Maximum Aggregate Diameter Research Articles

Mesoscale modelling of CRTS II slab tracks subjected to thermal action and vehicle loads

Evaluation of the damage and deformation of cast-in-situ concrete joints between the precast concrete track slabs of the China Railway Track System (CRTS) II is crucial to the safe operation of high-speed railways. To investigate the damage and deformation evolution of concrete joints under thermal action (caused by the natural meteorological environment) and vehicle loads, a two-dimensional thermal–mechanical coupled numerical model of concrete joints at the mesoscale was developed. This model analyses the influence of three factors – concrete strength, maximum diameter of the joint concrete aggregate and vehicle speed. First, meteorology and heat transfer theory were used in thermal simulations. Then, the non-linear characteristics of the joint concrete were modelled as a two-phase composite material based on the random aggregate algorithm and strain-based elastic damage theory at the mesoscale. The cohesive zone model was used to simulate the interfaces between precast slabs. The reliability of the proposed model was assessed using field measurements. The results of a numerical example showed that the maximum aggregate diameter of the joint concrete significantly affected damage evolution in the joint concrete and concrete strength has a slight effect on joint uplift.

Mechanical and Hydraulic Properties of Recycled Concrete Aggregates Mixed with Clay Brick Aggregates and Particle Breakage Characteristics for Unbound Road Base and Subbase Materials in Vietnam

The construction industry is one of the key industries with high potential for the circular economy; the promotion of reuse and recycling of construction and demolition waste (CDW) is essential for sustainable urban development. In this study, a series of compaction, California bearing ratio, saturated hydraulic conductivity, and particle breakage tests of well– and poor–graded mixtures of recycled clay brick aggregates (RCBs) and recycled concrete aggregates (RCAs) with maximum aggregate diameters of 19, 25, and 37.5 mm were carried out to examine the practical application of those mixtures to unbound roadbed materials in Vietnam. The experimental results suggest that the maximum amount of RCBs added to RCAs should be less than 30% when applied to unbound roadbed materials. In addition, it was found that the mixing proportions of RCBs and RCAs and the maximum aggregate diameter, gradation of aggregates, and initial moisture condition control the saturated hydraulic conductivity. Further, the particle breakage characteristics under compaction were carefully examined, and it was found that the percentage increment/decrement, as well as a newly introduced method of estimating the mixing proportions of RCAs and RCBs in the fine fraction (<2.36 mm), is effective in understanding the mechanism of particle breakage of RCA and RCB mixtures.

Dynamic splitting tensile behaviors of ceramic aggregate concrete: An experimental and mesoscopic study

AbstractThis paper presents an experimental and numerical study on the dynamic splitting tensile properties of ceramic aggregate concrete (CAC) that is composed of ceramic aggregates and mortar matrix. The maximum ceramic aggregate diameter includes 0.3, 0.6, and 0.9 cm. A series of split‐tension tests of CAC specimens were conducted first. Parametric studies such as the effects of aggregate size and strain rate, on the splitting tensile behaviors of CAC were presented in terms of tensile strength, stress–strain curve, failure patterns, and so on. Subsequently, we developed a three‐dimensional two‐phase mesoscale model for CAC, where the random distribution and size characteristics of ceramic aggregates in concrete were fully considered. Employing the developed mesoscopic model, systematic mesoscopic simulations were performed to investigate the mesoscopic responses of CAC under dynamic split‐tension loadings. Results indicated that the mechanic properties and cracking behaviors of CAC are associated with many factors, such as aggregate diameter, aggregate distribution and strain rate. Besides, there was a good agreement between the tested and numerical results, demonstrating that the developed mesoscale model has a significant reliability and potential in simulating the mechanical properties of CAC.

