Cation Exchange Capacity (CEC), texture, consistency and organic matter in soil assessment for earth construction: The case of earth mortars

Abstract

There is a rapid development of earth construction the last few decades followed by an increased interest in scientific research in this field. One of the issues that have arisen is which soils are suitable for construction and can be designated as construction soils and which are not. Thus, the main objective of this paper is to investigate the relation between physical soil properties and mechanical properties of the dried building material. In this context, the Cation Exchange Capacity (CEC) of the soil is investigated in this research as an innovative tool in soil assessment for earth building. The distinct advantage of CEC is its dependence on clay type and organic matter apart from clay content, which is the soil property most frequently used in soil assessment for building purposes. This study focuses on earth mortars, on which little experimental research has been carried out despite their widespread use. In order to overcome the issues often mentioned in literature of using a certain soil and then generalizing the results, it was decided to use a wide range of soils with different textures from various regions of Greece. So, 26 soils were collected and a total of 49 earth mortar mixes were fabricated in two phases. The soil properties assessed were texture, Atterberg limits, CEC, mineralogy and organic matter content, while the hardened mortar properties assessed were compressive strength, flexural strength, dry density and linear shrinkage. It was found that CEC provides stronger correlation with compressive strength and linear shrinkage than clay content and Plasticity Index. A linear correlation between linear shrinkage and compressive strength was also established. Finally, it is shown that the soils with high organic matter content used in this research, are unsuitable for earth building despite having sufficient compressive strength.