Corrosion Resistance Coefficient Research Articles

Dry–Wet Cyclic Sulfate Attack Mechanism of High-Volume Fly Ash Self-Compacting Concrete

High-volume fly ash replacing cement helps to improve the fluidity, volume stability, durability, and economy of self-compacting concrete (SCC). Sulfate attack is the most common form of the durability damage of hydraulic concrete; in particular, the performance degradation at the water level change position is more significant. Therefore, research on the influence effect and mechanism of fly ash on the durability is of great significance. In this paper, the change regularity of the SCC physical and mechanical properties with the fly ash replacement percentage and dry–wet cycles were studied by 60 dry–wet cycles of sulfate attack test. The 6 h electric flux, MIP, and SEM were used to study the performance degradation mechanism of SCC cured for 56 days, which had also been attacked by sulfate. The results show that the physical and mechanical properties of SCC increased first and then decreased with the dry–wet cycles of sulfate attack. After 10–15 cycles, the corresponding properties increased slightly, and then decreased gradually. When the fly ash content was 40%, the corrosion resistance coefficient, relative dynamic elastic modulus, and flexural strength retention were higher than those of the control specimen. However, when the fly ash content was 50%, they were close to the control and deteriorated obviously with the further addition of fly ash. For pore sizes in the range of 120–1000 nm, the porosity of SCC cured for 56 days was inversely proportional to the 6 h electric flux and the retention of mechanical properties, indicating that the porosity of the large pores is the decisive factor affecting the chloride ion permeability and corrosion resistance. The incorporation of fly ash in SCC can change the sulfate attack products and destruction mechanism. The sulfate attack damage of SCC with 40% of fly ash and the control specimen was dominated by ettringite crystallization and expansion, while those with a fly ash content of 50% and 60% had no obvious corrosion products, and the microstructures became looser. The appropriate fly ash replacement percentage could significantly improve the corrosion resistance of SCC.

Моделирование характеристик износа при скольжении композиционного материала на основе политетрафторэтилена (ПТФЭ), армированного углеродным волокном, в паре трения с SS304 (12Х18Н10Т)

Introduction. Over the last decade, composite materials based on polytetrafluoroethylene (PTFE) have been increasingly used as alternative materials for automotive applications. PTFE is characterized by a low coefficient of friction, hardness and corrosion resistance. However, this material has a high wear rate. A group of researchers attempted to improve the wear resistance of PTFE material by reinforcing it with different fillers. The purpose of the work: This study experimentally investigates the dry sliding wear characteristics of a PTFE composite reinforced with carbon fiber (35 wt.%) compared to SS304 stainless steel. In addition, experimental mathematical and ANN models are developed to predict the specific wear rate, taking into account the influence of pressure, sliding speed, and interface temperature. The methods of investigation. Dry sliding experiments were performed on a pin-on-disk wear testing machine with varying the normal load on the pin, disk rotation, and interface temperature. Experiments were planned systematically to investigate the effect of input parameters on specific wear rates with a wide range of design space. In total, fifteen experiments were carried out at a 5-kilometer distance without repeating the central run experiment. Sliding velocities were obtained by selecting the track diameter on the disk and corresponding rotation of the disk. A feedforward back-propagation machine learning algorithm was used to the ANN model. Results and Discussion. This study finds better prediction accuracy with the ANN architecture having two hidden layers with 150 neurons on each layer. This study finds an increase in specific wear rates with normal load, sliding velocity, and interface temperature. However, the increase is more prominent at higher process parameters. The normal load followed by sliding velocity most significantly affects the specific wear rate. The results predicted by the developed models for specific wear rates are in good agreement with the experimental values with an average error close to 10%. This shows that the model could be reliably used to obtain the wear rate of PTFE composite reinforced with carbon fiber (35 wt.%) compared to SS304 stainless steel. This study finds scope for further studies considering the effect of varying ANN architectures, different amount of neurons, and hidden layers on the prediction accuracy of the wear rate.

