Maximum Aggregate Size Research Articles

Laboratory Evaluation of Wear Particle Emissions and Suspended Dust in Tire–Asphalt Concrete Pavement Friction

This study aims to evaluate the tire–road-wear particles (TRWPs) and suspended dust generated based on the nominal maximum aggregate size (NMAS) of the polymer-modified stone mastic asphalt (SMA) mixtures indoors. The SMA mixtures containing styrene butadiene styrene (SBS) polymer and the NMASs of 19, 13, 10, 8, and 6 mm were used. Dust was generated from the wear of the tires and the pavement inside the indoor chamber by using the laboratory tire–road-wear particle generation and evaluation tester (LTRWP tester) developed by Korea Expressway Corporation (KEC). In this method, a cylindrical asphalt-mixture specimen rotates in the center, and a load is applied using three tires on the sides of the test specimen. During the test, a digital sensor was used to measure the concentration for each particle size. After the test was completed, the dust was collected and weighed. According to the test results, the generated TRWP emissions were reduced by approximately 0.15 g as the NMAS of the SMA mixture decreased by 1 mm. TRWP emissions decreased by 20% when using the 6 mm SMA mixture compared to the 13 mm SMA mixture. For practical application, a predicted equation of TRWP emissions estimation was developed by using the concentration of suspended dust measured by the digital sensor in the LTRWP tester. LTRWP can be used as an indoor test method to evaluate pavement and tire materials to reduce the amount of dust generated from tire and pavement wear.

Leveraging clay formwork 3D printing for reinforced concrete construction

ABSTRACT Robotic clay formwork three-dimensional printing combined with incremental concrete casting controls concrete's hydrostatic pressure and enables the production of building-scale structures. Clay formwork is self-demolding and less carbon intensive than concrete and polymer, often used in formwork additive manufacturing. This research investigates the recycling and reuse of clay to re-print formworks and tailors a self-compacting concrete formula with 60% reduced cement content and 90% larger maximum aggregate size. The study then explores integrating steel fibers and longitudinal rebars into the fabrication process to provide shear and bending reinforcement. When comparing the load-bearing behaviour of the fabricated beams against those cast traditionally using wooden formworks, the fabricated beams demonstrated 20% lower load-bearing capacity, with peak load mid-span deflections staying in a similar range. While more investigation is required to address formwork deformations using mixed steel fibers and recycled clay, this research paves the way for more sustainable concrete construction practices.

Prediction of concrete cracking behavior under different strain rates based on the boundary effects model

Predicting the cracking behavior of concrete under different strain rates through fracture parameters has been a longstanding topic of interest. In this study, the effect of concrete strength and strain rate on the fracture toughness and initial fracture energy for three-point bending notched beams is investigated by boundary effect model (BEM). With the help of BEM, only a series of basic parameters (such as tensile strength, maximum aggregate size and specimen size) are used in the process of calculating the fracture toughness and initial fracture energy. The cumbersome concrete fracture experiment is avoided in this model. The initial fracture toughness and unstable fracture toughness, predicted by BEM are agreed with the experimental results in the literature. The results demonstrate that BEM is valid for predicting the fracture toughness of different concrete strengths, even at increased strain rates. As the loading strain rate increases, the initial fracture toughness of different concrete strength shows a slight growth with increasing loading strain rate, which indicates that the concrete needs more energy to reach the cracking condition.

Experimental Research on Gradation Range and Performance of SMAC13.

Stone matrix asphalt and asphalt concrete mixture with 13.2 mm nominal maximum aggregate size (named SMA13 and AC13, respectively) are widely used in the surface course of asphalt pavement in China. Generally, the pavement performance of SMA13 is superior to that of AC13, while the cost of the former is significantly higher than that of the latter. The objective of this paper was to develop a new hot mix asphalt (named SMAC13) whose performance and cost are between SMA13 and AC13. A boundary sieve size (BSS) of 2.36 mm was selected between fine and coarse aggregates. Based on the union set of aggregate gradation ranges of SMA13 and AC13, the family of gradation curves in the forms of S shapes were designed in terms of the BSS passing rate. According to the evaluation of the skeleton interlock of coarse aggregate of the gradation curve family, the aggregate gradation range of SMAC13 was determined. Also, the performance of three kinds of asphalt mixtures were compared through laboratory tests. The results indicated that SMA13 shows the best rutting resistance, followed by SMAC13 then AC13, while in terms of low-temperature performance in resistance to cracking, the sequence is SMAC13, AC13, and SMA13. The sequence of water stability is AC13, SMAC13, and SMA13. Furthermore, the cost of SMAC13 is 25% less than that of SMA13. Therefore, SMAC13 can be used as an alternative for the surface course of asphalt pavement in terms of performance and cost.

