|
Canada’s “Rock to Road” Magazine
2005
Buyers’ Guide Issue
For a copy of the issue
that contains these articles with colour photos, click
here.
OHMPA
seminar links quality and performance
By Andy Bateman, Engineering
Editor
Quality
= Performance, a relationship that is easy to accept
but hard to prove, was the theme of the 2004 Ontario Hot
Mix Producers Association (OHMPA) technical seminar held in early December
in Thornhill, Ont. Building on this theme, presentation topics also
included the supply, cost and quality of asphalt cement, the increasing
scarcity of quality aggregates in Ontario, a new specification on Superpave
for municipalities and the improvement of longitudinal joints.
The keynote speaker for this year’s seminar was John
Epps who has spent more than 30 years in the asphalt industry as a researcher,
teacher and professional engineer. Epps opened with a broad overview
on major issues facing the hot mix industry, followed by a personal
view on the meaning of “quality” and “performance”
and the challenges of proving the relationship between the two. Issues
noted by Epps included the increased demand for highways, major changes
within the hot mix asphalt industry, funding; environmental, safety,
and health issues, as well as quality. Epps added that although the
findings presented were based on US data, many of the overall trends
affecting the industry were similar to those in Canada.
Demand for highways been increasing rapidly in recent years,
with data for the period 1970 to 1997 showing a 64 per cent increase
in the number of licensed drivers, an 87 per cent increase in the number
of registered vehicles increased by 87 per cent and a 131 per cent increase
in the number of miles travelled. Over the same time frame, however,
the number of road miles has increased by only 6 per cent. This increased
demand has also been occurring during a period of significant downsizing
in public agencies. About two thirds of US State Departments of Transportation
(DOTs) have downsized since 1997 and this trend is expected to continue
as the workforce ages. In parallel with this downsizing, there has been
a significant transfer of responsibility from the public agencies to
contractors who, in addition to construction, are becoming increasingly
involved in design, construction management, quality, maintenance and
operations. Contractors long established low bid approach to winning
work now has the added dimensions of this transfer of responsibility,
reward for quality innovation and interaction with a reduced public
agency workforce. Contractors are now also dealing with Quality Control/Quality
Assurance (QC/QA) programs, end result specifications, warranty or guarantee
programs, design build or design, build and operate programs. In the
future increased revenues are expected and welcome, but this is in conflict
when combined with increased customer demand and reduced agency workforce.
Epps defined quality as having two elements –
the meeting of specifications and customer satisfaction. Meeting specifications
involve the use of measurements of quality and being on target within
those measurements with low variability. Examples include asphalt binder
properties, aggregate properties, and HMA mixture properties. Epps pointed
out that overall QC/QA variability is the sum of variability in three
areas – sampling, test methods and materials and construction.
Sampling variability, for instance, may be due to variations in sampling
location as samples is done up to five locations – asphalt plant
conveyor/or chute, a truck at the plant, a site windrow, the paver hopper
and also from the loose mat behind the paver. Test method variability
occurs within a laboratory and between laboratories, while materials
and construction variability (often assumed to be the main source of
variability) is the net result of variations in the materials and the
construction methods used. Customer satisfaction, Epps’ other
measure of quality, comes from a road that looks good with minimal ravelling,
bleeding, cracks and marks while providing a smooth quiet ride, good
stop performance (friction and hydro planning) and colour.
Epps proposed that performance has three main elements
– structural performance, functional performance, and performance
measurement. Structural performance is a function of the ability of
pavement components such as subgrade and base course to deal effectively
with the applied loads, while functional performance includes ride quality,
noise, friction and colour. Epps differentiated between failure that
was load related such as fatigue cracking and failure due to non-load
related issues such as thermal (temperature related) cracking. Performance
is still mostly measured by visual pavement condition surveys, although
the use of automated devices to measure smoothness, skid resistance
and noise generation is increasing.
Putting everything together, Epps concluded that the
relationship (mathematical model) between measurements of quality and
measurements of performance is not well defined and needs further research,
adding that meaningful research will be very costly.
