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.
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.
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.
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.
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.
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.
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.
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.
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.