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Expansion damage in medium–low reactivity dolomite limestone poses significant challenges in construction and engineering projects. This study investigates the potential of fly ash in inhibiting expansion damage in such limestone formations based on RILEM AAR-5 method. Through a series of laboratory experiments, various proportions of fly ash instead of cement, respectively, were prepared and subjected to varying alkali content conditions immersion tests to simulate expansion conditions. The expansion rates and extents were monitored and compared between pure limestone samples and those mixed with different proportions of fly ash. Additionally, scanning electron microscopy (SEM) analysis was employed to investigate the microstructure of the dolomite limestone–fly ash mixtures to understand the inhibition mechanisms. Results indicate that fly ash demonstrates promising inhibitory effects on expansion damage in medium–low reactivity dolomite limestone across the addition of 40% fly ash and alkali content of 0.70%. The reaction products are calcite, brucite, and a mixture of Mg-Si-Al phases and the reaction area is within 100 μm from the boundary when the cement alkali content is 1.50% without any fly ash. However, no reaction products were found at the boundary after adding 40% fly ash when lowering the cement alkali content to 0.70%. This research contributes to a better understanding of the interaction between fly ash and dolomite limestone in inhibiting expansion damage, providing valuable insights for engineering applications. [ABSTRACT FROM AUTHOR]

Large amounts of chloride ions (Cl−) and sulfate ions (SO42−) are present in salt-washing wastewater, making it unsuitable for direct release. Adsorption can be used to eliminate Cl− and SO42− from salt-washing wastewater, and hydrotalcite is an excellent adsorbent with high adsorption properties for these ions because of a layered bimetallic hydroxide structure. The selective extraction of various metals, such as calcium, magnesium, aluminum, and iron, from steel slag via acid leaching facilitates the utilization of steel slag in the preparation of hydrotalcite. In this study, the leaching mechanism of metal in steel slag was investigated using steel slag as a raw material and acetic acid as the reaction medium. The study obtained the optimal leaching mechanism for preparing hydrotalcite. Hydrotalcite was synthesized from the steel slag leaching solution by hydrothermal synthesis, and its structure was characterized. The adsorption performance of Cl− and SO42− in salt-washing wastewater was investigated by solution adsorption experiments. The removal rates of Cl− and SO42− in salt-washing wastewater reached 12.8% and 38.0%, respectively. After multiple adsorption cycles, the removal rates increased to 98.0% for Cl− and 96.4% for SO42−. [ABSTRACT FROM AUTHOR]

To reduce the mining of high-grade magnesite and solve the environmental pollution caused by magnesite tailings, magnesite tailings were used to produce MgO expansion agent (MEA), and a detailed study of its performance was carried out in this study. Firstly, the effects of different calcination times on the calcination products, the specific surface area, and the activity of MEA were analyzed. Then, the MEA produced by calcinating at 950 °C for 1 h was taken as the research object, and the effects of its content on the expansion performance, compressive strength, and flexural strength of the mortar were studied. The results showed that the decomposition of magnesite tailings after high-temperature calcination produced MEA, and the longer the calcination time, the lower the activity. The calcined tailings could compensate for the shrinkage of the mortar, and the expansion increased with the increase in curing temperature. What is more, when the content was less than 8%, the hydration of MEA filled the pores and improved the compactness, so the strength of the mortar increased with the increase in the expansion agent content. When the dosage was greater than 8%, excessive expansion increased the porosity, causing harmful expansion of the mortar and damaging its integrity, leading to a decrease in strength. Fly ash reduced the expansion of mortar, and after adding 30% fly ash, the expansion decreased by 20.0–36.1%, and the ability to suppress expansion decreased with the increase in curing temperature. [ABSTRACT FROM AUTHOR]

