Experimental Study on the Mechanical Properties of Crumb Rubber Concrete after Elevated Temperature.

To reduce the environmental damage caused by waste rubber, crumb rubber concrete (CRC) was prepared by replacing some fine aggregates with crumb rubber. The effects of elevated temperature as well as crumb rubber content on the mechanical properties of the prepared CRC were studied. The crumb rubber contents were 0%, 10%, and 20%, while CRC was subjected to atmospheric temperatures (AT) of 300 °C, 500 °C, and 700 °C. The concrete without crumb rubber content was used as the control group at the atmospheric temperature. The mass loss, thermal conductivity characteristics, compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, and stress-strain characteristics of CRC at elevated temperatures were studied. The experimental results show that: (1) With the increase in crumb rubber content and temperature, the cracks on the surface of the specimen gradually widen while the mass loss of the specimen increases. (2) With the increase in crumb rubber content and temperature, the cube compressive strength, splitting tensile strength, axial compressive strength, and elastic modulus of CRC decrease, yet the plastic failure characteristics of CRC are more obvious. (3) The influences of elevated temperature on strength and elastic modulus are as follows: splitting tensile strength > elastic modulus > axial compressive strength > cubic compressive strength. (4) With the increase in temperature, the stress-strain curve of the CRC tends to flatten, the peak stress decreases, and the corresponding peak strain significantly increases. With the increase in crumb rubber content, there is a great decrease in peak stress, yet the corresponding peak strain is basically the same. The use of CRC can be prioritized in applications that increase toughness rather than strength.

Seasonality of the Meridional Overturning Circulation in the subpolar North Atlantic.

Understanding the variability of the Atlantic Meridional Overturning Circulation is essential for better predictions of our changing climate. Here we present an updated time series (August 2014 to June 2020) from the Overturning in the Subpolar North Atlantic Program. The 6-year time series allows us to observe the seasonality of the subpolar overturning and meridional heat and freshwater transports. The overturning peaks in late spring and reaches a minimum in early winter, with a peak-to-trough range of 9.0 Sv. The overturning seasonal timing can be explained by winter transformation and the export of dense water, modulated by a seasonally varying Ekman transport. Furthermore, over 55% of the total meridional freshwater transport variability can be explained by its seasonality, largely owing to overturning dynamics. Our results provide the first observational analysis of seasonality in the subpolar North Atlantic overturning and highlight its important contribution to the total overturning variability observed to date.

Experimental Study on Toughness of Engineered Cementitious Composites with Desert Sand.

In this paper, engineered cementitious composites (ECCs) were prepared with desert sand instead of ordinary sand, and the toughness properties of the ECCs were studied. The particle size of the desert sand was 0.075-0.3 mm, which is defined as ultrafine sand. The ordinary sand was sieved into one control group with a size of 0.075-0.3 mm and three other reference groups. Together with the desert sand group, a total of five groups of ECC specimens were created. Through a uniaxial tensile test, three-point bending test and single-seam tensile test on the ECC specimens, the influence of aggregate particle size and sand type on the ECC tensile strength, deformation capacity, initial crack strength, cement-matrix-fracture toughness, multiple cracking characteristics and strain-hardening properties were studied. The experimental results show that the 28d tensile strain of the four groups of the ordinary sand specimens was 8.13%, 4.37%, 4.51% and 4.23%, respectively, which exceeded 2% and satisfied the requirements for the minimum strain of the ECCs. It is easier to achieve the ECC strain hardening with sand with a fine particle size; thus, a particle size below 0.3 mm is preferred when preparing the ECCs to achieve a high toughness. The multiple cracking performance (MCP) and the pseudostrain hardening (PSH) of desert sand and ordinary sand with a 0.075-0.3 mm grain size were 2.88 and 2.33, and 8.76 and 8.17, respectively, all of which meet the strength criteria and energy criteria and have similar properties. The tensile strength and tensile deformation of the desert sand group were 4.97 MPa and 6.78%, respectively, and the deformation capacity and strain-strengthening performance were outstanding. It is verified that it is feasible to use desert sand instead of ordinary sand to prepare the ECCs.

A strong summer phytoplankton bloom southeast of Vietnam in 2007, a transitional year from El Niño to La Niña.

