Experimental and Analytical Characterization of Regenerated/nano Cellulose Composites

Fiber-reinforced composite materials are increasingly used for structural and engineering purposes. In particular, composites reinforced with natural fiber systems are becoming more and more popular due to their biodegradability and abundance; added to that other properties such as transparency, dimensional stability and good mechanical behavior. However, major issues remain to properly understand their behavior and enable their widespread use. In this thesis, the mechanical behavior of cellulose fiber/epoxy composites is investigated. The natural fiber systems studied fall into three categories: unidirectional regenerated cellulose fibers, triaxially braided quasi-isotropic regenerated cellulose fibers and micro-fibrillated cellulose in the form of nanocellulose scaffolds. Different methods of fabrication including wet layup, resin infusion, hot pressing and combinations of the three processes were investigated. Mechanical testing of tension coupons or three-point bending was performed to assess the mechanical behavior. When permitted, mechanical testing was accompanied by other validation techniques to help understand the mechanical behavior including digital image correlation (DIC) and acoustic emission. The effect of temperature and loading frequency on the mechanical behavior was also investigated by performing short beam testing using Dynamic Mechanical Analysis (DMA). Environmental effects, mainly the effect of moisture on the behavior of the fibers and the composites was also investigated. Additionally, the effect of the level of cure of the resin was found to have a detrimental effect on the mechanical behavior of the composites and was studied using DMA and Digital Scanning Calorimetry (DSC). Finally, the experimental results were extended and validated using numerical solutions and finite element simulations. Results show that thermal and mechanical properties are highly sensitive to the different factors being investigated; mainly humidity, temperature, manufacturing procedure and parameters, fiber content, as well as the level of curing of the epoxy

Sustainable pavement applications utilizing quarry by-products and recycled/nontraditional aggregate materials

