Recyclin Roads

7/31/2019 Recyclin Roads

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The Road

Recycled

F U L L - D E P T H R E C L A M A T I O N W I T H C E M E N T

Reuse existing materials on site

Extend pavement life with a stronger base

Save natural resources and money

Recycling Renaissance:

FDR with Cement


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P o r t l a n d C e m e n t A s s o c i a t i o n

Roads are a national resource. Roads have made it pos-sible for this country to reach social, economic and mil-

itary sophistication. Its important that we do all we

can to preserve them, maintain them, update them and rehabilitate them

as needed. The reauthorization of TEA-21 will have an impact on

what the future holds for this precious resource but even at the high-

est conceivable level of passage there will always be the need to

stretch the dollars as far as possible.

Typically when we think of roads, we think of the Interstate system

and urban traffic congestion. We often forget about the thousands of

miles of rural, farm-to-market roads, secondary roads and service

roads that are just as important to the overall function of our road sys-

tem. These too must be maintained and updated. While there are

any number of approaches to road reconstruction, In-Place Full-Depth

Reclamation or Recycling with cement offers everyone a win-win sit-

uation: its cost effective and stretches tax dollars; it can be done in

a relatively short time frame; with cement, its durable and long last-

ing. This process rebuilds worn out asphalt pavements by recycling the

existing roadway. The old asphalt and base materials are pulverized,

mixed with cement and water, and compacted to produce a strong,durable base for either an asphalt or concrete surface. Since the old

material is being used, it doesnt have to be hauled away, and new mate-

rial doesnt have to be brought in.

A surface consisting of a thin bituminous chip seal, hot-mix asphalt,

or concrete completes the road. The recycled base will be stronger, more

uniform, and more moisture resistant than the original base, resulting

in a long, low-maintenance life. The most important factor is that

recycling costs are normally at least 25 percent to 50 percent less than

the removal and replacement of the old pavement.

Conserving virgin construction materials through recycling with

cement makes smart economic and strategic sense. Our aggressive coast-

to-coast growth over the last century has seriously depleted once

plentiful aggregate supplies. Unless youre in the business, you never

realize how expensive rocks are. In many areas aggregates either come

from distant quarries at great expense or from local sources offering

only marginal quality. Continuing to exhaust these valuable resources

to rebuild existing roads only exacerbates the problem.

If the old asphalt and base materials are not recycled, they must

be disposed of or stockpiled, increasing transportation costs and

using valuable landfill space. In some regions, old asphalt can no longer

be land filled. Environmental laws are becoming strict, adding to the

expense of mining new materials and disposing of the old.

Recycling old roads with cement makes them a renewable resource.

The original investment in virgin road materials becomes a one-

time cost, which is renewed through cement stabilization and addition

of a new, thin surface course. Stabilizing the old road, its asphalt

surface, granular base, and underlying sub grade soil with cement, cre-

ates a strong pavement foundation.

The basic procedure is simple. The complete recycling process can be

finished in one day, and local traffic flow restored almost immediately.

How Do You Do It?

The procedure includes the following steps:

Thickness Design Pavement thickness can be determined by

using PCAs Thickness Design for Soil-Cement Pavements (EB068).

Other methods, such as the American Association of State Highway

Fu l l -Depth Rec lamat ion With

Cement


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and Transportation Officials (AASHTO) Guide for Design of Pavement

Structures can also be used.

Site Investigation The site should be investigated to determinethe cause of failure. Cores or test holes should be used to determine

layer thicknesses and to obtain samples of the material to be recy-

cled (which can include asphalt surface, base course aggregate,

and subgrade).

Lab Evaluation Material samples from the site should be pulver-

ized in the lab to create an aggregate-soil mix that will be similar to

that expected from the recycling process. The mix design procedure is

the same as that performed for soil-cement. Refer to PCA publication

EB052, Soil-Cement Laboratory Handbook. This includes the determi-

nation of maximum dry density and optimum moisture content. If

unconfined compressive strength is used to determine cement content,

a 7-day strength of 300 to 400 psi is recommended.