Ultra-high strength ZrTiAl alloy fabricated by laser metal deposition and subsequent heat treatment

Because of the excellent properties of radiation resistance, corrosion resistance and low thermal expansion coefficient, Zirconium (Zr) based alloys have became one of the most potential new structural materials in the field of aeronautics and astronautics. In recent years, many new Zr based alloys have been developed. However, the “Banana-type” strength-plasticity inversion relation is still hard to breakthrough. According to the extreme non-equilibrium dynamic conditions of laser metal deposition (LMD) and the idea of nano-coherent phase strengthening and toughening, in this paper, ultra-high strength ZrTiAl alloy with good elongation has been fabricated by LMD and subsequent heat treatment. The combination of micrometer-scale hexagonal close-packed (HCP) α matrix phase and nano-coherent D019-(TiZr)3Al precipitated phase exhibits excellent comprehensive mechanical properties with ultra-high strength (1620 MPa) and good elongation (11%). In addition, the microstructure evolution, the phase transformation, and the mechanism of deformation have also been discussed.

Sulphate resistance of silane coupling agent reinforced metakaolin geopolymer composites

Sulphate resistance is an important index for evaluating geopolymer durability. This study investigates the beneficial effects of silane coupling agent (SCA) addition on the sulphate corrosion resistance of metakaolin-based geopolymer composites via strength tests and various characterisation techniques such as XRD, FTIR, SEM-EDS, and 29Si NMR. The results show that the compressive and tensile strengths and corrosion resistance coefficient of the geopolymer first increased, then decreased with increasing SCA dosages. The geopolymer incorporated with the optimum dosage of 0.1 wt% SCA exhibits the highest strengths, fluidity, and sulphate resistance coefficient. SCA addition effectively compacts the pore structure, thus making it difficult for SO42− to invade the matrix. The SEM-EDS diagram reveals that before and after sulphate attack, the Na content of the pure geopolymer decreased from 7.37 wt% to 3.84 wt%, and the mass ratio decreased by 47%. However, the Na content of the geopolymer composite modified with SCA decreased from 5.64 wt% to 4.85 wt%, and the mass ratio only decreased by 14%, indicating that the addition of SCA reduced the Na precipitation rate of the geopolymer in the sulphate environment. The 29Si NMR spectrum also reveals that the addition of SCA inhibits the resonance peak shift from Q4 to Q3 after 56 d of sulphate attack, which indicates improvement in the stability of the three-dimensional network structure in the geopolymer.

STUDY OF ACID RESISTANCE OF HYBRID ALKALI ACTIVATED NORMAL HARDENING CEMENTS

One of the reason of loses of main production sources nowadays for chemical, food and special industries is the degradation of equipment and constructions caused by acid corrosion. Traditional materials are characterized by various disadvantages, among them: high costs of the material, low water resistance, hard technology and danger for the personal.
 One of the ways to obtain acid resistant material is the use of alkali activated cements, which are known are the resistant to the aggressive environments. Increasing of acid resistance is possible by reducing of system basicity level.
 The presented studies have proved the possibility to obtain acid resistant materials, able to be hardening in normal condition, so far as possibility to partial replacement of the conditional alumina silicates by alumina silicates with technogenic origin, namely, red mud from alumina production under Bayer process. Reducing of basicity level make it possible to increase corrosion resistance coefficient up to 0.88. Also thus a way material became more ecologically friendly and lowering the cost of material.

