Road Talk Fall Vol 24, no 3: Fall 2018


Sustainable Projects Introduction

The ministry’s Materials Engineering & Research Office (MERO) provides standards, policies and guidelines for the materials used in the construction of Ontario’s provincial highways and bridges (aggregates, asphalt, chemicals, concrete, metals, paint, soils etc.). In support of the annual Capital Construction Program, MERO staff work to ensure that quality materials, products and technologies are used, safeguarding public safety and protecting infrastructure investments. MERO supports innovation by evaluating and introducing new products and processes that are more environmentally friendly, reduce greenhouse gas emissions, and result in longer life, as well as being cost effective and efficient. The articles that follow, on Ground Improvement Techniques and Warm Mix Asphalt are examples of the ministry’s commitment to sustainability.

Warm Mix Asphalt Reduces Longitudinal Joint Cracking on Ontario Highways

Results are in on the performance of Ontario’s Ministry of Transportation (MTO) Warm Mix Asphalt (WMA) pavements. In the spring of 2011, the ministry published an article titled Cooling Off by Getting Warm - A Greener Alternative to Hot Mix Asphalt - the article provided an overview of WMA technology and ten of the ministry’s WMA contracts constructed from 2008 to 2010, with a commitment to monitor pavement performance. WMA’s lower production temperature was expected to improve joint quality, reduce cracking caused by asphalt oxidation, and generally outperform Hot Mix Asphalt (HMA). Monitoring of longitudinal cracking confirmed improved performance on that criterion.

WMA is produced using technology that allows for mixing, handling and compaction of an asphaltic concrete mixture, at temperatures typically 20 to 50°C lower than conventional HMA. This reduction in temperature requires less energy and generates fewer emissions, making it a “greener” alternative. WMA technologies are categorized in three ways: organic additives, chemical additives, and foaming processes. Generally, additives are added to the asphalt and/or changes are made to the production processes in order to improve workability of the cooler mix.

The ministry’s WMA contracts have undergone a comprehensive monitoring program for pavement performance evaluation. Eight of the 2008-2010 contracts included an HMA section adjacent to the WMA section for performance comparison while exposed to the same highway environment.

In 2016, these eight contracts were visually evaluated for longitudinal joint performance using iVision, a web-based application that allows synchronized viewing of highway corridor images, pavement images and pavement condition data. Evaluation results showed that the WMA sections experienced approximately 50 per cent slight longitudinal joint cracking, compared to the HMA sections which experienced up to 75 per cent moderate longitudinal joint cracking.

Overall, WMA joints were equal to or less visible than those of HMA. Figure 1 gives an example of WMA’s superior longitudinal joint performance over HMA.

Warm Mix Ashphalt (WMA) pavement Hot Mix Asphalt (HMA) pavement

Figure 1: Images of WMA Pavement (top) vs. HMA Pavement (bottom) showing better longitudinal joint performance for WMA after six years of service.

The initial cost of WMA is marginally higher than HMA due to the cost of additives. However, considering the improved performance and anticipated longer life, the life-cycle cost of WMA is expected to be similar to or less than HMA.

Further Testing Using the FHWA Specific Pavement Study SPS-10

In 2013, the U.S. Department of Transportation (USDOT) Federal Highway Administration (FHWA) introduced its tenth Specific Pavement Study (SPS-10) as part of their Long Term Pavement Performance Plan (LTPP). The study, titled Warm-Mix Asphalt Overlay of Asphalt Pavements, is designed to evaluate long-term field performance of WMA relative to HMA.

Sampling Area (34m); Buffer Area (15m); 01 HMA Control Section (150m); Buffer Area (15m); Sampling Area (34m); Transition Area; Sampling Area (34m); Buffer Area (15m); 02 WMA Foaming Process Test Section (150m);	Buffer Area (15m); Sampling Area (34m); Transition Area; Sampling Area (34m); Buffer Area (15m); 03 WMA Chemical Additive Test Section (150m);	Buffer Area (15m); Sampling Area (34m)

Figure 2: Example of an SPS-10 construction layout (not to scale)

General construction involves building a minimum of two test sections using various WMA technologies in addition to a HMA control section. To improve data reliability, both sides of each section consist of a buffer area between a materials sampling area, and are separated by a transition area, as shown in Figure 2. Production and placement of the WMA must be less than or equal to 135 oC, or at least 16 oC less than the HMA section.

