Chemical sulphate corrosion on cement composites in various model environments

Background: Cementitious composites, which are subject to increasing demands, are often exposed to various external attacks, such as aggressive groundwater and surface water, chemicals in the soil, gas penetration, or phenomena related to water freezing and melting. One of the most common reasons for the deterioration of cement composites is the corrosion process. Corrosion results in irreversible damage that occurs during the chemical reaction of the material with the components of the environment. Methods: The paper deals with experimental study of chemical sulphate corrosion of cement composites prepared from three types of cement: ordinary Portland cement; sulphate-resistant cement; and special hybrid cement, and industrial by-products and wastes: silica fume, zeolite and a special mineral admixture based on blast furnace granular slag as cement partial substitutes. Samples of cement composites were subjected to corrosion experiments in a sulphate environment, which took place in the laboratory under model conditions for 180 resp. 270 days. Results: The deterioration parameters: changes in the weight and thickness of the samples, surface and mineralogical changes, leachability of the basic components of the cement matrix as well as changes in the liquid phase proved the degradation process due to chemical sulphate corrosion, model solutions of H2SO4 with pH 3 and 4, and solution of MgSO4 with c (SO4 2 - ) = 3 and 10 g /L. Conclusion: By comparing the leachability of the alkali components from cement composites, it can be concluded that for the most aggressive model solution (H2SO4 with pH 3), both slagcontaining formulations are the most stable in terms of the total ratio of leached calcium and silicon. This finding is also supported by the results of water absorbency tests, which confirmed that despite the increase in absorbency after chemical corrosion, cement composites with slag content reach the lowest values.

The Flame-Retardant Mechanisms and Preparation of Polymer Composites and Their Potential Application in Construction Engineering

Against the background of people’s increasing awareness of personal safety and property safety, the flame retardancy (FR) of materials has increasingly become the focus of attention in the field of construction engineering. A variety of materials have been developed in research and production in this field. Polymers have many advantages, such as their light weight, low water absorption, high flexibility, good chemical corrosion resistance, high specific strength, high specific modulus and low thermal conductivity, and are often applied to the field of construction engineering. However, the FR of unmodified polymer is not ideal, and new methods to make it more flame retardant are needed to enhance the FR. This article primarily introduces the flame-retardant mechanism of fire retardancy. It summarizes the preparation of polymer flame-retardant materials by adding different flame-retardant agents, and the application and research progress related to polymer flame-retardant materials in construction engineering.

Durability Control of Brickwork's Material Including Operation Parameters of the Building Enclosure

This paper aims to develop a method to determine material durability based on physicochemical laws that describe chemical corrosion in building enclosures. The subject of this research is studying the chemical corrosion in the material in building constructions. The object of this research is the material of building ceramics. Methods that the authors used for reaching this goal include developing a multi-staged process of material degradation of building ceramics, conduction of thermodynamic calculations, and conducting laboratory research on process kinetics. The results of kinetic researches are generalized based on a developed mathematical model. This comprehensive approach to solving the goal task allowed obtaining the following results: research methods of chemical processes in brick material and its plaster on humidification were developed. A mathematical model for evaluating material degradation in time with the changing climatic influence on enclosure was developed.

Detailed analysis of chemical corrosion of ultra-thin wires used in drift chamber detectors

Ultra-thin metallic anode and cathode wires are frequently employed in low-mass gaseous detectors for precision experiments, where the amount of material crossed by charged particles must be minimised. We present here the results of an analysis of the mechanical stress and chemical corrosion effects observed in 40 and 50 μm diameter silver plated aluminum wires mounted within the volume of the MEG II drift chamber, which caused the breakage of about one hundred wires (over a total of ≈ 12000). This analysis is based on the careful inspection of the broken wires by means of optical and electronic microscopes and on a detailed recording of all breaking incidents. We present a simple empirical model which relates the number of broken wires to their exposure time to atmospheric relative humidity and to their mechanical tension, which is necessary for mechanical stability in the presence of electrostatic fields of several kV/cm. Finally we discuss how wire breakages can be avoided or at least strongly reduced by operating in controlled atmosphere during the mounting stages of the wires within the drift chamber and by choosing a 25 % thicker wire diameter, which has very small effects on the detector resolution and efficiency and can be obtained by using a safer fabrication technique.

STRUCTURAL PARAMETERS OF CONCRETE CORROSION RESISTANCE

This article describes the problem of corrosion of concrete at the enterprises of the wine and fruit and vegetable industry in Moldova, the kind of organic acids that destroy concrete are considered. Such a specific type of chemical corrosion as leaching is also considered. The reaction of the influence of malic acid on concrete is reflected, as a result of which readily soluble calcium malic acid is formed. The structural parameter of corrosion resistance to chemical corrosion has been studied. The formula for the corrosion resistance of concrete is derived and explained. The structural parameter of resistance to chemical corrosion is investigated on various types of concrete. The formula for coefficient resistance of concrete to chemical corrosion is derived. Also, two dependencies are displayed: Dependence of the coefficient of resistance of concrete to chemical corrosion on the volume of cement stone; Dependence of the coefficient of concrete resistance to leaching corrosion on the structural parameter.