МОДИФІКОВАНІ СУЛЬФАТОСТІЙКІ ПОРТЛАНДЦЕМЕНТИ З ДОБАВКОЮ ЦЕОЛІТУ

The article shows that one of the ways to increase the sulfate resistance of cements is to use as an additive of pozzolanic action based on highly dispersed zeolite, which increases the corrosion resistance of concrete. Physical-chemical properties of zeolite tuff as a mineral constituent of Portland cements with the addition of pozzolana are presented. The use of modern grinding technology by separate grinding of Portland cement clinker and natural zeolite in mills with separators of the latest generation allows to obtain high quality Portland cement with zeolite CEM II/A-P 42.5 R PJSC "Ivano-Frankivsk Cement", characterized by high early strength. It is shown that the replacement of the clinker component with zeolite leads to a decrease the content of clinker minerals C3S and C3A in cements, which significantly limit the corrosion resistance of cement stone. Highly dispersed zeolite is characterized by increased pozzolanic activity (after 28 days, the absorption of Ca(OH)2 is 200-250 mg/g). Due to pozzolanic reaction with the formation of C-S-H-phases, the content of calcium hydroxide in the paste based on CEM II/A-P 42.5 R is reduced by 2 times compared to Portland cement CEM I 42.5 R. Decrease in the concentration of Ca(OH)2 in cement pastes eliminates the possibility of the formation of a significant amount of ettringite, which causes sulfate corrosion of cement stone. It was found that during the hardening of Portland cement CEM II/A-P 42.5 R under the influence of sulfate and magnesium media, the coefficient of corrosion resistance Ks after 56 days is 1.16 and 0.98, respectively, while for samples based on Portland cement CEM I 42.5 R Ks decreases by 1.2-1.3 times. The results of researches of influence of aggressive environments on corrosion resistance of Portland cement with the increased content of zeolite type CEM ІІ/В-Р 42.5 are resulted. For Portland cement CEM ІІ/В-Р 42.5 the coefficient of corrosion resistance in the conditions of sulphate environment Кс90 = 1.47. Portland cements with zeolite strength class 42.5, modified with superplasticizers of polycarboxylate type, are characterized by high sulfate resistance and should be used for the manufacture of concrete classes C25/30...C50/60 for construction of dams, hydraulic structures, sewers storage of waste from livestock farms, etc. Modified rapid-hardening Portland cements with the zeolite additive provide technical, environmental and economic effects in the manufacture of concrete and reinforced concretes of hydraulic structures.

Research on the sulfate resistance of cement-based materials incorporating dolomite powder

The effects of dolomite powder on the sulfate resistance of cement-based materials with water-binder ratio (w/b) of 0.55 and 0.36 were investigated in this manuscript. Scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and pressure testing machine were used to determine the apparent morphology, micro-morphology, mass increase rate, flexural strength and compressive strength of cement-based materials containing dolomite powder. The sulfate resistance of mortars was improved with increasing dolomite powder dosage. Generally, the flexural strength and compressive strength of mortars in Na2SO4 solution were higher than those in water. Within 150 days of immersion, the corrosion resistance coefficient and compressive corrosion resistance coefficient of mortars increased with increasing dolomite powder dosage. The pore structure of cement-based materials became more compact with the addition of dolomite powder. Accordingly, the sulfate resistance was improved by controlling the dynamics stage due to the fact that the pore structure of cement-based materials was refined with the addition of dolomite powder. The 150-day compressive corrosion resistance coefficients of mortars with a w/b of 0.55 in the case of dolomite powder at 0 and 30 wt% replacement levels were less than 1, suggesting that long-term immersion in sulfate solution increased the deterioration rate of cement-based materials.

Manufacturing of Ceramic Reinforced Metal Matrix Composites (Al/Sicp) And Their Characterization Through Powder Metallurgy Methods

Metal Matrix Composites is two or more combination material with aluminum metal as matrix and devolved to fix metal act, strength, high temperature stability and hardness. Metal matrix composites have been developed so many because it has low density, corrosion proof, cheap and easy fabrication. Powder metallurgy technique is one of metal matrix composites fabrication process in solid state that is still developed because more economic, doesn't need difficult equipment. Aluminum that use in this research is Al alloy type 2124. Metal matrix composites fabrication process with powder metallurgy method using wet mixing with pure ethanol, cold compaction 300 MPa and inert gas atmospheric using Nitrogen gas (N2) at sintering process. Variation of sinter temperature that used is 450, 500, 550, and 600 oC with highly temperature average 5 oC/min and holding time for 1 hour and with speed flow Nitrogen gas (N2) 5 lt/min with pressure 1000 kgf/cm2. From research result can be concluded the mechanical properties and physical properties from metal matrix composites reinforced ceramics Al/SiCp increase with sinter temperature highly and with reinforcement particle addition SiC can increase mechanical properties and physical properties such as: hardness, wear resistance, coefficient of thermal expansion and corrosion resistance. From microstructure analysis, particle Sic distributed homogeneously at test specimen based on SEM analysis, and structure crystal analysis test result XRD show that dominant phase appear is Al, and Sic.

