Bauxite Aggregate Research Articles

Effect of Steel Fibers on the Properties of Refractory Free Cement Concrete

Free cement refractory concrete is a type of refractory concrete with replacing alumina cement by bonding materials such as white kaolin, red kaolin and fumed silica. The free cement refractory concrete used in many applications like Petrochemicals, iron furnaces and cement production industries. The research clarifies the effect of steel fibers with two types crimped steel fibers and hooked steel fibers with percentages 0.5%, 1% and 1.5% by volume from weight of bauxite aggregates. The additions of steel fibers with two types gave good properties in high temperatures where the specimens keep the dimension without failure and the properties made the best. the percentage of increasing for thermal conductivity was 44% for 1.5% crimped fibers and 42.8% for 1.5% hooked end fibers and the percentage increasing in bulk density of free cement refractory concrete was 30% for 1.5% crimped fibers and 27% for 15% hooked end fibers . From this study can be concluded that the best types of steel fibers which used in free cement refractory concrete is the crimped type with percentage 1.5%.

Using bauxite as alternative for coarse aggregate in asphalt mixture: Improving skid resistance

The depletion of natural resources promotes to search for alternative of virgin pavement materials with the aim of ensuring the performance of pavement especially skid resistance, which is often linked to financial and health services of the country. To solve the issues, the paper attempts to employ bauxite as alternative for coarse aggregate of surface layer to improve skid resistance. To this end, the performance of calcined bauxite aggregate was characterized on the basis of some laboratory tests. Thereafter, radar chart method was used to evaluate the comprehensive skid resistance of different aggregates, followed by preparing asphalt mixture based on optimization results. Currently, the skid resistance of asphalt mixture composed of different aggregate was examined by the three-wheel polishing device (TWPD) combined with dynamic friction tester (DFT). After the process, the multiple linear regression model was performed considering the morphological, mineral and chemical characteristics of aggregate with the aim of predicting the long-term skid resistance. As for physical and mechanical properties, the different grades of calcined bauxites show an increase about 20%∼200% compared with limestone. From the radar chart method, it was observed that calcined bauxite, especially 88# calcined bauxite, was found to exist highest comprehensive skid resistance. It is obvious that the model involving mineral and chemical properties is able to exist higher accuracy, adjusted R2 having values even exceed 0.9. In addition, it was found that the cost-benefit of 88# calcined bauxite and 75# calcined bauxite were 22.82 and 12.70 respectively. Herein, the study allows us a feasible approach to ensure the demand of pavement and mitigate the challenge for environment.

Laboratory evaluation of microwave heating and skid resistance of pavement friction surfacing using calcined bauxite and magnetite aggregates

A high friction surface treatment (HFST) with magnetite (MT) aggregates instead of conventional calcined bauxite (CB) aggregates as microwave absorbers were prepared in this paper. The deicing properties by microwave heating and long-term skid resistance of HFST with different proportions of CB and MT aggregate were evaluated. The deicing properties by microwave heating of HFST were determined by electromagnetic characteristics, heating surface temperature, and microwave deicing time (MDT) tests. The long-term skid resistance of the HFST was characterized by conducting dynamic friction coefficient and mean profile depth (MPD) tests after long-term polishing using a three-wheel polishing device. The results showed that the electromagnetic characteristics of HFST were enhanced greatly by the addition of MT. The microwave heating efficiency of HFST was enhanced by the increase of MT substitution rate, which further enhanced its microwave deicing efficiency. The microwave deicing efficiency of HFST with MT substitution rate of 25% was 1.4 times that of HFST with MT substitution rate of 0%. Long-term skid resistance of HFST was reduced by the addition of MT, however, HFST with MT substitution rate of 25% also maintained a terminal μ40 and μ60 above 0.7, which can provide higher friction comparable with other high friction aggregate such as taconite, basalt, emery and flint. To improve the deicing properties by microwave heating and maintain high skid resistance, 25% MT replacement rate in HFST is recommended.