Modeling the international roughness index performance on semi-rigid pavements in single carriageway roads

Pavement deterioration models are a vital feature in any pavement management system since they are capable of predicting the evolution of pavement characteristics. Pavement roughness is measured by most of the highway administrations due to its relation to comfort and safety, generally by means of the International Roughness Index (IRI). The Regional Government of Biscay (Spain) has collected IRI values since 2000 on its road network. Although many models have been developed for flexible pavements, very few have been proposed for semi-rigid pavements. The paper aims to develop IRI prediction models for semi-rigid pavements in single-carriageway roads. Considering the high quantity of available information in the database, deterministic models were selected. Due to the importance of the pavement structure in IRI evolution observed in flexible models, only segments with completely known pavement details were employed, i.e., a section where the complete structure is known: materials and thickness of existing layers above the subgrade. The pavement age, as precise as practical, and the accumulated total traffic and heavy traffic through the section were identified as roughness accelerating factors. Conversely, the materials used in base and subbase layers, their thickness, and the total thickness of bituminous layers were observed as degradation reducing factors. Possible treated base and subbase materials included in the model were soil–cement, gravel-cement, and gravel and slag. The obtained model achieved a determination coefficient (R2) of 0.569. Additionally, the bituminous material of the surface layer was verified as an affecting factor too, which can be introduced to improve the model’s accuracy. Possible surface layer materials included dense (D) and semi-dense (S) asphalt concrete, with a maximum aggregate diameter of 16 and 22 mm, discontinuous mixing (BBTM 11A) and porous asphalt (PA 11). The additional model achieved a higher determination coefficient (0.645) and, hence, a more accurate IRI prediction resulted.

Fracture properties of rubberized concrete under different temperature and humidity conditions based on digital image correlation technique

Rubberized concrete is a kind of environmentally friendly construction material. Application of waste rubbers in concretes by replacing traditional aggregates has high feasibility for the recycling materials. However, the fracture properties of rubberized concrete will be influenced greatly because of the low adhesive properties between the cement paste and rubber particle. In this study, the effects of temperature and humidity on the fracture performance of rubber concrete were studied by three-point bending test. The digital image correlation technique was used to study the cracking and fracture properties of the rubberized concrete under different temperature and humidity conditions. The results indicated that Mode I was the main fracture failure mode of the rubberized concrete. The maximum width of the fracture process zone (FPZ) and crack width of the beam specimen in the rubberized concrete were similar to those in ordinary concrete. The width of the FPZ was approximately half of the maximum aggregate diameter. The crack width of the rubberized concrete specimen linearly decreased with height. The temperature and humidity has remarkable influence on fracture properties of rubberized concrete. With an increase in ambient temperature, the fracture toughness and fracture energy of the rubberized concrete initially increased gradually, and then decreased. The fracture toughness and fracture energy of the rubberized concrete slightly increased with the increment in ambient humidity. The technique of digital image correlation has advantages in measuring fracture parameters of rubberized concrete, and the results obtained from this study can greatly promote the further application of rubberized concrete.

Three-dimensional meso-numerical simulation of heterogeneous concrete under freeze-thaw

Combined with the heterogeneity of concrete, a three-dimensional meso-numerical calculation model of concrete under freeze-thaw was established. Moreover, the material development of concrete was carried out by using the VUSDFLD user subroutine of ABAQUS to achieve the simulation of cracking characteristics on concrete. A calculation model for cracking of concrete under freeze-thaw was established. The model can be used to study the mechanical properties of concrete under freeze-thaw. By comparing the calculation results and test results of relative dynamic elastic modulus of concrete under freeze-thaw, the effectiveness of the calculation method was verified. On this basis, the mechanical properties of concrete with different aggregate diameter after freeze-thaw were analyzed. The influence of aggregate diameter on frost resistance of concrete were obtained. The results show that the meso-numerical simulation method can effectively reflect the mechanical properties of freeze-thaw concrete. This method was used to analyze the mesoscopic characteristics of 25 groups concrete under freeze-thaw. The calculation results verify the applicability of the method to freeze-thaw concrete. The simulation model can effectively describe the stress-strain evolution behavior of freeze-thaw concrete. The maximum aggregate diameter has little influence on the frost resistance of concrete.