Study on the Effect of Asphalt Static Conditions on the Tensile Properties of Acidic Aggregate Hydraulic Asphalt Concrete.

Hydraulic asphalt concrete is known for its excellent seepage control performance and strong deformation resistance. This engineering material has widespread applications in the seepage control structures of hydraulic buildings. Recent projects have investigated the use of acidic aggregates to improve economic efficiency. However, they have also highlighted the weaker adhesion between acidic aggregates and asphalt, which necessitates stringent construction process control. This study investigates the impact of resting conditions on the tensile properties of acidic aggregate hydraulic asphalt concrete. The results of the tensile testing indicate that the storage time significantly affects the performance of asphalt concrete. The tensile strength of the specimens without anti-stripping agents decreased from 1.711 MPa to 0.914 MPa after resting periods of 0, 10, 20, and 30 days. The specimens treated with anti-stripping agents also showed a decrease in tensile strength over time, similar to the trend observed in the previous specimens. Digital specimen simulations indicated a decrease in cohesion between the asphalt and the aggregate from 5.375 MPa to 2.664 MPa after 30 days, representing a reduction of 50.44%. To counteract the effect of the storage time on the bonding between acidic aggregates and asphalt, this study recommends reducing the grading index and maximum size of aggregates, decreasing the coarse aggregate content, and selecting smooth aggregate shapes.

Improved size effect law (SEL) considering size-dependent fracture process zone (FPZ) for quasi-brittle materials

Establishing a mechanistic model to simultaneously capture the descending size effect (DSE) and the change from DSE to the ascending size effect (ASE) remains a challenging issue for quasi-brittle materials. A size-dependent fracture process zone (FPZ) model is proposed and verified by experimental and simulative results. Subsequently, the size effect law (SEL) of unnotched specimens is improved by considering the size-dependent FPZ model, which is termed the improved SEL in this paper. Parametric studies are conducted for a better understanding of the improved SEL. It is found that the underlying mechanism of the DSE and the change from DSE to ASE is the competition between the relative rates of FPZ and specimen size change with respect to specimen size. The ASE is obtained when the relative rate of FPZ change is higher than that of specimen size. Conversely, the DSE is observed. No size effect exists when the relative rate of FPZ change is equal to that of specimen size. Experimental and simulative results are adopted to validate the improved SEL of unnotched specimens. The validation of the improved SEL indicates that the improved SEL not only accurately predicts the DSE, but also correctly captures the change from DSE to ASE. In addition, the size effect of nominal strength with different maximum aggregate size is well captured by the improved SEL. The fitting parameters of the improved SEL lie in the given interval. By comparing the determination coefficients R2 of the SEL, unified size effect law (USEL), and improved SEL, it is found that the R2 of the improved SEL is higher than that of the SEL for the DSE and is close to that of the IUSEL for the change from DSE to ASE. Therefore, it is recommended that engineers and researchers use the improved SEL to describe the DSE and the change from DSE to ASE of unnotched specimens.

A multi-gradient analysis of microscopic void characteristics' influence on the mechanical properties of open-graded friction course bituminous pavement

The mechanical properties of the open-graded friction course (OGFC) bituminous pavement are tied to its microscopic void structure, but multiple void parameters influence void formation and distribution. Solely using air voids as an indicator of pavement stability is challenging. Thus, a multi-gradient analysis of void structure factors is vital for advancing OGFC pavement's mechanical property research. This study used computerized tomography (CT) and digital image processing (DIP) to gather data on void structure distribution, size, and complexity in OGFC bituminous mixtures. Mechanical experiments assessed high-temperature deformation, low-temperature cracking, and water damage resistance. Analysis of void parameters' influence led to a predictive model for mechanical property in OGFC mixtures. The study found that as air voids increase within the 18 %–24 % range, both equivalent void diameter and void fractal dimension increase, while void count decreases. Conversely, coarser gradation and a larger nominal maximum aggregate size (NMAS) lead to increased equivalent void diameter but decreased void fractal dimension, reducing void complexity. The mechanical properties of OGFC mixtures decline with rising air voids but improve with coarser gradation and larger NMAS. The predictive model highlights the void fractal dimension and NMAS as critical indicators, with other factors showing weaker influence or multicollinearity issues that are unfit for model fitting. The findings could provide useful references for the structural design, property evaluation, and quality control of OGFC bituminous pavements in actual road construction.