Experimental research on saline soil erosion resistance of magnesium phosphate cement pastes

The durability of concrete structures is affected by dry-wet and freeze–thaw cycling, and erosion by saline soils, such as those common to western China. In this study, the anti-erosion properties of magnesium phosphate cement paste (MPC) in salinized soil were investigated. The influences of the magnesium-to-phosphorus ratio (M/P), water-to-cement ratio (W/C), borax-to-magnesium ratio (B/M) and fly ash admixtures were studied in MPC specimens subjected to dry-wet cycle tests in water and saline solutions, with naturally cured specimens used as controls. The compressive strength of MPC was analysed by range analysis, analysis of variance and factor index analysis under various numbers of dry-wet cycles. Mass losses were quantified, morphologies were observed, and X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TG-DSC) were used to assess MPC before and after erosion. It was found that M/P and B/M were the major influences on the compressive strength of MPC. In MPC under natural curing, M/P was a strong influence on strength, while in MPC in water and saline solution, B/M was more important. The MPC slurry was most resistant to saline soil erosion with a 20% fly ash admixture, M/P = 2.5, borax admixture = 0.09 and water-cement ratio = 0.17. After dry-wet cycling, the MPC’s mass in water gradually decreased while that in saline solution gradually increased. With 40% fly ash, the compressive strength corrosion resistance coefficient of MPC placed in saline solution for 180 dry-wet cycles was 78.28%, indicating that a moderate amount of fly ash can enhance the saline soil anti-erosion performance of MPC. According to TG-DSC and XRD analyses, when MPC was subject to dry-wet cycling in water, the content of MgKPO4·6H2O(MKP) was the highest. The content was lower under natural curing and lowest in the saline solution. According to SEM, the degree of hydration of MPC was higher under dry-wet cycling than under natural curing, but the crystal structure of MKP was loosely arranged, which reduced the strength of the MPC.

Spark Plasma Sintering of Copper-Niobium-Graphite Composites, and the Investigations of Their Microstructure and Properties

The microstructures and properties of ternary copper-niobium-graphite (Cu-Nb(nano)10-C4, and Cu-Nb(micron)10-C4) composites produced via spark plasma sintering (SPS) technique have been investigated for their potential use as electrical connection materials at high-temperature application. Nowadays, there is much activity in the development of such material all over the world. This study was aimed to compare the effect of adding the nano and micron particles sizes of Nb powders in the microstructures and properties of Cu-Nb-C composites sintered at 700 and 650 °C temperatures. The investigated materials have been produced via the SPS method. The microstructures were observed by electron microscopy technique, the wear test was observed by Anton-Paar TRB3 tribometer, thermal diffusivity was observed by LFA427 NETzschlaser flash device within the temperature of 100–900 °C, and the corrosion test was performed by potentiodynamic polarization. The discoveries have been presented in the manuscript and were discussed with reference to the microstructure development, the composite with nanoparticles sintered at 650 °C displayed closed thermal stabilities as temperature increased, and it recorded a low coefficient of friction and suitable corrosion resistance, which correspond to requirements for electrical contacting materials. The SPS method of production of the composites caused initial microstructure refinement and improved the properties of the composites.

Durability and life prediction of fly ash geopolymer concrete in corrosion environments caused by dry and wet circulation.

The use of tailings, waste rock, fly ash, and slag to prepare geopolymer concrete can effectively solve the problems of land resources occupied by tailings and waste rock, low utilization rate, and environmental pollution. Using a dry-wet circulation method, fly ash for a different corrosion solution to geopolymer concrete (referred to as TWGPC) was analyzed. Through an appearance change, the corrosion resistance coefficient of the compressive strength, relative dynamic elastic modulus, tensile splitting strength, relative mass, and durability were investigated, using scanning electron microscopy (SEM) analysis of the microstructure, The life of TWGPC was predicted based on the GM(1,1) prediction model of grey system theory. The test results show that with an increase in the number of dry-wet cycles, the surface of the specimen crystallizes, cracks, spalls, and exhibits other phenomena. The compressive strength corrosion coefficient, relative dynamic elastic modulus, crack tensile strength, and relative mass show a trend of increasing first and then decreasing, finally reaching the peak value after 40 cycles. The erosion products generated by the early reaction fill the slurry aggregate pores and improve the strength of TWGPC. In a later stage, a large number of erosion products absorb water and expand; the internal pores of TWGPC are connected, leading to a decrease in strength. Cl- inhibits the corrosion of SO42- in concrete and improves the durability of concrete.

