Use of construction and demolition materials to improve geotechnical properties of a clay

A study was conducted to explore the various effects of construction and demolition materials (CDMs), which are considered to be solid waste materials (SWMs), on the geotechnical properties of clay. The properties of the mixed samples were investigated by adding crushed brick pieces (CBPs), dumped asphalt pieces (DAPs), and crushed concrete pieces (CCPs) into clay. The laboratory tests included the testing of consistency limits, California bearing ratio (CBR), unconfined compressive strength (UCS), swelling, consolidation, and direct shear. A series of plate loading tests on clay with 10% CDMs was also carried out in a specially-designed model box made of reinforced concrete with a dimension of 2.0m diameter and depth of 1.5m to gain a deep understanding of the samples. The results show that when the CDMs percentages were 20%, there were decreases of about 15% and 25% in liquid limit and plasticity index of clay, respectively. Small increases of about 3% in γdrymax for the clay were noticed when the DAPs and CCPs content was increased from 5% to 20%. A reduction of about 35% of wopt for clay was shown by increasing the DAP percentage to 20%. The CBR and UCS strength values of the clay were increases by around 25% by increasing the CDMs percentage from 5% to 20%. In the direct shear test, 10% of all CDMs additions gave out the maximum angle of internal friction. In the plate load test, the addition of 10% CDMs increased the ultimate bearing capacity of clay by about 50% to 75%. The oedometer characteristics, including the swelling and consolidation of CDMs-clay mixtures, were controlled mainly by the type and content of CDMs in the clay. Using Plaxis 2D for the program, a remarkable matching of the results of the numerical simulation and the plate load test was observed (R2=0.97).