Characterizing Polymer-Treated Field Clays and Smart Cement-Clay Interaction

To ensure the stability and durability of infrastructure, the problems due to expansive clays need to be addressed with a high priority of concern. The distress caused by the expansive and shrinkage behavior of clays, could result in a massive rehabilitation of damaged roads, residential and commercial buildings. The cost of these projects scales up with the type of stabilizers, lack of proper quality control i.e., excess or inadequate usage of stabilizers, time and labor. In the current market, there are very few methods which focus on treatment of moist soils and ensure a proper quality control coupled with an economic method of soil stabilization. In this study, soil borings under the highway near William P. Hobby Airport, Houston, TX, were extracted and characterized to be expansive in nature. 18 field soils, varying liquid limit from 50%-90%, were studied and treated using 2.25%, 4.5%, 6% and 9% of polyacrylamide, out of which 4 soils (WL = 54%, 62%, 72% and 88%) were studied in detail with 4.5% of polyacrylamide. To ensure the adequacy of treatment, commercial clays i.e. kaolinite and bentonite with a liquid limit of 720% and 50% were treated and studied. The liquid limit had an average decrease of 22%, 29%, 29.5% and 30% for 2.25%, 4.5%, 6% and 9% respectively. The bentonite showed a decrease in liquid limit from 720% to 510% and 483 % for dosages of 2.25% and 4.5% pure polymer respectively. The plastic limit had an average increase of 5.1%, 9.1%, 9.2% and 9.1% for 2.25%, 4.5%, 6% and 9% respectively. The plastic limit of bentonite increased from 78% to 90% and 110% for 2.25% and 4.5% of polymer respectively. The soils with a liquid limit of 54%, 62%, 72% and 88% had a pH of 6.77, 6.67, 6.55 and 6.5 respectively. After the dosage of 4.5% pure polymer, the pH of the 4 soils reduced to 5.7. The OMC of the CH soils with a liquid limit of 54%, 62%, 72% and 88% increased from 15% to 22%, 17% to 22%, 20% to 22% and 22% to 23% respectively after 4.5% pure polymer treatment. vii The maximum dry density reduced from 1.6 g/cm3 to 1.52 g/cm3 , 1.59 g/cm3 to 1.5 g/cm3 , 1.56 g/cm3 to 1.48 g/cm3 and 1.54 g/cm3 to 1.42 g/cm3 respectively after 4.5% pure polymer treatment. After 4.5% pure polymer treatment, the maximum value of modified expansion index (MEI) of the 4 CH soils (WL = 54%, 62%, 72% and 88%) reduced from 6 to 0.64, 6.7 to 1.6, 14.7 to 2 and 16.8 to 2.6 respectively. A majority, of soils have been reduced into the MI or OI region of classification, after the polymer treatment. The above phenomena (reducing from CH to MI or OI) showed a positive trend in the treatment with 2.25%, 4.5%, 6% and 9% pure polymer treatment. The change in electrical resistivity after 4.5% polymer treatment reduced with the expansion index of the soil, predicted using the power model, with a correlation coefficient of 0.6. The CH soil exhibited a Case 2 behavior, representing a pure resistive behavior at high frequencies (≥300 KHz ). Additionally, this study presents methods which could reduce the shrinkage behavior of class H cement. Smart Cement (Conductive filler = 0.01%, W/C = 0.38) was substituted with 2%, 4% and 6% bentonite clay by its weight to counter the shrinkage and reduced the shrinkage by 44.6%, 74.5%, 84.8% respectively, in the first 24 hours of curing. The curing and piezoresistive behavior of smart cement-bentonite mix was found to be a non-linear relationship. The piezoresistivity of the control sample, 2% bentonite, 4% bentonite and 6% bentonite was found to be 67.4% and 62.9%, 49.1% and 46.4% respectively. The average sensitivity of these samples was 6.8 %/MPa, 9.8 %/MPa, 12.8 %/MPa and 12.6 %/MPa respectively, showing an inverse relationship with the piezoresistive behavior.