Mitigation of Expansion in Clays by Mixing with Tezontle

Abstract

The purpose of this study is to demonstrate that the expansion of clays or silts can be reduced by mixing them with porous materials such as tezontle (a type of volcanic rock). The tests presented in this article were conducted at the geotechnical laboratory of the Autonomous University of Querétaro. Expansive soils are a type of material that can undergo significant volume changes upon contact with water, generally when the soil is partially saturated and subsequently becomes saturated. Currently, several methods exist to stabilize these materials, such as the addition of hydrated lime or quicklime, cement, or fly ash. Methods can also be used to prevent water from coming into contact with the soil, such as drainage systems, waterproofing, and, in some cases, the construction of foundations that prevent contact with the clays (piles or waffle slabs with spacing between ribs). This research presents an alternative to reduce the percentage of expansion by mixing clay with tezontle, as this type of material is commonly found in some locations. For this purpose, percentages of 5, 10, and 15 were added, with grain sizes ranging from 19 to 4.75 mm. The expansion of the mixture was measured in a CBR mold under a load equal to that of the clay in its natural state. This allowed us to find that clay expansion can be mitigated by combining it with tezontle gravel. The results indicate that when a load is applied to the soil and it is subsequently saturated, a settlement of 0.24%, 0.3%, and 0.43% is experienced for each percentage of tezontle added, followed by swelling. In this case, there is a decrease in the percentage of expansion of 2.48% with the addition of 5% tezontle, 2.82% with the addition of 10% tezontle, and 3.21% with the addition of 15% tezontle, relative to the dry weight of the soil. This means that the percentage of expansion can be reduced by adding tezontle to the soil; however, a small collapse will occur first.