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TRANSPORTATION RESEARCH BOARD
@NASEMTRB#TRBwebinar
Using Otta Seal as a Surface Treatment on Low-
Volume RoadsAugust 4, 2020
The Transportation Research Board
has met the standards and
requirements of the Registered
Continuing Education Providers
Program. Credit earned on completion
of this program will be reported to
RCEP. A certificate of completion will
be issued to participants that have
registered and attended the entire
session. As such, it does not include
content that may be deemed or
construed to be an approval or
endorsement by RCEP.
PDH Certification Information:
•1.5 Professional Development Hour (PDH) – see follow-up email for instructions•You must attend the entire webinar to be eligible to receive PDH credits•Questions? Contact Reggie Gillum at [email protected]
#TRBwebinar
Learning Objectives
#TRBwebinar
1. Define Otta seal
2. Identify current practices for installing a well-performing and long-lasting Otta seal surfacing
3. Determine how Otta seal performs as an alternative to the traditional bituminous surface treatment techniques
Using Otta Seal as a Surface Treatment on Low-Volume Roads
Webinar arranged byTRB Committee AKM80 “Aggregates”
Learning Objectives
At the end of this webinar, you will be able to:
• Define Otta seal
• Identify current practices for installing a well-performing and long-lasting Otta seal surfacing
• Determine how Otta seal performs as an alternative to the traditional bituminous surface treatment techniques
2
Today’s Panelists: #TRB Webinar
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Andrew Dawson, Ph.D.,Chair, TRB’s Aggregates Cmte.
Halil Ceylan, Ph.D., Iowa State University
Brian P. Moore, P.E., Iowa County Engineers Association
Lee Bjerke, P.E., Winneshiek County, Iowa
Andrew Dawson The University of Nottingham
• Who am I?
– Until last month Associate Prof., Univ. Nottingham, UK
• 37+ years
– Now ‘retired’ due to Covid-9 economic squeeze
– Chair, TRB’s Aggregates Committee
• Expertise
– Pavement and geotechnical engineer
– Specializing in unbound road layers & drains / LVRs
4
“Otta” seals
• Otta
– Small town in Norway (<2000 persons)
5
“Otta Seal” surfacing
6
• Developed in the early-mid ‘60sby Norwegian Road Research Lab.
• First applied at Otta, Norway
• A kind of “Chip-Seal+”
• ‘Exported’ by Norwegian aid program in ’70s-80s
• First to Africa …
• … then spread to many other places
• First paper at TRB in 1983
This Webinar
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Our 3 Speakers aim to give a wide coverage:
• Background
• Rationale / Logic
• Principles
• Practicalities
• Experience & Economics
Question & Answers
8
TRB Webinar: Using Otta Seal as a Surface Treatment on Low-Volume Roads
#1 Problems with Iowa Gravel Roads
Brian P. Moore, P.E.Iowa Secondary Road Research EngineerIowa County Engineers Association (ICEA)
Brian P. Moore, P.E.Iowa County Engineers Association (ICEA)
• Iowa Secondary Road Research Engineer
– 2018-Present
• Wapello County Engineer, Iowa
– 2001-2018
• Ringgold/Decatur Engineer, Iowa
– 1998-2001
• Member NACE Low-Volume Road Committee
9
Iowa’s Granular Roads
• Iowa has over 72,000 miles of granular County owned roads
• In 2019 Iowa’s County road departments spent over $129 million on granular road material and another $37.5 million blading granular roads
• Largest non labor budget item for County road departments
• Granular network vital to Iowa’s agricultural and manufacturing economy getting products to market
10
Heavy Agricultural Equipment
• Low volume of traffic but must support very heavy agricultural equipment
11
Regional Characteristics
12
Iowa’s Problem
• Roads built with natural material
• Heaving
• Frost boil
• Potholes
• Uncomfortable travel
• Seasonally impassable roads
13
Seasonal Effects
14
Summer Spring
Spring Thaw
15
Spring Thaw (Cont’d)
16
Iowa’s Need
• Solution to stabilize granular roads
• Desire to provide the public with a lower cost, longer lasting, more reliable granular driving surface requiring less maintenance
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TRB Webinar: Using Otta Seal as a Surface Treatment on Low-Volume Roads
#2 Otta seals: History, Principles, and Guidelines
Halil Ceylan, Ph.D. Dept. of Civil, Construction and Environmental Engineering (CCEE)
Program for Sustainable Pavement Engineering and Research (PROSPER)
Institute for Transportation (InTrans)Iowa State University (ISU)
Halil Ceylan, Ph.D., Iowa State University (ISU)
• Professor, Civil, Construction and Environmental Engineering
• ISU Site Director, PEGASAS - FAA COE on General Aviation
• Director, Program for Sustainable Pavement Engineering & Research (PROSPER) at Institute for Transportation
• More than 20 years of experience in pavement evaluation, design, maintenance, preservation, and rehabilitation
• Sustainable low-volume road materials and construction technologies, training, and research
19
Credit
• Mr. Charles Øverby, a Retired Chief Roads Engineer at the Norwegian Public Roads Administration (NPRA) & the author of the NPRA Guideline, “A Guide to the Use of Otta Seals”
20Mr. Charles Øverby Publication No. 93 from NPRA from 1999
Acknowledgments
• Iowa Highway Research Board (IHRB)
• Iowa Department of Transportation (Iowa DOT)
• Iowa County Engineers and Iowa DOT Engineers
• Former and current research team members from ISU’s PROSPER Research Team at InTrans
21
Outline
• Background and History
• Principles
• Guideline
• Summary
22
Background and History
• The unpaved road network in Norway was in a poor condition in the 1960´s
– In the early 1960´s, 50% or 40,000 km were gravel roads.
