Jaime Horta-Rangel

Cellular Concrete Bricks with Recycled Expanded Polystyrene Aggregate

Cellular concrete bricks were obtained by using a lightweight mortar with recycled expanded polystyrene aggregate instead of sandy materials. After determining the block properties (absorption, compressive strength, and tensile stresses), it was found that this brick meets the requirements of the masonry standards used in Mexico. The obtained material is lighter than the commercial ones, which facilitates their rapid elaboration, quality control, and transportation. It is less permeable, which helps prevent moisture formation retaining its strength due to the greater adherence shown with dry polystyrene. It was more flexible, which makes it less vulnerable to cracking walls due to soil displacements. Furthermore, it is economical, because it uses recyclable material and has properties that prevent deterioration increasing its useful life. We recommend the use of the fully dry EP under a dry environment to obtain the best properties of brick.

An Optimization Approach to the Computer Simulation of Composite Materials

A procedure for the optimal modal design of a beam made of a composite material was developed. The two components considered for the composite are a light concrete as the matrix and a polyester fiber as the filler. The fibers inside of the matrix tend to aggregate and to take this into account in the modeling, a subroutine that generates random finite elements corresponding to the fiber clusters was constructed. Three-dimensional simulation using a volumetric model allows to obtain the solutions by means of a coupled modal analysis-optimization procedure, by employing the ANSYS software. The weight of the beam is considered as the objective function. Restrictions are imposed on the first resonant frequency as well as on the design parameters: percentage of fiber polyester, density of the components, and thickness of the beam. The results provide the optimum set of solutions in terms of the parameters that minimize the weight of the beam, while maintaining the first frequency within a specified range of values.

Geocharacterisation of the “Tepetates”

Tepetate formations are generally found in regions where climate presents a very well-defined dry season. The original materials are basically pyroclastic projections under rain or flood shapes. Tepetates are indurated earthy materials from Mexico that have been reported with different names in different countries. These materials have been subject of investigation by very different areas such as geology and edaphology related to their origin, constitution, minerals and location, and also to the agronomy focusing in its improvement and incorporation as a fertile soil. This material has also been used as an earthen structure like embankments for pavements and residential flooring and as a substitution material for problematic soil such as the expansive clays without serious studies that validate its behaviour. In this article, there appears a research work of the behaviour of the tepetates as earthen structures. We concluded that those methodologies in this study create a new material completely different from the original (indurated). Moreover, the types of cement in the tepetates have different behaviours. The lack of tepetate characterisation in the mentioned applications is contributing to create an image of a relatively homogeneous material, which can occasionally be the case but is not a generality.

Modal behaviour of bones during fracture

A common cause of human disability is related to the fracture of bones, complex structural materials whose properties vary with time. An analytical study (using ANSYS, a commercial finite element package) of bones under fracture conditions is presented, focusing on the frequency variation versus depth of crack, as well as on the evolution of strength in the fracture area.

Computer Simulation of Failure Process of a Fiber-reinforced Concrete Composite with Randomly Distributed Fiber Clusters

Fiber-reinforced concrete (FRC) composites to date are not fully researched with regard to the mechanical behavior of the random distribution of the fibers inside the matrix, which tend to bundle (fiber clusters). In this work we study the influence of the random distribution of fibers in the matrix by means of computer modeling applied to structural plane specimen subjected to tension loading. Increasing the tension load the failure will appear first in the weak concrete zones induced by the random distribution of inclusion elements. These failure elements are now modified as air elements, and the process goes on until collapse. As a result of this process the stress—strain plots of the sample until failure, and the stress—strain graph at the time of gradual application of the tension stress are found. We compare the obtained results with Kerner`s model. Computer modeling is achieved by the ANSYS program coupling a subroutine written in APDL language.

Shift of natural frequencies in earthquake‐damaged structures: an optimization approach

Purpose – Earthquakes can produce important damage in civil infrastructure, including buildings and bridges, representing an important impact on the economy of many countries. The damage is particularly severe when the dominant frequency of the quake approaches one of the resonant frequencies of the structure. One typical failure occurs through the weakening of some beam‐column joints, generally along with the presence of cracking. The standard procedure for repairing this is by reinforcing the damaged zone with steel plates, sleeves or by means of a new section of reinforced concrete covering the old one. These arrangements change the mechanical stiffness and the mass of the structure itself. Accordingly, this work aims to study these mass and stiffness changes of structures through a non‐linear optimization of the modal analysis of the structure.Design/methodology/approach – The paper analyzes the potential shifts in natural frequencies of the structure and thus proposes the best conditions under which ...

Computer simulation of a pressure‐volume‐temperature process

Purpose – The study of pressure‐volume‐temperature (PVT) process is necessary to understand the physical behaviour of materials. This paper seeks to develop a simulation procedure to predict phase behaviour.Design/methodology/approach – The procedure consisted of the application of a thermo‐mechanical nonlinear model that simulated the behavior of the test sample in the PVT apparatus. Software Ansys was used for modeling this case, making a subroutine in APDL language. The real time data of the experimental procedure in PVT apparatus were applied in the computer simulation, that is the real time of application of pressure and heating scaling of the sample were taken into account. A specific case was simulated and its results compared with those obtained from the real experimental test. In order to evaluate phase changes, enthalpy was considered using an approximated expression described in the paper.Findings – Results obtained from the simulation were compared with the resulting isobaric graphics of the e...

Polymer-Cement Mortar with Quarry Waste as Sand Replacement

The activities of carved Quarry extraction generate problems of landscape pollution such is the case of solid waste discharged into open land dumps in central Mexico. This article presents the technological application of this solid waste in a new polymeric material with properties similar to those of a traditional mortar. It is concluded that the polymeric material uses low amounts of cement with respect to the traditional mortar, and it is elaborated with the recycled quarry as they are presented in its granulometry. The polymer used favored a low water/cement ratio (0.3) which did not allow to decrease resistance due to the fine nature of the materials (residues and cement) in addition to maintaining the workability of the material. The quarry residue was classified as silt with low plasticity and was characterized by X-ray diffraction and Fluorescence to identify 76% of SiO2, which is why it was used as a stone aggregate even though the fines content was approximately 93%. The maximum compression resistance obtained at 28 days were 8 Mpa with the polymer/solid ratios of 0.10, water/solids of 0.30, and quarry/solids of 0.67. Linear equations were analyzed for more representative values with R squared adjustment.

Finite element/percolation theory modelling of the micromechanical behavior of clayey soils

A hybrid model for soils, which combines percolation theory and finite element method is presented. The internal soil structure is modelled via the finite element method, and percolation networks are used for analyzing its mechanical behaviour. Through a microscopic characterization of elastic properties of soil grains, the model is generated. The effective percolation threshold obtained is lower than that of the network geometric percolation. The effective mechanical properties predicted are successfully compared to published experimental results.