Functional carbon dot (CDs) were prepared for carrying drugs, and the load-release mechanisms and cytotoxicity of CDs-drugs were studied. The prepared CDs with –NH2 modifying can be used as carriers ...to transport drugs (containing –C=O group, such as DOX) to improve their pH targeting, or carry drugs (containing –COOH group, such as FAC) to improve their intestinal absorbability.
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Carbon dot (CDs) were prepared for carrying DOX (Doxorubicin) or FAC (Ferric ammonium citrate), and the loading mechanism and release kinetics of CDs-drugs were studied. CDs were prepared using peony pollen and urea, and characterized by TEM, XRD, 13C NMR, XPS, UV, FT-IR, DLS and zeta potential. The obtained CDs were rich of –NH2 group on the surface, amorphous phase, spherical morphology with the diameter about 5 nm, and had a blue fluorescence with the quantum yield (QY) of 12%. Iron disorders can cause cancer or anemia. DOX is used for treating cancer, but has severe side effects. FAC is an iron supplement agent, but had low bioavailability. CDs carried DOX (or FAC) through –N=C– (or –CONH–) bond, had high loading efficiency for DOX (37.2%) and FAC (54.0%) by optimizing mass ratios of mCDs to mdrug and reacted overnight. Cellular experiments showed that CDs-drugs had lower cytotoxicity than free drugs and CDs co-located with the drug. In vitro release indicated that CDs-DOX had pH-targeted property and CDs-FAC could be absorbed easily. CDs-drug release belonged to Weibull model, and release mechanism was determined by the bonding way between CDs and drug. CDs had potential applications in delivery drugs with –C=O or –COOH group.
Gypsum modification is an effective strategy to improve the water resistance of magnesium oxychloride cement paste (MOCP), but its early-ages performance evolution has not received much attention. ...The exothermic characteristics and hydration kinetic parameters of MOCP with different contents and types of gypsum are investigated. The results show that the incorporation of gypsum to the MOCP reduces the cumulative heat release of the MOCP and prolongs the induction and acceleration periods. The hydration kinetic parameters also show that the scale factor (A) of MOCP decreases with increasing gypsum content. Incorporation of natural gypsum (NG) to MOCP reduces its nucleation rate and growth rate, while an appropriate amount of flue gas desulfurization gypsum can provide nucleation sites and increase its growth rate. The early-age compressive strength of the gypsum-modified MOCP is reduced due to the reduction in the reaction product (5-phase), but NG can act as a micro-aggregate to alleviate its negative impact on the sample strength.
Sisal fiber exhibits a fibrous and porous structure with significant surface roughness, making it highly suitable for storing phase change materials (PCMs). Its intricate morphology further aids in ...mitigating the risk of PCM leakage. This research successfully employs vacuum adsorption to encapsulate paraffin within sisal fiber, yielding a potentially cost-effective, durable, and environmentally friendly phase change energy storage medium. A systematic investigation was carried out to evaluate the effects of sisal-to-paraffin mass ratio, fiber length, vacuum level, and negative pressure duration on the loading rate of paraffin. The experimental results demonstrate that a paraffin loading rate of 8 wt% can be achieved by subjecting a 3 mm sisal fiber to vacuum adsorption with 16 wt% paraffin for 1 h at -0.1 MPa. Through the utilization of nano-CT imaging enhancement technology, along with petrographic microscopy, this study elucidates the mechanism underlying paraffin storage within sisal fiber during vacuum adsorption. The observations reveal that a substantial portion of paraffin is primarily stored within the pores of the fiber, while a smaller quantity is firmly adsorbed onto its surface, thus yielding a durable phase change energy storage medium. The research findings contribute to both the theoretical foundations and the available practical guidance for the fabrication and implementation of paraffin/sisal fiber composite phase change energy storage mediums.
3D concrete printing technology has enabled the construction of full-scale bridges. However, structural carbon emissions due to higher cement content and limitations of embedded reinforcement have ...limited its widespread adoption. This paper presents a non-reinforced 3D printed concrete box arch bridge and describes its design, construction, dismantlement, and reconstruction, as well as evaluation of the carrying capacity of reconstructed primary arch ring. The bridge adheres to current technical principles and bridge engineering specifications. By taking into account the mechanical anisotropy and primary stress characteristics of the arch, the design negates the need for reinforcement. The study showcases the reusability and potential carbon emission reduction through block printing, on-site assembly, block removal, and secondary usage. The safety of the reconstructed arch bridge was confirmed through an in-situ load test.
•The structural build-up of cement pastes with ground limestone was studied.•The interparticle forces explained the physical effect in the structural build-up.•The hydration kinetics revealed the ...chemical effect in the structural build-up.•The structural build-up was related with interparticle forces, hydration kinetics.
In this paper, the influences of ground limestone content, fineness and water to binder ratio (W/B) on the structural build-up of cement pastes were studied. The interparticle forces and hydration kinetics were introduced to reveal the micro-mechanism of structural build-up of cement-ground limestone pastes. The results showed that the addition of ground limestone decreased the structural build-up rate of cement pastes and the structural build-up rate declined with increasing the ground limestone content and increased with increasing the ground limestone fineness. The reduction in W/B resulted in the increase of the structural build-up rate. The calculated total interparticle force based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory (van der Waals force and electrical double layer force) and cohesive force due to ion-ion correlations explained the physical effect in the structural build-up of cement-ground limestone pastes. The nucleation rate constant (KN) and growth rate constant (KG) of the hydration products based on boundary nucleation and growth (BNG) model played an important role in the structural build-up of cement-ground limestone pastes and revealed its mechanism of chemical action. A semi-empirical model of the structural build-up rate and the total interparticle forces, hydration kinetics parameters, etc. was established and verified, whose estimated values were close to the experimental values in general. The model revealed the structural build-up process of cement-ground limestone pastes from both physical and chemical perspectives.
