Carbon dots (CDs) as a newfangled and eco-friendly nanomaterial exhibit a promising engineering application in strengthening mechanical properties of cement matrices. However, the modification effectiveness of CDs on mechanical performance lacks enough investigation. More seriously, the influence of their sizes is still a research gap, enormously hindering their further application in cement-based materials. Herein, the size-induced effect of CDs on mechanical properties of cement mortar is systematically disclosed for the first time. Specifically, three kinds of CDs with diverse sizes are deliberately synthesized via calcinating the cheap and nontoxic raw material (i.e., citric acid). The relationship between the mechanical performance and the sizes of CDs is determined through the compressive strength test. More importantly, the mechanism of their size-induced effect on mechanical properties is comprehensively studied based on the analyses of phase composition and pore structure. The consequences illustrate that the compressive strength of mortar modified by CDs with average sizes of 12.53, 5.86, and 1.81 nm increases by 6.6%, 15.7% and 9.4% separately, compared to the blank group after 7-d curing. With the sizes of CDs reducing ranging from 12.5 to 1.81 nm, the compressive strength of CDs-modified mortar firstly increases and then decreases. The related mechanism is attributed to the combined effect of CDs-induced nucleation and air entrainment. As the sizes of CDs decrease, the intensities of both the nucleation effect and air entrainment effect gradually strengthen, thereby accelerating the cement hydration to generate more C-S-H and introducing the harmful pores. This work fills the research gap of the effect caused by CDs sizes on mechanical properties for cement-based materials. This would guide preparation of CDs with suitable sizes toward increasing mechanical properties of cement matrices, thus facilitating the development of high-performance concrete by CDs-based nanomodification. 

Deciphering size-induced influence of carbon dots on mechanical performance of cement composites

Carbon dots (CDs) as a novel and green nanomaterial exhibit a promising application in enhancing the chloride binding capacity of cement to extend the service life of reinforced concrete (RC) structures. However, their size influence on the enhancement of chloride binding is still a research gap, enormously hindering the further employment of CDs toward cement system. Herein, their size-induced effect on chloride binding actions of cement is comprehensively unveiled using CDs with various sizes for the first time. Specifically, three kinds of CDs with different sizes are controllably prepared through simply altering the calcinating time of citric acid. And the relationship between sizes of CDs and chloride binding capacity of cement is confirmed through the equilibrium tests. More importantly, the mechanism for the effect of CDs sizes on chloride binding is reasonably proposed according to the alteration analyses of phase compositions. The consequences demonstrate that the chloride binding capacity in cement modified by CDs with average sizes of 1.73, 5.79, and 12.37 nm increases by 41%, 20%, and 14% respectively, compared with that of the blank group after 28-d immersion in 3 mol/L NaCl solution. This testifies that the chloride binding capacity of CDs-incorporated cement is negatively correlative with CDs sizes. The related mechanism is that CDs with smaller sizes can provide more nucleation sites to promote cement hydration, further advancing the production of C–S–H gels and monosulfate (Ms), thus more markedly enhancing the physical adsorption and chemical binding of chloride ions in cement pastes. This work would guide the preparation of CDs with more suitable sizes to improve the chloride binding ability of cement, thus anticipated to extend the service life of RC structures in coastal environment, ultimately reducing the CO2 emission from cement industry. 

Effect of carbon dots with different sizes on chloride binding of cement

Recently, there has been considerable interest in utilizing various forms of graphene derivatives for producing high-strength concrete. Among these derivatives are superstructure of graphene quantum dots (GQDs), particularly in their assemblies of carbon dots, which is innovative in cement. This research investigates the impact of graphene derivatives known as supra-GQDs on the mechanical properties and microstructure analysis of cement composites, compared with the control mixture and GQDs solution. The results found that supra-GQDs exhibit enhanced mechanical characteristics. The composite containing 1.2 % supra-GQDs had higher compressive and flexural strengths than the control by 40 % and 108 %, respectively. The study also identified a microstructural bridging mechanism involving the seeding and crystal growth of the C-S-H phase, leading to refined pore structure and less nano-, meso-, and micro-pores. The measured total pore volume reduced by 30 % when compared to GQDs solution. This investigation provides novel insight into the potential of utilizing supra-GQDs in cement composites, opening promising possibilities for high-performance concrete in the construction industry. 

