Diana Podborochynski

Mechanistic Laboratory Evaluation and Field Construction of Recycled Concrete Materials for Use in Road Substructures

Given the renewal of urban infrastructure and the increased costs of landfilling concrete rubble materials, opportunities exist to optimize the reclamation and recycling of portland cement concrete (PCC) and hot-mix asphalt concrete (HMAC) rubble through their innovative use in road rehabilitation. The primary objective of this study was to demonstrate the ability to reclaim, process, and recycle stockpiled concrete materials to provide improved structural mechanistic–climatic material properties and to meet or exceed the mechanical properties of conventional granular road materials. This research was based on advancements made in 2009 as part of the Green Streets Infrastructure Program in the city of Saskatoon, Saskatchewan, Canada. A second objective of this research was to pilot the field application of reclaimed and recycled HMAC and PCC rubble in typical urban road reconstruction applications. Recycled HMAC and PCC materials were used in the pilot reconstruction of a road that was exhibiting substructure moisture problems and structural failure. This study showed that recycled HMAC and PCC rubble materials could be processed to achieve mechanistic laboratory properties that exceeded those of conventional granular-based materials. This study also demonstrated efficient constructability and high end-product structural asset value of a typical rehabilitated urban road structure test section in the city of Saskatoon by using recycled HMAC and PCC rubble. On the basis on these findings, the use of quality processed HMAC and PCC rubble materials for road reconstruction was found to be a technical and environmentally sustainable solution.

Saskatchewan Field Case Study of Triaxial Frequency Sweep Characterization to Predict Failure of a Granular Base across Increasing Fines Content and Traffic Speed Applications

Approximately one-third of the Saskatchewan provincial highway system is comprised of granular base structures with a thin asphaltic or double seal surfacing. Unfortunately, significant portions of the Saskatchewan thin granular system were not constructed to primary legal weight limit standards and are now exhibiting varying degrees load related distresses and in many cases, structural failures. Based on field performance observations, many of the failures are commonly observed within the granular base layer, particularly when the base is comprised of high fines content, and/or when exposed to high deviatoric stress states. A recent increase in load spectra due to increasing truck traffic has resulted in much of the Saskatchewan granular base systems needing structural rehabilitation. In order to optimize the road structure upgrade treatment, it is desirable to better understand the material constitutive relations of granular base materials across fines content, triaxial stress states, and load frequencies representative of those induced within thin granular base pavements in the field. This research employed triaxial frequency sweep characterization to characterize the mechanical material constitutive behavior of a typical Saskatchewan Type 33 granular base across increasing fines content, triaxial stress state, and load frequency. Based on the findings of this study, increased fines content was found to significantly degrade the mechanical behavior of the standard Saskatchewan Type 33 granular base material in terms of dynamic modulus and phase angle. This research showed that under realistic field state conditions in Saskatchewan, phase angle may be an indicator of elevated viscous behavior within the granular base. Based on the mechanical material properties measured, it was also found that the current specified limits for fines content may not be sufficient to ensure optimal mechanistic structural behavior of thin granular pavement systems under severe traffic load conditions.

Field investigation of granular base rehabilitation project incorporating a woven geotextile separation layer, sand, and cement stabilization

Full-depth reclamation and cement strengthening has been used successfully to dry and strengthen granular pavements. However, some thin pavements fail due to severe wetting-up of the subgrade, thus...

Ground-Penetrating Radar Evaluation of Moisture and Frost across Typical Saskatchewan Road Soils

This study was undertaken to evaluate the effect of soil type, moisture content, and the presence of frost on road substructure permittivity. Permittivity sensitivity of typical road soils was characterized in the laboratory to provide baseline dielectric constant values which were compared to field ground penetrating radar (GPR) survey results. Both laboratory devices, the complex dielectric network analyzer and the Adek Percometer, as well as the field GPR system were used in this study to measure the dielectric constant of soils. All three systems differentiated between coarse-grained and fine grained soils. In addition, at temperatures below freezing, all three systems identified an increase in water content in soils; however, when frozen, the sensitivity of dielectric constant across soil type and moisture content was significantly reduced. Based on the findings of this study, GPR technology has the ability to characterize in situ substructure soil type and moisture content of typical Saskatchewan road substructure soils. Given the influence of road soil type and moisture content on in-service road performance, this ability could provide road engineers with accurate estimates of in situ structural condition of road structures for preservation and rehabilitation planning and optimization purposes.

Triaxial frequency sweep characterization of Saskatchewan hot mix asphaltic concrete across asphalt cement binder type

The purpose of this research was to determine how asphalt cement binder types influence the mechanical behaviour of hot mix asphalt concrete mixes. This research employed triaxial frequency sweep characterization of a typical City of Saskatoon Hot Mix Type A2 and a typical Saskatchewan Ministry of Highways and Infrastructure Hot Mix Type 70 across a range of triaxial load frequencies and stress states representative of Saskatchewan field state conditions. The asphaltic mixes were evaluated across four asphalt cement binder types typically employed by Saskatchewan road agencies. Based on the findings of this study, the mechanical behaviour of both asphalt mixes evaluated were found to be highly sensitive to load rate, stress state, as well as asphaltic binder type. It was concluded that load rate, field stress state, and asphalt binder type should be incorporated into the structural design of hot mix asphalt concrete pavements to ensure adequate mix performance, particularly when placed in severe field con...

