CHARACTERIZATION OF CEMENTITIOUSLY STABILIZED SUBGRADES FOR MECHANISTIC-EMPIRICAL PAVEMENT DESIGN

Pavements are vulnerable to subgrade layer performance because it acts as a foundation. Due to significant increase in truck traffic, pavement engineers are challenged to build more strong and long-lasting pavements. To increase the load-bearing capacity of pavements, subgrade layer is often stabilized with cementitious additives. Thus, an overall characterization of cementitiously stabilized subgrade layer is important for enhanced short- and long-term pavement performance.In this study, the effect of type and amount of additive on the short- and long-term performance of stabilized subgrade in terms of material properties recommended by the new Mechanistic Empirical Pavement Design Guide (MEPDG) is examined. A total of four soils commonly encountered as subgrades in Oklahoma and three locally available cementitious additives namely, hydrated lime, class C fly ash (CFA) and cement kiln dust (CKD) are utilized. Cylindrical specimens are compacted, cured for 28 days, and then subjected to different stress sequences to determine the resilient modulus (Mr) followed by modulus of elasticity (ME) and unconfined compressive strength (UCS) test. Results show that the changes in the Mr, ME and UCS values of stabilized specimens depend on the soil type and properties of additives. The long-term performance of stabilized soil specimens is investigated by conducting freeze-thaw (F-T) cycling, vacuum saturation and tube suction tests on 7-day cured stabilized soil specimens. Also, specimens are capillary-soaked for 60 days and tested for Mr, as an additional indicator of long-term performance. This study is motivated by the fact that during the service life of pavement stabilized layers are subjected to F-T cycles and moisture variations. It is found that that UCS value of all the stabilized specimens decreased with increase in the number of F-T cycles. A strong correlation is observed between UCS values retained after vacuum saturation and F-T cycles indicating that vacuum saturation could be used as a time-efficient and inexpensive method for evaluating durability of stabilized soils.For Level 2 design of pavements, a total of four stress-based statistical models and two feed-forward-type artificial neural network (ANN) models, are evaluated for predicting Mr of 28-day cured stabilized specimens. Specifically, one semi-log stress-based, three log-log stress-based, one Multi-Layer Perceptrons Network (MLPN), and one Radial Basis Function Network (RBFN) are developed. Overall, semi-log stress-based and MLPN neural network are found to show best acceptable performance for the present evaluation and validation datasets. Further, correlations are presented for stress-based models to correlate Mr with compacted specimen characteristics and soil/additive properties.In addition, the effect of type of additive on indirect tensile and fatigue characteristics of selected stabilized soil specimens is evaluated. This study is based on the fact that stabilized layer is subjected to tensile stresses under wheel loading. Thus, the resilient modulus in tension (Mrt), fatigue life and strength in tension (σt) or flexure (represented by modulus of rupture, MOR) becomes another important design parameter within the mechanistic framework. Cylindrical specimens are subjected to different stress sequences in indirect tension to study the Mrt, whereas beam specimens are subjected to repeated cycles of reloading-unloading in a four-point beam fatigue apparatus for evaluating fatigue life and flexural stiffness. It is found that all three cementitious additives improved the Mrt, σt and MOR values; however, degree of improvement varied with the type of additive and soil. The magnitude of resilient modulus in tension is found lower than it is in compression. Findings from this study shed light on the differences in properties of cementitiously stabilized soil in indirect tension, flexure and compression. The fatigue life values and model of stabilized specimens is expected to provide a better understanding of performance of cementitiously stabilized layers in mechanistic sense.Further, this study encompasses the differences in the design of semi-rigid pavements developed using AASHTO 1993 and AASHTO 2002 MEPDG methodologies. The design curves for fatigue performance prediction of stabilized layers are developed for different cementitiously stabilized pavement sections. It is found that the design thickness is influenced by the type of soil, additive, selection of material property and design method. Cost comparisons of sections stabilized with different percentage and type of additives is also made. Knowledge gained from the parametric analysis of different sections using AASHTO 1993 and MEPDG is expected to be useful to pavement designers and others in implementation of the new MEPDG for future pavement design

State-of-the-Practice Review on the Field-Curing Methods for Evaluating Strength of Concrete Test Specimen

The purpose of this research was to build up the understanding of the current state –of –the practice for field-curing methods of concrete specimens. Specifically, a comprehensive literature review and questionnaire survey were prepared to identify the selection criteria and details of field-curing methods correspondingly. The comparison of literature data and survey outcomes shows that most transportation agencies use field-cured cylinders followed by the maturity method for the decision on when to open pavement to traffic or remove form/falsework. The most commonly used field method was curing near (or on) the casted concrete in the same manner as concrete item represented. The cylindrical specimens are mostly field cured in insulated boxes such as a cooler or under burlap/insulation near the concrete item. On the other hand, beams are mostly field-cured in a damp sandpit or under burlap/insulation near the concrete item. The information provided in this paper could be used by transportation agencies for determining an appropriate cost-effective field-curing technique which is representative of strength gain of the in-place concrete item.  &nbsp