23
A national road during the thaw period.
Background and History (Cont’d)
• The cost of a bituminous treatment, equal to the maintenance of a gravel roads
– The investment should be earned back in a few years through reduced maintenance cost only
– The road user should find the quality and performance of the surface close to other conventional bituminous surfacings
24
Background and History (Cont’d)
• The surfacing should– Be cheap and easy to carry out– Utilize locally available material– Be impervious to prevent water into the moisture susceptible base
material– Be very flexible, durable and easy to maintain
• In the mid 1960’s trials were carried out in the “Otta Valley” in Norway where its name derives from
• By 1985, 12,000 km were surfaced with an Otta seal
• In the late 1970’s, the Otta seal concept was implemented in Kenya and Botswana under the NORAD technical assistance program
25
Background and History (Cont’d)
• Where have the Otta seal been used ?
26
Norway 12,000 km (Due to strengthening
operations, the km of Otta Seals has been
reduced to 4,000 km in 2004)
Sweden 4,000 km
Iceland 2,000 km
Kenya 500 km
Botswana 3,000 km (1/3 of the
paved road network)
Zimbabwe 80 km
South Africa 25 km
Namibia Trials
Mozambique 50 km ?
Ghana 30 km ?
Tanzania 100 km
Bangladesh 20 km ?
Chile 30 km ?
Nepal 40 km ?
Australia Trials
New Zealand Trials
Falkland Island 15 km ?
Tonga Islands 4 km ?
USA: more than 50 road segment trials/projects in Iowa, Minnesota, and South Dakota
Background and History (Cont’d)
• USA experiences (Iowa, Minnesota, and South Dakota)
27
Background and History (Cont’d)
• Otta seal in Botswana, after 25 years in service!
28
Images from Otta seal project site, MN-74, Winona County, MN (Built in 2001)
Images from Otta seal project site, MN-74, Winona County, MN (Built in 2001)
Images from Otta seal project site, MN-74, Winona County, MN (Built in 2001)
Outline
• Background and History
• Principles
• Guideline
• Summary
32
Otta Seals: What is It?
• An Otta seal is formed by placing graded aggregate on a relatively thick film of comparatively soft binders which, with rolling and trafficking, can work its way upwards through the aggregate interstices
• In this manner, the graded aggregate relies on both mechanical interlocking and bitumen binding for its strength - a bit like a bituminous premix
33
Mechanism of Performance of Surfacing Types
34
Under trafficking, the seal acts as a stress-dispersing mat comprised of a bitumen/aggregate admixture – a mechanism of performance which is quite different to that of chip seal surfacing
35
Chip seal Otta sealVS.