Epps continued an informative presentation with a review of sample preparation
techniques, noting that samples may be laboratory mixed and laboratory
compacted for mix design, field mixed and laboratory compacted for production
control, and field mixed and field compacted for placement control.
Sample preparation is used to predict performance from samples, although
it is known that the laboratory does not equal the field with respect
to either mixing or compaction. Samples are prepared to provide information
for the bid as well as information for process control and information
for QC/QA programs. Typical quality measurement tests for production
include the asphalt binder, aggregates and the mixture, while typical
quality measurement tests for placement include in-place air voids,
smoothness, segregation, and irregularities. There are numerous hot
mix asphalt accelerated pavement tests (APT) that are performed at laboratory,
prototype or full-scale levels. To close, Epps posed the following question
to attendees: “Bearing all of the issues discussed in mind, what
approach would you use to design, build, finance and operate a 40-year
project?” Project elements to be included in the approach would
include the bid process, mixture design, process control, quality control
and quality assurance.
In Binder Issues: Quality Supply and Cost, Peter Grass,
president of the Asphalt Institute, focused on the issues of quality,
supply and cost as they relate to asphalt binder. Grass began with an
overview of global trends in crude oil supply, noting that although
oil is 45 per cent more expensive today than it was at the beginning
of this year, its price is still well below the inflation adjusted peak
of the late 1970’s and early 1980’s. Looking forward, some
forecasters believe that oil prices could be in the US$30-40 per barrel
range in 2005. The US strategic Petroleum Reserve now stands at about
670 million barrels after the addition of 40 million barrels in 2004
and is expected to increase still further to 700 million barrels by
May 2005. Global demand for oil is expected to continue growing, rising
from 81.4 million barrels/day in 2004 to 83.2 million barrels/day in
2005.
With respect to US domestic oil production, Hurricane Ivan caused the
worst disruption ever in production capacity, with a shortfall in overall
production of 25.5 million barrels and still running at 400 000 barrels/day
below capacity. Massive oil rigs were capsized by the storm, while the
Gulf of Mexico’s extensive network of underwater pipelines was
damaged by numerous submarine avalanches, triggered by some of the biggest
waves on record. The result is effectively no spare production capacity
in the US as most the Gulf of Mexico’s production is sweet crude
and many US refineries are capable of processing only sweet crude. The
situation has been made worse by the fact that there has been no new
US refinery built in almost 30 years and the costs to upgrade a refinery
to process lower grade crude are around $800 million. At the same time,
US exploration activity remains low. Meanwhile, overall global production
is expanding, with several OPEC members including Saudi Arabia, Kuwait
and Nigeria all planning to significantly increase output over the next
few years. Putting all these factors together, the US dependence on
foreign oil has increased from 41 per cent in 1980 to 61per cent today.
China is now second only to the US in energy consumption, with increasing
dependency on imported crude oil and gas for the next 30 years.
“Are we running out of oil?” In response
to this perennial question, Grass noted that the 70 million barrels/day
consumed in 2003 represent a 70 per cent increase since 1970, while
current estimates put global reserves at 1.0 - 1.2 trillion barrels.
Based on these current estimates, there are some 50 years of oil “left”,
although Grass added that we will never run out for a number of reasons.
Among these reasons are the forces of supply and demand in which prices
rise as supply falls to reduce demand. At the same time, the US is becoming
more energy efficient, based on calculations of energy consumed per
dollar of GDP or oil consumed per $1000 of GDP. However, while we won’t
physically run out, we may economically run out. To explain this point,
Grass noted the slow pace of proposals to increase US supply, such as
a new refinery in Arizona or pipelines from Canada is due to daunting
economic, environmental, political or physical challenges.
Grass added that Canada is in the fortunate position
of having a good availability of high quality asphalt for its paving
projects. Some 3.1 million tonnes of asphalt was used here in paving
applications in 2003, while a further 1.0 -1.5 million tonnes was exported
to the US. Changing topics, Grass concluded his presentation with a
review of improvements in low temperature binder tests and specifications
from before 1990 (pre SHRP) and after 1990 (SHRP and post SHRP), as
well as current training initiatives by the Asphalt Institute.
