Desiccation cracking of polymer-bentonite mixtures: An experimental investigation

Despite some evidence that polymer addition may enhance the resistance of clay to desiccation cracking, the topic remains under-researched. This study evaluated the effect of sodium carboxymethyl cellulose (Na-CMC) additive on the formation of crack patterns in bentonite clay undergoing dehydration. Thirteen groups of amended and unamended mixtures, prepared with two different mixing methods and several Na-CMC types and dosages, were exposed to air dehydration in petri dishes under different environmental conditions of temperature, humidity and friction. Moisture loss was tracked in real-time and surface cracking was recorded with a digital camera at regular intervals. Captured photos were analyzed by image processing to quantify crack ratio and surface area of soil clods. The results indicated that polymer-modified samples consistently exhibited reduced levels of desiccation cracking compared to unmodified ones under different environmental conditions. Na-CMC with a degree of substitution (DS) of 0.9, corresponding to peak viscosity of polymer, generated a higher resistance to cracking than DS of 0.7 or 1.2. In addition, dry mixing seemed to be more effective than wet mixing in increasing mixture resistance to desiccation cracking.