Settling of Asphaltene Aggregates inn-Alkane Diluted Bitumen

The settling rate of asphaltene aggregates is a key design parameter for partial deasphalting processes, and yet few data and models are available for these systems. The settling rates of asphaltene aggregates were measured in two Western Canadian bitumens diluted with n-heptane or n-pentane at 21 °C and atmospheric pressure. The density and viscosity of the mixtures, the size distributions of the aggregates, and the fractal dimensions of the aggregates were also measured. The asphaltene aggregates settled as a zone, that is, all aggregates settled at the same rate. The settling rates increased with increasing n-alkane content, reached a maximum at approximately 75 wt % n-alkane and then decreased at higher dilutions. The maximum settling rate corresponded to the maximum aggregate diameter and fractal dimension. The maximum settling rate in n-pentane diluted bitumen was 2 orders of magnitude greater than in the same bitumen diluted with n-heptane. The difference was attributed to the lower density and viscosity of the medium, larger aggregates, and higher fractal dimensions in n-pentane versus n-heptane. The settling rates were modeled with Stokes’ law modified to include the fractal dimension of the aggregates. Since zone settling was observed, the settling rate was determined from a single average diameter applied to all of the aggregates. The Sauter mean diameter was found to provide the most consistent results for the diluted bitumen systems in this study. No other form of hindering was required to match the data. The model matched the measured settling rates to within 20% of the maximum settling rate. The model is sensitive to the fractal dimension of the aggregates, and therefore precise determination of the fractal dimension is critical or it must be tuned to match the settling data.

PENGARUH PERSENTASE PENAMBAHAN SIKA VISCOCRETE-10 TERHADAP KUAT TEKAN BETON

Building structure often use concrete as the main structural material, in which the concrete-forming materials such as cement, sand, gravel, water and additives. The aim of study is to investigate the influence of addition of Sika Viscocrete-10 toward concrete compressive strength. Concrete is planned with Water Cement Ratio 0.3. Slump values obtained for normal concrete with maximum aggregate diameter of 25.4 mm is 7.8 cm. The values are in accordance with the slump plan of 7.5 to 10 cm, meanwhile values slump that use Sika Viscocrete-10 as much as 0.5% is 19.5 cm; Sika Viscocrete-10 as much as 1% is 21.9 cm; Sika Viscocrete-10 as much as 1.5% is 23 cm; and Sika Viscocrete-10 as much as 1.8% is 24.7 cm. Based on these test results, the conclusion is addition of Sika Viscocrete-10 is able to enhance the workability value of concrete, so it is easy to work. Concrete mix design using the American Concrete Institute (ACI). Specimens used in this study is a standard concrete cylinder diameter of 150 mm and a height of 300 m, tested after the age of 14 days. Number of test specimens for all treatments is 25 with 5 specimens in each treatment. The average compressive strength of concrete with normal mixture is 295.43 kg/cm2; for concrete with Sika Viscocrete-10 as mush as 0.5% is of 376.50 kg/cm2; Sika Viscocrete-10 as mush as 1% is 452.94 kg/cm2; Sika Viscocrete-10 as mush as 1.5% is 501.63 kg/cm;2 and Sika Viscocrete-10 as mush as 1.8% is 515.78 kg/cm2. Concrete compressive strength greater with increasing percentage of Sika Viscocrete-10.

Bond Behaviour Between Reinforcing Bars and Geopolymer Concrete By Using Pull-out Test

This paper presents the effect of the reinforcing bar diameter (db) and concrete cover thickness to reinforcing bar diameter ratio (c/db) to the bond strength between reinforcing bar and geopolymer concrete by using the experimental pull-out test. The mass ratio of sodium hydroxide (NaOH) to sodium silicate (Na2SiO3) was 2.5 with an 8 M concentration of sodium hydroxide were used in this research. Class F fly ash from Suralaya Power Station, Banten, Indonesia was used as raw material to produce geopolymer concrete. The maximum diameter of coarse aggregate was 10 mm. The result indicated that the maximum pull-out load on reinforcing bar diameter of 16 mm was higher than the diameter of 13 mm. The pull-out failure occurred on the ratio of c/db more than equal of 4.3. The bond strength increased as the ratio of c/db increased, up to 4.3. However, more than 4.3 was the insignificant effect.