The busy morning schedule was wrapped up by Ralph
Scholz of the Region of Niagara who presented OPSS Specifications for
Superpave for Municipal Use. Scholz explained that November 30, 2004
saw the publication of three related hot mix Ontario Provincial Standard
Specifications (OPSS); a revised OPSS 310 construction specification
for hot mix asphalt, a revised OPSS 1003 material specification covering
aggregates for hot mix asphalt and a new material specification, OPSS
1151, for Superpave and Stone Mastic mixtures. Less than a year previously,
in winter 2003, the Ontario Good Roads Association (OGRA) had approached
OPS requesting that a specification be created to provide the municipal
user with a base specification to implement Superpave mixes. In the
event, a technical team coordinated by OGRA and representing industry,
consultants and municipalities produced a very detailed specification
in just six weeks. The OPS fast tracked the subsequent review process
and the three specifications were published, with a few minor edits,
within the challenging November 2004 time frame. So what does this all
mean for Ontario municipalities? For the Region of Niagara it probably
means that the tonnage of Superpave asphalts placed in the next five
years will be more than the previous five years – perhaps not
difficult to do since the previous five year’s total was zero!
Superpave and Stone Mastic Asphalt (SMA) are the emerging
asphalt technologies while traditional Marshall mixes have evolved over
75 years based on empirical design and correlating field data. Newer
mix designs are based on newer test methods that relate more closely
to field conditions (e.g. Performance Grade Asphalt Cement). New research
is focused primarily on Superpave and SMA mixtures, with the MTO scheduled
to fully implement Superpave mixes by 2006, using ERS Specifications.
All municipalities now have a parallel specification to OPSS 1150 to
begin trial projects using Superpave and build a knowledge base. Scholz
added that background information must be explored thoroughly by all
(owners, designers, CA’s, contractors and laboratories) to ensure
the proper use and application of the specifications. As Superpave is
not without its own nuances, both technical and economical, requiring
further scrutiny, Scholz encouraged everyone involved to explore opportunities
to attend technology transfer workshops.
The seminar’s afternoon session focussed on
the improvement of longitudinal joints as one of the industry’s
ongoing challenges. OHMPA’s Vince Aurilio listed textbook problems
associated with longitudinal joints including the inability to obtain
joint density, tender, dry or harsh mixes, rapid cooling of the mat,
a lack of material in the joint, poor compaction techniques, not rolling
the joint soon enough, rolling the joint too fast, segregation of the
hot mix asphalt and operational constraints. Aurilio explained that
the first pull of the paver generally leaves an area of low density
along the unconfined longitudinal edges of the mat. Hot mix asphalt
compaction is only possible if the mixture is at the proper compaction
temperature and the mixture is confined. Top confinement comes from
the force of rollers, while bottom confinement comes from the base or
subgrade materials and side confinement is provided by internal mix
forces. Effective longitudinal joint solutions all require proper procedures
and quality workmanship.
Echelon paving (two pavers laying adjacent mats at
the same time) facilitates hot joint construction, while proper rolling
methods for rolling from the hot side, cold side and pinch rolling should
be used. Proper construction methods and materials include the use of
tapered joints, cutting wheels, edge restraining devices and joint adhesive.
Longitudinal joint research case studies in the US confirm that hot
joints constructed with echelon paving are likely to provide greater
joint density. Aurilio then described a number of effective compaction
techniques including rolling from the hot side with 150 mm overlap onto
the cold side, rolling from the cold side with 150 mm overlap onto the
hot side and rolling from the hot side with 150 mm pinch.
Making his second appearance of the day, Jon Epps
reviewed the challenges in making a sound longitudinal joint, such as
the cold surface of the first pass (cold) mat and segregated material
on its outside edge. In addition, the second (hot) pass requires proper
overlap and sufficient material for roll down to ensure a sound joint.
