Automatic enhancement of vascular configuration for self-healing concrete through reinforcement learning approach

Vascular self-healing concrete (SHC) has great potential to mitigate the environmental impact of the construction industry by increasing the durability of structures. Designing concrete with high initial mechanical properties by searching a specific arrangement of vascular structure is of great importance. Herein, an automatic optimization method is proposed to arrange vascular configuration for minimizing the adverse influence of vascular system through a reinforcement learning (RL) approach. A case study is carried out to optimize a concrete beam with 3 pores (representing a vascular network) positioned in the beam midspan within a design space of 40 possibilities. The optimization is performed by the interaction between RL agent and Abaqus simulation environment with the change of target properties as a reward signal. The results illustrates that the RL approach is able to automatically enhance the vascular arrangement of SHC given the fact that the 3-pore structures that have the maximum target mechanical property (i.e., peak load or fracture energy) are accessed for all of the independent runs. The RL optimization method is capable of identifying the structure with high fracture energy in the new optimization task for 4-pore concrete structure.</p

Modalna analiza ramovskih konstrukcija primenom metode spektralnih elemenata

Dinamička analiza ramovskih konstrukcija u frekventnom domenu ima niz prednosti. Za gredne elemente mogu se primeniti spektralni elementi čija je dinamička matrica krutosti frekventno zavisna, dobijena rešavanjem diferencijalne jednačine štapa. U njoj su, pored elastičnog dela, sadržani i inercijalni deo i prigušenje. U radu su prikazane teorijske osnove metode spektralnih elemenata, i primena ove metode u modalnoj analizi ramovskih konstrukcija. Prikazano je poređenje dobijenih rezultata sa rezultatima dobijenim primenom metode konačnih elemenata

Towards understanding the influence of porosity on mechanical and fracture behaviour of quasi-brittle materials:experiments and modelling

In this work, porosity-property relationships of quasi-brittle materials are explored through a combined experimental and numerical approach. In the experimental part, hemihyrate gypsum plaster powder (CaSO 4 ⋅1/2H 2 O CaSO4⋅1/2H2O) and expanded spherical polystyrene beads (1.5–2.0 mm dia.) have been mixed to form a model material with controlled additions of porosity. The expanded polystyrene beads represent pores within the bulk due to their light weight and low strength compared with plaster. Varying the addition of infill allows the production of a material with different percentages of porosity: 0, 10, 20, 30 and 31 vol%. The size and location of these pores have been characterised by 3D X-ray computed tomography. Beams of the size of 20×20×150 20×20×150 mm were cast and loaded under four-point bending to obtain the mechanical characteristics of each porosity level. The elastic modulus and flexural strength are found to decrease with increased porosity. Fractography studies have been undertaken to identify the role of the pores on the fracture path. Based on the known porosity, a 3D model of each microstructure has been built and the deformation and fracture was computed using a lattice-based multi-scale finite element model. This model predicted similar trends as the experimental results and was able to quantify the fractured sites. The results from this model material experimental data and the lattice model predictions are discussed with respect to the role of porosity on the deformation and fracture of quasi-brittle materials

Towards understanding the influence of porosity on mechanical and fracture behaviour of quasi-brittle materials:experiments and modelling

In this work, porosity-property relationships of quasi-brittle materials are explored through a combined experimental and numerical approach. In the experimental part, hemihyrate gypsum plaster powder (CaSO 4 ⋅1/2H 2 O CaSO4⋅1/2H2O) and expanded spherical polystyrene beads (1.5–2.0 mm dia.) have been mixed to form a model material with controlled additions of porosity. The expanded polystyrene beads represent pores within the bulk due to their light weight and low strength compared with plaster. Varying the addition of infill allows the production of a material with different percentages of porosity: 0, 10, 20, 30 and 31 vol%. The size and location of these pores have been characterised by 3D X-ray computed tomography. Beams of the size of 20×20×150 20×20×150 mm were cast and loaded under four-point bending to obtain the mechanical characteristics of each porosity level. The elastic modulus and flexural strength are found to decrease with increased porosity. Fractography studies have been undertaken to identify the role of the pores on the fracture path. Based on the known porosity, a 3D model of each microstructure has been built and the deformation and fracture was computed using a lattice-based multi-scale finite element model. This model predicted similar trends as the experimental results and was able to quantify the fractured sites. The results from this model material experimental data and the lattice model predictions are discussed with respect to the role of porosity on the deformation and fracture of quasi-brittle materials

