| |
 |
|
|
|
|
University
of Newcastle upon Tyne
|
|
|
|
| The use of RESIBLOCK
'22' in |
| Discrete
Element
Pavement Systems
|
|
| John Knapton -
BSc. PhD. C.Eng. FICE. FIHT. M.Cons.E. |
| Professor of Structural
Engineering, University of Newcastle upon Tyne
|
| |
| |
|
Executive Summary
This Report uses case studies to
define the reasons for pavements failing and identifies those
types of use where RESIBLOCK '22' will enhance the strength
and durability of a pavement so avoiding failure. A Total
Quality
Chart is presented which allows its user to identify those
applications where RESIBLOCK '22' should be specified to
ensure that the
pavement achieves maximum performance and avoids failure. Case
studies are presented for seven areas which have underperformed
and for two areas which have performed well. The Total Quality
Chart includes an appraisal of any unusual environmental
conditions
which might prevail. It also takes into account the public
profile of the project and how visible the project is to
the general
public. By integrating these "soft" factors with
the traditionally applied technical issues, the Report shows
how
a pavement can be guaranteed to perform to the client's requirements
and how RESIBLOCK '22' can significantly contribute to this.
Introduction
During the last 25 years, the Author
has been involved in the design, specification, construction,
development and usage of pavers both in the UK and elsewhere.
He has participated in the development of a body of knowledge
which is sufficient to ensure that pavers can be used successfully
to surface all categories of pavements. National and international
standards have evolved for materials, installation procedures
and design methods. Special attention has been paid to developing
the technologies associated with heavily trafficked highway
pavements, heavily loaded industrial areas, aircraft pavements
and pavements subjected to adverse environmental conditions
such as vacuum sweeping, flooding and extremes of climate.
Because
of this, there is now sufficient information available to satisfy
the needs of all potential paver specifiers. Yet the incidence
of pavements performing less well than the client expected
has
not diminished. An area where there is as yet no definitive
guidance is in the application of paver joint specialist
pre-polymer
urethanes (SPPU’s) such as RESIBLOCK '22'. This Report
defines those applications and includes a simple to use chart
which informs the user which pavement categories will be enhanced
by the use of RESIBLOCK '22'.
Recent developments in paver
pavement technology and markets
Although there is some evidence
that streets were surfaced with brick sized concrete blocks
bedded on sand in Belgium in the 1930's , it is usually accepted
that the modern paving stone era commenced in Rotterdam immediately
after the second world war. Traditionally, Dutch city streets
were surfaced with brick but the shortage of coal throughout
Northern Europe following the war led to a shortfall in the
number of bricks needed for the more pressing need of house
reconstruction. The Rotterdam city engineer used concrete
pavers
as a temporary substitute and this led to all Dutch authorities
adopting concrete units such that by 1970, 15,000,000 m2
of
concrete pavers were being installed annually. More recently,
there has been a shift back to brick. The Dutch have adopted
similar dimensions for both concrete and brick, which explains
the term "Holland Stone" used in the US to describe
rectangular concrete paving units.
The Dutch experience was paralleled
in West Germany through the 1950's and 1960's with the 1963
recession leading to many German building block manufacturers
switching to paving units in order to keep their machines in
production. A fundamental difference between the developments
in the two countries is that West German manufacturers preferred
proprietary shapes which led to the establishment of shape-orientated
promotional groups which have had a significant international
impact. Essentially, all other countries and regions adopt a
mix of Dutch or German tradition, some favouring one strand
and some integrating elements of both. Commonly pavers are introduced
to new regions by German industrial interests - shape licensors,
paver plant manufacturers and installation equipment designers
- but as markets mature, the more straightforward Dutch tradition
frequently predominates. For example pavers were introduced
to the UK in the late 1960's and by 1973, all of the UK production
comprised pavers of either West German origin, or near copies,
whereas by 1990, over 90% of UK pavers were rectangular and
followed Dutch tradition.
Of course, many European city streets
have been surfaced with small element systems for 200 years
or more and indeed, Roman Empire city streets were usually surfaced
with stone units over 2000 years ago. The essential factors
in the modern resurgence of pavers are mass produced low cost
units manufactured to accurate dimensions to facilitate cost
effective installation. Also, modern pavers are engineered to
allow their safe use by fast and heavy traffic, whilst at the
same time being compatible with the needs of pedestrians in
terms of slip, skid, abrasion and durability.
An interesting issue is whether
mechanical installation will become commonplace during the
next few years. So far, manual installation has proven cost
effective
and machines have been introduced when special factors militate
against manual laying. For example, health & safety legislation
has led to the introduction of installation systems in Rotterdam.
