Study on Synergistic Effect of Xanthan Gum and Sodium Methylsiliconate on Mechanical Strength and Water Stability of Phosphogypsum Road-Based Materials.

To address the issues of low strength, poor water stability, and hazardous substance leaching associated with using phosphogypsum (PG) as a direct road-based material, the traditional approach involves employing inorganic cementing materials to stabilize PG, effectively addressing the problems. This study innovatively utilizes the xanthan gum (XG) and sodium methylsiliconate (SM) as curing agents for PG to solve the above problems. An organic curing agent stabilized PG was prepared by dry mixing XG and PG. The unconfined compressive strength, water stability, and leaching behavior of stabilized PG were investigated, the leaching behavior was characterized by ion leaching concentration, and the mechanisms behind the strength development of stabilized PG were explored by SEM and FTIR. The experimental results indicate that the single incorporation of XG reduced the strength and water stability of stabilized PG, while the single incorporation of SM had a limited effect on strength and water stability. In addition, the dual incorporation of XG and SM significantly improved the strength and water stability of stabilized PG. At the same time, the dual incorporation of XG and SM greatly reduced the leaching of hazardous substances from stabilized PG. These results demonstrate the feasibility of using stabilized PG for road base materials.

Research on the Performance of Superhydrophobic Cement-Based Materials Based on Composite Hydrophobic Agents.

The utilization of a novel monolithic superhydrophobic cement material effectively prevents water infiltration and enhances the longevity of the material. A method for improving superhydrophobic concrete was investigated with the aim of increasing its strength and reducing its cost by compounding superhydrophobic substances with water repellents. The experimental tests encompassed the assessment of the compressive strength, contact angle, and water absorption of the superhydrophobic cementitious materials. The findings demonstrate that an increase in the dosage of isobutyltriethoxysilane (IBTES) progressively enhances the contact angle of the specimen, but significantly diminishes its compressive strength. The contact angle of SIKS mirrors that of SIS3, with a superior compressive strength that is 68% higher. Moreover, superhydrophobicity directly influences the water absorption of cementitious materials, with a more pronounced superhydrophobic effect leading to a lower water absorption rate. The water absorption of cementitious materials is influenced by the combined effect of porosity and superhydrophobicity. Furthermore, FT-IR tests unveil functional mappings, such as -CH3 which can reduce the surface energy of materials, signifying successful modification with hydrophobic substances.

Mesocosm experimental study on sustainable riparian restoration using sediment-modified planting eco-concrete.

The continued deterioration of riparian ecosystems is a worldwide concern, which can lead to soil erosion, plant degradation, biodiversity loss, and water quality decline. Here, taking into account waste resource utilization and eco-environmental friendliness, the sediment-modified planting eco-concrete with both H. verticillata and T. orientalis (SEC-H&T) was prepared and explored for the first time to achieve sustainable riparian restoration. Concrete mechanical characterizations showed that the compressive strength and porosity of SEC with 30% sediment content could reach up to 15.8 MPa and 21.25%, respectively. The mechanical properties and the sediment utilization levels of SEC were appropriately balanced, and potentially toxic element leaching results verified the environmental safety of eco-concrete modified with dredged sediments. Plant physiological parameters of both aquatic plants (biomass, chlorophyll, protein and starch) were observed to reach the normal levels in SEC during the 30-day culture period, and T. orientalis seemed better adapted to SEC environment than H. verticillate. Importantly, compared to SEC-H and SEC-T, SEC-H&T could effectively reduce the concentrations of COD, TN and TP by 58.59%, 74.00% and 79.98% in water, respectively. Notably, water purification mechanisms by SEC-H&T were further elucidated from the perspective of microbial community responses. Shannon index of bacterial diversity and proliferation of specific populations dominating nutrient transformation (such as Bacillus and Nitrospira) was increased under the synergy of SEC and aquatic plants. Correspondingly, functional genes involved in nitrogen and phosphorus transformation (such as nosZ and phoU) were also enriched. Our study can not only showcase an effective and flexible approach to recycle dredged sediments into eco-concrete with low environment impacts, but also provide a promising alternative for sustainable riparian restoration.

Prediction of Temperature Development of Concrete with Set-Controlling Admixture Based on a New Hydration Kinetics Model.

Temperature control is needed in the construction process of massive concrete and it can avoid the concrete cracks. Prediction of temperature development based on a hydration kinetics model can reduce the need for adiabatic temperature rise tests for concrete. However, the existing hydration kinetics model cannot accurately describe the hydration process of cement, thereby limiting the ability to further accurately predict the temperature rise of concrete based on the hydration kinetics model. This paper aims to establish a new hydration kinetics model, which is based on nucleation and growth model, and to predict the temperature development of concrete with set-controlling admixture based on this model. In this paper, the nucleation and growth of hydration products and the diffusion of free water by the modified boundary of nucleation and growth (BNG) model and the modified Fuji and Kondo's model are described. The relationship between nucleation rate and apparent activation energy and the relationship between effective diffusion coefficient and apparent activation energy are linear. However, the relationship between growth rate and apparent activation is exponential. Finally, the temperature development of concrete can be calculated by the hydration degree of the cement.

Ultrasonic-assisted electrodeposition of Ni/diamond composite coatings and its structure and electrochemical properties.

Ni/diamond composite coatings have been synthesized by ultrasonic-assisted electrodeposition in a Ni electroplating bath containing diamond nanoparticles. The influences of current density and ultrasonic agitation on the coating composition, morphology, topography, phase structure, and electrochemical characteristics of the electrodeposits were evaluated. Ultrasonic agitation was provided using an external ultrasonic bath at a frequency of 40 kHz and acoustic power of 300 W. Coating samples were also prepared under magnetic stirring for comparison with the ultrasonic-assisted deposits. This work reveals that the diamonds have been incorporated and evenly distributed in the composites. The coatings exhibit dense, granular like morphology with pyramid-like grains. As current density increases, the diamond amount of ultrasonic-assisted electrodeposits first increased to maximum of 11.4 wt% at 3 A dm-2 and then decreases to 9.9 wt% at 5 A dm-2, and the RTC of the preferred orientation (200) plane increases from 76.3% up to 93.4%. The crystallite size was 60-80 nm and the Ra of the magnetic and ultrasonic agitations were 116 nm, 110 nm, respectively. The maximum Rp of 39.9, 50.3 kΩ cm2 was obtained at 4 A dm-2 when respectively immersed 30 min and 7 days, illustrating the best corrosion resistance of the coatings of 4 A dm-2. The effects of mechanical and ultrasonic agitations on the mechanism of the co-electrodeposition process were both proposed. The incorporation of diamond particles enhances the hardness and wear-resisting property of the electrodeposits. The ultrasonic-assisted electrodeposited Ni/diamond coating has better corrosion resistance than that prepared under mechanical stirring conditions.