Epps then compared three types of longitudinal joint geometry; natural
response of material, cut joint and wedge or taper joint (with or without
notch), pointing out the advantages and disadvantages of each. On the
essential topic of longitudinal joint compaction, Epps explained that
a different approach was required, depending on whether site conditions
allowed access to the cold side. Rolling from the cold side would include
a first roller pass with the drum mostly on the cold side with the remainder
on the hot side. When rolling from the hot side with overlap, the drum
should be positioned such that most of the drum travels on the hot side
while about 150 mm of the drum width travels on the cold side. Alternatively,
if rolling is completed from the hot side with no overlap, the edge
of drum nearest the joint should be kept 150 mm back from the joint
on the first pass and the remaining 150 mm hot strip should be compacted
on the second pass. The compaction approach for unconfined edges depends
on the thickness of the lifts; on thin lifts the edge of the drum should
be hung 150 mm over the unprotected edge. For thick lifts however, the
drum should be kept 150 mm back from the unconfined edge on the roller’s
first pass and then hung over the edge of the lift for the second pass.
Epps concluded this presentation with an overview of joint density research
by the National Center for Asphalt Technology (NCAT), several US State
and local governments, together with an overview of general joint specifications
of the Federal Aviation Administration (FAA).
A number of OHMPA’s supplier members followed
with brief presentations on products to improve longitudinal joints.
Mike McLean, of OHMPA supplier member McAsphalt Limited, provided details
of the company’s XJB (extruded joint bond), described as an innovative
maintenance product for treating hot mix asphalt joints to prevent future
crack formation. Applications for this product are said to include longitudinal
joints, transverse joints, mill and fill joints, street cuts, curb and
gutter joints and concrete edges. During application, the joint bond
is first heated in a pumper kettle (typically towed behind a light truck)
and then applied to the joint by hose in a two-person operation. Typical
application rates are between 0.3 to 0.5 kg per metre of joint. In busy
traffic conditions, the joint bond can be placed under traffic and is
also said to be unaffected by traffic driving across it. In addition,
XJB is said to work well on cold joints. The product was developed after
extensive testing and examples of its application included US state
roads in addition to the Indianapolis motor speedway. It is said to
perform over a broad range of temperature range grading as a PG 82-40
under Superpave, thereby allowing the product to remain flexible under
extreme weather conditions.
Bob Kieswetter of Heat Design Equipment explained
how the company’s heater systems aid longitudinal joint construction.
Each heater unit is relatively simple, consisting of a rectangular heater
plenum, ceramic heater cartridge, and a protective skirt. During operation,
the propane is ignited within the cartridge and the heated ceramic blanket
emits high intensity infrared rays onto the asphalt below. The infrared
radiation quickly penetrates the asphalt and turns to heat, thereby
avoiding the potential damage that can occur with open flame heating
systems. The heater units are 450 mm wide and either 900 mm or 1200
mm long and can be arranged into a frame to make large or small heater
decks. Support equipment includes an inspirator to control the air gas
mixture, propane source, CGA approved vaporizer and adjustable regulators.
These decks can be mounted directly onto the paver or, in more recent
variations, mounted on a towed trailer.
Two Quebec contractors have refined the process still
further by making the portable heater decks self-propelled rather than
towed units. In operation, the uncompacted cold edge is reheated to
110 C by the heaters (to a minimum depth of 12.5 mm) and is further
heated by the placement of the adjacent hot lane. This combined heating
enables the joint to be compacted to a satisfactory density and facilitates
the construction of a seamless bond with the new hot lane. This arrangement
also avoids common joint problems such as the crushing of aggregate
against the hard edge to create new uncoated aggregate faces or the
premature cooling of the hot lane prior to compaction. Kieswetter adds
that that the number of heaters chosen for any particular application
is calculated, based on input parameters such as required paving speed,
initial temperature, reheated temperature and specific heat of the asphalt.
Rounding out the day’s events were the seminar’s
trade show, together with live and silent auctions that provided support
for research and development as well as the University of Waterloo’s
Centre for Pavement and Transportation Technology.
Back to top
Customized
paving method improves mat uniformity, rideability
By Andy Bateman,
Engineering Editor
A unique
windrow attachment is improving mat uniformity and rideability for an
Ontario roadbuilder.
