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The official publication of the Concrete Society of Southern Africa NPC
NUMBER 160 . March 2020 . ISSN 1682-6116
Future Concrete Seminar
Africa’s longest suspension bridge
Machine learning applied
in infrastructure
PLATINUM MEMBERS
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CONTENTS
Editor’s comment................................................................................................................ 4
President’s message............................................................................................................ 6
NATIONAL BUDGET
National budget heralds little cheer for construction......................................................... 7
FULTON AWARDS WINNER
Maputo-Katembe Bridge and North Link roads, Mozambique........................................... 8
TECHNICAL PAPER
Using Machine Learning for Condition Assessment of Concrete Infrastructure............ 14
ADIEU
Goodbye to John Sheath............................................................................................. 18
INDUSTRY NEWS
Growing readymix markets with Chryso technology.................................................... 19
Heritage and height mark Concor Western Cape’s landmark project........................... 20
Rehabilitation of the M1 Double Decker...................................................................... 21
Metrorail safety wall built with Echo panels ............................................................... 22
Concor buildings constructing Oxford Parks Phase 1................................................... 24
Consider concrete roads to cut down on potholes, says TCI........................................ 26
AfriSam urban quarry and plant define good neighbourliness .................................... 27
Continuous pours by AfriSam for Gothic at Waterfall Mall.......................................... 28
Training for batchers – key players in quality concrete production................................ 29
Modern flooring products save time............................................................................ 30
a.b.e. supplies renowned glazing products for Africa’s tallest building......................... 32
SOCIETY NEWS
CSSA Awards bursary for 2020.................................................................................... 33
Feedback: 2019 Study Bursary holder........................................................................... 33
Inland Branch Chatter ................................................................................................ 34
ACTIVITIES CALENDAR............................................................................................. 35
MEMBERSHIP DETAILS............................................................................................. 37
COVER: The Maputo-Katembe Bridge,
Africa’s longest suspension bridge.
Page 8.
100
95
75
25
5
0
CONCRETE BETON 3
editor’s comment
W
hen dreams come true, it is difficult to suppress the sense of excitement one feels about
new beginnings and fresh opportunities.
While I am not denying that the issues causing concern over the last few years are
still part and parcel of the Society’s existence, I am a firm believer in making a positive impact in
those areas which one can control and influence in the short term.
John Sheath’s retirement (read more about that on p. 18) has left the CSSA with a
strong leadership base to carry on from. I, and many others, will remain ever grateful for the
managerial skills, guidance, and visionary leadership he has vested in the Society and the lives of
many individuals.
Building on a solid foundation is a pre-requisite for the success of future initiatives. The past
accomplishments of the Society make us confident that the much talked about consolidation
process will incorporate many of the CSSA ‘distinctives’, as our outgoing President, Prof Mark
Alexander, mentions in his message. A process of this magnitude takes time and effort to get it
right and for those getting impatient with what seems to be a drawn-out process, the message
is that the future vision of the consolidated body will remain true to what the Society has always
stood for – promoting excellence in concrete.
The current value-offering of The Society will not be compromised. Instead, similar offerings,
and much more, can be driven from a consolidated body, creating new and powerful platforms
for the benefit of all stakeholders.
An exciting future is being chartered for the concrete community is Southern Africa, and I
certainly wish to be part of this.
Apart from the regional events been organised by the Branch committees, we have two major
I am living my ideal: being events which both promise to be stimulating:
• Future Concrete 2020: The impact of 4IR on concrete design, manufacture, construction and
CEO of the Concrete Society management on 12 May in Johannesburg and 14 May in Cape Town.
and editor of the only • YCRETS 2020: The Young Concrete Researchers, Engineers and Technologist Symposium
1-3 July at Wits aims to create a platform to bring together young individuals who work
non-commercial magazine on the development, design and application of concrete and cementitious based materials,
dedicated to concrete in in Southern Africa.
Southern Africa, Concrete Beton. I urge you to maximise the benefits of your membership by actively engaging with The Society at
events. I also invite personal interaction, suggestions and comment from members.
The adage that behind every successful man is a strong woman, encourages me to pose
the question: what will happen if two strong women were at the helm? Natasja Pols, our very
efficient administrator, and I are up for the challenge to keep the CSSA head office buzzing.
For the continued love of concrete,
Hanlie
Hanlie Turner, CEO & Editor
OUR VISION ADMINISTRATOR Postal: P O Box 75364, Lynnwood Ridge, 0040
To be the most relevant forum for those who N L Pols Tel: +27 12 348 5305
have an interest in concrete.
HONORARY LIFE MEMBERS E-mail: admin@concretesociety.co.za
OUR MISSION P R A Flower, D P Samson, C J Thompson Web: www.concretesociety.co.za
To promote excellence and innovation in the M O de Kock (Prof), M G Alexander (Prof)
use of concrete and to provide a forum for The Concrete Society of Southern Africa NPC
networking and for sharing knowledge and EDITORIAL COMMITTEE (CSSA), its directors, officers, employees,
information on concrete-related matters. Chair: W P Boshoff (Prof), G C Fanourakis (Prof), representatives and agents are not liable for any
G P A G van Zijl (Prof), E P Kearsley (Prof), death, harm or injury caused to any person or
OFFICE BEARERS H D Beushausen (Prof) any loss, destruction or damage caused to any
President: M G Alexander (Prof), person’s property or possessions arising from
Editor: H Turner
goods supplied, or services rendered by
Vice-President: R Raghubir,
the CSSA.
Design, layout and production:
Immediate Past President: H Turner.
DesignWright, Tel: +27 83 448 4264 © COPYRIGHT All editorial material published
ELECTED DIRECTORS in Concrete Beton is reserved to the Concrete
Reproduction and print: Society. Requests for permission to use any of the
W P Boshoff (Prof), R Jacobs, B D Perrie,
Jetline Corporate Print Solutions (Pty) Ltd,
R Maliehe, J Kanjee. material, in part or in full, should be addressed to
Tel: 011 566-0501
the Chief Executive Officer of the CSSA.