Chemo-physical mechanisms of high-strength cement composites with suprastructure of graphene quantum dots

Nanoparticles (NPs) based on agro-wastes and plant extracts have recently gained attention as supplementary cementitious materials (SCMs) in cement-based construction materials (CBMs) because they are environmentally friendly, low-energy consuming, and affordable. However, the sources, synthesis methods, characteristics, and effects of these materials on the performance of CBMs have not been thoroughly investigated. To address this gap, we comprehensively reviewed the research on agro-based NPs used in CBMs. We performed a scientometric analysis and a comprehensive review of publications in Scopus, Web of Science, and PubMed databases and gray literature from 2005 to 2023. Various agro-based NPs have been extracted for cementitious material application, and predominantly nano-silica particles hold great potential as SCMs. The pre-treatment methods employed to produce agro-based NPs, and the physicochemical and morphological characteristics of NPs produced are presented. Moreover, the influence of agro-based NPs on fresh and hardened properties, microstructure, and durability properties of CBMs are discussed in detail. Our review established that agro-based NPs improve all performance properties of strength, microstructure, and durability of all the tested CBMs except for their rheological properties. The use of agro-based NPs is beneficial at low dosages of up to 5%, while detrimental at high proportions. We also discussed the environmental benefits of using agro-based NPs in CBMs and the challenges future research should focus on in this new research frontier. Our review findings will serve as an inventory of the theoretical and practical methods for processing agro-based NPs and their use in CBMs. 

Application of green agro-based nanoparticles in cement-based construction materials: A systematic review

The porous hydrophilic nature of cement-based material is susceptible to water and corrosive media, severely reducing the durability. In this paper, methyl siloxane-based hydrophobic powder was prepared, and its effect on the physicochemical and anti-corrosion properties of mortar with different water-cement ratios were investigated. The results show that the addition of hydrophobic powder significantly improved the hydrophobic properties of mortars. Especially for the mortars with w/c ratios of 0.2 and 0.4, it showed superhydrophobicity with a water contact angle up to 156.5 ° and 152.3 ° respectively. Lower w/c ratio mortar has a denser microstructure, which reduces the water absorption rate of the mortar, and the hydrophobic powder enhances the hydrophobic effect of low w/c ratio mortar more significantly. The methyl siloxane groups in the hydrophobic powders will bind to the C-S-H gel in the mortar through Si-O bonding, preventing the C-S-H gel connections from forming a continuous network structure. This increased the pore volume and reduced the compressive strength by 14.6%-22.7%, but the total hydration degree was increased, and significant corrosion protection of the steel rebar was demonstrated. 

Study on physicochemical and anti-corrosion performance of methylsiloxane-based hydrophobic powder modified mortar

Preparation of Biomass Carbon Dots for Foam Stabilizer of Foamed Concrete

Strengthening and Toughening Mechanisms of Cnts/Mg-Al Composites Prepared Via Powder Metallurgy Combined with Hot Extrusion

Micro visualization has become an important means of solving colloid and interface scientific problems in enhanced oil recovery. It can establish a relationship between a series of performance evaluations of an oil-water interface under macroscopic dimensions and the actual application effect in confined space, and more truly and reliably reflect the starting and migration behavior of crude oil or emulsion in rock pores. In this article, zwitterionic surfactant alkyl sulfobetaine (ASB) and anionic extended surfactant alkyl polyoxypropylene sulfate (A145) were employed as flooding surfactants. The macroscopic properties of the surfactant solutions, such as the oil-water interfacial tension (IFT), the interfacial dilational rheology and the viscosity of crude oil emulsions, have been measured. At the same time, we link these parameters with the oil displacement effect in several visual glass models and confirm the main factors affecting the migration ability of emulsions in micro-scale pores. The experimental results show that ASB reduces the IFT through mixed adsorption with crude oil fractions. The flat arrangement of the large hydrophilic group of ASB molecules enhances the interactions between the surfactant molecules on the oil-water interface. Compared with sulfate, betaine has higher interfacial membrane strength and emulsion viscosity. A145 has a strong ability to reduce the IFT against crude oil because of the larger size effect of the PO chains at the oil side of the interface. However, the membrane strength of A145 is moderate and the emulsion does not show a viscosity-increasing effect. During the displacement process, the deformation ability of the front emulsions or oil banks is the main controlling factor of the displacement efficiency, which is determined by the membrane strength and emulsion viscosity. The strong interfacial membrane strength and the high emulsion viscosity are not conducive to the migration of droplets in pore throats and may result in low displacement efficiency.

/pdf/how-to-regulate-the-migration-ability-of-emulsions-in-micro-1dbu76rs.pdf

How to Regulate the Migration Ability of Emulsions in Micro-Scale Pores: Droplet Size or Membrane Strength?

Characteristics Analysis of Long Afterglow Phosphor with Sio2 Coating and Evaluation its Influence on the Properties of Self-Luminescent Cement-Based Materials

Sensitivity Analysis of Multi-Row Fan-Shaped Holes to Flow Parameters on the Pressure Surface

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