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This study is involved with presenting a multi-level micromechanical model for predicting the coefficients of thermal expansion (CTE) of randomly distributed and oriented short hybrid fiber reinforced concrete (HFRC), which includes the cement paste level, concrete level, and HFRC level. In this micromechanical model, the inner products (IP), outer products (OP), calcium hydroxide (CH), unhydrated clinker, sands, aggregates and hybrid fibers are comprehensively considered. A substepping homogenization framework is presented to realize the upscaling from the microstructure to macro HFRC, based on which the overall CTE of HFRC is determined. In addition, the volume fractions of phases at each level are also presented to facilitate the prediction of CTE. Comparisons with experimental data from previous studies are implemented level by level. Subsequently, the influences of the water-cement ratio, the hydration degree, the aggregate property and the fiber property on the CTE are discussed carefully.

As tensile crack-bridging constitutive relations play an important role in the multiple cracking behaviors of Strain-Hardening Cementitious Composites (SHCCs), careful control of the crack-bridging relations is the key to a successful design of the materials. This study theoretically explores the crack-bridging relations of SHCCs with fixed total volume fraction (2.5%) of hybrid polyvinyl alcohol (PVA) and steel fibers. Since a large number of experiments at the single-fiber level are needed to determine the parameters for the micromechanical model, the snubbing coefficient, fiber strength reduction factor and Cook-Gordon parameter for mono-fiber composites were theoretically calibrated rather than experimentally obtained in this study. With these calibrated parameters, the crack-bridging relations of hybrid-fiber SHCCs were then modeled and compared to the test results. The superposition principle was used to address the contributions of different types of fibers, and the interaction between PVA and steel fibers was considered through the matrix micro-spalling in the modeling. The theoretically modeled crack-bridging relations of hybrid-fiber SHCCs were in good agreement with the test curves in terms of the tensile strength and the corresponding crack opening. The findings in this study provide a better understanding of fiber hybridizations in SHCCs.

This paper presents a discrete micromechanical model for predicting high strength concrete compressive strength. A numerical model is proposed based on a Voronoi tessellation which represents concrete as a set of aggregates interacting within a cement matrix. A static yield design approach is conducted at the mesoscopic scale to determine the maximum bearable compressive stress. Then, an analytical model is derived based on the numerical results. The geometric and mechanical effects are decoupled enabling a micromechanical explanation of the maximum paste thickness and the aggregates’ size distribution effects on concrete compressive strength. Finally, the analytical model is calibrated and validated on experimental results taken from literature.

There is a demand for multi scale micromechanical models to disclose and analyze the effects of microstructure on macro mechanical properties of hybrid fiber reinforced concrete (HFRC). This study involved presenting a multi-level micromechanical model that involves cement paste level, concrete level, and hybrid fiber reinforced concrete level to quantitatively predict the effective isotropic and elastic properties of HFRC under ambient temperature. For the purposes of homogenization, the volume fractions of different phases at different levels are determined by means of a modified Power’s model. In the multi-level micromechanical model, hydration products of clinker, sand, coarse aggregate, and hybrid fiber are comprehensively considered. A homogenization stepping framework is presented to realize upscaling from microstructural properties to the effective elastic properties of a macrostructure for HFRC. Additionally, several substepping homogenizations are also presented to estimate the effective elastic properties of an equivalent medium with respect to the cement paste and hybrid fiber reinforced concrete. Comparisons with experimental data from extant studies are implemented level by level. Subsequently, the influences of aggregate, sand, fiber type, and hydration degree on the properties of HFRC are discussed based on a proposed multi-level micromechanical model. Finally, the mixture ratio of steel fiber and w/c are investigated with respect to the HFRC design to obtain anticipated elastic properties.

Inter-particle effect and imperfect interface are the two major challenges during the micromechanical modeling of asphalt mixture due to its complex heterogeneity. This paper presents the development and validation of a micromechanical model regarding this concern. The linear spring model is adopted to simulate the imperfect interface between asphalt mortar and aggregates, and the replacement procedure is established to incorporate the imperfect interface effect into the Ju-Chen (J-C) model to coupling inter-particle effect and imperfect interface. The proposed model is used to predict the dynamic modulus of asphalt mixture and analyze the influence of inter-particle effect and imperfect interface. The results show that the predictions decrease with the interface parameter m r / m θ but increase with parameter Y ( g ) . The imperfect interfacial bonding weakens the overall property of asphalt mixture and the weaken effect for composites with stronger inter-particle effect is more significant.

For the past several years, research in the field of self-healing construction materials becomes a hotspot with broad application prospects. This paper mainly focuses on the self-healing cementitious composites with microcapsules. To quantitatively interpret the self-healing effect of micro-encapsulated healing agents on microcrack-induced damage, a three-dimensional evolutionary micromechanical model is established to predict the mechanical response of the cementitious composites with the microcapsules subjected to tensile loading during the damage-healing process. The evolutionary domains of microcrack growth (DMG) and the corresponding compliances at the initial, activated and repaired stages are obtained. On the basis of the proposed 3D micromechanical model of the self-healing cementitious composites with microcapsules, elaborate studies of constitutive relations and compliance are conducted to investigate the effects of various system parameters involving the healing efficiency, fracture toughness and preloading-induced damage degrees on the compliances and stress-strain relations. The results indicate that relatively significant healing efficiency, preloading-induced damage degree and the fracture toughness of polymerized healing agent with the matrix will lead to higher tensile strength and stiffness. However, based on the two different failure modes of self-healing concrete, the excessive values of healing efficiency, preloading-induced damage degree and the fracture toughness of polymerized healing agent with the matrix will not affect the tensile strength of the cementitious composites. For the sake of the desired optimal healing effect, the specific parameters of both the matrix and the microcapsules should be selected carefully.