Images from Otta seal project site, MN-74, Winona County, MN (Built in 2001)
Types of Otta Seals
• Single Otta seal
– With/without sand cover seal
• Double Otta seal
– With/without sand cover seal
36
Note that the use of a sand cover seal is recommenced to reduce the rate of oxidation of the surfacing asphalt binder under hot temperature conditions
Thickness of Otta Seal
• A single Otta seal will exhibit a thickness of about 16 mm and a double about twice that thickness
37
38
Second layer
First layer
Images from Otta seal project site, MN-74, Winona County, MN (Built in 2001)
Performance Characteristics
• The texture of an Otta seal is playing a vital role in its performance
• The dense textures as formed by many particles of a relatively thick layer of aggregates where the interstices are filled with comparatively soft bitumen at with a relatively high has binder content has been found to be very durable
39
Performance Characteristics (Cont’d)
• Often preferred on roads with low bearing capacity due to its flexible behavior
• It seems that the close-texture grading as formed by the Otta seal concept is less susceptible to binder ageing than a chip seal
40
Grading Requirements
41
Aggregate Used in Otta Seals
• Decomposed granite (uncrushed)
• Gravel (screened)
• Lime stone (crushed)
• Silcrete (crushed)
• Ferricrete (as dug and screened)
• Laterite
• Ongoing trials in Iowa
– Slag as aggregates in Louisa County, Iowa
42
Outline
• Background and History
• Principles
• Guideline
• Summary
43
Guideline
• Publication No. 93 from NPRA from 1999– There is a need to update this
guideline for USA condition and construction practices (e.g., asphalt emulsion, recycled aggregate materials, and so on)
• Ongoing “TR-753, Evaluation of Otta Seal Surfacing for Low-volume Roads in Iowa, Phase II Study” by Iowa State University (ISU) sponsored from Iowa Highway Research Board (IHRB)– To develop a proposed technical
specification draft addressing the requirements on various items involved in real Otta Seal construction for Iowa-specific conditions
44
Pavement Strength
• Like all other bituminous surface treatments, an Otta seal will not contribute significantly to the structural strength of the pavement
• The pavement layers and drainage must therefore be adequately designed and constructed to withstand the expected traffic loading through its design life
45
General Aggregate Grading, Strength Requirements and Spread Rates
46
Asphalt Binder Types Commonly Used for Otta Seal
• Cutback asphalt and penetration grade bitumen
– The recommended binder types by NPRA guideline No.93
– PG commonly used in European Otta seal projects
– Cutback commonly used in African projects
• Asphalt emulsion
– Commonly used in USA Otta seal projects (e.g., Iowa, Minnesota, South Dakota, and so on.)
47
Cutback Asphalt and Penetration Grade Bitumen
48
Unless cut back to 150/200 v. grade using engine oil, used or new.
The best option is to use Pen. Bitumen 150/200 and cut back (MC 3000 or MC 800) to required viscosity using power paraffin.
All cutting back can easily be carried out on site providing certain safety measures are applied.
Cutback Asphalt and Penetration Grade Bitumen (Cont’d)
• Binder spray rates
– It should be noted that aggregate with high water absorption (fines (dust) on lime stone, ferricrete and laterite) will require a higher spray rate and lower viscosity than given NPRA guideline No 93
– The rolling procedure adopted during construction will also influence the spray rates and binder viscosity required
49
Traffic level at time of construction (AADT)
Hot spray rates(liter/m2)
< 100 1.8 – 2.2
100 - 500 1.8 – 2.0
> 500 1.6 – 1.8
Asphalt Emulsion
• HFMS-2s – Used for the Cherokee County Otta seal project in 2017 and
most of Otta seal projects in Iowa since then
– Minnesota and South Dakota applied this binder type for Otta seal projects
– Binder spray rates
• It is recommended to increase the spray rate due to the high water content in emulsions
• Iowa and Minnesota experience is 2.3±0.02 liter/m2 , and most of previous projects in Iowa and Minnesota have shown satisfactory performance
• South Dakota tried various binder spray rates on first and second layer Otta seal and performance also varied
50
Equipment
• Asphalt distributor
• Aggregate spreader
• Pneumatic-tired rollers
• Static steel wheel roller
• Broom
51
Construction Sequences
52
Normally not required
Binder type depends on aggregate grading and traffic. Normally MC 3000 or MC 800 viscosity ranges. In hot climate, also 150/200 pen. bitumen grade
A wide range of aggregates can be used, fines included. Both mechanical chip-spreaders and labor based methods can be used in the spreading of aggregate
Excessive rolling with pneumatic tire rollers is essential to achieve a good result. Sufficient rolling in the construction of Otta seals can not be over emphasized!