Engineering high-performance cementitious matrices for improved projectile impact resistance with silane, micro fibrillated cellulose and fine calcined bauxite aggregate

This experimental study evaluated the effectiveness of passive and active strategies in improving the projectile impact resistance of cementitious matrices. The principle of the passive approach is to reinforce the matrix by substituting weak Van de Waal's forces between hydration products with covalent bonds which have the orders of magnitude higher dissociation energy. A silane coupling agent (SCA) and micro fibrillated cellulose (MFC) were selected as the vehicles to engineering the bond scheme at the molecular scale by forming a covalently linked organic-inorganic hybrid. The mechanism of the active strategy is to aggravate damage to the projectile and thus leave less energy available for the penetration process. This is achieved by incorporating exceptionally hard calcined bauxite aggregates (CBA). Impact tests were conducted utilizing 8-mm-diameter conical-nosed steel projectiles at a designed velocity of 650 m/s. Damage was quantified by the depth of penetration (DOP) and equivalent crater diameter (ECD). Results indicated that the SCA and MFC modified matrices resulted in a 30% and 20% reduction in DOP, respectively. The crack intensity was decreased tremendously or even absent for the SCA and MFC modified matrices compared with the prominent cracks of the control radiated from the cratering region. Matrices incorporating fine CBA or siliceous aggregates led to a 55% and 38% smaller DOP, respectively. Crushing of aggregates and appreciable deformation, severe scratches, and significant mass loss of retrieved projectiles were observed. Matrices including fine CBA or siliceous aggregate maintained excellent integrity and drastically less severe cracking on the impact surface as well as the interior region compared with the control.

Restrained shrinkage behavior of internally-cured UHPC using calcined bauxite aggregate in the ring test and UHPC-concrete composite slab

Ultra-high performance concrete (UHPC) can be a good candidate for bridge deck overlay or repair materials of structural members due to its superior mechanical properties or durability. However, large autogenous shrinkage characterized by UHPC may be an obstacle to extending its applications. A novel internal curing (IC) agent, calcined bauxite (CB) aggregate, has been developed to effectively reduce the autogenous shrinkage of UHPC and meantime enhance its mechanical properties. This study further examines its efficiencies in solving shrinkage issues by restrained ring test and large-scale UHPC-concrete composite slabs. In restrained ring tests, when both no fibers, the IC UHPC matrix with CB aggregate shows smaller crack width (0.25 versus 1.0 mm at 9 d) and delayed (5.2 d versus 3.6 d) onset of cracking than the normal UHPC matrix; when having fibers, the normal UHPC shows micro-cracking while no cracking was detected in IC UHPC even observed at one year. Normal UHPC overlay shows more serious delamination and curling than the IC UHPC overlay, and it also shows a hairline crack on the side surface at midspan. Early-age exposure to drying at 1 d has a detrimental effect by exhibiting the most severe delamination and curling of the UHPC overlay, and reinforcement in UHPC layer is effective in reducing its shrinkage strain.

Post-mortem analysis of MgO–Al2O3–C bricks containing bauxite used in steel ladle walls

A serious problem with integrated masonry linings ladle was that the ladle wall bricks were difficult to be partially replaced. Thus, the service life of the ladle was determined by the properties of ladle wall bricks. In this study, the new generation of MgO–Al2O3–C bricks with bauxite aggregates was tested in a ladle lining of an integrated steel ladle for 103 cycles, and the corroded microstructure of the used brick was investigated. A multilayered structure of bauxite aggregates could be observed in the used brick, which inhibited the slag penetration along the boundary of the magnesia aggregates and reduced the degree of the aggregates fall off from the used bricks. Besides, during the process of slag penetration, bauxite aggregates could melt into the slag, which increased the viscosity of the slag and weakened the penetration ability of the slag. The MgO–Al2O3–C bricks with bauxite addition could improve the service life of the ladle to a certain extent.