Repetitive Strain Injury (RSI) is becoming recognised as
an
unacceptable consequence of long term employment in the manual
installation of pavers. Mechanical laying has been introduced
to Cyprus where young men prefer to find employment in tourism.
Some proprietary German shapes are near impossible to place
by hand and their promoters consider them to represent the
forerunners
of the next generation of pavers.
The Author estimates that paver
usage has risen from virtually nil fifty years ago to 0.7 billion
square metres per annum by 2000. Germany remains the single
largest market with upwards of 100 million square metres
per
annum. Other significant markets include 30 million square
metres per annum in North America, over 20 million square
metres in
the UK with many countries worldwide achieving figures of the
order of 10 million. Figures are difficult to establish for
developing countries but it is clear that on a per capita
basis,
African usage is close to European and parts of Asia, have
significant industries. There has been a constant growth
in Central and
South America and China uses pavers commonly - the 400,000m2
Hong Kong airport pavers were imported from China. In summary,
for each person on Earth, 0.13 m2 of pavers are installed
annually
and the Author expects this figure to rise to 0.2m2 by 2020.
The increase will occur as a result of market penetration
increasing
year on year in western countries where population growth is
often zero or sometimes negative and as a surge in developing
countries which will outstrip population growth as the appropriateness
of pavers becomes evident. Paver joint SPPU’s such as
RESIBLOCK '22' were developed in the mid-1980's, initially
at Luton Airport,
the world's first application of pavers for commercial aircraft
pavements. Initially perceived as an aid to paver joints
resisting
jet blast and propeller wash, its uses extended through the
late 1980's and the 1990's to many categories of pavements
where
air, gases, liquids, traffic and adverse weather conditions
might remove jointing sand from pavements surfaced with pavers.
It was also used to improve hygiene where contaminants would
otherwise penetrate joints and has been proven to prevent
the
development of unsightly efflorescence on the surface of pavers
The next Section describes a series
of landmark projects which have informed the body of knowledge
and which together define the state of the block paving art
and which demonstrate the value of paver joint SPPU stabilisers.
By studying these case studies, the Author has developed the
Total Quality Chart which is the focus of this Report (Figure
26). A major conclusion from the following is the high proportion
of failures in which loss of jointing material has been a contributory,
or initiating factor - failures which would have been avoided
had RESIBLOCK '22' been applied in the first instance rather
than as part of the repair. Together, they point to the need
to consider joint stabilisation for a range of pavement categories.
Landmark projects in developing
an understanding of paver pavements
The case studies described here
represent the waypoints which have guided the Author towards
his understanding of paver pavements. In each case, the project
has failed in one or more respects or it includes an innovative
element which has pointed the way towards a clearer understanding
of the behaviour of a pavement surfaced with pavers. The following
four issues need to be considered if the pavement is to satisfy
the conflicting needs of all of the parties involved in the
development of a project.
Issue 1: Environmental: special
external factors which affect performance
Issue 2: Visibility: how many
people will see the project and from what distance
Issue 3: Traffic: nature, weight
and frequency of loads
Issue 4: Public profile: the
contribution of the project to the enhancement of the physical
world
The case studies are described by
reference to the four Issues and the way in which quantifying
each Issue would have influenced the development of the project
is explained. The critical factors in the case studies are summarised
in Table 1 according to the four Issues which have been found
to be relevant to pavement performance.
Case 1 - Bellevue Metro Interchange,
Washington State, US.
Figures 1 to 3 show the way in which
areas of rigidly set brick pavers gradually deteriorated in
this bus station. The cement mortar bedding material failed
to take into account the Environmental and Traffic Issues. There
are many instances where similar failures have occurred and
the Author has found that rigidly bedded pavers cannot sustain
heavy channelised traffic, particularly at bus stops. It is
essential that flexibly bedded pavement systems are used - those
pavements which were previously designed and constructed to
act in a rigid fashion should now be treated as flexible pavements,
usually with the application of RESIBLOCK '22'.
Case 2 - Trench Lock Works, Telford,
UK.
Figures 4 to 6 show the condition
of the road after 5,000,000 Cumulative Standard Axles (csa's).
It is the access road to a brick manufacturer and is trafficked
by heavy vehicles delivering the firm's products. It is important
in that it is an early example of a paver road having regular
heavy vehicles in an industrial context. The road remains serviceable
as a result of its reinforced concrete base and the use of bedding
and jointing sands which would fall into Category 2. Several
parts of this pavement have been treated successfully with joint
stabilisation SPPU materials (materials identical in chemical
composition to Resiblock, but predating it)
Case 3 - Bahrain Airport. (See
Figures 7 to 9)
The area comprises an airport vehicle
service and parking area. Many of the pavers spalled as a result
of the rectangular units having no spacers and being installed
in a tightly packed manner. The problem was exacerbated by the
absence of an adequate base. The problem would have been largely
resolved by ensuring that jointing material was present and
would have been fully resolved by so doing and providing RESIBLOCK
'22'.