CHIEF EXECUTIVE OFFICER OFFICIAL PUBLICATION OF THE Although the CSSA does its best to ensure
H Turner Concrete Society of Southern Africa NPC that information contained herein is accurate,
BRANCH CHAIRS Physical: Suite 423, The Hillside, no liabilities for negligence are accepted by the
P Flannigan, B Hunt, H van Wijk, T Coetzee. 318 The Hillside Street, Lynnwood, 0081. CSSA, its offices, its members, publishers or
agents.
4 NUMBER 160 | MARCH 2020
president’s message
I
wish to welcome our new CEO, Mrs Hanlie These include the Future Concrete 2020 1-day
Turner, and to assure her of the Board’s and seminar in May (Gauteng and Cape Town),
members’ support for her role in the coming the ‘Young Concrete Researchers, Engineers,
months. and Technologists Symposium’ to be held at
I will leave it to her to reflect more on Wits University, 1-3 July 2020, the launch of
the process of consolidation of the various the 2021 Fulton Awards round by way of a call
concrete-related organisation, which is for nominations in June 2020, a Road Show
moving towards finality. Suffice to say that on concrete bridges in September 2020, and
this will be a very challenging year for the of course the regional branch functions. (For
Concrete Society. We will need to negotiate details on these and other events, please visit
our role in the new consolidated organisation, https://concretesociety.co.za/events) I hope
look to retain the values in this organisation this shows that the CSSA is still very much
that the CSSA has always held, and seek to active and seeking to provide value to its
ensure that our members continue to derive members.
benefit from the activities of the organisation. Some brief reflections on my period as
The CSSA ‘distinctives’ that we wish to CSSA president.
retain in the new organisation include this This has been both challenging and
magazine, Concrete Beton, technical road rewarding. The period in which we are living
shows, seminars and workshops, site visits, is, as I have previously written, one where
networking opportunities, student events, and many public and professional organisations
the flagship Fulton Awards. are facing uncertain futures, with massive
The reality, however, is that the CSSA as societal and generational shift. We have had
we have known it will become transformed to grapple with this in the CSSA. But it is clear
into a very different organisation. This will that there is still a strong cohort of ‘concrete
offer new opportunities, while at the same people’ who are as enthusiastic and committed
This is my last presidential time, the previous operating environment will to excellence in concrete construction as
message in Concrete Beton change. The Board will be at pains to ensure ever around the country, and with whom
that the opportunities are maximised for all it has been a delight to interact. There have
before the CSSA Annual General our members. Clearly, we still need to report been many opportunities for personal and
Meeting and election of the new back to our members on the final proposals in professional interaction, and I am grateful to
order to obtain general approval, and so there all the individuals with whom I have had the
president in March 2020. are still several steps to be followed. privilege of working.
Looking to 2020 and some key events that
are coming up, I would like to encourage all of Hambani kahle, CSSA!
us to support these initiatives to our benefit.
Mark Alexander
PrEng, President
Snapshots of Mark’s two years as president
6 NUMBER 160 | MARCH 2020
NATIONAL BUDGET
National budget heralds little cheer for construction
With the International Monetary Fund (IMF) predicting a growth rate of only 0,8% for
South Africa in 2020, the signs for any recovery in the construction sector are not good,
according to Dr Azar Jammine, director and chief economist at Econometrix.
T
his was the sober assessment Cement sales
shared by Dr Jammine at Dr Jammine said that cement sales had fallen quite sharply over the
AfriSam’s Annual National past year, by some 5% or so. He was “reasonably hopeful”, though,
Budget breakfast event held in that cement demand might be able to achieve about 2% growth
Sandton in February. Even more over the next few years. While there was “no total collapse”, he did
worrying, he said, was that acknowledge that the cement industry was one of worst-faring sectors
this estimate was made before during the current downturn.
the impact of the coronavirus AfriSam sales and marketing executive Richard Tomes noted that
outbreak in China began being cement imports were rising and were having a negative impact on job
felt. The economic growth picture, creation in the country.
therefore, has the potential to “As part of the mining sector, we comply with legislative
deteriorate even further. requirements such as Social and Labour Plans, which mean that the
It was against this background playing field is not level between us and importers,” Tomes said. “There
Dr Azar Jammine.
that Minister of Finance Tito is also the recently introduced carbon tax applied to local producers,
Mboweni had delivered his budget speech, where he committed which importers do not have to pay.”
government to redirect spending towards infrastructure and away from
public sector wages. Construction worst hit
“Most of the upturn in cement demand that we hope for [in the The economy performed poorly in 2019, said Dr Jammine. Some
immediate future] will come from infrastructural investment projects 131,000 jobs were lost in the construction sector– representing 8,8% of
rather than from the building industry,” Dr Jammine said. the workforce. This was the most jobs lost by any sector in the economy.
The building segment was particularly badly hit.
Fate of economy “The outlook for the building industry in the coming year looks very
Dr Jammine argued that the fate of the economy now relied on bleak,” he said. “Building completion statistics – especially for flats and
President Ramaphosa’s ability to implement the plans announced by townhouses – are collapsing.”
Minister Mboweni, and to push reforms that could attract investors and Fewer non-residential and residential building plans were being
make government spending more efficient. passed, and this also did not bode well for the building industry in the
“The president has pledged himself to jump-start investment in short-term.
the economy,” he said. “The Sustainable Infrastructure Symposium “Despite the extensive work that has gone into ensuring that
was held to produce a suite of projects – to send positive signals to AfriSam is operationally efficient, both in its cement as well as readymix
investors.” concrete and aggregate business units, the impact of the declining
Jammine cautioned, however, that members of his cabinet and infrastructure spend has had a severe impact on the company’s overall
his party were not always on the same page – restricting the positive performance,” Tomes commented.
impact of his decisions. Among the potential advances in government With the cement business being highly energy intensive, the impact
efforts, he highlighted the specialised units that had been created in of load shedding and increased energy costs have led to significant
the Office of the President, to address obstacles to investment and increases in production costs. This cannot be fully recovered from the
service delivery. market and means that there would be severe margin squeeze in the
sector which is literally struggling to keep its head above water.