Pulverization The first step in construction is to pulverize the road-

way with a machine similar to a giant roto-tiller. It pulverizes and

blends the asphalt surface with the base. There are several manufacturers

that produce machines especially designed for quality full-depth recla-

mation. Pulverization is usually 6 to 12 inches deep, which on secondary

roads will typically include all of the surface and base, plus some

part of the subgrade. To achieve the proper gradation after pulveriza-

tion, more than one pass of the equipment may be necessary. The par-

ticle distribution should have 100 percent smaller than 2 inches (50 mm)and 55 percent passing a No. 4 (6-mm) sieve.

Shaping And Grading The

pulverized material is shaped

to the desired cross-section

and grade. This could involve

additional earthwork in order to

widen the roadway. Final base

elevation requirements may

necessitate a small amount of

material removal or addition.

Spreading Cement Cement

is spread in a measured

amount on the surface of the

shaped roadway, in either dry

or slurry form.

Water Application Wateris added to bring the aggre-

gate-soil mixture to optimum moisture content (water content at max-

imum dry density as determined by ASTM D558), either in front of the

pulverizer/ reclaimer or in the mixing chamber.

Mixing The aggregate-soil-cement-water mixture is combined and

blended with the pulverizing/ reclaimer machinery. Depending on the


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Write In 136 - Or Reply Online

Full-Depth Reclamation

with cement, or FDR,

uses old asphalt and

underlying base

material to build a

new road. Existing

pavement is pulverized,

mixed with cement and

water, and compacted

to produce a strong,

durable base for

either an asphalt or

concrete surface.

Existing materials are

recycled on site. Theres no

need to haul in new aggregate

or haul out old materials for

disposal. FDR conserves

natural resources, saves

energy, and reduces waste.

A stronger base means

longer life. Stronger than

an unstabilized base, acement-stabilized base

FDR is an economically

and environmentally

sound decision

0022-03-343

keeps water out and standsup to heavy, constantlyincreasing traffic loads,reducing maintenance andprolonging pavement life.

Recycling saves money.FDR with cement costs up to

50% less than removal and

replacementof old pavement

or thick overlays.

To find out more, visit our Web site at

www.cement.org/FDR

Recycle Failed Pavement withCement

Recycle Failed Pavement withCement


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There are many opportunities to gain from the environmental

and economic advantages of Full Depth Reclamation (FDR) with

cement. Although the most obvious applications are rural roads,

virtually any paved surface in need of rejuvenation, especially if there

are indications of base problems, is worth consideration.

Essentially what has to happen is the old pavement has to be pul-

verized, in place and then mixed with the original base materials.

Cement is spread across the surface either as a dry material or

slurry mix. Water is added. The ingredients are mixed in place and

the material compacted and then allowed to cure before the finish

surface is applied.

The end-result quality depends on:

The pulverization

(100 percent smaller than 2 inches)

The cement content

The moisture content

The mixing

The density The curing

Milling machines and reclaimers are not the same machine. Prob-

ably the most significant difference is that milling machines discharge

the removed road materials while reclaimers retain these materials in

a mixing chamber and discharge them back onto the roadbed from which

they were removed.

The basic makeup of a reclaimer includes: the drive unit and the

milling/mixing unit; operators station; rotor; mixing chamber; water tanks;

chassis or frame; drive axles and steering axles; brakes; a host of

sophisticated electronics and multiple hydraulic systems. Typical

options include items like working light packages; four-wheel drive (if

this is not a standard feature); water spray systems; emulsion systems

and other interesting goodies designed to make the operator more

comfortable and more productive.

In the U.S. there are four manufacturers producing and distributing

reclaimers: Bomag, Caterpillar, CMI and Wirtgen. These machines

are designed, engineered and manufactured to handle FDR projects effec-

tively and efficiently.

Bomags offerings include the MPH 122 Stabilizer/Recycler; the MPH

362/364-R/S/SDM Recycler, Stabilizer, Stabilizer Deep Mix; and the MPH

454 R/S Recycler/Stabilizer. All the machines feature hydrostatic

drive. All wheel drive is standard on all of the machines except the MPH

364 that has a front wheel drive option.

The operators station is designed to be comfortable and ergonom-

ically friendly giving the operator good visibility and easy-to-use

controls. The equipment is designed for easy maintenance with

major components positioned for easy access and service. Accord-

ing to Bomag the cutting teeth are quick and easy to replace. The rotor

end segments are bolted on and in case of excess wear, can be

replaced without removing the rotor.