Fracture behavior of lightweight mullite-SiC refractories with porous aggregates coated with glass ceramic

Owing to the periodic mechanical stresses frequently suffered by refractories applied in cement rotary kilns, the study of fracture behavior is particularly significant for long life, safety, and reliable operation. In this work, bauxite aggregates and lightweight mullite aggregates with and without glass ceramic coatings were utilized in mullite-SiC refractories, and the fracture properties of the refractories were investigated and compared using the Brazilian test, digital image correlation technology, crack propagation path analysis, etc. The results show that the application of a glass ceramic coating on the surface of lightweight aggregates strengthens the interface between the porous mullite aggregates and the matrix, not only improving the compressive and tensile strength of the material but also increasing the number of crack branches and further improving fracture toughness. The compressive strength, tensile strength, and tensile displacement of refractories with 50 vol% coated lightweight aggregate increased by 53.1%, 67.6%, and 42.3%, respectively, compared to traditional mullite-SiC refractories.

Influence of Calcined Bauxite Aggregate on the Resistance of Cement Composites Subjected to Small Caliber Deformable Projectile Impact

This paper presents an experimental investigation on the influence of calcined bauxite aggregate (CBA) on the resistance of cement composites subjected to small caliber deformable projectile impact at a designed velocity of 400 m/s. The deformable projectile was made from copper with a purity of 99.5% and a diameter of 8.0 mm. Compared to mixtures with conventional coarse granite aggregate and/or siliceous fine aggregate, the incorporation of either fine or coarse CBA or their combination is beneficial in reducing the depth of penetration (DOP), equivalent crater diameter (CD), and crater volume (CV) caused by deformable projectile impact. CBA is found to be more effective in controlling the DOP and CV in comparison to the CD. Replacing of conventional aggregate with CBA leads to more severe damage to the projectiles (e.g., projectile length reduction, diameter increase, and mass loss). Relative effective hardness is an effective indicator to the deformation potential and penetration capacity of a deformable projectile to impact cement composites incorporating CBA.

Internal curing efficiency and key properties of UHPC influenced by dry or prewetted calcined bauxite aggregate with different particle size

A strong and porous aggregate (calcined bauxite, CB) has been applied as novel internal curing (IC) agent in UHPC to counteract its high autogenous shrinkage. However, in view of intelligently UHPC mixture design to acquire satisfactory workability, mechanical properties, and low-shrinkage UHPC, the influences of CB particle size and IC water incorporation methods are not well explored yet, and thereby are investigated in this study. UHPCs with different particle sizes (1 ∼ 3 mm, 3 ∼ 5 mm, and 5 ∼ 8 mm) of CB and methods of prewetting CB or using dry CB with adding IC water during mixing were investigated, together with preparing a reference UHPC (no CB). Multiple microstructural characterization techniques were used to explore the underlying mechanisms. Results show that the UHPCs with any condition of CB aggregate all obtained promoted mechanical properties and significantly reduced autogenous shrinkage compared to the reference UHPC. The large CB led to the highest compressive strength increment while the small and medium CB resulted in similar increments; more shrinkage reduction (higher IC efficiency) was achieved with the medium or small CB (above 70% reduction) than with large CB (58% reduction). The prewetting practice resulted in slightly more strength increment than using dry CB with adding IC water during mixing, and these two practices reached similar IC efficiency. Microstructural analysis with TG test and BSE observation confirmed the promoted hydration in the UHPCs caused by the IC effect of CB aggregate; reduced total porosity was observed in these UHPCs with CB by MIP test.

Effect of Hollow Corundum Microspheres Additive on Physical and Mechanical Properties and Thermal Shock Resistance Behavior of Bauxite Based Refractory Castable.

