Effect Of Aggregate Size Research Articles

Meso-scale analysis of the aggregate size influence on the mechanical properties of heterogeneous materials using the Brazilian splitting test

The effect of the aggregate size on the behavior of the hardened concrete under splitting tensile loading is studied in this paper. The studies of Tasdemir et al., 2001 [19], Appa et al., 2011 [2], Li et al., 2014 [13] show that the behavior of heterogeneous materials which are subjected to loading depends on many parameters such as volume fraction, aggregate type, and aggregate size, etc. In this paper an investigation was made to study the effect of aggregate size on the mechanical properties of heterogeneous materials such as concrete in the context of the Brazilian splitting test.Five finite element simulations have been carried out in this research to study the behavior of concrete under diametral compression load. Cylinder specimens of concrete with 50 mm of thickness and 110 mm of diameters have been regarded. Five diameters of aggregate have been employed in the analyses, ranging from 4 to 16 mm.This study has employed a meso-scale model (mechanical model) based upon a 3D lattice approach, representing with explicitly heterogeneity and failure mechanism of the concrete. This model considers the concrete to be a two-phase material in which aggregates are melt within the cement paste. Because of using a non-adapted meshing process to mesh the microstructure, a weak discontinuity (jump in the deformation field) is introduced in the kinematics.The results of the numerical simulations show the ability of the meso-scale model to evaluate the mechanical failure in the context of the Brazilian splitting test. Also, the results show that (1) the maximum tensile stress, (2) the fracture energy and (3) the maximum crack opening are all have been increased when the aggregate diameter was increased.

Effects of Aggregate Size on the Rutting and Stripping Resistance of Recycled Asphalt Mixtures

AbstractThe objective of this paper was to examine the effect of the nominal maximum aggregate size (NMAS) on the rutting and stripping performance of Georgia asphalt mixtures containing reclaimed ...

Prediction of compressive strength of self-compacting concrete by ANFIS models

Abstract Many studies predict the compressive strength of conventional concrete from hardened characteristics; however, in the case of self-compacting concrete, these investigations are very rare. There is no study to predict the compressive strength of self-compacting concrete from mixture proportions and slump flow. This paper designs ANFIS models to establish relationship between the compressive strength as output, and slump flow and mixture proportions as input in eighteen combinations of input parameters. The applied dada is taken from 55 previously conducted experimental studies. Effect of each parameter on the compressive strength and its importance level in the developed model has been investigated. Based on the error size in each combination analysis, weighting factor and importance level of each parameter is evaluated to apply the correction factors to get the most optimized relationship. Obtained results indicate that the model including all input data (slump flow and mixture proportions) gives the best prediction of the compressive strength. Excluding the slump flow from combinations affects the prediction of compressive strength, considerably. However it's not as much as the effect of the maximum aggregate size and aggregate volume in the mixture design. In addition, different values of powder volume, aggregate volume and paste content in the mixture reveal different ascending and descending effects on the compressive strength.

Combined effects of steel fiber and coarse aggregate size on the compressive and flexural toughness of high-strength concrete

This paper investigates the effects of steel fiber content and coarse aggregate size on the mechanical properties of high-strength concrete with a specified compressive strength value of 60 MPa. The paper also explores the correlation between the compressive and flexural toughness of high-strength steel fiber-reinforced concrete (SFRC). For this purpose, twelve high-strength SFRC mixtures with four fiber volume fraction of steel fiber (Vf = 0.5%, 1.0%, 1.5%, and 2.0%) and different aggregate sizes were designed and fabricated. Compressive and flexural tests for each concrete mixture were conducted, and the test results were used to investigate the effects of steel fiber volume fraction and aggregate size on the compressive and flexural toughness of high-strength SFRC prims. The results indicate that the mechanical properties of SFRC are related more closely to volume fraction than to aggregate size. The compressive and flexural toughness ratios of the SFRC significantly improved with an increase in fiber content. Also, equations that are suggested to determine the compressive toughness ratio based on the equivalent flexural strength ratio were used to predict the mechanical properties of the SFRC in this study.