Designed
and developed entirely in-house, the attachment’s job within the
paving process is to create a windrow of remixed hot mix asphalt. According
to Murray Ritchie, construction and materials manager for the Murray
Group Ltd., the attachment is a cost effective way of providing a steady
flow of remixed asphalt to the main paver, while eliminating the truck
bumps and segregation problems often associated with direct truck discharge.
Most important of all, this paving method provides a uniform mat with
significantly improved rideability.
The attachment itself takes the place of the screed
originally mounted on the rear of a stock Blaw-Knox PF 500 paver. In
operation, this modified unit leads the paving train and receives hot
mix asphalt from conventional end dump trucks. The paver’s feed
controls are used to regulate material flow to the attachment where
it is remixed and deposited behind the paver in a windrow of specific
size and shape. Travelling some distance behind, an asphalt pick–up
machine recovers the material and transfers it to the main paver which
then lays the mat to the required width and thickness.
Aggregates & Roadbuilding saw the unique paving train in action
earlier this season just outside the village of Drayton Ont. In this
resurfacing application, Murray’s crew was paving a 50 mm surface
lift of HL4 mix on a two-lane rural road while also dealing with pavement
utilities and surprisingly heavy traffic.
The windrow produced by the attachment was recovered
by a Caterpillar BG 650 pick–up machine and transferred to the
Caterpillar AP 1000B paver placing the mat. Equipment on the AP 1000B
included a 10-20B Extend-A-Mat screed and Topcon sonic averaging ski,
as well as a hopper insert to increase process inventory. Behind the
paver, compaction equipment included a Dynapac CC422HF dual steel drum
unit in the breakdown position, followed by a Caterpillar PS-360B pneumatic
compactor in the secondary position and a Caterpillar CB-534C dual steel
drum finishing roller. Hot mix asphalt on the contract was supplied
from Murray’s Elora plant, some 12 km from the job.
Viewed from above, the side plates of the attachment
funnel to the rear, thereby causing material near the plates to fold
over and remix with the central section as the unit moves forward. Above
the material, a curved strike off plate enables the crew to adjust the
height of the windrow. Locking arms on the side plates prevent the whole
attachment from riding up and mercury tilt switches help to regulate
the volume of feed material.
Ritchie explains that the PF 500 paver carrying the
attachment was bought used specifically for this purpose. On arrival,
its screed was removed and the attachment designed to fit the screed
mounting arms. Trials were conducted in Murray’s yard using granular
base as the feed material to confirm that the windrow concept would
work efficiently in a full–scale operation.
Now in its second season, the unit went into service
a short time later following successful trials and some minor adjustments.
In addition to resurfacing applications, the windrow/pick-up system
is said to work equally well in base asphalt applications where the
hot mix is laid directly on compacted granular base material. In such
cases, the windrow is recovered cleanly by the pick-up machine, with
minimal pick-up of the underlying base.
Clients of the system to date include the Counties
of Wellington, Perth and Grey as well as the Ontario Ministry of Transportation
(MTO). On the Drayton contract, Greg Morphy, pavement inspector for
the County of Wellington, reports that the system has delivered a significant
improvement in mat uniformity and has also eliminated the familiar problem
of end load segregation.
Credit for the successful design and implementation
of the attachment goes to all of Murray’s shop employees. The
Murray Group Ltd is based in Moorefield, Ont.
Back to top
Contractor’s
trucks deliver increased payload, flexibility and comfort
By Andy Bateman,
Engineering Editor
The custom-built
trucks of a London, Ont. contractor are delivering increased payload,
flexibility and comfort.
For owner Jack Vanderweg, the challenge was to specify trucks that could
deal effectively with the bulk haulage of aggregates, demolition and
site excavation material in both highway and off road applications.
Vanderweg is the principal of Jackal Trades Inc., whose diverse activities
include haulage, sewer and water main construction, city snowploughing
and concrete recycling. Building on extensive experience of owning and
operating trucks, Vanderweg’s three new trucks all incorporate
tandem tandem (two drive and two steering) axle configuration, automatic
transmission and a custom built steel body. Aggregates & Roadbuilding
saw two of these units in a London site application, hauling excavated
overburden for berm construction at Try Recycling’s new composting
facility.