Simulation-aided design of tubular polymeric capsules for self-healing concrete

Polymeric capsules can have an advantage over glass capsules used up to now as proof-of-concept carriers in self-healing concrete. They allow easier processing and afford the possibility to fine tune their mechanical properties. Out of the multiple requirements for capsules used in this context, the capability of rupturing when crossed by a crack in concrete of a typical size is one of the most relevant, as without it no healing agent is released into the crack. This study assessed the fitness of five types of polymeric capsules to fulfill this requirement by using a numerical model to screen the best performing ones and verifying their fitness with experimental methods. Capsules made of a specific type of poly(methyl methacrylate) (PMMA) were considered fit for the intended application, rupturing at average crack sizes of 69 and 128 μm, respectively for a wall thickness of ~0.3 and ~0.7 mm. Thicker walls were considered unfit, as they ruptured for crack sizes much higher than 100 μm. Other types of PMMA used and polylactic acid were equally unfit for the same reason. There was overall good fitting between model output and experimental results and an elongation at break of 1.5% is recommended regarding polymers for this application

Accelerated carbonation of ordinary Portland cement paste and its effects on microstructure and transport properties

Coupling of carbonation and chlorides ingress mechanisms is very common in concrete under certain exposure conditions such as coastal environments. The aggravation/ mitigation of corrosion by the existence of carbonation lies on the fact that microstructural changes due to carbonation result in changes on the transport properties of the material. In this study we investigate and quantify evolving transport properties of ordinary Portland cement paste, such as porosity, tortuosity and intrinsic permeability. Dual X-ray micro computed tomography (micro CT) is used for the quantification of porosity. Furthermore Dynamic Vapour Sorption (DVS) measurements are carried out to resolve water retention and relative permeability curves. The authors expect to provide insights into the mechanisms of accelerated carbonation in both types of cement paste, as well as data for input and validation of numerical and analytical models on this degradation phenomenon

Influence of Micro-Pore Connectivity and Micro-Fractures on Calcium Leaching of Cement Pastes — A Coupled Simulation Approach

A coupled numerical approach is used to evaluate the influence of pore connectivity and microcracks on leaching kinetics in fully saturated cement paste. The unique advantage of the numerical model is the ability to construct and evaluate a material with controlled properties, which is very difficult under experimental conditions. Our analysis is based on two virtual microstructures, which are different in terms of pore connectivity but the same in terms of porosity and the amount of solid phases. Numerical fracturing was performed on these microstructures. The non-fractured and fractured microstructures were both subjected to chemical leaching. Results show that despite very different material physical properties, for example, pore connectivity and effective diffusivity, the leaching kinetics remain the same as long as the amount of soluble phases, i.e., buffering capacity, is the same. The leaching kinetics also remains the same in the presence of microcracks

Auxetic cementitious composites (ACCs) with excellent compressive ductility: Experiments and modeling

Auxetic cementitious composites (ACCs) with improved mechanical properties are created, by casting 3D printed polymeric auxetic reinforcement structures inside cementitious mortar. Four types of ACCs incorporating reinforcement with different auxetic mechanisms were prepared: “re-entrant” (RE), “rotating-square” (RS), “chiral” (CR) and “missing-rib” (MR). Experiments and finite element models were used to study the compressive behavior of the ACCs. The results indicate that all ACCs have high compressive ductility. Specifically, the RE shows the highest ductility, manifested by 853% and 708% higher energy absorption than the reference mortar and the auxetic structure itself, respectively. In addition, the RE and RS are found to exhibit stronger crack-arresting effect under compression. Therefore, they achieved comparable compressive strength to the reference mortar, which is considerably higher than CR and MR. Furthermore, decreasing the volumetric ratio of the auxetic structure by half, the ductility of the RS reduces by 32.2%, while decreasing the water-to-binder ratio of the cementitious matrix from 0.4 to 0.3 only increases the compressive strength by 18.5%. Moreover, the two-dimensional finite element analyses used herein show a good match with experiments but become less accurate at high strain levels, due to their inability to capture the out-of-plane failure of the ACCs

Micromechanical Models for FDM 3D-Printed Polymers: A Review

Due to its large number of advantages compared to traditional subtractive manufacturing techniques, additive manufacturing (AM) has gained increasing attention and popularity. Among the most common AM techniques is fused filament fabrication (FFF), usually referred to by its trademarked name: fused deposition modeling (FDM). This is the most efficient technique for manufacturing physical three-dimensional thermoplastics, such that FDM machines are nowadays the most common. Regardless of the 3D-printing methodology, AM techniques involve layer-by-layer deposition. Generally, this layer-wise process introduces anisotropy into the produced parts. The manufacturing procedure creates parts possessing heterogeneities at the micro (usually up to 1 mm) and meso (mm to cm) length scales, such as voids and pores, whose size, shape, and spatial distribution are mainly influenced by the so-called printing process parameters. Therefore, it is crucial to investigate their influence on the mechanical properties of FDM 3D-printed parts. This review starts with the identification of the printing process parameters that are considered to affect the micromechanical composition of FDM 3D-printed polymers. In what follows, their (negative) influence is attributed to characteristic mechanical properties. The remainder of this work reviews the state of the art in geometrical, numerical, and experimental analyses of FDM-printed parts. Finally, conclusions are drawn for each of the aforementioned analyses in view of microstructural modeling