Clod Smashers

Before there can be pavement, there must be packed dirt

Compaction Article April 16, 2003
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Buy a can of coffee at the store. Bring it home. Dump it out
on the kitchen table. Then sweep it over the edge of the table so it falls back
into the can and notice that it does not all fit until you rap on the can to
make the coffee granules pack down.

"What we have just done is introduce vibration to the
contents of the can," Steve Wilson, manager of marketing services at
Compaction America, told ROADS & BRIDGES.

Wilson likes to use the coffee analogy to illustrate
compaction, one of the most important concepts in roadbed prep.

To lay good pavement, there has to be a good, compacted soil
base that will support the level of traffic expected on the pavement and act as
an effective barrier to water, which otherwise might erode the soil and
collapse the road.

How to achieve the desired level of compaction in soil is as
complicated as the different types of soil. The basic types of soil are
granular and cohesive. Granular soils are stone-based, like sand, and don't
stick together in a clump when they are squeezed. Cohesive soils have high clay
content and can be squeezed into a ball. Between granular and cohesive on the
soil spectrum is a world of geology.

Soil compaction experts also consider the amount of moisture
and other ingredients in the soil. When the native soil is not quite right for
a job, other material can be brought in.

"For better compaction control, we're better off doing
multiple lifts rather than one or two major, large lifts," said Wilson.
"We can control the process better in that respect. Just like with asphalt
paving, you typically will see a minimum of two lifts, sometimes three. There's
as much sophistication in soil compaction as there is in asphalt."

Moisture actually helps with compaction by lubricating the
soil particles so they slide against each other and find a more dense
configuration. If the soil at hand doesn't bind together, the roadbed prep
contractor may add water by spraying it on the surface or injecting it into the
ground.

Altering the recipe

If the soil has too much moisture, the contractor may add
lime to dry it out a little.

If the soil is "weak," meaning less cohesive, the
contractor may add a binding agent, typically portland cement, fly ash or
calcium chloride, to make it more like concrete.

More information on another additive that can be used to
stabilize soil for compaction can be found in Use of Cement Kiln Dust in
Stabilizing Clay Soils, a publication of the Portland Cement Association (PCA).

Cement kiln dust (CKD) is a waste product generated by the
production of portland cement. As a waste product, there are no specifications
for it, so its properties can vary quite a bit from one production plant to
another.

"If you look at a typical cement production facility,
and they are producing more or less uniform CKD, and you knew the specific properties
of that material, then you could successfully incorporate it into various types
of soil," Mike Ayers, a spokesman for the American Concrete Pavement
Association, told ROADS & BRIDGES, "because CKDs don't tend to change
all that much within a production plant."

The other additives are proven commodities. The primary
advantage of CKD is its relatively low cost.

CKD can be used to increase the strength of clay soils,
lower their plasticity or reduce their expansion characteristics. The
properties of a CKD-soil mixture depend a great deal on the size of the CKD
particles, the soil type and the free lime available in the CKD.

Ayers does not think CKD use will increase significantly in
the short term to the exclusion of lime, cement and fly ash, but if there is a
cement production plant near a soil jobsite, the CKD can be put to good use.

Measuring dirt

It also is possible to overcompact and damage the structure
of the material. To make sure that does not happen, Compaction America's Bomag
brand manufactures the Terrameter. The Terrameter makes it easier to find the
proper density by riding on the roller and measuring the density throughout the
compaction process.

The BTM 05 Terrameter continually measures stiffness,
settlement, deformation and load-bearing capacity of soil and granular
materials. As the Terrameter passes across the ground, the measuring system
continually produces an Omega value, a measurement of compaction quality. The
Terrameter monitors interaction between the acceleration of the vibrating drum
and the dynamic stiffness of the material, which increases as compaction
progresses.

During each measuring pass, the Terrameter calculates the
average Omega value and compares it with previous passes. An indicator on the
instrument panel displays the average Omega value. Poorly compacted spots,
represented by low Omega values, can be identified and located on the printout.

A green light on the control panel indicates the roller is
compacting effectively. If the required Omega value is achieved before the
green light goes out, the operator may finish compacting the area and print the
results. If the average Omega value increase between two passes is minimal, the
green light will go out, signifying that maximum economical compaction has been
attained.

The Terrameter can be field or factory installed on all
models of the Bomag BW213-3 Series and the BW219DH-3 model.

One of the newest of Compaction America's soil compactors is
the Hypac C840C single-drum vibratory roller series. The series includes the
22,928-lb C840C, a smooth-drum model that works best on granular, mixed and
semicohesive soils, and the 25,089-lb C842C, which features 150 individual
contact pads for performance on cohesive soils.

Both rollers feature 144-hp, water-cooled diesel engines and
hydrostatic travel and vibration drives. Both offer dual amplitudes and
operating frequencies of 2,160 and 1,800 vibrations per minute (vpm).

In high amplitude, the C840C achieves a maximum of 53,100 lb
of centrifugal force, while the C842C produces a maximum of 61,875 lb. Maximum
working speed for both units is 8.4 mph.

Products

What follows are brief descriptions of a few of the roadbed
preparation product announcements we have received recently. It is not meant to
be a comprehensive survey of products currently on the market.

Greetings from Tampa

After months of selecting the right kind of technology,
engineering and design, Minneapolis-based Caterpillar Paving Products Inc.
unveiled seven new machines--the AP-655C asphalt paver, the CB-534D and CB-534D
XW asphalt compactors and the 500E Series vibratory soil compactors--at a
Florida press event on Jan. 24.

