Water and alkali salts in the hydrating and hardened green cement-based materials: Hydration process, moisture content and transport

Reducing CO2 emissions in the production of cementitious binder is the most effective way to decrease the environmental impact of the construction industry, so a large amount of supplementary cementitious materials (SCMs) has been used in the green concrete. Both the SCMs and alkali salts in binders influence the hydration process and the structure in hardened cement-based materials. Experiments were performed to investigate the effects of them on the hydration reaction in fresh paste, the pore structure and moisture transport in hardened pastes because these properties determine the durability of concrete during its service life. The composition and morphology of hydration products were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrical conductivity of hydrating paste was real-time monitored by a newly invented device to detect the structure change during hydration. An easy procedure was developed to determine the water distribution in paste. Electrical conductivity of the pore solution was calculated with the volume of evaporable water and chemical composition of the binders. The moisture transport in hardened pastes was measured by the new procedure and setup. The chloride migration in paste was measured by the rapid chloride migration method (RCM). The mercury intrusion porosimeter (MIP) was used to test the pore size distribution.The results show that the precipitation of C-S-H is a nonclassical nucleation process. The initial structure building starts with the nucleation of primary globules. It grows by particle attachment and potassium salts influence not only the size of primary globule floc but also the packing orientation. A large increase in the heat release after the induction period may be due to the growing attachment rate of flocs instead of the dissolution of etch pits. The duration of induction period correlates to the size of primary floc. Al ion will change the size of floc to prolong the low-rate period, but alkali salts can mitigate the effect from it. A hypothesis regarding the dissolution of C3S and the nucleation of C-S-H within the near-surface region narrows the gap in the current theories. The hydration reactivity of binders can be indicated by the evolution of electrical conductivity, formation factor and its growth rate in the hydrating pastes. The electrical properties of pastes are related to the setting, pore connectivity and volume of evaporable water. An increase in the water-binder ratio (w/b) lowers the electrical conductivity of pore solution due to the dilution of alkali concentration. However, it increases the connectivity of pore solution and reduces the formation factor of pastes. The blending of slag decreases the conductivity of pore solution and increases the formation factor. Fly ash induces a higher connectivity of pores at the early age owing to its lower reactivity compared to clinker, but the connectivity of pores in the fly ash paste is much lower than the plain pastes after long-term hydration (1 year). Limestone increases the connectivity of pore solution at the early age, but its filling effect becomes effective after a certain hydration age. The relationship between volume of evaporable water and formation factor can be well demonstrated by the extended percolation theory, and this provides theoretical basis for an in-situ detecting of evaporable water in pastes by electrical conductivity. The procedure developed in this study can measure the moisture transport properties in both steady-state and non-steady state transport condition. The moisture transport coefficient in the hardened cement paste is RH dependent. The differences in RH dependency are due to discrepancies in the critical RH for percolation of liquid in pastes. The blended pastes have a more complex pore structure and lower concentration of alkali ions in pore solution, so the critical RH of the blended pastes is higher than that of OPC. The blending of fly ash and slag evidently reduce the moisture and chloride diffusivity in pastes due to its reduction effect in formation factor and pore connectivity. Formation factor is the major determinant for the moisture transport at a high RH interval, but porosity of small pores (middle capillary and mesopores) becomes the major determinant at a low RH. This study provides the meaningful data for the prediction and simulation of moisture and ion (e.g. chloride) transport in concrete during its service life with a continuous long-term hydration

Analysis on the path of labor identity regression among higher vocational college students in the context of professional attainment education

In order to improve the practical needs of professional attainment education, it is of great significance for higher vocational colleges to train the qualified practical talents who respect labor, care for the grass-roots and have a sense of responsibility in the process of strengthening their labor identity education. Faced with the lack of student labor identity in higher vocational colleges, combined with the Marxist Theory of labor and human rights, this paper proposes the path to realize the regression of labor identity in higher vocational college students, so as to provide reference for further promoting and innovating professional attainment education in higher vocational colleges