On the 362/364 models there is a selectable 2-speed rotor design to

give the operator better control over production volume. The 454 features

a selectable 3-speed rotor, and on the 122 the rotor is a variable speed

unit. Four-wheel drive and steer are standard features on these machines.

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Bomag MPH 122 MPH362/364 R/S/SD MPH 454 R/S

Operating Wt. 45,636 lbs 39,000 lbs. 46,300 lbs.

Engine horsepower 442 360 450

Working speed 211 fpm 187 fpm 221 fpm

Rotor configuration Center slung Rear slung Rear slung

Rotor Drive Hydrostatic Hydrostatic Hydrostatic

Rotor Width 91.7 in. 79 in. 96 in.

Outside diameter 48.2 in. 44/48/59.5 in. 48 in.Max cutting depth 19.7 in. 12/14/21 in. 15 in.

Number of teeth 194 168/70/70 196/82

Cutter direction Upward Upward Upward

Cutter speeds 2 2 3

Equipment For

Fu l l -Depth Rec lamat ion/Recyc l ing


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Caterpillar has two models, the RM-250C and the RM-350B.

Both machines can be converted from a reclaimer configuration to a

mixer or stabilizer on the job. On the 250C you have 3 rotor options,

breakaway reclamation, quick-change stabilization and combinationrotors. The teeth in the breakaway and combination rotors can be

replaced without welding.

Both of the Cat machines use mechanical drives to operate the rotors.

On the 250 a direct mechanical drive transfers engine power to the

rotor and has 3 operating speeds to better match the materials being

reclaimed and the depth of the cuts. A heavy-duty shear disc or

optional torque limited protects the rotor drive

components from torsional stress and shocks.

Drive chains, rated at 135,000 pounds, are

located on both ends of the rotor. On the 350B

the rotor drive is the same except that a Cat

powershift transmission is used to transfer

engine power to the rotor.

On both models the rotor and mixing cham-

ber are mid-mounted to take advantage of the

machines weight. They come standard with an open operators station,

and a ROPS and cab option.

The 250C is front wheel driven but there is a rear wheel assist

option that increases the tractive effort by 22 percent in first gear,

34 percent in second and 64 percent in fourth. The bigger 350B is

an all-wheel drive unit.

Depth of cut can be controlled manually or automatically with an actu-

al rotor height displayed on machines dashboard. Sophisticated elec-tronics and state-of-the-art hydraulics are designed to minimize operator

fatigue and frustration. Four-wheel drive and steer are standard.

CMI Terex has five models available. They manufacture a wide range

of cutters to expand the application possibilities for these machines.

The RS 325 is the only one of the lineup that has a rear slung rotor.

The other models are center mount. 4-wheel drive is standard on all

models. All models come with 4-wheel steer as standard with vari-

ous steering configurations from which the operator can select.

On the 500C, 650B and 800 models a microprocessor based con-

trol system automatically maintains cutting depth, cross slope and

travel speed. An engine load sensing system automatically adjusts

travel speed to cutting conditions. LCD readout provides the oper-

ator with continuous display of machine functions.

Options, depending on the model include a larger cutter mandrel that

increases the cutting depth to 20 inches; ROPS; water spray systems,

asphalt distribution systems and a Kennametal change random pattern

cutter mandrel.

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CMI Terex RS-325 RS-425 RS-500C RS-650B RS-800

Operating weight 31,200 lbs. 49,000 lbs. 60,460 lbs. 63,500 lbs. 67,500 lbs.

Working speed 200/360 fpm 175 fpm 210 fpm 210 fpm 210 fpm

Horsepower 330 425 525 650 800

Rotor Configuration Read slung Center Center Center Center

Rotor drive Mechanical Mechanical Mechanical Mechanical Mechanical

Rotor width 75 in. 96 in. 96 in. 96 in. 96 in.

Rotor diameter 50 in. 50 in. 50 in. 50 in. 50 in.

Cutting depth 16 in. * 16 in. 16 in. 16 in. 16 in.

Number of teeth 223 218 218 218

Cutter direction Upward Upward Bi-directional Bi-directional Bi-directional

Cutter speeds 2 3 4 4 4

Caterpillar RM-250C RM-350B

Operating weight 35,635 - 37,000 lbs. 48,270 - 53,680 lbs.