The 500E Series soil compactors--CP-563E, CS-563, CS-573E and
CS-583E--introduced in Tampa carry Caterpillar's dual pump propel system. The
innovation provides separate hydraulic flow to the rear wheels and the drum for
improved tractive effort in soft underfoot conditions or steep slope
applications and allows for control on a grade in forward and reverse.

The CS-563E (smooth drum) and CP-563E (padfoot) are designed
to handle compaction where common fill lift thickness is less than 12 in. or
where density requirements do not exceed 95% of standard Proctor. The CS-573E
(smooth drum) works with fill lift thickness greater than 12 in. and when
density requirements exceed 95% of standard Proctor. The toughest of the set,
the CS-583E (smooth drum), is for very demanding applications where common fill
lift thickness is greater than 18 in. or where density requirements exceed 98%
of standard Proctor.

Smaller is better

Shannon Chastain Enterprises Inc., Eatonton, Ga., has found
a niche for itself in making graders that are the right size for jobs on the
scale of driveways, parking lots and subdivision streets.

The company started building the Basic 601 Hydrostatic
Articulating Grader last fall. It can be trailered behind a 1-ton pickup. It is
powered by a 49.5-hp, four-cylinder engine.

The graders in the Chastain line can be equipped with a
laser grading system, Shannon Chastain, the owner of the company, told Roads
& Bridges. "You set up the transit level to the grade depth that
you're looking for and you're able to get within 1/8 or 1/4 in. of perfect grade.
Tennis courts or certain parking pads require that close tolerances."

The Basic 601 grader sports an 8-ft reversible blade that
can turn 40° left or right. The blade can shift 2 ft side to side, and it
also can tilt 40°. The grader can be outfitted with a dozer blade, a loader
bucket, a scarifier or a light package.

Higher accuracy

Two new versions of the 5600 Total Stations are available
from Trimble Navigation Limited, Sunnyvale, Calif.--the Trimble 5601 DR Total
Station and the Trimble 5601 IR Total Station using an infrared EDM.

The Trimble 5601 DR Total Station delivers an accuracy of
±1 mm to a single prism up to 5,000 m away.

The Trimble 5601 IR Total Station has an angular accuracy of
1° and control unit flexibility for use in applications such as control
work, deformation monitoring and industrial applications. Its infrared EDM is
accurate to ±0.8 mm up to 50 m and to ±1 mm up to 2,800 m.

Redesigned graders

The Laterra line of motor graders has a unique blade
geometry, according to Komatsu America Corp., Vernon Hills, Ill., that allows a
true 90° bankslope position for easy blade maneuvering while providing
exceptional reach and ground clearance.

The line ranges in operating weight from 30,535 to 34,390 lb
and in horsepower from 140 to 200 hp. Variable horsepower is available for all
models.

Lightweight roller

The 3,088-lb AR-13H tandem drum roller is built for asphalt
and sublayer granular and mixed soil compaction jobs. The AR-13H from
Multiquip, Carson, Calif., boasts 3,100 lb of centrifugal force with 4,000 vpm.
It has a 35.7-in.-wide drum and travels at up to 4.8 mph.

The AR-13H sports a 1.25-in. clearance on the right side for
close operation near walls and obstacles, a 19-in. curb clearance ensuring
flush compaction to the curb and unobstructed driver sight lines. The AR-13H's
front drum vibration with static rear drum provides a smooth surface.

Breaking rocks in the roadbed

For those times when life throws a boulder into your path
and you decide to break through it instead of pulling it out or going around,
Tramac Corp., Parsippany, N.J., offers the 125SX hydraulic breaker. The
1,000-ft-lb hammer easily mounts to skid-steer loaders, loader backhoes, small
excavators up to 22,000 lb and Tramac Standard Duty Rockbreaking Boom Systems.
The 125SX is designed for medium-to-hard breaking operations in rock, concrete,
asphalt and industrial materials.

The 125SX comes with two features unique to Tramac: an
Energy Recovery Valve (ERV) and a Built-in Pressure Regulator. The ERV system
recycles rebound energy, adding it to the next blow. The Built-in Pressure
Regulator maintains correct operating pressure for constant performance.

Pushing through

For jobs that require pushing earth rather than pounding it,
Caterpillar Inc.'s latest wheel dozer incorporates the Peoria, Ill., company's
latest clean-burning engine technology and the Advanced Diesel Engine Module.
The control system improves the performance and fuel efficiency of the 814F
wheel dozer while reducing smoke and emissions. The control system also speeds
diagnostic time and allows the engine to be integrated with the electronically
controlled planetary powershift transmission.

The result is a 47,877-lb machine with 240 net hp and a
blade capacity of 3.49 cu yd.

Rugby, anyone?

The latest automatic self-leveling laser from Leica
Geosystems GR LLC, Grand Rapids, Mich., is the Rugby 100LR for general
construction functions, such as concrete forming, pad placement, setting
foundations and elevation indication. It has a working range of 2,500 ft, an
automatic elevation alert function, manual grade up to ±10% and
automatic cross-axis self-leveling. Its housing of high-impact plastic and
rubber is built to be rugged. A simple five-switch keypad controls all
functions.

Wide beam

The latest auto-tracking total stations from Topcon
Positioning Systems Inc., Pleasanton, Calif., employ a "wide beam"
tracking system to lock on to and follow the reflector even as it moves through
brush and around trees. The faster servomotor in the GTS-810 Series tracks the
prism at 10°/second to ensure quick re-acquisition of the prism whenever
obstructions "unlock" the beam. Three models are available with
accuracies of 1, 3 and 5 in., respectively.

About the author: 
Allen Zeyher is Associate Editor of Roads & Bridges.
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