Modification of crumb rubber cement interface and its effect on strength and viscoelastic properties
Due to an increasing amount of waste tires being produced yearly, environmental concerns arise as waste tires in landfills pose both a fire hazard, and a habitat for rodents and mosquitos. As a result, the reuse of waste tires in the form of crumb rubber in concrete has been attempted. Previous research work has shown that the inclusion of crumb rubber in concrete results in a drastic decrease in compressive strength due to the incompatibilities between rubber and cement paste. The limitations related to the use of crumb rubber concrete are related to the interfacial transition zone between rubber and paste. Due to mismatches in free surface energy, coefficient of thermal expansion, and elastic modulus between rubber and cement paste, it has been observed that an interfacial gap is present; furthermore, entrapped air, microcracks, and inconsistent degree of hydration of cement paste has been observed at the transition zone. The research work presented here attempts to improve understanding about what conditions alter the local microstructure of crumb rubber cement interface; furthermore, the limitations and concerns in characterization of rubberized concrete from literature are detailed and studied, and modifications to testing matrix are attempted to better understand and quantify issues at the rubber-paste interface. The research work presented is subdivided into four tasks. The first task involves altering the design mix of rubberized cement paste to improve interface and performance. Within the first task, uses Type I and Type K expansive cement blend as a means of physically interlocking rubber and paste. The first task also includes usage of shrinkage reducing admixture in bulk mixture and as a pretreatment to alter the surface chemistry of rubber, and testing its effect on the performance of rubberized cement paste samples. The second task involves understanding how curing conditions alter the interface and subsequent mechanical performance of rubberized samples; the effect of relative humidity and temperature are explored. The third task involves targeted testing of the interface of various rubberized cement paste mixtures; understanding of interface performance, interfacial gap, and entrapped air quantity are explored. The fourth task involves a specialized application of crumb rubber in concrete; low-density rubberized foam concrete samples are cast and tested for application as engineering materials arresting system.
interfacial transition zone, crumb rubber, rubberized concrete, shrinkage reducing admixture, calcium sulfoaluminate cement
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign