Polygonal Aggregates Research Articles

Uncertainties quantification for damage localization in concrete based on Bayesian method

The presence of defects in concrete can diminish load-bearing capacity of structures, giving rise to potential concerns regarding safety and durability. Thus, a method that enhances the sensitivity, resolution and robustness of damage localization is critically necessary to assess the condition of concrete structures. This research presents a damage localization method based on Bayesian probabilistic fusion, and uncertainties from measurement and identification process are considered and quantified. The likelihood function is constructed based on the hyperbola-based damage localization method, and the posterior distributions of unknown parameters are calculated via Bayesian theorem combined with measurement data. Furthermore, a meso-level finite element model is established, wherein the concrete medium is considered as a three-phase composite material consisting of polygonal aggregates, mortar matrix and interface transition zones. Owing to the meso-level modeling, the propagation behavior of stress waves within concrete and complicated interactions between stress waves and concrete internal structures can be better characterized. Finally, the damage information, time-difference-of arrival, is extracted from the response signals and the efficiency of the proposed method is verified numerically. The numerical results demonstrate that the proposed probabilistic fusion method outperforms the conventional hyperbola-based method in terms of achieving high spatial resolution and resilience in damage localization.

Discrete element analysis of heat transfer characteristics of concrete pavement under electrical heating for snow melting and deicing

The carbon fiber electrothermal method is an efficient approach for snow melting and deicing of pavements in the cold winter. The heat transfer mechanism needs to be explored for the carbon fiber electrothermal system design, especially how the microstructure affects the thermal behavior of pavement. To do so, a discrete element method (DEM) based heat transfer model considering the pavement microstructure has been established in the current study. The shape and content of coarse-grained aggregates have been represented by using the irregular polygonal aggregate method. The accuracy and feasibility of the proposed model were verified by comparing the numerical results with the measured data. On this basis, the heat transfer characteristics of pavements during snow melting and deicing using the carbon fiber electrothermal method have been investigated. The results show that the ambient temperature and the carbon fiber heating wire (CFHW) temperature are the two primary factors affecting the heating efficiency and the maximum temperature on the pavement surface. The spacing and buried depth of the CFHW also play a crucial role in determining the temperature rise rate and the uniformity of temperature distribution of the road surface layer. Furthermore, the effect of the aggregate content on the overall heating rate is not as significant as that of the specific heat capacity ratio of the aggregate to the mortar, suggesting modifying the thermal conductivity of aggregates to enhance deicing efficiency rather than changing the aggregate contents. The effects of the CFHW design parameters on the temperature distribution of the pavement surface are also investigated. The maximum and minimum temperatures of the pavement layer decrease gradually with the increase of the laying spacing and burial depth of the CFHW, but the temperature difference increases with the increase of the laying spacing of the CFHW and decreases with the increase of the burial depth. The research results can provide a reference for the optimization design of snow melting and deicing of pavements by the CFHW heating method.

Evidence of fluid-induced myrmekite formation after alkali-feldspar megacrysts: an example from a meta-porphyritic granitoid in Makrohar, Madhya Pradesh, India

Abstract A meta-porphyritic granitoid in the Makrohar Granulite Belt, Central India contains extensive myrmekite. This work evaluates the controls of fluid in relation to deformation and the formation of myrmekite all along the periphery of an alkali-feldspar megacryst. Two different myrmekite morphologies are present: (1) vermicular intergrowth of plagioclase (An38–39) and quartz (Myr1); and (2) polygonal aggregates of coarse plagioclase (An45–46) and quartz (Myr2). Petrographic features suggest that myrmekite Myr1 nucleates on alkali-feldspar and plagioclase porphyroclasts and the myrmekite front moved into the alkali feldspar by replacing it; and that myrmekite Myr2 and the secondary biotite which replaces plagioclase porphyroclasts and garnet form together. Deformation had a decisive role in forming the polygonal aggregates of Myr2, however field and microtextural features do not support any significant control of deformation during the formation of Myr1. Reaction modelling and a mass-balance calculation suggest that Ca and Na are added to, and K is removed from, the alkali feldspar during the myrmekite formation at nearly constant Si and Al. However, the secondary biotite-forming reaction, consumes K and releases Ca. Interpretation of the reaction textures in different isothermal–isobaric sections of μK2O–μCaO in the KCFASH system suggest that CaO and K2O moved in opposite directions for myrmekitisation and along their respective chemical potential gradients created between the sites of formation of myrmekite and secondary biotite. The feedback mechanism which operated between the two reaction sites was controlled by infiltration of brine-rich fluid in the meta-granitoid during a regional hydration event (550–600oC and 5–6 kbar). Volume reduction of ~10% during the formation Myr1 and Myr2 drew the brine-rich fluid towards the alkali feldspar and thus facilitated the process of myrmekite formation. Variation in the morphology of quartz in the myrmekite is attributed to the cooling of the complex.

