A Comparison between Cement and Crushed Concrete in Improving the Strength of Soft Soils: A Review

Abstract

Civil engineering projects, including buildings, bridges, retaining walls, etc., require soil with an adequate bearing capacity to support the heavy loads exerted by these structures within the allowable settlement limits. Practically, not all soils provide sufficient bearing capacity, and it is required to spend much time, effort, and cost to prepare such soils for different projects. Soft clayey soils are repeatedly encountered in civil engineering projects, and improving their capacity is essential. This improvement can be achieved by mixing some materials with soft soils to improve their behavior, like Portland cement, lime, fly ash, sand, etc. The high cost and the high depletion of natural resources associated with the manufacture of such mixing materials made it necessary to use some recycled materials instead. Moreover, the extraction of natural resources releases carbon dioxide (CO₂) emissions and consequently causes pollution. Construction and demolition wastes form a large quantity of overall waste materials. Crushed concrete resulting from the demolition of old buildings or concrete barriers is widely available and can be used as recycled mixing material to enhance soil properties. This research reviews some research papers investigating the effects of recycled crushed concrete, as compared with Portland cement, on the compaction characteristics, compressive strength, and California-bearing-ratio (CBR) of soft soils.