Mi G. Chorzepa

Mesoscale Fracture Analysis of Multiphase Cementitious Composites Using Peridynamics

Concrete is a complex heterogeneous material, and thus, it is important to develop numerical modeling methods to enhance the prediction accuracy of the fracture mechanism. In this study, a two-dimensional mesoscale model is developed using a non-ordinary state-based peridynamic (NOSBPD) method. Fracture in a concrete cube specimen subjected to pure tension is studied. The presence of heterogeneous materials consisting of coarse aggregates, interfacial transition zones, air voids and cementitious matrix is characterized as particle points in a two-dimensional mesoscale model. Coarse aggregates and voids are generated using uniform probability distributions, while a statistical study is provided to comprise the effect of random distributions of constituent materials. In obtaining the steady-state response, an incremental and iterative solver is adopted for the dynamic relaxation method. Load-displacement curves and damage patterns are compared with available experimental and finite element analysis (FEA) results. Although the proposed model uses much simpler material damage models and discretization schemes, the load-displacement curves show no difference from the FEA results. Furthermore, no mesh refinement is necessary, as fracture is inherently characterized by bond breakages. Finally, a sensitivity study is conducted to understand the effect of aggregate volume fraction and porosity on the load capacity of the proposed mesoscale model.

Formulation of symmetry boundary modeling in non-ordinary state-based peridynamics and coupling with finite element analysis

Peridynamics is an effective method in computational solid mechanics for dealing with discontinuities. However, its computational cost limits its applications, especially when used in the most general form, non-ordinary state-based peridynamics. This paper considers two approaches which decrease the computational cost. The first approach accounts for symmetry boundary conditions in a peridynamic body. In nonlocal peridynamics, boundary conditions are applied to an area. Therefore, when modeling the symmetry boundary condition, assuming fixed particles around the symmetry axis yields incorrect results. The present formulation introduces constraints which allow modeling of local symmetry conditions. Second, the finite-element–peridynamic coupling method is adopted for non-ordinary state-based peridynamics. The coupling method enables the use of peridynamics around discontinuities like cracks, and the faster finite element for the surrounding body. These two methods effectively reduce the solution time with an acceptable accuracy. The validity of these approaches is studied through various examples. Also, ductile crack growth in a compact tension specimen is studied, applying the presented methods. Good agreement is found when comparing experimental results with corresponding numerical results obtained using either fully peridynamic or coupled models.

Effect of cement content and recycled rubber particle size on the performance of rubber-modified concrete

ABSTRACT According to the Rubber Manufacturer’s Association, the United States generated 3664 thousand metric tons of scrap tires in 2015. While most waste tires are repurposed, approximately 409.5 thousand metric tons were disposed in landfills. This study investigates an alternative use of the waste tires as a replacement of natural aggregates in concrete mixtures. This study investigated fresh concrete properties and compressive strength. Different coarse and fine aggregate rubber particle sizes were evaluated: 19-mm tire chips (TCs) and 30-mesh crumb rubber (CR). TCs were used to replace coarse aggregates, while CR was used to replace fine aggregate in the concrete mixtures in increments of 10% by volume. Concrete strength loss was reduced with a fine aggregate replacement with CR as opposed to greater losses of strength exhibited by a coarse aggregate replacement with TCs. Adequate strengths were achieved at replacement levels as high as 40% by volume with CR, whereas satisfactory strengths were achieved with only a 10% replacement of coarse aggregates with TCs. Acceptable strengths were obtained from mixtures utilizing a combination of the two rubber sizes. Cement content was observed to have greater influence on rubberized concrete compressive strength at lower rubber contents than higher levels.

Assessing Benefits of Using Geogrids in Pavements Founded on Problematic Soils

Geogrids are becoming a popular alternative for soil reinforcement in highway pavement construction to achieve improved performance in regions with soft problematic soils or with a reduction in aggregate layer thickness to reduce construction costs. To examine the potential benefits of geogrids for soil improvement, measurement of permanent deformation using triaxial tests is used in practice. However, soil subgrade improvement in a reinforced pavement system is achieved by lateral distribution of vertical stresses at the reinforcing layer, through the tensile properties of the geogrid material. Therefore, it is desirable to conduct large-scale testing to more accurately monitor the behavior of soil when geogrid is present. The current study seeks to verify the behavior of geogrid reinforced pavement systems through large-scale wheel tests performed with problematic subgrade soils found in North Georgia. The large scale specimen was prepared in a 6 feet long × 6 feet wide × 2 feet deep metal box and consisted of 12 in. of aggregate base overlying 12 in. of subgrade soil. Pressure sensors were installed near the bottom of the aggregate base layer and near the top and bottom of the subgrade layer to monitor stress distributions within the pavement system. This paper presents preliminary results showing vertical stress variations obtained experimentally in aggregate base and subgrade soils under large-scale simulated traffic tire loading. The development of a bench scale system to complement the large scale loading system and allow for microstructure evolution studies is also described.

Forensic Investigation of Pavement: Practices in North America and a Pilot Investigation

AbstractState agencies/provinces and civil engineers must remain current in forensic pavement investigation procedures and inspection technologies to efficiently maintain public roads. Preliminary ...