The Effect of Mechanical Stabilization and Improving Soil Gradation on the Compressive Strength of Adobe: A Case Experiment for Improving Adobe’s Physical Behavior in the Ardakan Region, Iran

As a country with lots of historical monuments built on earthen structures, Iran has a brilliant background in using adobes as a building material; a fact which has recently brought with it a return to this kind of architecture in spite of the decreasing use of soil architecture in the last few decades. So improving and optimizing clayey materials has been considered an appropriate way to defy the decline of this kind of architecture and revive it, and also to protect the invaluable heritage of soil architecture.This study begins with the presupposition that the mechanical properties of adobe can be improved through understanding soil, and aims at understanding how the improvement of soil gradation affects adobe’s compressive strength as an effective parameter in the stability of clayey buildings. So six mines of Ardakan’s traditional soil (which had been used since the old times in making adobes and is endorsed by Ardakan’s masons) are selected based on the experience of the city’s native architects; then the compressive samples are made through both the traditional method and also using more recent methods of mechanical stabilization emphasizing on physical stabilization (i.e. improving soil gradation and adding improved sand to the soil), and finally the samples are tested and analyzed. In this study, a sample of improved sand is used to improve the gradation of all the mines’ soils, and the results of the tests for compressive strength imply the improvement of this parameter in the adobes made of these soils in comparison with those made through traditional methods. Furthermore, adding different percentages of sand results in a decrease or fluctuation in adobe’s compressive strength; so one can claim that in order to improve the compressive strength of the resulting adobe, in addition to mechanical stabilization, one should also try improving soil gradation.