Effect of aggregate characteristics on properties of cemented sand and gravel

Abstract To improve the stability of cemented sand and gravel (CSG) dam construction materials, artificial aggregates can be selected to replace missing natural aggregates, and aggregate grading optimization can be carried out to meet the needs of engineering applications. This article uses finite-element analysis software to explore the influence of aggregate characteristics on the performance and destruction characteristics of CSG materials through numerical simulation. The results show that (1) with the increase of circular natural sand gravel aggregates, the peak stress and elastic modulus of the sample increase, while the strength also increases. (2) Compared to circular aggregates, polygonal aggregates have more edges and corners, which exacerbate the deformation disharmony between mortar and aggregates; the phenomenon of stress concentration is more obvious, so under the same loading step, the degree of damage of polygonal aggregates is greater than that of circular aggregates. (3) After the freeze–thaw cycle test, the deterioration of parameters in the CSG resulted in more severe damage and strength loss of the crushed stone aggregate than the circular aggregate sample. This conclusion can provide a reference for the design of CSG mix ratio in engineering sites.

A novel method for generation of random aggregate structure and its application in soil-rock mixture

The generation of random aggregate structure (RAS) is encountered in many fields and has received wide attention. The random sequential addition (RSA) is a frequently-used approach that can generate RAS by dispersing particles randomly and sequentially. The classical RSA is not efficient due to the excessive overlap detections involved in every trial of placing new aggregates. In this work, a new version of RSA called correlative element method (CEM) is proposed based on the concept of “correlative element” on a background grid. The overlap detection is replaced by the checking of the occupied state of correlative elements. Furthermore, a multilayer CEM is also presented to guarantee the minimum gap between adjacent aggregates, leading to a more evenly distributed aggregate model. The proposed CEM can handle not only polygonal aggregates but also circular and elliptical aggregates in a unified way. Other related issues, such as the aspect ratio and orientation of aggregates, the packing density, and the efficiency of the proposed CEM are also tested and discussed. The results show that the proposed CEM has advantages of easy implementation, high efficiency, and wide application range. Finally, the proposed CEM is applied to simulate the direct shear test of soil-rock mixture.

A methodology for parameter identification and calibration of the cohesive element based meso-scale concrete model

Meso-scale analysis techniques have demonstrated superiority in analyzing structural cracking and crack propagation compared to conventional methods. The cohesive element based meso-scale analysis technique has gained widespread acceptance due to its clear analytical concepts and the ability to simulate complex fracture modes. However, the cohesive zone model (CZM) requires numerous parameters for different fractures patterns, and the impact of each cohesive element parameter on the mechanical properties of the meso-scale model remains uncertain. This limitation restricts the applicability of CZM models in concrete structure analysis. Even experienced researchers often rely on trial-and-error methodologies or empirical methods to determine cohesive element parameters. The present study aims to investigate the effects of cohesive element parameters in the CZM concrete model under static axial loading and propose a feasible method for determining these parameters through a parametric analysis. Initially, a Python script was developed to generate random aggregate models, modify polygonal aggregates, and insert cohesive elements. Subsequently, numerical simulations were conducted on two-dimensional standard concrete specimens under axial compression and tension. Based on the results of the parametric analysis, a novel prediction formula and an inverse method for cohesive element parameters were introduced. Additionally, the accuracy of the novel method was validated in accordance with the Chinese Code. The results indicate that the proposed method exhibits exceptional capabilities in predicting initial stiffness, uniaxial strength, and corresponding strain. However, the prediction of the descending segment of the stress–strain curve lacks precision. In summary, the methods presented in this study demonstrate high accuracy, which can provide a reference basis for researchers and promote the application of CZM meso analysis method.