Quarry By-products (QB), usually less than 0.25 in. (6 mm) in size, are the residual deposits from the production of required grades of aggregates and are often stockpiled in excess quantities at the quarries. More than 175 million US tons of QB are produced every year from the 3,000 operating quarries around the US. QB pose environmental and economic challenges as they accumulate in large quantities in landfills or interfere with quarry operations. With recent focus on sustainable construction practices and the scarcity of natural resources, more common and sustainable uses of by-product materials such as QB are becoming imperative. This dissertation focuses on the introduction and evaluation of new sustainable applications of QB and/or QB mixed with other marginal, virgin or recycled aggregate materials in pavements. The selected QB applications were evaluated through the construction of full-scale pavement test sections utilizing QB in targeted sustainable applications, and testing them with heavy wheel loads through Accelerated Pavement Testing (APT). The QB applications studied included both unbound and bound (chemically stabilized) pavement subsurface/foundation layers. The studied QB pavement applications were in five categories: (1) Using QB for filling voids between large stones as aggregate subgrade on soft subgrades; (2) increased fines content (e.g. 15% QB fines passing No. 200 sieve) in dense-graded aggregate subbase over soft subgrade soils; (3) using QB as a cement or fly ash-treated subbase (e.g., in inverted pavements); (4) using QB as a cement-treated base material; and (5) for base course applications, blending QB with coarse aggregate fractions of recycled materials and stabilizing the blends with 3% cement or 10% class C fly ash. In preparation for the field evaluations, several laboratory studies were conducted to finalize the designs of intended QB applications. The main laboratory studies were: (1) A packing study of QB with recycled coarse aggregates to determine the optimum blending ratio; (2) a packing study to aid the construction of large aggregate subgrade with QB materials filling the inherent voids; and, (3) Unconfined Compressive Strength (UCS) tests for chemically stabilized QB samples. Fifteen full-scale pavement test sections utilizing QB applications and one conventional flexible section were constructed in three ‘Test Cells.’ Cell 1 had four paved and four unpaved test sections to study construction platforms and low volume road applications of QB. Cells 2 and 3 studied chemically stabilized QB applications for base and subbase layers. Construction activities included engineering the top 305 mm (12 in.) of existing subgrade to a California Bearing Ratio (CBR) = 1% for Cell 1 test sections and to a CBR = 6% for all the pavement test sections in Cells 2 and 3. Subgrade modification was achieved through moisture adjustment and compaction. The construction of the QB layers were successfully achieved and extensively monitored. The data for nuclear density measurements and moisture contents indicated that nearly all the test sections were constructed at or near the targeted optimum moisture contents and achieved proper densities. A Lightweight Deflectometer (LWD) was used to assess the stiffness of the constructed layers after the construction of each lift. It was also used to monitor the increase in stiffness of the chemically stabilized layers. The increase in stiffness of the chemically stabilized layers was the highest for cement-stabilized test sections and usually lower for fly ash-stabilized sections. Following the paving of test sections with Hot Mix Asphalt (HMA), Falling Weight Deflectometer (FWD) tests were conducted on all finished surfaces. Significantly low deflection values were measured for the sections with cement-stabilized QB and QB blends with recycled aggregates. APT was conducted using the Advanced Transportation Loading Assembly (ATLAS). A constant unidirectional wheel load of 10 kips (44.5 kN), a tire pressure of 110 psi (760 kPa), and a constant speed of 5 mph (8 km/h) were assigned. The exceptionally good performance of some of the stabilized QB applications in Cells 2 and 3 necessitated trafficking in excess of 100,000 passes; an increased wheel load/tire pressure combination of 14 kip (62.3 kN)/ 125 psi (862 kPa) was adopted for the additional 35,000 passes. Four of the test sections in Cells 2 and 3 were instrumented with soil pressure cells on top of the engineered CBR = 6% subgrade. Data collected from these pressure cells showed that significantly low vertical pressures were transmitted to the subgrade for sections with stabilized bases/subbases. Measurements for rutting progression for the construction platform and HMA-paved test sections in Cell 1 showed good performance for the sections constructed with 15% nonplastic fines and with blends of large aggregate subgrade rocks with QB. Measurements of rutting progression in Cells 2 and 3 indicated exceptionally good performance of sections with blends of QB and recycled coarse aggregates stabilized with cement. Generally, sections stabilized with cement accumulated lower rutting than those stabilized with fly ash. No significant differences in rutting performance were detected for sections with QB from two different aggregate sources. For the inverted section with a cement-stabilized QB subbase, measured rut amounts were significantly lower than those in the test section with the fly ash-stabilized QB subbase. None of the stabilized sections showed any signs of cracks. Additional testing and forensic analyses were conducted after the APT study to better assess the performance of the constructed sections. These tests included: (1) FWD testing before and after APT; (2) HMA coring; (3) Dynamic Cone Penetrometer (DCP) testing for the aggregate subbase/base layers; (4) flooded tests for the aggregate subgrade/QB test sections; and (5) trenching to assess uniformity of construction and determine as-constructed layer thicknesses. Results from these forensic tests further supported the conclusions from the APT study indicating the overall quite satisfactory performance for the studied sustainable QB applications. Mechanistic analysis was conducted using GT-PAVE axisymmetric finite-element program to analyze the FWD results, and to calculate response benefits based on resilient FWD deflection for various design thicknesses and material properties. Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) studies were conducted to assess the environmental impacts and cost benefits for the studied QB applications. LCA and LCCA results for three scenarios, i.e. as-constructed and as-designed pavement thicknesses studied though APT and newly proposed pavement sections for low volume pavement alternatives, indicated that chemically stabilized QB and QB blended with recycled coarse aggregates could be successfully used to construct sustainable, resilient, and low cost pavements. Particularly, pavement structures with a low 3% cement-stabilized QB applications created high stiffness base/subbase layers in this study; they exhibited significant response benefits due to low FWD measured and predicted surface deflections and can withstand higher traffic volumes over pavement life

A Framework to Utilize Shear Strength Properties for Evaluating Rutting Potentials of Unbound Aggregate Materials

This paper presents shear strength and permanent deformation trends of four unbound aggregate materials, commonly used for base and subbase layers in the state of North Carolina, USA, studied through repeated load triaxial testing, using the University of Illinois FastCell equipment. A testing and modeling framework has been established to develop a proper permanent deformation prediction model, referred to herein as the UIUC rutting model, with number of load applications. According to the framework, the unbound aggregate shear strength properties are incorporated into the model using the ratio of the applied wheel load shear stress to the mobilized shear strength, i.e., the Shear Stress Ratio (SSR). This requires conducting repeated load permanent deformation tests at SSR values of 0.25, 0.5 and 0.75 to determine the trends in permanent deformation accumulation. The prediction ability of the developed UIUC rutting model is evaluated in this paper for the four materials tested at both an engineered target gradation and source gradations