Engine horsepower 335 500

Rotor Configuration Breakaway/combination/ Breakaway/combination/

stabilizer stabilizer

Rotor Drive Mechanical Mechanical

Rotor width 96 in. 96 /90 in.

Outside Diameter 45/48/54 in. 52/54/58 in.

Cutting depth 13/15/18 in. 15/16/20 in.

Number of teeth 180/108/58 188/200/58

Cutting direction Reclaimer - upcut Reclaimer -upcut

Stabilizer --downcut

Cutter speeds 2 3


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According to the manufacturer, the mechanical rotor drive system

increases productivity. On the 3 larger machines elevation control is

manual or automatic with individual controls for the left front, left rear

and right side. An optional cross slope control is available.

Wirtgen has two models the WR 2500 S and the WR 2500 SK. The

2500 S has a wide cutter option available. One of the features is the

volume of the mixing chamber adjusts automatically according to the

amount of material being processed. The manufacturer describes the

operation station as a fun place to work. The operator can run the

machine from an optional fully enclosed cab.

All machine functions are activated through microprocessors. The

operator has access to critical operating information with Wirtgens Con-

trol Graphic Center (CGC), which lets him monitor any and all functions

at any time. Milling depth is displayed on the CGC panel.

Automatic power control adjusts the feed rate as a function of the

engine load. The operator can deactivate the system and control the

feed manually.

Tool change is quick and easy. An optional hydraulically driven

drum turning attachment makes it easier to rotate the drum while

changing tools.

The Wirtgen machines feature 4-wheeld drive and 4-wheel steer as

standard. The manufacturer has a variety of options that make it pos-

sible for machine owners to fit the machine to their application needs.

As noted, there are other ways of doing FDR but none are as effi-

cient as using a machine specifically designed for this application. The

combination of these machines and the economic benefits offered

by FDR make it possible to stretch highway dollars for miles.

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Wirtgen WR 2500 S (std.) WR 2500 (opt.) WR 2500 SK

Operating weight 72,600 lbs. 75,460 lbs. 82,720 lbs.

Working speed 49.2 to 655 fpm 49.2 to 655 fpm 49.2 to 655 fpm

Horsepower 670 670 670

Rotor configuration Center Center CenterRotor drive Mechanical Mechanical Mechanical

Rotor width 97.5 in. 121.9 in. 97.5 in.

Rotor diameter 59.2 in. 59.2 in. 59.2 in.

Cutting depth 20 in. 20 in. 20 in.

Number of teeth 224 224 224

Cutter direction Bi-directional Bi-directional Bi-directional

Cutter speeds 4 4 4

A good foundation is important for any structure, especiallypavements. The pavement base provides the thickness andstiffness necessary to carry heavy traffic loads.

Stabilized pavement bases, such as soil-cement and cement-treat-ed base have provided economical, long-lasting pavement foundationsfor over 60 years. These pavements combine soil and/or aggregatewith cement and water, which are then compacted to high density.

The advantages of stabilization are many:Cement stabilization increases the stiffness and strength of the base

material. A stiffer base reduces deflections due to traffic loads,which results in lower strains in the asphalt surface. This delaysthe onset of surface distress, such as fatigue cracking, and extendspavement life.

The strong uniform support provided by cement stabilization resultsin reduced stresses applied to the subgrade. A thinner cement-sta-bilized section can reduce subgrade stresses more than a thicker layerof untreated aggregate base. Subgrade failures, potholes, and roadroughness are thus reduced.

Moisture intrusion is the nemesis of pavement bases. Cement-sta-bilized pavements form a moisture-resistant base that keeps waterout and maintains higher levels of strength, even when saturated.

A cement-stabilized base also reduces the potential for pumpingof subgrade fines.

Start With A Good Foundation

A stabilized base spreads loads and

reduces stress on the subgrade.

Unstabilized Granular Base Cement-Stabilized Base


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In recent years, the highway industry throughout the

United States has become increasingly concerned

about extensively deteriorated and under-designed

pavements. Many of these pavements have long passed the

time for which they can be effectively patched or spot

repaired in order to accommodate an economically feasible

or effective overlay. Cold, in-place full depth recycling is

proving to be a solution to these problems.

South Carolina Route 97 in York County had been an

extreme and constant maintenance problem for many years.

