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• Organic and inorganic thickening agents complement each other in cement paste. • Thickening agents can improve paste stability and resistance to deformation. • HPMC reduces the degree of damage to the internal structure of the paste. • Trace amounts of RPP and HPMC can promote paste hydration. The rheological and thixotropic properties, as well as the establishment of dynamic and static structures effectively reflect the workability of the cement paste. In order to investigate the effects of organic and inorganic composite thickening agents on fresh cement paste, the rheological curves, structural recovery rate, storage modulus G ′ and loss modulus G ″ of cement pastes mixed with limestone powder (LP), re-dispersible polymer powder (RPP) and hydroxypropyl methyl cellulose ether (HPMC) were tested by Anton Paar MCR 102 rotary rheometer. The results showed that LP and RPP reduced the yield stress and enhanced workability, and LP also improved the establishment of static structures. The incorporation of HPMC facilitated the recovery rate of static structure, and obviously improved the deformation resistance of the cement paste by reducing the difference between the G ′ and the G ″. However, a single thickening agent was hard to balance the rheological parameters of the pastes. While the combination of LP, RPP and HPMC could improve the rate of structure establishment and recovery, and increase the deformation resistance as well as the stability of the paste. The dense filling effect of LP, the film-forming and bridging effect of RPP, and the winding and water retention effects of HPMC together made up the synergistic effect to further improve the stability of the pastes. [ABSTRACT FROM AUTHOR]

Water treatment sludge was successfully thermally converted to obtain biochar as a stable material with resource potential. This research explored the application of sludge biochar as a supplementary cementitious material. The cement paste samples incorporating different amounts of sludge biochar were prepared, hardened, and analyzed for performance. The results show an improvement in hydration kinetics and mechanical properties of cement paste incorporating biochar, compared to raw sewage sludge. The mineralogical, thermal and microscopic analyses show evidence of pozzolanic activity of the biochar. The samples with 2% and 5% biochar showed higher heat release than the reference material. Specimens with 1%, 2% and 5% biochar showed a slightly higher compressive strength at 28 days compared to the reference material. Sludge conversion to biochar will incur an estimated cost of US$398.23/ton, which is likely to be offset by the substantial benefits from avoiding landfill and saving valuable cementitious materials. Therefore, this research has demonstrated that through conversion to biochar, water treatment sludge can be promoted as a sustainable and alternative cementitious material for cement with minimum environmental impacts, hence contributing to circular economy. [Display omitted] • Biochar was successfully prepared from water treatment sludge. • Biochar was more effective in the hydration of cement paste than sludge. • 1–5% biochar substitution improved compressive strength than reference material. • Biochar production cost is estimated and can be offset by major environmental benefits. [ABSTRACT FROM AUTHOR]

• The effects of metal powders on the mechanical properties of UHSC with steel fibers are studied. • Hydration degree, pore structure characteristics, and micro interface morphology of UHSC are also investigated. • A statistical damage constitutive model can reasonably describe the compressive stress-strain behavior of UHSC. • The mechanical properties and microstructure of UHSC are improved by adding metal powders. In this work, the mechanical properties of ultra-high strength cement-based materials (UHSC) incorporating metal powders and steel fibers under steam curing and autoclave curing were studied, with the special attention devoted to the flexural load-deflection response and compressive stress-strain behavior. Additionally, the hydration degree, pore structure characteristics and micro interface morphology were investigated to provide a thorough insight into the enhancement mechanism of metal powders and steel fibers on UHSC. The results show that the incorporation of Fe and Cu powders could enhance the flexural performance of UHSC, including the increased flexural strength and energy absorption capacity. Under uniaxial compression, improved peak stress, secant modulus, and energy absorption capacity of UHSC could be observed after the addition of Fe powders, but this improvement was negligible after the addition of Cu powders. Moreover, the statistical damage constitutive model based on strain equivalence hypothesis and improved statistical damage theory could reasonably describe the stress-strain behavior of UHSC under uniaxial compression. Furthermore, incorporating Fe and Cu powders could ameliorate the pore structure of UHSC, in which the harmful pores was converted into less harmful pores. Micro-interface morphology demonstrated that metal powders were closely bonded with cement paste, and no cracks or micro pores could be detected around the interface. [ABSTRACT FROM AUTHOR]

• Specimens made on-site using the same raw materials and processes. • Bubble defect areas were divided into 13 classifications. • Correlation between the distribution of bubble defects and the splitting tensile strength. In this research, the bonding performance of the interlayer interface was investigated via the two main factors of the size and number of bubble defects in combination with field tests. The mechanical index of the splitting tensile strength was used to characterize the bonding performance of the interlayer interface. The bubble defect areas of the specimens were divided into 13 classes. Via the statistical analysis of the bubble defects, the probability of the occurrence of small bubble defects was found to be greater than that of large bubble defects. For the same or a similar area ratio of bubble defects, the splitting tensile strengths of specimens with different bubble sizes were found to be different. The bond strength near the perfusion hole area was found to be relatively weak. The splitting tensile strength was also found to be larger at locations farther away from the perfusion hole area. This work provides an effective reference for the scientific evaluation of the pouring quality of the self-compacting concrete filling layer. [ABSTRACT FROM AUTHOR]

