Effect Of Aggregate Size Research Articles

Experimental study on anchorage performance of rockbolts by adding steel aggregates into resin anchoring agents.

Pull-out testing was carried out to evaluate the effects of shape, size and concentration of steel aggregates on anchorage performance. Steel grit with particle sizes of 1.5, 2.0, and 2.8 mm and steel shot diameters of 1.4, 2.0, and 2.5 mm were used as steel aggregates and were added into the resin anchoring agent. For each kind of steel aggregate, either 30, 40 or 50 aggregates were used to evaluate the effects of different steel aggregate densities. Anchorage specimens were prepared using ϕ20mm rebar bolts and steel sleeves. Compressive and shear strengths of resin containing steel aggregates, the pullout curve, and the circumferential strain of the sleeves were measured, and the energy consumption was calculated. Results show that compressive and shear strengths of resin containing steel grit and steel shot are increased by 8.4%-17.0% compared to pure resin. For the aggregate numbers of 30, 40 and 50, the anchoring force is increased by 7.9%, 7.5% and 6.5%; energy consumption is increased by 19.2%, 15.0% and 18.6%; and the circumferential strain of the specimen is increased by 28.4%, 25.1% and 39.5%, respectively. The effect of aggregate size on anchoring performance is significant; that is, the aggregate sizes of 1.4~1.5, 2.0 and 2.5~2.8 mm increase the anchoring force, energy consumption and sleeve circumferential strain by 8.5%, 4.6% and 8.7%, 16.0%, 8.4% and 28.4%, and 17.9%, 23.3% and 51.9%, respectively. The relationships of the anchoring force, energy consumption, and circumferential strain with steel aggregate quantity and size are formulated. Results show that the addition of steel aggregates increases the compressive and shear strengths of the resin, and steel aggregate quantity and size have significant impact on anchoring performance. This paper provides the basis for optimization of resin anchoring agents used in the mining industry. The impact of anchoring agent shear strength and residual shear strength on the anchoring effect were also discussed based on the failure analysis of the anchoring section.

Experiment Study and Finite Element Analysis of the Coupling Effect of Steel Fiber Length and Coarse Aggregate Maximum Size on the Fracture Properties of Concrete

The effects of steel fiber length (lf = 30 mm, 40 mm, 50 mm and 60 mm) and coarse aggregate maximum size (Dmax = 10 mm, 20 mm, 30 mm and 40 mm) on fractural properties of steel fiber reinforced concrete (SFRC) was investigated. The results show that the fracture energy (Gf) of SFRC reaches its maximum when Dmax increases to 30 mm, and it increases first and then decreases as lf increases, but it still has a significant increase compared to the control concrete. The Gf ratio increases first and then decreases as the lf/Dmax increases. The Gf of the SFRC fracture surface follows the same trend as the fractal dimension. The rational range of the lf/Dmax is 2.5–4 for the considerable strengthening effect of steel fiber on fracture performances of concrete with the Dmax of 10 mm and 20 mm and 1.5–2.33 for that concrete with the Dmax of 30 mm and 40 mm. The finite element analysis results are compared with the experimental results, and the results show that the fracture process of the finite element model is consistent with the experiment.

Effect of rubber aggregate size on static and dynamic compressive properties of rubberized concrete

AbstractThis study experimentally examines the effect of rubber aggregate size on the static and dynamic behavior of rubberized concrete. Rubberized concrete specimens were prepared with different maximum rubber aggregate sizes ranging from 1 to 3 mm to 3 to 5 mm while the rubber content was kept constant at 15% by volume. The dynamic compressive behavior of rubberized concrete was investigated by using split Hopkinson pressure bar (SHPB) tests. The experimental results have shown that rubberized concrete with smaller rubber aggregates showed higher static compressive strength as compared to that with larger rubber aggregates. Meanwhile, the rubber aggregate size did not considerably affect the density of rubberized concrete. The use of smaller rubber aggregate size mitigated the slump reduction of rubberized concrete. Rubberized concrete exhibited obvious sensitivity to strain rate and those with larger rubber aggregates showed higher strain rate sensitivity. The progressive damage of rubberized concrete showed more ductile behavior with bulging failure, which was different from the typical concrete under compression. In general, the use of smaller rubber aggregate size was beneficial to the static compressive strength but less effective to the dynamic compressive strength of rubberized concrete as compared to those with larger rubber aggregates.

