T. López-Lara

Sustainable Use of Tepetate Composite in Earthen Structure

One of the best indicators for construction sustainability is the use of earthy local materials which are completely recyclables and savers of energy during their life cycle. Tepetate is an underestimated earth-natural material, vast and economic, used only in a compacted form in backfills for layers of low resistance in pavements and platforms of buildings. This volcanic soil, named in different ways in several countries, is found in the central region of Mexico. Its resistance as compacted material is very low, of the order of 0.08 MPa. In this work, an improved sustainable-tepetate composite, using CaOH, is presented. This research includes the determination of mechanical properties as well as the physicochemical characterization of the sustainable-tepetate composite behavior. It can be concluded that the strength of the proposed composite increases significantly, immediately after treatment and with time. X-Ray Diffraction shows that all the mineralogical phases prevail in the natural tepetate and only a new phase appeared (calcite), which increases with time. This and the reaction of CaOH with clay content are very likely associated with the continuous strength increase of the composite.

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.

Use of Effective Stresses to Model the Collapse upon Wetting in Unsaturated Soils

AbstractThis paper presents the modeling of the phenomenon of collapse upon wetting using the effective stress approach. To this purpose, Bishop’s effective stress equation is applied in addition to an elastoplastic framework for the volumetric behavior of unsaturated soils. Bishop’s parameter χ is obtained from a porous-solid model that is able to simulate the soil-water retention curves during wetting-drying cycles. The proposed framework includes the hysteresis of the retention curve and to some extent the hydro-mechanical coupling of unsaturated soils. This model is able to reproduce quite precisely the phenomenon of collapse upon wetting using a single valued compressibility index. It also represents a unifying framework for saturated and unsaturated soils.

An Analysis of the Thermal Conductivity of Composite Materials (CPC-30R/Charcoal from Sugarcane Bagasse) Using the Hot Insulated Plate Technique

The production of new thermally insulating composite materials from solid residues such as charcoal from sugarcane bagasse (CSB) is of great importance because it takes advantage of materials that might otherwise pollute the environment. Therefore, for this study, we obtained composite materials based on a portland cement (CPC-30R) matrix and CSB particles with a 4 : 1 water-cement ratio and CSB concentrations of 5%, 10%, and 15% by weight. The thermal conductivities of these materials were characterized following ASTM guideline C177, their CSB morphological properties were analyzed using scanning electron microscopy (SEM), and their compositions were determined using energy-dispersive spectrometer (EDS). The results show that the composite materials have reduced thermal conductivities. The metallic oxide percentage composition of the CSB was also determined. It was observed that there was a reduction in thermal conductivity when CSB was used as compared to 100% CPC-30R, and the influence of the CSB concentration on thermal conductivity was measured.

Final Distribution of CaO and pH Evolution in CaO-treated Clays

The final distribution of the CaO within Ca-treated clays was determined many years after the original treatment, i.e., when the soil-CaO reaction was completed, along with a study of evolution of the corresponding pH. The results reveal that the value of pH accepted in the literature as an indication of the end of the reaction, may not be the actual case.

Application of Optimum Compaction Energy in the Development of Bricks Made with Construction Trash Soils

In general, bricks frequently show different densities and therefore different resistances because the compaction energy is not considered in their production. Expansive soils represent a problem for light buildings over them because of volumetric instability. A generalized solution has been to extract them and substitute them by inert soil; thus they become construction trash. So, in this work the compaction energy aspect and the use of construction trash soils in the elaboration of resistant masonry bricks of homogeneous and controlled density are a new contribution in the production of bricks of better quality. First, the soil was stabilized with CaOH which leads to a decrease in its volumetric changes. Then, they were compacted with a specific energy for obtaining an optimal and maximum controlled density to ensure an increase in strength. Our results show that two optimal compaction energies can be considered with respect to the variation of optimum moisture in masonry bricks of expansive soil stabilized with lime. The first is when the optimal humidity reaches its smallest value (integrated soil lumps) and the second is when humidity increases (disintegrated soil lumps), after reaching its lowest value. We also conclude that high compaction energy does not improve density values.

Tepetate as Construction Material

AbstractTepetate is a common material in central Mexico, which is frequently used in the construction industry. It is extracted from natural sites and commercialized without alteration. In general, it is used to construct backfills. However, there is a lack of information regarding this material for the construction industry. In this research, the properties of tepetate as a material for construction (plasticity, permeability, and strength under compaction conditions) were obtained. According to the studies of tepetate, it exhibits a wide range of values for these properties, thus making it less reliable as a homogeneous material for construction. Additionally, it has very low strength as a construction material. It is recommended as a standard practice to perform studies on the material before its use in construction.

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.

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.

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...