The Feasibility of Waterproof Microcapsule System for Bacteria-Based Self-Healing Cementitious Material

In this study, a waterproof material was used to fabricate microcapsule by interfacial curing reaction to encapsulate an alkaliphilic spore-forming bacterium. The technical feasibility of encapsulated spores and the influence of three kinds of curing agent on the calcium precipitation activity (CPA) of the bacterium were studied. Furthermore, micromorphology of microcapsules was observed by Scanning Electron Microscopy (SEM). Afterwards, the thermal stability and thermolysis temperature were determined by TGA thermal analyzer. Moreover, the CPA of broken/ unbroken microcapsules was evaluated. In addition, water resistance was evaluated by adding microcapsules in the water for 1, 3, 7, 14, 28, and 56 days. Finally, light microscope was applied to trace the self-healing behavior of encapsulated mineralization bacterium in cement paste specimens. The results showed that compared with unbroken microcapsules, higher CPA was achieved by breaking the microcapsule to release the bacterium, suggesting good protection for the encapsulated spores. Three curing agents showed nearly similar influence on the spores, while KH792 performed relatively better, and thus was used to fabricate microcapsule with the core/shell weight ratio being 1:1. Our results also indicated that ER microcapsules could keep unbroken in the water for 2 months. Compared with the specimens without embedded bacterium, the healed crack area of specimens embedded with bacterial microcapsules was monitored, suggesting effective self-healing of concrete crack can be achieved by introducing encapsulated mineralization microorganisms into concrete structures. Therefore, we put forward that this waterproof epoxy resin microcapsules could be potential for the application of self-healing concrete

Dynamical Properties of Environmental High-Performance Composites with Calcined Clay

Concrete structures may be exposed to dynamic loadings within short periods such as earthquakes and vehicles load, resulting in substantial damage to human life and property because of the collapse of concrete structures. The research achievements on dynamic properties of high-performance composites with LC3 (HPC-LC3) are limited, although dynamic loadings are commonly encountered in infrastructure. The study aims to develop a new-green concrete product (HPC-LC3) with high dynamical properties and promote its mass use in a vibration service environment by investigating dynamical properties of HPC-LC3. Dynamical properties of structure can be promoted at material level by means of enhancing the inherent ability of cement-matrix materials to passively absorb the vibrational energy. Dynamic properties of traditional HPC may be improved by incorporated LC3 because of excellent mechanical properties. The fiber pull-out, thermogravimetric analysis (TGA), (nuclear magnetic resonance) NMR, and microstructure test were used to reveal the enhanced mechanism of dynamic properties in the HPC with LC3 (HPC-LC3), and the economic efficiency of HPC is also evaluated to promote its mass application. The results indicate that the dynamic properties of HPC-LC3 increased by 47% in damping capacity, 102% in storage modulus, 16% in energy dissipation, in comparison with the reference (HPC-OPC). Meanwhile, compared with the reference, the compressive and flexural strengths of LC3-50 increased by 14% and 27%. TGA and NMR results indicate that LC3-50 shows better hydration characteristics, longer alumina-silicate chain length (from 3.9 to 8) than HPC-OPC. The proposed composites reduced embodied energy, embedded CO2 emissions, and costs of HPC by up to 33%, 45%, and 7%, respectively. Thus, the green product (HPC-LC3) with 30%–40% calcined clay, high dynamic properties and more sustainable, will be recommended to mass use in a vibration service environment

Measuring Coverage in MNCH:A Validation Study Linking Population Survey Derived Coverage to Maternal, Newborn, and Child Health Care Records in Rural China

Accurate data on coverage of key maternal, newborn, and child health (MNCH) interventions are crucial for monitoring progress toward the Millennium Development Goals 4 and 5. Coverage estimates are primarily obtained from routine population surveys through self-reporting, the validity of which is not well understood. We aimed to examine the validity of the coverage of selected MNCH interventions in Gongcheng County, China.We conducted a validation study by comparing women's self-reported coverage of MNCH interventions relating to antenatal and postnatal care, mode of delivery, and child vaccinations in a community survey with their paper- and electronic-based health care records, treating the health care records as the reference standard. Of 936 women recruited, 914 (97.6%) completed the survey. Results show that self-reported coverage of these interventions had moderate to high sensitivity (0.57 [95% confidence interval (CI): 0.50-0.63] to 0.99 [95% CI: 0.98-1.00]) and low to high specificity (0 to 0.83 [95% CI: 0.80-0.86]). Despite varying overall validity, with the area under the receiver operating characteristic curve (AUC) ranging between 0.49 [95% CI: 0.39-0.57] and 0.90 [95% CI: 0.88-0.92], bias in the coverage estimates at the population level was small to moderate, with the test to actual positive (TAP) ratio ranging between 0.8 and 1.5 for 24 of the 28 indicators examined. Our ability to accurately estimate validity was affected by several caveats associated with the reference standard. Caution should be exercised when generalizing the results to other settings.The overall validity of self-reported coverage was moderate across selected MNCH indicators. However, at the population level, self-reported coverage appears to have small to moderate degree of bias. Accuracy of the coverage was particularly high for indicators with high recorded coverage or low recorded coverage but high specificity. The study provides insights into the accuracy of self-reports based on a population survey in low- and middle-income countries. Similar studies applying an improved reference standard are warranted in the future

Effect of Combined Fermentation of Leuconostoc and Lactiplantibacillus on the Quality of Low-salt Pickled Radish

