC treatment affected the surface porosity of the hardened Portland cement mortar at the nanoscale. Up to two-thirds of the small pores (0.001–0.01 µm) were replaced by medium-sized pores (0.01–0.06 µm), which may be significant for chloride ingress. Although the porosity and phase composition alterations were confirmed using other techniques (EIS and XRD), corrosion tests revealed that they did not significantly affect the time until the corrosion activation of the steel coupons in the mortar. Full article

Circulating fluidized bed combustion (CFBC) ash, a byproduct typically generated from coal-fired CFBC power plant boilers, contains high content of free lime and anhydrite. Due to its chemical composition, CFBC ash exhibits self-cementing properties; however, its performance is limited. One approach to enhancing the self-cementing properties of CFBC ash is through the incorporation of mineral admixtures such as gypsum. This study investigated the influence of desulfurization gypsum (DG) on the self-cementing behavior of CFBC ash. To this end, paste and mortar specimens were prepared and evaluated for their hydration and mechanical characteristics. The hydration behavior was analyzed using isothermal calorimetry, thermogravimetric analysis (TGA), setting time measurements, and X-ray diffraction (XRD) analysis. Mechanical properties were assessed by measuring the compressive strength at various curing ages. Additionally, changes in microstructure were examined by evaluating the pore size distribution through mercury intrusion porosimetry (MIP). The experimental results indicate that the appropriate incorporation of DG enhances the hydraulic reactivity of CFBC ash and significantly improves the compressive strength. Full article

Negative temperature environments inhibit bacterial survival in cementitious materials and reduce the self-healing ability of bacteria. To address this challenge, acid-etched alumina hollow spheres are proposed as carriers to encapsulate microorganisms in cementitious materials. The effects of these carriers on the mechanical properties, thermal conductivity, self-healing properties, and self-healing products of specimens after exposure to −20 °C were investigated. Finally, the self-healing mechanism was examined and analyzed. The results demonstrated the effectiveness of the acid-etched hollow microbeads as bacterial carriers. The addition of the alumina hollow spheres participating in the cement hydration reaction enhanced the mechanical properties of the mortar and reduced its thermal conductivity, which supported bacterial survival in the negative temperature environment. Although negative temperature environments may reduce bacterial populations, the hydrolysis of aluminum ions in the alumina hollow spheres during bacterial metabolism resulted in the precipitation of aluminum hydroxide flocs. These flocs adsorbed free calcium carbonate in the pores, converting it into effective calcium carbonate with cementing properties, thus enhancing the crack healing capability of the examined specimens. This microbe-based self-healing strategy, utilizing alumina hollow spheres as bacterial carriers, is anticipated to provide an effective solution for achieving efficient crack self-healing in mortars that is resistant to the detrimental effects of negative temperature conditions. Full article

Utilizing supplementary cementitious materials is an effective way to fabricate low-carbon cement-based materials. In this paper, the composite mortars with good properties were prepared by mixing them with basic oxygen furnace slag (BOFS), Bayer red mud (BRM), and phosphogypsum (PG). The influences of the replacement amounts of BRM and PG on the mechanical properties, hydration characteristic, chloride corrosion resistance, and microstructure of the materials were investigated. The results showed that simply adding 10 wt% BRM slightly modified the properties of the composite mortars. With the increase in PG, the mechanical strength and corrosion resistance coefficient K_C of the mortars first increased and then decreased, in contrast to the chloride migration coefficient D_RCM and electric flux Q. Among the samples, sample S3, with 6 wt% BRM and 4 wt% PG, had the best properties, a flexural strength of 6.6 MPa, and a compressive strength of 43.5 MPa at a curing age of 28 d. And the values of D_RCM and Q of the sample, respectively, decreased by 44.06% and 22.83% compared with the control sample, along with the value of K_C corroded after 120 d increasing by 16.33%. The microstructure analysis indicated that the alkali activation of BRM promoted the generation of lamellar portlandite and reticular and granular C-S-H gel. The free aluminum in BRM could dissolve into C-S-H gel to induce the generation of C-A-S-H gel. Furthermore, the generated amount of ettringite increased by adding PG. The aforementioned improvement in mechanical properties is primarily attributed to BRM promoting the hydration of the composite mortars and inducing the transformation of the C-S-H gel into C-A-S-H gel, and PG promoting the generation of ettringite. Moreover, the filling effects of BRM and PG decreased the porosity and number of harmful pores. It increased the compactness of the microstructure to endow the composite mortars with excellent chloride corrosion resistance. Full article

