sustainable pavements case studiesgeotextiles are permeable polymer fabrics used for soil...

Contact: Terry Beaudry, Cold Mix Asphalt, Pavement Reclamation, Recycling, Grading, Base, & Aggregate Engineer, 651-366-5456 [email protected] 1

Sustainable Pavements Case Studies

Pavement projects are one of the largest segments of MnDOT’s budget. MnDOT has a statutory responsibility to maximize the long-term benefits received for each state transportation investment and to ensure that project planning and implementation are consistent with the state’s environmental goals.1 It follows that pavement projects should make use of technologies and techniques that maximize project longevity and minimize environmental impacts.

The following case studies were developed in 2020-2021 to demonstrate the economic and environmental benefits of using sustainable road construction materials and practices. These techniques can increase the longevity of the pavement surface and decrease the life-cycle costs of installation and maintenance. The sustainable pavement techniques included are Cold In-Place Recycling, (stabilized) Full-Depth Reclamation, Geosynthetics and Gravel Stabilizers. Cold In-Place Recycling or Full-Depth Reclamation can be considered for any resurfacing project, while

Geosynthetics can be applied to any new construction or reconstruction project between the base and subgrade layers. Gravel stabilizers can be used on gravel roads and have the potential to provide benefits for gravel shoulders, but more research is needed to quantify the benefits. The techniques featured in these case studies focus on the foundation layers of the road, but these are not the only techniques that contribute to pavement sustainability. Future case studies could highlight additional techniques including 60-year concrete mix designs with well graded aggregate, high pozzolan substitution, stainless steel dowels and certain drainage systems.

These case studies can be used by project managers planners, and engineers to demonstrate the benefits of each of these sustainable pavement technologies to decision-makers on a project. They provide a brief overview of each technology and examples of the cost savings, materials savings and longevity benefits.

1 https://www.revisor.mn.gov/statutes/cite/174.01


Cold In-Place Recycling and Cold Central Plant Recycling

Cold In-place Recycling is an asphalt rehabilitation technique where existing pavement materials are reused in place. The recycling process uses Reclaimed Asphalt Pavement material generated by milling, planing, or crushing, which is mixed in-place with a recycling agent without the application of heat. CIR can be performed at full depth or partial depth.

• Full depth: layers of the asphalt, subbase, and bases are crushed, mixed with binder, and laid as a stabilized base course

• Partial depth: a portion of the asphalt layer is crushed and laid as a base course

The CIR process uses a single- or multi-unit train with a series of machines to mill, crush, mix, and pave the asphalt pavement, depending on the project. This process can differ depending on how the RAP is managed, the type of recycling agents and additives used, and how the recycled material is mixed and placed.

Cold Central Plant Recycling is similar to CIR except the recycling operation is done at a mobile or central plant location. Milled asphalt material is transported to a central location to be processed and new CCPR mixture is returned to the construction site to serve as the base layer in pavement rehabilitation.

Benefits

Pakes et al. 2017

On average, CIR reduces energy and CO2 emissions 23% compared to conventional overlay

CIR uses ~20% less water than conventional overlay(Pakes et al. 2017)

Virgin aggregate consumption can be reduced ~ 37% with CIR(Pakes et al. 2017)


Full Depth Reclamation is a pavement recycling technique where all the asphalt pavement section and a predetermined amount of underlying materials are ground together and treated to produce a stabilized base course. FDR uses the ground-up asphalt and base and foamed or emulsified asphalt, chemical agents, and geosynthetics.

The reclaimed materials in FDR are stabilized by mechanical, chemical, or bituminous means. Mechanical stabilization uses geotextiles or geogrids. Chemical stabilization uses a chemical additive (e.g., Portland cement or proprietary chemicals). Bituminous stabilization uses asphalt emulsion or foamed asphalt.

FDR is a multi-step approach that includes initial grinding of asphalt and base and subsequently the addition of stabilizers. The main steps are pavement pulverization, the introduction of additive(s), shaping the mixed material, compaction, and application of wearing or surface course. Required equipment includes a reclaimer, compactor(s), motor grader, water truck, and finishing roller, and in some cases a van feeder or milling machine.

Benefits

Above: compared to conventional reconstruct

FDR saves > 90% in new materials and ~ 80% in fuel consumption

Life-Cycle Cost Analysis indicates that FDR costs ~ 16% less to maintain than conventional overlay*VDOT (2011)

Construction costs can be reduced >40% with FDR *GDOT (2006)

Full Depth Reclamation

© 2005 Portland Cement Association


Geosynthetics

Geosynthetics are polymer-based materials, including geogrids and geotextiles, used to stabilize terrain and improve the strength and stiffness of pavement layers.

Geogrids are formed into relatively rigid, grid-like configurations, typically used for reinforcement and confinement. These can be placed between subgrade and base layers of roads to add strength and stiffness and to slow deterioration.

Geotextiles are permeable polymer fabrics used for soil separation, filtration and drainage, and erosion control. Geosynthetics can be used on small and large projects and should be considered for all new construction, lane extensions, and full-depth reclamation projects.

Geotextile and Geogrid Placement at MnROAD

Benefits

Geogrid Reinforced Aggregate - MnDOT D2, Bemidji (2011)

CO2 savings of ~31% with geosynthetic reinforced soil instead of virgin aggregate for road foundation*WRAP (2009)

Service life prolonged up to 16% with geotextile reinforcement*Hossain & Schmidt (2009)

A separation geotextile can decrease maintenance costs 5-15% over a 9-year period*Geosynthetic Materials Association (GMA)

In soft subgrades, geosynthetics can reduce aggregate base thickness by ~26%*Cuelho and Perkins (2017)


Gravel stabilizers are chemical additives applied to a road surface to stabilize gravel aggregates. They are typically applied with a spray bar when new gravel is added to a road and worked in with a motor grader. Gravel stabilizers have proven cost-effective and reduce fuel use and consumption of natural resources (i.e. gravel).

