Edwin Kruger & Ravi Ronny The South African National Roads - - PowerPoint PPT Presentation

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Engineering Approaches to Concrete Bridge Repair and Protection

Edwin Kruger & Ravi Ronny

The South African National Roads Agency SOC Limited (SANRAL)

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Maybe should entitle talk

(unsafe) (ugly but safe)

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CONTENT

• Introduction
• Bridge Management System
• Identification of Bridge Repair projects/Strategy
• Rehabilitation/Repair Specifications
• Concrete Protection
• Background on durability and testing in SA
• SANRAL durability specifications
• Conclusions

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Introduc Introduction ion

Where does a rehabilitation plan start?

• At design stage!
• Normal design life is 50 or a 100 years for a
• bridge. However if a bridge is built for a mine

that only has a life of 10 years then durability is not considered a high priority - only cost – What a mistake!

• The environment is influenced by what is left

behind even when a project has served its

• purpose. We all have a responsibility to the

generations that follow. As engineers w e have an ethical duty tow ards society.

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Causes of Defects

• 1. Bad initial design and detailing
• 2. Bad Construction
• 3. Lack of attention to durability of concrete

materials used at time of design (mix design) and construction (placing)

• 4. Accidental Damage (eg. Over-height

vehicles)

• 5. Extreme weather or other natural events

like earthquakes

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First Steps

• 1. Inspect structures according to a set

system.

• 2. Decide which structures to rehabilitate
• 3. Do more detailed project level

inspections.

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CO COTO’s ’s def defec ects-bas based ed Bridge M dge Managem anagement ent S System em (B (BMS MS)

(COTO = COMMI TTEE OF TRANSPORT OFFI CI ALS)

• The BMS is network based system. This is only the start.

(Step 1)

• Based on visual inspection data
• Aesthetics, although not the primary consideration, is

more and more assuming a more major role when bridge repair projects are identified.

• Only qualified structural bridge engineers who undergo

specific training may do inspections. They must know what they are looking at!

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Requirements of a BMS System

• Must be simple and affordable (affordable

inspections)

• Must give believable priority answers to both

the lay person and knowledgeable person

• Must lead to actual projects
• Do not inspect just to say one has inspected.

Must act on results

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The he DER rat rating ing syst stem em

The BMS used by SANRAL and soon all COTO authorities (which includes all provinces and Metros) is based on the so-called DER system where: D (Degree) – Degree of Defect (scale of 1 to 4) E (Extent) – Extent of Defect (scale of 1 to 4) R (Relevancy) – Relevancy of Defect on item inspected (How important) (scale of 1 to 4)

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Example of an Inspection report (extract)

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Output utput from rom B BMS

• Bridge Priority lists are generated by the BMS
• The present algorithm used in the BMS gives weightings to

the different bridge elements. New TMH 22 (presently only draft) will give a deduct based method which will give much the same results. There will thus be a common method for all assets including road pavements etc. Can be applied universally to almost any asset. TMH = TECHNICAL MANUAL for HIGHWAYS (Compulsory) TRH = TECHNICAL RECOMMENDATION FOR HIGHWAYS (Only recommendations)

• From the priority lists projects are initiated
• Defective structures generally appear in groups where

environmental conditions are similar.

• Structurally deficient structures due to design or detailing

errors are scattered.

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The priority list annually Example of part of such a list

SANRAL has upwards of 9000 structures Can not look at structures individually but only the worst and then to do something about repairing them.

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Det etailed ailed projec project Ins nspec pections ions & & Budget udget Esti timat ates es

• The initial inspections at network level in most

BMSs worldwide are generally visual

• Only once projects are identified then more

detailed project inspections takes place

• Depending on the detailed inspections

diagnostic testing may be needed such as in chloride environments.

• Initial project budgets are extracted out of the

visual defect quantities of the BMS

• Only once detailed inspections are completed

(which may include diagnostic tests) are more accurate estimates prepared

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Diagnos iagnostic ic T Tes esting ting

In order to specify correct repair methods diagnostic testing of concrete is needed. Test done are for:

• Cover
• Carbonation
• Chloride ingress
• ASR tests
• Chlorides & sulphates in ground water tests

Not all the above tests are necessary in all cases

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Tes esting ing during during as asses essm sment ent phas phase

• SANRAL uses standard tender documents for

tenders for diagnostic tests depending on extent

• f repairs required.
• Traffic accommodation is a large cost and may

exceed the testing costs.

• All representative elements may be tested.
• Better to allow additional testing in the repair

contracts as extent of concrete degradation may be difficult to ascertain

• Testing could also include for concrete strengths

and cover tests

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Rehabilit ehabilitation/ ation/Repair epair Spec pecifications ifications

• SANRAL developed standard specifications for repair of

structures known as Series 12000 (New Chapter 13 of revised COTO)

• This specification mostly relates to concrete repairs and is

comprehensively detailed.

