Publications

T4 DNA Polymerase-Proofread DNA Binding Identifier for Sensitive Homogeneous Immunoassays

Aptamer-based homogeneous immunoassays exhibit considerable potential in the domains of bioanalysis and biodiagnosis owing to their universality in analyzing both proteins and small molecules as well as their compatibility with nucleic acid amplification technologies. Nevertheless, the substantial signal leakage by nonspecific aptamer allostery poses a challenge to enhancing sensitivity further. Herein, we reported a T4 DNA polymerase-proofread DNA binding identifier (ReID). This strategy could harness the dual-enzymatic activity of T4 DNA polymerase to eliminate the leaked signal, thereby efficiently integrating target-induced aptamer allostery with subsequent polymerase chain reaction signal amplification. Moreover, we explored the regulation mechanism of dNTPs concentration on the dual-enzymatic activity of the T4 DNA polymerase. As a result, this strategy achieved an ultrasensitive protein detection limit of 8 fg/mL, validating the effectiveness of this proofreading approach. The universality was further confirmed by highly sensitive detection of small molecules. The exploration of ReID represents a significant advancement in the sensitivity and universality of immunoassays, even demonstrating the potential for multiple proteomic assays, offering a novel perspective for the development of high-performance homogeneous immunoassays.

The Role of Porosity on Degradation of Concrete Under Severe Internal and External Brine Attack in Confined Conditions

It has been observed that a trench wall embedded in the soil of the Dead Sea has lost strength and is deteriorating due to brine attack. This phenomenon demonstrates that concrete wall structural stability and durability can be seriously endangered. Yet conventional analysis using macroscopic models is considered an oversimplification, as it neglects the existing micro-cracking and other nonlinearities that are endemic to such deterioration. The current study describes a multiscale formulation for estimating the anticipated reduction in strength of a concrete wall exposed to both external and internal briny water. Our methodology provides an upscale formulation to predict concrete response under aggressive environmental and partially confined conditions. The proposed method uses the concept of a "fictitious" water-to-cement (w/c) ratio to express the microstructural changes that cause an increase in material porosity, thus reflecting the material's degradation through leaching. Simulation results indicate that under the partially confined conditions representing actual ground pressure, the trench wall will remain stable for a service life of 40 years. Furthermore, the proposed model was experimentally calibrated and validated and found in agreement with experimental results.

Microstructure characteristics in the cement paste containing micronized sand filler

In recent decades, the cement industry became aware, more and more, of the economic and environmental problems of concrete associated with the use of ordinary Portland cement (OPC). Attempts have been made to partially replace the cement by active or inert components, such as limestone filler, fly ash and finer sands. Whether the blend material is feasible and guarantees the long term properties in comparison with OPC is still an open research area. In this study, cement pastes with an without micronized sand have been investigated by means of mercury intrustion porosimetry (MIP) and electronic scanning electron microscope (ESEM). The proportion of replacement was 20% by weight. From the results, paste with micronized sand (CM6) can increase the rate of hydration compared with OPC paste when the water to binder ratio is kept constant (w/b = 0.4). When the water to cement ratio is kept constant w/c = 0.4), paste with micronized sand has lower porosity and finer pore structure compared with OPC paste. Seen from the interfacial transition area, big pores and mainly located around sand particles. Sand particles can give some contribution to compensate the increasing of porosity in CM6.

A review of the chloride transport properties of cracked concrete: experiments and simulations

Modelling of water permeability in cementitious materials

Micro- and meso-scale pore structure in mortar in relation to aggregate content

Assessment of Structural Feature and Ionic Diffusivity of ITZ in Blended Cementitious Composites

In this paper, we present a study about the assessment of structural feature and ionic diffusivity of interfacial transition zone (ITZ) in blended cementitious composites, which are made of Portland cement, blast furnace slag and limestone filler. In particular, three mortar series are examined with respect to varying replacement levels of supplementary cementitious materials (SCMs), curing age and water-to-binder (w/b) ratio. Based on the techniques of experimental measurement and numerical simulation, i.e., the backscattered electron (BSE) image analysis and the HYMOSTRUC model, the structural features of ITZ in designed mortars are elaborated in a quantitative manner. Thereafter, a lattice Boltzmann method based computer modeling of ionic diffusion in the ITZ is performed to predict the ionic diffusivity. Results indicate that the ITZ differs much from bulk paste, which is of significant importance in blended cementitious composites. The structural feature and the ionic diffusivity of ITZ are prominently affected by various casting factors, such as replacement levels of SCMs, curing age and w/b ratio.

Understanding Chloride Diffusion Coefficient in Cementitious Materials

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients.

