Experimental study on solid-liquid separation of construction waste slurry by additive agent-combined vacuum preloading

The vacuum preloading method dealing with soils with high moisture content in large area and the flocculation precipitation method used in sewage treatment are combined to achieve solid-liquid separation of construction waste slurry. A series of sedimentation column tests are performed on the waste slurry of a pile foundation project in Shanghai by using four different kinds of flocculants, and an optimum flocculant is obtained. Vacuum preloading model tests are carried out on the optimum flocculant and the slurry proportioning. During testing, the water yield and the height of slurry surface are monitored. Furthermore, the tests on moisture content, particle size distribution, mercury intrusion porosimetry and scanning electron microscopy are also carried out. It is found that: (1) After adding the flocculants, the moisture content of the waste slurry declines from 163% to 96%, and it is reduced to 37% by vacuum preloading. (2) After adding the flocculants, the clay content decreases, and the silt content increases. That is to say, flocculation will make small particles larger. (3) After the treatment, the porosity of waste slurry obviously decreases along the radial direction. The technology of solid-liquid separation by flocculants and vacuum preloading is feasible and effective, and is worthy to be used in engineering practice.