Private sector must push “AfriSam has already taken out all its inefficient capacity and gone
These units include the Investment and Infrastructure Office, and the through the pain of right-sizing the business to cope with the current
Project Management Office, and they are expected to work closely challenging environment. Unless we see an upturn in demand in the
with the Presidential Infrastructure Coordinating Commission, Invest short to medium term, we might have to revisit some of our other cost
South Africa and the Ease of Doing Business Task Team to remove saving initiatives, especially our overhead costs and capex expenditure.
impediments to investment. He said the private sector should engage For now, we will continue to focus on being efficient and delivering
actively with these initiatives to help produce results. value to our customers and end consumers to the best of our ability,”
“I would urge AfriSam to start pushing the Presidency to get these Tomes concluded. s
offices going, to speed up delivery and attract more investment,” said
Contact information: Website: www.afrisam.com
Dr Jammine. “According to the President, the intention is there, but we
Facebook: @AfriSamSA, Twitter: @AfriSam, LinkedIn: AfriSam
are not delivering on this.”
He noted the Presidency’s concern with declining infrastructure,
particularly in municipal water systems and municipal roads. It also
saw the need to create technical, engineering and financial capacity in
collaboration with the private sector.
CONCRETE BETON 7
fulton awards winner
Maputo-Katembe Bridge and North Link roads,
Mozambique
After its completion and inauguration in November 2018, the
Maputo Bridge not only became the longest suspension bridge
in Africa, but also one of the most durable concrete structures
built in Southern Africa, with a main span of 680 m and total
length of 1225 m between the anchor blocks.
C
onstruction of the bridge started in mid-2014 with a total project of bridges were constructed and connected: the North Approach is
value, including the southern link roads, of approx. US$750 a balanced cantilever bridge which was constructed via segmental
million. Design and execution were carried out by China Road launcher, connecting to the main span making up the suspension
and Bridge Corporation (CRBC), based on FIDIC’s Silver book EPC bridge, ending in the post tensioned T-beam bridge which is called the
contract. German consultant GAUFF Engineering was responsible for South Approach.
quality supervision as well as design verification against Eurocode. Moreover, three further bridges connecting the main structure
The main bridge consists of two reinforced concrete approach to the existing Maputo infrastructure were built under the same EPC
viaducts from the North and South banks respectively, which connect contract as cast in place pre-stressed concrete bridges. They are the A
to the main span, a suspension bridge made up of a segmental steel Ramp (508 m), N Ramp (230 m) and the K Ramp (240 m).
box girder deck, held up by two large RC anchorage blocks where the The bridge concept was designed to Chinese standards with the
bottom part below ground level is filled in the shaft in rectangular overall design verified against Eurocode specifications.
chambers of different levels with sand (25 % of weight) and concrete Geological site conditions were made up of various strata comprised
(75 % of weight). of imported fill, tidal silt in the upper layers with fine sand and clay in
The bridge carries four lanes of traffic, two in each direction, with the lower layers. The groundwater level was also extremely high due to
a design speed of 80 km/h. its proximity to the bay. These adverse soil conditions required several
The North and South approach bridges were built utilizing different foundation engineering solutions; diaphragm walls for the
two different design and construction methods based on the local anchorage shafts; bored piles up to a diameter of 2.2 m drilled with
conditions. a slurry suspension; subsoil stabilization using cement-stabilized earth
In the North, the first 240 m of the approach bridge was constructed piles; high-pressure grouting below the diaphragm walls; lowering of
with use of 30 m-long precast post-tensioned T-beams. The next 853 the groundwater; pile loading tests with embedded hydraulic cylinders;
m was constructed utilizing balanced cantilever construction methods driven reinforced-concrete piles and sheet piling. These foundation
rising towards the main bridge with a gentle S-curve. The southern solutions all required a highly workable fluid concrete, so that casting
approach bridge was constructed using prefabricated post-tensioned at extreme depths could be achieved with self-compaction over a long
T-beams of 30 m and 45 m culminating in a total length of 1234 m. period of time during these procedures.
The approach bridges connect on each side to a single-span double- Construction of the shafts of the anchor blocks on the North and
hinged suspension bridge with a centre span of 680 m. The side spans South banks started in early 2015. Each gravity anchorage is made up
are 260 m and 285 m long respectively. In reality, 3 different types of the foundation, splay-saddle buttress, and anchorage chambers,
8 NUMBER 160 | MARCH 2020
fulton awards winner
devices. Steel pipes were installed into the reinforcement cages to
facilitate cross-hole sonic logging tests to detect any abnormalities in
the self-compacting concrete. Gradually as the excavation works inside
of the shafts progressed, the diaphragm wall was reinforced by an
internal cast-in-situ concrete lining ring, which was extended up to a
thickness of 2.5 m towards the bottom. The foundation level at the
shaft bottom itself has to carry a tremendous load. The south anchorage
block weighs an impressive 170000 t with approx. 75% of concrete and
25 % of sand filling.
Extensive soil and bearing capacity investigations and studies
showed that additional soil improvement measures were necessary at
the bottom of the 37.50 m deep excavation. One third of the bottom in-
situ surface bearing capacity met the required design bearing capacity;
an additional 1.5 m depth was excavated from the other third and
replaced with C20 concrete and the remaining third was strengthened
by installation of 28 unreinforced concrete piles 12 m long and with a
diameter of 1.5 m.
As there was no comparable project in Mozambique for the design
of the bridge foundation piles, the design was based on the findings
of a geotechnical investigation which started two years ahead of the
actual construction work. Pile construction for the towers and foreshore
bridge piers began simultaneously with the anchorage excavation, and
before pile production could begin, their bearing capacity was verified
using static test loads. Based on the findings all piles were optimized in
both diameter and length. These tests were performed by the University
of Nanjing.
