Influence Of Aggregate Size Research Articles

Influence of aggregate size and notch depth ratio on fracture performance of steel slag pervious concrete

Steel slag pervious concrete (SSPC) is a promising sustainable pavement material for sponge city construction. The influence of aggregate size and notch depth ratio on fracture performance of SSPC was studied in this work. Considering two kinds of aggregate size (4–6 mm and 10–20 mm) and four kinds of notch depth ratio (0.2, 0.3, 0.4, 0.5), the three-point bending test of a rectangular beam with a single side notch was carried out, and the whole fracture process was monitored by acoustic emission. The experimental results show that the fracture behavior of SSPC has obvious boundary effect. Meanwhile, large-size aggregates can improve the fracture strength and fracture energy of SSPC, which is related to the stronger mechanical interlocking and bonding between aggregates caused by thicker slurry layer on the surface of large-size aggregates. In addition, the acoustic emission monitoring results show that the internal wave source activity and strength are higher in the fracture process of large-size aggregate specimens, and there are more shear cracks. Finally, the PFC3D numerical model established by the discrete element theory was used to simulate the fracture behavior of SSPC. The results show that the particle flow code is an effective method to study the fracture behavior of pervious concrete.

Crack mechanisms in concrete – from micro to macro scale

The paper discusses a fictitious crack model of concrete in tension proposed by Hillerborg. This model presents a concept that illustrates the mechanism of crack initiation and its propagation in concrete on meso-level. It has proven to be a very useful tool for practical use, for both numerical and experimental research. The model was derived from findings on crack mechanisms on more advanced micro- and macro-scale, as presented in this paper. One of the paramount issues regarding crack analysis is the influence of aggregate size on mechanical and fracture parameters of concrete, and also on micro-crack development and associated macro-crack formation. Although significant progress in recognizing crack mechanisms in concrete has been achieved, there are still some aspects that should be studied in depth, for example the role of aggregate particles on crack development. This problem is analysed in the paper as well.

Influence of aggregate size on flexural fatigue response of concrete

Plain concrete used in pavements undergoes fatigue damage with repeated traffic and thermal loading. Numerous studies were conducted previously to evaluate the effect of various parameters on the fracture behavior of concrete. Nominal maximum aggregate size which is one of the parameters investigated in the past, to evaluate the fracture characteristics was focused to influence the fracture energy of concrete significantly. This could be due to a larger crack path and greater crack growth resistance offered by the larger aggregates in the fracture process zone. Hence, it is worthwhile to investigate the effect of nominal maximum aggregate size (NMAS) of aggregate on the fatigue life of concrete. This factor, if influential, might be a feasible approach for field application to control the fatigue performance of concrete. In the present study, the effect of nominal maximum aggregate size was evaluated under different stress levels (80, 85, and 90%) and different frequencies of loading (2, 5, and 10 Hz). For this purpose, flexural fatigue test was conducted on concrete beam specimens. The specimens were prepared with a blend of fine aggregate and coarse aggregate with two different nominal maximum aggregate sizes (10 mm and 20 mm, designated as S10 and S20 respectively). A total of 100 specimens of 100 mm × 100 mm × 500 mm size were used in the experimental investigation. The results show that the fatigue life of samples with S10 mixture is significantly higher compared to S20 mixture for 80% stress level but are almost similar for 90% stress level irrespective of the loading frequency. The fatigue results are in better agreement with three-parameter Weibull distribution compared to other distributions such as lognormal as confirmed by the goodness of fit test Anderson-Darling statistic. The value of β, the Weibull distribution characteristic shape parameter, obtained as less than 1.0 in this study, indicates the risk of early life failures for the considered stress levels. The survival probability plots and p-value statistics suggest that stress level influences the fatigue life estimation for both S10 and S20 samples but not the loading frequency. Based on the present study, it can be concluded that smaller nominal maximum aggregate size is more beneficial for the fatigue performance of concrete.

Experimental Study on the Vegetation Growing Recycled Concrete and Synergistic Effect with Plant Roots.

