Date of Award

Fall 2022

Document Type

Open Access Dissertation

Department

Civil and Environmental Engineering

First Advisor

Fabio Matta

Abstract

The comprehensive understanding and experimental characterization of the overall compressive behavior of earth masonry block materials, such as compressed and stabilized earth blocks (CSEBs), are essential for developing analytical and numerical tools to predict the mechanical response and designing earth masonry structures. Furthermore, advancing the understanding of the extent of the influence of testing parameters on the material's response, such as specimen geometry, is a critical step towards standardization.

CSEBs are produced by compressing a mixture of soil, water, and a stabilizer (e.g., Portland cement). The heterogeneity of the material accrues from the variety of soil particle morphology and potential dry density variations that results from the manufacturing process; both of these factors might affect the homogeneity and directional dependency of the mechanical properties. Yet, there is a lack of conclusive experimental evidence describing these aspects at a scale comparable to that suitable for material characterization, such as in the case of uniaxial compressive strength. On the other hand, the compressive strength and stress-strain response of earth masonry block materials are sensitive to the specimen aspect ratio, cross-sectional shape, and boundary conditions. However, the extent of the effect of these parameters is not fully understood, thus limiting the establishment of a standard test method. Furthermore, the information available on Young’s modulus and Poisson’s ratio is limited and scattered.

This research encompasses three experimental projects and a study on outreach activities for pre-college students. The experimental projects investigated a representative prototype CSEB material. The first project focused on characterizing the material physico-mechanical homogeneity and isotropy based on two criteria: (1) structural and chemical composition of the soil-cement matrix at the micro- and meso-scale, and (2) compressive strength and initial stiffness as a function of the loading direction relative to the compaction pressure and the location within a given block. The second project evaluated the effect of three parameters on the specimen’s compressive strength. These parameters included friction at the loading interface and the aspect ratio, and the crosssectional shape of the specimen. The third project continued the experimental program and data analysis, which included three-dimensional digital image correlation (3D-DIC) deformation measurements to evaluate the specimen geometry effect on the stress-strain response, focusing on the characterization of the constitutive behavior of the material. It was determined that the material investigated can be regarded as homogeneous and isotropic, that the specimen aspect ratio exerts an important influence on the compressive strength whereas the influence of cross-sectional shape is negligible, and that either cylinder or prism specimens with an aspect ratio of 2.0 are suitable to characterize a stress-strain response representative of the material’s constitutive behavior.

The study on outreach proposes an adaptable pedagogical framework to provide meaningful structure for on-campus outreach activities for science, technology, engineering, and mathematics (STEM) that emphasize collaborative, hands-on learning experiences for pre-college students. The successful implementation of the framework was demonstrated by designing and assessing a summer workshop on hazard-resistant earth masonry construction in which 85 high-school students participated over three consecutive years.

Rights

© 2022, Erika Lorena Rengifo-López

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