In order to study the effects of different lactic acid bacteria on the quality of pickled radish, pickled radish was prepared with Leuconostoc mesenteroides AP7, Lactiplantibacillus pentosus LP10 and AP7-LP10 combination. The changes in physicochemical indicators, color differences, texture properties and sensory indicators during the fermentation process were analyzed. The results showed that the decrease rate of pH and reducing sugar content and the increase rate of total acid and lactic acid in the inoculated group were better than those in the natural fermentation group (P<0.05). For the inoculated group, the nitrite content was low, and no nitrite peak appeared. The pectinase activity remained at a low level. For the AP7-LP10 and AP7 groups, the L* was higher than that of the other two groups (P<0.05), and the browning index and polyphenol oxidase activity remained at a low level. After 7 days of fermentation, the hardness of AP7-LP10 group (70.92±3.94 N) was higher than that of other groups (P<0.05). The sensory score of AP7-LP10 was the highest (92±2.11). In summary, the pickled radish inoculated with lactic acid bacteria is fast to mature and safe. The combination of AP7-LP10 can improve the quality of pickled radish

Influence mechanisms of CaCO3/NaAlO2 ratios in carbonaluminate cementitious materials

This study investigated the carbonaluminate cementitious materials (i.e., sodium aluminate (NaAlO2)-activated limestone pastes) with gradient calcite (CaCO3)/NaAlO2 molar ratios ranging from 1:1 to 6:1 (samples M1 to M6). NaAlO2 dosage affected the reaction process, hydration product, and cementitious property of the formed pastes. The thermonatrite (Na2CO3·H2O) and AH3 phase as hydration products exist in all the samples. Microcrystalline AH3 phase (crystallite size is near 22 nm) held a superior cementitious property, which was evidenced by diffraction spots scattered on concentric rings in transmission electron microscopy (TEM) results. Other hydrates varied with the CaCO3/NaAlO2 ratio. In case of lower CaCO3/NaAlO2 ratio (i.e., M1), NaAlO2 was incompletely consumed. The residual NaAlO2 promoted the formation of cubic-shaped katoite (3CaO·Al2O3·6H2O). Such hydrate barely contributed to the cementitious property of the formed matrix. When the CaCO3/NaAlO2 ratio reached 1.5:1 (e.g., M1.5-M6), NaAlO2 was entirely consumed, and monocarboaluminate (Mc, 3CaO·Al2O3·CaCO3·11H2O) instead of katoite was preferentially generated. The amounts of total hydrates decreased with the increasing CaCO3/NaAlO2 ratio, leading to the degraded properties of formed matrix. Thus, the 28-day compressive strength of M1.5 was the highest among these samples, reaching 35.55 MPa

Electrochemical Impedance Spectroscopy on the Hydration Behavior of the Mortar with Marine Sand

It is important to utilize marine sand as raw materials in civil engineering. The influence of the marine sand to the properties of cement and steel materials are concerned. In this paper, the electrochemical impedance spectroscopy (EIS) method is introduced to study the hydration behavior of the mortar with marine sand, in order to make an interpretation of the function of marine sand on the cement materials. The results of experiments show that the hydration of mortar with marine sand is a complex procedure and it holds both dielectric characteristic(low frequency in EIS) and electrolytic characteristic(high frequency in EIS). The releasing of Cl- is a continuous procedure and it is long term acceleration for hydration of mortar. The more concentration of Cl-, the more contents of hydration product Ca(OH)2 is produced from the surface of C-S-H gels. It will make the proportion C-S-H gels decreasing, whereas the proportion of Ca(OH)2 and ettringite increasing

Study on water sorptivity of the surface layer of concrete

This paper presents the results from a study of water sorptivity of concrete surface layer. The sorptivity is characterized by a surface sorptivity index as measured by Autoclam. In this study, different types of concrete were immersed in ultrapure water and NaCl solution prior to the sorptivity test. The influences of several factors on the value and evolution of concrete surface sorptivity index are discussed. It is found that: concrete surface sorptivity is a function of the pore structure, higher porosity and lower tortuosity lead to higher surface sorptivity; as cured in moist condition for 1 month, the surface sorptivity is an increasing function of w/c in plain cement concretes, and an increasing function of fly ash replacement if w/b is kept constant; surface sorptivity increases as immersed in ultrapure water in the first month of immersion due to leaching, and decreases thereafter as the continuous hydration of cementitious materials makes the pore structure finer and finer; the immersion in NaCl solution limits the effect of leaching because of the formation of calcium oxychloride compounds, and results in lower long-term surface sorptivity index as compared with the ultrapure water immersion, due to the formation of Friedel's salt which reduces the pore volume and blocks the pore network

Gradient Learning under Tilted Empirical Risk Minimization

Gradient Learning (GL), aiming to estimate the gradient of target function, has attracted much attention in variable selection problems due to its mild structure requirements and wide applicability. Despite rapid progress, the majority of the existing GL works are based on the empirical risk minimization (ERM) principle, which may face the degraded performance under complex data environment, e.g., non-Gaussian noise. To alleviate this sensitiveness, we propose a new GL model with the help of the tilted ERM criterion, and establish its theoretical support from the function approximation viewpoint. Specifically, the operator approximation technique plays the crucial role in our analysis. To solve the proposed learning objective, a gradient descent method is proposed, and the convergence analysis is provided. Finally, simulated experimental results validate the effectiveness of our approach when the input variables are correlated