Vegetation growing recycled concrete (VGRC) is a relatively new building material that has both biocompatibility and engineering function. The basic performance of VGRC was investigated by experimental analysis, and the hydration products and pore structure of different VGRC mix proportions were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and industrial computed tomography (CT). The results show that ultrafine slag can reduce Ca(OH)2 content in cementing material and has a filling effect on micropores. VGRC has the best performance; the internal pore distribution is uniform when porosity is 20–25%, and the ultrafine slag content is 40%. The compressive strength of VGRC is greatly damaged by the quick-freezing method, while the degree of damage from natural freeze–thaw cycles is relatively small. Soaking in acid solution can effectively reduce the internal pore alkalinity of VGRC. Most plants can grow normally in vegetation concrete, and plant roots can penetrate 6-cm thick concrete blocks after being planted for 60 days. The compressive strength of VGRC decreased after turf planting of 30 days and then increased slowly. The permeability coefficient of VGRC increases with the increase in porosity and aggregate size and decreases after planting and covering. The frost resistance of VGRC is enhanced, and the influence of aggregate size and porosity is small after turf planting.

Influence of aggregate size on compressive strength of pervious concrete

The aggregate size is an important factor influencing the compressive strength of pervious concrete. This work is focused on the study of the relationship among aggregate size, compressive strength, pore structure, cementitious paste thickness, and then understanding the influence of aggregate size on the compressive strength of pervious concrete. Eight groups of pervious concrete samples with almost the same porosity but different aggregate size were prepared. The 2D/3D pore characteristics and fractal dimension were extracted and analyzed based on CT images. The cementitious paste thickness was determined by a modified semi-manual hand measurement method. Test results show that the compressive strength increases rapidly with the increase of aggregate size at first, while the aggregate size is beyond 7 mm the effect of aggregate size on compressive strength is not so obvious. The compressive strength changes with aggregate size can be mainly attributed to the effect of aggregate size on pores characteristics and cementitious paste thickness. It is found that the compressive strength is most sensitive to the content of the small pores (0–1.5 mm2). The increase of the small pores content will decrease the compressive strength. With the increase of fractal dimension of the pores, the compressive strength first increases and then decreases. While the cementitious paste thickness is less than 1.15 mm, the compressive strength increases slowly with the cementitious paste thickness increases. Once the cementitious paste thickness exceeds 1.15 mm, the compressive strength remains relatively stable.

Properties of pervious concrete made from steel slag and magnesium phosphate cement

Abstract The new pervious concrete (PC) were prepared using magnesium phosphate cement (MPC) as binding and waste steel slag as coarse aggregate. A series of laboratory experiments were carried out to study the influence of aggregate size and molding method on the compressive strength, flexural strength, porosity and water permeability coefficient of magnesium phosphate cement steel slag pervious concrete (MSPC). Experimental results showed that the influence of aggregate size on compressive strength is different when different molding methods were adopted. Through comparative analysis, the MSPC with medium particle size formed by vibration molding had the highest compressive strength, and the maximum can reach 41.5 MPa. Based on the excellent bonding strength of MPC, the MSPC has better flexural strength than traditional PC, and the maximum 28-day flexural strength can reach 8.0 MPa. The porosity increases with the increase of aggregate size, and which is in the range of 23.8–26.5% for all the MSPC mixtures. Similarly, the water permeability coefficient of MSPC increases as the increase of aggregate size, and with the range from 5.85 to 7.10 mm/s. The 28-day bend-press ratio of MSPC is close to 1/5. Unlike the traditional PC, the mechanical strength of MSPC increased first and then decreased with the porosity, while regardless of aggregate size and molding method, the water permeability coefficient increased linearly with the porosity. The test results indicate that the MSPC made of steel slag aggregates and MPC is a very promising eco-friendly PC.

Strength, Permeability, and Freeze-Thaw Durability of Pervious Concrete with Different Aggregate Sizes, Porosities, and Water-Binder Ratios

Pervious concrete (PC), as an environmental friendly material, can be very important in solving urban problems and mitigating the impact of climate change; i.e., flooding, urban heat island phenomena, and groundwater decline. The objective of this research is to evaluate the strength, permeability, and freeze-thaw durability of PC with different aggregate sizes, porosities, and water-binder ratios. The orthogonal experiment method is employed in the study and nine experiments are conducted. The compressive strength, flexural strength, permeability coefficient, porosity, density, and freeze-thaw durability of PC mixtures are tested. Range analysis and variance analysis are carried out to analyze the collected data and estimate the influence of aggregate size, porosity, and water-binder ratio on PC properties. The results indicate that porosity is the most important factor determining the properties of PC. High porosity results in better permeability, but negatively affects the mechanical strength and freeze-thaw durability. PC of 15% porosity can obtain high compressive strength in excess of 20 MPa and favorable freeze-thaw durability of 80 cycles without sacrificing excessive permeability. Aggregate size also has a significant effect on freeze-thaw durability and mechanical strength. Small aggregate size is advantageous for PC properties. PC with 4.75–9.5 mm coarse aggregate presents excellent freeze-thaw durability. The influence of the water-binder ratio on PC properties is not as significant as that of aggregate size and porosity. An optimal mix ratio is required to trade-off between permeability, mechanical strength, and freeze-thaw durability.

