Effects of Manufactured Sand and Steam-Curing Temperature on the Compressive Strength of Recycled Concrete with Different Water/Binder Ratios.

New building materials (manufactured sand and recycled coarse aggregates) can conserve raw materials and protect the environment. Prefabricated members can shorten the construction time of a structure. To use manufactured sand and recycled coarse aggregate in the preparation of precast member concrete, an economical and practical steam-curing scheme must be developed such that the compressive strength of precast manufactured sand recycled concrete (MRC) meets the requirements for hoisting. The effects of different steam-curing temperatures (standard curing, 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C) on the compressive strength of MRC with three water/binder ratios (W/B) (0.46, 0.42, and 0.38) were studied. In addition, the microstructure of MRC was examined using a scanning electron microscope. The equivalent age-compressive strength model was used to estimate the recycled concrete with manufactured sand. The results showed that the strength of MRC with a water-cement ratio of 0.46, 0.42, and 0.38 reached 33.9, 38.7, and 45.1 MPa, respectively, after 28 days of standard curing. The results also indicated that an increase in the steam-curing temperature had a positive effect on the early compressive strength of MRC and a negative effect on the 28 d compressive strength. This behavior was more obvious for MRC with a low W/B ratio. For MRC with a W/B of 0.46, 0.42, and 0.38, after steam-curing for 6 h, the compressive strength reached 32-65%, 36-70%, and 40-77% of the design strength, respectively. The optimum steam-curing temperatures for MRC with W/B of 0.46, 0.42, and 0.38 were 60 °C, 60 °C, and 50 °C. A decrease in W/B has a negative impact on the accuracy of MRC estimation using the equivalent age-compressive strength model. The maximum deviation of the prediction was within 10%, and the accuracy of the model was acceptable. This study provides a useful reference for the production of prefabricated MRC components in factories and subsequent construction.

How to establishing an indicators framework for evaluating the performances in primary TB control institutions under the new TB control model? Based on a Delphi study conducted in Guangxi, China.

BACKGROUND: In China, the new TB control model of trinity form had been implemented in all parts, and the comprehensively evaluation to the performances in primary TB control institutions were closely related to the working capacity and quality of TB service, but there was still no an unified evaluation indicators framework in practice and few relevant studies. The purpose of this study was to establish an indicators framework for comprehensively evaluating the performances in primary TB control institutions under the new TB control model of trinity form in Guangxi, China. METHODS: The Delphi method was used to establish an indicators framework for comprehensively evaluating the performances in primary TB control institutions under the new TB control model of trinity form, and the analytic hierarchy process(AHP) was used to determine the weights of all levels of indicators, from September 2021 to December 2021 in Guangxi, China. RESULTS: A total of 14 experts who had at least 10 years working experience and engaged in TB prevention and control and public health management from health committee, CDC, TB designated hospitals and university of Guangxi were consulted in two rounds. The average age of the experts were (43.3 ± 7.549) years old, and the effective recovery rate of the questionnaire was 100.0%. The average value of authority coefficient of experts (Cr) in the two rounds of consultation was above 0.800. The Kendall's harmony coefficient (W) of experts' opinions on the first-level indicators, the second-level indicators and the third-level indicators were 0.786, 0.201 and 0.169, respectively, which were statistically significant (P < 0.05). Finally, an indicators framework was established, which included 2 first-level indicators, 10 second-level indicators and 37 third-level indicators. The results of analytic hierarchy process (AHP) showed that the consistency test of all levels of indicators were CI < 0.10, which indicating that the weight of each indicator was acceptable. CONCLUSION: The indicators framework established in this study was in line with the reality, had reasonable weights, and could provide a scientific evaluation tool for comprehensively evaluating the performances in primary TB control institutions under the new TB control model of trinity form in Guangxi, China.

Comprehensive Evaluation of the Sustainability of Waste Concrete towards Structural Concrete Application in Freeze-Thaw Environment.