Application of 3D-DIC to characterize the effect of aggregate size and volume on non-uniform shrinkage strain distribution in concrete

To elucidate the effect of aggregate size and volume on the non-uniform strain distribution in concrete, drying shrinkage of mortar and concretes were determined with 3D digital image correlation (3D-DIC). The distribution of shrinkage displacements and strains in mortar and concrete were analyzed. The results show that 3D-DIC makes it possible to measure non-uniform displacement distributions initiated by shrinkage in mortar and concrete. The non-uniformity became more remarkable with drying time. The presence of aggregates larger than 5 mm in concrete have locally changed the displacement and strain fields. Aggregates within 5–25 mm make non-uniform strain of concrete more fluctuant, especially when the aggregate size is larger than 10 mm. The maximum and minimum principal strain distributions became more heterogeneous with decreasing volume of aggregates.

Effect of Aggregate Size on the Spalling of High-Strength Wall Panels Exposed to Hydrocarbon Fire

AbstractConcrete spalling has been widely accepted as being caused by a thermomechanical process resulting from high thermal gradients, as well as a moisture-clog process attributable to the buildu...

Kinetics of NaCl induced gelation of soy protein aggregates: Effects of temperature, aggregate size, and protein concentration

Soy protein aggregates with different sizes were prepared by heating soy protein isolate (SPI) in solution and characterized with light scattering. NaCl induced gelation of aqueous solutions of these aggregates was investigated as a function of protein concentration (10–75 g L−1), NaCl concentration (0–0.5 M) and temperature (20–80 °C). The structure and the mechanical properties of the gels were investigated with confocal laser scanning microscopy and oscillatory shear measurements. The gel stiffness did not depend on the size of the preformed aggregates nor on the salt concentration, but increased with increasing protein concentration. Gelation of preformed aggregates was compared with that of native SPI, which showed that gelation of aggregates was faster and occurred at lower protein concentrations and temperatures. The stiffness of gels formed by native SPI and preformed aggregates was not significantly different, but the structure of gels formed by aggregates was more homogeneous. For all systems, the gel time had an Arrhenius temperature dependence characterized by an activation energy of 72 kJ mol−1. A more limited investigation of gelation induced by adding CaCl2 was done to study the effect of the valence of the cation.

Effects of aggregate size on the compressibility and air permeability of lime-treated fine-grained soil

The aggregate size of soils is an essential parameter in lime treatment: the thermo-hydro-mechanical behaviour of lime-treated soils can be greatly affected by the aggregate size of soils before treatment. In particular, the compression behaviour and the pore-size distributions of treated soils are expected to be different with different aggregate sizes, leading to different compressibility and permeability of soils. This study aims to investigate the aggregate size effects on the compressibility and air permeability of a lime-treated soil by performing air permeability measurements in oedometer compression tests on a silt with two different maximum aggregate sizes (Dmax=5 and 0.4mm) and treated with 2% quicklime. The tests were performed on both untreated and treated samples at various curing times (t=7, 28, 60 and 90days). Results showed that lime treatment significantly improves the compression behaviour of soil due to both the flocculation process and the pozzolanic reaction. The treated samples prepared with smaller aggregates have higher oedometer modulus, suggesting a better lime distribution and the production of more cementitious compounds. Air permeability of soil is strongly related to the aggregate size: the soil with smaller aggregates can have a value of one order of magnitude lower than that with larger aggregates. Further examination showed that in the case of smaller aggregates, the morphology of macro-pores and the efficiency of air flow are more sensitive to lime treatment.