In 2014, the ministry participated in the SPS-10 study by selecting five full-width test sections, consisting of two undivided lanes on Highway 48, located approximately 28 km northeast of Newmarket. The sections included:

  • One HMA control section
  • One WMA section produced using foaming process
  • Two WMA sections produced with different chemical additives
  • One WMA section produced with an organic additive

The sections were reviewed and accepted by the FHWA, and construction began in 2016. The ministry was responsible for contract administration and construction of the sections, which were completed in June 2017. FHWA is responsible for collecting performance data and conducting materials testing, as well as providing data analysis and reporting for 15 years. The resulting data is stored in the LTPP database and available online. FHWA applies a series of quality control checks to the data as they are collected in the field and prior to entry into the database.

The FHWA study’s objective is to investigate the sensitivity of WMA technology to moisture damage, low temperature cracking, fatigue cracking, and permanent deformation. Primary factors are weather, traffic loading, and WMA mix design. Secondary factors are in-situ density, Reclaimed Asphalt Pavement (RAP) content, subgrade type, existing pavement condition, roadway geometry, and layer thickness. The performance measurements collected pre and post overlay included:

  • Falling Weight Deflectometer (FWD) – in-field non-destructive testing used to determine pavement structural integrity
  • Manual Distress Surveys (MDS) - used to identify pavement distress types and severities; transverse and longitudinal profile measurements; and surface texture measurements
  • Elevation surveys for overlay thickness
  • Compacted core sampling and testing
  • Nuclear gauge density measurements for compaction
  • Non-compacted bulk material sampling and testing

Temperatures were monitored and recorded during asphalt production in the plant, delivery to the work site, and while the asphalt was laid. Figure 3(a) is an image of a chemical test section during paving operations on Ontario’s SPS-10 site. Figure 3(b) is a thermal image of the same section, showing an average paving temperature of 124 oC; about 20oC cooler than a typical paving temperature for HMA.

Images of Ontario SPS-10 WMA overlay construction

Figure 3(a): The paving operation of a chemical WMA test section

Figure 3(a): The paving operation of a chemical WMA test section

Figure 3(b): A thermal image of the same WMA test section

Figure 3(b): A thermal image of the same WMA test section

Participants in the SPS-10 study include Arizona, Florida, Manitoba, Missouri, New Mexico, Nevada, Oklahoma, Ontario, Oregon, Texas, and Washington. The Ontario SPS-10 site is the second constructed in the North Atlantic region which is considered a wet-freeze climate. The sections are contained within an 8.2 km segment of Highway 48, as shown in Figure 4.

Figure 4: Ontario SPS-10 Location Overview, ©2018 Google

Figure 4: Ontario SPS-10 Location Overview, ©2018 Google

MTO’s participation in the SPS-10 study is an excellent opportunity to learn how WMA performs under Ontario’s specific climatic settings with differing material and construction specifications, while contributing to a North American knowledge base.

An annual program is now underway at the five test sections on Highway 48 to monitor pavement performance attributes for the next 15 years. This continued monitoring will determine whether the WMA sections crack less than HMA. Based on those future findings, the ministry will have the opportunity to refine their specifications for WMA use.

For more information please contact:

Seyed Tabib, Senior Bituminous Engineer, Bituminous Section, Materials Engineering & Research Office, Highway Standards Branch at (416) 235-3544, or at Seyed.Tabib@Ontario.ca

Additional Sources of Information:

Ontario Ministry of Transportation Road Talk article, Warm Mix Asphalt – A Greener Alternative to Hot Mix Asphalt. To request a copy of the 2011 article, please contact RoadTalk@ontario.ca, stating your request in either the subject or the body of your message.

The U.S Department of Transportation Federal Highway Administration – Warm Mix Asphalt information page: https://www.fhwa.dot.gov/pavement/asphalt/wma.cfm

The U.S Department of Transportation Federal Highway Administration – Specific Pavement Studies information page: https://www.fhwa.dot.gov/research/tfhrc/programs/infrastructure/pavements/ltpp/sps.cfm



Reducing a Project’s Carbon Footprint with New Ground Improvement Methods

pier installation at highway 15 crosby creek

Aggregate pier installation at Hwy 15 Crosby Creek.

Every year the Ministry of Transportation (MTO) manages construction projects that include significant foundation components, such as road embankment construction, stabilization of shallow and deep foundations, and building retaining structures. New ground improvement techniques are being introduced to ministry foundation projects to enhance foundation engineering and reduce the carbon footprint of foundation projects.

The ministry manages over 16,500 kms of road network including over 2,800 bridges, structural and non-structural culverts, retaining walls, tunnels, ferries and airports. Maintaining and enhancing ministry infrastructure requires large volumes of foundation work.