Stochastic cohesive law of concrete based on energy consumption equivalence

A method for determining the stochastic cohesive law of concrete was developed using a parallel spring model. This method is based on the energy consumption equivalence between stochastic damage and fracture and assumes that the micro-spring failure strain is a lognormal stochastic variable. The stochastic cohesive laws of dam concrete and wet-screening concrete with different maximum aggregate diameters were obtained. The fracture processes of notched three-point bending beams were calculated, and the characteristic lengths of the dam and wet-screening concrete were suggested as 6–8 times the maximum aggregate diameter.

Study on the Damage Risk of Dam Concrete Suffering Alkali-Silicareaction Based on 7 Years Outdoor Field Exposure Testing, Part I: The Influence of Maximum Size of Aggregate

Alkali-aggregate reaction is one of the most serious concrete durability problems threating the safety of dam. Some accelerated test methods with high temperature and high alkalinity are usually used in laboratory to evaluate the reactivity of aggregates or the effectiveness of suppression measures. In this paper, an outdoor field exposure station was built to objectively assess the damage risk of real dam concrete suffering alkali-silica reaction. 25 concrete blocks measuring 450 by 450 by 450 mm in size were tested at first stage, all immersed into water to simulate the environment of dam concrete. The influences of the size of aggregate and the amount of cementing materials were tested at the same time. After 7 years field exposure testing, the results showed that: the crack risk of blocks was not proportional to the expansion rates, but influenced by the maximum diameter of aggregate. The block with bigger aggregate had smaller expansion rate, but cracked more easily. If the sizes of aggregate were the same, less cementing materials would cause bigger expansion. The constraint effect is bigger than the effect of alkali content increasing caused by increasing the amount of cementing materials.

PENGGUNAAN VARIASI UKURAN DIAMETER BUTIR MAKSIMUM AGREGAT KASAR TERHADAP KUAT TEKAN BETON

This study aims to determine the use of variations in the size of the maximum grain diameter of coarse aggregate on compressive strength of concrete with fas 0.45 by cylindrical test specimen size 15 x 30 cm. Planning mix desing using a modified method of ACI with fas value of 0.45 and the value of the planned 75-100 mm slump. This study includes compressive strength performed at age 7 days and 28 days, treatment is normally carried out with care marinade soaked in the tub for 7 days and 28 days. Compressive strength test results obtained in the test specimen 7 days old premises gravel size is 20.50 Mpa 12.5 mm, 19 mm, 16.99 MPa, 16.76 MPa is 25 mm and 31.5 mm was 14.57 Mpa , while the age at 28 days was 30.51 MPa 12.5 mm, 19 mm, 24.86 MPa, 21.85 MPa is 25 mm and 31.5 mm was 21.66 Mpa. So the smaller the aggregate maximum compressive strength used was obtained by the higher and conversely the greater the maximum aggregate used dihasikan compressive strength lower. keywords: compressive strength, maximum grain diameter

Mechanical properties optimization of resin mineral composite for machine tool bed

