Recycling of Construction Waste Concrete as a Stabilizer for Gypseous Soils

Abstract

This study presents the possibility of recycling Crushed Waste Concrete resulting from the demolition of buildings, and making practical use of these abundantly available materials, by grinding them and adding them in different proportions to gypseous soils to increase their maximum bearing capacity and reduce compressibility. A laboratory model with dimensions (300*300 *600mm) of galvanized steel, 4 mm thick, was used to study the effect of mixing (0%, 2%, 4%, 6%, and 8%) Crushed Waste Concrete with three types of water-flooded natural gypseous soils with different percentages of gypsum (30%, 46%, and 66%). Loading tests were carried on square steel footing (70*70mm) and 9mm thick, placed on these soils. More than 15 tests were conducted on the laboratory model, in addition to the usual classification tests on the soils used in the study. All tests were carried after submerging gypseous soils due 24 hours. The study showed a clear improvement in the susceptibility of the three gypseous soils using all the addition percentages of concrete powder, the best percentage was 8%, while the improvement rates were less using 2%, 4%, and 6%. As the bearing capacity of the soil increased after mixing it with this ratio due to filling the voids formed as a result of melting gypsum during the water immersion process, which compensated for it at this stage. Mixing gypseous soil with crushed waste concrete by 8% increases ultimate bearing stress about 8 times, while it is 2.5 times for model mixed with 2% of this additive, compared with the untreated one.

The Estimation of One-Dimensional Collapse for Highly Gypseous Soils

“…A sudden increase in compressibility occurs when these soils are fully or partially saturated accompanied by structure collapse of the soil. This can cause severe damage and even collapse of the structures found on or in such soils [1][2][3][4].…”

“…Gypseous soils are considered metastable or collapsible soils, and a large number of researchers have estimated the collapse potential for high Gypseous soil using the double oedometer test which was proposed by Jennings & Knight (1957) [4][5][6][7][8][9][10]. The collapse potential value is correlated with a qualitative collapse classification as shown in Table 1.…”