Coherent and Compact Zinc Electrodeposition Enabled by Compressing the Electric Double Layer of the Deposits

The porous hexagonal-platelet Zinc (Zn) deposits exacerbate the chemical corrosion and deteriorate the reversibility of the Zn electrodes in aqueous electrolytes. Based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, to turn the messy Zn deposits into agglomerate ones, the challenge is to weaken the electric double layer repulsive force, which is the main reason preventing the dense Zn deposits, between the electrodeposited Zn particles. Here, we proposed a strategy to compress the electric double layer and regulate the forces between the electrodeposited Zn particles by introducing inert charges to the surface of the Zn deposits. The results of the electron microscopies revealed dense and coherent electrodeposition of Zn, indicating that the van der Waals attraction between the deposits becomes governing during electrodeposition. Such results could be attributed to the adsorbed inert charges on Zn deposits decrease the net charges and weaken the electric double layer repulsive force. This design enables the Zn||Zn cells a long-term plating/stripping stability for > 1200 h, a high average Coulombic Efficiency of 99.9% for > 2100 h, and steady charge/discharge responses even under a draconian deep-discharge condition of 80% depth of discharge of Zn (DODZn). In addition, the Zn||VS2 full cells demonstrate significantly improved electrochemical reversibility and capacity retention.

TiO2-Coated ZnO Nanowire Arrays: A Photocatalyst with Enhanced Chemical Corrosion Resistance

Photocatalysis is proven to be the most efficient and environmentally friendly method for the degradation of organic pollutants in water purification. To meet the requirement of large-scale water treatment, there are two important points: One is the lifetime and chemical stability of the photocatalyst material, especially in the complex and harsh aqueous conditions. The other is the ease of synthesis of such photocatalysts with specific nano-morphology. In this work, two common photocatalyst materials, zinc oxide (ZnO) and titanium dioxide (TiO2), are selected to form more sustainable photocatalysts with high chemical stability. This involves the combination of both TiO2 and ZnO in a two-step simple synthesis method. It appears advantageous to exploit the conformal deposition of atomic layer deposition (ALD) to achieve nanometer-thick TiO2 coating on ZnO nanowires (NWs) with a high aspect ratio, which are firmly anchored to a substrate and exhibit a large specific surface area. The high chemical stability of the ALD TiO2 coating has been investigated in detail and proven to be effective under both strong acid and strong alkaline aqueous solutions. In addition, photocatalysis experiments with organic dyes show that via this simple two-step synthesis method, the produced ZnO/TiO2 tandem does indeed exhibit improved chemical stability in a harsh environment, while allowing efficient photodegradation.

Experimental Study on the Structural Features and Corrosion Characteristics of Dolomite and Limestone in the Karst Stone Mountainous Areas in Northern Guangxi

Taking dolomite and limestone in Guilin and Liuzhou regions in the north of Guangxi Province as research objects, this paper analyzed their mineral composition and chemical composition, and then carried out the chemical corrosion test, the corrosion test under the chemical-temperature actions, and the corrosion test under the action of vibration load, respectively. The results showed that: (i) the dolomite in northern Guangxi mainly has fine crystalline texture and massive structure with low content of acid insoluble matters, while limestone mainly has powder crystalline texture and massive structure with high content of acid insoluble matters, and the purity of both dolomite and limestone are very high; (ii) the difference of corrosion between dolomite and limestone mainly depends on the ratio of CaO/MgO in their chemical composition, and the content of silica and acid insoluble matters; (iii) the corrosion rates of the pure dolomite and the pure limestone are basically the same under the same external conditions; (iv) temperature and vibration load have relatively large influence on the corrosion rates of dolomite and limestone, and the corrosion rates of dolomite and limestone increase with the increase of temperature, but the influence of vibration load on the corrosion rate is more significant than temperature. This research can provide theoretical basis and technical support for large-scale engineering construction and prevention of karst geologic disasters in karst stone mountainous areas in the northern Guangxi. Keywords: dolomite and limestone; structural features; corrosion characteristics; northern Guangxi

Numerical simulation analysis of tunnel construction mechanical response considering shotcrete hardening process

At present, tunnel construction mechanics studies basically do not consider the hardening process of shotcrete. In order to reveal the hardening process of sprayed concrete in a sulfate environment and the influence of sulfate corrosion on tunnel stability, the model parameters were determined in combination with the change rules of mechanical parameters of shotcrete obtained in the author’s experiment. The MIDAS GTSNX finite element software was used to analyze the effect of the hardening process of the shotcrete, chemical corrosion, and physical corrosion of sulfate on the displacement and stress of the surrounding rock of the tunnel. The results show that considering the hardening process of shotcrete, the growth rate of tunnel clearance displacement increases, and the stress increase slows in the early stage of shotcrete (The tunnel lining structure is applied, and the second step of excavation is carried out). With the increase of time or the construction steps, the stress of shotcrete increases significantly, and the clearance displacement growth rate significantly decreased. The influence of the chemical and physical corrosion of shotcrete on the stress and displacement of the surrounding rock of the tunnel is similar to considering the hardening process of shotcrete. indicating that sulfate corrosion has an inhibitory effect on the hardening process of shotcrete and increased construction risk.