Influence of aggregate size and inclusion of polypropylene and steel fibers on the hot permeability of ultra-high performance concrete (UHPC) at elevated temperature

Explosive spalling is one of the most detrimental problems for ultra-high performance concrete (UHPC) in fire condition due to the risks of breaching the integrity of concrete structures. This paper investigates the influence of aggregate size and inclusion of PP and steel fibers on the intrinsic permeability of UHPC at elevated temperature. Hot permeability measurements were performed on UHPCs subjected to elevated temperature up to 300 °C. Microstructure of UHPC samples before and after the exposure to elevated temperature was studied to reveal potential mechanisms responsible for the change of permeability. Results showed that the inclusion of PP fibers or larger aggregates significantly increases the hot permeability while the addition of steel fiber does not contribute to the enhancement of the permeability of UHPC at elevated temperature. The combined use of PP fibers and larger aggregates in UHPC showed synergistic effect and resulted in the significant increase of permeability at elevated temperature, which is mainly attributed to the formation of interconnected micro-crack networks at elevated temperature due to the melting of PP fiber and thermal expansion and mismatch between the aggregate/fiber and matrix.

The influence of aggregate size fraction and horizon position on microbial community composition

The influence of horizon position and aggregate size on bacterial and fungal community composition was determined. From nine sites, soils were collected from the top three horizon positions (H1, H2 and H3). Physical fractionation separated samples into large macroaggregate (LM, >2000 μm), macroaggregate (MAC, >250 μm), microaggregate (MIC, <250 μm), and silt and clay (SC, 53 μm) fractions. In all samples, the structure of the bacterial and fungal community composition was assessed via restriction fragment length polymorphism (T-RFLP), and for the four aggregate sizes from the top two horizons positions an in-depth analysis of the bacterial community was conducted using next generation sequencing (NGS). Bacterial and fungal communities both differed between aggregate-sizes. Changes in the composition of the bacterial and fungal communities also occurred among horizon positions, with a significant interaction between aggregate size and horizon position evident for the bacterial community. Using NGS, it was shown that aggregate-size had a significant effect on the bacterial community in both horizon positions at both the phyla and family taxonomic levels. MAC and MIC significantly differed in the % relative abundance of bacterial groups, potentially indicating differing predation pressures. These results indicate that both horizon position and aggregate size support distinct microbial communities. Understanding these parameters is critical in our comprehension of the patterns of microbial diversity in soil.

3‐D mesoscale simulation of crack‐permeability coupling in the Brazilian splitting test

SummaryIn this paper, mesoscale hydromechanical simulations are performed to study (1) fracture features and (2) crack‐gas permeability coupling evolution in the context of the tensile splitting test. The mesostructure is based on a 2‐phase 3‐D representation of heterogeneous materials, such as concrete, where stiff aggregates are embedded into a mortar matrix. To take into account these heterogeneities without any mesh adaptation, a weak discontinuity is introduced into the strain field. In addition, a strong discontinuity is also added to take into account microcracking. This mechanical model is cast into the framework of the enhanced finite element method. Concerning the coupling with gas permeability, a double‐porosity method is used to simulate the flow through the cracks and the porosity. The apparent gas permeability is afterwards evaluated by a homogenization method. On the basis of finite element simulations, influence of aggregate size on ultimate crack opening, macroscopic ultimate tensile stress, total dissipated energy, and gas permeability evolution is numerically investigated. Furthermore, gas permeability evolution is also compared with experimental results from the literature. In addition, in the spirit of a sequential multiscale approach, macroscale gas permeability equations are identified from the hydromechanical results coming from the mesoscale computations. These equations lead to a relation between macroscale gas permeability evolution and crack opening. Besides, we show how the aggregate size influences the percolation threshold and that after this threshold, a cubic relation between macroscale gas permeability and crack opening is obtained.

