Inhibition of desiccation cracking of clayey barriers through the addition of polymers

Experimental investigation of interactions between water-soluble polymers and pure Na-montmorillonite and 90:10 mixes of sand (0.150mm-0.425mm): Na-montmorillonite was performed to establish the effects of such interactions on the volume change and fracture patterns of these soils. Four polymers--polyvinyl alcohol (PVA), polyethylene oxide (PEO), carboxymethyl cellulose Na-salt (CMC), and chitosan (CHT)--in concentrations ranging from 0.1g/L to 5g/L were mixed with the soils prior to subjecting them to shrinkage, swelling and desiccation tests. Viscosities of these solutions were also measured in order to estimate polymer molecular lengths and their effect on soil-polymer interactions. Swelling tests of 2g/L Na-montmorillonite indicated that there is a threshold concentration between 0.1g/L and 3g/L at which transition occurs from flocculation to swelling of Na-montmorillonite when it is suspended in CHT solution, and that swelling index of Na-montmorillonite increases with increasing polymer chainlength when suspended in CMC solutions. Separate mixes of CHT and PEO solutions with 90:10 sand:clay exhibited better shrinkage characteristics at lower polymer solution concentrations than at higher polymer solution concentrations. When the clay was mixed with CMC solution, shrinkage ratio decreased with increasing polymer chainlength. Results of desiccation tests indicated that when polymer solutions are added to 90:10 sand:clay at a low concentration, some areas are left susceptible to crack formations, up to a critical polymer solution concentration of about 3g/L. Further increase in polymer content reduces the sizes of the susceptible regions. Desiccation tests also indicated that PVA can inhibit desiccation cracking potential of 90:10 sand:clay the most and CMC, the least. However CMC was able to extended drying time beyond that obtained for other polymers. Drying rates of 90:10 sand:Na-montmorillonite impregnated with all polymer solutions converged after about 10 hours. (Abstract shortened by UMI.).