The production of the piles followed the international reverse-
circulation-drilling method. A total of 283 piles was constructed for
the approach bridges, each with a diameter of 1.5 m and an average
depth of 50 m, and 48 piles were installed for the towers, 24 at each
tower, and each with a diameter of 2.2 m and length of 105 m at the
South tower and 95 m at the North tower and a further 91 piles for
the bridges of the ramps. The quality and integrity of the concrete in all
of which some are empty, and some are filled with concrete and piles was verified by a third party from South Africa making use of CSL
sand requiring a specific density, all adding to the total weight of the after more than 28 days. Concrete cubes were manufactured for 7, 28,
structure. Each shaft has an external diameter of 50 m, a wall thickness 90 and even 365-day compressive strength tests and slump testing was
of 1.2 m and a wall panel depth up to 56 m. The anchorage structure done on every truck to confirm workability.
on the south side of the crossing with the final excavation depth of The towers of the bridge are a frame-shaped structure composed
37.50 m below ground level is believed to be one of the deepest open of two vertical legs connected by an upper transverse girder at the top
shafts in the world at the time of construction. and a lower transverse girder approximately 45 m from the north tower
In addition to the excavation profile, the verticality of the diaphragm base and 42 m from the south tower base. To increase lateral stability
wall panels was permanently monitored using special Koden measuring both tower legs were inclined at 2º towards the bridge’s centreline.
Post-tensioned 45 m-long T-beams connect to Pylon M2. Free cantilever bridge (spans < 119 m) and the northern anchor block.
CONCRETE BETON 9
fulton awards winner K-Ramp and K-Line going from National Road EN1. Bridge and ramps of 978 m to North Approach Bridge. South Pylon - the tallest structure in Maputo (138 m). A total of 1234 m of T-beams connect Katembe to Main Bridge. Large retaining wall of the N-Ramp. 10 NUMBER 160 | MARCH 2020
fulton awards winner
The main structure of the tower is comprised of rectangular
hollow box sections, each with a height of 7 m and a width of 5 m.
The wall thickness of the upper part of the tower is 1 m, and this
increases to 1.2 m towards the bottom, resulting in a total thickness
of 1.8 m at the base. The final height of the tower on the North
side (Maputo) above the pile cap is 137.1 m and on the South side
(Katembe) is 138.1 m.
The superstructure for the North Approach Bridge was designed
as full pre-stressed concrete with 3-dimensional prestressing. The
cross sections of the cast-insitu box girder of this 853 m long
balanced cantilever bridge is a double cell box on the relevant piers
N08 to N15. For the prestressing of the 3 vertical webs, for each
50 cm two rows of thread bars with an outer diameter of 32 mm
are used. Their yield strength is fpk = 785 MPa, elastic modulus
E = 2.0 x 105 MPa with a control stress for the prestressing
procedures at 0.9 x fpk = 706.5 MPa.
The superstructure is continuously joined to the substructure of
the Pier N09 to N12. For that procedure vertical bars with a length of
up to 20 m are also used to complete the required anchoring during
the construction stages only. At the Piers N13, N14 and N15 the
cast-insitu box girder is supported by pot bearings. As a temporary
anchoring, four solid reinforced concrete blocks ensured the required
anchoring during the construction. After the completion of the
superstructure, the temporary connections were removed, and the
previously installed bearings took over the complete loading.
Strands with a nominal diameter of 15.2 mm for the prestressing
for the longitudinal webs and transversal top slab, the diaphragms
of the first segment of the box girder, the T-beams, pier caps and
the lower and upper cross beam of the pylons are built in. The
characteristic of the strand with a high strength and low relaxation
steel material follows a yield strength of fpk=1860 MPa, an elastic
modulus Ep = 1.95 x 105 MPa and a relaxation rate less than 0.035.
The designed control stress was 0.75 fpk = 1390 MPa during the
A STRONG FOUNDATION FOR
prestressing actions.
Strands with a nominal diameter of 15.2 mm for the prestressing
for the longitudinal webs and transversal top slab, the diaphragms INFRASTRUCTURE SUCCESS
of the first segment of the box girder, the T-beams, pier caps and
the lower and upper cross beam of the pylons are built in. The ROCLA is South Africa’s leading
characteristic of the strand with a high strength and low relaxation manufacturer of pre-cast
steel material follows a yield strength of fpk=1860 MPa, an elastic concrete products.
modulus Ep = 1.95 x 105 MPa and a relaxation rate less than 0.035.
The designed control stress was 0.75 fpk = 1390 MPa during the Surpassing 100 years of
prestressing actions. product excellence.
After the strands were installed in the embedded plastic corrugated
pipes and the concrete reached 85 % of the required strength, the • Pipes
prestressing procedure could be performed. During tensioning • Culverts
procedure, the tension force and elongation were controlled, and the • Manholes
theoretical elongation compared to the measured elongation. The • Poles
latter had to be in an allowed range of ±6%. • Retaining walls
The purpose of the upper and lower beams is to brace the tower • Roadside furniture
legs, and these are made up of rectangular hollow box type sections. • Sanitation
The upper beam is 5.5 m deep and 6 m wide, with a wall thickness of
800 mm, and the lower 6 m deep and 6 m wide, with a wall thickness
Including other related products within
of 1.0 m.
infrastructure development and related
The main cable consists of 91 bundles containing 91 wires of
industries.
5 mm-diameter, which are draped over the main cable saddles of the
towers and connected to the anchor blocks on each side of the river.
The total length of the wires in both cables are a staggering 21878 Visit us on
km. The cables are bound with fixed strapping tape and hot-cast www.rocla.co.za
sockets are provided on both ends. Each hot-cast socket is composed for our nationwide branchesfulton awards winner
of an anchor cup, cover plate, wire divider plate and a zinc copper alloy
which is cast inside the anchor cup. These cables are one of only 27
dehumidified suspension cables in the world!
For the hangers, galvanised high strength steel wires will be used.
The transverse distance between the main cables and hangers is 21.88
m and the standard distance between the hangers along the bridges
The beauty of concrete in geometry in construction. main span orientation is 12 m, with the length of hangers ranging from
73 m at the towers to 3 m at midspan.