Effect of recycled rubber aggregate size on fracture and other mechanical properties of structural concrete

Rubberised concrete (RC) is a green and environmentally friendly concrete type that can be used as a sustainable production material. However, investigations on the structural applications of RC are limited due to its increased cost and decrease in strength. In this study, economical mixture designs were formulated with low-level replacements of rubber aggregates from recycled end-of-life tyres, as a prospective approach. The size effect with coarse (15 mm tyre shreds) and fine (2–4 mm tyre crumbs) rubber aggregates on the fresh and mechanical properties of structural concrete, specifically its fracture properties, was investigated, incorporating preliminary testing and constitutive models. The damage evaluation and characteristics of Mode I fracture behaviour of RC were investigated using three-point bending tests on notched beams. Using digital image correlation which possibly can be used to replace the conventional tools, the crack patterns on the beams were detected and crack mouth opening displacements were measured. The rubber replacements led to crack bridging effects. Overall, the results indicate that addition of recycled tyre aggregates at low percentages results in improved ductility and higher energy absorption and thereby improving the toughness of concrete, with marginal impacts on its strength and other properties. Furthermore, the selected mathematical models for compression and fracture can be used to evaluate the performance of RC structural elements with different rubber replacement levels. The modified RC can be potentially applied to structural components for earthquake resistance, integral bridges, or impact resistant road barriers.

Effects of Coarse Aggregate Shape and Texture on Engineering Properties of Roller Compacted Concrete Prepared for High Traffic Routes

Abstract Use of roller-compacted concrete in pavement construction is increasing. Roller compacted concrete is a zero-slump, highly compacted concrete that is placed by equipment similar to that used in asphalt pavement construction. This investigation was conducted to collect the state-of-the-art information on effects of coarse aggregate size and texture on the strength and workability of roller-compacted concrete (RCC) for pavement construction and maintenance. Concrete specimens containing cubical and rough coarse aggregate, irregular and rough coarse aggregate, angular and rough coarse aggregate, rounded/spherical and smooth coarse aggregate, and flaky/elongated and rough coarse aggregate were prepared at 1:3:3 concrete mix ratio and 0.4 water cement ratio. Laboratory testing of specimens derived from the concrete specimens showed excellent results for cubical and rough coarse aggregate, irregular and rough coarse aggregate, and angular and rough coarse aggregate. Specimens from the rounded/spherical and smooth coarse aggregate, and flaky/elongated and rough coarse aggregate performed poorly in laboratory. The study therefore recommends the use of cubical and rough coarse aggregate, and irregular and rough coarse aggregate in the production of roller-compacted concrete for pavement construction and maintenance.

Inverse analysis of concrete meso-constitutive model parameters considering aggregate size effect

Article Inverse analysis of concrete meso-constitutive model parameters considering aggregate size effect was published on January 1, 2021 in the journal Science and Engineering of Composite Materials (volume 28, issue 1).

Development of alkali-silica reaction model considering the effect of aggregate size

The expansion of concrete members due to the alkali-silica reaction (ASR) is influenced by various factors such as temperature, humidity, aggregate size, aggregate reactivity, and alkali components; among these factors, the aggregate size induces a pessimum effect in which maximum expansion due to the ASR appears in aggregates of a specific size. This makes it extremely difficult to define the relationship between aggregate size and the expansion of concrete in a simple manner. Therefore, this study aims to develop a model to estimate the expansion of concrete members subjected to ASR, taking the pessimum effect of fine aggregate (i.e., sand) size less than 5.0 mm into consideration. Based on a multi-scale chemo-hygral computational system developed by the authors in previous research, the alkali adsorption mechanism was introduced for a phenomenon in which the expansion reduces as the aggregate size decreases, while the mechanism of reduction in the penetration depth ratio of the ASR gel was introduced for a phenomenon in which the expansion reduces as the aggregate size increases. The proposed model was verified in detail by comparing it with ASR test results according to the aggregate size reported in the literature. It was found that the proposed model reasonably evaluated both the expansion of specimens according to the aggregate size and the pessimum effect that resulted in the maximum expansion of concrete members at a specific aggregate size.