Arrested tectonic development: Preservation of high-temperature fabrics in the sinistral Caiçara shear zone (Borborema province, northeastern Brazil)

The protracted duration of shearing in large-scale shear zones and/or their reactivation may obscure the metamorphic conditions under which the mylonites initially formed. Here, we describe the case of the high-temperature Caiçara shear zone (Borborema Province, northeastern Brazil), which shows only limited overprint by low temperature fabrics. The NE-trending Caiçara shear zone is ∼35 km long and comprises a 2 to 5 km-wide mylonitic belt. The shear zone was characterized by using kinematic analysis, including field and microstructural observations and measurement of quartz c-axis. The mylonitic foliation is steeply NW-dipping and contains a shallowly SW-plunging stretching lineation. Kinematic criteria (e.g., asymmetric porphyroclasts, S–C fabrics, asymmetric folds, C′-type shear bands) are consistent with sinistral shear. The dominant microstructures (e.g., chessboard extinction in quartz, grain boundary migration and subgrain rotation recrystallization in quartz, and polygonal aggregates of feldspar around porphyroclasts) and application of the opening angle thermometer indicate deformation dominantly at temperatures higher than ∼ 600 °C. In contrast to the common situation in the central Borborema Province, the Caiçara shear zone is unconnected to other shear zones. We attribute preservation of high-T fabrics to cessation of shearing in an early stage of development, preventing continuous fabric development at decreasing temperature conditions.

A novel numerical algorithm for 2D and 3D modelling of recycled aggregate with different geometries

The establishment of an aggregate model that better matches real situations is one of the prerequisites to studying the mechanical properties of concrete. Previous models have focused on aggregates with regular shapes; however, this differs from the morphology of real aggregates, particularly recycled aggregate (RA). Due to the presence of adhered mortar, RA has more complex structural characteristics than natural aggregate (NA). It is therefore difficult to model RA, especially the distributions of irregular angles and sharp corners. A new modelling method based on the compression of circles and spheres is proposed in order to obtain circular, elliptical and convex polygonal aggregates in two-dimensional (2D) models and spherical, ellipsoidal and convex polyhedral aggregates in three-dimensional (3D) models. The compression method has excellent scalability and applies to both NA and RA in both 2D and 3D models. Using the proposed compression modelling method, the aspect ratios, sharp corners, flakes, edges and needles of RA and NA can be characterised. Random aggregate models showed that the compression modelling method was able to construct 2D and 3D geometric models of concrete made with NA and RA with desirable aggregate distributions and aggregate morphological characteristics.

Mesoscale synergistic effect mechanism of aggregate grading and specimen size on compressive strength of concrete with large aggregate size

In this paper, a 2D finite element model with a mesoscale level was established. The effects of content, maximum particle size, and shape of aggregate on the strength of concrete were simulated. In addition, five mesoscopic models of aggregate gradation and specimen side length (100–450 mm) were established to investigate the influence law of aggregate grading and model size on the compressive strength of concrete. The simulation results were also compared and verified with four theoretical size-effect models. The results showed that the compressive strength shows a trend of decreasing and then increasing with the increase of aggregate content and falling with the growth of maximum aggregate size dmax. The peak stress of convex polygonal aggregates is higher than that of round and elliptical. In addition, when the ratio of model side length to the maximum aggregate particle size is about 3.5, the compressive strength gradually decreases with the increase of specimen size, up to 27.65 % decreased, showing a pronounced size effect. After comparative analysis, the simulated data in this paper fitted well with the Bažant’s Type-2, Kim’s modified, Jin’s modified, and Carpinteri’s size effect law (SEL). In addition, the data obtained from the simulation of this paper would better reflect the existing test conclusions. The mesoscale model established in this paper can significantly improve the effectiveness and efficiency of full-graded concrete modeling, and better simulate the strength difference between full-graded and wet-screened specimens. The difficulties in the mesoscale numerical simulation are solved to a certain extent.

Multiscale Theoretical Model of Thermal Conductivity of Concrete and the Mesoscale Simulation of Its Temperature Field

Temperature field analysis is the precondition of studying the heat and mass transfer and durability of a concrete building; thermal conductivity is a key parameter that affects the distribution of the temperature field of concrete. Through reasonable assumptions and simplifications, the relationship between the micro-microscopic composition of concrete and its macroscopic thermal conductivity is established, and a multiscale theoretical model of thermal conductivity considering the influence of interface transition zone (ITZ) is proposed. The model can predict the thermal conductivities of concrete and its components at an arbitrary saturation. Subsequently, the influence of saturation, water-cement ratio, volume fraction and type of coarse aggregate, and sand ratio is researched. Moreover, according to the prediction results of the proposed model, a mesoscale simulation of the concrete temperature field is carried out. The results demonstrate that the presence of aggregate and ITZ leads to the isotherm deflection and abruption at the junction of the phases. Meanwhile, the heat flux density at the corners of the polygonal aggregate is significantly higher than at other positions; the phenomenon, first named the “corner effect” in the research, causes the temperature field distribution of concrete containing polygonal aggregates to be more uneven than that of circular and elliptical aggregates, and it is more likely to produce temperature-induced cracks. The research helps explain the influence mechanism of material components on the thermal conductivity of concrete and the distribution of its temperature field and provides a basis for the fine simulation of concrete thermal crack growth and creep at variable temperatures.