The Volvo VHD trucks each combine a Simard tandem
steering, an Allison automatic transmission and a Lagace steel body.
Overall truck performance has met Vanderweg’s expectations to
date, both in terms of operating efficiency and operator comfort. The
tandem steering axle set up delivers improved steering while the automatic
transmission adds to the truck’s smooth and quiet ride, particularly
in London’s notorious stop and go traffic. These Volvo VHD64B200
trucks are in the 32-36 tonnes (71 000 to 80 000 lbs) Gross Vehicle
Weight (GVW) class. Their Volvo VE D12 - 425 engines, producing 425
hp at a governed 2100 rpm and 1450 ft lbs of torque at 1100 rpm, are
teamed with Allison HD 4560D 6 speed automatic transmissions.
Vanderweg explains that the additional steer
axle provides a number of benefits including improved truck manoeuvrability
and reduced wear on steering components and tires, all in addition to
increased payload. The decision to specify the tandem steering axle
also reflects Vanderweg’s experience with other types of additional
axle, including a straight lift axle and an air lift self-steering axle.
While both these of set ups provided the necessary load capacity, each
was found to have inherent disadvantages. For instance, even large radius
curves could be a challenge when the straight lift axle was down, as
the single front steering axle had to overcome the natural tendency
of the three trailing axles to continue travelling in a straight line.
To counteract this effect, the operator could choose to raise the lift
axle while cornering, but in doing so may inadvertently create an axle
overload condition. With respect to air lift self-steering axles, Vanderweg
found that this design works well in normal conditions on paved surfaces,
but could cause problems in certain off road situations, “When
reversing over rough ground, a self steer axle follows the ground profile
because the camber on these axles is designed to follow the front axle
only when travelling forward. As a result, steering can become uncontrolled
in reverse. We had one situation where a loaded truck was reversing
over a sharp knoll on a construction site.
“At one point, the lift axle was bearing
most of the weight of the front end of the truck while the steering
(front) axle was only lightly loaded. This created the undesirable situation
in which, for a few moments at least, the truck followed the uneven
ground profile and the operator was unable to control the direction
of travel.”
By contrast, Vanderweg reports that the tandem
steering axle fitted to the three new trucks aids steering in all situations,
as well as providing a more comfortable weight sensitive air ride for
the operator. The Simard AMS air suspension consists of an air/spring
combination that, according to its manufacturers, provides increased
load capacity and improved load distribution. The manufacturer also
claims improved driving stability and improved traction in rough conditions
from a system that requires minimal maintenance. Additional reported
benefits include extended life for tires and steering components and
system adaptability to all makes of truck.
The Lagace truck bodies were specified as a result of good experience
with an older truck body from the same shop which is still largely dent
free and sealed, despite several years of tough duty. An ingenious feature
on the new bodies allows the tailgate to be switched from top hinged
to side hinged in a few seconds. This switch can be useful when hauling
awkwardly shaped loads such as tree stumps that are prone to jamming
in a top hinged tailgate. By switching from top hinged to side hinged,
the tailgate can be swung completely away from the rear opening to provide
a wide clear access. This feature has also been useful on factory demolition
jobs where the truck can back up to a loading platform, thereby allowing
a small unit such as a skid steer to drive directly into the body to
dump. Similarly, the feature allows skid steers or other small pieces
of equipment to be carried to job sites inside the body. In one case,
four pieces of equipment, namely tractor backhoe, dozer, skid steer
and the truck itself were taken to a job site in a single trip. The
two tracked machines were carried on a float towed behind the truck,
with the skid steer carried in the truck box.
Emmanuel Simard et Fils, manufacturer of the
air spring front tandem suspension, is based in Baie-Saint-Paul, Que.
Truck body manufacturer Lagace & Frères Inc. is located in
Beloeil, Que.
Back
to top
2005
Buyers’ Guide issue
Aggregates
and Roadbuilding Magazine
4999 St Catherine Street West. Suite 315
Westmount, Quebec H3Z 1T3
Tel: (514) 487-9868 Fax: (514) 487-9276
EMail: rocktoroad@sympatico.ca
|