Each hanger consists of 61 parallel steel wires, 5 mm in diameter,
with a strength grade of 1770 MPa. In total there are 55 hangers
attached each side to the 57 steel box segments which make up the
main span.
For the construction of the adjoining concrete bridges to the longest
conventional suspension bridge in Africa, cement type CEM II 42.5
A-LN is supplied by Cimentos de Mozambique (CM). This is a Portland
Limestone Cement comprising between 80-94 % clinker and between
6-20% limestone. It has the ability to produce cement strengths
between 42.5 MPa and 62.5 MPa. Two different manufacturers from
South Africa were used to supply the project with Fly Ash (FA) to induce
Pozzolanic activity within the cement. All the fly ash supplied conformed
to SANS 50450-1:2011 requirements for concrete.
The advantage of the addition of FA in the range of up to 40% of
the total cementitious materials for the fresh concrete lies in improving
workability and reduces water requirement for a given slump and
slightly retards the setting time. Concrete had to be pumped up to a
height of 140 m to the top of the saddle house.
For the hardened concrete the main advantages were a massive
decrease in the CO2e emissions, strength development with age
and a reduction in production costs. Other improvements were the
reinforcement’s resistance to chloride attack, improvement to sulphates
resistance, refinement of pore structure, reduction of permeability,
prevention and retardation of the alkali-silica reaction, reduction of heat
generation caused by hydration and also significantly reducing the risk
of thermal cracking that could possibly have taken place during the
casting of the 3 x 4000 m³ anchorage bases. Internal cooling systems
were extensively used throughout the project.
Heat of hydration had to be controlled during the casting of Two of the unique aspects of the concrete on this project was the
anchor blocks and other elements. addition of up to 40% fly ash and a specially formulated superplasticizer.
12 NUMBER 160 | MARCH 2020fulton awards winner
This not only offers immediate cost savings (
characteristics without segregation and a delayed setting time, the
R100 million value’ category.
water reducing and ion exchange effect of the superplasticizer also
greatly contributed to the durability and strength of the concrete.
The Durability was in fact confirmed by the University of Cape PROJECT TEAM
Town’s Concrete Materials & Structural Integrity Unit (CoMSIRU) which Client: Empresa de Desenvolvimento de Maputo Sul, E.P. (EDMS)
tested samples that were cored 9 months after casting from the bottom Principal Agent: China Road and Bridge Corporation (CRBC)
slab of the anchorage, the report stated that the result of the cores Consultants: Gauff GmbH & Co.
tested was the best ever obtained from site manufactured concrete Specialist suppliers:CM Cimentos de Moçambique; Ulula Ash
tested at their facility.
In total 21 different concrete mix designs ranging from C20 to C50
were designed and tested. Supply of aggregate came from 4 different
suppliers as there was concrete manufactured 7 days a week as it was
not possible to have a continuous supply from only one supplier. The
North and South bank operated independently and thus each had their
own concrete mix designs.
Further durability testing was performed at Concrete Testing
Services in Johannesburg on the concrete cover that varied between
50 mm and up to 150 mm thick.
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6024 Ashak Constrctn A5 March 2020 Concrete Beton adtechnical paper
Using Machine Learning for Condition
Assessment of Concrete Infrastructure
A review of the associated challenges and potential benefits.
by Leandro F.M. Sanchez and Marcelo Terra.
C
ivil infrastructure is critical for society, connecting nations’ Currently, industry professionals rely on standard protocols to perform
businesses, communities, and people; driving the global condition assessments of critical concrete infrastructure to determine
economy; and improving the quality of life of human beings. the cause and extent of damage (that is, to diagnose distress), evaluate
Usually, concrete infrastructure is designed with a life span of 50 to 75 the structural consequences, and access the likelihood of further
years. This so-called “service life” depends on the governing design deterioration (that is, to formulate a prognosis); and to initiate timely
standard, the structure type (for example, a dam, sewer system, and efficient management actions. Assessment is based largely on tools
pavement, bridge structure, or tunnel), its environment (weather and/or that appraise mechanical properties, physical integrity, and durability of
chemical exposure), and the way the structure is maintained. the deteriorated materials and structural components.2,4-6
It is widely known that some critical structures built in the 1960s to
the 1980s in Canada and worldwide are now reaching the end of their Techniques to Assess Damage in Concrete
service lives; action is thus needed to ensure adequate performance Bérubé et al.7 developed a management protocol of aging structures
over the remaining years of service—or even to extend the life spans of based on several chemical, physical, and mechanical laboratory test
these structures beyond their design service lives. Moreover, many of procedures. Building on these, improved guidelines have been
these structures already present clear signs of distress due to severe proposed.8 Sanchez et al.2,9-11 proposed optimized testing protocols
damage mechanisms. In many cases, such distress could decrease a and models to diagnose and better understand numerous distress
structure’s performance to unacceptable thresholds (Fig. 1). processes in concrete, such as AAR, delayed ettringite formation (DEF),
In this context, alkali-aggregate reaction (AAR) is one of the most and cyclic freezing and thawing (FT). The established approach is a
important damage mechanisms affecting the overall performance of multilevel analysis, which makes use of advanced microscopic
concrete infrastructure worldwide.1,2 Two distinct AAR mechanisms are examination and mechanical testing techniques. Among the most
currently recognized: promising proposed techniques are microscopy methods such as the
• Alkali-silica reaction (ASR) is a chemical reaction between unstable damage rating index (DRI) and quantitative image analysis (IA)
silica mineral phases from the aggregates used in concrete and the techniques (Fig. 2).1,6 The DRI method is performed using a
alkali ions found in the concrete pore solution. It is by far the most stereomicroscope (15 to 16× magnification)—damage features are
common reaction mechanism found in concrete around the world2; counted within 10 x 10 mm (0.4 x 0.4 in.) grids drawn on the surface
and of a polished concrete section.10,12,13 Figure 3 illustrates damage features
• Alkali-carbonate reaction (ACR) is a chemical reaction that happens within one grid on a specimen. The number of incidents corresponding
in concrete in the presence of limestone and/or dolomite aggregates. to each type of feature is then weighted to reflect that feature’s relative
Currently, there is no consensus in the technical community on the importance toward the deterioration mechanism, and these weighted
real mechanisms causing ACR-induced expansion and damage. Yet counts are summed. The weights used in the method were originally
the dedolomitization of dolomite seems to be one of the potential selected on a logical yet ad hoc basis10,12; these were recently modified
causes.2,3 to reduce variability between experts.12 It has been
shown that DRI values are clearly associated with induced expansion
and damage caused by AAR, DEF, and FT.2,9-11 Nevertheless, the method
is time-consuming and subjective— successful application is heavily
dependent on the skill and experience of the person performing the
analysis. Recently, Rivard et al.6 proposed the quantitative IA technique
(refer to Fig. 2(b)). Crack density and total length have been correlated
with induced expansion, but correct crack quantification
crucially depends on successful sample preparation (polishing and
impregnation with epoxy).
