Assessing durability of PFA-blended concrete

Abstract

The 28-day compressive strength is all too often considered the sole criterion for approving concrete mixes in the construction industry. Other important properties of concrete, such as water permeability, chloride diffusion and other principal factors that influence its durability are rarely quantified due to their costly and time-consuming nature of testing. All too often it is assumed that higher compressive strengths of concrete automatically result in more durable structures - an assumption which may not be entirely true. Concrete mixes which are found to satisfy their required strengths may not always e durable ones. Thus, it is of relevant importance to understand and develop relationships between concrete's compressive strength and certain durability indices, so as to be utilized to determine latter performances knowing former ones. The purpose of this study was to better understand the relationship between traditional specifications for concrete design and certain durability indicators. In order to better examine these relationships, equipment for testing air and water permeability, chloride ponding, non-steady-state chloride migration and electrical resistivity was setup throughout the course of study. Concrete mixes were prepared with different percentage replacements of PFA- a pozzolan known to have performance-enhancing properties. A series of paste mixes having different water-powder ratios, as well as percentage-replacements of PFA were prepared in order to establish basic strength-development profiles at 3,7 and 28days testing. A secondary series of concrete mixes were then prepared for testing for compressive strength, tensile splitting strength, non-steady-state chloride migration, oxygen and water permeability, chloride ponding and electrical resistivity at 7, 28,56 and 90 days. Results show the different relationships between tests carried out* leaving great potential for specifying and quantifying performance-based concrete