Influence of Ceramic Wastes as a Recycled Coarse Aggregate with Different Maximum Sizes on the Concrete

Background Natural raw resources needed for concrete construction are continuously being depleted as a result of infrastructure development that is increasing. As a result, waste material substitutes are highly favored because they adopt a sustainable strategy. Objective In this study, the possibility of substituting natural coarse aggregates with coarse aggregate made from ceramic wall tiles with three different maximum aggregate sizes (12.5, 19, and 25 mm) in three partial replacement levels of natural coarse aggregate by (25, 50, and 75%) was investigated. Methods Concrete's hardened density, compressive and splitting tensile strengths, ultrasonic pulse velocity, water absorption, and volume of permeable pores were all tested experimentally. Results Results indicated that with the increment of the maximum aggregate size, each of the hardened densities, the compressive and splitting tensile strengths and the rate of water absorption diminished while pulse velocity enhanced, regardless of the substitution rate of ceramic aggregate. However, for all maximum aggregate sizes, the mixture containing 25% ceramic coarse aggregate showed a small improvement in mechanical properties. Compared to the reference mixture, which had compressive strengths of 29.31, 38.73, and 47.13 MPa at 7, 28, and 90 days for the 12.5 mm maximum aggregate size, the improvement ratios were 8.9%, 3.7%, and 2.7% at 7, 28, and 90 days, respectively. Moreover, because of increased heterogeneity, internal bleeding, and the development of microcracks in the larger coarse aggregate sizes, concrete with lower ceramic coarse aggregate sizes has a stronger bond than that of the latter. Results also indicated that the mechanical performance of concrete mixtures having ceramic aggregate slightly improved with 25% ceramic coarse aggregate, then lowered in the mixtures with 50% and 75%, consecutively, at all ages. Concrete using ceramic aggregate displays a poor transition zone because of the improper binding between the paste and the coarse ceramic aggregate caused by the aggregate's porcelain texture. Additionally, the water absorption of concrete mixtures containing ceramic aggregate increased with the increase in the percentage of ceramic coarse aggregate. Conclusion The employing of ceramic waste aggregate was shown to contribute to sustainable development and a cleaner environment by producing sustainable concrete from the recycling of ceramic wastes. Each of the hardened density, compressive strength, splitting tensile strength, and water absorption of concrete mixtures decreased and the pulse velocity enhanced as the maximum aggregate size increased. The mechanical properties decreased at all ages in the mixtures containing 50 and 75% of the aggregate, whereas they slightly increased in the mixture containing 25% of the aggregate.

Tensile performance and cracking characteristics of sustainable textile-reinforced cementitious composites utilizing expanded glass aggregate and fly ash replacement

In this study, sustainable textile-reinforced cementitious composites (TRC) were developed using lightweight expanded glass (EG) aggregates combined with fly ash (FA) as a partial cement replacement. Recycled nylon fibers were incorporated to enhance the cementitious matrix. The tensile performances and cracking characteristics of the developed TRC materials were comprehensively investigated. The key parameters investigated included the lightweight aggregate size, FA replacement content, fabric reinforcement ratio, and volume fraction of additional nylon fibers. The experimental results revealed that utilizing FA replacement content within the range of 20–30% and employing maximum EG aggregate sizes of 0.5 mm and 1.0 mm had a negligible influence on cracking characteristics and the tensile performance of TRC. Conversely, an adverse effect was observed with a 50% FA replacement content and a maximum EG size of 2.0 mm. Moreover, employing a higher fabric reinforcement ratio and an increased volume fraction of dispersed nylon fibers in the matrix endowed the TRC with favorable tensile performance and cracking characteristics. Eventually, an analytical model simulating the tensile stress-strain responses of TRC composites based on the cracking characteristics and stochastic matrix theory was proposed. The proposed model exhibits a reasonable correlation with the experimental results.