Compaction and Rolling Mechanism
• Extensive rolling and compaction with 12-ton pneumatic rollers is important to bond the aggregate with the binder
• Fully loaded heavy trucks can be used for rolling and compaction only if mechanical compactors are not available
• The whole operation crew should be in a “train” during the construction
53
Sweeping
• It is important to sweep the surface one month after construction, if Otta seal is applied in only one layer
• However, for double Otta seal, it is required to sweep the surface prior to application of 2nd layer
• It is required that - during the first few months after Otta seal construction - the aggregate dislodge by traffic be broomed to the side of road
• The aggregates should be spread on wheel paths on road surface to prevent any bleeding potential in Otta seal future performance
54
Otta Seal Surface Appearance
55
One day after application Two weeks after application
Three months after application Six months after application
Outline
• Background and History
• Principles
• Guideline
• Summary
56
Summary
• Otta seal method has developed from being an economical “maintenance seal” to a fully fledged bituminous surfacing with few or no other limitations regarding traffic than one would apply to other sprayed bituminous surfacing types
• The Otta seal method is an example of the innovative use of local, often marginal quality materials, in combination with appropriate bituminous binders to produce a durable surfacing
57
Summary (Cont’d)
• Key factors to achieve successful Otta seal projects – Gradation is the most critical property for aggregate selection
but the allowed aggregate gradation limits are in a wide range
– The recommended binder spay rate in NPRA guideline No. 93 for cutback asphalts needs to be modified on the basis of asphalt content in asphalt emulsion (i.e., increasing the spray rate due to the high water content in emulsions
– Aggregate spreading is another critical aspect that influences the Otta seal construction and the resulting performance
– Extensive rolling and compaction with 12-ton pneumatic rollers is important to bond the aggregate with the binder
– It is recommended to train the construction crew and introduce them to Otta seal construction procedures
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TRB Webinar: Using Otta Seal as a Surface Treatment on Low-Volume Roads
#3 Iowa’s Experience & Economics
Brian P. Moore, P.E.Iowa Secondary Road Research EngineerIowa County Engineers Association (ICEA)
Lee Bjerke, P.E.Winneshiek County Engineer, Iowa
Lee Bjerke, P.E.,Winneshiek County Engineer, Iowa
• Winneshiek County Engineer
– 2001 – Present
• Interim Fayette County Engineer
– 2004 & 2013
• Interim Howard County Engineer
– 2006
• NACE Low-Volume Roads Committee, Pavement Preservation Committee, and Emergency Preparedness Committee
• Licensed PE in Iowa, Wisconsin and Minnesota
60
Our Problem
• Winneshiek County has “villages” that had old and dilapidated seal coat streets that were being ignored and were impossible to maintain to any level
• Board was looking for low cost “surfacing” for some roadways that have higher traffic counts
• A few HMA/good condition seal coat roads that needed to be resealed
• Solution – Experiment with Otta seal for village streets, as a surface treatment, and base stabilize roadways and apply a double Otta seal
61
Villages of Winneshiek County
62
Villages of Hesper, Burr Oak, Kendallville, Bluffton, Freeport, Frankville and Festina
<25vpd, mostly car and pickup traffic. Heaviest loads are from County equipment doing maintenance work
Villages of Winneshiek County
• Otta seal $2.50/SY
• Contractor rolled for 3 hours on each Village
• County rolled with partially loaded tandem trucks day two for the entire 8 hour day
63
Villages of Winneshiek County
64
260th St. OttaSeal over poor seal coat
254th St. Otta Seal over granular surfaced road
170th Ave. Otta Seal over fair seal coat
River Road
• 26’ to 28’ wide by 1,300’ long granular road section between two river bridges, 380 vpd, heavy truck traffic due to Gjetley Quarry
• Heavily pot holed, blading lasts maybe a week• Solution – base stabilize with Base One® and apply
double Otta sealCost –• $3.15/SY for Base One® (prep and mixing done by County
forces) • $5.19/SY for double Otta seal (2nd day rolling done by
County forces)• Added 1,500 ton/mile ¾” road stone prior to stabilization
to help strengthen the base $10.50/ton in place
65
River Road
66
Siewers Spring Road
• 24’ wide by 2,400’ long granular road section between DNR Fish Hatchery and Decorah City limits
• 330vpd with negligible truck traffic
• Hilly with washing when we get even light rains. Blades make special trip to maintain, surrounded by paved roads
• $3.15/SY Base One® (prep and mixing done by County forces)
• $5.19/SY double Otta seal (2nd day rolling done by County forces)
• Added 1,500 ton/mile ¾” road stone prior to stabilization to help strengthen the base $10.50/ton in place
67
Siewers Spring Road
68
Looking Forward
• We looked into all roads we would want to Otta seal and had enough material crushed to do that. Roughly half the pile remains
• Due to funding issues (decline in valuation, decline in local option sales tax, decline in road use tax) the second phase of the Otta seal is on hold
69
Winneshiek Conclusion
• Otta seals work!!