Resin mineral composite attracted much attention in the field of elementary machine components because of the excellent performance in alleviating vibration. However, applications of resin mineral composite are restricted due to its limited mechanical properties. In this paper, the effects of the aggregate gradation, the maximum diameter of the aggregate, and the mass fraction of the resin on the mechanical strength were investigated. In addition, influences of fiber types (glass fiber and carbon fiber), fiber length, mass content of fiber, and surface treating techniques (ultrasonic cleaning, oxidation by HNO3, coupling treatment by silane) on the mechanical strength of resin mineral composite were also investigated. Experimental results show that the compressive strength of resin mineral composite first increases and then decreases as the maximum aggregate diameter, the fractal dimension of the aggregate gradation, and the resin dosage increase. The best compressive strength was obtained when the maximum diameter of aggregate is 15 mm, the fractal dimension of the aggregate gradation is 2.45, and the mass fraction of the resin is 9%. Results also show that the best mechanical strength was obtained when the lengths of the fibers are 10 mm and the mass fraction of the glass (carbon) fiber is 0.1% (0.05%). Compared with resin mineral composite with no fibers, the compressive strengths of resin mineral composite reinforced by glass fibers and carbon fibers treated with three-step treating technique increased by 16.62 and 14.63%, respectively. And the flexural strength of resin mineral composite reinforced with carbon fibers treated with three-step treating technique increased by 18.3%. The flexural strength of resin mineral composite reinforced with glass fiber treated with two- and three-step treating technique increased by 9.67 and 5.7%, respectively. In addition, the mechanism of the influences of the fiber whose surfaces were treated on the mechanical strength of resin mineral composite was revealed by scanning electron microscopy.

Prediction of Young’s Modulus of Concrete with Two Types of Elliptical Aggregate

The purpose of this paper is to present a lattice method for predicting the Youngs modulus of concrete with two types of elliptical aggregate. After distributing fine and coarse aggregates within a rectangular unit, the finite element method is adopted to estimate the Youngs modulus of concrete. Compared with previous studies, the method considers the aggregate shape effect and the difference in Youngs modulus between fine aggregate and coarse aggregate. After the validity of the method is verified with two sets of experimental results, the effects of various factors on the Young s modulus of concrete are quantified. It is found that the Young's modulus of concrete increases with an increase in aggregate aspect ratio, minimum aggregate diameter, or both, but decreases by increasing the interfacial transition zone thickness. It is also found that the maximum aggregate diameter and aggregate gradation have little effect on the Young's modulus of concrete.

Kinetics of Asphaltene Aggregation in Crude Oil Studied by Confocal Laser-Scanning Microscopy

This paper presents results of our study of the kinetics of asphaltene aggregation as a function of different precipitants, solvents, and the Hildebrand solubility parameter δ. The aggregation was studied in situ in the crude oil using confocal laser-scanning microscopy. We observe that the kinetics of asphaltene aggregation strongly depends upon the Hildebrand solubility parameter of the mixture. The aggregation process, which occurs when adding precipitant close to the precipitation onset point, can be described by a diffusion-limited aggregation (DLA) process. A slight change of the Hildebrand solubility parameter away from the precipitation onset point into the precipitation regime leads to a different kinetic mechanism. In this regime, we observe that the aggregate size increases almost linearly over time, which is an indication of the crossover between DLA and reaction-limited aggregation (RLA). The maximum mean aggregate diameter increases from 18 μm near the onset point to 90 μm away from the onse...

STUDIES ON REPRESENTATIVE VOLUME ELEMENT SIZE OF CONCRETE BASED ON MESO-STRUCTURE STATISTICS

In this paper, a definition of a representative volume element (RVE) based on the meso-structure of concrete, as well as a method for determining the RVE size of concrete is proposed by means of statistical analyses of the mesoscale structural characteristics of concrete. The voxel concept is employed to calculate the statistical variable of a volume fraction, the average diameter and fineness module of a coarse aggregate. Accordingly, the RVE size of one-grade concrete is quantitatively determined. The effects of an aggregate gradation, the aggregate volume fraction on RVE size are also studied.?The data show that: the RVE size decreases with the increase of the aggregate volume fraction and gradually become stable; the ratio of RVE size to the maximum aggregate diameter for one-grade concrete is larger than that for two-grade concrete. The results have implications in choosing a meso-structure of concrete for the mechanical study at meso level and numerical simulation.

