Using Otta Seal as a Surface Treatment on Low- Volume...

TRANSPORTATION RESEARCH BOARD

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Using Otta Seal as a Surface Treatment on Low-

Volume RoadsAugust 4, 2020

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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

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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

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“Otta” seals

• Otta

– Small town in Norway (<2000 persons)

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“Otta Seal” surfacing

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• 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

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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

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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

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Heavy Agricultural Equipment

• Low volume of traffic but must support very heavy agricultural equipment

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Regional Characteristics

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Iowa’s Problem

• Roads built with natural material

• Heaving

• Frost boil

• Potholes

• Uncomfortable travel

• Seasonally impassable roads

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Seasonal Effects

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Summer Spring

Spring Thaw

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Spring Thaw (Cont’d)

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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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#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

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http://www.ccee.iastate.edu/

https://www.pegasas.aero/index.php

http://www.intrans.iastate.edu/prosper/

http://www.intrans.iastate.edu/

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

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Outline

• Background and History

• Principles

• Guideline

• Summary

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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.

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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

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• 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

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• Where have the Otta seal been used ?

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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


• USA experiences (Iowa, Minnesota, and South Dakota)

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• Otta seal in Botswana, after 25 years in service!

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Images from Otta seal project site, MN-74, Winona County, MN (Built in 2001)

Outline


• Principles

• Guideline

• Summary

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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

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Mechanism of Performance of Surfacing Types

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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

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Chip seal Otta sealVS.


Types of Otta Seals

• Single Otta seal

– With/without sand cover seal

• Double Otta seal

– With/without sand cover seal

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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

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Second layer

First layer


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

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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

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Grading Requirements

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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

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Outline


• Principles

• Guideline

• Summary

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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

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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

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General Aggregate Grading, Strength Requirements and Spread Rates

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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.)

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Cutback Asphalt and Penetration Grade Bitumen

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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

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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

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Equipment

• Asphalt distributor

• Aggregate spreader

• Pneumatic-tired rollers

• Static steel wheel roller

• Broom

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Construction Sequences

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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

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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

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Otta Seal Surface Appearance

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One day after application Two weeks after application

Three months after application Six months after application

Outline


• Principles

• Guideline

• Summary

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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

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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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#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

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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

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Villages of Winneshiek County

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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


• 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

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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

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River Road

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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

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Siewers Spring Road

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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

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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

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Otta Seal Construction

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• Binder spraying

• Aggregate application

• Roller compaction

Otta Seal Surface Appearance

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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

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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

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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)

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Spring #1


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Spring #2

Otta Seal: Ringgold County (w/Base Stabilization)

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Otta Seal:Buchanan County (w/Base Stabilization)

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Otta Seal:Louisa County (Slag w/Base Stabilization)

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Otta Seal:Cherokee County (HMA)

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Otta Seal:Buchanan County (Concrete)

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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

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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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mailto:[email protected]



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#4 Questions & Answers

Moderated byAndrew Dawson

Chair: TRB Aggregates Committee

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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

[email protected]

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