This paper analyses the effect of hollow corundum microspheres (HCM) on both physical-mechanical properties (density, ultrasonic pulse velocity, modulus of elasticity, and compressive strength) and thermal shock resistance behavior of refractory medium cement castable with bauxite aggregate. Moreover, the scanning electron microscopy (SEM) results of HCM and refractory castable samples are presented in the paper. It was found that the replacement of bauxite of 0–0.1 mm fraction by HCM (2.5%, 5%, and 10% by weight of dry mix) had no significant effect on the density and compressive strength of castable, while the modulus of elasticity decreased by 15%. Ultrasonic pulse velocity (Vup) values and the visual analysis of the samples after thermal cycling showed that a small amount of HCM in composition of refractory castable could reduce the formation and propagation of cracks and thus increase its thermal shock resistance.

Effect of chemical composition of calcined bauxite aggregates on mechanical and physical properties for high friction surface course

This paper attempts to show the impact of chemical components on the mechanical and physical performance of calcined bauxite, especially the long-term skid resistance. Firstly, the mechanical and physical properties of five types of calcined bauxites including, the polished stone value (PSV), crush value, Los Angeles Abrasion value (LAA), adhesion property, bulk density and water absorption were tested. The X-ray fluorescence (XRF) and X-ray diffraction (XRD) were applied to examine the chemical and mineral components of aggregate. The Pearson correlation coefficient and Pearson correlation coefficient matrix by Statistic Package for Social Science (SPSS) were utilized to study the relationship between chemical components and mechanical, physical properties of calcined bauxite. Then, the long-term skid resistance of calcined bauxite aggregate was carried out in the laboratory by accelerated polish machine and British Pendulum Tester. The polishing mechanism and the influence of chemical components on the skid resistance of calcined bauxite aggregates were gained by linear regression methods. The asymptotic model was adopted to fit the relationship between British pendulum number (BPN) and polish times. The results indicate that the chemical compositions of calcined bauxite aggregate including Al2O3 and SiO2 along with indicator SiO2/Al2O3 show significant impact on the mechanical and physical properties of calcined bauxites. The final value of PSV (PSVf) is significantly correlated with average grain size (D), corundum, mullite and Aggregate Hardness Parameter (AHP) of calcined bauxite. The asymptotic model can describe the decay process of polish of calcined bauxite with polish time. The PSVn can be expressed with PSVf and SiO2/Al2O3 by linear equation. In addition, the incorporation of calcined bauxite improves MPD (Mean Profile Depth) and BPN of limestone asphalt mixture. This provides a new and interesting way for selecting suitable aggregate used in the pavement surface layer.

Study on the Performance and Adhesion Behavior of Ultrathin Wearing Course Using Calcined Bauxite as Aggregate

An ultrathin wearing course is an effective maintenance treatment for prolonging the service life of asphalt pavements, which have been widely used in the field of pavement construction and road maintenance. However, the repeated vehicle load and wear results in a decreased durability of ultrathin wear course cover pavement. Hence, the gradation of ultrathin wear course was designed using calcined bauxite in this study, and the water stability, low-temperature properties, resistance to permanent deformation, and salt erosion were investigated through a laboratory test. Results indicated that the addition of a nonammonia antistripping agent significantly improves the water stability of the asphalt mixture with calcined bauxite and its ability to resist salt erosion as well as improve its low-temperature deformation ability. At the same time, polyphosphoric acid improves the adhesion between asphalt and calcined bauxite aggregate and the high-temperature performance of asphalt mixture but has limited improvement in water stability and resistance to salt erosion. This research is conducive to the widespread use of calcined bauxite aggregates in road pavements and is of great significance for improving the durability of ultrathin wear course asphalt pavements.

Effect of aggregate type and polishing level on the long-term skid resistance of thin friction course