Study of fractured surfaces of concrete caused by projectile impact

In recent years several studies presented different parameters and criteria to describe the damage of concrete specimens caused by projectile impact. The parameter used most to characterize damage is the volume of the craters on the front and rear side of the concrete specimen. In this study the damage of concrete specimens is described as a fractured area. In order to describe the whole fractured area it is necessary to consider the crater surfaces and the fractured surface area of the fragments generated by impact. The crater surfaces were analysed using a 3-dimensional laser-scanner system. The fragments were measured with a camera particle analyser. Their surfaces were determined taking into account the following parameters: Feret diameter, length, volume distribution and sphericity. A triaxial ellipsoid model was developed by means of these parameters. The whole fractured surface area is given by the sum of the specimen surface after perforating and the fragments surface minus the specimen surface before perforation. The fragment surface is decisive for the fractured surface and depends on the number of fragments of each size class. This study confirms previously gained results using new parameters: A larger maximum aggregate diameter enhances the impact resistance of concrete against projectiles.

An n-layered spherical inclusion model for predicting the elastic moduli of concrete with inhomogeneous ITZ

Abstract An n -layered spherical inclusion model is presented in this paper for predicting the elastic moduli of concrete with inhomogeneous interfacial transition zone (ITZ). In this model, concrete is represented as a three-phase composite material, composed of the aggregate, bulk paste, and an inhomogeneous ITZ. An analytical solution for the ITZ volume fraction is derived for the general aggregate gradation. By constituting a semi-empirical initial cement gradient model, the local water/cement ratio, degree of hydration, and porosity at the ITZ are estimated. The inhomogeneous ITZ is then divided into a series of homogenous concentric shell elements of equal thickness. The elastic moduli of concrete are determined by solving the n -layered spherical inclusion problem. Finally, the validity of the model is verified with three independent sets of experimental data and the effects of the maximum aggregate diameter, aggregate gradation, and ITZ thickness on the Young’s modulus of concrete are evaluated in a quantitative manner. The paper concludes that the proposed n -layered spherical inclusion model can be used to predict the elastic moduli of concrete.

Numerical calculation and influencing factors of the volume fraction of interfacial transition zone in concrete

The determination of volume fraction of interfacial transition zone (ITZ) is very important for investigating the quantitative relationship between the microstructure and macroscopical property of concrete. In this paper, based on Lu and Torquato’s most nearest surface distribution function, a calculating process of volume fraction of ITZ is given in detail according to the actual sieve curve in concrete. Then, quantitative formulas are put forward to measure the influencing factors on the ITZ volume fraction. In order to validate the given model, the volume fractions of ITZ obtained by numerical calculation are compared with those by computer simulation. The results show that the two are in good agreement. The order of the factors influencing the ITZ volume fraction is the ITZ thickness, the volume fraction of aggregate and the maximum aggregate diameter for Fuller gradation in turn. The ITZ volume fraction obtained from the equal volume fraction (EVF) gradation is always larger than that from the Fuller gradation for a given volume fraction of aggregate.

ITZ volume fraction in concrete with spheroidal aggregate particles and application: Part II. Prediction of the chloride diffusivity of concrete

Owing to its importance in the durability assessment of reinforced concrete structures located in a marine or de-icing salt environment, it is essential to determine the chloride diffusivity of concrete. The intention of the present paper is to present an analytical solution for the chloride diffusivity of concrete with aggregate shape effect. A three-phase composite spheroid model for the concrete matrix is proposed to represent the heterogeneous nature of concrete and to take into account the aggregate shape effect. By reducing the three-phase composite spheroid to two two-phase composite spheroids, an analytical solution for the chloride diffusivity of concrete is derived. After the validity of the derived analytical solution is verified with two sets of experimental results, the effects of main factors that affect the chloride diffusivity of concrete are evaluated in a quantitative manner. It is found that the chloride diffusivity of concrete increases with the increase of the thickness and chloride diffusivity of the interfacial transition zone (ITZ), but decreases with the increase of the aspect ratio of spheroidal particles and the maximum aggregate diameter. It is also found that the aggregate gradation has a significant influence on the chloride diffusivity of concrete. The paper concludes that the analytical solution derived here can predict the chloride diffusivity of concrete with reasonable accuracy.