The electrocatalytic performance of the Ir/C catalyst as the anodic catalyst in the amperometric and electrochemical NH3 sensor was investigated.The experimental results illustrated that in the NaClO4 neutral electrolyte,the electrocatalytic performance of the Ir/C catalyst for the NH3 oxidation is related to the Ir loading in the Ir/C catalyst.Among the Ir/C catalysts with different Ir loading,the best electrocatalytic activity,stability and sensitivity were achieved by the Ir/C catalyst with 10% Ir loadings.In addition,the current densities of the NH3 oxidation at the Ir/C catalysts with the different Ir loadings were linearly proportional to the NH3 concentration.The Ir/C catalyst has a potential application in the amperometric and electrochemical NH3 sensor.
High temperature is one of the critical factors leading to the change in concrete performance since it affects the physical structure and chemical components of concrete. However, some concrete structures are continuously subjected to moderately elevated temperatures (typically less than 200 ℃) when operating, such as chimneys for the metallurgical industry and structures in nuclear power plants. The deterioration process of these structures could be caused and accelerated by a high-temperature environment. Thus, the safety and performance of these concrete structures at elevated temperatures during service life are crucial. This paper aims to investigate the change in concrete performance exposed to sustained moderately high temperatures. The concrete cured for 56 days was subjected to temperatures ranging from 65℃ to 200 ℃ for 28 days. The mechanical properties of concrete at different heating temperatures were tested, including compressive strength, splitting tensile strength and modulus of elasticity. Meanwhile, concrete’s durability after heating was evaluated using the concrete electrical resistivity test. The concrete elevated-temperature performance was compared to identical concretes at room temperatures, and the evolution of each property was analyzed. Based on experimental results, the long-term performance of concrete in a moderately elevated temperature environment is predicted.
The newly repaired Kaifeng City Wall has serious cracks, shedding and other issues on the surface, which constitute a significant problem. It is of great significance for the restoration of Kaifeng City Wall to explore the repair materials and techniques suitable for Kaifeng City Wall. The pH, particle gradation, compressive strength and SEM were tested on soil samples with different lime and MgO contents under different slaking times. With the increase of slaking time, the pH value first increased and then decreased. The relationship between pH value and strength showed three stages. The strength of lime-containing soil samples increased first, then decreased and then increased. The MgO content of soil samples showed an opposite trend. The particle gradation was significantly improved with increasing aging time. The main reason for the reduction of soil strength is the calcium carbonate crystals and magnesite microcracks produced by lime and MgO in the later stage of slaking.
Salinization has an important impact on the degradation of ancient masonry buildings, and systematically mastering the law of salt migration and degradation of ancient masonry buildings is an important part of the protection of ancient buildings. In this paper, the damage law of gray bricks under the action of salt crystallization is studied. The orthogonal test method is used to carry out cyclic degradation tests on gray bricks. The nominal strength is proposed as a mechanical parameter to measure the structural damage of grey bricks, and the change in compressive strength and crystallization pressure of the samples after the test is measured and analyzed. The results show that the damage of different salts in the gray bricks shows a certain difference. Magnesium sulfate and sodium chloride cause significant damage to the surface of the gray bricks, while calcium chloride does not cause significant damage to the surface of the gray bricks. When the concentrations of sodium chloride solution, calcium chloride solution and magnesium sulfate solution are less than 13.73 mol/L, 11.47 mol/L and 17 mol/L, respectively, the nominal strength of gray brick samples increases; In the range of 9.9 mol/L and 4.73-8.94 mol/L, the crystallization pressure began to appear inside the sample. The research results provide an important scientific basis for evaluating the damage caused by salting to the damage of porous ancient building materials such as masonry.
The height of Gongboxia concrete face slab rock-fill dam is 132.20 m,and the dam located in the earthquake area with asymmetric river valley.The weather there is cold and dry,with great temperature difference.The complex lithology leads to huge difference with excavate material.To master dam operation,typical monitoring sections were chosen,and both manual and automatic monitoring items were arranged.Further,the management of safety monitoring was brought into the dam safety information management system for the upstream cascade hydropower stations on the Yellow River,which was of great meaning to dam safety and operation.This paper introduced the arrangement of safety monitoring system and its management,for reference.
Based on the identification method about the of security existing buildings,according to the approximate Probability-based limit state design method of the current codes,the failure's influential parameter was regarded as weight function of the structure member of the building,the whole reliability parameter applied to the buildings reliable rated has been analyzed.The rating method has been advanced by weight function.It has been applied to a practical engineering example.
The silty clay in the lower reaches of the Yellow River is characterized by loose structure, low strength, and strong capillary effect. Based on the technology of ancient glutinous rice mortar and microbial‐induced calcium carbonate precipitation (MICP), experiments on optimal mass ratio of cementitious liquid to bacterial liquid and optimal concentration of cementitious liquid for MICP and improved MICP technology were carried out by measuring the production of CaCO 3 , and direct shear test and unconfined compressive strength test of plain silt, glutinous mixing silt, and improved silt with MICP and modified MICP were conducted. The microstructure of the reaction products of MICP and improved MICP technology were also evaluated based on scanning electron microscopy (SEM). Research results showed that the mechanical properties of silt with glutinous rice slurry were effectively improved. With the increase in the concentration of glutinous rice slurry, the strength and internal friction angle of soil samples first increased and then decreased, and the cohesion presented a linear increasing trend. When the concentration of cementitious liquid was 0.5 M and the mass ratio of cementitious liquid to bacterial liquid was 2 : 1, the amount of CaCO 3 formed was the most, and the conversion rate of Ca 2+ was more than 80%. The improved MICP could increase the conversion rate of Ca 2+ (93.44%). An improved MICP showed that glutinous rice slurry could improve bacterial activity, increase the urease content in the bacterial solution, and promote the production of CaCO 3 . Silt cohesion and internal friction angle of the silt were improved by the improved MICP technology, and the strengthening effect of mechanical properties of modified MICP‐reinforced soil is better than that of the MICP‐reinforced soil; conventional MICP technology could also improve the soil cohesion, but the improvement in the internal friction angle was not obvious. The SEM results indicated that compared with the reaction product of MICP technology, the structure of the product of improved MICP technology is more compact, resulting in a marked reinforcement of MICP performance with glutinous rice slurry. This study provides new insights into enhancing the mechanical behaviour of MICP‐treated silt in the Yellow River Basin with glutinous rice slurry.
Generally, brick buildings are in the open-air environment year round, and damage to them is aggravated by the effect of repeated freezing and thawing cycles. In order to determine freeze-thaw damage and deterioration mechanism, the initial moisture content of gray brick specimens was set as 20%, 40%, 60%, 80%, 100%. The effects of moisture content and the number of freeze-thaw cycles on the quality, mechanical properties and microstructure of gray brick were investigated by uniaxial compression tests and scanning electron microscopy (SEM) tests. Numerical simulations were applied to model the freezing and thawing process. The results showed that: as the number of freeze-thaw cycles increased, the mass loss rate and peak strength reduction rate of gray brick both increased. The initial moisture content had a greater impact on damage to gray brick due to freeze-thaw; ω = 80% was defined as the limit moisture content of gray brick. Under the repeated action of freeze-thaw cycles, the areas affected by thermal stress were mainly concentrated in the center of the outer surface and the center of the side of gray bricks. The maximum thermal stress after 55 freeze-thaw cycles was 1.522 × 10-2 MPa. This research results provide a theoretical basis for the prevention and protection of frost damage of brick buildings in a freeze-thaw environment.
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