Tracing the Trends of General Construction and Demolition Waste Research Using LDA Modeling Combined With Topic Intensity.

The study of construction and demolition waste (CDW) has attracted more and more attentions with the increasing CDW pollution caused by the large-scale infrastructure construction. This study used the Latent Dirichlet Allocation (LDA) combined with topic intensity to discover hot topics and development trends in the study area of CDW. First, the LDA was used for topic modeling to extract the existing topics from textual data. Second, the topic intensity was calculated for the extracted topics and the numerical values of the topic intensity represented the popularity of the topics. In this study, 4 topics were extracted from 1,849 relevant articles through the LDA modeling and topic intensity calculation. The results showed that the topic of "CDW management" had an upward trend. Topics such as "recycled aggregate," "environmental impact," and "study of CDW on soil" all showed a downward trend. The methods of this study can dig into the topics of CDW study and help scholars to engage in this field for better understanding the prevalence and evolution trends of these topics.

Deep insight on mechanism and contribution of As(V) removal by thermal modification waste concrete powder.

Expanding the utilization strategy of waste concrete powder (WCP) is conducive to minimizing the environmental burden caused by construction & demolition wastes (C&DW). In this study, WCP prepared in the laboratory was thermally treated and used to remove As(V) from wastewater. Batch adsorption tests were implemented to explore the influence factors such as modification temperature (0-850 °C), pH (1.00-12.00), dosage (2-50 g/L), co-coexisting ions (SO42-, NO3-, Cl- and PO43-) and temperature (25-45 °C). Various methods including spectroscopic tests, Rietveld refinement and sequential extraction process were employed to examine the mechanisms and their contribution to As(V) removal. Results show that the As(V) removal capacity of WCP was slightly enhanced after treatment at 200 °C, the pseudo-second-order kinetics model and Langmuir model could describe the adsorption process well. The maximum uptake capacity for As(V) calculated by Langmuir model at 25, 35 and 45 °C were 31.89, 25.56 and 17.42 mg/g respectively, and the removal rate reached a maximum of 95.37% (C0 = 100 mg/L). Thermodynamically, the As(V) elimination was exothermic and spontaneous. The ettringite produced by rehydration of WCP proved to be essential for As(V) removal. Electrostatic attraction, precipitation, complexation and ion exchange were identified to be the main mechanisms of As(V) adsorption. This study confirmed the potential of WCP in removing As(V) from wastewater and provided a new insight into the removal mechanisms.

Sustainable stabilization/solidification of arsenic-containing soil by blast slag and cement blends.

Arsenic (As) is a naturally occurring trace element that may pose a threat to human health and the ecosystem, while effective remediation and sustainable reuse of As-containing soil is a challenge. This study investigated the geoenvironmental characteristics of a geogenic As-rich soil, and green binders (ground granulated blast slag (GGBS) and cement blends) were employed for the stabilization/solidification (S/S) of the soil under field-relevant conditions. Results indicate that the use of 10% binder could effectively immobilize As and chemical stabilization/physical encapsulation jointly determined the leaching characteristics of the S/S soils. The geogenic As could be effectively immobilized at the pH range of 5.5-6.5. The increasing use of GGBS enhanced the strength of the 28-d cured S/S soils because of long-term pozzolanic reaction, but also slightly improved the As leachability. Besides, the moisture content of the contaminated soils should be suitably adjusted to allow for desirable compaction of S/S soils, which resulted in high compressive strength and low of As leachability. Results show that soil moisture content of 20% was the most appropriate, which resulted in the highest strength and relatively lower As leaching. In summary, this study presents a sustainable S/S binder for recycling As-contaminated soil by using a combination of cement and GGBS.

Novel microcapsules for internal curing of high-performance cementitious system.

Conventional internal curing materials for high-performance cementitious system cannot easily have artificial modifications, such that the curing effect is difficult to control during the process. In this study, a novel microcapsule is proposed for controlled internal curing of cement-based materials. The microcapsules are synthesized by a double emulsion method to form a polymer shell-water core structure. The sensitivity of polymer shell to alkaline environments is used to trigger the release of core water. Thus, water release can be controlled by tailoring the shell thickness and microcapsules sizes by changing the polymer dosage and stirring rate during synthesis. The experimental results indicate that the novel microcapsules can effectively release water for internal curing of a cementitious matrix, which exhibits a high curing efficiency in terms of nearly autogenous shrinkage and increases the compressive strength. The novel microcapsules could be promising internal curing agents to enhance high-performance cement-based materials.

Innovative reuse of concrete slurry waste from ready-mixed concrete plants in construction products.

Concrete slurry waste (CSW) is generated from ready-mixed concrete plants during concrete production and is classified as a corrosive hazardous material. If it is disposed of at landfills, it would cause detrimental effects for our surrounding environment and ecosystems due to its high pH value as well as heavy metal contamination and accumulation. A new method in this study has been introduced to effectively reuse CSW in new construction products. In this method, the calcium-silicate rich CSW in the fresh state was considered as a cementitious paste as well as a CO2 capture medium. The experimental results showed that the pH values of the collected CSWs stored for 28 days ranged from 12.5 to 13.0 and a drastic decrease of pH value was detected after accelerated mineral carbonation. The theoretically calculated CO2 sequestration extent of CSWs was from 27.05% to 31.23%. The practical water to solid ratio in the fresh CSW varied from 0.76 to 1.12, which had a significant impact on the compressive strength of the mixture with CSWs. After subjecting to accelerated mineral carbonation, rapid initial strength development and lower drying shrinkage for the prepared concrete mixture were achieved.

Breastfeeding and the incidence of endometrial cancer: A meta-analysis.

Several epidemiological studies have investigated the association between breastfeeding and endometrial cancer (EC). However, the results of the studies are controversial. Thus, we conduct this meta-analysis to explore the association between breastfeeding and EC and to evaluate the possible does-response relationship between duration of breastfeeding and EC. PubMed, Web of Science, Chinese National Knowledge Infrastructure, China biology medical literature database, Wan fang databases and Database of Chinese Scientific and Technical Periodicals were searched for eligible observational studies up to 11 July 2015. Random effects model was used to calculate the pooled relative risks (RRs) and restricted cubic spline model was adopted for the does-response analysis.Fifteen articles with 623570 participants were identified. The RRs of these studies suggested that breastfeeding was associated with the reduced risk of EC (high versus low/no: RR = 0.74; 95% confidence interval (CI), 0.58-0.95). In subgroup analyses, a significant association of breastfeeding with EC risk was found in Asia (RR = 0.57, 95% CI 0.37-0.87), and an inverse association of breastfeeding with EC risk was found in cohort studies (RR = 0.62, 95% CI 0.41-0.94). The results were also significant after adjusted for hormone use (RR = 0.63, 95% CI 0.41-0.97) and body mass index (RR=0.65, 95% CI 0.44-0.96). A linear relationship was found of breastfeeding with EC (p for nonlinearity = 0.93), and it indicated that EC risk decreased by 1.2% for one month increment of breastfeeding. This meta-analysis indicates that long term breastfeeding might be associated with decreased risk of EC.