Effect of Fiber and Aggregate Size on Fracture Parameters Of High Strength Concrete

The present experimental investigation was to study the behavior of high strength concrete with different aggregate sizes and fiber variation influences on fracture characteristics. Total of 72 beams of various sizes are casted with different aggregate sizes (20mm, 16mm and 10mm) and with different volume fraction of fibers (0%, 0.5%, 1% and 1.5%). According to the notch depth ratios of different sizes of beams notches were made at centre of the beam. The casted and cured beams were tested on loading frame with three point loading. From the obtained results and graphs, the fracture parameters like fracture energy, brittleness number and failure stresses were analyzed by the size effect method (SEM). It was found that fracture energy (GF) and fracture toughness (KIC) increases from decreasing the aggregate size from 20mm to 10mm. By increasing the volume of fibers, brittleness number (β) decreases and fracture process zone (CF) increases.

Specimens size, aggregate size, and aggregate type effect on spalling of concrete in fire

SummaryThis paper attempted to isolate variables that govern concrete spalling when exposed to a hydrocarbon fire. The influence of specimen size was investigated by studying 4 specimen sizes consisting of cylinders, columns, and panels. Three aggregate sizes, 7 mm, 14 mm, and 20 mm were used in the concrete mixes to determine their effect on concrete spalling. Influence of aggregate type on concrete spalling was also investigated. Forty‐two different specimens were considered in this investigation. Concrete spalling was quantified as nominal spalling depth, which has been presented as a new way of quantifying the degree of concrete spalling. The results indicated that specimen size did have an effect on the spalling of concrete under hydrocarbon fire exposure and that nominal spalling depth of concrete increases as the specimen size increases. Aggregate size effect was evident when the maximum aggregate size increased from 7 mm to 20 mm, and explosive spalling was more severe for specimens with small size aggregates. Specimens with 14‐mm aggregate size showed inconsistent results and the spalling behavior witnessed was more random and sporadic. The type of aggregate used has no clear bearing on concrete spalling given both aggregates had similar linear expansion profiles.

Ionic strength dependence of aggregate size and morphology on polymer-clay flocculation

Polymer-driven flocculation of suspended particles is a critical process for many applications, including composite materials synthesis, paper manufacturing, and water treatment. However, the role of solution physicochemical properties on the polymer-particle assembly dynamics is nontrivial, particularly for non-spherical, polydisperse particulates such as natural clays. In this work, we study the effects of ionic strength and aggregate size and structure on the polymer behavior and flocculation performance with anisotropic bentonite clay particles. Using jar tests, laser diffraction, confocal microscopy, and X-ray diffraction, we demonstrate that for smectite clay particles, the final floc structure is largely informed by ionic-strength driven changes to the initial clay aggregate size and surface structure. With increasing bentonite aggregate size, a transition from a networked to a patched polymer − aggregate floc structure is observed, independent of ionic strength during flocculation. Solutions were studied over four orders of magnitude of NaCl ionic strength. Initial, pre-flocculated bentonite aggregate sizes ranging from 0.015μm to 15μm were used, produced by tuning the initial solution ionic strength. Bentonite aggregate size and structure were measured with laser and X-ray diffraction, internal floc structure was visualized using confocal microscopy, and macro floc structure (fractal dimension) was measured with optical imaging. These results shed new light on the fundamental complexity of ionic strength dependence and the importance of the aggregate size and structure of the initial dispersion, in determining optimal reagent dosing and structure control for flocculation of anisotropic clays.

Effect of aggregate size on liquid absorption characteristics of konjac glucomannan superabsorbent

ABSTRACTIn this article, four kinds of konjac glucomannan based superabsorbent polymers (KSAPs) with different aggregate sizes were obtained by sieving the KSAP powders manually. They were characterized by scanning electronic microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and optical contact angle (OCA), and the effects of aggregate size on liquid absorption characteristics of KSAP were studied in detail. The results show that the coarse KSAP particles were aggregated by many microspheres, while the fine particles were well dispersed with 50–150 µm particle size. OCA dynamic images showed the enhanced hydrophilicity for the finer particles. The liquid absorption measurements demonstrated that water and physiological saline absorption velocity of KSAP increased for the finer particles, while their ultimate water holding capacity decreased accordingly. The liquid absorption capacity of the finest sample (75 µm) could reach its maximum value (332.5 ± 5.6 g/g) in 0.5 min, while the coarsest sample (850 µm) reached the maximum value (532.5 ± 1.2 g/g) in 16 min. The reason for this phenomenon was discussed, and a new model was proposed to explain it. We believe that the results of this article would be meaningful in application of KSAP as superabsorbent materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45416.