Effect of Size of Coarse Aggregate on Mechanical Properties of Metakaolin-Based Geopolymer Concrete and Ordinary Concrete.

Geopolymer binders are a promising alternative to ordinary Portland cement (OPC) because they can significantly reduce CO2 emissions. However, to apply geopolymer in concrete, it is critical to understand the compatibility between the coarse aggregate and the geopolymer binder. Experimental studies were conducted to explore the effect of the size of the coarse aggregate on the mechanical properties and microstructure of a metakaolin-based geopolymer (MKGP) concrete and ordinary concrete. Three coarse aggregate size grades (5–10 mm, 10–16 mm, and 16–20 mm) were adopted to prepare the specimens. The microstructure of the concretes was investigated with scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and mercury intrusion porosimetry (MIP). Results showed an opposite coarse aggregate size effect between OPC and MKGP specimens in terms of compressive strength. SEM/EDS analysis indicated that the MKGP concrete has a weaker microstructure compared to OPC concrete induced by a higher porosity. The differences in mechanical properties and pore structure between the MKGP and OPC concrete are attributed to the greatly differing shrinkages triggered by the large surface area and penny-shaped particles of metakaolin. The findings in this work help tailor the mechanical properties and microstructure of MKGP concrete for future engineering applications.

Evaluation of The Effect of Gradation on Mechanical properties of Stone Mastic Asphalt Mixtures

For stone mastic asphalt (SMA) mixtures, the aggregate gradation is the significant requirement to achieve the best structural design. In this research, an attempt to evaluate the effect of nominal maximum aggregate size (NMAS) and gradation on SMA volumetric and mechanical properties. Samples for each mixture were designed and fabricated according to NAPA specifications. A total of 9 SMA mixtures with three NMASs, each with three different aggregate gradations, one asphalt binder (styrene butadiene styrene SBS) modified binder were studied. Volumetric analysis of specimens revealed that the voids in the mineral aggregate (VMA), and voids filled with asphalt (VFA) rise with a reduction in NMAS. SMA samples with higher NMAS have lower optimum asphalt than those of lower NMAS. From the laboratory study, SMA mixes fabricated utilizing the upper limit of gradation showed the highest mechanical properties in terms of Marshall Stability and indirect tensile strength. It was recorded also that the SMA mixtures with larger NMAS had higher ITS and Marshall stability contrasted to the others. This improvement could be because of the larger portion of coarse aggregate in the SMA mixture.

Investigation of the density, porosity, and permeability properties of pervious concrete with different methods

Due to the porous structure of pervious concrete (PC), it is very important to correctly determine the voids inside and around the sample that affect the density, porosity, and permeability properties of the concrete. This study aimed to find simple and effective methods and to compare the methods used to determine density and porosity measurements of PC mixtures in the form of cylinders, cubes, and prisms of different sizes. Porosity, density and permeability tests of silica fume added pervious concrete with different aggregate sizes (2–4 mm, 4–8 mm, and 8–16 mm) and different aggregate/binder (A/B) ratios (2, 2.5, and 3) were performed. Also, changes in the permeability of PC by using constant head and falling head permeability tests were investigated. The effect of aggregate size, and aggregate/binder ratio on porosity, permeability, and density were also examined. Correlations between porosity and permeability, porosity and density, and falling head method and constant head method were examined. As a result, it was determined that measurement methods significantly affected density, porosity, and permeability values of PC. Besides, the method of covering with the stretch film was found to be the most effective method in determining the density and porosity of PC among the methods in this study.