Case 4 - Leeds
Figures 10 to 12 show the condition
of pavers installed in a city centre street after very little
use. The pavers had been deliberately spaced to fit into
previously
constructed surrounds. This led to loss of interlock. Effectively,
this is the opposite problem to the one described in Case
Study
3. Together, they point to the importance of installing the
pavers "hand tight" so that the joint remains filled
and generates interlock. The problem was resolved by the
application
of a joint stabilising SPPU.
Case 5 - Luton Airport
Figures 13 to 15 show the Eastern
Turning Circle at Luton Airport which failed on a number of
occasions, culminating in a significant failure which damaged
an aircraft. A court hearing failed to establish the cause
with
any degree of certainty but adequate maintenance, drainage
of the bedding material and loss of jointing material in
an area
subject to regular jet blast were all points of discussion
(the Author represented one of the parties to the ensuing
litigation).
Other factors which may have contributed to the difficulties
include the use of machines to install clusters and the need
to undertake the work through the night with a morning deadline
when the runway was back in service. Much of the development
of the technology of pavers for aircraft pavements took place
collaboratively by Luton Airport and the Author. The work
has
been published by the Civil Aviation Authority in the UK and
by the Interlocking Concrete Pavement Institute, with the
approval
of the Federal Aviation Administration, in the US. Effectively,
joint stabilising SPPU’s were "invented" at
Luton in order to prevent the erosion of jointing and bedding
sands
by jet blast and propeller wash.
Case 6 - Pine Street, Seattle
(Fig. 16).
The project comprised granite pavers
installed over a bedding material which contained an abnormal
proportion (>10%) finer than 75 microns (No. 200 sieve
size). It developed ruts during the first day's trafficking
and was
eventually reconstructed with a bedding sand with only 0.1%
passing the 75 micron sieve. That was in 1989 since when
it
has withstood heavy traffic for over 10 years with no significant
maintenance being required. This project and several which
showed
similar traits in the UK led to the development of enhanced
specifications for bedding materials. Research at Newcastle
University has confirmed the need to restrict bedding materials
in heavily trafficked projects to naturally occurring sands
with limited amounts of material passing a 75 micron sieve.
The use of a joint stabilisation SPPU was the key element
in
the successful repair of Pine Street.
Case 7 - Victoria Road, Hartlepool
(See Figs 17 to 19)
This heavily trafficked town centre
street was constructed in 1993 and has withstood 7,000,000 csa's
with no problems. This is as a result of the use of an enhanced
specification sand and with the paver joints including a SPPU
stabiliser. The base comprised steel fibre reinforced concrete
installed by a laser guided screeding machine shown in Fig 18
to ensure accurate levels and therefore a consistently thick
bedding layer
Case 8 - Parking Deck, Dublin.
Figs 20 to 22 show details of the
project in which proprietary shaped pavers were laid by machine
over a coarse grit. The fine jointing sand was subsequently
washed and/or vibrated into the bedding sand, so leaving the
pavers in a non-interlocking state. The laying system whereby
0.5m2 clusters were installed without cross linking exacerbated
the failure. Also, cluster laid systems develop a wider joint
around the perimeter of each cluster, so diminishing interlock.
This project highlights the need to ensure compatibility between
jointing and bedding materials. The use of a SPPU joint stabiliser
would have avoided this problem.
Case 9 - Paphos Promenade.
Figs. 23 to 25 show the condition
of the promenade following a severe storm which flooded the
pavement. Most of the pavers were washed into Paphos Harbour.
The area should have been treated with a SPPU joint stabiliser
but the contractor had not followed the specification. Research
undertaken at Newcastle University into SPPU stabilisers has
demonstrated their ability to greatly reduce the permeability
of paver joints.
The above case studies represent
a small proportion of the projects with which the Author has
been involved. They have been chosen because they each led to
a greater understanding of the way in which pavers behave and
because they represent a class of problem which has occurred
elsewhere with greater of lesser regularity.
