Influence of the Original Concrete Strength and Initial Moisture Condition on the Properties Improvement of Recycled Coarse Aggregate via Accelerated Carbonation Reactions.

The physical and mechanical properties of recycled coarse aggregate (RCA) are worse than those of natural coarse aggregate (NCA), and the overall performance of recycled concrete prepared from RCA is worse than that of natural aggregate concrete. Treatment of RCA by CO2-accelerated carbonation effectively improves the macroscopic properties of RCA. The degree of influence of raw material factors, i.e., the original concrete strength (OCS) and initial moisture content (IMC) of RCA, on the carbonation of RCAs is very complex. Herein, an accelerated carbonation experiment for RCA with different material factors as variables was carried out to explore the influence of the abovementioned factors on the physical properties of carbonated recycled coarse aggregate (CRCA). By analyzing the microstructure of the RCA with the best modification effect before and after carbonation, the carbonation modification mechanism of the RCA was revealed. The physical performance indexes, including the apparent density, water absorption and carbonation rate, of the dried RCA with an OCS of C40 and C50 were significantly improved. The research results can provide basic data and theoretical support for promoting the popularization and application of RCA and recycled concrete in practical engineering.

Synergistic Effects of Environmental Relative Humidity and Initial Water Content of Recycled Concrete Aggregate on the Improvement in Properties via Carbonation Reactions.

Moisture is the basis of CO2 transport and carbonation reactions in the internal pores of cement-based materials. Too much or too little moisture influences the effect of the carbonation modification of CO2 on recycled concrete aggregate (RCA). During the carbonation reaction process of RCA, moisture is mainly derived from the environmental relative humidity (RH) and the initial water content (IWC) of the RCA itself. According to the available literature, most of the studies on the effect of moisture on the carbonation modification of RCA considered either RH or IWC. Further investigations of the synergistic effects of RH and IWC on the improvement in the properties of carbonated recycled concrete aggregate (CRCA) are needed. In this study, accelerated carbonation experiments were conducted for RCA samples with different IWCs under different environmental RHs. The results showed that the best moisture conditions for CRCA property improvement were confirmed as RH = 70% for the dry-state IWC and RH = 50% for the saturated-state IWC. When the RCAs were carbonized under the conditions of high RH with low IWC and low RH with high IWC, CO2 had good abilities to permeate and diffuse, with the improvement in CRCA properties achieving excellent levels of performance.

Influencing factors of health resource allocation and utilisation before and after COVID-19 based on RIF-I-OLS decomposition method: a longitudinal retrospective study in Guangdong Province, China.

OBJECTIVES: To explore factors that influenced the health resource allocation and utilisation before and after COVID-19, and subsequently offer sensible recommendations for advancing the scientific distribution of health resources. DESIGN: A longitudinal survey using 2017-2020 data, which were collected for analysis. SETTING: The study was conducted based on data collected from the Health Commission of Guangdong Province's website. OUTCOME MEASURES: Eight health resource indicators and four health resource utilisation indicators were included in the factor analysis. Four indices were calculated to measure the inequality in health resource allocation and utilisation. We analysed factors for the inequality indices using the recentred influence function index ordinary least squares decomposition method. RESULTS: The health resource inequality indices peaked in 2020 (Gini coefficient (Gini): 0.578, Absolute Gini coefficient (AGini): 1.136, Concentration Index (CI): 0.417, Absolute CI (ACI): 0.821), whereas the health resource utilisation inequality indices declined year by year, thus reaching their lowest point in that same year. The majority of inequality indices in the annual change of health resource allocation were at their lowest in 2020 (Gini: -1.672, AGini: 0.046, CI: -0.189, ACI: 0.005), while the use of health resources declined dramatically, showing a negative growth trend. The inequality indices of health resource allocation and utilisation in 2020 were affected by a number of variables, including the COVID-19 level, (p<0.05), while the proportion of expenditure on public health was the most significant one. CONCLUSIONS: Guangdong Province's health resource allocation and utilisation were still concentrated in economically developed regions from 2017 to 2020. The health resource allocation inequality indices increased, especially under COVID-19, but the health resource utilisation inequality indices decreased. Measures should be taken to adjust the health resource allocation scientifically, which will fulfil the changing needs and the use of resources more efficiently. One effective measure is reasonably increasing the proportion of expenditure on public health.