Interlayer adhesion and strength of structures in Contour Crafting - Effects of aggregate size, extrusion rate, and layer thickness

Abstract Contour Crafting (CC) is a method that builds coherent concrete structures in a layer-by-layer fabrication fashion. During fabrication, layers must be bonded together to make a homogenous structure, as there is no vibration or external force during layer deposition. This research investigates the structural integrity of Contour Crafted structures using experimental approaches to analyze the bond strength between layers. Initially, a concrete mixture which the compressive and tensile strength is significantly improved through modifying the aggregate size and aggregate to cement ratio is developed. The mixture is compatible with an existing extrusion system and it is tested to quantify the strength at interface for different extrusion rate and layer thickness. The results show that an improvement of up to 16% at interface is achievable for different fabrication conditions.

Nonlinear FE modelling and parametric study on flexural performance of ECC beams

Engineered Cementitious Composite (ECC) is a special class of the new generation of high performance fiber reinforced cementitious composites (HPFRCC) featuring high ductility with relatively low fiber content. In this research, the mechanical performance of ECC beams will be investigated with respect to the effect of slag and aggregate size and amount, by employing nonlinear finite element method. The validity of the models was verified with the experimental results of the ECC beams under monotonic loading. Based on the numerical analysis method, nonlinear parametric study was then conducted to evaluate the influence of the ECC aggregate content (AC), ECC compressive strength (fECC), maximum aggregate size (Dmax) and slag amount (ϕ) parameters on the flexural stress, deflection, load and strain of ECC beams. The simulation results indicated that when increase the slag and aggregate size and content no definite trend in flexural strength is observed and the ductility of ECC is negatively influenced by the increase of slag and aggregate size and content. Also, the ECC beams revealed enhancement in terms of flexural stress, strain, and midspan deflection when compared with the reference beam (microsilica MSC), where, the average improvement percentage of the specimens were 61.55%, 725%, and 879%, respectively. These results are quite similar to that of the experimental results, which provides that the finite element model is in accordance with the desirable flexural behaviour of the ECC beams. Furthermore, the proposed models can be used to predict the flexural behaviour of ECC beams with great accuracy.

Effects of Particle Sizes and Cement Pastes on Mechanical Properties of Pervious Concrete

The purpose of this study is to determine the effects of aggregate size as well as the paste volume on unit weight, connected porosity, water permeability coefficient, compressive strength, and flexural strength of pervious concrete. Four aggregate sizes and four filled percentages of voids by cement pastes were selected as variables. Test results show that the unit weight, compressive strength, and flexural strength of pervious concrete increased with an increase of the filled percentage of voids by cement pastes, but decreased the connected porosity and water permeability coefficient. Pervious concrete with aggregate size of 0.24 – 0.4cm and 90% filled percentage of voids by cement pastes had the highest compressive strength of 25 MPa. Meanwhile, the water permeability of this mixture was higher than 0.01 cm/s which can be classified as the pervious concrete according to the Japan Road Association (JRA).

Determining aggregate size & shape effect on concrete microcracking under compression by means of a degree of reversibility method

Crack initiation and propagation along the Interfacial Transition Zone (ITZ) depends on the stress concentration in the ITZ and also to the matrix quality surrounding it. Under uniaxial compression tensile strains are produced in the transversal directions creating cracks along the axial direction. Thus, evaluation of the degree of reversibility with the level of loading determines the extent of microcracking within the material at a certain loading level. In this study, the effect of the aggregate size and shape and also the mortar matrix quality on the degree of reversibility were evaluated by subjecting the specimens to three different compressive stress levels. The degree of mechanical interlocking and internal stress concentration around the aggregate, related to the aggregate surface characteristics, has a significant influence on microcracking behaviour of concrete. Furthermore, aggregate surface characteristics become more pronounced with increased matrix quality.