Both DRI and quantitative IA require experts to perform time-
consuming petrographic microscopy of samples. Thus, the methods are
not scalable, and they are not widely accessible.1-11 This means that
for the foreseeable future, many structures may remain with neither
proper inspection nor adequate protection against potential loss of
serviceability and performance. However, machine learning (ML)
techniques provide potential solutions that promise to reduce the
subjectivity yet increase the speed, reproducibility, accessibility, and
accuracy of diagnoses.
Fig. 1: A concrete foundation near Québec, Canada. The surface
cracking and leachate are indicative of alkali-aggregate reaction (AAR).
14 NUMBER 160 | MARCH 2020technical paper
Automating Microscopic Procedures through ML from the University of Ottawa, Ottawa, ON, Canada, performed a
ML is a field of artificial intelligence that develops algorithms to enable proof-of-concept evaluation of using deep-learning algorithms (ML
systems to make predictions or take actions based on learning from systems comprising many layers of neurons) to recognize the seven
data, rather than following explicitly pre-programmed instructions.14,15 distinct types of cracks assessed through the DRI method (Fig. 3(a)). The
In Phase I of a study aimed at automating DRI assessments, students study required the training of an algorithm, using about 200 digital
images of square grids on 24 AAR-affected concrete samples. The
samples contained a wide range of reactive aggregate sizes and mineral
types; exhibited compressive strengths of 25, 35, and 45 MPa (3630,
5080, and 6530 psi); and exhibited expansion levels of 0.05, 0.12, 0.20,
and 0.30%. All specimens were prepared by cutting and polishing, and
the DRI was manually evaluated for each. The images were also labeled
to identify the damage features on each, and these labeled images
were used as training data for an ML algorithm.
To automate the assessment of concrete samples, the Phase I
researchers applied a convolutional neural network (CNN) algorithm to
identify damage features in the images of the concrete samples. In
broad terms, CNN algorithms comprise a class of artificial neural
networks that include digital filters to identify changes in contrast and
(a)
color among the pixels within a photo. Such algorithms have been very
successfully applied for the classification of objects in photos and
videos.16,17
Depending on the depth of the network and the number of pixels
in the input images, CNN algorithms can include thousands (in some
cases, millions) of parameters (commonly termed weights). These
weights are successively adjusted during the training of a CNN model,
in which the algorithm’s predictions of features are compared against
ground-truth data (multiple labeled images). The errors between the
predictions and the ground-truth data are minimized by adjusting the
weights in successive passes through the training data.
When trained with enough examples, a CNN model can, with great
accuracy, predict the labels in new images. For our experiment, the
(b)
training examples were images of 10 x 10 mm regions on polished
concrete specimens, and the images were labeled with a 0 or 1 (yes/no)
Fig. 2: Polished concrete samples: (a) sample prepared for damage
rating index (DRI) analysis by drawing 10 mm (0.4 in.) square grids for each of the seven DRI damage features. Several CNN architectures
on the surface; and (b) sample prepared for quantitative image were tested, and the one that yielded the best performance was
analysis (IA) by impregnating with an epoxy dye that fluoresces selected for the remainder of Phase I.
under UV illumination9
Damage Weighting
feature factor
Cracks in coarse aggregate (CCA) 0.25
Opened cracks in coarse aggregate (OCA) 2
Crack with reaction product in coarse aggregate
2
(OCAG)
Coarse aggregate debonded (CAD) 3
Disaggregated/corroded aggregate particle (DAP) 2
Cracks in cement paste (CCP) 3
Cracks with reaction product in cement paste
3
(CCPG)
(a)
Fig. 3: Using the damage rating index (DRI) method, weighting (b)
factors are applied to damage features identified in a petrographic
examination: (a) weighting factors are assigned to each feature to
reflect its relative importance toward deterioration; and (b) an exemplar micrograph of a 10 mm (0.4 in.)
square grid section on a specimen, with labels added to indicate damage features9
CONCRETE BETON 15technical paper
Results and Ongoing Developments We plan to leverage an algorithm with feature-extraction techniques
Once trained, the ML system in Phase I could predict the seven different that have been highly successful in texture analysis for biomedical
DRI features (or concepts) with an average accuracy of 64%. Given the images (for lesion detection), as it has been trained on large image
small amount of training data (only 200 images), this is a very high datasets. We intend to apply our concrete-specific training data (images)
accuracy, as CNN models are generally trained with thousands (in some to extend the algorithm to identification of damage features. This
cases, millions) of images. However, the DRI value was not calculated Fig. 4: Comprehensive damage protocol for assessing damage in critical
for any of the images because the crack detectors developed in this first aging infrastructureis a standard workaround for successfully training
approach were still considered to be too imprecise. algorithms when only limited problem-specific data are available.
