New development in civil engg.

Recent Developments in Civil
Engineering NDT in the UK
John Bungey
Department of Civil Engineering
The University of Liverpool
Liverpool L69 3GQ UK
ABSTRACT
Some recent developments in research,
equipment and practical applications are
reviewed together with on-going activities. The
last NDT-CE conference to be held in the UK was
in 1997, and attention is focused on the period
since that event. Techniques include subsurface
radar, dynamic response, acoustic emission,
electrochemical reinforcement corrosion
assessment, ultrasonics, chloride detection,
magnetic imaging and soils performance,
together with pull-out and maturity insitu
concrete early age strength estimation.
Dissemination of research to industry is
considered, including the role of the British
Institute of NDT and other organisations such as
the Concrete Society and Highways Agency.
Potential future trends are noted both in the UK
and broader international context.
INTRODUCTION
The full scope of NDT activity in the UK within
the Civil Engineering industry was reviewed at
the NDT-CE conference held in Tokyo in 2000
[1]. Areas considered included assessment of
ground conditions and location of buried
features, testing of highway and airfield
pavements, structural integrity (both overall and
localised) and materials properties using
numerous different techniques. In general, the
wide-ranging activity identified at that time
continues, whilst this report focuses upon a
number of areas in which there have been
particular recent developments. A selection of
recent and ongoing research projects are
identified which have either resulted in
commercial application, or offer particular
promise. Equipment developments and
availability for practical field applications are
similarly reported in relation to industrial usage
of NDT.
The current situation for support of NDT
research and industrial dissemination of results
is also considered in the context of recent and
ongoing activity and future trends. Some of the
activity and developments are reported in other
papers presented to this conference, and these
should be consulted for more detailed
information in such cases.
RECENT ADVANCES IN EQUIPMENT
Commercially available equipment now
includes:-
'PUNDIT PLUS' - which is a new generation,
microprocessor-based, development of the
long-established PUNDIT ultrasonic tester
widely used on concrete, now offering data
storage facilities [2].
New sub-surface radar equipment for testing
concrete structures offering improved
portability, and higher frequency antennas with
improved performance characteristics.
New hand-held 4-probe resistivity test
equipment for concrete structures, with
automatic data storage.
Acoustic-Emission (AE) equipment suitable for
routine field use, including one system
developed in the UK.
Improved covermeters, including a 'borehole
probe' device.
Improved radiography systems including
reductions in size and increased energy levels,
together with better image capture and
processing as well as safety features (eg
'MEGASCAN [TM]').
Laser-based surface strain and pavement
deformation measuring devices.
Several specialist test companies have also
successfully developed equipment
configurations and software for use in specific
situations for example, multiple radar antenna
arrays for highway surveys. Another interesting
example is the 'TERRIG' system [3] for
determining the bearing capacity of material
below existing concrete ground-slabs based on
load/deflection measurements as illustrated in
figure 1. This is particularly useful when an
assessment of floor capacity is needed relating
to change of use.
Fig 1: The 'TERRIG' System [3].
These improvements in availability and
performance of equipment have all led to
enhanced field usage of the techniques and
helped to improve awareness of the potential
benefits to be gained from non-destructive
testing within the civil engineering community.
SUPPORT FOR RESEARCH AND
DISSEMINATION
In considering research and development
activity, it is perhaps useful to examine the
principal mechanisms for funding, undertaking
the work, and dissemination of results. These
have been outlined in Figure 2 which shows the
key interactions between Government, Industry,
Professional organisations, Research
organisations and Universities.
Direct government funding, channelled in some
cases through bodies such as the Highways
Agency (responsible for Motorway Bridges),
tends to focus on short to medium term
projects relating to a clear industrial need -
often with a strong review and developmental
content. An example of this is the wide ranging
work on NDT methods applied to masonry
structures, as well as post-tensioned concrete,
undertaken at the University of Edinburgh over
recent years.
Much of this work is undertaken by industrial
research organisations, possibly with some
specialised university input, and perhaps also
with industrial financial contributions. The
Cardington European Concrete Building project
is a good example, with work undertaken by the
University of Liverpool and Queens University,
Belfast on early-age insitu concrete strength
assessment using maturity and pull-out
methods as part of a wider range of overall
activity managed by the Building Research
Establishment (BRE). This has led to a Technical
Report [4] published through the BRE as well as
Best Practice Guides for industry.
Research Council (eg Engineering and Physical
Science Research Council - EPSRC) and EU
funding tends to focus on more basic research
activity, usually with strong industrial
collaboration and input. In this case,
development into commercially usable systems
is undertaken by industry - sometimes in the
form of spin-off exploitation companies.