EXPERIMENTAL INVESTIGATION AND INTELLIGENT PREDICTION OF MECHANICAL STRENGTH OF PERVIOUS CONCRETE

This study determines the mechanical strength characteristics of pervious concrete using fuzzy logic. During construction, the process of determining the quality of concrete produced takes about 28 days before testing, training the fuzzy logic model through the research data gotten from the laboratory experiments in order to intelligently predict the mechanical strength of pervious concrete. Crushed granite was used in this experiment to ensure the pervious concrete has a little degree of fine aggregates and the maximum size of coarse aggregate used was 20 mm. Compressive, flexural and split tensile strength tests were carried out on pervious concrete of mixing ratios 1:4, 1:5 and 1:6 with each of the mixing ratios having varying water to cement ratios of 0.4, 0.5, 0.6 and 0.7. The developed fuzzy logic model was applied to predict the mechanical strengths of the concrete by using data obtained from experimental results, with input parameters of water content, crushing value, weight and density and the mechanical strengths as the output parameters employing the triangular membership function. The model was calibrated using the error measures of the root mean square error (RMSE), mean absolute percentage error (MAPE) and R squared were computed for the model. In this study, it was observed that higher water to cement ratio slightly reduces the mechanical strength of PC but increases the workability compared to increase in cement to granite ratio which notably increases the strength and reduced the workability, alternatively, higher water to cement ratio causes a notable decrease in permeability of the pervious concrete. The correlation between the experimental and predicted values was excellent. This shows that fuzzy logic can be used to predict the mechanical properties of pervious concrete, and fuzzy logic can also be used to appropriately deduce missing values in the mechanical properties of PC subject to further research

Influence of Specimen Geometries on the Viscoelastic Properties of Bituminous Mixtures in Torsion

A standard test method for determining the linear viscoelastic properties of bituminous mixtures in torsion prescribes the use of a dynamic shear rheometer. The method uses a prismoidal specimen (rectangular cross section) sliced from a Superpave gyratory compacted sample. However, the geometry utilized in the standard is a non-axisymmetric cross section, which leads to the development of warping stress when the specimen is tested in torsion using a dynamic shear rheometer. On the other hand, axisymmetric geometry, such as cylinder (circular cross section), does not warp when subjected to torsion. This study investigates the influence of the two specimen geometries, namely prismoidal and cylindrical, on the linear viscoelastic properties of bituminous mixtures in torsion. The specimens are obtained from a bituminous mixture with a nominal maximum aggregate size of 13.2 mm, and statistical analysis is carried out to determine whether the material constitution in the specimen geometries is identical. A frequency sweep experiment is conducted at 10, 20, and 30°C with a constant strain amplitude of 0.001% in the frequency range of 0.01 Hz to 20 Hz. The absolute shear modulus of the prismoidal specimens is found to be higher than that of cylindrical specimens because of warping stresses in prismoidal specimens. It was seen that the effect of warping stress is greater at higher temperatures and lower frequencies. Correction factors are used to correct the absolute shear modulus of prismoidal specimens. These findings highlight the importance of considering correction factors for warping when characterizing prismoidal bituminous mixtures in torsion.

Determination of dam concrete strength parameters considering the effects of ambient environment, member size and aggregate size: A case study of Baihetan Dam

The inconsistency in strength parameters between full-graded dam concrete and wet-sieved concrete is primarily attributed to variations in curing conditions, member size, and aggregate size. To ensure more reliable strength parameters for the structural analysis of the Baihetan Dam, comprehensive strength tests were conducted on site-casting full-graded and wet-sieved concrete. Full-graded concrete specimens and a portion of wet-sieved concrete specimens underwent natural curing on site or in close proximity to the laboratory, while the remaining wet-sieved concrete specimens were cured in seven large environmental chambers with controlled temperatures and relative humidity. The quantitative effects of curing conditions, specimen size and maximum aggregate size on the compressive and splitting tensile strength of dam concrete were obtained through strength tests. Subsequently, based on the test results, by introducing the equivalent age-adjusted coefficient Cea, the member size-adjusted coefficient Cms and the aggregate size-adjusted coefficient Cas, a strength determination method for full-graded concrete that can consider the above three factors was proposed and validated. Finally, according to the measured temperature and relative humidity history of the dam concrete and ambient environment, the real strength parameters of the full-graded concrete of Baihetan dam were determined by the proposed method. The validation and practical application of the proposed method indicate that this method can meet the actual use requirements of the Baihetan dam project, and can provide more reliable full-graded concrete strength parameters for dam structure analysis than traditional methods.