Ongoing research is currently being carried out by a new team at With these innovations and approximately 10,000 new, high-
the University of Ottawa using additional training data to improve the resolution images of DRI grid areas from AAR-affected concrete, we
accuracy of the predictions and also to use this refined model to hope to reach human accuracy levels of 90% or greater in the counting
compute DRI numbers. The goal is to fully automate the DRI test of cracks.
protocol to assess AAR-affected concrete and predict not just crack We are currently predicting the DRI directly with a neural network.
types but an actual DRI. Finally, in a further step (Phase III), it is planned However, this results in the loss of interpretability. We therefore intend
to use the refined ML system to evaluate other damage mechanisms to apply the existing DRI method (combining crack counts for individual
such as external and internal sulfate attack, FT damage, and steel damage types), evaluated in conjunction with the Phase II CNN
corrosion, so that the proposed approach might become a algorithm. In this sense, the machine will replace only the petrographer’s
comprehensive protocol to assess critical aging infrastructure (Fig. 4). ability to identify and count cracks associated with each damage
The Phase I crack detectors have already been significantly improved feature.
and may now recognize cracks through 1 mm2 (0.002 in.2) images Once the new automated DRI approach is successfully implemented
with about 80% accuracy. Additional improvements are in progress to for AAR cases, forthcoming steps will pursue its extension for a much
increase this further. Moreover, Phase II is currently underway, with wider variety of damage mechanisms, establishing a revolutionary
almost 4000 new images from 36 new specimens (already DRI assessed) comprehensive automated protocol for assessing damage in concrete.
representing distinct mixture designs and expansion levels. The ultimate Finally, other innovative studies in this context are about to be started in
goal of the Phase II work is to use the same explicit DRI formula that an parallel, including automation of the counting of entrained air voids in
expert petrographer would apply based on crack counts. concrete. Soon, we also expect to develop applications (apps) that will
automate the visual inspection of critical concrete infrastructure by
Forthcoming Projects providing preliminary diagnoses of the causes and extents of damage
To apply ML in any field, achieving high accuracy requires training the using only images captured on smartphones.
model with large amounts of data. Fortunately, many highly accurate For readers who would like to learn more about artificial intelligence,
CNN models are already available, and they can be extended to new numerous online resources are available. For example, a particularly
applications through what is commonly termed transfer learning. In dynamic and enlightening explanation of neural networks is available at
effect, the major portions of these existing algorithms are highly capable www.3blue1brown.com/. s
of identifying changes in contrast and features within images. To apply
transfer learning, only a small percentage of the model weights must be
retrained to identify unique features such as cracks in concrete.
Fig. 4: Comprehensive damage protocol for assessing damage in critical aging infrastructure.
16 NUMBER 160 | MARCH 2020technical paper
References
1. Fournier, B., and Bérubé, M., “Alkali-Aggregate Reaction 7. Bérubé, M.A.; Smaoui, N.; Fournier, B.; Bissonnette, B.; and
in Concrete: A Review of Basic Concepts and Engineering Durand, B., “Evaluation of the Expansion Attained to Date by
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2. Sanchez, L.F.M.; Fournier, B.; Jolin, M.; and Duchesne, J., No. 3, Feb. 2011, pp. 463-479.
“Reliable Quantification of AAR Damage Through Assessment of 8. Fournier, B.; Bérubé, M.A.; Folliard, K.J.; and Thomas, M.,
the Damage Rating Index (DRI),” Cement and Concrete Research, “Report on Diagnosis, Prognosis, and Mitigation of Alkali-
V. 67, Jan. 2015, pp. 74-92. Silica Reaction (ASR) in Transportation Structures,” FHWA-
3. Grattan-Bellew, P.E.; Mitchell, L.D.; Margeson, J.; and Min, D., “Is HIF-09-004, U.S. Department of Transportation, Federal Highway
Alkali-Carbonate Reaction Just a Variant of Alkali-Silica Reaction Administration, Washington, DC, 2010, 147 pp.
ACR = ASR?” Cement and Concrete Research, V. 40, No. 4, Apr. 9. Sanchez, L.F.M.; Fournier, B.; Jolin, M.; Bedoya, M.A.B.; Bastien,
2010, pp. 556-562. J.; and Duchesne, J., “Use of Damage Rating Index to Quantify
4. Grattan-Bellew, P.E., and Danay, A., “Comparison of Laboratory Alkali-Silica Reaction Damage in Concrete: Fine versus Coarse
and Field Evaluation of AAR in Large Dams,” Proceedings of the Aggregate,” ACI Materials Journal, V. 113, No. 4, July-Aug.
International Conference on Concrete AAR in Hydroelectric Plant 2016, pp. 395-407.
and Dams, Frederickton, NB, Canada, 1992. 10. Sanchez, L.F.M.; Fournier, B.; Jolin, M.; Mitchell, D.; and Bastien,
5. Grattan-Bellew, P.E., and Mitchell, L., “Quantitative Petrographic J., “Overall Assessment of Alkali-Aggregate Reaction (AAR) in
Analysis of Concrete—The Damage Rating Index (DRI) Method,” Concretes Presenting Different Strengths and Incorporating a
Proceedings of the Eighth CANMET/ACI International Conference Wide Range of Reactive Aggregate Types and Natures,” Cement
on Recent Advances in Concrete Technology/Marc-Andre Bérubé and Concrete Research, V. 93, Mar. 2017, pp. 17-31.
Symposium on Alkali-Aggregate Reactivity in Concrete, Montreal, 11. Sanchez, L.F.M.; Drimalas, T.; Fournier, B.; Mitchell, D.;
QC, Canada, 2006, pp. 321-334. and Bastien, J., “Comprehensive Damage Assessment in
6. Rivard. P.; Fournier, B.; and Ballivy, G., “Quantitative Assessment Concrete Affected by Different Internal Swelling Reaction (ISR)
of Concrete Damage Due to Alkali-Silica Reaction (ASR) by Mechanisms,” Cement and Concrete Research, V. 107, May
Petrographic Analysis,” 11th International Conference on Alkali- 2018, pp. 284-303.
Aggregate Reaction, Québec City, QC, Canada, 2000, 12. Villeneuve, V., and Fournier, B., “Determination of the Damage
pp. 889-898. in Concrete Affected by ASR—the Damage Rating Index (DRI),”
14th International Conference on Alkali-Aggregate Reaction in
Concrete (ICAAR), Austin, TX, 2012.