This section of distressed pavement stretches from the

Chester County line north to Hickory Grove, a distance of approxi-mately 16 miles.

Originally constructed in the 1930s as secondary roads 33 and 39, Route

97 was first improved in 1948 as SC Route 907 and Road 39 by Dicker-

son Incorporated, of North Carolina, for a cost of $144,055. In 1975

another 10-mile section of the highway was reconstructed.

Shortly after the completion of this road, slips and other forms of

pavement stress began to appear. The department investigated these

problems in depth, but no definitive answers could be reached.In 1983, after years of problems, the department let a resurfacing

contract to overlay the worst sections. Once again problems sur-

faced as slips and failures began to occur. None of these occur-

rences could be directly tied to the asphalt mix since it met all

department requirements, and no problems had been noted at the plant

or in the lay-down process.

For the next 12 years, this highway deteriorated rapidly and required

weekly maintenance. The work consisted of failure repair

through partial or full-depth patching. In areas where con-

stant problems kept reoccurring, the DOT had to remove and

replace extreme depths with asphalt. These costs amount-

ed to approximately $34,500 per year.

In addition to these routine maintenance procedures, the

department scheduled full depth repair using a Bomag on

some occasions, trying to better and more permanently repair

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Rehabi l i ta t ing

Above: A view of a deteriorated roadway prior to rehabilitation.

Left: The finished roadway prior to the application of the asphalt con-

crete binder course and surface course.

Route 97Cold, in-place full depth recyclingis proving to be an effectivesolution for damaged roads.By Frank S. Bland Jr., P.E., District Four Construction Engineer,

South Carolina Department of Highways. Edited by Christina

Fisher. Pictures courtesy of Site-Prep, Inc. of N.C.


9/15

areas where standard methods

just did not do the job. These

repairs created additionalexpenses amounting to

$25,000 over five years.

To free the maintenance

unit of this constant respon-

sibility, the department decid-

ed to let this section of

roadway to contract. The main concern was finding the best method

of repairing the existing pavement and applying a suitable overlay that

would be maintenance free and provide the public a uniform section

of pavement for which they had so patiently waited.

Because the condition of the pavement was so poor, it was decid-

ed that the most effective way to rehabilitate the road would be to use

in-place recycling by incorporating cement

into the top 6 inches of the pavement

and base/sub-base to create a stable

foundation upon which the remainder of

the pavement structure could be placed.

Cold, in-place full depth recycling,

or reclaiming of flexible pavement, is arehabilitation technique in which the

existing bituminous surface and part or

all of the underlying base

and/or sub-base materials

are pulverized in place to a

specified particle size range

and mixed cold with either

standard or non-standard

additives to form a new sta-

bilized base course.

In order to meet the

design criteria, the top 6

inches of cement modified

base was followed by the

placement of a type A single

treatment. This treatment

would act as a seal to hold

in the moisture and provide a temporary surface on which traffic

could continue to move. This would then be overlaid with 225 pounds

of asphalt concrete binder

course and 175 pounds of

asphalt concrete surfacecourse.

Once the department decid-

ed upon this method of con-

struction, the contract and

special provisions for this new

venture were developed,

although the department had limited knowledge and no practical

experience in this relatively new technique. The prices had to be

assumed in order to come up with some estimated cost. Therefore, it

was determined that the department would let the contract for only a

10-mile portion of the road. The remaining six miles would be added

if the contract amount was less than the estimate cost but in an

amount great enough to cover

the additional length.

Sloan Construction Compa-

ny of Greenville, South Car-

olina, won the contract with a

bid of $1,611,538, which

allowed for the completion ofthe additional six miles. Sloan

Construction subcontracted

the base work to Base Con-

struction Company, Inc, Colum-

bus, Ohio, which specializes

in this type of construction.

Base Construction representatives

explained the process and discussed

any problems that could be encountered

during the project.

The prime contractors plans were

to begin placing the surface treatment

approximately three days behind the

stabilization procedure. Two days after

this, the placement of binder would

follow and continue until the entire

roadway had been overlaid. The final

riding surface placement would begin if time and weather permitted.

Since this work was beginning in a traditionally poor time of year for

12


Various rollers and compaction equipment are then used on the new road bed toachieve the correct density.

It would have cost the department

$1,637,375 to prepare the base for theasphalt layers. The price to stabilize the entire

length of the project was $513,480.