This study investigates the development of two sustainable cements, CEM II/B-LL and CEM VI, in accordance with the UNI EN 197-1 and 197-5 standards. CEM II/B-LL was produced by replacing Portland cement with limestone (LS) at varying dosages (0%, 15%, 25%, and 35% by mass), and CEM VI was made by substituting blast furnace slag with limestone at different levels (0%, 10%, 20%, 30%, and 40% by mass). The results show that both binders are classified as structural cements. LS substitution increases the setting time of CEM II/B-LL but does not significantly affect the setting time of CEM VI. When cured at low temperatures (10 °C), CEM VI mortars retain their mechanical properties even at high LS levels, making them particularly suitable for cold climates. Mortar properties such as total porosity and capillary water absorption increase with LS content, with CEM VI exhibiting lower sensitivity to LS additions. Free shrinkage in CEM II/B-LL mortars decreases with LS content, whereas in CEM VI mortars, it initially increases with up to 20% LS and then decreases at higher LS levels (30–40%). Restrained shrinkage is also lower in CEM VI than in CEM II/B-LL. The Global Warming Potential (GWP) of CEM II/B-LL decreases significantly with increased LS content, whereas in CEM VI, it remains almost constant up to a 40% substitution. However, CEM VI demonstrates a 50% lower environmental impact compared to CEM II/B-LL, underscoring its superior sustainability. 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

In this paper, the early drying shrinkage coefficients of different hydraulic cement mortars are calibrated through laboratory experiments for moderate-heat Portland cement (MHPC) and low-heat Portland cement (LHPC). By developing an improved mesoscale modeling approach, a 3D highly detailed simulation of concrete was generated, which incorporates the phases of mortar, aggregates, and interfacial transition zone (ITZ). The simulation result is in good agreement with the concrete early drying shrinkage experiment, exhibiting an error of less than 4.99% after 28 days. Subsequently, the mesoscale model is employed to explain the influence of the ambient humidity, cement type, and aggregate volume ratio on the early drying shrinkage performance of concrete. The results show that the early drying shrinkage coefficient of the LHPC is approximately 82% of the MHPC. Additionally, the depth of ambient humidity influence is about 15 mm from the concrete surface after 28 days. The early drying shrinkage can be controlled by increasing ambient humidity via the LHPC or raising the aggregate volume ratio. The mass-loss rate of concrete decreases as the ambient humidity or aggregate volume ratio increases during the process of drying shrinkage. Furthermore, the results quantify the influence patterns of various factors on drying shrinkage, thereby facilitating their application in assessing the cracking time induced by early drying shrinkage in roller-compacted concrete (RCC) dams. This provides theoretical guidance for crack prevention in concrete structures and aids in developing strategies for the construction of crack-free dams. Full article

Microbially induced calcium carbonate precipitation (MICP) presents a sustainable, environmentally friendly solution for repairing cracks in cement-based materials, such as mortar and concrete. This self-healing approach mechanism enables the matrix to autonomously close its own cracks over time. In this study, specimens (50 mm in diameter and 25 mm in height) were exposed to submersion and a wet–dry cycle environment. The solution considered a nutrient-rich suspension with calcium lactate, urea, calcium nitrate, and Bacillus subtilis or Sporosarcina pasteurii in a biomineralization approach. The self-healing efficiency was assessed through optical microscopy combined with image processing, focusing on the analysis of the superficial crack closure area. S. and B. subtilis exhibited notable capabilities in effectively healing cracks, respectively, 8 mm² and 5 mm² at 35 days. Healing was particularly effective in samples placed in a submerged environment, especially with a 69 mM concentration of calcium lactate in bacterial suspensions containing B. subtilis, where 87.5% of a 4 mm² crack was closed within 21 days. In contrast, free calcium ions in the solution, resulting from anhydrous cement hydration, proved ineffective for S. pasteurii biomineralization in urea-rich environments. However, the addition of an external calcium source (calcium nitrate) significantly enhanced crack closure, emphasizing the critical role of calcium availability in optimizing MICP for bio-agents in cement-based materials. These findings highlight the potential of MICP to advance sustainable self-healing concrete technologies. 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

This study aimed to investigate the feasibility of using geopolymer paste (GP) as an adhesive agent for (i) anchoring steel bars in concrete substrates, (ii) repairing concrete, and (iii) repairing limestone and granite masonry blocks commonly found in historic buildings. In this investigation, seven cement-free GP mixes were developed with different combinations of binder materials (slag, silica fume, and metakaolin). The mechanical properties, adhesive performance, and production cost of the developed GP mixes were compared to those of a commercially epoxy adhesive mortar (EAM). The results obtained from this study indicated that the use of GPs enhanced the bonding between steel bars and concrete substrates, achieving bonding strengths that were 19.7% to 49.2% higher than those of control specimens with steel bars directly installed during casting. In concrete repairs, the GPs were able to restore about 60.6% to 87.9% of the original capacity of the control beams. Furthermore, GPs exhibited a promising performance in repairing limestone and granite masonry blocks, highlighting their potential suitability for masonry structures. The best adhesive performance was observed when a ternary binder material system consisting of 70% slag, 20% metakaolin and 10% silica fume was used. This combination, compared to the investigated EAM, showed comparable adhesive properties at a significantly low cost, indicating the viability of GPs as a cost-effective, eco-friendly adhesive agent. Full article