Changes in microstructure and water retention property of a lime-treated saline soil during curing

This study aims at investigating the lime treatment effect on the changes in microstructure and water retention property of compacted saline soil, with consideration of the aggregate size effect. Two soil powders with different maximum aggregate sizes (Dmax = 0.4 and 5 mm) were prepared and stabilized by 2% lime. The microstructure, total suction and matric suction were determined at various curing times. Results showed that the lime treatment caused a rapid decrease in micro-pores and an increase in macro-pores due to the flocculation of soil particles. During curing, the percentage of micro-pores decreased and that of nano-pores increased slightly. Due to the modification of microstructure, the matric suction increased significantly at 90-day curing. However, the curing time effect on the total suction was insignificant. This was due to the fact that the Ca2+ and Mg2+ in soil pore water and the Ca2+ from hydrated lime were consumed in the precipitations of CaCO3 and Mg(OH)2, cation exchanges and pozzolanic reaction, resulting in a reduction in osmotic suction. Therefore, the increase in total suction was slight, as the increase in matric suction was balanced by the decrease in osmotic suction. The treated specimens with larger aggregates exhibited a larger modal size and thus had a smaller air entry value. The aggregate size effect on the water retention property of total suction and matric suction was found to be insignificant, which could be explained by the similar pore size distribution at micro-pore range and the same soil mineralogy for specimens with different aggregates.

Assessing the impact of soil aggregate size on mineralization of nitrogen in different soils, China

Soil aggregates play a critical role to support the development of soil nitrogen (N) pools, but the underlying mechanism by which soil aggregate size impacts N mineralization remains unclear. The objective of this study was to determine the effect of aggregate size in soil N mineralization through cultivation experiments of different type soils. The topsoil samples of ten typical profiles in different regions of China were collected, and a series of laboratory column incubation experiments were conducted to quantify the relationship between the distribution of soil aggregate size and the concentration and mass of mineral N (i.e., NH4-N and NO3-N) under N fertilizer addition. The results indicated that the weight of aggregate with different sizes was less affected by the intensity of fertilization, which was mainly influenced by the soil types. In most soils, the weight of soil aggregates of 1–0.5 mm accounted for the largest proportion of aggregates in the five categories (i.e., 5–2 mm, 2–1 mm, 1–0.5 mm, 0.5–0.25 mm, and < 0.25 mm). Moreover, the intermediate aggregates (1–0.5 mm and 0.5–0.25 mm) were detected to have the highest mineral N concentration and mass, and they were also demonstrated to be significantly (P < 0.05) correlated to the potential nitrogen mineralization (PNM) rates in most soils. Subsequently, the obtained PNM indices were classified into three levels: i.e., >65% (highly responsive), 45%–65% (moderately responsive), and < 45% (lowly responsive), and we proposed the preliminary strategies on fertilizer types, agricultural intensity, and crop selection for different soils. The outcome of this study provides new insights into the relationship between soil aggregate sizes and N mineralization abilities and will help in developing guidelines for fertilizer management.

Effect of coarse aggregate size on non-uniform stress/strain and drying-induced microcracking in concrete

Non-uniform stresses, strains and microcracking of the concretes with three coarse aggregate sizes (5–10 mm, 10–16 mm, 16–20 mm) dried under 40% relative humidity (RH) for 60 days were quantified using digital image correlation and lattice fracture modelling. The influencing mechanism of coarse aggregate size on the drying-induced microcracking of concrete was clarified: (1) As the coarse aggregate size decreases, propagation paths of microcracking are increased, which increase the number of small microcracks and release the drying shrinkage force from mortar phase. (2) Tensile stress shells surrounding the coarse aggregates become thinner, thereby decreasing the area of large microcracks. As the coarse aggregate size decreased from 16-20 mm to 5–10 mm, the average thickness of tensile stress shells decreased from 2.13 mm to 1.09 mm at the beginning of drying, and the area of the microcracks >5 μm in width decreased from 796.6 mm2/m2 to 340.2 mm2/m2 at 60 days since drying.