This amounted to a savings of 69 percent.


10/15

construction, weather would play a major role in how far

we could go.

Base Construction moved onto the job and began workon November 13, 1995. Progress was slow at first as the

contractor and department personnel began to get a feel

for the types of materials onsite and how they compared

with jobs already completed in other areas of the country.

During this learning phase, Hamm Corporation sent their

specialist, Ace Wise, to our location to share his expertise

with the department.

It was decided that the temperature restrictions for

soil cement could be relaxed somewhat due to the ground

temperature in this region and the heat of hydration from

the process. Looking at results from other areas of the coun-

try, it was decided that we could begin work at 25 degrees

Fahrenheit and rising as long as we anticipated temperatures to get

above 35 degrees during the day.

Due to the near 100 percent compaction effort, the department

determined that light passenger vehicles could immediately use the road

with no damage. The road was detoured for all vehicles with six tires

or larger in an effort to protect the treated area from extreme and dam-

aging loads.With the wide variation in pavement thickness and the need to run

with some consistency to create a continuous beam effect, the con-

tractor asked that the department consider placing a 9-inch stabilized

depth in all areas to avoid jumping back and forth from 6-inch to 9-

inch depths. This would create consistency with only a few areas need-

ing 12-inch treatment.

To begin the stabilization procedure, cement tankers placed raw

cement onto one lane of Route 97 to create a 6 percent addition. This

cement was then blended into the structure with two overlapping pass-

es of a Hamm RACO 250 soil stabilizer-asphalt/recycler. The properamount of water was added by the equipments spray system, which

has the capability to meter out the exact amount specified to achieve

maximum compaction.

Productivity, which was measured by the number of feet per

mile, varied as the machine encountered pavement of varying

thicknesses and composition. However, on an average, the

machine traveled at a speed of 30 feet/minute under ideal con-

ditions. We placed a maximum of 10 tankers of cement in a

one-day period. However, on the average, we placed between

five and six tankers per day. This would amount to stabilizing

a 12-foot lane for a distance of approximately 3,500 feet, or

approximately 5,000 square yards of stabilization.

Once the machine had completed its passes, the spreading

and shaping operation began using a motorgrader. As a part

of this spreading operation, the mixture was shaped so that

13


Above: Water is added during the blending process and while the newroad bed cures.

Left: A layer of cement is placed on the roads surface to be blended with

the pulverized road bed with the asphalt/recycler.


11/15

when compacted it was within close conformity with the lines, grades

and cross-sections that originally existed.

The compaction and finish grading came next. The mixture should becompacted when it will bear the weight of the roller or compactor

without undue displacement, cracking or shoving of the premixed

materials. A suitably sized, single drum vibratory padfoot compactor nor-

mally achieves initial density of the loose, newly reclaimed base course.

On our project the initial and final density was accomplished using a Hamm

2520 vibratory padfoot roller.

The Hamm GRW 5 pneumatic roller then finished rolling the area to

mechanically seal the surface and to complete our compaction process.

It also served as a proof roller for the area and indicat-

ed any possible soft spots. The new base was com-

pacted to an average density of 98 percent of standard

proctor density.

The area was allowed to cure under light traffic (pas-

senger vehicles) by maintaining a water type curing

process for three days, which was then followed by the

placement of bituminous surfacing single treatment.

This sealed the road and minimized damage, allowing light

traffic to continue to travel the area. All heavy loads

were detoured.The cold, in-place, full depth flexible pavement recy-

cling was completed and the remainder of the work

was no more than a resurfacing project. This amounted

to the placement of 225 pounds per square yard of an

asphalt concrete binder course and 175 pounds per square yard of

asphalt concrete surface course.

There are many advantages and benefits to this process, and some

of these include:

All work takes place on the

existing pavement section.

Full-depth reclamation resulting

in a stable base at significant savings

over conventional methods.

Reuse of natural resources.

Ability to eliminate reflective cracking.

Improved resistance to water

penetration of the subgrade.

Adaptability to treat all types of

reflective pavement distress.

Minimal hauling costs, as the

procedure occurs in place.

Traffic can be maintained duringthe reclamation proceedings.

Reclamation process is environmentally safe.

The speed of the operation allows for minimum

inconvenience to the public.

Provides good beam effect that distributes traffic load evenly

throughout pavement.