RTeQTL: Real-Time Online Engine for Expression Quantitative Trait Loci Analyses

Our database tool, called Real-Time Engine for Expression Quantitative Trait Loci Analyses (RTeQTL), can efficiently provide eQTL association results that are not available in existing eQTL databases browsers. These functions include (i) single SNP (single-nucleotide polymorphism) and (ii) two-SNP conditional eQTL effects on gene expression regardless of the magnitude of P-values. The database is based on lymphoblastoid cell lines from >900 samples with global gene expression and genome-wide genotyped and imputed SNP data. The detailed result for any pairs of gene and SNPs can be efficiently computed and browsed online, as well as downloaded in batch mode. This is the only tool that can assess the independent effect of a disease- or trait-associated SNP on gene expression conditioning on other SNPs of interest, such as the top eQTL of the same gene. It is also useful to identify eQTLs for candidate genes, which are often missed in existing eQTL browsers, which only store results with genome-wide significant P-value. Additional analyses stratifying by gender can also be easily achieved by this tool. Database URL: http://eqtl.rc.fas.harvard.edu

System and method of analyzing vibrations and identifying failure signatures in the vibrations

An apparatus, computer program product and method of analyzing structures. Intrinsic Mode Functions (IMFs) are extracted from the data and the most energetic IMF is selected. A spline is fit to the envelope for the selected IMF. The spline derivative is determined. A stability spectrum is developed by separating the positive and negative results into two different spectra representing stable (positive) and unstable (negative) damping factors. The stability spectrum and the non-linearity indicator are applied to the data to isolate unstable vibrations

Structural optimum design of bistable cylindrical shell for broadband energy harvesting application

AbstractThe shallow cylindrical structure is suitable to develop broadband vibration energy harvesters due to the property of the inherent mechanical bistability. In this letter, the optimum design of the bistable cylindrical shell for broadband energy harvesting application is investigated from the structural point of view. The output power is evaluated by the concept of the harvestable power, which balances the frequency of snap through and the referred output energy associated with each snap through. The non-dimensional harvestable power is analytically expressed as the function of the non-dimensional curvature parameter and one constructed parameter. The universal dependence of the optimal curvature parameter and the associated optimal harvestable power on the constructed parameter is derived, which can be well approximated by the linear relation in double logarithmic coordinate

Long-term performance of reinforced concrete under a de-icing road environment

In the middle of 1990, over 30 different mixes of concretes with eight different binders and water-binder ratios of 0.3 to 0.75 were exposed to a highway environment with a heavy de-icing salt spread for the examination of long-term performance, including chloride penetration, reinforcement corrosion and frost attack. This paper presents the results from this long-term study regarding chloride penetration and reinforcement corrosion. The results show that the chloride penetration in concretes under a de-icing salt road environment is much weaker than that in concretes under marine splash environment in Sweden. The estimated critical chloride content for the corrosion initiation is about 0.3 % by mass of binder for rebars with uncracked concrete cover. Considering the chloride redistribution in the surface zone, ClinConc model has been modified so that it can present a better description of the chloride profiles in the concretes at such an exposure site

A Unified Framework for Mutual Improvement of SLAM and Semantic Segmentation

This paper presents a novel framework for simultaneously implementing localization and segmentation, which are two of the most important vision-based tasks for robotics. While the goals and techniques used for them were considered to be different previously, we show that by making use of the intermediate results of the two modules, their performance can be enhanced at the same time. Our framework is able to handle both the instantaneous motion and long-term changes of instances in localization with the help of the segmentation result, which also benefits from the refined 3D pose information. We conduct experiments on various datasets, and prove that our framework works effectively on improving the precision and robustness of the two tasks and outperforms existing localization and segmentation algorithms.Comment: 7 pages, 5 figures.This work has been accepted by ICRA 2019. The demo video can be found at https://youtu.be/Bkt53dAehj