Study on critical crack length of wet-sieved and fully graded concrete under mode I loading

The critical crack lengths of wet-sieved concrete and fully graded concrete obtained from experimental measurements, numerical simulation and an analytical solution based on linear elastic fracture mechanics were quantitatively compared. Experiments were conducted on wedge-splitting specimens with depths of 200–1500 mm and a maximum aggregate size of 150 mm. Strain gauges and clip gauges were pasted and mounted along the direction of crack growth to measure the critical crack length. Numerical and analytical methods were used to calculate the critical crack length. The average relative error between the analytical calculations and measurements was still 14%, even for a specimen depth of 1500 mm. The effective fracture toughness was calculated by combining the peak load and critical crack length, resulting in an average relative error of 17%. These results indicate that the existing analytical method for determining the critical crack length is inadequate. Consequently, a modified analytical method was adopted, using 95% of the peak load in the post-peak region and the corresponding crack mouth opening displacement, which provided results that agreed well with the experimental data. Furthermore, the effective fracture toughness could be reasonably derived using the critical crack length from the modified analytical method.

Study on fracture characteristics and fracture mechanism of fully recycled aggregate concrete using AE and DIC techniques

Fracture behaviors of manufactured sand-recycled coarse aggregate concrete (MSRCAC), recycled fine aggregate concrete (RFAC), and fully recycled aggregate concrete (FRAC) were investigated by performing three-point bending tests on single-edge notched beams using acoustic emission (AE) and digital image correlation (DIC) techniques. The effects of recycled fine aggregate (RFA), recycled coarse aggregate (RCA), and their interaction on fracture parameters, AE characteristics and fracture process zone (FPZ) of concrete were comparatively analyzed. The results indicated that it was mainly transgranular failure and intergranular failure for RFAC, while transgranular failure for MSRCAC and FRAC. The RFA and RCA reduced the initial fracture toughness, unstable fracture toughness and fracture energy of concrete, and their interaction resulted in poor fracture properties of FRAC. In addition, the RFA and RCA significantly increased the AE activities, the proportion of tensile cracks, and the high-frequency amplitude and peak frequency of concrete. The toughening effect of FPZ was weakened by the RFA and RCA, resulting in an obvious increase in FPZ length and damage propagation of FRAC. Meanwhile, the width of FPZ was reduced, the maximum FPZ width of concrete with different combinations of recycled aggregates was approximately 1.8–3.1 times the maximum aggregate size, which could be explained as the RFA and RCA reduced the aggregate interlocking effect of concrete, while the RCA had a greater effect on the damage mechanism and FPZ of concrete than the RFA.

Effect of Gradation Variation on Mixture Properties in Stone Mastic Asphalt Mixtures with Carbon Fiber and Hybrid Aggregate

Due to advantages like abrasion resistance, increased operating and service life, high coarse aggregate content and high resistance to deformation, increased fatigue life, and others, stone mastic asphalt (SMA) mixtures have recently become a popular asphalt pavement type in road sections such as highways, tunnels, and bridges. There hasn't been much research on the topic, despite the fact that gradation significantly affects the performance of SMA combinations. In this study, the experimental findings of three distinct gradations of SMA mixtures with hybrid materials (basalt coarse aggregate, limestone fine aggregate) and carbon fiber were compared. As a result, it was concluded that the hybrid aggregate used with carbon fiber, maximum aggregate size, and coarse aggregate % had a positive impact SMA mixtures.

A damage constitutive model for concrete under uniaxial compression capturing strain localization

This paper presents a damage constitutive equation capturing the feature of strain localization and, on this basis, proposes a novel damage constitutive model for concrete under uniaxial compression. It is found that the proposed model can better simulate the stiffness degradation behavior of concrete under cyclic loading, well reproduce the dependency of the post-peak stress-strain curve on specimen or measuring length under monotonic loading, and provide FE simulation results that are insensitive to mesh size. Influence of the maximum aggregate size on the strain localization zone length is discussed.

Numerical modeling of the funnel multiphysical flow of fresh self-compacting concrete considering proportionate heterogeneity of aggregates

Filling ability is one of the prominent rheological properties of the self-compacting concrete (SCC), which has been studied in this research work deploying the functional behavior of the concrete through the studied funnel apparatus using the coupled ANSYS-SPH interface. Seven (7) model cases were studied and optimized. The aim of this numerical study is to propose a more sustainable mix of coarse and fine aggregates proportion that allows for most minimum flow time to enhance a more efficient filling of forms during concreting. The maximum size of the coarse aggregates considered is 20 mm and that of the fine aggregates is below 4 mm. The Bingham model properties for the multiphysics (SPH)-ANSYS models’ simulation are; viscosity = 20 ≤ μ ≤ 100 and the yield stress = 50 ≤τ0≤200\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le {\ au }_{0}\\le 200$$\\end{document}, standard flow time, t (s) ranges; 6 ≤ t ≤ 25 and the funnel volume is 12 L. The minimum boundary flow time, which represents the time it takes for the SCC to completely flow through a specified distance, typically measured in seconds was modeled for in the seven (7) model cases. The second case with 40% coarse mixed with 60% fine completely flowed out in 16 s, thus fulfilling the minimum flow time. This minimum flow time was considered alongside other relevant parameters and tests, such as slump flow, passing ability, segregation resistance, and rheological properties (stresses), to comprehensively assess the filling ability of SCC in this model. By considering these factors and the optimized mix (40%C + 60%F:16s), engineers and researchers can optimize the SCC mix design to achieve the desired flowability and filling performance for their specific construction applications. The multiphase optimized mix was further simulated using the coupled interface of the ANSYS-SPH platform operating with the CFX command at air temperature of 25 °C. The results show energy reduction jump at the optimized flow time. Ideally, the mix, 40%C + 60%F:16s has been proposed as the mix with the most efficient flow to achieve the filling ability for sustainable structural concrete construction.