Effect of coarse aggregate size on the compressive behaviour of geopolymer concrete

The utilisation of ordinary Portland cement not only consumes significant amount of natural resources but also causes pollution to the environment due to Carbon emission. As a result, a replacement material for cement including the use of fly ash becomes a solution to this environmental concern. Accordingly, the compressive strength of cement-based concrete depends primarily on several factors such as the size of gravel. Therefore, it is worth studying to find out whether this factor likewise influences the compressive behaviour of geopolymer concrete. This study experimentally investigated the effect of the particle size of coarse aggregate on the compressive behaviour of fly ash geopolymer concrete. Compressive tests have been carried out on a 100 mm × 200 mm cylindrical specimen using a compression testing machine. The results showed that the fly ash geopolymer concrete specimens exhibited brittle failure mode characterised by splitting, shear, columnar and conical type of failure. It was found that the size of the coarse aggregate that offered a maximum compressive strength is in the range of 12.5–25 mm. Furthermore, the size of the coarse aggregate does not affect the trend results on ambient vs. oven-cured specimen, as well as the days of curing.

Effect of aggregate size on stress-strain behavior of concrete confined by fiber composites

There is no consensus in extant literature on the size effect of fiber reinforced polymer (FRP) confined concrete columns. This work studies the size effect by studying the influence of aggregate size on the stress-strain behavior of FRP confined concrete. Experimental tests were conducted on concrete cylinders with different aggregate sizes and fixed specimen dimensions. Aggregate size shows no effect on the stress-strain behavior of unconfined concrete but has significant effect in the transitional region of the stress-strain curve of FRP confined concrete. However, no significant effect exists on the hardening slope of the stress-strain curve and the ultimate strength of FRP confined concrete. Based on the experimental results and Bazant’s law of size effect, a new method is proposed for modeling the stress-strain relationship of FRP confined concrete allowing for size effect.

Oil-in-water emulsions stabilized by whey protein aggregates: Effect of aggregate size, pH of aggregation and emulsion pH

ABSTRACTOil-in-water emulsions (60% oil (w/w)) were prepared using whey protein aggregates as the sole emulsifying agent. The effects of whey protein aggregate size (the diameter between 0.92 and 10.9 µm), the pH of emulsions (4–8.6) and storage time on physical properties, droplet size, and stability of emulsions were investigated. The results indicate that increment of whey protein aggregate size caused an increase in the firmness, droplet size, and viscosity of emulsions, and also a decrease in the emulsion creaming. The emulsion viscosity, firmness, and droplet size were reduced by increasing the emulsion pH; however, the creaming process was accelerated. Viscosity, creaming, and droplet size of emulsions were increased slightly during 21 days storage at 40°C.

Effects of steel fibre-aggregate interaction on mechanical behaviour of steel fibre reinforced concrete

ABSTRACTThis work investigated the effects of fibre type, dosage and maximum aggregate size on the mechanical behaviour of concrete reinforced with steel fibres. Hooked-end steel fibres with 50 and 60 mm length and aspect ratios (length/diameter) of 45, 65 and 80 were used with maximum sizes of coarse aggregate of 10 and 20 mm. The same mix proportions of concrete were used throughout the investigation. Flexural testing of 600 mm square panels was performed. Subsequently, cores were taken from these panels and X-ray computed tomography was used to analyse the positioning of fibres in hardened concrete. The experimental results show that the performance of steel fibre-reinforced concrete improved drastically when compared to plain concrete without fibres. Longer, thinner fibres and smaller aggregates were noted to give the best results.