Quantitative characterization and elastic properties of interfacial transition zone around coarse aggregate in concrete

Backscattered electron images (BSE) obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone (ITZ) in concrete. Influences of aggregate size (5, 10, 20, and 30 mm), water to cement ratio (0.23, 0.35 and 0.53) and curing time (from 3d to 90d) on the microstructure of interfacial transition zone between coarse aggregate and bulk cement matrix were investigated. The volume percentage of detectable porosity and unhydrated cement in ITZ was quantitatively analyzed and compared with that in the matrix of various concretes. Nanoindentation technology was applied to obtain the elastic properties of ITZ and matrix, and the elastic modulus of concrete was then calculated based on the Lu & Torquato model and self-consistence scheme by using the ITZ thickness and elastic modulus obtained from this investigation. The experimental results demonstrated that the microstructure and thickness of ITZ in concrete vary with a variety of factors, like aggregate size, water to cement ratio and curing time. The relative low elastic properties of ITZ should be paid attention to, especially for early age concrete.

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.

Influence of aggregate size on photoactivity of N-doped TiO2 particles in aqueous suspensions under visible light irradiation

Abstract This work is focused on the study of the correlation between the photocatalytic activity of N-doped TiO2 particles, achieved by a designed synthesis, and their degree of aggregation in aqueous suspension. N-doped TiO2 photocatalyst particles, suspended in bidistilled water, presented a trimodal (in the nano-micro metric range) aggregate size distribution. This distribution resulted monomodal, in the nanometric range, when in the aqueous solution was added an organic dispersing agent (azulene). This behavior was associated to the presence, on the N-doped TiO2 particle surfaces, of an organic phase which was detected by thermal and infrared analysis. This organic phase was assumed to have a stabilizing function for nanoparticles. The influence of aggregate size of N-doped TiO2 photocatalyst on the photocatalytic degradation of methylene blue has been studied. The aggregate size distribution of photocatalyst influenced the amount of methylene blue adsorbed on catalyst surface and increased the photocatalytic activity. The influence of operating parameters such as the amount of dispersing agent and the amount of photocatalyst in aqueous suspensions has also been examined.

Influence of Aggregate Size on Self Compacting Concrete using Nafores 801 Liquid as Plasticizer

Self-Compacting Concrete (SCC) is highly useful in congested reinforced structures where vibration or compaction prove difficult. It's a concrete that can flow, consolidate under its own weight and completely fill the formwork without further vibration. In this research, laboratory investigation of SCC mix prepared from three different recipe set of aggregates (20mm, 12.5mm, and 10mm) down size and mix designed for 1: 1 1 /2: 3 mixing proportion with w/b ratio of 0.56 and Sulphonated Naphthalene Formaldehyde dosage (1.2% by weight of cement) was affirmed based on field trial. The SNF acting as Super plasticizer (Water Reducing Agent) and influence of the admixture was examined via the workability tests. However, it was examined by using the slump flow test, V - flow, and L - box test. The designed mix achieved consistency and self compatibility under its own weight without any external vibration or compaction. 150mm x150mm x 150mm cube specimen cast was done and thereafter cured for twenty eight (28) days. The strength development for each of the specimen at 3, 7, and 28 days for the respective mix was examined and the results showed that increase in the compressive strength with respect to the curing age, enhancement in workability, reduction in shrinkage, and bleeding of the concrete mix of SCC holds to the inclusion of Super Plasticizer in the mix. The significance of this research work lies in its attempt to provide information on the performance of Self Compacting Concrete made from different recipe sets of aggregate and its major advantage in salvaging time and labour. Keywords: Aggregate, Curing, Self-Compacting Concrete (SCC), Sulphonated Naphthalene Formaldehyde, Plasticizer, Strength, and Workability.

Effects of aggregate morphology and size on laser-induced incandescence and scattering from black carbon (mature soot)

We have used a Single-Particle Soot Photometer (SP2) to measure time-resolved laser-induced incandescence (LII) and laser scatter from combustion-generated mature soot with a fractal dimension of 1.88 extracted from a burner. We have also made measurements on restructured mature-soot particles with a fractal dimension of 2.3–2.4. We reproduced the LII and laser-scatter temporal profiles with an energy- and mass-balance model, which accounted for heating of particles passed through a CW-laser beam over laser–particle interaction times of ~10μs. The results demonstrate a strong influence of aggregate size and morphology on LII and scattering signals. Conductive cooling competes with absorptive heating on these time scales; the effects are reduced with increasing aggregate size and fractal dimension. These effects can lead to a significant delay in the onset of the LII signal and may explain an apparent low bias in the SP2 measurements for small particle sizes, particularly for fresh, mature soot. The results also reveal significant perturbations to the measured scattering signal from LII interference and suggest rapid expansion of the aggregates during sublimation.