Mesoscale Finite Element Modeling of Mortar under Sulfate Attack.

In this paper, a 2D mesoscale finite element (FE) numerical model of mortar, considering the influence of the ITZ, was proposed to evaluate the corrosion of mortar in sodium sulfate. On the mesoscale, the corroded mortar was regarded as a three-phase composite material composed of sand, cement paste, and an interface transition zone (ITZ). Firstly, the volume fractions and mechanical parameters (elastic modulus, Poisson’s ratio, and strength) of the mesoscale phases were obtained. Then, the cement paste and the ITZ were combined to form an equivalent matrix by homogenization methods, and the calibrated constitutive relations of the equivalent matrix were established. Subsequently, a two-dimensional (2D) random circular aggregate (RCA) model and a 2D random polygonal aggregate (RPA) model of corroded mortar were established using the random aggregate model. The failure process of corroded mortar specimens under uniaxial compression was simulated by the mesoscale FE numerical model. Comparing the simulation results with the measured stress–strain curves of the uniaxial compression test, it was found that the simulation results of the 2D RP model were closer to the experimental results than those of the 2D RC model. Meanwhile, the numerical simulation results were in good agreement with the experimental results, and the error values of peak stress between the simulation results and the measured results were within 7%, which showed that the 2D mesoscale FE model could accurately predict the results of a uniaxial compression test of a mortar specimen under sulfate attack.

Mesoscopic study on fracture behavior of fully graded concrete under uniaxial tension by using the phase-field method

The applicability and rationality of the phase-filed method are systematically analyzed for utilization in mesoscopic study on fully graded concrete under uniaxial tension. In this study, two kinds of mesoscopic models for fully graded concrete are generated by the polygonal characteristic parameter transformation method, and their complicated mechanical response and fracture behavior are investigated using the phase-filed method. Numerical simulations of uniaxial tensile experiments are conducted to study the effects of step time, element parameters, and meso-structures on the crack propagation and fracture mechanical response of fully graded concrete. Moreover, the computational efficiency and convergence of the phase-field method are systematically analyzed using various model setup. It is found that the numerical results of stress–strain curves and crack propagation paths are both in good agreement with the experimental results and the output from the distributed cohesive element method, and phase-field method demonstrates advantages in numerical stability. The accuracy and efficiency of this approach, which combines phase-field method and random polygonal aggregate models, are tested to study the fracture behavior of fully graded concrete.

A transient creep investigation applied to the mesoscopic analysis of plain concrete under uniaxial compression at high temperature

A new methodology to investigate transient creep at the material level in terms of Load Induced Thermal Strain (LITS) by means of numerical mesoscopic analysis is proposed. 2D three-phase axisymmetric analyses for plain concrete cylindrical specimens are performed. Concrete phases are represented by the ITZ, the inclusions (coarse aggregates) and the matrix (cement paste including fine aggregates). The aggregates are placed using the take and place method and normal random distribution. An appropriate finite element mesh with coupled temperature-displacement is adopted using concrete damaged plasticity model in Abaqus. The numerical values are compared with a LITS semi-empirical model and experimental results available in the literature. For the analyses, LITS is uncoupled into matrix strain (dehydration of Calcium-Silicate-Hydrates), aggregate strain (geomechanical properties degradation) and mechanical strain (thermal expansion restraint). A parametric analysis is performed to investigate the sensitivity of the model due to different aggregate distributions and mechanical properties variations. A comparison of concretes with circular and polygonal aggregate shapes is performed, highlighting the main differences between the materials behavior and some challenges imposed to the model calibration. In general, a good correlation between the numerical and the experimental results was observed. The numerical model was able to represent LITS nonlinear behavior due to variations of the applied load. In addition, the numerical results, in terms of load path analysis with preloaded and preheated specimens, are in agreement with experimental observations. LITS acceleration is clearly demonstrated and the results showed that the boundary conditions play an important role in the total deformation.