A water-soluble ternary copolymer bearing carboxyl, sulfonic, and amide functional groups was synthesized using ammonium persulfate-catalyzed free radical polymerization in water, resulting in high monomer conversion. This copolymer was then complexed with aluminum sulfate, forming an admixture containing Al(SO₄)(OH)·5H₂O, which was subsequently combined with silica gel. Characterization revealed that the synthesized copolymer formed a large, thin membrane that covered both the aluminum compounds and the silica gel blocks. The introduction of this complex admixture, combining the copolymer and aluminum sulfate, not only reduced the setting times of the cement paste but also enhanced the mechanical strengths of the mortar compared to using aluminum sulfate alone. The complex admixture led to the formation of katoite, metajennite, and C₃A (tricalcium aluminate) in the mortar, demonstrating significant linking effects, whereas pure aluminum sulfate could not completely transform C₃S within 24 h. Further addition of silica gel to the complex admixture further shortened the setting times of the paste, slightly reduced compressive strength, but improved flexural strength compared to the initial complex admixture. The silicon components appeared to fill the micropores and mesopores of the mortar, accelerating cement setting and enhancing flexural strength, while slightly decreasing compressive strength. This study contributed to the development of new cementing accelerators with improved hardening properties. Full article

Two water-soluble block copolymers composed of acrylic acid (AA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and optionally maleic anhydride (MAH) were synthesized through ammonium persulfate-catalyzed free radical polymerization in water. The introduction of aluminum sulfate (AS) into the resulting mixtures significantly reduced the setting times of the paste and enhanced the mechanical strength of the mortar compared to both the additive-free control and experiments facilitated solely by pure AS. This improvement was primarily attributed to the inhibition of rapid Al³⁺ hydrolysis, which was achieved through coordination of the synthesized block copolymers, along with the formation of newly identified hydrolytic intermediates. Notably, the ternary copolymer (AA–AMPS–MAH) exhibited superior performance compared to that of the binary copolymer (AA–AMPS). In the early stages of cement setting, clusters of ettringite (AFt) were found to be immobilized over newly detected linkage phases, including unusual calcium silicate hydrate and epistilbite. In contrast to the well-documented role of polymers in retarding cement hydration, this study presents a novel approach by providing both accelerating and hardening agents for cement setting, which has significant implications for the future design of cement additives. Full article

This paper presents a novel low-carbon binder formulated from fly ash (FA), ground granulated blast furnace slag, steel slag, and desulfurization gypsum as a quaternary solid waste-based material. It specifically examines the influence of FA content on the mechanical properties and hydration reactions of the quaternary solid waste-based binder. The mortar test results indicate that the optimal FA content is 10%, which yields a 28-day compressive strength 11.28% higher than that of the control group without FA. The spherical particles of fly ash reduce the overall water demand and provide a “lubricating” effect to the paste due to their continuous gradation, improving the fluidity of the slag-steel slag-gypsum cementitious materials. The micro test results indicate that fly ash has minimal effect on the early hydration products and process of the solid waste-based cementitious materials, but after 7 days, it continuously dissolves silicon-oxygen tetrahedrons or aluminum-oxygen tetrahedrons, consuming Ca²⁺ and OH⁻ in the system. After 28 days, the amount of ettringite and C-(A)-S-H gel generated increases significantly. The pozzolanic activity of fly ash is mainly stimulated by the Ca(OH)₂ from steel slag in the later hydration stage. Additionally, spherical fly ash particles can fill the voids in the hardened paste, reducing the formation of cracks and weak zones, and thereby contributing to a denser overall structure of the hydrated binder. The findings of this paper provide data support for the development of low-carbon cement-free binders using fly ash in conjunction with metallurgical slags, thereby contributing to the low-carbon advancement of the construction materials industry. Full article

Concrete production is associated with extensive energy consumption and significant CO₂ emissions. In addition, tremendous amounts of freshwater are used as a mixing agent. Urgency is increasing to develop sustainable cementitious materials and promote freshwater-saving strategies. An environmentally friendly alternative binder, seawater mixed with one part alkali activated material, is studied. In this work, a cradle-to-gate life cycle assessment was applied to study the equivalent CO₂ emission and cost properties of the clinker-free binder. The seawater mixed mortar possesses comparable mechanical properties to Portland cement, with 3 d flexural and compressive strengths of 5.3 MPa and 25.2 MPa. In addition, the mortar developed in this work is of similar cost as commercial cement, but reduces CO₂ emissions by 44.8%. Full article