Numerical Study on the Influence of Aggregate Size on Skid Resistance Performance of Porous Pavements

Porous pavements are often used as a means to improve skid resistance during wet weather. During the design and construction phases, porosity is often used as the single parameter representing porous pavement drainage capacity. However, it is insufficient to use this parameter to predict frictional performance on porous pavements because pavement mix with different aggregate sizes and yet having identical porosity values can yield significantly different skid resistance behaviors. This paper presents a numerical framework to analyze the influence of aggregate size on porous pavement skid resistance. It was found that despite having identical porosity, pavement mix with larger aggregates can provide higher permeability value, which consequently reduces the water film thickness on the pavement surface under a given rainfall intensity and relieves the hydrodynamic pressure buildup underneath the tire. Porous pavements constructed with larger-size aggregates for a given porosity are found to exhibit better skid resistance performance.

Numerical Study on Drying Shrinkage of Concrete Affected by Aggregate Size

This paper describes new insights on the influence of aggregate size on drying shrinkage of concrete through numerical simulation. Using a two-dimensional finite element method, it is demonstrated that it is impossible to reproduce the impact of aggregate size on concrete drying shrinkage by simply considering crack opening in the mortar matrix. From this result, it is deduced that the effect of aggregate size on concrete shrinkage is influenced by aggregate surface area. The application of a constitutive law that considers the characteristics of ITZ to coarse aggregate elements successfully reproduced the damage and shrinkage strain of concretes with different aggregate sizes. A certain range of virtual ITZ pore thickness in the model was found to allow simulation of the real phenomenon. It is concluded that ITZ characteristics should be taken into account when considering aggregate behavior in drying concrete.

The Influence of Aggregate Size and Binder Material on the Properties of Pervious Concrete

Specimens were prepared by altering parameters such as aggregate sizes, binder materials, and the amounts of binder used and were subsequently tested by using permeability, porosity, mechanical strength, and soundness tests. The results indicated that the water permeability coefficient and connected porosity decreased as the amount of binder used increased and increased with increasing aggregate size. In the mechanical strength test, the compressive, splitting tensile, and flexural strengths increased as the amount of binder used increased and decreased with the increase of aggregate size. Highly viscous binder enhanced compressive strength, water permeability, and the resistance to sulfate attacks. In the mechanics and sulfate soundness tests, the mix proportion of alkali-activated slag paste used in this study exhibited a superior performance than the Portland cement pervious concrete (the control) did, but the difference in water permeability between the two types of concrete was insignificant. The mix proportions of cement paste containing 20% and 30% silica fume exhibited less mechanical strength than the control did. Moreover, compared with the control, the cement paste containing silica fume demonstrated poor resistance to sulfate attacks, and the difference in the water permeability between such specimen and the control was not noticeable.

Evaluating the Influence of Aggregate Size on Permeability of Porous Pavements Using Finite Volume Simulation

Porous pavement is widely used to enhance wet weather skid resistance on highways through its superior drainage capacity. Porosity within the porous pavement structure typically serves as the control variable during the design and construction phases, while permeability is the functional parameter indicating drainage performance during the operation phase. One potential implication of using porosity during design and construction and permeability during operations is that porous pavement layer pore structures resulting from different aggregate sizes can result in different permeability values despite having identical porosity values. Recognizing this issue, this paper first presents a theoretical analysis on the drainage capacity of porous pavement. Outflow tests on typical porous pavements with various aggregate sizes are then simulated using the finite volume method and simulation results are validated against experimental measurements. It is concluded from our study that aggregate size has a significant influence on the permeability of porous pavement and should be included during pavement design, construction and operations.

Investigation on Adhesive Behavior between Binder and Aggregate by Vialit Test under Low Temperature

Raveling, mainly caused by interfacial failure between binder and aggregate or cohesive failure of asphalt mortar, is one of the major causes of premature failure in asphalt pavements, and it also accelerates the severity of other distresses. The experiential adhesive experiment named Vialit Test under low temperature was chosen to investigate the adhesion behavior between binder and aggregate in this paper. The influence of aggregate size, aggregate types, binder types and impact energy were discussed. Quantity of ravelling aggregates and weight loss of aggregate and binders were used to evaluate the adhesive performance. Test results demonstrate that aggregate types have limited effects on the adhesion at low temperature, while aggregate size, binder types and impact energy have significant effects on adhesive performance between binder and aggregate. Binders with fine fillers exhibit better adhesion to aggregate when compares with pure asphalt.