13. Dunbar, P., and Grattan-Bellew, P., “Results of Damage
Rating Evaluation of Condition of Concrete from a Number
ACI member Leandro F.M. Sanchez of Structures Affected by ASR,” Proceedings of CANMET/
is an Assistant Professor in the ACI International Workshop on Alkali-Aggregate Reactions in
Department of Civil Engineering at the Concrete, Dartmouth, NS, Canada, 1995, pp. 257-266.
University of Ottawa. He is a member 14. Maini, V., and Sabri, S., “Machine Learning for Humans (Part
of ACI Committees 201, Durability of 2.1: Supervised Learning),” 2017, 97 pp. https://medium.com/
Concrete; 211, Proportioning Concrete machine-learning-for-humans/why-machine-learning-matters-
Mixtures; 221, Aggregates; and 555, 6164faf1df12.
Concrete with Recycled Materials.
15. Unsupervised Learning: Foundations of Neural Computation
Sanchez is also a member of RILEM
(Computational Neuroscience), first edition, G. Hinton and T.J.
committees on alkali-aggregate reaction
Sejnowski, eds., A Bradford Book, 1999, 398 pp.
and recycled concrete aggregates. His
research interests include concrete 16. Krizhevsky, A.; Sutskever, I.; and Hinton, G.E., “ImageNet
durability and assessment and Classification with Deep Convolutional Neural Networks,”
rehabilitation of aging civil infrastructure. Advances in Neural Information Processing Systems 25, F. Pereira,
C.J.C. Burges, L. Bottou, and K.Q. Weinberger, eds., 2012, pp.
ACI student member Marcelo Terra 1097-1105.
is an MS candidate in civil engineering 17. Ciresan, D.C.; Meier, U.; Masci, J.; Gambardella, L.M.; and
at the University of Ottawa. His current Schmidhuber, J., “Flexible, High Performance Convolutional
research work includes the use of artificial Neural Networks for Image Classification,” Proceedings of the
intelligence to design and appraise Twenty-Second International Joint Conference on Artificial
concrete materials. He has over 20 years Intelligence, Barcelona, Catalonia, Spain, V. 2, 2011,
of experience in the concrete industry in pp. 1237-1242.
Brazil. Terra received his BS in mechanical
engineering from the University of Mogi Reproduced from Concrete International - November 2019,pages
das Cruzes, São Paulo, Brazil. 35-39, by kind permission of the American Concrete Institute.
CONCRETE BETON 17ADIEU
Goodbye to John Sheath
A
s the CSSA bid farewell to John at the He spent 13 very fruitful and happy years at
end of 2019 after nine years as CEO, C&CI until his retirement in 2009. However, at
and many more years in the industry, 63 he was not ready to ‘hang up his boots’, so
this is a glimpse into the man behind the he took up a commission with Ash Resources
business persona. to assist them with their Strategic Planning.
John was born in 1946 in Southampton, John had been very active on a voluntary
England and was the youngest of four children. basis with the Concrete Society (CSSA) since
His mother died of a brain hemorrhage when joining the C&CI, so when, at the end of his 18
he was 18 months old, and so he had some month contract with Ash Resources, he was
very difficult early years growing up. offered the position of CEO of the CSSA, he
At 20 he joined Borden Chemical gladly accepted.
UK, focused on manufacturing resins He had been a CSSA member for some
and adhesives for the furniture, foundry, years, a branch committee member, branch
packaging, footwear and motor industries. secretary, branch treasurer, member of
He worked his way up the organisation council and then National President. He was
through what was then the traditional route also awarded the Society’s National Concrete
in marketing – sales office, office manager, Achiever Award in 1999 and Inland Branch
technical salesman, marketing assistant and Concrete Achiever Award in 2019.
finally marketing manager. Here he spent nine pleasant years at the
John, 1975.
It was at Borden Chemical that John was Society’s Head Office, but then, at the age of
mentored by the Director of his division, John the corporate identity of the company to 73 he decided to completely retire.
King, and where he learnt how to manage that of Expandite, a well-known construction When asked about the highlights of his
people, make decisions and lead by example. chemical company serving the construction career, John listed many:
During that time, he gained the UK Diploma and mining industries. • Obtaining his Diploma in Marketing
in Marketing Management. This was his first contact with the Management
In 1980 John was offered a contract in construction and mining sectors, and he was • Working under a fantastic mentor and
South Africa working for Borden’s licensee ultimately promoted to Marketing Director boss at Borden Chemical
there – General Chemical Corporation of the company, a position he held for ten • Emigrating to South Africa
(Genkem). years. This included the time when John was • Changing the corporate identity of Burmah
In 1981, John and the family emigrated transferred to Fosroc, with the sale of the Adhesives and Sealant to Expandite (for
to South Africa and he spent the next two Expandite construction chemical business to which he received an award from the
years setting up a new division manufacturing that company. Company)
and marketing a new range of phenolic resin In 1996 he joined the Cement and Concrete • Gaining the Katse Dam contracts and
compounds for injection and compression Institute (C&CI) as Marketing Manager with visiting the site on many occasions
moulding. In 1983 he joined a Burmah- the task of shifting the organisation from a • Achieving Company Director status
Castrol company – Burmah Adhesives and technically oriented Institute to more of a • Passing the Chartered Marketer board
sealants where his first task was to change marketing one. exam to become a CM (SA)
• Being appointed CEO of the Concrete
Society
John regrets that having retired, he cannot see
the completion of the consolidation process.
His vision remains to see the emergence
of a dynamic, relevant consolidated concrete
organisation that represents the whole
industry, and which maintains the ‘concrete
community’ spirit that prevails in the Society.
John married Mollie in 1967. They have a
son Mathew (46), a daughter Caroline (43) and
five grandchildren between 8 and 18 years.
John and Mollie have since relocated to
Sedgefield in the Western Cape, where he
will have time to pursue his interests of gym,
kayaking, Formula 1, photography, wildlife,
gardening and DIY.
We wish John and Mollie health and
One of the first in SA to gain Chartered John in retirement. happiness in their new venture. s
Marketer (CMSA) status.
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