Modified cement mortar was prepared by incorporating a superabsorbent polymer (SAP) with two kinds of dosing state, dry powdery SAP and swelled SAP (where the SAP has been pre-wetted in tap water), respectively. The mechanical properties, drying shrinkage and freeze–thaw resistance of the mortars were compared and analyzed with the variation of SAP content and entrained water-to-cement ratios. Additionally, the effect of SAP on the microstructure of mortar was characterized by scanning electron microscopy (SEM). The results indicate that agglomerative accumulation is formed in the voids of mortar after water desorption from SAP and there are abundant hydration products, most of which are C-S-H gels, around the SAP voids. The incorporation of the powdery SAP increases the 28 d compressive strength of the mortars by about 10% to 50%, while for the incorporation of swelled SAP, the 28 d compressive strength of the mortar can be increased by about −26% to 6%. At a dosage of 0.1% SAP and an entrained water–cement ratio of 0.06, the powdery SAP and the swelled SAP can reduce the mortar shrinkage rate by about 32.2% and 14.5%, respectively. Both the incorporation of powdery and swelled SAP has a positive effect on the freeze–thaw resistance of cement mortar. In particular, for powdery SAP with an entrained water-to-cement ratio of 0.06, the mass loss rate after 300 cycles is still lower than 5%.

This research used the profile data measured extensively in the Yellow Sea and Bohai Sea (YSBS) to explain the temporal and spatial distribution characteristics of optical properties and systematically analyzed the influencing mechanisms of the seasonal variations of optical properties in the YSBS in conjunction with synchronously measured hydrological and biogeochemical data in vertical profiles. The main conclusions obtained are as follows: the vertical variations in the optical properties in the YSBS are mainly influenced by the stratification effect, vertical mixing function, and phytoplankton growth process; and the variations of optical properties are dominated by the change of particle characteristics. The backscattering ratio can be used to discriminate particle types as a proxy of particulate bulk refractive index. In the YSBS, for waters with a backscattering ratio of less than 0.012, the variations of optical properties are dominated by the phytoplankton particles. For waters with a backscattering ratio greater than 0.012, the variations of optical properties are dominated by inorganic sediment particles. In addition, for the YSBS, the variations in optical properties of upper surface layer waters can be elucidated well by the vertical variations.

No abstract

No abstract

Understanding the optimal wavelength for detecting the water column profile from a light detection and ranging (lidar) system is important in the design of oceanographic lidar systems. In this research, the optimal wavelength for detecting the water column profile using a lidar system at the global scale was analyzed based on the inherent optical properties of water. In addition, assuming that the lidar system had a premium detection characteristic in its hardware design, the maximum detectable depth using the established optimal wavelength was analyzed and compared with the mixed layer depth measured by Argo data at the global scale. The conclusions drawn are as follows: first, the optimal wavelengths for the lidar system are between the blue and green bands. For the open ocean, the optimal wavelengths are between 420 and 510 nm, and for coastal waters, the optimal wavelengths are between 520 and 580 nm. To obtain the best detection ability using a lidar system, the best configuration is to use a lidar system with multiple bands. In addition, a 490 nm wavelength is recommended when an oceanographic lidar system is used at the global scale with a single wavelength. Second, for the recommended 490 nm band, a lidar system with the 4 attenuating length detection ability can penetrate the mixed layer for 80% of global waters.