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Figure D2 (a) 3D mesostructure of concrete consisting of mortar and spherical aggregates with a specific fraction f_ca = 38% spatially distributed, (b) statistical analysis of highest probability of occurrence of aggregate fraction in a 2D mesostructure extracted from 3D mesostructure of concrete. It is observed that a skewed normal distribution (fitted red curve) describes the distribution of aggregate fraction with a mean value f_ca = 45% in 2D mesostructures extracted from 3D mesostructure.
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A finite element-based multiscale model is employed to examine the early-age mechanical behavior of cementitious composites under a mode-I loading condition. The mechanical response of early-age mortar and concrete are influenced by the time-dependent development of mechanical properties of the cement paste as well as the mechanical and morphologic...
Citations
... The adhesion of mortar layer on the surface of recycled aggregate leads to a decrease in mechanical properties and durability of recycled aggregate concrete. Strengthening treatment of recycled aggregate is effective for removing or strengthening the mortar layer, which can be narrow the gap between recycled aggregate and natural aggregate (Evangelista et al., 2015;Esmaeeli et al., 2019;Evangelista and Guedes, 2019;Pawluczuk et al., 2019). Filling pre-wetting, pickling, inorganic material filling, and carbonation are the major methods to strengthen recycled aggregates. ...
The physical and mechanical properties of recycled aggregates (RA) among different particle sizes are compared. Results demonstrate that adhesive mortar content is a significant factor in determining the properties of recycled aggregate concrete (RAC). The adhesive mortar content on the surface of recycled aggregates is critical in selecting the most efficient strengthening treatment, and effects of the strengthening treatment on properties of RA with different particle sizes was reported. The utilization of RA was suggested to classify into fine powder aggregate, fine aggregate, coarse aggregate based on the particle size, i.e., the multi-scale grading utilization. The most suitable strengthening treatment was reviewed for RA with various particle size to improve the it’s utilization efficiency.
... 53 While these approaches are promising, there is a potential to predict mechanical behavior using fracture mechanics. [54][55][56][57][58] Fracture mechanics can natively predict flexural strength, 54,55,58 which can be used as a target criterion in the performance-based mixture design approach. ...
... 53 While these approaches are promising, there is a potential to predict mechanical behavior using fracture mechanics. [54][55][56][57][58] Fracture mechanics can natively predict flexural strength, 54,55,58 which can be used as a target criterion in the performance-based mixture design approach. ...
... 71 As the crack length and representative volume decreases, the characteristic fracture length scale becomes relevant, and other considerations should be considered. 54 While in this work the initial crack size was calculated to be 0.3 mm from the ball-on-three-balls (B3B) experiments, a statistical approach is also used that takes into account the variability in the defect size and distribution of defects using a Weibull distribution of tensile strength and fracture energy in the finite element analysis (FEA) model. ...
... Previous works have demonstrated the ability of multiscale homogenization technique as an effective way to predict the behavior of the large homogenized systems by considering the details and heterogeneities at lower scales. Nguyen et al. (2012aNguyen et al. ( , 2012b and Esmaeeli et al. (2019) successfully predicted the macroscopic failure behavior of the concrete by considering microscale details using a multistep model. In these models, the time-dependent mechanical properties of the cement paste, as a purely brittle material, were first defined at the microscale (i.e., the lowest length scale). ...
... The study by Autumn et al. (2000) revealed the exceptional ability of geckos to climb vertical surfaces due to the (obtained from the mesoscale simulations) and coarse aggregates. Cracks were then allowed to initiate, propagate, and interact on the cement paste fine/coarse aggregates, mortar and in their respective interfaces (Esmaeeli et al., 2019). In general, these multiscale approaches allow us to couple both micro-and macroscales and predict the homogenized behavior even when fracture and other mechanisms of localization are present (Aragón et al., 2013;Kulkarni et al., 2009;Matouš et al., 2008). ...
Hook-and-loop-like joints have been widely used in many engineering applications and even observed in nature. The demand for computational models to predict the behavior of fasteners is increasing as they will be key for reducing design process time and manufacturing costs. Here, we develop a bottom-up two-scale modeling strategy, which enables us to capture the mechanical performance of a hook-and-loop fastener at both micro- and macroscales. In particular, we employ a two-scale homogenization approach capable of predicting the mechanical behavior of the hook-and-loop fastener. The model starts with a micromechanical model of a hook-and-loop fastener which considers the detailed geometry of the individual building blocks of the hook-and-loop fastener and their statistical geometrical variability through a so-called Representative Hook and Loop Element (RHLE) computational domain. The second scale considers the homogenization of the micromechanical model into a Detachment Process Zone (DPZ) which reveals an emerging length scale. The resulting effective traction-separation law concept is then employed at the macroscale with a Double Cantilever Beam (DCB) test using a macroscale model, which is then validated with experiments. The results suggest that the two-scale model strategy is able to predict the mechanical behavior of hook-and-loop fastener and to capture the main deformation and dissipative mechanisms at the relevant length scales.
