Performane Characterization Of Stabilized Materials In Pavement Foundations

Cementitious Stabilization has been widely used to improve the strength and durability of granular materials for the construction and rehabilitation of pavement structures. Improved mechanical properties and durability of the stabilized materials combined with relatively low cost makes it an attractive method for design engineers. Although this technique appears simple and straight forward, engineering properties of individual soils and aggregates may alter widely due to heterogeneity in soil composition, difference in micro structure among soils, heterogeneity of geologic deposits and differences in chemical interactions of water with soil particles. These differences necessitate the comprehensive study in order to provide the best design framework and specific treatment options for stabilization of base and subgrade layers in pavement foundations. The main objective of this study is to provide the specific treatment options for stabilized base aggregates and subgrade soils in pavement foundations. This research also aims to evaluate and update current laboratory mixture design specifications, improve the field construction guidelines, and to calibrate field performance models for stabilized virgin aggregates and reclaimed materials for incorporation into the Mechanistic Empirical Pavement Design Guide (MEPDG). To accomplish these objectives, a survey initially conducted to gather the existing knowledge of the materials used, and tests performed to characterize the cement treated materials across TxDOT districts. This information then served as the basis for the selection of the type and sources of base aggregates and subgrade soils for inclusion in the experiment matrix. Eight different aggregate base materials such as limestone aggregates, siliceous gravel, RCA, FDR, and RAP as well as seven different subgrade soils such as clay and sand were incorporated in this research effort. All permutations of the experiment design were prepared in different levels of stabilizer content to cover a wide spectrum of treatment from light stabilization to heavily stabilized systems. Different quantities of calcium-based stabilizing agents such as cement, lime, and fly ash in combination with polypropylene fibers were incorporated in the mixture design. Moreover, four curing conditioning procedures were incorporated to study the influence of the moisture ingress on the mechanical performance of the stabilized materials. More than 3000 specimens, considering the replicates, were prepared and subjected to various laboratory test to characterize the strength, resilient properties, and permanent deformation potential of cement treated systems. Around 500 nondestructive laboratory tests such as free-free resonant column and dielectric value tests were performed before the running mechanical tests. Additionally, the comprehensive database of pavement section parameters and material properties were developed using the field nondestructive testing equipment such as FWD and GPR of representative pavement sections and the datasets from previous studies across the United States. This database then served as a representative sample for the calibration of the fatigue performance model for the cement stabilized layers in pavement structure. The post processing results showed the superior performance of the combination of cement and polypropylene fiber compared to other chemical additives in stabilized expansive soils. Addition of fiber-cement to expansive soils was considered as an efficient strategy for improving strength and volumetric stability of subgrade layers with high plasticity and high sulfate soils. New compaction procedures such as vibratory hammer and gyratory compactor for stabilized base and subgrade materials were analyzed as an alternative to traditional impact hammer compaction. The results revealed that gyratory compactor has higher capability to simulate the field compacted condition due to providing more uniform specimens and minimizing the interface barrier between layers and particle breakage compared to the other compaction methods. Moreover, a series of statistically robust relationships between the laboratory achieved data was developed using genetic expression programming as a computational intelligence technique to develop closed-form solutions for the strength and resilient properties of stabilized virgin and reclaimed materials. This can potentially serve as the precursor for rapid turnaround mixture design by eliminating unnecessary permutations for efficient design of cement stabilized base layers