Effects of concrete heterogeneity on FRP-concrete bond behaviour: Experimental and mesoscale numerical studies

Extensive experimental and numerical studies have been conducted to understand the bond behaviour of FRP-concrete interfaces with the assumption of homogenous materials. This study is aimed at a better understanding of the effects of concrete heterogeneity on the FRP-concrete bond behaviour, by a combination of experiments and mesoscale numerical modelling. FRP-concrete and FRP-mortar bonded joints were tested using a four-point bending setup. The crack initiation and propagation process with interfacial debonding until failure was accurately captured by the digital image correlation (DIC) technique. The results show that the presence of coarse aggregates in the FRP-concrete joints leads to 19% higher bond strength, but much higher variations in the bond strength and the strain distribution across the width of FRP sheets, than the FRP-mortar joints. Monte Carlo simulations of mesoscale finite element models with random distribution of polygonal aggregates were then carried out for the FRP-concrete bond tests. It is found that the distribution of coarse aggregates significantly affects the overall force–deflection responses as well as the simulated fracture processes and final failure modes that are highly comparable with the DIC observations.

Mesoscale numerical analysis and test on the effect of debonding defect of rectangular CFSTs on wave propagation with a homogenization method

In this paper, in order to distinguish the influence of both interface debonding defect and the mesoscale structure of concrete core on the stress wave field and the response of an embedded Piezoelectric-lead-zirconate-titanate (PZT) sensor in rectangular concrete filled steel tube (RCFST) members efficiently, a two dimensional (2D) mesoscale numerical concrete homogenization approach for concrete core considering the random distribution of circular, elliptical and irregular polygonal aggregates is proposed firstly. Then, mesoscale simulation on stress wave fields within the cross-section of RCFST members with and without interface debonding defects using both mesoscale models and their homogenization models are carried out, respectively. The effect of both mesoscale structure of concrete core and the interface debonding defects on the stress wave field of each member is discussed and the efficiency of the homogenization approach is illustrated. Therefore, the time-domain response of an PZT sensor embedded in the concrete core of RCFST members coupled with PZT patches under sweep frequency excitation signal is determined with multi-physics field simulation and compared when both mesoscale models and their homogenization models are used. Then, the sensitivity of the wavelet packet energy of the embedded PZT sensor response on the variation of both mesoscale structure of concrete core and the dimension of interface debonding defects is investigated in details. Finally, in order to illustrate the difference in the significance of the effect of interface debonding defect and the mesoscale structure of concrete core on stress wave propagation, comparative test with a set of RCFST members without and with interface debonding defects is carried out. Test results also show that the influence of interface debonding defects on embedded PZT sensor response and the stress wave fields is dominant. The detectability of interface debonding detection approach using stress wave measurement is illustrated efficiently with the proposed equivalent homogenization mesoscale modelling approach even the mesoscale structure of the concrete core is considered.

Statistical analysis of the critical percolation of ITZ around polygonal aggregates in three-phase concrete materials

Concrete is generally regarded as a kind of three-phase granular material composed of aggregates, interfacial transition zone (ITZ) and bulk cement paste, among which ITZ is an inescapable transport path of aggressive agents due to its high porosity. As the weakest part in concrete, the existence of ITZ usually triggers an unfavorable change of the holistic properties of concrete structures. In particular, the percolation behavior of ITZ is likely to be an important factor that accelerates the penetration of aggressive agents. Previous studies about the percolation of ITZ around aggregates are mainly carried out based on the models of circles, spheres and ellipsoids, which are very different from the real features of aggregates. In this work, the regular polygons which are more similar to the geometrical shapes of fine and coarse aggregates are applied to represent the aggregate particles. The ITZ around these aggregates is simplified to the soft interphase layer with identical thickness and the models of concrete structures can be modeled by the random sequential addtion (RSA) algorithm. By combining with the continuum percolation models of hard core/soft shell, the percolation properties of ITZ around different 2D multi-sized aggregates are studied in detail and the effect of both aggregates and ITZ on the percolation thresholds ϕagg,c of ITZ is quantified. Based on the obtained values of ϕagg,c here, an approximately numerical formula of ϕagg,c is proposed and its reliability is further verified by comparing with the results in the literature. The comparison confirms that the proposed model can be utilized to predict the critical thresholds of ITZ around various polygonal particles with the broad particle size range and ITZ thickness. The research findings may provide a helpful guidance for the design and optimization of concrete materials.