• Thin friction course with 88# calcined bauxite shows satisfactory skid resistance. • Aggregate mineral/chemical compositions affect the long–term skid resistance of TFC. • The attenuation rate of aggregate’s PSV has a strong correlation with that of μ 40 . This study was attempted to investigate the influence of aggregate type and polishing level on the long–term skid resistance of thin friction course particularly with calcined bauxite. The PSV (Polished Stone Value) test, self-designed three wheel polishing device (TWPD) and dynamic friction tester (DFT) were applied to examine the friction performance of asphalt mixture and aggregate at different polishing cycles in laboratory. The mineral hardness of aggregate was linked with the skid resistance of aggregate and thin friction course by regression analysis. The grey correlation and t -test were utilized to evaluate the factors that influenced the skid resistance of thin friction course. It is found that better skid resistance value is observed for thin friction course by 88# calcined bauxite than by limestone, basalt and 75# calcined bauxite at each polishing level. PSV presents most significant influence for both terminal value and initial value of μ 60 . The PSV attenuation rate of aggregate has a strong correlation with the attenuation rate of μ 40 . The aggregate hardness parameter presents the ability of the aggregate and asphalt mixture to keep long–term skid resistance. In addition, calcined bauxite aggregate owns extensively applied potential in the thin friction course in China.

Effect of calcined bauxite powder or aggregate on the shrinkage properties of UHPC

Commonly used internal curing (IC) agents (super absorbent polymers or lightweight aggregate) to mitigate the higher levels of autogenous shrinkage in UHPC could possibly lead to a negative effect on the mechanical properties of concrete due to the increased void created by the agents, the not-well estimated added water for IC, or low strength of the materials. In this study, a new type of calcined bauxite (CB) aggregate was found to be stronger than normal aggregate and exhibit a porous structure. Different quantities of this aggregate and its powder product were applied to estimate their effect on the mechanical and shrinkage properties of non-fibrous UHPC matrixes and UHPCs with steel fibers. The maintained higher internal relative humidity and significantly reduced autogenous shrinkage (more than 65%) demonstrate that the use of either dry or prewetted CB aggregate can both provide IC effect in UHPC. It reveals that the dry CB aggregate absorbs water during mixing and releases them after setting. Both the compressive and tensile strength of UHPC mixtures were significantly improved by using CB aggregate as compared to the reference mixture, which is due to the actual lower effective w/b, enhanced properties of the ITZ, and increased hydration by internal curing. However, the powder product of CB did not provide IC effect, but a higher content of CB powder (600 kg/m3) helped enhance the strength of UHPC matrix while the one with 300 kg/m3 of CB powder obtained similar strength both compared to the reference mixture.

Internal Curing by Porous Calcined Bauxite Aggregate in Ultrahigh-Performance Concrete

AbstractUltra-high performance concrete (UHPC) has more severe autogenous shrinkage than ordinary concrete, which may lead to increased cracking risks. Thus, a suitable and effective agent for inte...

Effect of bauxite aggregate in cement composites on mechanical properties and resistance against high-velocity projectile impact

This paper investigates the effect of the bauxite sand and coarse aggregate on the quasi-static mechanical properties and resistance against high-velocity projectile impact of cement composites with 28-day compressive strengths from 34.2 to 197.2 MPa, in comparison to that of the siliceous sand and granite coarse aggregate. Mechanical properties investigated include compressive strength, elastic modulus, compressive stress-strain behavior, splitting tensile strength, and effective hardness index. Impact resistance was evaluated using 8.0-mm-diameter, 7.8-g-mass, conical-nosed projectiles at velocities of approximately 400 m/s. The results indicate that the bauxite sand and coarse aggregate are beneficial for enhancing mechanical properties and impact resistance of cement composites compared to the siliceous sand and granite coarse aggregate. The concrete incorporating both bauxite sand and coarse aggregate exhibits compressive strength of about 200 MPa and elastic modulus of about 105 GPa at 28 days under ambient curing conditions, and better impact resistance than a granite rock specimen. This study will provide insights into the development of advanced cement composites with superior mechanical properties and impact resistance for protective structures.

