Search

To promote the safe use of MgO expansive agent (MEA) in mass concrete, the influence of fineness and sintering temperature of MEA on the expansion, mechanical properties, and microstructure of fly ash-Portland cement pastes was studied. The results indicate that the agent prepared at 950 °C does not adversely affect the compressive strength of the pastes. Whereas the agent prepared at 1150 °C (MII) has a marked negative impact on the volume stability and strength of the pastes. Furthermore, incorporating MII with coarser particle size results in a larger expansion, greater strength loss, and coarser pore structure. The presence of fly ash delays the hydration of MgO, making more MgO available for the formation of Mg(OH)2at the late age. Meanwhile, the pozzolanic reaction leads to decreased total porosity, leaving less space available for the accommodation of Mg(OH)2. Consequently, fly ash cement pastes suffer greater strength loss than plain cement pastes when the destructive expansion occurs due to the delayed hydration of MgO.

The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versushuman-influenced climate are poorly known despite being essential for predicting future effects on natural ecosystems and human societies such as crop yield, wildfires, and health. Here we combine regionally distinct reconstructions of pre-industrial summer vapor pressure deficit variability from Europe’s largest oxygen-isotope network of tree-ring cellulose with observational records and Earth system model simulations with and without human forcing included. We demonstrate that an intensification of atmospheric drying during the recent decades across different European target regions is unprecedented in a pre-industrial context and that it is attributed to human influence with more than 98% probability. The magnitude of this trend is largest in Western and Central Europe, the Alps and Pyrenees region, and the smallest in southern Fennoscandia. In view of the extreme drought and compound events of the recent years, further atmospheric drying poses an enhanced risk to vegetation, specifically in the densely populated areas of the European temperate lowlands.

Terrestrial ecosystems have taken up about 32% of the total anthropogenic CO2emissions in the past six decades1. Large uncertainties in terrestrial carbon–climate feedbacks, however, make it difficult to predict how the land carbon sink will respond to future climate change2. Interannual variations in the atmospheric CO2growth rate (CGR) are dominated by land–atmosphere carbon fluxes in the tropics, providing an opportunity to explore land carbon–climate interactions3–6. It is thought that variations in CGR are largely controlled by temperature7–10but there is also evidence for a tight coupling between water availability and CGR11. Here, we use a record of global atmospheric CO2, terrestrial water storage and precipitation data to investigate changes in the interannual relationship between tropical land climate conditions and CGR under a changing climate. We find that the interannual relationship between tropical water availability and CGR became increasingly negative during 1989–2018 compared to 1960–1989. This could be related to spatiotemporal changes in tropical water availability anomalies driven by shifts in El Niño/Southern Oscillation teleconnections, including declining spatial compensatory water effects9. We also demonstrate that most state-of-the-art coupled Earth System and Land Surface models do not reproduce the intensifying water–carbon coupling. Our results indicate that tropical water availability is increasingly controlling the interannual variability of the terrestrial carbon cycle and modulating tropical terrestrial carbon–climate feedbacks.

Density functional theory calculations are carried out to explore the adsorption behaviour of perfluorooctane sulfonate (PFOS) on pristine and fluorinated graphene. Then, the effects of different degrees of fluorination of graphene on the adsorption of PFOS are systematically investigated by analysis of the adsorption energy (Eads), electron transfer and partial density of states. Finally, the unique adsorption behaviour of PFOS on graphene and fluorinated graphene is demonstrated by a companion study of four other organic molecules, namely hepta-fluorobutyric acid, phenanthrene, phenol and perfluorooctanoate.

CO2-mixing by directly injecting CO2into fresh cement-based materials is a burgeoning technology to produce low-carbon cement products. The objective of this study is to investigate the influence of the calcium carbide slag (CCS) content on the properties and carbon sequestration efficiency of cement pastes mixed under direct CO2injection conditions. The results indicate that the addition of CCS reduced the fluidity of the cement pastes, accelerated the setting process, increased volume shrinkage, and reduced compressive strength. Following the injection of CO2into the cement pastes, calcium hydroxide (CH) was carbonated to form calcium carbonate (CC) particles which fill the voids in the cement pastes, thereby reducing volume shrinkage and increasing compressive strength. A lower CO2inflow rate (2L/min) was more beneficial to the workability of the cement pastes, while a high inflow rate (6L/min) can lead to insufficient hydration and affect the development of strength. However, a higher CO2inflow rate was favorable for improving carbon sequestration efficiency. The highest amountof carbon sequestration can be reached at 6.93%, when the CCS content is 10% and the CO2inflow rate is 6L/min.