Examples here include work at Imperial College
on ultrasonic testing of rock bolts, and at
Queens University, Belfast on insitu concrete
strength and permeability testing methods.
An important new development is the recent
establishment of the EPSRC supported Research
Centre for NDE (see Figure 2). This is led by
Imperial College and Strathclyde University and
involves several other Universities, with major
industrial input to support activity ranging from
longer-term strategic core research to short-
term industrial technology solutions. This will
seek to provide improved coordination of NDE
research and increased University/Industry
collaboration. The total funding over the next
few years will be substantial, but the scale of
Civil Engineering activity to be included is
unclear at present, and may be relatively small.
Fig 2: Outline of support for research and
dissemination.
In-house industrial research tends to focus on
development of particular systems or
procedures (including software) for direct
commercial use, with dissemination limited to a
marketing role. In all other areas however,
industrial-level dissemination and technology
transfer is promoted by bodies such as the
British Institute of NDT and the Concrete Society
through technical journals, conferences,
seminars, guidance notes and technical reports.
In some cases, these include research-level
dissemination, although specialist international
conferences and scientific journals are the
primary route for this activity, often
supplementing industrial dissemination.
RECENT AND CURRENT RESEARCH AND
INDUSTRIAL USAGE
It is convenient to consider this in terms of
technique rather than application. International
trends over the preceding four-year period were
reviewed in 1997 [5], and it is interesting to
note that subsequent activity in the UK has
continued to reflect many of these. In
particular, new interests focus on assessment of
sub-surface integrity and monitoring, rather
than insitu strength (apart from early age
development), although prediction of future
performance is an important issue. There has
also been increased activity relating to masonry
structures and railway track-beds in response to
national concerns.
Acoustic emission
This is an area in which there has been
substantial increase in industrial usage within
Civil Engineering. Reported applications, to
bridges in particular, cover a wide range of
monitoring situations including:-
Orthotropic steel deck weld cracking;
Steel box deck weld crack propagation [6];
Fatigue of shear-studs in steel/concrete
composite construction;
Reinforced concrete half-joint cracking;
Reinforced concrete hinge joint corrosion;
Post-tensioned concrete tendon wire fracture
[7];
Roller bearing cracking;
Spherical bearing friction and plinth cracking;
Load testing of masonry arches.
This has been possible as a result of improved
instrumentation and the ability to isolate traffic
and other environmental noise from genuine
acoustic emission sources. Much of this has
been stimulated by research on steel structures
at Cardiff University, but it is known that there
is current research activity on reinforced
concrete and masonry at Loughborough and
Edinburgh Universities including use for
corrosion monitoring.
Sub-surface Radar
There has been continued growth in industrial
usage, coupled with wide-ranging research
activity including:-
Antenna performance characterisation including
coupling effects, antenna development for
measurement of insitu concrete dielectric
properties taking account of moisture gradients,
and development of neural networks for
reinforcing bar identification (University of
Liverpool).
The work on insitu dielectric property
assessment is described in more detail
elsewhere in this Conference and utilises a horn
antenna operating in the frequency domain with
an inversion/optimisation routine to reconstruct
the dielectric profile of the material tested [8].
This has been validated on simple layered
materials in the laboratory, and is shown in
Figure 3 during site trials on a car-park structure
using a portable network-analyser system.
Inspection of masonry structures, including use
of tomography, and non-metallic ducts in post-
tensioned concrete; signal velocity assessment
in materials (University of Edinburgh).
Assessment of depth of surface cracking in
flexible highway pavement using high frequency
systems (Transport Research Laboratory).
Characterisation of railway track-bed ballast
(Transport Research Laboratory [TRL] and
University of Edinburgh, Aperio).
Other ongoing research activity includes
participation in the EU SMARTRAD programme
within which the Building Research
Establishment is developing processing software
to improve interpretation capabilities. It should
be noted that many examples of practical use
recognise the advantages of combination with
other techniques such as thermography or in
some cases, such as tunnel inspections, with
ground conductivity.
Ultrasonics
High frequency 'Guided wave' techniques [9]
have been very successfully applied to testing
steel rock bolts as illustrated in Figure 4 and has
been developed commercially as noted above.
In coal mines bolts are typically about 20mm
diameter and up to 3m length, with testing
aimed at detecting fractures and major defects.
Minimising leakage of the energy into the
surrounding rock is crucial to success, with
curvature effects causing particular problems.
Efforts are being made by the same group at
Imperial College to apply the guided wave
technique to inspection of rails and, using
arrays, to large steel plate structures such as
storage tanks. Work with guided acoustic waves
has also shown promise in detecting leakage of
metallic water pipes from the effects on signal
propagation of the surrounding soil properties.