Properties evolution of calcium sulfoaluminate cement blended with ground granulated blast furnace slag suffered from sulfate attack

In this work, sulfate resistance of calcium sulfoaluminate cement (CSAC) blended with ground granulated blast furnace slag (GGBFS) was studied. The mass change, compressive strength, corrosion resistance coefficient, relative dynamic elastic modulus and deformation of CSAC-GGBFS mortars exposed to 5% Na2SO4 solution for different time were monitored. At the same time, the mineral phases, pore structure and microstructure of hardened cement pastes after sulfate attack were determined using X-ray diffraction (XRD), thermal analysis, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Results showed that the relative dynamic elastic modulus and compressive strength of the CSAC-GGBFS mortars increased continuously when the specimens were immersed in 5% Na2SO4 solution; besides, after 360 days of exposure, the compressive strength was 12% higher than the specimens cured in water. Meanwhile, the specimens displayed good dimensional stability after sulfate attack. What's more, no new mineral phases were found for the CSAC-GGBFS mixtures suffered from sulfate attack for 360 days, while the amount of AFt and C–S–H gels increased and the total porosity reduced. The CSAC-GGBFS mixtures showed excellent resistance to sulfate attack and can be applied in high sulfate environment.

Experimental Study on Durability and Mechanical Properties of High Ductile Concrete under Long-Term Sulfate Attack

Uniaxial compression on high ductile concrete after erosion by different concentrations of sulfate solutions was conducted. The compressive strength, mass change fraction, corrosion resistance coefficient and other parameters on the basic mechanical properties of high ductile concrete is studied. The erosion form and uniaxial compression failure characteristics of the samples was analyzed. And using scanning electron microscope to observe the microscopic morphology of the samples, it is found that sulfate and age accelerate the damage to high ductile concrete, with its damage mechanism revealed. The test results are as follows: with the increase of age, the compressive strength and quality of high ductile concrete in 5%, 10% and saturated sulfate solution will increase first and then decrease; the mass change fraction of high ductile concrete is greater than that of ordinary concrete, it has the characteristics of self-compacting before the erosion age of 270 days, Then, as the sulfate solution concentration increases, the damage of the high ductile concrete becomes more serious. The comparison test with ordinary concrete shows that high ductile concrete has higher resistance to sulfate attack. This research can provide experimental basis for the application of high ductile concrete in engineering under sulfate corrosion environment.

Evaluation of the wear and corrosion resistance of coated parallel gate valve

This paper aims to experimentally evaluate the wear and corrosion resistance of the coated active parts surfaces of a cut off valve. This paper presents the electrochemical corrosion, hardness and wear tests of the gate valve coated surfaces with a plastic material, in order to evaluate the seat and gate valve couple behaviour in an aggressive medium containing crude oil with sand particles. Uncoated and coated surfaces were compared and evaluated by the coefficient of friction, wear rates and corrosion resistance. A comparison process between the previous results of the CFD analysis for erosion wear and the test results, at the covered gate valve, is also presented. Keywords: gate valve, solid lubricant, coefficient of friction, corrosion resistance, wear resistance.

An Investigation on the Mechanical Properties of Aluminium 6061 Alloy Reinforced with Boron Carbide and Silicon Carbide

Abstract: Aluminium alloys are widely utilised in the aerospace and automobile industries due to their low density and strong mechanical qualities, as well as their superior corrosion and wear resistance and low thermal coefficient of expansion as compared to traditional metals and alloys. These material’s superior mechanical qualities and inexpensive production costs make them an appealing alternative for a wide range of scientific and technical applications. In this study, we strive to present a literature review on the overall performance of reinforced composites created by the stir casting method, as well as the effect of process factors on the properties of Aluminium-based MMC. The literature review framework in this paper provides a clear overview that the process parameters play important role for optimum properties of Aluminium based Metal Matrix Composites. As reinforcing elements in Metal Matrix Composites, Boron Carbide and Silicon Carbide play an important role. The MMCs were successfully produced using the liquid metallurgy process. Scanning electron microscopy was used to examine the morphology and microstructure of Al-B4C and Al-SiC composites. The addition of 2, 4 and 6 wt% B4C and SiC particles increased several mechanical parameters such as ultimate tensile strength and hardness. It was also discovered that the mechanical behaviour of B4C particulates AMC is superior to that of SiC particulates AMC. Keywords: Aluminum, Metal matrix composite, SiC, B4C, Tensile test, Hardness test and SEM Analysis.