Simulation of Chloride Diffusion in Concrete Based on a New Mesoscopic Numerical Method

Chloride diffusion‐induced corrosion is a major factor that affects the durability of concrete structures. Thus, the study of chloride diffusion in concrete is important. In this study, a mesoscopic structure model is proposed and used to investigate chloride diffusion in concrete. The concrete is assumed to be a heterogeneous material composed of two phases of aggregate and mortar matrix. The aggregates are randomly distributed convex polygons. The chloride diffusion is assumed to occur only in the mortar matrix phase. The modified chloride diffusion coefficient in the mesoscale model is proposed. The effect of a single aggregate in chloride diffusion in concrete is analyzed. The present numerical model is validated on the basis of the experimental data. The influence of aggregate in the presented model, including aggregate random distribution form, aggregate content, and the validity of polygonal aggregate based on circle, is explored further. The simulation results indicate that the polygonal aggregate random distribution has a negligible influence on chloride diffusion in concrete, the polygonal aggregate content has a certain effect, and the presented mesoscale numerical model is an effect method for predicting the chloride diffusion in concrete.

Model for Predicting the Tortuosity of Transport Paths in Cement-Based Materials.

The tortuosity of the pore structure is an important factor affecting medium (water and harmful ions) transport in cement-based materials. In this study, a new tortuosity model was established to reveal the effect of aggregate size, morphology, and graded media on the transport path in cement-based materials. Based on the stereological principle and the geometric algorithm, the distribution model of the ideal pebble and polygonal aggregate in cement-based materials was given first. Then, based on the image processing technology and MATLAB software, the morphology of the actual aggregate was also characterized to prove the similarity relationship between the ideal aggregate and actual aggregate. The reliability of the tortuosity model was verified by the mercury intrusion porosimetry test and data from other literature. Based on the tortuosity model, the influences of the aggregate particle shape parameters, hydration degree, and water-to-cement ratio on the tortuosity of the transport path were analyzed. Finally, the tortuosity model was further simplified to facilitate engineering application.

Clinopyroxene episyenites in a Proterozoic rapakivi granite, SE Finland \u2014 recrystallization textures, mass transfer and implications for the petrology of A-type granite complexes

Na-metasomatic augite and aegirine-augite episyenites are hosted by subalkaline amphibole granites in the 1.644 Ga Suomenniemi rapakivi granite complex, southeastern Finland. In an examined drill core, episyenites are bordered by up to 50-cm-wide zones of Na-enriched augite-bearing granite in which alkali feldspar forms rims on plagioclase, and aggregates of augite and magnetite have formed by fluid-induced dehydration of hastingsite and biotite. In the episyenites, quartz has been partially removed, alkali feldspar (An<1Ab50Or50) and plagioclase have been partially recrystallized to granoblastic polygonal aggregates, and clinopyroxene (augite or aegirine-augite) has coarsened and been enriched in the aegirine component. Mass balance modeling implies addition of mainly Na, depletion of Si, F, Rb, Ba, Sr and 10–20% volume loss (by quartz dissolution) in the episyenitized zones in the drill core. Quartz-depletion and recrystallization may have been caused by several superimposed stages of alteration, probably related to voluminous dike- and A-type granite magmatism in the Suomenniemi area 10–15 m.y. after the emplacement of the Suomenniemi complex. Because of the coarse recrystallization textures and near-solidus recrystallization temperatures, distinguishing these fenite-like metasomatic rocks from igneous syenites is not trivial. In epizonal A-type granite complexes, high-temperature episyenites may be more common than currently thought.

A numerical method for estimating the elastic modulus of recycled concrete

This paper aims at presenting a numerical method for estimating the elastic modulus of recycled concrete with crushed aggregates. In the method, polygonal aggregates following a given sieve curve are generated, and placed into a square simulation element with the aid of the periodic boundary condition and the overlap criterion of two polygonal aggregates. The mesostructure of recycled concrete is reconstructed by embedding an old interfacial transition zone (ITZ) layer inside each recycled aggregate and by coating all the aggregates with a new ITZ layer. The square simulation element is discretized into a regular grid and a representative point is selected from each sub-element. The iterative method is combined with the fast Fourier transform to evaluate the elastic modulus of recycled concrete. After the validity of the numerical method is verified with experimental results, a sensitivity analysis is conducted to evaluate the effects of key factors on the elastic modulus of recycled concrete. Numerical results show that the elastic modulus of recycled concrete increases with the increase of the total aggregate content and the elastic moduli of old and new ITZ but decreases with increasing the replacement ratio of recycled aggregate and the thicknesses of old and new ITZ. It is also shown that, for a replacement ratio of recycled aggregate smaller than 0.3, the elastic modulus of recycled concrete is reduced by no more than 10%.