... Moreover, these models cannot readily reflect the effect of other mesocomponents in concrete on the elastic modulus. In the study of reference [16], a finite element-based multiscale model is employed to examine the early-age mechanical behavior of cementitious composites under a mode-I loading condition. ...
In this research, we developed a four-phase model, which takes the aggregate gradation and porosity into account in the prediction of the elastic modulus of concrete, based on the micromechanical theories. The model has been verified with experimental results. First, using the Mori Tanaka and the differential self-consistent (DSC) methods, the pores in both the mortar and interfacial transition zone (ITZ) were homogenized. Then, the continuously graded aggregates were divided into finite aggregate size intervals. Further, using the generalized self-consistent model and multiphase composite model derived from the Mori Tanaka method, an aggregate gradation model for the prediction of the elastic modulus of concrete was developed. By simulating the pores in concrete with expanded polystyrene sphere (EPS) grains, the effect of overall porosity on the elastic modulus of concrete was investigated. The research results show that aggregate gradation and porosity have remarkable influence on the elastic modulus of concrete, and the proposed model is effective to estimate the elastic modulus of concrete, the deviation between the predicted elastic modulus and experimental elastic modulus is less than 8%. The elastic modulus decreases with increasing ITZ porosity. However, for ITZ porosity exceeding 40%, the decrease in the elastic modulus is large with increasing ITZ porosity. For a fixed overall porosity, the ITZ porosity owned more influences than the mortar porosity on the elastic modulus of concrete. Enhancing the ITZ elastic modulus and decreasing the ITZ thickness are efficient in increasing the elastic modulus of concrete.
... For example, typical strong engineering fibers such as carbon or glass fibers are brittle, whereas, most tough engineering polymers have low strength. To address both strength and toughness simultaneously requires advanced material design that incorporates strong and tough materials with energy dissipation strategies [1][2][3][4]. Carbon nanotube (CNT) with exceptional strength, stiffness, and toughness has been considered a promising material to achieve this goal [5]. However, agglomeration of CNTs due to their strong van der Waals interactions limits their solubility and dispersion and reduces both strength and toughness of the final product [6,7]. ...
... Figure 2 represents the molecular model for different Vf of cellulose, CNC (Vf = 100%) and a multilayer cellulose wrap with no CNT (Vf = 100%). [1][2][3][4][5][6][7][8][9][10] surfaces as the most recommended structure model for CNC is studied here [24,31]. According to previous theoretical study, increasing the diameter of the single-walled cellulose nanotubes results in a more stable structure due to more stable inter-molecular hydrogen bonds [46]. ...
Improving the adhesion properties of carbon nanotubes (CNTs) at the molecular scale can significantly enhance dispersion of CNT fibers in polymer matrix and unleash the dormant extraordinary mechanical properties of CNTs in CNT-polymer nanocomposites. Inspired by the outstanding adhesion, dispersion, mechanical, and surface functionalization properties of crystalline nanocellulose (CNC), this paper studies the mechanical and adhesion properties of CNT wrapped by aligned cellulose chains around CNT using molecular dynamic simulations. The strength, elastic modulus, and toughness of CNT-cellulose fiber for different cellulose contents are obtained from tensile and compression tests. Additionally, the effect of adding cellulose on the surface energy, interfacial shear modulus, and strength is evaluated. The result shows that even adding a single layer cellulose wrap (≈55% content) significantly decreases the mechanical properties, however, it also dramatically enhances the adhesion energy, interfacial shear strength, and modulus. Adding more cellulose layers, subsequently, deceases and increases mechanical properties and adhesion properties, respectively. In addition, analysis of nanopapers of pristine CNT, pristine CNC, and CNT-wrapped cellulose reveals that CNT-wrapped cellulose nanopapers are strong, stiff, and tough, while for CNT and CNC either strength or toughness is compromised. This research shows that cellulose wraps provide CNT fibers with tunable mechanical properties and adhesion energy that could yield strong and tough materials due to the excellent mechanical properties of CNT and active surface and hydrogen bonding of cellulose.
... Research on the recycling of concrete is mainly devoted to finding the most effective way to obtain recycled aggregates of the best quality, which usually means removing the impurities from the surface of the natural aggregate grains. The recycled aggregate's quality is closely related to the adhered cement paste properties, since the bond between the natural aggregates and the cement paste is usually weak in the interfacial transition zone [5][6][7][8]. It is widely accepted that the presence of cement paste in recycling concrete aggregate causes its worse physical, mechanical and chemical properties compared to natural aggregates. ...
... Research on the recycling of concrete is mainly devoted to finding the most effective way to obtain recycled aggregates of the best quality, which usually means removing the impurities from the surface of the natural aggregate grains. The recycled aggregate's quality is closely related to the adhered cement paste properties, since the bond between the natural aggregates and the cement paste is usually weak in the interfacial transition zone [5][6][7][8]. It is widely accepted that the presence of cement paste in recycling concrete aggregate causes its worse physical, mechanical and chemical properties compared to natural aggregates. ...