Stabilizers for gravel roads are used throughout Minnesota, especially in the northwest. Based on data from Polk County, after an initial investment of $3,000-$10,000 per road-mile (depending on product used and depth of stabilization), agencies using stabilizers could see a 75% reduction in grading and a 33% reduction in both gravel and calcium chloride (used as a dust suppressant).

Benefits

*Based on calculations from Polk County’s use of gravel stabilizers. See Appendix A for calculations.

Polk County Road without Stabilization

Polk County Road with Stabilization

Up to 55% reduction in maintenance costs

Aggregate savings of up to 127 tons per road-mile per year

Up to 75% reduction of diesel fuel from less grading and gravel, or 169 gallons per road-mile per year

Stabilizers for Gravel Roads

Appendix A. Yearly Cost and Fuel Savings for Gravel Roads using Gravel Stabilizers Author: Terry Beaudry MnDOT Grading and Base Engineer Date: 12/23/2020 Saving Data Obtained from Polk County, MN Assumptions: *(Polk County Data): 2” of Gravel used every five years without stabilizers.

Stabilizers reduce the amount of gravel used by 33%. Stabilizers reduce the amount of grading by 75%.

Stabilizers reduce the amount of CaCl2 by 50%. Thirty Weeks of Grading/Year Grade 1.5 times per week (this is for an average county gravel road) Gravel Costs $12/Ton.

£ Average Speed of motor grader when grading: 4 mph, “How to Grade a Gravel Road, KHPlant” € Fuel Consumption when Operating Motor Grader: 5 Gallon/Hr, “Hourly Fuel consumption Tables, JS Cole” Δ Gravel Weight = 135#/SY Inch, MnDOT Grading and Base Manual β CaCL2: $1.14 per gallon Average Bid Price µ CaCL2 application rate 0.2 Gallons/SY, MnDOT Grading and Base Manual å $145/Hour to operate Grader Square yards in a 24’ roadway for 1 mile = 8 yards x 1,760 yards = 14,080 SY A) Yearly costs for Gravel and Fuel use without Gravel Stabilizers 1) Gravel Tons used and Costs per mile * 2” every 5 years or 0.4”/gravel per year * Gravel costs $12/Ton * Δ Gravel Weight = 135#/SY Inch Gravel used per mile/year = 135#/SY Inch x 0.4 inch/year x 14,080 SY/Mile x tons/2000 # = 380 tons/mile/year Gravel Cost/Mile/Year = 380 tons/mile/year x $12/Ton = $4,560 per mile/year 2) CaCl2 Costs per mile β Cost: $1.42 per gallon µ Application Rate: 0.2 gallons/sy $1.42/gallon x 0.2 gallon/sy = $0.284/SY/Year CaCl2 Cost/Mile/Year = $0.284/SY/Year x 14,080 SY = $3,999 3) Motor Grading Costs per mile Assumptions

• å $145/Hour to operate Grader (average bid price) • £ Operate at 4 MPH • Four Passes to grade full width, therefore one hour to grade one mile • * 30 Weeks of Grading/Year

• * Grade 1.5 times per week (this is for an average county gravel road) • Therefore 45 Hours of motor grader use per mile per year

Cost/Mile/Year to run Motor grader = $145 x 30 weeks x 1.5 times/week = $6,525/year Total without Gravel Stabilizer = $4,562 + $3,999 + $6,525 = $15,086/Mile/Year

B) Cost and Fuel Use When Using Gravel Stabilizer 1.1) Gravel 2/3 the tons use = 2/3 x 380 Tons/mile = 253 Tons/mile 1.2) Gravel 2/3rds the cost = 2/3 x $4,562 = $3,041/year 2) CaCl2 1/2 cost = 1/2 x $3,999 = $2,000 3.1) Motor Grader 1/4 cost = $6,525 x 1/4 = $1,631 3.2) Motor Grader 1/4 use = 45 hours/4 = 11.25 hours 4) Gravel Stabilizer = $0.12/SY inch

0.4 inches x 2/3 of gravel every year, therefore, $0.12/SY inch x 0.4 x 2/3 inch/year x 14,080 SY/Mile = $451/Mile/year

5) Total cost with Gravel Stabilizer = $3,041 + $2,000 + $1,631 + $451 = $7,123

6) % Savings Using Stabilizer = (15,086 – 7,123)/15,086 = 53% C) Motor Grader Fuel and Aggregate Saving Assumptions

* Save 75% of grading € 5 gallons/hour to run a motor grader From above 45 hours per year to grade a mile of road

Motor Grader Fuel Savings 0.75 x 45 hours/mile x 5 gallons per hour = 169 gallons/mile of road Aggregate Savings 380 - 253 = 127/Tons/mile/year of Aggregate Saved D) Additional Savings and Advantages Not Calculated

• Fuel Saving in production of aggregate • Fuel Saving in placing and hauling of aggregate • Fuel and material savings for production of CaCl2 • Less CaCl2 lost to environment • Safety improvements as less trucks are hauling to maintain roads • Safety improvements as grader, aggregate spreading, and chloride treatments are

operating less on roadway • Consumer fuel savings as roadways are better maintained

sustainable pavements case studiesgeotextiles are permeable polymer fabrics used for soil...

Documents