Asphalt rates can be reduced due to the increased strength

of the new base.

Using this process, we obtained a much-improved base at significant

savings. If this project had been let using conventional means of full depth

patching, it would have cost the department $1,637,375 to prepare the

base for the asphalt layers. The price to stabilize the entire length of the

project was $513,480. This amounted to a savings of 69 percent and

allowed us to complete an additional amount of mileage.

As we neared the end of the project, cores and follow-up testing deter-

mined what structural number we attained and what the actual truck

carrying capacity was. These tests will mean better and more realis-

tic designs in the future.

We will continue to study this project to be better able to evaluate

cold, in-place, full depth flexible pavement reclamation. However, from

visual observation and the growing number of states beginning to

use this process, we feel it is definitely a viable technique to rehabilitate

roads that have extensive failures and base problems.

14


Once the new base material has been blended, spreading and shaping can begin with a motorgrader.


12/15

type of mixing equipment, uniform blending of materials can usually

be achieved in one pass of the mixer.

Compaction Although requirements vary, the mixture is compact-

ed to a minimum density of 96 percent to 98 percent of standard

Proctor density (ASTM D558). The compaction is usually performed with

smooth-wheeled or sheeps-foot vibratory rollers. A pneumatic-tired roller

may follow to finish the surface. Final compaction should take placeno more than 3 hours past initial mixing of the cement. The field den-

sity and moisture are monitored for quality control purposes.

Curing On light-traffic roads, the compacted base can

accept traffic almost immediately after construction. For prop-

er hydration, the soil cement is kept moist by periodical-

ly applying water to the surface. Curing begins immediately after final

compaction and is continued for several days. The application of the prime

coat should occur as soon as possible to ensure that moisture is sealed

inside the base.

Pavement Surface The new pavement surface consisting of a

chip seal, hot-mix asphalt, or concrete is constructed to complete the

recycling process.

Quality Control Recycling with cement follows the same basic pro-

cedures used for normal soil-cement operations. The

success of a recycling project depends upon the care-

ful attention to the following control factors:

Adequate pulverization

Proper cement content

Proper moisture content

Adequate density

Adequate curing

Traffic Control All operations can be performed

under normal construction traffic control. Disrup-

tive road closures are not required.

End Result A high-quality, long-lasting, inex-

pensive road that was reconditioned in a minimal

amount of time with a minimum degree of incon-

venience to its users.

4


Savings in Energy Use

Full-Depth Recycling vs. New Base

Based on 1 mile of 24-foot-wide 2-lane road,

6-inch base and 2-inch asphalt surface

Number of trucks needed

New Roadway Material(tons)

Material Landfilled

(cu. yd.)

Disel Fuel Consumed

(gal.)


13/155


When severe alligator cracking reared its ugly head

along a heavily trafficked truck route cutting

across North Texas, state engineers faced a chal-

lenge. Drop offs along the narrow, hilly two-lane US 79 highway

meant that building detours would be

expensive and impractical. We had

to keep traffic on it while we

strengthened it, says Mark Stur-

rock, assistant area engineer, Jack-

sonville area office, Texas Dept. of

Transportation.

So engineers decided to recycle the

roadway in-place, a process that

allows traffic to flow with construc-

tion underway. They tested lime and

cement to determine which materi-

al worked best, says Sturrock. Full-depth recycling with cement provedthe most efficient way to keep the road open and not double-handle

the material, he says.

In March 2002, crews from Madden Contracting Inc, Minden, La., began

the $7.4-million contract to rebuild an 11-mile stretch of US 79 west of

Jacksonville, Texas. It

was the Jacksonville

offices first full-depth

recycling (FDR) with

cement project.

Madden mixed the

existing asphalt and

base with more than

8,000 tons of cement,

or 4-percent cement

by dry weight, into

333,864 square yards of roadway to create a strong, long-lasting

base. Five inches of Type C asphalt topped the new road.

Finished last February, four months ahead of schedule, the project

was deemed a tremendous success, says Ken Smith, the state

inspector overseeing the project. With cement, you get a tremendous

amount of strength.

Initially though, Smith questioned whether the contractor could obtain

density after pulverizing the existing roadway, mixing in cement 13 inch-

es deep, and compacting in one lift. On the projects first day, DaveKirkland, Maddens project superintendent, used a nuclear density gauge

to show Smith that they were

meeting compaction require-

ments. We were hitting 98

percent density with no prob-

lems whatsoever, says Smith.