To promote the in-situ and structural application of waste concrete in cold regions, the sustainable application potential of waste concrete in a freeze-thaw (F-T) environment was comprehensively evaluated from three aspects of performance, environmental load, and economic benefit. The recycled aggregate concrete (RAC) was produced by recycled coarse aggregate (RCA), which was obtained from the crushing of natural aggregate concrete (NAC) after every F-T 150 cycles until F-T failure. The effects of F-T damage of parent concrete on the physical properties of RCA and mechanical and frost resistance of RAC under 35% flexural stress were studied. Besides, the sustainability of NAC and RAC was compared and analyzed by emergy theory. The results suggested that the physical properties of RCA deteriorated gradually with the accumulation of F-T damage to parent concrete. The RCA obtained from parent concrete that suffered F-T damage could be used as coarse aggregate for structural concrete when F-T damage is smaller than 0.367. The F-T damage of parent concrete had an adverse effect on the mechanical properties and frost resistance of RAC. The frost resistance of RAC obtained from parent concrete with larger F-T damage was worse. The RAC prepared from parent concrete without F-T failure can serve 50 years in cold regions, while that with F-T failure can only serve 30 years. The F-T damage microelements were dispersed in the adhesive mortar of RCA and transferred to RAC, resulting in the reduction of the mechanical properties and frost resistance of RAC. Emergy analysis showed that the reuse of waste concrete after F-T failure required higher economic input, higher environment load, lower output efficiency, and sustainability. The performance, environmental load and economic benefit of RAC prepared by using waste concrete after F-T failure were inferior to that of waste concrete without F-T failure. Waste concrete after F-T failure is not recommended to be used as coarse aggregate for structural concrete.

Healthcare Professionals' Views of the Integrated County Healthcare Consortium in Zhejiang, China.

Introduction: The integrated county healthcare consortium (ICHC) is becoming an important measure to improve the capacity of primary-level medical services and to achieve grading diagnosis and treatment system in China. However, it is not clear whether health professionals are satisfied with this reform and what are the problems with it. This study aimed to understand the satisfaction of healthcare professionals to the ICHC in Zhejiang Province, China, and analyze the problems and improvement measures of the ICHC. Methods: A cross-sectional study was carried out in the 11 pilot counties (cities and districts) implementing the construction of the ICHC in Zhejiang in November 2019. Healthcare professionals from the leading county-level hospital, three township health centers (THCs) or community health centers (CHCs) in each ICHC were invited to participate in this survey. Results: A total of 3531 healthcare professionals were included, 85.92% of the participants agreed that the integration of the Centers for Disease Control and Prevention (CDC) and other professional public health institutions into the construction of ICHC could actively promote basic public health work. The most severe problem was the lack of financial guarantee fund input (severity score: 2.92 ± 1.76). The most crucial measure to promote the construction of the ICHC was to increase government financial input and improve the security mechanism (importance score: 4.81 ± 0.47). The satisfaction of the healthcare professionals to the ICHC was 89.41%. The satisfaction of healthcare professionals from county-level hospitals was 2.37 (95% CI: 1.760-3.238) times higher than that of healthcare professionals from the township health centers (THCs) or community health centers (CHCs). The satisfaction of health professionals with a college degree or below was 3.215 (95% CI: 1.413-6.786) times higher than that of health professionals with a master's degree or above. Conclusions: Zhejiang Province has taken adequate measures to promote the construction of the ICHC. However, there are still some problems. Appropriate and effective policies should be implemented to enhance policy coordination and promote competition among ICHCs, as well as to strengthen medical service quality management and improve performance appraisal scheme.

Degradation of Tetracycline on SiO2-TiO2-C Aerogel Photocatalysts under Visible Light.

SiO2-TiO2-C aerogel photocatalysts with different carbon loadings were synthesized by using sol-gel chemistry. The anatase crystal and nonmetal carbon dopant were introduced during the sol preparation and formed by hydrothermal treatment, which can simultaneously enhance the adsorption ability and visible light photo-activity. A high surface area (759 g cm-3) SiO2-TiO2-C aerogel composite can remove up to 80% tetracycline hydrochloride within 180 min under visible light. The characterization of the gel structures shows that the homogeneous dispersion of O, Si, Ti and C in the skeleton, indicating that hydrothermal synthesis could provide a very feasible way for the preparation of composite materials. n(C):n(Ti) molar ratio of 3.5 gives the best catalytic performance of the hybrid aerogel, and the cyclic test still confirms over 60% degradation activity after seven use cycles. All catalysis reaction followed the pseudo-first-order rate reaction with high correlation coefficient. The electrons and holes in the compound could be effectively restrained with doping proper amount of C, and ESR results indicate that the oxidation process was dominated by the hydroxyl radical (•OH) and superoxide radical (•O2-) generated in the system.