The process of recycling concrete rubble is accompanied by the formation of a large amount of fine fraction, which cannot be reused as aggregate. The results of research on the possibility of using recycled cement mortar (RCM), obtained during concrete recycling, as a cementitious supplementary material, are presented. The experimental research was carried out on the basis of two variables determining the recycling process: X 1-temperature (range of variation 288-712 • C) and X 2-time (range of variation 30-90 min) of thermal treatment of concrete rubble. The experiment included 10 series of new composites made with RCMs subjected to different variants of thermal treatment, and two additional control series. The best treatment parameters were determined based on the assessment of selected physical and mechanical properties of the new cement composites, as well as the analysis of characteristics and microstructure of RCM. The test results showed that proper thermal treatment of concrete rubble makes it possible to obtain a high-quality fine fraction, which has the properties of an active addition and can be used as a partial replacement for cement in mortars and concretes.
... The schematic diagram of the shield mechanism of GO in the GO-cement sample is illustrated in Figure 16. Esmaeeli et al. [44] reported that the early-age tensile stiffness and strength development of cementitious composites, such as mortar and concrete, were examined using a finite element model. Future study is needed to model the initiation and propagation of cracks in GO-cement composites using a mesomechanical model. ...
... illustrated in Figure 16. Esmaeeli et al. [44] reported that the early-age tensile stiffness and strength development of cementitious composites, such as mortar and concrete, were examined using a finite element model. Future study is needed to model the initiation and propagation of cracks in GO-cement composites using a mesomechanical model. ...
The effects of the water–binder ratio and different graphene oxide (GO) sizes on the mechanical properties of GO-cement composites were systematically studied by preparing GO-cement mortars. The scanning electron microscopy observation (SEM) of the surface and fracture surface of cement pastes was carried out to study the morphology of cement hydration crystals in GO-cement systems under different space conditions. It was found that GO nanosheets significantly improved the compressive, flexural, and tensile strengths of cement mortars. When the dosage of GO nanosheets was 0.03% by weight of cement, the compressive, flexural, and tensile strengths at 28 days increased by 21.37%, 39.62%, and 53.77%, respectively, but GO was not found to be able to regulate the formation of flower-like cement hydration crystals. It was only shown that the growth space had an important influence on the morphology of hydrates. A possible working mechanism was proposed by which GO nanosheets prevented the expansion of microcracks in the cement pastes via a shield effect, thus enhancing the strength and toughness of the cement composites.
... Cohesive Zone model is one the most powerful models in the fracture mechanics and finite element framework for incorporating fracture process and modeling crack propagation. For example, Esmaeeli et al, used a multiscale cohesive zone model for predicting fracture of cementitious composites at early age by inserting cohesive elements between cement and aggregates and showed that crack can propagate both in cement and aggregate depending on the cement age [20]. We use cohesive elements to define the adhesion between two beams and he parameters that define the used law were selected based on the fracture toughness of CNC. ...
Crystalline nanocellulose (CNC) is a new promising green material that gained significant attention in the past decade. This study evaluates the effects of pattern interfaces on the fracture toughness in naturally joined double cantilever beam of crystalline nanocellulose (CNC) nanofilms. Three different patterns, e.i., triangular, trapezoidal and circular with different geometric properties were considered and compared with flat (no pattern) interface. We use a multiscale framework by using adhesion and elastic properties are nanoscale from molecular dynamics and upscale the values to the properties of cohesive element in finite element framework. The result shows that pattern interfaces significantly improve the toughness of CNC nanofilms. In particular, trapezoidal interface increase the fracture toughness by 140%.
... G f should be obtained experimentally by means of notched beam tests. When such tests are not available, the fracture mechanism based model of Hadi et al. [39] may be used. In lieu of that, Equation (11) can be used after the statistical approach provided by Bažant and Becq-Giraudon [40]. ...
Grouted dowel connections are used extensively in precast load bearing walls owing to their simple construction and forgiving tolerances. Current design guidelines do not adequately consider the composite nature of such connections. Moreover, robust numerical models for these connections are yet to be developed. Therefore, a finite element model of grouted dowel connections was developed in this paper. The model adopts a phenomenological bond-slip constitutive law to predict the load versus slip response of grouted bars and considers tensile yielding of the reinforcement. The local bond-slip law used was generated from carefully designed experiments to eliminate spurious effects associated with bond testing. The model was validated using experimental results on grouted connections, as well as data retrieved from the open literature. Excellent agreement between experimental and numerical results was observed, highlighting the accuracy of the model in depicting interfacial stresses of the assembly. The model requires simple calibration, is computationally efficient, and can accurately simulate the failure behavior of bars embedded in grouted connections.