Investigation of Adhesion Properties between Asphalt and Calcined Bauxite Aggregate

This article presents a study evaluating the adhesion properties between asphalt and calcined bauxite. Limestone and granite were also compared with calcined bauxite. For this purpose, asphalt bond strength, surface free energy, and phase angle of asphalt and aggregate were tested. The chemical reaction and mechanical adhesion of asphalt–aggregate were also investigated using Fourier transform infrared spectroscopy (FTIR) and a surface roughness test. The results showed that the higher the alumina content of the calcined bauxite, the greater the adhesion. The adhesion properties of asphalt and aggregate were ranked as follows: limestone > calcined bauxite > granite. Based on the results of the gray correlation analysis, it can be concluded that the intermolecular interactions between asphalt and aggregate play a major role in adhesion. The interlocking caused by surface texture also affects adhesion to some extent. The larger work of adhesion and the more complex surface texture of calcined bauxite with higher alumina content are the main reasons for its higher adhesion. Calcined bauxite with low alumina content should be treated to enhance adhesion before it is used in asphalt mixtures for wearing courses.

An Investigation of the Polishing Behavior of Calcined Bauxite Aggregate

The application of top-grade calcined bauxite to improve the skid resistance of pavement surface coatings increases construction costs and causes excessive tire wear. Therefore, it is necessary to investigate the polishing behavior of different grades of calcined bauxite aggregate. The polished stone value of calcined bauxite was measured after the standard polishing time and the extended polishing time. The Los Angeles (L.A.) abrasion and the crushing value, profile roughness, hardness, X-ray diffraction, and micromorphology were also tested. The results showed that the calcined bauxite above 75# (the ratio of corundum to mullite by weight, C/M > 1) satisfied the requirement of the ultra-thin friction course. Compared with basalt, the calcined bauxite above 80# (C/M > 3) has better long-term skid resistance, even though the pavement surface is subject to heavier traffic. Due to the higher cohesion of lower porosity, more hard minerals to keep the surface roughness, and less soft minerals to smooth the surface roughness, calcined bauxite with a higher corundum content has the better skid resistance. There is a power law relationship between C/M and Polished Stone Value (PSV). Considering the diminishing returns of higher-grade calcined bauxite, it is necessary to accurately select the appropriate C/M of calcined bauxite before use in pavement surface coatings.

Evaluation of the Factors Affecting the Wear Resistance of Calcined Bauxite Aggregates

The continuous use of load-bearing road surfaces often results in degradation over time, particularly if they are constructed from cement or aggregates that were poorly polished. Surfaces prepared from calcined bauxite exhibit good skid resistance properties, and this work describes a comparison of the wear resistance of six different kinds of calcined bauxite with the aim of identifying the best material for road construction. Our results suggest that wear resistance of calcined bauxite is not only related to its hardness, but also dependent on the hardness dispersion throughout the aggregate and its elastic modulus. These data provide important information to enable the correct grade of bauxite clinker to be chosen for constructing high-friction road surfaces with good wear and skid resistance properties.

Laboratory and Field Evaluation of Single Layer and Double Layer High Friction Surface Treatments

High friction surface treatment (HFST) has been proactively used as a solution to extreme friction demands at locations such as horizontal curves, ramps, bridge decks, and intersections. Considerable efforts have been made to evaluate the use of HFST across the United States (U.S.) The American Association of State Highway and Transportation Officials (AASHTO) has issued a provisional specification, i.e., AASHTO PP 79-14, to help state Departments of Transportation (DOTs) to successfully apply HFST. This paper presents a further effort made by the authors to evaluate and compare the friction performance and durability of single and double layer HFTS systems with calcined bauxite aggregate. The laboratory accelerated polishing was conducted to evaluate the effects of aggregate candidate gradations on the friction performance, such as friction coefficient and macrotexture mean profile depth (MPD), and to determine the aggregate gradation for field evaluation. Field evaluation was conducted on both single and double layer HFST systems using test strips under actual traffic polishing over a time period of nine months that covered an entire snow season. It was found that larger aggregate size tends to yield larger MPD, but larger MPD does not necessarily imply larger friction. The double layer HFST did not outperform the single layer HFST with respect to friction and durability. If the properties of calcined bauxite aggregate are precisely defined, either surface friction or MPD can solely be utilized as the frictional metric for quality assurance (QA) of HFST.