Effects of aggregate sizes on the performance of laterized concrete

Due to the high costs of traditional concrete materials in Nigeria, such as river sand, there is an increasing demand to explore alternative materials like laterite for fine aggregates. Although laterite is abundant in Nigeria, its full potential in the construction industry remains untapped. Previous studies have shown that partially replacing river sand with laterite produces concrete with competitive strength properties. This research aims to validate and extend these findings, evaluating the impact of different aggregate sizes (12 mm, 20 mm, and 40 mm) on the strength of concrete with 10% and 25% laterite replacements for fine aggregate. Results revealed that as the laterite percentage increased, compressive, flexural, and split tensile strengths decreased. While 0% and 10% laterite replacements met the required strength, the mix with 25% laterite fell short. Increasing maximum coarse aggregate size led to higher strengths, with 40 mm sizes exhibiting the highest, and 12 mm the lowest. Compressive strengths ranged from 22.1 to 37.6 N/mm2, flexural strengths from 4.07 to 5.99 N/mm2 and split-tensile strengths from 2.93 to 4.30 N/mm2. This research highlights the need for meticulous mix design adjustments when using laterite, balancing workability with strength objectives. The developed regression models offer a valuable tool for predicting concrete properties based on mix parameters, providing insights for optimizing laterized concrete designs across diverse construction applications and supporting sustainable building practices.

Investigating the fracture toughness of the self compacting concrete using ENDB samples by changing the aggregate size and percent of steel fiber

In reality, concrete structures are normally under various loadings, and results of different studies have shown that cracks in these structures and their materials, due to their nature as well as the loading type, do not develop along the crack plane (pure mode I); rather, they expand under mixed modes, making the crack growth studies under these modes a very important issue. In the crack growth phenomenon, the fracture toughness is a very effective parameter usually calculated by ENDB samples because they are easy to handle. In this study, several samples were made by changing the maximum aggregates size (dmax = 9.5, 12.5 & 19 mm) and the amount of hooked-end steel fibers (SF = 0.1, 0.3 & 0.5%), and tested under different loading modes (pure/mixed modes I and III) using the strain control jack device. According to the results, the lowest fracture toughness belonged to pure mode III, aggregates with dmax = 12.5 mm performed better in the self-compacting concrete reinforced with steel fiber, Also, the results show that the increasing trend of steel fibers does not have a positive effect on the fracture toughness performance.

Effects of coarse aggregates size on dynamic characteristics of ultra-high performance concrete: Towards enhanced impact resistance

Coarse aggregates are recently used to address the high production costs and severe autogenous shrinkage of ultra-high performance concrete (UHPC), however, the influence of coarse aggregates size on the dynamic performances of UHPC remains poorly comprehended. Herein, the impact of coarse aggregates on the dynamic performances of UHPC is explored through a multiscale method with the focus on hydration products, micromechanical property, meso-scale fracture and macro-scale dynamic mechanical characteristics. Results show that the increasing maximum coarse aggregates size slightly enhances both the total amount and the elastic modulus of hydration products. The rise of the maximum coarse aggregate size enhances the percentage of fracture across coarse aggregates, thus, improving the impact resistance of UHPC. Regardless of the strain rates, the toughness and dynamic compressive strength enhance with the expanding maximum coarse aggregate size, while the dynamic increase factor and peak strain decrease with the rising coarser aggregates size. The damage degree of UHPC enhances with strain rate but reduces with the increasing maximum aggregate size. A conceptual enhancement mechanism of increasing maximum coarse aggregate size on the impact resistance is proposed. The present results promote the wider engineering application of UHPC containing coarse aggregates.