• Electric curing is proposed for the rapid curing of cement at room temperature. • Suitable electrical curing regime can effectively improve the early strength of cement. • Joule heat is the key to accelerate the hydration of cement. • Electric curing consumes much less energy than steam curing. To understand the effects of direct electric curing condition on the mechanical strength and microstructure of cement paste, a series of experiments were carried out to investigate the effects of alternative current voltages and frequency on compressive strength of samples. And the corresponding microstructure of samples were also analyzed by several measurements including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and mercury intrusion porometer. The results show that alternative current electric voltage and frequency can greatly influence the early compressive strength of a cement paste. And a suitable electric curing condition can make hardened cement paste keep a steady growth of compressive strength and excellent microstructure. The Joule heat of direct electric curing on cement paste is the main reason that accelerates the hydration and improve the early strength development of sample. This study will provide an important technical support for exploring low carbon rapid electric curing method to produce green high early strength cement concrete prefabricated element. [ABSTRACT FROM AUTHOR]

• The effect of plastic viscosity of SCC mixtures on mechanical properties is studied between SCC layer and steam-cured concrete. • Fractal dimension is used to characterize the characteristics of bonding surface. • The microstructure characteristics of the bonding interface are obtained. • The bonding interface zone model is established and the optimal value of plastic viscosity is obtained. In CRTSIII ballastless track structure, the bonding interface between self-compacting concrete (SCC) filling layer and steam-cured concrete track slab not only affected the interaction between filling layer and track slab, but also affected the effect and bond stiffness of connecting reinforcement, which was one of the key links of the whole track structure. Quality control of rheological properties of SCC mixture was proving to be critical for the success of the bond between steam-cured concrete and SCC layer concrete. In this research, the fractal dimension was calculated to characterize the bonding interface characteristics with different plastic viscosities. Moreover, the effect of plastic viscosity on mechanical properties was studied between SCC layer and steam-cured concrete. The bonding interface zone between SCC layer and steam-cured concrete was defined by microhardness and BSE tests. The experimental results indicated that the fractal dimension can better characterize the characteristics of bond surface and had a negative correlation with splitting tensile strength. Mechanical properties and bonding interface structure between steam-cured concrete and SCC layer improved with increasing the plastic viscosity of SCC mixture, especially when the viscosity was greater than 100 pa.s. The bonding interface zone model was established to explain the mechanism of the bond between steam-cured concrete and SCC layer. [ABSTRACT FROM AUTHOR]

Generally, tunnel waste is stacked in the slag field nearby for landfilling, which is harmful to sustainable development. The broken rocks and rock powder among the tunnel waste can be recycled to produce machine-made sand, producing many by-products calling rock powder. Based on the practical project, three types of waste basalt powder (BP), from tunnel excavation waste and by-products (rock powder) of machine-made sand producing from tunnel excavation waste in Sichuan-Tibet railway construction sites, was used to prepare an eco-friendly UHPC. The BP is used to replace the cement and is included in the design UHPC based on Modified Andreasen &Andersen particle packing model (MAA). Moreover, the chemical and physical behaviors and ecological evaluation of the designed UHPC and UHPC pasted were discussed. The results showed that when BP (Specific surface area 4.6582 m2/g) replaces up to 15%, the highest compressive strength of designed UHPC (220 MPa) was obtained. Compared with quartz powder, the pozzolanic activity of BP was generally low and increased with the increase of reaction temperature. However, the presence of BP and its fineness in UHPC pastes increased the values of the total autogenous shrinkage and decreased the total heat release at an early age of designed UHPC pastes, this effect is more pronounced with temperature increasing. Based on a quartering method with embodied carbon dioxide emissions and the compressive strength, UHPC with waste BP reduced embodied carbon dioxide and possessed higher compressive strength and lower environmental impact than the control samples of UHPC. [ABSTRACT FROM AUTHOR]

The reclamation and reuse of electrolytic manganese residue (EMR) as a bulk hazard solid waste are limited by its residual ammonia nitrogen (NH 4 + -N) and manganese (Mn 2+ ). This work adopts a co-processing strategy comprising air-jet milling (AJM) and horizontal-shaking leaching (HSL) for refining and leaching disposal of NH 4 + -N and Mn 2+ in EMR. Results indicate that the co-use of AJM and HSL could significantly enhance the leaching of NH 4 + -N and Mn 2+ in EMR. Under optimal milling conditions (50 Hz frequency, 10 min milling time, 12 h oscillation time, 400 rpm rate, 30 ℃ temperature, and solid-to-liquid ratio of 1:30), NH 4 + -N and Mn 2+ leaching efficiencies were optimized to 96.73% and 97.35%, respectively, while the fineness of EMR was refined to 1.78 µm. The leaching efficiencies of NH 4 + -N and Mn 2+ were 58.83% and 46.96% higher than those attained without AJM processing. The AJM used strong airflow to give necessary kinetic energy to EMR particles, which then collided and sifted to become refined particles. The AJM disposal converted kinetic energy into heat energy upon particle collisions, causing EMR phase transformation, and particularly hydrated sulfate dehydration. The work provides a fire-new and high-efficiency method for significantly and simply leaching NH 4 + -N and Mn 2+ from EMR., Competing Interests: Declaration of Competing Interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “Enhanced green remediation and refinement disposal of electrolytic manganese residue using air-jet milling and horizontal-shaking leaching”., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Rheological curves of cement-fly ash (C-FA) paste incorporating nanomaterials including nano-SiO 2 (NS), nano-CaCO 3 (NC) and nano-Al 2 O 3 (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel-Bulkley (H-B) model, and the influences of these nanomaterials on rheological properties of C-FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C-FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C-FA paste. When the content of NS and NA were 2 wt%, the rheological index of C-FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C-FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m 2 /g) and NA (120 m 2 /g) are much larger than that of NC (40 m 2 /g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time.