Hydration Mechanism of Sustainable Clinker-Free Steel Slag Binder and Its Application in Mine Backfill

More than 600 million tons of slag are generated globally every year, leading to multiple environmental issues. Thus, research on applications of slags is crucial. The use of steel slag in cement is limited by its low hydraulic activity and volumetric instability. In the current study, we present a clinker-free steel slag binder (SSB) and discuss the coupled alkali–sulfate activation mechanism. The f-CaO was consumed during hydration, thus minimizing the expansion risk. SSB hydration products demonstrated a higher quantity and quality compared with cement, indicating excellent performance. We tested the SSB in a practical mine backfill application, investigating the effects of binder content, concentration, and aggregate grain size on the mechanical and rheological properties of the backfilling mixtures. The results demonstrate the ability of SSB to completely replace Portland cement with half the binder content dose without affecting the strength or flowability of the backfilling mixtures.

Marshall Parameters of Hot Mix Asphalt with Variable Filler Types and Aggregate Gradations

This research aims to evaluate the effect of aggregate nominal maximum size and type of filler on Marshall properties of asphalt mixture. A planned laboratory study is implemented by preparing the asphalt samples using locally available materials and an asphalt binder of 40-50 penetration grade (AC-20). Three types of aggregate nominal maximum size according to SCRB specifications and three types of fillers including limestone dust, cement and hydrated lime were used. Three bitumen contents were used led to nine types of mixtures were prepared and tested that includes all the variables studied. The optimum asphalt content of the asphalt mixture was determined to be 4.75%w using the Marshall method of mix design. A total of 81 Marshall specimens were prepared and tested. The results showed that the aggregate nominal maximum size and filler type have a variable effect on Marshall properties while optimum asphalt content has a significant effect on Marshall Properties regardless of other variables in the mixture. Experimental results showed that using cement as a filler material can significantly increase the Marshall Stability compared to that of using hydrated lime and limestone dust.

Investigation of Flexural Capacity of Concrete Containing Liquid Silicone Rubber

Despite the great use of concrete, tensile strength and low flexibility and brittleness are its weaknesses. Many solutions have been provided to eliminate the mentioned defects. In order to increase the flexibility of concrete in previous studies, crushed rubber tire particles have been added to concrete. Recycling car tires helps the environment and makes concrete much more flexible than regular concrete. In this research, silicone rubber has been replaced by 0%, 2%, 4%, 8%, 12.5%, 25%, and 50% of mineral aggregates. This rubber was initially in liquid form, which, after mixing with ordinary concrete, dispersed into the concrete texture and formed a uniform mixture, and this liquid rubber became a flexible solid after 24 hours. Concrete containing silicone rubber is a new composite with new properties, and in this research, it is called Hybrid Silicone Rubber Concrete (HSRC). Also, to evaluate the effect of aggregate size in making experimental specimens, two coarse to fine aggregate ratios of G/S = 0.7, 1.1 were considered. Flexural strength tests were performed on hardened concrete beam specimens. The results showed that, with increasing the amount of silicone rubber in concrete, flexural strength decreased and this percentage of strength reduction was compared with the percentage of reduction in compression and splitting tensile strength. It was found that the reduction of flexural strength was less than compression and splitting tensile strength. Larger deformation was observed during all tests when the concentration of silicone rubber increased. It was observed that the higher the amount of silicone rubber in the specimens, the less noise and the less separation of aggregates with which the failure of the specimens was associated.