And the process is fast. Mad-

den crews processed 10 loads

of cement, or 260 tons, per day.

There really were no nega-

tives but the tempo was fast. It

kept us on our toes, says

Smith. Its simpler than fooling

with lime because you have to

cut lime twice, adds Madden.

The success of the FDR proj-

ect encouraged engineers to design a second one for US 79 now

underway east of Jacksonville. The 10-mile, $6.1-million project is slat-

ed for completion to finish next summer.

Cement St rengthens

US 79By Jeff Hawk

With cement, you get a tremendous amount of strength.Ken Smith, TxDOT inspector

On a completed stretch of US 79 outside New Summerfield, Texas, TxDOT inspector Ken Smith called his first recycling with cementproject a tremendous success.

TxDOT inspector Ken Smith digs up a section ofpulverized roadway to check its depth.


14/15

Performing Full-Depth Reclamation (FDR) on failed asphalt

pavements makes simple sense. The existing in-place

materials are reclaimed instead of importing expensive

virgin aggregates. By building a new stabilized base you provide an

excellent foundation for future pavement performance.

The selection and use of the stabilizing agent to construct the new

stabilized base is not a simple matter. Selecting the wrong stabiliz-

ing agent can lead to expensive premature pavement failures and

early repairs. The most common stabilizing agents in use today for FDR

are: cement, lime, asphalt emulsion, and foamed asphalt. Calcium chlo-

ride is sometimes used to improve compaction and control dust, but

it does not add significant strength to the base.

When designed and built properly, cement will perform well under

almost all conditions. The other agents, however, are nowhere near

as versatile and projects must be carefully screened to see if the con-

ditions are right for their use.

When an existing road is being reclaimed, a high degree a mate-

rial variation will likely be encountered during construction. This is

why versatility in a stabilizing agent is important. Different locations

may have different subgrade and base materials. Another factor is

that different asphalt patches of varying depths and mix may have

been used over the years. The good news is that cement can be used

successfully with virtually all types of aggregate and soil types.

This is not true with other stabilizing agents.

Lime

Lime provides increased strength to compacted soil through a chem-

ical reaction with clay minerals. If these clay particles are not pres-

ent in the reclaimed pavement materials (or if fly-ash is not added to

provide the needed minerals), then no pozzolanic reaction can take place

to provide increased strength.

6


Stabilizing Pavements There s Nothi ng As Versat i le A s Cement

Bad road foundations always cause bad roads.

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15/15


Cement, in contrast, provides its own chemical reaction by reacting

with the water in the reclaimed pavement and providing high strength

through hydration. This reaction will take place regardless of thetype of aggregate or soil. In addition, if clay minerals are present, cement

will also provide the same pozzolanic reaction that lime does, creat-

ing even more long-term strength.

Asphalt Emulsion

Using an asphalt emulsion with the FDR

process leads to a complicated reaction with the

reclaimed asphalt. The emulsion will rejuve-

nate some (but not all) of the old asphalt

cement, leading to a possibility that more emul-

sion may be available than what is desired. If

too much emulsion is present, the mix becomes

too rich and will not compact or cure properly.

On the other hand, if theres too little emul-

sion the particles in the mix will not bond

together and raveling can occur.

In contrast, using cement as the stabilizing

agent simply treats the reclaimed asphalt as

black gravel, and no rejuvenationof the old asphalt cement occurs.

This leads to more uniform con-

struction and fewer surprises in the

field when different amounts of old

asphalt are encountered in the

reclaimed mix.

Foamed Asphalt

This FDR stabilizing agent is cre-

ated by mixing asphalt emulsion

under pressure with cold water,

which foams the asphalt before it is

mixed with the reclaimed materials.

This process is very sensitive to

the mix of reclaimed materials (pro-

portions of old asphalt, gravel, sand,

and fines). If the mixture is not

properly designed, or if conditions

change in the field, failure can occur.

As mentioned, cement is far more versatile and can perform well

under varying mixtures of reclaimed pavement materials. To build the

best product, a cement treated material needs to be properly designedand constructed, but the risks taken by a road agency are much less than

with using other stabilizing agents.

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