Group Selection and Learning for a Lab-Based Construction Management Course

In construction industries’ projects, working in groups is a normal practice. Group work in a classroom is defined as students working collaboratively in a group so that everyone can participate on a collective task. The results from literature review indicate that group work is more effective method of learning as compared to individual work. However, only limited studies reported influence of group selection method on the learning of groups. To fill the gap in this area, the main objective of this study was to find out which selection method is the best to use and helps students to perform better in the course. Therefore, a total of three group selection methods, namely, random-selection by instructor, performance-based-selection by instructor and individual-selection by student were utilized. The target subjects used in the proposed study were students enrolled in two different lab-based construction management courses. The learning of each group was evaluated by calculating an average of scores received by all fellow members in the corresponding lab projects. Additionally, at the end of the semester, students were asked to complete a questionnaire. Data from all the questionnaires was also used for evaluating influence of group selection method on learning of students

Multivariate Regression and Variance in Concrete Curing Methods: Strength Prediction with Experiments

Because concrete strengths and quality are affected by various factors, multivariate regression models are often used to analyze the differences between predicted and target outputs. However, the variableness of a predicted output and how individual input parameters affect prediction reliabilities are still uncertain in practical applications, especially for the prediction of compressive strengths of concrete. This study aims to develop multivariate models for predicting concrete strengths and providing the variance analysis of prediction results by comparisons with experiment outcomes. First, this paper provides an in-depth examination of established variance analysis methods in the context of commonly used multivariate regression models. Then, based on Gaussian process regression, this study melds principal component analysis (PCA), linear discriminant analysis (LDA), and multivariate analysis of variance (MANOVA) to assess the variability in concrete strength prediction using different curing methods. This innovative approach proves effective in evaluating the precision of the correlation and regression models (R-squared values ≥ 0.9049). The comparison between prediction results and experiment outcomes shows that retaining heat in cylinders can make them become too hot and overestimate in-place concrete strength. This study improves the methodologies of regression modeling for variance analysis and improves the reliability of concrete strength prediction. Additionally, the outcomes of this research can help save a substantial amount of financial resources and time that are required to obtain experimental data on the strengths of concrete components

Strength and permeability of pervious composite prepared by using post-consumer plastic waste bottles

This study focused on developing and evaluating a novel form of pervious polyethylene terephthalate (PET) plastic composite. This novel composite, called as PPC, produced from plastic waste, soil and aggregates, will offer an effective technique for reducing storm water runoff and help divert a large amount of plastic from landfills and incinerators. PPC samples with different PET to soil/aggregate ratios were prepared and then tested for indirect tensile strength and permeability. Permeability was conducted in a unique manner by designing and fabricating a new testing equipment. Both indirect tensile strength and permeability were within the expected values found in the literature for porous pavements. Results showed that indirect tensile strength values increased with PET content. It was also found that using PET alone is not strong enough in binding aggregates and therefore, a soil/PET ratio of one was found optimum for providing maximum strength. Permeability values decreased with the decrease of A/P (aggregate/PET) ratio which in general indicates that lower PET and higher aggregate content is suitable for higher permeability. A soil/PET ratio of one was found to provide higher permeability but strength could compromise. Findings from this study indicated that developed PPC could be used for low-strength construction such as driveways, sidewalks and parking lots

Design of semi-rigid type of flexible pavements

The primary objective of the study presented in this paper is to develop design curves for performance prediction of stabilized layers and to compare semi-rigid flexible pavement designs between the empirical AASHTO 1993 and the mechanistic-empirical pavement design methodologies. Specifically, comparisons were made for a range of different sections consisting of cementitious layers stabilized with different types and percentages of additives. It is found that the design thickness is influenced by the type of soil, additive, selection of material property and design method. Cost comparisons of sections stabilized with different percentage and type of additives showed that CKD-stabilization provides economically low cost sections as compared to lime- and CFA-stabilized sections. Knowledge gained from the parametric analysis of different sections using AASHTO 1993 and MEPDG is expected to be useful to pavement designers and others in implementation of the new MEPDG for future pavement design. Keywords: Semi-rigid, Mechanistic, Resilient modulus, Fatigue life, Reliability, Traffi

Strength and permeability of pervious composite prepared by using post-consumer plastic waste bottles

This study focused on developing and evaluating a novel form of pervious polyethylene terephthalate (PET) plastic composite. This novel composite, called as PPC, produced from plastic waste, soil and aggregates, will offer an effective technique for reducing storm water runoff and help divert a large amount of plastic from landfills and incinerators. PPC samples with different PET to soil/aggregate ratios were prepared and then tested for indirect tensile strength and permeability. Permeability was conducted in a unique manner by designing and fabricating a new testing equipment. Both indirect tensile strength and permeability were within the expected values found in the literature for porous pavements. Results showed that indirect tensile strength values increased with PET content. It was also found that using PET alone is not strong enough in binding aggregates and therefore, a soil/PET ratio of one was found optimum for providing maximum strength. Permeability values decreased with the decrease of A/P (aggregate/PET) ratio which in general indicates that lower PET and higher aggregate content is suitable for higher permeability. A soil/PET ratio of one was found to provide higher permeability but strength could compromise. Findings from this study indicated that developed PPC could be used for low-strength construction such as driveways, sidewalks and parking lots