• A COTO committee has been established to review/ rewrite

sections

• f

the Standard COLTO (Now COTO) Specifications including Series 12000 repair specifications into a new e COTO Standard Specification document. A draft hopefully will be available towards the latter of 2015

• r early 2016
• Performance specifications are now the norm for SANRAL

in which contractors (and their suppliers) have to supply performance guarantees

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Concrete Protection

• Very
• ld

concrete showing signs

• f

distress, carbonated or chlorinated concrete needs protection

• This is generally improved by coating with a silane

penetrant coating and not barrier coatings (carbonation). Barrier coatings must breathe.

• Barrier coatings while in the short terms provide

protection and aesthetics, often have maintenance problems in the long term if not properly executed.

• Concrete not having sufficient cover may be coated

with corrosion inhibitors to create additional protection.

• Where chlorides are present and depending on

extent, could be removed using zinc anodes or by physical extraction.

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Photos of typical defects (most led to demolition)

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Problem roblems enc encount

• untered

ered

• Consultants general lack of rehabilitation

knowledge

• Consulting Engineer’s desire for perfection
• Massive

proposed expenditures for unnecessary work

• Product marketing by suppliers
• Be

careful

• f

so-called life extending products and the products themselves have limited life spans and you might get locked into never ending cycle of repair of the product rather than the structure

• Initial BMS budget estimates were too low.

Now includes traffic accommodation

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Durability urability S Spec pecif ific icat ations

• ns

Comparative Testing

• RILEM international test program 2007 under TC 189-NEC investigated various

test methods used internationally for concrete penetrability

• Includes the three well known South African Durability Index test methods.
• The results proved the acceptability of both the Oxygen Permeability (OP)and

Chloride Conductivity (CC) tests

• Further work is however still required for acceptability of the Water Sorptivity

(WS) test

• Based on this, testing is done on all three indexes on SANRAL projects but with
• nly the OP index as a performance criteria. Draft SANS test are almost approved.

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Durabili ability Spec ecif ific icat ations ions

• Specifying of OPI/ Sorptivity/ Chloride

conductivity is now related to cover, and environmental class (See Table 6000/ 1)

Link - Table_60001_Concrete_Durability.pdf

• The above is now incorporated in draft

revision of COTO Specifications.

• All service providers undertaking work on

SANRAL projects (soon in COTO for durability concrete) in any part of SA are obligated to specify the performance criteria.

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Durabili ability Spec ecif ific icat ations ions (Long ng term benef nefit its)

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Les Lessons

• ns learnt

learnt

• Limited extended life before further repairs

to 15 years is now requested to avoid “Rolls Royce” solutions. Client must accept the risk

• Use far less barrier coatings in the future for

carbonated concrete

• Use of silanes/ siloxanes instead of barrier

coatings in certain applications

• Drawings must be complete before project

handover to Contractor. Lead times to allow for testing needs to be increased

• Get

guarantees early in contract. If necessary withhold payment.

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Conclu clusio sion

• Our

defects-based BMS has proved effective in prioritization

• Performance guarantees for products results in a more

positive approach

• Emphasis now on durability and not strength only
• The cost of associated items such as traffic accommodation

and access contributes a large percentage of repair costs

• Hopefully less future maintenance on newly built structures
• Having performance criteria for asset preservation built into

strategic objectives ensures that bridges do get repaired

• Aesthetics is important to the public.

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Hopef

• pefully

ully w we w e will ill see les ee less of this

• f this

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And nd more

• re of
• f this

this

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And nd

Konrad Lorenz 1973 Nobel Prize winner for Physiology or Medicine Civilized Man's Deadly Sins

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To quote from his autobiography

“Surprisingly late, I got involved with the danger of man's destruction of his natural environment and of the devastating vicious circle of commercial competition and economical growth. Regarding culture as a living system and considering its disturbances in the light of illnesses led me to the opinion that the main threat to humanity's further existence lies in that which may well be called mass neurosis. One might also say that the main problems with which humanity is faced, are moral and ethical problems.”

28

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29

To further quote from Dr Lorenz who in 1973 in “Die acht Todsünden der zivilisierten Menschheit”

• r translated

The Eight Deadly Sins of Civilized Man stated:

“ the senses of aesthetics and ethics are apparently very closely related, so that the aesthetic quality of the environment must directly affect man’s ethical behaviour.” and “The beauty of nature and the beauty of the man-made cultural environment are apparently both necessary to maintain man’s mental and psychic health. Total blindness of the soul to all that is beautiful is a mental disease that is rapidly spreading today and which we must take seriously because it makes us insensitive to the ethically obnoxious.”

ETHICS AND AESTHETICS?

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And nd let let us us not not forget forget thos those w e we e serv erve

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THAN ANK YO K YOU

?