Ambient-Dried Silica Aerogel Powders Derived from Coal Gangue by Using One-Pot Method.

In this paper, we report a new and convenient method for the synthesis of insulating aerogel by recycling solid waste coal gangue, which can reduce the industrial production cost of silica aerogels and realize high value-added utilization of solid waste. Sodium silicate was prepared from a cheap industrial waste coal gangue as the precursor for silica aerogels, which was used for silica wet gel preparation by a one pot method; this method of solvent exchange/surface modification was carried out quickly by mechanical stirring process, and the wet gels derived from coal gangue were dried under ambient pressure condition. A high surface area (~748 m2/g) nanostructured aerogel with a 3D open porous microstructure was synthesized, which exhibits a low density (~0.18 g/cm3) and a superior thermal insulation performance (~0.033 W·m-1·K-1). More significantly, the synthetic yield of silica aerogel powder by recycling coal gangue can reach 92%.

Resistance to Sulfuric Acid Corrosion of Geopolymer Concrete Based on Different Binding Materials and Alkali Concentrations.

Geopolymer binder is expected to be an optimum alternative to Portland cement due to its excellent engineering properties of high strength, acid corrosion resistance, low permeability, good chemical resistance, and excellent fire resistance. To study the sulfuric acid corrosion resistance of geopolymer concrete (GPC) with different binding materials and concentrations of sodium hydroxide solution (NaOH), metakaolin, high-calcium fly ash, and low-calcium fly ash were chosen as binding materials of GPC for the geopolymerization process. A mixture of sodium silicate solution (Na2SiO3) and NaOH solution with different concentrations (8 M and 12 M) was selected as the alkaline activator with a ratio (Na2SiO3/NaOH) of 1.5. GPC specimens were immersed in the sulfuric acid solution with the pH value of 1 for 6 days and then naturally dried for 1 day until 98 days. The macroscopic properties of GPC were characterized by visual appearance, compressive strength, mass loss, and neutralization depth. The materials were characterized by SEM, XRD, and FTIR. The results indicated that at the immersion time of 28 d, the compressive strength of two types of fly ash-based GPC increased to some extent due to the presence of gypsum, but this phenomenon was not observed in metakaolin-based GPC. After 98 d of immersion, the residual strength of fly ash based GPC was still higher, which reached more than 25 MPa, while the metakaolin-based GPC failed. Furthermore, due to the rigid 3D networks of aluminosilicate in fly ash-based GPC, the mass of all GPC decreased slightly during the immersion period, and then tended to be stable in the later period. On the contrary, in metakaolin-based GPC, the incomplete geopolymerization led to the compressive strength being too low to meet the application of practical engineering. In addition, the compressive strength of GPC activated by 12 M NaOH was higher than the GPC activated by 8 M NaOH, which is owing to the formation of gel depended on the concentration of alkali OH ion, low NaOH concentration weakened chemical reaction, and reduced compressive strength. Additionally, according to the testing results of neutralization depth, the neutralization depth of high-calcium fly ash-based GPC activated by 12 M NaOH suffered acid attack for 98 d was only 6.9 mm, which is the minimum value. Therefore, the best performance was observed in GPC prepared with high-calcium fly ash and 12 M NaOH solution, which is attributed to gypsum crystals that block the pores of the specimen and improve the microstructure of GPC, inhibiting further corrosion of sulfuric acid.

Snow Melting Performance of Graphene Composite Conductive Concrete in Severe Cold Environment.

The use of conductive concrete is an effective way to address snow and ice accretion on roads in cold regions because of its energy saving and high efficiency without interruption of traffic. Composite conductive concrete was prepared using graphene, carbon fiber, and steel fiber, and the optimum dosage of graphene was explored with resistivity as the criterion. Subsequently, under the conditions of an initial temperature of -15 °C and a wind speed of 20 km/h, the extremely severe snow event environment in cold regions was simulated. The effects of electrode spacing and electric voltage on snow melting performance of conductive concrete slab were explored. Results showed that graphene can significantly improve the conductivity of conductive concrete; the optimal content of graphene was 0.4% of cement mass in terms of resistivity. The snow-melting power of conductive concrete slab decreased with increase in electrode spacing and increased with increase in on-voltage. For an optimal input voltage of 156 V and an optimal electrode spacing of 10 cm, the time required to melt a 24 h snow thickness (21 cm), accumulated during a simulated severe snow event, was only 2 h, which provides an empirical basis for the application of graphene composite conductive concrete to pavement snow melting in cold regions.