Drought has the potential to significantly decrease net primary production (NPP). However, the drought sensitivity of NPP remains unclear globally. Here we investigated the response of NPP to drought for the period 1982–2011 using NPP derived from satellite models, eight dynamic global vegetation models (DGVMs), and several drought indices. Our results indicate that the sign of drought response of NPP is consistent across satellites and DGVMs globally. Both the model and satellite data show a unimodal distribution of drought sensitivity across climatic gradients and indicate that semiarid regions are the most drought‐sensitive areas. In addition, a decreasing drought trend was significantly correlated with an increasing trend in satellite‐derived NPP or DGVM‐derived NPP globally. However, the DGVM‐derived NPP is more sensitive to drought than the satellite‐derived NPP over most vegetated land areas and presents a stronger correlation with drought, higher drought sensitivity, and larger slopes between NPP and drought trends. The overresponse of the DGVM‐derived NPP to drought relative to the satellite‐derived NPP could be attributed to the higher drought sensitivity of the simulated leaf area index and overresponse of the DGVM‐derived NPP to the vapor pressure deficit. Overall, large uncertainties remain in the response of NPP to drought and additional long‐term observations are required to better represent NPP responses to water stress in DGVM models. The sign of NPP's response to drought is consistent across satellite‐derived NPP and DGVM‐derived NPP over most vegetated areasThe drought sensitivity of satellite‐derived NPP and DGVM‐derived NPP peaks in semiarid regions globallyThe DGVM‐derived NPP is more sensitive to drought than the satellite‐derived NPP

Macro‐Porous Hydrogels In article 2200717by Zhenming Wang, Hongping Zhang, and co‐workers, a novel sponge‐like macro‐porous hydrogel with stable macro‐porous structures is developed via a facile, fast approach induced by Ti3C2MXene additives. It not only shows good antioxidant and antibacterial properties but also shows good material exchange capacity due to the interconnected pore structure. All these advantages provide the sponge‐like hydrogel with a potential application for promoting the repair of diabetic wounds.

Hydrogels with soft and wet properties have been intensively investigated for chronic disease tissue repair. Nevertheless, tissue engineering hydrogels containing high water content are often simultaneously suffered from low porous size and low water‐resistant capacities, leading to undesirable surgery outcomes. Here, a novel sponge‐like macro‐porous hydrogel (SM‐hydrogel) with stable macro‐porous structures and anti‐swelling performances is developed via a facile, fast yet robust approach induced by Ti3C2MXene additives. The MXene‐induced SM‐hydrogels (80% water content) with 200–300 µm open macropores, demonstrating ideal mass/nutrient infiltration capability at ≈20‐fold higher water/blood‐transport velocity over that of the nonporous hydrogels. Moreover, the highly strong interactions between MXene and polymer chains endow the SM‐hydrogels with excellent anti‐swelling capability, promising equilibrium SM‐hydrogels with identical macro‐porous structures and toughened mechanical performances. The SM‐hydrogel with versatile functions such as facilitating mass transport, antibacterial (bacterial viability in (Acrylic acid‐co‐Methacrylamide dopamine) copolymer‐Ti3C2MXene below 25%), and reactive oxygen species scavenging capacities (96% scavenging ratio at 120 min) synergistically promotes diabetic wound healing (compared with non‐porous hydrogels the wound closure rate increased from 39% to 81% within 7 days). Therefore, the durable SM‐hydrogels exhibit connective macro‐porous structures and bears versatile functions induced by MXene, demonstrating its great potential for wound tissue engineering. A sponge‐like macroporous hydrogel (SM‐hydrogel) with versatile therapeutic functions is developed. The SM‐hydrogel has simultaneous macro‐porous structures (200–300 µm), mechanical fatigue resistance, anti‐swelling, and antibacterial capabilities. Additionally, SM‐hydrogel achieves a satisfactory ability for treating diabetic wounds, enabling its great potential in chronic wound treatment applications.

It is well known that the toughness and freeze-thaw resistance of concrete can be improved by rubber aggregate (RA) while it significantly reduces the compressive strength. In this study, a simple semi-empirical prediction model of strength reduction factor (SRF) for rubberized concrete (RuC) is proposed to evaluate the compressive-strength reducing behavior of RuC. The model takes the volume fraction of RA as an independent variable and can be used to quantitatively describe the influence of different composition factors on compressive strength. In addition, a database containing more than 321 groups of reported experimental results is established to validate the proposed model. The main influencing factors of SRF are also clarified, including the content, particle size, surface property and replacement method of RA. According to the above factors, scientific classification and statistical fitting analysis are carried out on the database to determine the model parameter b. It is found that the proposed SRF model has good universality and predictability, which can be used to guide the mix design of RuC.

There are two common problems in the application of rubber aggregate concrete (RAC). One problem is that the rubber aggregate floats easily, which leads to a reduction in the workability of the mixture and delamination of the matrix. Another problem is that the mechanical properties of RAC are greatly reduced after hardening due to the poor interfacial bonding between rubber and the cement matrix (R-C). In this study, a novel modification method of waste rubber powder (WRP) combining mechanochemistry action, ultrasonic energy accumulation and the coating effect was proposed. The particle size distribution, specific surface area, hydrophilicity, morphology and structure of rubber were characterized by a laser particle size analyser, scanning electron microscopy (SEM), etc. The distribution of WRP in the cement-based materials was determined. The interfacial bonding and microstructure of R-C were analysed by SEM. The compressive and flexural strengths of cement-based materials with different contents of rubber were studied. The results showed that the R-C interface was significantly improved, and rubber particles were uniformly distributed in the cement mortar. The particle size of rubber particles showed a standard normal distribution, the surface cracks and pores were filled and coated, and the hydrophilic angle decreased from 94.6° to 68.0°. The cracks and voids of the R-C interface disappeared, and the compressive and flexural strengths of the mortar increased by 70% and 50%, respectively. The R-C interface and the distribution of rubber particles were found to play a major role in influencing the mechanical properties of RAC.