• We stuck to the literature put out by the Norwegian Public Roads Administration on gradation, which was over $15/ton to crush. Spendy
• We did use an emulsion vs. a cut back and had no problems
• Roll, roll, roll, roll, roll, roll! Once you are done with that, start rolling it
• Like everything, base is key
• We didn’t beef up our village streets but the prior seal coats lasted for years
70
Otta Seal Construction
71
• Binder spraying
• Aggregate application
• Roller compaction
Otta Seal Surface Appearance
72
72
Three months after application
One day after application One day after application
Six months after applicationSix months after application
Service Life
• Typical range of service lives of bituminous surface treatments
73
Type of seal Typical range of service life (years)
Sand Seal 2 - 4
Slurry Seal 2 - 6
Single Chip Seal 4 - 6
Double Sand Seal 6 - 9
Double Chip Seal 7 - 10
Single Otta Seal + Sand Seal 8 – 10 +
Cape Seal (13mm + single slurry) 8 - 10
Cape Seal (19mm + double slurry) 10 - 14
Double Otta Seal 12 – 16 +
Otta Seal Versus Chip Seal
• The analysis results reveal that Otta seal is more cost effective than chip seal in certain regions without having good-quality aggregate materials
• Transportation cost is a key factor affecting equivalent uniform annual cost (EUAC) for chip seal
7474
Double chip seal
Double Otta seal
0.2 0.4 0.6 0.8
Binder
Service life
Transportation costs
Aggregate cost
Discount rate
EUAC
0.2 0.3 0.4 0.5 0.6 0.7
Binder
Service life
Aggregate cost
Discount rate
Transportation costs
EUAC
0.37 USD/ yd.2 0.58 USD/ yd.2 0.25 USD/ yd.2 0.35 USD/ yd.2
Construction Details
75
COUNTY Cherokee Buchanan Louisa Ringgold
AADT 130-210 30-500 70 60
MILEAGE 5.7 1.2 1 6EXISTING SURFACE
Gravel Gravel, PCC, ACC Gravel Gravel
2018 Otta Seal Construction
Double Otta Seal Construction Costs
COUNTY Cherokee Buchanan Louisa Ringgold
COSTS $55K / Mile $62K / Mile $82K / Mile $43K / Mile
Otta Seal: Cherokee County (Gravel)
76
Spring #1
Otta Seal: Cherokee County (Gravel)
77
Otta Seal: Cherokee County (Gravel)
78
Spring #2
Otta Seal: Ringgold County (w/Base Stabilization)
79
Otta Seal:Buchanan County (w/Base Stabilization)
80
Otta Seal:Louisa County (Slag w/Base Stabilization)
81
Otta Seal:Cherokee County (HMA)
82
Otta Seal:Buchanan County (Concrete)
83
Positive Aspects of using Otta Seal
• Flexibility with respect to the use of locally available natural aggregates for producing the graded aggregate. Thus, crushed or uncrushed aggregate or a combination of both can be used in the construction of Otta seal
• Construction can be performed with county equipment and labor• Existing contractors can construct Otta seal projects without
needing to use any special equipment• Lowered maintenance costs due to reduced need of blading and
adding of aggregate to Otta seal roads• Enhanced durability of pavements and aggregate treated with Otta
seal• Greatly reduced loss of aggregate (dust) of Otta seal constructed on
existing aggregate surfaces• Favorably public acceptance of Otta seal due to reduction of dust
on existing aggregate roads
84
85
Thank You!
Contact Information
Halil Ceylan, Ph.D. Brian P. Moore, P.E. Lee Bjerke, P.E.
813 Bissell Road410 Town Engineering Bldg. Iowa State University, Ames, IA 50011
Phone: +1 (515) 294-8051Fax: +1 (515) 294-8216E-mail: [email protected]
800 Lincoln Way, Building 5, Iowa County Engineers Association Service Bureau, Ames, IA 50010
Phone: +1 (515)-239-1419E-mail: [email protected]
201 W. Main Street, Winneshiek County Engineer’s Office Decorah, IA 52101
Phone: +1 (563)-382-2951Fax: +1 (563)-387-3906E-mail: [email protected]
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TRB Webinar: Using Otta Seal as a Surface Treatment on Low-Volume Roads
#4 Questions & Answers
Moderated byAndrew Dawson
Chair: TRB Aggregates Committee
88
Questions & Answers
Using Otta Seal as a Surface Treatment on Low-Volume Roads
That concludes our webinar
Thank you for attending
Special thanks to Brian, Halil & Lee
If you have further questions, please contact the appropriate speaker …
… or contact me and I’ll try to get one of our speakers to respond electronically
89
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