Foam concrete boasts widespread applications in backfill engineering, energy-efficient insulation components, and road infrastructure. However, the foam concrete with lower density tends to possess ...the lower stability. The unstable characteristics of foam concrete restricts its application. In this study, the feasibility of employing biochars to increase stability of foamed concrete is investigated. The rheological properties of base mix are carried out to analyze the foam concrete stability. The analysis of water state, interparticle distance and ion concentration are tested to analyze the stabilization mechanisms. Our findings demonstrate that the introduction of corn husk biochar (CHBC) within the base mix expedites flocculation formation, reducing interparticle distance and subsequently elevating the yield stress. Conversely, the inclusion of rice husk biochar (RHBC) diminishes ion concentration, heightening repulsion forces between particles and thereby reducing yield stress of base mix. Higher yield stress exert the higher constraining force and frictional force to the bubbles, thereby decreasing bubble size in fresh foamed concrete, bettering pore structure, compressive strength and foam stability of foamed concrete. Additionally, the increase in CHBC content enhances pore sphericity, potentially attributed to decreased bubble deformation parameters Caη.
The static yield stress evolution of cement paste is mainly driven by the colloidal force and cement hydration, while their respective roles and contributions are not yet clear. In this paper, three ...stages are distinguished in the first 3 h evolution of static yield stress of cement pastes (with or without steel slag powder), including the initial stage (up to 30 min), the induction stage (30–60 min) and the acceleration stage (after 60 min). It was found that colloidal force mainly contributes to the large static yield stress before the acceleration stage. The role of hydration was found to have determined the evolution trend of the static yield stress since the induction stage, which was identified by quantifying the interaction force between the C-S-H instead of solely considering C-S-H volume fraction. Based on quantitative results, how the physico-chemical parameters control the static yield stress evolution at each stage is identified comprehensively. This study provides a deep and quantitative understanding of structural build-up process of cement paste.
•How the static yield stress evolution is controlled by physico-chemical parameters is identified.•The colloidal force contributes to the large static yield stress before the acceleration stage.•The cement hydration determines the evolution trend of the static yield stress since the induction stage.
•The hydration mechanism and model of RHA were summarized and commented.•The relationship between chemical reaction and internal curing effects of RHA was illuminated.•The effects of RHA on main ...properties of cement-based materials were reviewed in detail.•The aspects on RHA which have not been sufficiently researched were refined.
Rice husk is a kind of agricultural waste with huge yield and wide distribution, which can get rice husk ash (RHA) containing a large amount of amorphous silica and porous structure by combusting under certain conditions. As a supplementary cementitious material (SCM), the RHA has high pozzolanic activity and internal curing characteristic. It was reported that RHA can significantly improve various performances of cement-based materials. This paper presents an overview of the physicochemical properties of RHA and its effects on the main performances of cementitious materials, e.g. cement hydration, strength, chloride penetration, sulfate resistance, carbonation and shrinkage. The hydration mechanism and the universal optimal content range of RHA are further discussed in depth. The main hydration modes of RHA particles are: (i) the dissolution reaction of micro-particles and (ii) the diffusion reaction of macro-particles. The main contribution of small-size particles to the cementitious system is the chemical effect of RHA, and the main function of large-size particles presents as the internal curing effect of RHA. Based on the summary and extraction of the macro-properties, it is considered that the preferred content range of RHA is 10–20%. Through a deeper and clearer understanding of the action mechanism of RHA in cementitious materials, it can provide ideas for further studies related to RHA and promote the green and sustainable application of RHA in cement-based materials.
Extrusion-based 3D-printed concrete (3DPC) structures are reported to hold mechanical anisotropy behaviors and weak transport properties compared with cast concrete. Fundamental insights into the ...pore structure discrepancy between printed and cast concrete are essential to the performance prediction and improvement strategy for 3DPC. This study analyzes the pore structure alternations in 3D-printed geopolymer concrete (3DPGC) with cast ones as the reference. Several pore characteristics, i.e., pore volume, distribution, specific surface area (SSA), shape and connectivity are investigated via X-ray CT and MIP. The results demonstrate that a larger porosity, coarser pore size distribution and higher pore SSA exist in 3DPGC compared with CGC. The coarser pore size distribution respectively lies in large voids (>0.2 mm) and small pores (<400 nm) for printed concrete. The pulling stress applied by nozzle movements during the extrusion process contributes to the pore elongation of printed concrete. The mechanical anisotropy of printed concrete without fibers originates from two factors: (i) Oriented pore elongation induces the discrepancy in stress concentration and deformation, and (ii) The weak interlayer presence may cause sliding between layers during loading. However, the pore elongation effect decays with the pore size reduction, limiting its impact on mechanical-anisotropic behaviors. Targeted strategies are then proposed for the matrix strengthening and mechanical anisotropy mitigation in printed concrete.
•Low pore sphericity and a high pore specific surface area exist in printed concrete, especially in large voids.•The pulling stress applied by nozzle movements during the extrusion process contributes to the pore elongation of printed concrete.•The mechanical anisotropy of printed concrete originates the oriented pore elongation and the interlayer presence.•The pore elongation effect decayed with the pore size reduction limits its impact on mechanical-anisotropic behaviors.