Shrinkage deformation of concrete has been one of the difficulties in the process of concrete performance research. Cracking of concrete caused by self-shrinkage and temperature-drop shrinkage has become a common problem in the concrete world, and cracking leads to a decrease in the durability of concrete and even a safety hazard. Mineral admixtures, such as fly ash and mineral powder, are widely used to improve the temperature drop shrinkage of mass concrete; fly ash can reduce the temperature rise of concrete while also reducing the self-shrinkage of concrete, there are different results on the effect of mineral powder on the self-shrinkage of concrete, but the admixture of fly ash will reduce the strength of concrete, and mineral admixtures have an inhibitory effect on the shrinkage compensation effect of MgO expander(MEA). The paper investigates the effect of mineral admixtures on the mechanical and deformation properties of C50 mass concrete with a MgO expander(MEA), aiming to determine the proportion of C50 mass concrete with good anti-cracking properties under working conditions. The experiments investigated the effect of fly ash admixture, mineral powder admixture and MgO expander admixture on the compressive strength and deformation of concrete under simulated working conditions of variable temperature and analyzed the effect of hydration of magnesite in MgO expander and pore structure of cement paste on deformation. The following main conclusions were obtained: 1. When the concrete compounded with mineral admixture was cured under variable temperature conditions, the compounded 30% fly ash and mineral powder decreased by 4.3%, 6.0% and 8.4% at 7d age, and the compounded 40% fly ash and mineral powder decreased by 3.4%, 2.8% and 2.3% at 7d age, respectively. The incorporation of MEA reduced the early compressive strength of concrete; when the total amount of compounding remained unchanged, the early compressive strength of concrete was gradually smaller as the proportion of compounding decreased. 2. The results of concrete deformation showed that when the temperature rose, the concrete expanded rapidly, and when the temperature dropped, the concrete also showed a certain shrinkage, and the deformation of concrete basically reached stability at 18d. 3. The compounding of 30% fly ash and mineral powder As the compounding ratio decreases, the deformation of concrete increases, and the 28d deformation of concrete with a compounding ratio of 2:1 is 280 × 10−6, while the final stable deformation of concrete with a compounding ratio of 2:1 in compounding 40% fly ash and mineral powder is the largest, with a maximum value of 230 × 10−6, respectively. Overall, the concrete with a total compounding of 30% and a compounding ratio of 2:1 has the best shrinkage resistance performance. [ABSTRACT FROM AUTHOR]

In order to improve the overall energy efficiency of multi-hop relaying networks for the formation of unmanned surface vessel, and reduce the possibility of outage in communication, a distributed multi-hop relaying spectrum allocation algorithm is put forward based on maximizing energy efficiency. Firstly, for the sake of making sure that the possibility of inter node communication interruptions is kept within the threshold, an analysis on Rician fading channel is conducted to calculate the minimum transmitting power needed in networks. Then, the number of maximum subcarriers is calculated and the asynchronous distributed pricing algorithm is applied to select the candidate subcarriers group. After that, the sub gradient method is used, by solving KKT conditions, to select the subcarriers from the candidate subcarrier group and allocate the power, therefore, a sub optimal solution of the optimal allocation is obtained. Finally, the effectiveness of the proposed algorithm is verified by the simulation analysis on the reliability and energy efficiency of networks. [ABSTRACT FROM AUTHOR]

In order to solve the problem that the node selection algorithm in marine heterogeneous wireless network is not effective in real time and does not match well with mobile nodes, a network access selection algorithm based on dynamic analytic hierarchy process (DAHP) and synergetic principle is proposed. On the basis of satisfying multi factor and staid node network selection, this algorithm uses the DAHP method to determine the subjective weight of the access n index, uses the synergetic correlation prindple to determine the objective weight, and uses received power to determine the location weight of moblle nodes. By redistributing the subjective, objective, and location weights, it takes into account the real-time network state and task communication needs around moblle nodes. The algorithm improves the real-time performance and the matching with mobile nodes. The simulation results show that compared with the traditional network selection algorithm based on AHP and the synergetics principle and the mobile node elgorithm based on distance, this elgorithm reduces the traffic blocking rate of nodes and improves the communication smoothness and real-tiime performance. [ABSTRACT FROM AUTHOR]