Corrosion-resistant facing material with of mineral binders and assets modified by sulfur melt

The paper considers the issues of obtaining a composite material based on gypsumbinder and sulfur with high performance. Technological factorsinfluencing the hardening coefficient, water resistance and chemical resistance of gypsum products impregnated in sulfur melt have beenstudied. The regularities of impregnation of gypsum matrix with sulfur melt are established takinginto account the capillary-porous structure of gypsum stone and physical and technical properties ofsulfur. The regularities of impregnation of gypsum matrix with sulfur melt are established taking intoaccount the capillary-porous structure of gypsum stone and physical and technical properties ofsulfur. Research and consideration of mass transfer indicators during impregnation of gypsumconcrete products with sulfur melt allowed to optimize the technology. Thus, by the method ofcapillary impregnation on the original laboratory installation, the mass transfer coefficients forsulfur were measured. As a result of these studies, the dependences of the mass transfer coefficienton the temperature of the sulfur melt, the rate of heating of the melt, the concentration of the fillerand the water-solid ratio were obtained. Products made of composite material based on gypsum andsulfur have the following construction and technical characteristics: compressive strength, not lessthan 30.0 MPa; flexural strength, not less than 6.0 MPa; water resistance coefficient, not less than0.7; coefficient of corrosion resistance, not less than 0.7; wear resistance, no more than 0.3 g / cm2 .Analysis of the main construction and technical characteristics of the composite material based ongypsum and sulfur shows that the resulting composite has high strength, water and corrosionresistance to various aggressive environments. Facing tiles made of this material have highperformance characteristics and should be used in the lining of buildings of railway infrastructure,drainage systems, fertilizer storage, floors and walls of the chemical and food industries.

Durability of a novel effective microfine cementitious grouting material in corrosion environments

High durability requirements of grouting materials have been proposed gradually in corrosion environments. To evaluate and improve durability of grouting material, ordinary Portland cement (OPC), microfine Portland cement (MC), microfine sulphoaluminate cement (MSAC), and newly developed effective microfine cement-based grout (EMCG) were selected. Early impermeability, flexural strength (FS), unconfined compressive strength (UCS), corrosion resistance coefficient (KFS and KUCS), volumetric and mass variations, characteristics of fracture surface, corrosion mineral, microstructure and pore size distribution are studied synergistically. The water-binder ratios (W/Bs) of OPC and microfine grouts are 1.0 and 1.0–1.5. The concentrations of sodium sulfate and sodium chloride corrosion solutions are 0.3%, 5% and 10%. Corrosion ages are 3d, 7d, 28d, 91d, 181d and 360d. The 3d or 7d impermeable pressure of EMCG exceeds 1.0 MPa. The anti-corrosion strength and durability of EMCG under the W/B of 1.5 are acceptable. KFS and KUCS of MC and OPC are low. Although KFS and KUCS of MSAC are over 1.0, its strength needs to be enhanced further. The KFS, KUCS and actual strength of EMCG are satisfied. The corrosion expansion rate of EMCG is the lowest (no more than 0.058%), and its effectiveness of hydration and anti-corrosion is the optimal. The EMCG’s interconnection degrees among gels are the highest, its number of holes is the minimum and its pore structure is satisfactory. The EMCG satisfies demands of high durability in corrosion environments in underground, hydraulic, civil and ocean engineering.

Towards potential applications of cement-polymer composites based on recycled polystyrene foam wastes on construction fields: Impact of exposure to water ecologies

Cement-polymer composites were developed to enhance the mechanical durability and reduce the porosity of cement, and to acquire a value-added end product useful for many applications in the construction sector. The novel product should be stable during exposure to various challenging environments, e.g., water of different quality, origin, and dissolved ions. The present work evaluated the impact of immersing the new cement-polymer composites (CPs), containing different fractions of recycled waste polystyrene foam, in plain, ground and sea water on the composites’ properties. After 420 days of immersion in all studied types of water, the obtained CPs showed acceptable compressive strength values (more than 30 MPa); in addition, corrosion resistance coefficients (K) were increased more than unity in comparison to non-immersed samples. Moreover, this study also determined alterations of internal architecture of composite specimens cured for 28 days after immersion for up to 420 days in water of different composition. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for these studies.