The construction of foundational components contributes to a project’s overall carbon footprint - an estimate of emissions of carbon dioxide (CO2) and other greenhouse gases (GHG). Foundation construction requires large amounts of natural resources which generate significant waste and emissions. The ministry recognizes the importance in reducing the environmental impacts of foundation processes and products.

Historically, when building roadway embankments over swamps or compressible soils, native materials were excavated then replaced with rock fill or select subgrade material (SSM). This involves a great deal of trucking of materials.

The next generation of foundation engineering design and construction for embankments involves improving the strength and compressibility of existing foundations and soils with new ground improvement techniques.

Ground improvement methods offer foundations engineering advantages by enabling faster construction of embankments and foundations without compromising quality and performance. The removal and replacement of existing soils is significantly reduced by using aggregate piers, rigid inclusions or controlled modulus columns. Soil removal may be avoided altogether by using Prefabricated Vertical Drains (PVDs), also known as wick drains. Further, by using these techniques, project fuel consumption and the use of natural resource materials are reduced.

  • Aggregate Piers –are columns of compacted stone installed in groups in poor soil to increase bearing pressure and mitigate settlement under structural footings. They are a cost-effective method to reinforce soft, cohesive soil and poor fill for all types of structures. Aggregate piers are formed when lifts of stone are introduced to an open hole and compacted using high-energy densification equipment. The phrase aggregate piers may be used to describe either a rammed pier or a vibrated pier, also called a vibro stone column (VSC).1
  • Rigid Inclusions – are stiff Ground Improvement elements that consist of aggregate mixed with cement or grout, or elements made of plain concrete. The elements are stiff enough to transfer the stress from a slab, footing or embankment load through soft soil layers down to a firm soil or weathered rock layer.2
  • Controlled Modulus Columns – Controlled modulus columns (CMC) are concrete columns placed in a network adapted to loads and settling criteria, combined with a granular bed. This distribution bed spreads the applied load between the ground and the CMC.3
  • Wick Drains - Wick drains, also known as Prefabricated Vertical Drains (PVDs), are installed to provide drainage paths for pore water in soft compressible soil.4

Recently, aggregate piers were used as a ground improvement technique to address settlement and stability requirements for the approach embankments associated with a new bridge at Crosby Creek on Highway 15. The approach embankments, 3.5 metres in height, were to be built on 4 metres of silty clay.

Rather than the removal of the silty clay stratum and rock fill, ground improvement was selected as an embankment design alternative. Removal of the silty clay would have required approximately 15,100 m3 of excavation, hauling of the excavated material, and supply and transportation of the same volume of rock fill. Post-construction monitoring confirms that the embankments are performing very well, demonstrating that ground improvement technology works. The ministry recognizes the benefits of ground improvement methods compared with the removal and replacement of silty clay from a sustainability perspective.

From a sustainability point of view, it is important that a proper assessment of foundation processes and products is performed. Only then, can sustainable choices be made. Moving forward, the ministry recommends a consistent approach to assess the benefits of alternative foundations. A life cycle assessment (LCA) tool can efficiently and comprehensively quantify the resources used and environmental impacts of foundation processes and products, and can help decide on alternatives that have less impact on the environment. Ground improvement has definite advantages from a foundations engineering perspective but it also has environmental and sustainability advantages which support LCA.

Life cycle assessment was not used to select the ground improvement method at the Hwy 15/Crosby Creek site. However, the ministry and academia are collaborating to assess sustainability by developing a systematic methodology for performing LCA of different foundation systems and products managed by the MTO. Performing LCA for the foundation component of ministry projects will be beneficial in developing standards and procedures for sustainability assessment. This process will result in sustainability optimization of the use of materials, energy and the environmental impacts of ministry projects.

For more information, please contact Tony Sangiuliano, Senior Foundation Engineer, at (416) 235-5267, or at Tony.J.Sangiuliano@ontario.ca

  1. Source: https://www.subsurfaceconstructors.com/services/ground-improvement/aggregate-piers-vibro-stone-columns/
  2. Source : http://www.geostructures.com/solutions/ground-improvement/geopier-rigid-inclusions#What is a Rigid Inclusion
  3. Source: http://menardcanada.ca/ground-improvement-solutions/controlled-modulus-columns/
  4. Source : http://www.haywardbaker.com/solutions/techniques/wick-drains

For more information on Wick Drain use at MTO, please request the Winter 2007 Road Talk publication at RoadTalk@ontario.ca

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