Modeling the Structural Response of Urban Subsurface Drainage Systems

In recent years, many City of Saskatoon (COS), Canada, roads have experienced premature failures. High water tables, increased precipitation, and poor surface drainage have caused increased moisture infiltration in road structures. Further deterioration of these aged pavements is attributable to heavy year-round loadings in urban traffic. To address these issues, COS piloted subsurface drainage and strain dissipation layers in some roads. These drainage systems were constructed with crushed portland cement concrete (PCC) rock and conventional virgin crushed rock. Given the empirical nature of conventional road design methods currently used by COS, the structural benefits of drainage systems are difficult to quantify. Therefore, a reliable method that directly incorporates recycled materials, substructure drainage systems, and diverse field conditions is needed. A mechanistic analysis of the drainage systems was piloted in rehabilitated COS pavement structures with a three-dimensional (3-D) nonlinear orthotropic computational road structural model. The 3-D mechanistic model was used to predict peak surface deflections and normal and shear strains in the structure. Modeling results showed that constructing pavement structures with a substructure drainage layer of crushed PCC rock improved the structural performance of the road system in terms of strains under applied traffic loads. The road model provided primary response predictions that correlated with deflections measured by a heavy weight deflectometer, before and after construction. Therefore, the road model used is a reliable pavement engineering analysis tool able to predict the in-field structural behavior of various road structures under diverse field state conditions.

Mechanistic characterization of cement stabilized marginal granular base materials for road construction

This study investigated the mechanistic climatic constitutive behaviour of granular materials from Saskatchewan, Texas, and Finland. This research employed triaxial frequency sweep testing to characterize various quality granular materials with and without cement modification. Cement stabilization showed a consistent improvement in the response of poor and well graded granular materials, relative to untreated granular materials in terms of both mechanical behavior and climatic durability. As a result, when cement stabilized, poorly graded (or dirty bases) with high fines and (or) fine sand content can be engineered to perform better in the field than well graded (or clean) bases. This research showed that climatic conditioning of laboratory samples significantly influences the mechanical behavior of both unstabilized and cement treated granular materials. Therefore, when characterizing granular base materials for structural design purposes, the mechanistic properties and the effect of climatic conditionin...

Mechanistic-Based Nondestructive Structural Asset Management Testing to Optimize Low-Volume Road Structural Upgrades

The Saskatchewan, Canada, Ministry of Highways and Infrastructure is investigating integrated structural asset management to help optimize investment in the rural low-volume road (LVR) network. Integrated ground-penetrating radar (GPR) and heavyweight deflectometer (HWD) testing were found to be very effective structural assessment tools that might be used to strategically rehabilitate, maintain, and upgrade Saskatchewans LVR network, which accounts for 80% of the ministrys total network. This paper demonstrates this integration at a project level to assess the pre- and postconstruction structural condition of two LVRs in Saskatchewan. The preconstruction GPR survey applied in this study showed locations of trapped moisture within the road structures granular materials. The postconstruction HWD assessed the end product structural integrity of the road after its rehabilitation treatment. The ability to strategically allocate limited financial resources across the extensive in-service LVR system in Saskatchewan on the basis of accurate structural asset management infrastructure performance data was essential for this project, given the high variability in Saskatchewan LVR structures.

Modeling In Situ Performance of Cement-Stabilized Granular Base Layers of Urban Roads

This study used a three-dimensional nonlinear orthotropic computational road model to measure the performance of reclaimed and recycled portland cement concrete (PCC) aggregates and reclaimed asphalt pavement (RAP) aggregates stabilized with cement as a base layer in a typical local road structure in the city of Saskatoon, Saskatchewan, Canada. The pavement structure was composed of 45-mm hot-mix asphalt concrete on a 225-mm granular base built directly over an in situ subgrade. The cross section was analyzed with a conventional granular base layer as a baseline and PCC and RAP base layers with 2% cement stabilization. The cement-stabilized PCC and RAP base layers showed improved shear strain and horizontal strain behavior when compared with the conventional granular base layer (which was not cement stabilized). This improvement con-firmed that cement stabilization of reclaimed PCC and RAP materials provided an enhanced primary response. This study demonstrated that typical thin Saskatoon pavement structures were highly dependent on the constitutive properties of base layer material. Stabilizing the PCC and RAP base layers with 2% cement reduced the maximum shear strains at the edge of the pavement structure by 12% and 25%, respectively, compared with the unstabilized conventional granular base layer. It was believed that the increased fracture and cohesion of the residual cementitious materials inherent to recycled granular base, as well as the cementitious binder added, improved structural performance.

Integrated Mechanistic-Based Framework for Sustainable “Green Street” Rehabilitation of Urban Low-Volume Roads:

This research developed a mechanistic-based framework for recycling rubble materials into high-value-added engineered road structural materials for use in urban road rehabilitation. Scientific-based engineering methods were integrated with advanced materials processing, road construction, and nondestructive asset management techniques to explicitly quantify the benefits of recycled material systems using reclaimed asphalt pavement (RAP) and portland cement concrete (PCC) rubble generated within the city of Saskatoon, Saskatchewan, Canada. The ability to process RAP and PCC rubble to meet or exceed conventional granular aggregate specifications with minimal waste was demonstrated. It was found that RAP and PCC aggregates can exceed the mechanistic material constitutive properties of conventional city of Saskatoon granular base aggregates by at least 30%. The mechanistic material property value of unstabilized RAP and PCC was demonstrated in addition to the benefits of various cold stabilization systems using cement and emulsion. Recycled RAP was used as a black base layer and PCC was used as a subbase course or a drainage and stress-dissipation layer, or both, in rehabilitated road structures of nine “Green Street” test sections constructed in Saskatoon. These test sections met or exceeded target structural designs and were validated by using nondestructive heavy-weight deflectometer testing. The use of recycled RAP and PCC rubble materials for urban road rehabilitation had economic, social, environmental, and energy benefits for the city of Saskatoon. Recycled rubble materials were found to provide a technically viable and cost-effective solution for rehabilitating urban low-volume roads relative to conventional granular aggregates.