Effect of Surface Treatment of Polypropylene (PP) Fiber on the Sulfate Corrosion Resistance of Cement Mortar

Sulfate erosion is one of the most complex and harmful chemical corrosion actions. Following sulfate erosion, concrete expands, cracks, dissolves, peels off, and decreases in strength, which affects the durability of structures. Polypropylene fiber (PP) is widely used in various concrete structures because of its good mechanical properties and chemical corrosion resistance. However, PP fiber has a number of shortcomings, such as a smooth surface, poor hydrophilicity, lack of active groups in the molecular chain, and agglomeration and poor dispersion in cement-based materials. These issues limit its application in cement-based materials. Although the use of a silane coupling agent to modify the surface of PP fiber is effective, the influence of treated PP fiber on the sulfate resistance of cement-based materials is not significant. In this study, a PP fiber treated with a silane coupling agent was used to examine effects of different cement-to-sand ratios (C/S) and dosages of the treated PP fiber on the sulfate erosion resistance of cement mortar. Furthermore, the apparent morphology, mass loss rate, flexural strength, corrosion resistance coefficient, and microstructure of the concrete were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results revealed that the PP fiber became rough after modification. Active groups were introduced on the fiber surface, which were well dispersed in the mortar and formed a good network distribution structure in the cement mortar, thereby slowing the erosion rate of the PP fiber mortar in a sodium sulfate solution. At a C/S ratio of 1:1 and a treated fiber dosage of 0.6%, the treated fiber mortar has exhibited good sulfate resistance. In addition, the monofilament fiber immersion test revealed that a layer of sodium sulfate crystals was deposited on the fiber surface, thereby increasing the roughness of the fiber surface and the pull-out force of the fiber from the cement matrix, this result indicated that the interfacial adhesion between the treated PP fiber and cement matrix was improved, which in turn led to the improvement in the sulfate erosion resistance of the treated PP fiber.

Study on Properties of Mg-Al Spinel Ceramics Prepared by Casting Sintering Method

Magnesium alumina spinel (MgAl2O4) is a composite mineral composed of MgO and Al2O3, and its theoretical chemical composition is 28.33 wt% MgO and 71.67 wt% Al2O3, with excellent properties such as high melting point, high hardness, high strength, high resistivity, wide energy band gap, low coefficient of thermal expansion, corrosion resistance and thermal shock. In the process of synthesizing magnesia-alumina spinel ceramics, it is important to select suitable sintering temperature, suitable holding time, suitable kinds of mineralizers and suitable amount of mineralizers in order to improve the strength and toughness of magnesia-alumina spinel ceramics and reduce the water absorption of magnesia-alumina spinel ceramics. In this study, using fused magnesia powder and alumina powder as main raw materials, sodium hexametaphosphate as water reducer, silica powder as binder and titanium dioxide powder as mineralizer, magnesia-alumina spinel ceramics were synthesized by casting and sintering. The effects of sintering temperature and holding time on the properties of magnesia-alumina spinel ceramics were studied. The most suitable sintering temperature is about 1600 °C and the most suitable holding time is about 4 h. Titanium dioxide powder was selected as mineralizer, and the effect of adding titanium dioxide powder on the properties of synthesized magnesia-alumina spinel ceramics was studied. The experimental results show that the addition of titanium dioxide powder can improve the bending strength and reduce the water absorption of the synthesized magnesia-alumina spinel ceramics. When the addition of titanium dioxide powder increased to 7%, the bending strength of magnesia-alumina spinel ceramics increased to 33 MPa, and the water absorption decreased to 2.8%. SEM analysis shows that the addition of titanium dioxide powder can promote the formation of magnesia-alumina spinel phase, refine the grain size of magnesia-alumina spinel and strengthen the microstructure of magnesia-alumina spinel ceramics.