Very few micromechanical models are available for hybrid fiber reinforced concrete (HFRC), although it has been widely applied in many structures. To quantitatively predict the effective properties of HFRC with the aggregate and interfacial transition zone (ITZ) effects, a multi-phase micromechanical framework is proposed based on the material’s microstructures. In the proposed model, the multi-types of fibers, aggregate, cement paste and ITZ are comprehensively considered. The volume fraction of the ITZ is analytically calculated based on the aggregate grading. Multi-level homogenization schemes are presented to predict the effective properties of HFRC. By utilizing the generalized self-consistent approach, the equivalent matrix composed by the aggregate, cement and the ITZ between them are obtained with the first and second level homogenization procedures. Through adding different types of fibers step by step into the equivalent matrix, the properties of HFRC are reached with the modifications to the Halpin-Tsai model. To demonstrate the feasibility of the proposed micromechanical framework, the predictions herein are compared with the experimental data, the Voigt upper bound and the Reuss lower bound. Finally, the influences of aggregate, ITZ, multi-types of fibers on the properties of HFRC are discussed based on the proposed micromechanical model.

In last decades, several computational strategies have been proposed for masonry structures, which form a large fraction of worldwide built heritage. In this study, a micromechanical model is proposed for tuff stone masonry by assuming a periodic composite with two components, namely tuff stones and mortar. A pressure-dependent failure rule was assigned to each component and mechanical properties were assigned according to material test results. The accuracy and robustness of the micromechanical model were assessed by simulating nonlinear response and crack patterns of masonry in different geometrical, boundary and loading conditions related to axial and diagonal compression tests. A satisfactory numerical-experimental comparison was found. Sensitivity to tensile and compressive strengths of masonry components was evaluated. Local limit states were associated with the overall nonlinear response of masonry and were statistically characterised for performance-based assessment. Finally, Monte Carlo simulations were performed to assess the influence of masonry inhomogeneity on experimental test simulations.

A micromechanical creep model is presented to predict the creep behavior of asphalt concrete (AC) and investigate the effect of imperfect interface between asphalt mastic and aggregates on the viscoelastic properties of AC. The linear spring layer model is introduced to characterize the interface imperfection. Based on the modified Mori–Tanaka method, the micromechanical model is developed. To describe the viscoelastic properties of AC with imperfect interface, micromechanical creep compliance formulation is obtained by incorporating the elastic–viscoelastic correspondence principle. The present prediction is compared with available experimental data in the literature to verify the proposed method. It is found that the micromechanical creep model has the capability to predict the creep behavior of AC. Interface effects on the creep behavior of AC are explored using the developed model. It is concluded that the imperfect interface between asphalt mastic and aggregates has a significant influence on the overall mechanical behavior of AC, and that the interfacial damage should be controlled within a certain extent.

The coefficient of thermal expansion (CTE) is a very important property of cement concrete. Concrete CTE represents the thermal expansion and/or contraction sensitivity of concrete, which highly relates to thermal cracks in concrete infrastructures, such as concrete dams and concrete pavements. The values of concrete CTE can be measured through laboratory testing or predicted using empirical models. While laboratory testing is time- and labor-consuming, the current concrete CTE prediction models are mainly based on empirical relationships. In this study, an improved micromechanical model was proposed to predict concrete CTE based on thermal mechanical analysis in which concrete was seen as a composite material. The original model developed by the authors can be found elsewhere. The improved CTE model was validated using a hierarchical approach with CTE measurements of cement paste, mortar, and concrete. The result indicates that the improved model was able to provide a better prediction on CTE values than the original model. Factors affecting concrete CTE were investigated utilizing the developed CTE prediction model. It was found that aggregate type was a major factor affecting concrete CTE, whereas water cement ratio did not have a significant effect on concrete CTE.

Asphalt oxidation is a chemical reaction between asphalt binders and oxygen that causes irreversible changes in the properties of asphalt materials used in pavement structures. This paper explores the influence of the air void phase of asphalt mixtures on oxidation. Microstructures of an asphalt mixture with probable internal air void structures were generated and implemented in finite elements, and they were used in combination with oxygen diffusion and chemical kinetics models to estimate the changes generated in the mechanical properties of the material. The results confirm that the air void phase strongly impacts the stiffening processes caused by oxidation in asphalt mixtures.

In this paper, the influence of steel fibers on the ultrasonic velocity of steel–fiber-reinforced cementitious materials was studied using a micromechanical model. To this end, a three-phase micromechanical model was extended and generalized to multiphase materials. Firstly, such a model was used to predict the influence of the geometry and volume fraction of steel inclusions on the ultrasonic velocity of steel–fiber-reinforced cementitious materials. Experimental validation was carried out on steel-reinforced and non-reinforced mortar specimens through destructive and non-destructive testing by ultrasound. Comparisons between predicted and measured ultrasonic velocity were in good agreement, with errors less than 1.5%. Moreover, the model was also validated on experimental data obtained from steel–fiber-reinforced concrete specimens [Yazici et al. Constr Build Mater 2007;21:1250–3].