Summer upwelling occurs frequently off the southeast Vietnam coast in the western South China Sea (SCS), where summer phytoplankton blooms generally appear during June-August. In this study, we investigate inter-annual variation of Ekman pumping and offshore transport, and its modulation on summer blooms southeast of Vietnam. The results indicate that there are low intensities of summer blooms in El Niño years, under higher sea surface temperatures (SST) and weaker winds. However, a different pattern of monthly chlorophyll a (Chl-a) blooms occurred in summer of 2007, a transitional stage from El Niño to La Niña, with weak (strong) wind and high (low) SST before (after) early July. There is a weak phytoplankton bloom before July 2007 and a strong phytoplankton bloom after July 2007. The abrupt change in the wind intensity may enhance the upwelling associated with Ekman pumping and offshore Ekman transport, bringing more high-nutrient water into the upper layer from the subsurface, and thus leading to an evident Chl-a bloom in the region.

Coastal sea level projections with improved accounting for vertical land motion.

Regional and coastal mean sea level projections in the Intergovernmental Panel for Climate Change (IPCC) Fifth Assessment Report (AR5) account only for vertical land motion (VLM) associated with glacial isostatic adjustment (GIA), which may significantly under- or over-estimate sea level rise. Here we adjust AR5-like regional projections with the VLM from Global Positioning Satellite (GPS) measurements and/or from a combination of altimetry and tide-gauge data, which include both GIA and non-GIA VLM. Our results at selected tide-gauge locations on the North American and East Asian coasts show drastically different projections with and without non-GIA VLM being accounted for. The present study points to the importance of correcting IPCC AR5 coastal projections for the non-GIA VLM in making adaptation decisions.

Influence of Typhoon Matsa on Phytoplankton Chlorophyll-a off East China.

Typhoons can cause strong disturbance, mixing, and upwelling in the upper layer of the oceans. Rich nutrients from the subsurface layer can be brought to the euphotic layer, which will induce the phytoplankton to breed and grow rapidly. In this paper, we investigate the impact of an intense and fast moving tropical storm, Typhoon Matsa, on phytoplankton chlorophyll-a (Chl-a) concentration off East China. By using satellite remote sensing data, we analyze the changes of Chl-a concentration, Sea Surface Temperature (SST) and wind speed in the pre- and post-typhoon periods. We also give a preliminary discussion on the different responses of the Chl-a concentration between nearshore and offshore waters. In nearshore/coastal regions where nutrients are generally rich, the Chl-a maximum occurs usually at the surface or at the layer close to the surface. And, in offshore tropical oligotrophic oceans, the subsurface maxima of Chl-a exist usually in the stratified water column. In an offshore area east of Taiwan, the Chl-a concentration rose gradually in about two weeks after the typhoon. However, in a coastal area north of Taiwan high Chl-a concentration decreased sharply before landfall, rebounded quickly to some degree after landfall, and restored gradually to the pre-typhoon level in about two weeks. The Chl-a concentration presented a negative correlation with the wind speed in the nearshore area during the typhoon, which is opposite to the response in the offshore waters. The phenomena may be attributable to onshore advection of low Chl-a water, coastal downwelling and intensified mixing, which together bring pre-typhoon surface Chl-a downward in the coastal area. In the offshore area, the typhoon may trigger increase of Chl-a concentration through uptake of nutrients by typhoon-induced upwelling and entrainment mixing.

Observing storm surges from space: Hurricane Igor off Newfoundland.

Coastal communities are becoming increasingly more vulnerable to storm surges under a changing climate. Tide gauges can be used to monitor alongshore variations of a storm surge, but not cross-shelf features. In this study we combine Jason-2 satellite measurements with tide-gauge data to study the storm surge caused by Hurricane Igor off Newfoundland. Satellite observations reveal a storm surge of 1 m in the early morning of September 22, 2010 (UTC) after the passage of the storm, consistent with the tide-gauge measurements. The post-storm sea level variations at St. John's and Argentia are associated with free equatorward-propagating continental shelf waves (with a phase speed of ~10 m/s and a cross-shelf decaying scale of ~100 km). The study clearly shows the utility of satellite altimetry in observing and understanding storm surges, complementing tide-gauge observations for the analysis of storm surge characteristics and for the validation and improvement of storm surge models.