Table 1. Factors and Issues relevant
to the landmark projects
| |
Environmental |
Visibility |
Traffic |
Public Profile |
| Bellevue Transit |
Bus stops Channelised |
Public pedestrian
area |
10,000,000 csa |
Feature paved area |
| Trench Lock Works |
Tight turning >1500kg |
Light pedestrian
commercial project |
5,000,000 csa |
Associated with
landmark building |
| Bahrain Airport |
Hot/dry climateTight
turning>1500kg |
Occasional pedestrian
use |
Heavy duty industrial |
No public impact |
| Leeds |
Vacuum sweeping |
City centre public
pedestrian area |
Less than 10,000
csa |
High profile civic
project - principle material |
| Luton Airport |
Maintenance access
difficult. Tight turning >1500kg |
Seen from distance |
Aircraft |
No public impact |
| Pine Street, Seattle |
Cold wet climate |
City centre public
pedestrian area |
10,000,000 csa |
High profile civic
project - principle material |
| Victoria Road,
Hartlepool |
Bus stop |
Town centre public
pedestrian area |
7,000,000 csa |
Civic project -
principle material |
| Parking Deck, Dublin |
Tight turning <1500kg |
Occasional pedestrian
use |
Lightly loaded <1500kg |
Associated with
landmark building |
| Paphos Promenade |
Flooding |
Public pedestrian
area |
Pedestrian |
Feature paved area |
Discussion of common themes
in pavement failures
When the above projects are analysed
collectively, several conclusions can be drawn. The first is
that whereas previous research has frequently focussed upon
ensuring that the pavement components remain unstressed, in
fact, failure rarely occurs as a result of straightforward overloading.
A surprisingly common theme which correlates particularly well
with performance and quality is the behaviour of the paver joints.
Some of the most spectacular failures have occurred as a result
of the paver joints ceasing to operate. The joints can be too
wide, too narrow, unfilled or filled with inappropriate material.
In any of these cases, the failure can be dramatic and sudden.
The joints need to be considered in conjunction with the bedding
material and care needs to taken to ensure that the jointing
material does not drop into the bedding material. RESIBLOCK
'22' will ensure that the jointing material remains in place
and would have eliminated all of the defects discussed in this
Report.
Bedding sands have initiated failure
when the material has been too fine to permit the unimpeded
flow of water. This has allowed hydrostatic pressure to develop
in the bedding sand which has in turn reduced the shear strength
of the sand. In the extreme case of Pine Street, Seattle, a
total collapse of the bedding sand occurred, resulting in quicksand
conditions, in which the sand adopts the rheology of a zero-shear
fluid. Bedding sand failure can be prevented by the application
of RESIBLOCK '22'.
Maintenance has been observed to
be a significant factor in pavement deterioration. Strangely,
the undertaking of excessive levels of maintenance has been
as dangerous as underestimating maintenance. For example, the
removal of untreated jointing material by vacuum cleaning equipment
has caused some difficulties. However, a major conclusion to
be drawn is that the client and the team responsible for providing
the pavement need to define maintenance in an explicit way.
Two extremes have been identified. On the one hand, it is common
for completed pavements to be left to deteriorate. On the other
hand, some authorities have developed a Statement of Engineering
Parameters, a legal document which sets out the anticipated
defects quantitatively year on year. Intermediate levels of
maintenance include repair on an as needed basis and repairing
only those defects which render a pavement dangerous to its
traffic.
From the above discussion, it can
be concluded that the output from a total quality approach to
pavement engineering should be information which defines:
1. Paver joints
2. Bedding material specifications
3. Characteristics of base material
4 Level of maintenance
5 Paver joint sealant material
Effectively, a means is required
of allowing the four Issues of Environment, Visibility, Traffic
and Public Profile to define the appropriate levels for
the above four outputs.
The Total Quality Chart described
in the next Section does so. *
For a copy of the base data for
this chart please email  at RESIBLOCK LTD
Conclusions
1. To date, guidance relating to
pavements surfaced with pavers has been fragmented with a bias
towards ensuring that the paving units and the structural base
are designed and specified accurately, whereas problems have
usually been associated with the jointing and bedding sand.
The majority of those filed pavements which the Author has investigated
would have worked had their joints been treated with RESIBLOCK
'22'
2. The procedure described in this
Report can be used to produce an outline specification which
will ensure that the resulting pavement will be appropriate
for its function.
3. A pavement specification can
be developed only when both technical and "soft" issues
such as environment, visibility and public profile are taken
into account. This applies to both initial construction and
the maintenance regime. The specification of Resiblock is driven
environmental factors, visibility, public profile and traffic
issues.
4. A pavement cannot be considered
to be fully specified until its maintenance regime has been
developed. At one extreme, a Statement of Engineering Parameters
can be developed which states explicitly how the pavement will
be managed through its prescribed life. At the other extreme,
the pavement can be allowed to deteriorate progressively so
it has zero value at the end of its design life. RESIBLOCK '22'
will enhance the long term performance of paver pavements and
will reduce the life cycle cost of a pavement. The reduction
in future maintenance spending, even taking into account discount
cash flow analysis will be greater than the initial application
cost.
5. The Total Quality Chart can be
used to assist in the development of a new pavement, to upgrade
an existing pavement (the upgrade might be in terms of enhancing
the maintenance regime) or to understand why an existing pavement
is underperforming.
|
