Date of Award
Master of Science
Kolay, Prabir K.
Ordinary Portland cement (OPC), is the ubiquitously available cement, has been used as a chemical stabilizer to improve the strength of weaker subgrade soil in pavement layers since longtime. The problem associated with using OPC cement is the emission of larger amount of carbon dioxide and as a result, its negative impact on the ecology. Calcium Sulfoaluminate Cement (CSAC) is a more recently developed cement that has been found to be quick setting and environmentally friendly, with its strength comparable to OPC cement. However, a limited number of literatures are available comparing the effect of these two cements in weaker subgrade stabilization.In the present research work, different tests on strength parameters have been performed for analyzing the behavior of these two commercially available cements in weaker subgrade soil stabilization. A locally available soil with high plasticity is selected as a primary soil to be stabilized with different percentages of these cements for testing the strength of the samples. The percentage of cement used in this study is 2.5%, 5.0% and 7.5% by dry weight of soil. The samples have been tested for Unconfined Compressive Strength (UCS), Ultrasonic Pulse Velocity (UPV) and Resilient Modulus (RM) Test. All the tests were performed according to the ASTM specified designations. The cyclic loading nature of RM (Resilient Modulus) test provides more reliable data to predict the behavior of the stabilized soil in subgrade layer rather than the static loading nature of loading in UCS test. Results from different tests showed that both cements were effective in improving the strength of the soil as compared to its natural untreated state. From UCS test, it was observed that samples prepared with CSAC cement were stronger when they were tested without curing. The percentage increment in the UCS value compared to the untreated soil ranged between 52.68% to 119.17% for CSAC treated samples, while for the corresponding dosage of OPC treated samples, the UCS value increased by 25.45% to 111.96% for uncured samples. However, when the samples were subjected to some degree of curing period, OPC treated samples showed greater strength. The maximum value of 255 psi was obtained for 7.5% CSAC treated samples at 28 days of curing but for same curing period and dosage of OPC treated sample, the UCS value reached up to 473 psi. The results from UPV test also showed that the samples are getting stronger with the addition of cement. The UPV value for untreated soil increased from 990.5 m/s to the maximum of 1647.8 m/s for CSAC treated samples. Similarly, for OPC treated sample, the maximum UPV value observed was around 2043.63 m/s. The UPV value of all OPC treated samples were found to be higher than corresponding percentage and curing period for CSAC treated samples. Linear regression analysis was performed between the results from the UPV and UCS test. A decent R2 value ranging from 0.91 to 0.99 was observed. Similar to the behavior observed from previous two tests, the resilient modulus value was also found to increase as the cement content increased. Results from RM test showed that the effect of stress state on the sample’s resiliency behavior was dependent on its stiffness behavior. Strain softening was observed in less stiff samples whereas for highly stiff samples, strain-hardening behavior was observed. For uncured samples, the resilient modulus value increased up to 113% for CSAC treated samples whereas the value increased up to 98% for OPC treated samples. At 28 days of curing, the samples prepared with 5% and 7.5% of both the cements showed comparable values. For OPC treated samples, the 28 days samples for all percentage of cements used showed comparable increase in the resilient modulus value. A regression analysis was performed between the laboratory measured resilient modulus value and predicted values from Uzan (1985) model. The results showed a fair correlation between the data with R2 values ranging from 0.73 to 0.90. The value shows that the model was fairly able to predict the resilient modulus based on Uzan (1985) equation.
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