Time-Dependent Shrinkage Model for Recycled Fine Aggregate Thermal Insulation Concrete.

In this study, the shrinkage performance of recycled aggregate thermal insulation concrete (RATIC) with added glazed hollow beads (GHB) was investigated and a time-dependent shrinkage model was proposed. Two types of recycled fine aggregate (RFA) were used to replace natural fine aggregate in RATIC: RFA from waste concrete (RFA1) and waste clay brick (RFA2). Besides, the mechanical properties and thermal insulation performance of RATIC were also studied. Results showed that the pozzolanic reaction caused by RFA2 effectively improved the mechanical properties of RATIC; 75% was the optimal replacement ratio of RATIC prepared by RFA2. Added RFA decreased the thermal conductivity of thermal insulation concrete (TIC). The total shrinkage strain of RATIC increased with the increase of the replacement ratio of RFA. The 150d total shrinkage of RATIC prepared by RFA1 was 1.46 times that of TIC and the 150d total shrinkage of RATIC prepared by RFA2 was 1.23 times. The addition of GHBs led to the increase of early total shrinkage strain of concrete. Under the combined action of the higher elastic modulus of RFA2 and the pozzolanic components contained in RFA2, the total shrinkage strain of RATIC prepared by RFA2 with the same replacement ratio was smaller than that of RATIC prepared by RFA1. For example, the final total shrinkage strain of RATIC prepared by RFA2 at 100% replacement ratio was about 18.6% less than that of RATIC prepared by RFA1. A time-dependent shrinkage model considering the influence of the elastic modulus of RFA and the addition of GHB on the total shrinkage of RATIC was proposed and validated by the experimental results.

Effect of Early Curing Temperature on the Tunnel Fire Resistance of Self-Compacting Concrete Coated with Aerogel Cement Paste.

In this paper, the effect of early curing temperature on the tunnel fire resistance of self-compacting concrete (SCC) coated with aerogel cement paste (ACP) was studied. The physical properties in terms of the compressive strength, flexural strength, and thermal conductivity of ACP were tested under different early curing temperatures. The tunnel fire resistance of ACP and SCC coated with ACP was determined, and the microstructure of ACP and SCC after a tunnel fire were characterized by scanning electron microscopy. The results show that the strength of ACP initially increased (by 10-40 °C) and then later decreased (by 40-60 °C) with the increase in early curing temperature. ACP under 40 °C early curing exhibited the minimum number of cracks and mass loss after the tunnel fire. Too high or too low early curing temperature reduced the thermal conductivity of ACP but accelerated the formation and expansion of microcracks during the tunnel fire. The residual compressive strength of SCC coated with ACP under 40 °C early curing after the tunnel fire was the highest, demonstrating the best tunnel fire resistance.

Effective Analysis of Inpatient Satisfaction: The Random Forest Algorithm.

PURPOSE: To identify the factors influencing inpatient satisfaction by fitting the optimal discriminant model. PATIENTS AND METHODS: A cross-sectional survey of inpatient satisfaction was conducted with 3888 patients in 16 large public hospitals in Zhejiang Province. Independent variables were screened by single-factor analysis, and the importance of all variables was comprehensively evaluated. The relationship between patients' overall satisfaction and influencing factors was established, the relative risk was evaluated by marginal benefit, and the optimal model was fitted using the receiver operating characteristic curve. RESULTS: Patients' overall satisfaction was 79.73%. The five most influential factors on inpatient satisfaction, in this order, were: patients' right to know, timely nursing response, satisfaction with medical staff service, integrity of medical staff, and accuracy of diagnosis. The prediction accuracy of the random forest model was higher than that of the multiple logistic regression and naive Bayesian models. CONCLUSION: Inpatient satisfaction is related to healthcare quality, diagnosis, and treatment process. Rapid identification and active improvement of the factors affecting patient satisfaction can reduce public hospital operating costs and improve patient experiences and the efficiency of health resource allocation. Public hospitals should strengthen the exchange of medical information between doctors and patients, shorten waiting time, and improve the level of medical technology, service attitude, and transparency of information disclosure.