Self-healing in cementitious materials: Materials, methods and service conditions

A mix design methodology of blast furnace slag and fly ash-based alkali-activated concrete

Although the application of blast furnace slag and fly ash-based alkali-activated concrete (BFS/FA-AAC) has both economic and environmental benefits, it is limited by the lack of a straightforward mix design method. In this paper, an experiment was conducted to investigate the effect of control factors, including the Na2O/binder ratio, the SiO2/Na2O ratio, the BFS/binder ratio, the water/binder ratio, and the water content on the workability (slump and rheology) of BFS/FA-AAC, and the effect of control factors include the Na2O/binder ratio, the SiO2/Na2O ratio, the BFS/binder ratio, the water/binder ratio, and the curing time on the compressive strength of BFS/FA-AAC. As a result, the influence degree and mechanism of each control factor on the performance of BFS/FA-AAC were quantitively explored and the accuracy of an empirical compressive strength formula was validated. Based on that, a practical mix design method of BFS/FA-AAC was eventually established. It is found that the mixture composition and content of paste can significantly influence the workability of BFS/FA-AAC. The compressive strength of BFS/FA-AAC is determined by control factors when the water content is within 160–195 kg/m3. The mechanical predictive method of BFS/FA-AAC is proven of high accuracy. The mixture designed by this methodology exhibits satisfied fresh and hardened performance as well as high environmental benefits.

Research Progress on Liquid Organophosphorus Esters Flame Retardants

This paper reviewed the recent liquid organophosphorus esters flame retardants developments,research status and the potential future trends.The classification,mechanism and synthetic methods of liquid organic flame retardant were also introduced.The development and problems in the application were outlined considering the aspects of halogen and halogen-free fire retardants and their development perspectives.

Simulation of the microstructure formation in hardening self-compacting cement paste containing limestone powder as filler via computer-based model

Connectivity of individual phase in cement paste and their impact on the concrete properties

Cement hydration system is a disorder and multiphase system where individual phase (briefly categorized as solid phase and pore phase) changes with time. In this paper, the connectivity of individual phase in hydrating cement paste is studied. The percolation phenomenon of solid phase and the de-percolation of capillary porosity are emphasized. Their impacts on the concrete properties are discussed as well. It was found at the percolation threshold of solid phase is strongly correlated with the setting of cement paste. The connectivity and the de-percolation threshold of capillary pores determine the water permeability. Based on these observation and, thanks to the advanced cement hydration and microstructure simulation model, the desired concrete properties are therefore can be designed by manipulating the mix components and proportion.

ASR: Insights into the cracking process via lattice fracture simulation at mesoscale based on the chemical reactions at microscale

In our former paper, based on a published 3D reactive transport model at microscale with the capability of simulating the chemical reactions involved in ASR, the location of expansive ASR gel related to the reactivity of aggregate, temperature, aggregate porosity and silica content in aggregate, is clarified. Based on the simulation results, in this paper, the cracking process at mesoscale in concrete induced by ASR in the early stage is investigated. The results show that the cracking process can be divided into four stages and three cracking routes are generalized with the behind chemical exposed environments specified. The cracking routes are found to be comparable with the experimental observed routes. For the first time, the cracking patterns induced by ASR in concrete at mesoscale is linked with the chemical reactions at microscale, which is the first step towards building a complete computational tool to predict ASR as realistic as possible.

Molecular dynamics and experimental study on the adhesion mechanism of polyvinyl alcohol (PVA) fiber in alkali-activated slag/fly ash

This paper aims to study the adhesion mechanism of polyvinyl alcohol (PVA) fiber within alkali-activated slag/fly ash (AASF) matrix using molecular dynamics (MD) simulation in combination with systematic experimental characterization. The adhesion of PVA to C-(N-)A-S-H gel with different Ca/(Si+Al) and Al/Si ratios was modeled using MD simulation, with the related adsorption enthalpy calculated and the adhesion mechanism explored. The experimentally attained chemical bonding energy of PVA fiber in AASF coincides well with the simulation results. In both cases, the adhesion enhances primarily with increasing Ca/(Si+Al) ratio of C-(N-)A-S-H gel. Additionally, MD simulation indicates preferential element distributions of Ca around PVA molecule, which was confirmed experimentally by the detection of the Ca-rich C-(N-)A-S-H gel in the interfacial transition zone (ITZ). This study provides further insights into the adhesion mechanism of PVA fiber to C-(N-)A-S-H gel formed in AASF, which is particularly valuable for the future development of PVA-based high-performance alkali-activated composites.

Internal curing by superabsorbent polymers in alkali-activated slag

In this study, internal curing by superabsorbent polymers (SAP) is utilized to mitigate self-desiccation and autogenous shrinkage of alkali-activated slag (AAS) pastes. Absorption and desorption kinetics of SAP incorporated in AAS pastes were studied with X-ray tomography. Internal curing delayed the peak of the rate of heat liberation but increased the total reaction degree of AAS pastes. Internal curing by SAP mitigated effectively the drop of internal relative humidity and the self-desiccation-induced autogenous shrinkage of AAS pastes. The cracking tendency of AAS pastes undergoing shrinkage in restrained conditions was also significantly reduced with SAP. Nonetheless, adding SAP, regardless of their content, cannot eliminate the autogenous shrinkage of AAS pastes, suggesting the existence of other autogenous shrinkage mechanism(s) besides self-desiccation.

Numerical simulation on moisture transport in cracked cement-based materials in view of self-healing of crack