Investigation of aggregate size effects on properties of basalt and carbon fibre-reinforced pervious concrete

Pervious concrete structure consists of meso-sized pores due to partial or complete elimination of fine aggregates, resulting in decreased mechanical properties in par with conventional concrete. Meanwhile, fibres were pronounced to improve the mechanical properties of concrete without affecting its durability. The main objective of the study is to compare the properties of basalt fibre-reinforced pervious concrete (BFRPC) and carbon fibre-reinforced pervious concrete (CFRPC) with two single-sized aggregates, namely 12.5 and 20 mm. The volume of both the fibres was varied from 0 to 0.4% at intervals of 0.1%. Pervious mix with 12.5 mm sized coarse aggregates and carbon fibre content of 0.2% (12.5CFRPC0.2) was observed as an optimum mix with respect to mechanical strengths as it improved the compressive strength, split tensile strength and flexural strength by 11.59%, 32.70% and 35.32%, respectively, compared with the conventional mix.

EFFECTS OF PARTICLE SIZE AND TYPE OF AGGREGATE ON MECHANICAL PROPERTIES AND ENVIRONMENTAL SAFETY OF UNBOUND ROAD BASE AND SUBBASE MATERIALS: A LITERATURE REVIEW

Unbound graded aggregates are used to construct the base and subbase of road pavement. The mechanical properties of unbound graded aggregates depend significantly on aggregate size and grading, especially on the maximum particle size (Dmax) and fines content (Fc; typically, the particle size of fines < 0.075 mm). Nowadays, not only natural aggregates (NA) but also recycled aggregates (RA) from construction and demolition waste are used in road construction. Many studies have been done to characterize the mechanical properties of RA, but a comprehensive understanding of the effects of aggregate size and grading on the mechanical properties has not been fully achieved due to the wide variety of material types and properties of RA. Therefore, this paper searched previous studies and reviewed the effects of particle size, type of aggregate, and mixing proportions of RA on mechanical properties such as compaction, bearing capacity, resilient modulus, and shear strength. In addition, some information on the environmental safety of RA, such as leachate pH and leaching of elements, are summarized. The results collected from the literature indicate that the mechanical properties of RA and their mixtures are mostly comparable to those of NA and can be used to construct road base and subbase. As well as the type of aggregate, Dmax of RA was also found to affect highly the relationships between the mechanical indices (e.g., the maximum dry density and California bearing ratio) and Fc and/or mixing proportion.

EXPERIMENTAL STUDY ON THE EFFECT OF DIFFERENT COARSE AGGREGATE SIZES ON THE STRENGTH OF CONCRETE

The purpose of this research work is to compare the effect of coarse aggregate sizes on the strength of concrete. Materials for this study were (water, fine and coarse aggregates and cement). Acceptability criteria for tests on basic materials for concreting were ascertain such as; water according to BS 2690 standard, Fine and coarse aggregates according to BS 812:1975, part 1 to 4 standard and Cement according to BS 12:1991. The acceptability criteria for testing fresh and hardened concrete such as Workability test (slump test in accordance with BS 1881:1983, part 102) and Compressive strength test (cube test in accordance with BS 1881:1983. The specimen size for crushing strength was 150mm x 150mm x 150mm, cured and tested for 7, 14 and 28 days with concrete grade 20 of minimum compressive strength of 14 N/mm2 (mix ratio of 1:2:4). From the result gotten, the concrete strength of aggregate size of 20mm to 28mm after 28 days was higher than that of 13.2mm to 19mm and that of 3.35mm to 10 mm.

Studying hydraulic conductivity of asphalt concrete using a database

A new database called AC/k-1624 containing over 1600 measurements of saturated hydraulic conductivity of asphalt concrete has been assembled and analysed. AC/k-1624 was used to investigate the effect of the grading entropy parameters on saturated hydraulic conductivity. A new prediction model comprising both air voids and grading entropy is presented. The database analysis using different predictors of asphalt hydraulic conductivity reveals that the gradation does affect the hydraulic conductivity, but the air void level is necessary to make reasonable a-priori assessments of hydraulic conductivity for asphalt concrete. The new empirical model is shown to have a good predictive capacity for hydraulic conductivity fitting more securely at higher values with more scatter observed at lower values. The effects of test type, gradation classification and Nominal Maximum Aggregate Size (NMAS) are also studied, revealing in general relatively modest influences on the computed regression coefficients.