Dense-Graded Aggregate Base Gradation Influencing Rutting Model Predictions

This paper presents findings from an ongoing research study at the University of Illinois focused on developing and calibrating an improved permanent deformation model for unbound aggregate materials through laboratory testing and characterization. The project scope included testing sixteen aggregate materials, commonly used in the state of North Carolina for pavement base courses, in the laboratory through monotonic and repeated load triaxial testing. This paper primarily focuses on quantifying effects of aggregate gradation on permanent deformation behavior. To accomplish this, four materials were tested at both: (1) “source gradations,” i.e. original gradations from quarry, and (2) an “engineered gradation,” i.e., standard reference gradation at which aggregate specimens were prepared for testing. Predictive rutting models were developed to consider the influences of shear strength and applied stress states on permanent deformation accumulation. Rutting model parameters obtained from testing aggregate specimen at one gradation could be used to reasonably predict the permanent deformation accumulation in another sample given the shear strength properties did not show notable differences. For specimens corresponding to significantly different amounts and/or plastic nature of fines, the permanent strain levels predicted using one set of model parameters differed significantly from those predicted using another set of model parameters developed for another gradation. Moreover, the effects of gradation on permanent strain accumulation were significantly more pronounced at the higher shear stress ratios (e.g. 0.75), compared to lower shear stress ratios; which is defined as the ratio between the shear stress applied to a specimen during repeated load triaxial testing compared to the corresponding shear strength under the same confinement

Field Performance Evaluation of Sustainable Aggregate By-product Applications

Research efforts at the Illinois Center for Transportation (ICT) focused on evaluating new sustainable applications of Quarry By-products (QB) or QB mixed with other marginal, virgin, or recycled aggregate materials in pavements, as unbound or chemically stabilized pavement layers. Sixteen full-scale test sections were constructed to evaluate the use of QB in base, subbase, and aggregate subgrade applications. The chemically stabilized test sections utilizing QB were stabilized with 3% cement or 10 % Class ‘C’ fly ash by dry weight and were constructed over a subgrade having an engineered unsoaked California bearing ratio (CBR) of 6% to study their effectiveness in low to medium volume flexible pavements. The unbound applications of QB investigated the use of QB to fill the voids between large aggregate subgrade rocks commonly used for rockfill applications on top of very soft subgrade soils, as well as using dense-graded aggregate subgrade layers with higher fines content up to 15% passing No. 200 sieve for soft subgrade remediation. These unbound test sections were constructed over a CBR=1% subgrade soil to investigate their effectiveness in both construction platforms and low volume road applications. All the field test sections were then evaluated in rutting and fatigue by applying traffic loading using a super-single wheel in Accelerated Pavement Testing (APT). Following APT, forensic analysis tests were conducted to further evaluate the test section performances; these tests included: Falling Weight Deflectometer (FWD) tests before and after trafficking, hot mix asphalt coring, Dynamic Cone Penetrometer (DCP) profiling of subsurface layers, and trenching to expose the cross sections of the constructed sections. In general, results from APT and forensic analyses indicated that satisfactory results and improved rutting performance were obtained from all the test sections utilizing QB applications. Therefore, the proposed QB applications are deemed to be readily implementable and can be successfully incorporated into standard pavement construction and rehabilitation practices.IDOT-R27-168Ope

Size and Shape Determination of Riprap and Large-sized Aggregates Using Field Imaging

Riprap rock and large-sized aggregates are extensively used in transportation, geotechnical, and hydraulic engineering applications. Traditional methods for assessing riprap categories based on particle weight may involve subjective visual inspection and time-consuming manual measurements. Aggregate imaging and segmentation techniques can efficiently characterize riprap particles for their size and morphological/shape properties to estimate particle weights. Particle size and morphological/shape characterization ensure the reliable and sustainable use of all aggregate skeleton materials at quarry production lines and construction sites. Aggregate imaging systems developed to date for size and shape characterization, however, have primarily focused on measurement of separated or non-overlapping aggregate particles. This research study presents an innovative approach for automated segmentation and morphological analyses of stockpile aggregate images based on deep-learning techniques. As a project outcome, a portable, deployable, and affordable field-imaging system is envisioned to estimate volumes of individual riprap rocks for field evaluation. A state-of-the-art object detection and segmentation framework is used to train an image-segmentation kernel from manually labeled 2D riprap images in order to facilitate automatic and user-independent segmentation of stockpile aggregate images. The segmentation results show good agreement with ground-truth validation, which entailed comparing the manual labeling to the automatically segmented images. A significant improvement to the efficiency of size and morphological analyses conducted on densely stacked and overlapping particle images is achieved. The algorithms are integrated into a software application with a user-friendly Graphical User Interface (GUI) for ease of operation. Based on the findings of this study, this stockpile aggregate image analysis program promises to become an efficient and innovative application for field-scale and in-place evaluations of aggregate materials. The innovative imaging-based system is envisioned to provide convenient, reliable, and sustainable solutions for the on-site quality assurance/quality control (QA/QC) tasks related to riprap rock and large-sized aggregate material characterization and classification.IDOT-R27-182Ope

