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

Engineering Approaches to Concrete Bridge Repair and Protection Creating Wealt Creat Wealth Throug rough Infrast Infra struct cture re Edwin Kruger & Ravi Ronny The South African National Roads Agency SOC Limited (SANRAL)

Maybe should entitle talk Creat Creating Wealt Wealth Throug rough (unsafe) Infra Infrast struct cture re (ugly but safe)

CONTENT  Introduction  Bridge Management System  Identification of Bridge Repair projects/Strategy  Rehabilitation/Repair Specifications Creating Wealt Creat Wealth Throug rough  Infrast Infra struct cture re Concrete Protection  Background on durability and testing in SA  SANRAL durability specifications  Conclusions

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 Creating Wealt Creat Wealth Throug rough a mistake! Infrast Infra struct cture re • 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.

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 Creating Wealt Creat Wealth Throug rough design) and construction (placing) Infrast Infra struct cture re 4. Accidental Damage (eg. Over-height vehicles) 5. Extreme weather or other natural events like earthquakes

First Steps 1. Inspect structures according to a set system. 2. Decide which structures to rehabilitate Creating Wealt Creat Wealth Throug rough Infrast Infra struct cture re 3. Do more detailed project level inspections.

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 Creat Creating Wealt Wealth more and more assuming a more major role when bridge Throug rough Infrast Infra struct cture re repair projects are identified. • Only qualified structural bridge engineers who undergo specific training may do inspections. They must know what they are looking at!

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 Creating Wealt Creat Wealth Throug rough Infrast Infra struct cture re • Must lead to actual projects • Do not inspect just to say one has inspected. Must act on results

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) Creating Wealt Creat Wealth Throug rough Infrast Infra struct cture re 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)

Example of an Inspection report (extract) Creat Creating Wealt Wealth Throug rough Infra Infrast struct cture re 10

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. Creating Wealt Creat Wealth TMH = TECHNICAL MANUAL for HIGHWAYS (Compulsory) Throug rough Infrast Infra struct cture re 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.

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 . Creat Creating Wealt Wealth Throug rough Infrast Infra struct cture re

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 Creat Creating Wealt Wealth diagnostic testing may be needed such as in Throug rough Infrast Infra struct cture re 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

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 Creat Creating Wealt Wealth Throug rough Infrast Infra struct cture re • ASR tests • Chlorides & sulphates in ground water tests Not all the above tests are necessary in all cases

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 of repairs required. • Traffic accommodation is a large cost and may exceed the testing costs. Creating Wealt Creat Wealth • All representative elements may be tested. Throug rough Infrast Infra struct cture re • 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

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 of the Standard COLTO (Now COTO) Specifications including Series 12000 repair specifications Creat Creating Wealt Wealth into a new e COTO Standard Specification document. A Throug rough Infrast Infra struct cture re draft hopefully will be available towards the latter of 2015 or early 2016 • Performance specifications are now the norm for SANRAL in which contractors (and their suppliers) have to supply performance guarantees

Concrete Protection • Very old concrete showing signs of 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. Creating Wealt Creat Wealth • Barrier coatings while in the short terms provide Throug rough protection and aesthetics, often have maintenance Infrast Infra struct cture re 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.

Photos of typical defects (most led to demolition) Creat Creating Wealt Wealth Throug rough Infra Infrast struct cture re

Problem roblems enc encount ountered ered • Consultants general lack of rehabilitation knowledge • Consulting Engineer’s desire for perfection • Massive proposed expenditures for unnecessary work • Product marketing by suppliers Creating Wealt Creat Wealth Throug rough Infrast Infra struct cture re • Be careful of 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

Durability urability S Spec pecif ific icat ations ons 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 Creat Creating Wealt Wealth (WS) test Throug rough Infrast Infra struct cture re - Based on this, testing is done on all three indexes on SANRAL projects but with only the OP index as a performance criteria. Draft SANS test are almost approved.