On the material level, the deterioration of ordinary Portland cement (OPC) paste at elevated temperature is attributed to chemical transitions and microstructural cracking. However, few studies on the quantitative characterisation of the degradation process of OPC paste have been reported and thus the quantitative relationship between microcracking and strength loss of OPC paste remains unclear. A simulation procedure for modelling the microstructural changes of OPC paste at elevated temperature was developed in this work. After the microstructural simulation, a virtual tensile test was performed on fire-damaged microstructures in order to evaluate the tensile strength and Young's modulus. The strength losses of OPC paste due to both chemical transitions and microcracking were then quantified.
Concrete is one of the most important construction materials in the world. However, Portland cement, one of the constituents of concrete, is responsible for about 5-10% of global CO2 emission. From sustainability point of view, it is important to search for materials which can be used to reduce or to replace Portland cement in concrete. In this study, micronized sand, with high purity SiO2, has been selected as cement replacement. Environmental impact of micronized sand was evaluated and compared with Portland cement. The footprints showed that micronized sand has much less impact than cement on environment. In all categories of sustainability, the environmental impact of sand was 2 orders of magnitude lower than that of Portland cement. It was found that the use of micronized sand as cement replacement gave a big contribution in the category “global warming”, i.e. reducing CO2 emission.
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.
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.
This study aims to investigate the evolution of the chemical and physical properties of cement pastes and the change of macro properties caused by the microstructural changes at elevated temperatures of self-compacting cement paste(SCCP) samples.In the experiments,the samples were exposed to a certain high temperature,then mercury instruction porosimetry(MIP) and scanning electron microscopy(SEM) were applied to investigate the microstructure.Gas permeability test was carried out to define the effect of microstructural changes on the permeability of SCCP samples.The influence of polypropylene(PP) fiber was also investigated.Different PP fiber dosages were used to compare both the micro and macro properties.Results show that the melting fibers can be absorbed by the surrounding pores.The total porosity does not show big change due to the melting of the PP fibers.And the connectivity of the pore will be greatly influenced by the melting of the PP fibers.
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.
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.
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.