Durability Aspects of Stabilized Quarry By-product Pavement Base and Subbase Applications

Recent research conducted at the Illinois Center for Transportation (ICT-R27-168) evaluated sustainable applications of quarry by-products (QB) or QB blended with coarse-recycled aggregates as chemically stabilized base and subbase layers. The research proved that stabilized QB pavement applications have satisfactory pavement performance. This project (ICT-R27-SP38) investigates the durability aspects of previously evaluated stabilized base/subbase QB applications due to fluctuations in temperature and moisture content, which induce freeze-thaw cycles during winter and wetting-drying conditions in the stabilized QB layers. Durability tests were conducted on samples extracted from field test sections previously evaluated with Accelerated Pavement Testing (APT) as well as on new samples compacted in the laboratory with the same material types and combinations. Field-extracted samples were exposed to multiple cycles of freezing and thawing and wetting and drying over three years in the field. Both laboratory and field samples were evaluated following the AASHTO T 135 wet-dry and AASHTO T 136 freeze-thaw durability test protocols, respectively. Results of durability testing indicated better wet-dry durability performance of QB samples when compared to freeze-thaw durability, particularly for samples stabilized with Type I Portland cement. The majority of field and laboratory samples had a cumulative soil-cement loss of 10% or lower following 12 cycles of wetting and drying indicating satisfactory performance. Note that 10% soil-cement loss is used in Illinois DOT practice to determine the percentage of stabilizing agent that ensures durability. Results also indicated that cement-stabilized QB materials benefited from long-term curing in the field, while fly ash–stabilized QB materials were less durable after exposure to multiple freeze-thaw and wet-dry cycles during and after APT testing. Further, durability samples having QB materials from dolomitic aggregate sources, i.e. having higher percentages of magnesium in their chemical composition as determined by X-Ray Fluorescence (XRF), exhibited better field performance trends than QB materials with primarily limestone (calcium oxide content) fines. This durability improvement was linked to the cementation observed in the dolomitic fines after exposure to freeze-thaw cycles in the field. Further, higher density and improved packing of QB materials observed in samples compacted at or near maximum dry density resulted in consistently better durability.IDOT-R27-SP38Ope

Review of Improved Subgrade and Stabilized Subbases to Evaluate Performance of Concrete Pavements

This report presents findings on the evaluation of foundation layers under concrete pavements in the state of Illinois. It also provides recommendations and scenarios where unbound granular layers can be safely used under concrete pavements as economical and well-performing subbase layers. The current practice and mechanistic design methods for constructing concrete pavements in Illinois was first evaluated, including historical studies that led to the current design procedures and policies. The performance of concrete pavements with unbound granular layers in Illinois were then evaluated, and several case studies of well-performing concrete pavements with granular subbases, high traffic levels, and low distress levels and severity were realized. Next, the practices of surrounding states were evaluated, and several Midwest states, i.e., Wisconsin, Minnesota, Iowa, and Michigan, were found to regularly use unbound granular layers under concrete pavements with no issues. A literature review on the most recent requirements and recommendations for designing granular subbases under concrete pavements was then presented. It is concluded that subbase layers under concrete pavements are mainly used to provide uniform support and prevent pumping. Based on the case study evaluations and literature, a stable, drainable, and durable daylighted granular subbase design is recommended for traffic factors up to 10.0. Stability is ensured by limiting the ratio of gravel-to-sand fractions in the aggregate mix between 1.3 and 1.9. Drainability requirements can be met by limiting the percentage of fines passing the No. 200 sieve (0.075 mm) to 4% and by checking the quality of drainage is at least fair based on the time required to drain 50% of the water. Lastly, a geotextile fabric is recommended for use below the granular subbase for separation to ensure drainability throughout design life.IDOT-ICT-193-5Ope

Steel Slag Aggregate Characteristics Evaluation as Railway Ballast

The use of recycled materials is a new tendency in the field of railway engineering. Steel slag aggregates (SSA) are one of the recycled materials derived from the steel industry. The application of SSA in ballasted railway tracks requires mechanical examination. In the present paper, the shear behavior of the ballast layer constructed by SSA and basalt aggregates was considered to assess the use of SSA as a substitution for basalt. In this regard, a series of large-direct shear tests were performed on basalt and SSA under various normal stresses. Based on the results, basalt aggregates have higher shear resistance than SSA for all normal stress. However, steel slag has sufficient shear strength as well as particle abrasion resistance. Overall, it was proven that the SSA has suitable stability against shear forces that could be applied on railway ballast.</p