Engineering properties of structural lightweight concrete containing expanded shale and clay with high volume class F and class C fly ash

Abstract

Structural optimization is a broad term in the construction sector, whereby material efficiency, as well as cost effectiveness of structures, are optimized. In concrete technology, high-performance lightweight concrete structures often represent such optimized properties, including cost-effectiveness and ease of application, while having a lower structural dead load. Although the use of lightweight concrete is often viewed as a sustainable practice, it does not address the high use and dependance on Portland cement, which has a high ecological footprint. In this regard, this study evaluates the engineering properties of structural lightweight concrete containing expanded shale and clay, as coarse aggregate, with a high quantity of coal fly ash (class F and C). For this purpose, a total of 15 mixes have been produced and a comprehensive series of physico-mechanical and durability tests have been conducted. Based on the results, it is found that expanded clay outperforms expanded shale in terms of physico-mechanical and durability properties of the resulting concrete, potentially due to its lower particle size distribution (used in this study) and the resulting porosity compared to expanded shale. Nonetheless, comparable physico-mechanical properties are achieved when expanded shale and clay are used, as a full replacement of limestone. In turn, the performance of class C fly ash is found to be better in mechanical, but lower in certain durability variables, compared to their class F companions. The result of this study is found significant and point to suitability of using expanded shale and clay in combination with high-volume fly ash.