Fig 4: Guided wave ultrasonic testing of rock
bolts [9].
Other developments continue at an
experimental stage to produce improved one-
sided pulse-echo transducers and signal
processing for use on concrete (in collaboration
with German partners) with penetration depths
up to 1m [10]. Air-coupled through
transmission transducers are also under
development at Warwick University. In both
cases, use is made of multi-frequency 'chirp'
technology.
Magnetic Imaging/Electrochemical Methods
Laboratory studies at University of Manchester
Institute of Science & Technology (UMIST) using
inductive magnetic imaging systems to locate
embedded reinforcing bars have been underway
for some years. Recent work, which has a strong
signal processing emphasis including use of
Synthetic Aperture Focussing Techniques,
includes detection of bar surface corrosion [11]
and procedures to speed-up the process prior to
commercialisation for field use. Work at
Liverpool and Heriot-Watt Universities using
electrochemical techniques such as Linear
Polarisation Resistance coupled with weight-loss
measurements continues to try to predict future
lifetime performance where corrosion is
present, whilst TRL are concerned with risk
assessment for bridges. Work on moisture and
chloride movement in cover zones using
embedded sensors is also underway at Belfast
and Heriot-Watt Universities [12].
Dynamic and Related Techniques
Seismic cross-hole methods using tomography
to detect disturbed ground beneath foundations
have been reported [13] by the British
Geological Survey, whilst other similar work
using ultrasonics is reported at this conference.
Efforts have also been made to characterise
physical characteristics of rail-track ballast from
impact tests and continuous surface wave
measurements (Napier University) whilst modal
wave detection of bridge damage is known to
be underway at Bristol University.
Alongside these, and other, projects has been an
increasing interest in the use of uncertainty
methods in the analysis of test results, with one
test company [14] providing a confidence rating
according to circumstances. The need for 'whole
systems planning' to avoid fragmentation of
inspection and testing responsibilities and the
consequent dangers of poor performance and
communication, is increasingly recognised [15]
and is an important worldwide issue.
DISSEMINATION ACTIVITY
The crucial role of dissemination of research
activity and industrial experience through
authoritative guidance documentation was
highlighted by the Author in 1997 [5]. This
reflected the importance placed by Schickert
[16] in 1995 upon transfer of research into
practical applications as the key to future NDT
success, and by Carino [17] upon
'standardisation' as being as vital as research.
Carino noted the under-funding of such activity,
and this situation remains, however there have
been some significant developments.
The Concrete Society published a major
Technical Report on radar testing of concrete in
1997 [18] and have recently produced a series
of Current Practice Sheets dealing with Half-Cell
Potential, Resistivity, and Linear Polarisation
[19] testing for reinforcement corrosion. A more
substantive report covering these techniques as
well as chloride and carbonation measurement
is in preparation. The Concrete Bridge
Development Group has published a Guide to
Durability Monitoring [20] encompassing a wide
range of NDT methods and the Highways
Agency is developing a set of Guidance Notes on
NDT. The initial parts of this latter document are
nearing completion and deal with testing
masonry arches using techniques such as radar,
pulse echo and conductivity, including
tomographic methods. Also included are post-
tensioned concrete beams using impact-echo
and ultrasonic tomography. These documents
will include guidance on specification and
commissioning of surveys. Other industrial
dissemination has included seminars and
meetings organised both by professional
organisations (see Figure 2) and specialist
companies to increase awareness of capabilities.
'Standardisation' activity has focussed on
European Standards, which in some cases are
scheduled to replace relevant British Standards
in the near future. The British Institute of NDT
has included a Civil Engineering session in the
programme of their annual conference in recent
years, whilst their journal 'INSIGHT' also
features an annual Civil Engineering issue. They
are also considering the establishment of a
Building/Civil special interest group and a
register of test companies. The biennial UK-
based International Conference on Structural
Faults and Repair continues to feature a
substantial number of NDT papers whilst
international journals such as NDT & E
International, and Construction and Building
Materials, often contain output from UK
research.
CONCLUSIONS
No attempt has been made to provide a fully
comprehensive account of all NDT activity in the
UK which is related to Civil Engineering. The
examples identified do however reflect the
principal areas of activity, including ongoing
work. Funding for basic work in Universities in
this field is increasingly difficult to obtain and it
is to be expected that future activity will tend
more and more be in the form of development
work by industrial research organisations and
industry itself. The need for education of the
wider industrial community of the capabilities
and potential for NDT and its management will
however continue worldwide.
ACKNOWLEDGEMENTS
Thanks are due to many Engineers and
researchers in the UK for information
incorporated in this paper, including Dr S G
Millard of Liverpool University, and to EPSRC for
financial support (Grant Ref GR/N 34130/01).
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