RepSem 2015, the 1st CSSA seminar for 2015 proved to be a success in terms of quality of speakers, spread of topics, attendance figures and overall organisation. More than 300 delegates attended the Concrete Repair and Protection seminar held at Stellenbosch, Port Elizabeth, Durban and Johannesburg, which was chaired by Hanlie Turner, Vice President of the CSSA.
Watch the video overview here, courtesy of Concrete.TV:
Prof Mark Alexander presented a thorough theoretical introduction to the fundamental causes of failure and deterioration mechanisms. The salient points of his presentation can be summarised as follows:
- Concrete deterioration usually involves a combination of complex mechanisms – mechanical, physical, and chemical
- Environment and its interaction with the structure is critical
- Concrete durability is of increasing concern, but is a more intractable problem to solve for many engineers
- Steel corrosion remains the most dominant form of reinforced concrete deterioration
- Constant development and improvement of repair techniques and strategies are needed to ensure longevity of current RC infrastructure
SANRAL’s perspective titled Engineering approaches to concrete bridge repair and protection was presented by Edwin Kruger in three of the venues, while Ravi Ronny made the presentation in Durban.
The causes of defects in bridges can usually be ascribed to one, or a combination of, the following factors:
- Bad initial design and detailing
- Bad construction
- Lack of attention to durability of concrete materials used at time of design (mix design) and construction (placing)
- Accidental Damage (e.g. Over-height vehicles)
- Extreme weather or other natural events like earthquakes
The Bridge Management System (BMS) used by SANRAL and soon all COTO authorities (which include all provinces and Metros), is based on the DER system: Degree of defect, Extent of defect and Relevancy of defect.
SANRAL has 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 very detailed.
- SANRAL has found that their defects-based BMS has proved effective in prioritization or repair projects
- Performance guarantees for products results in a more positive approach.
- The emphasis has shifted to 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
The presenters made a final and passionate plea to take aesthetics into account for all projects, as structures are built for the public and the users of these structures, not merely as functional infrastructure.
Three speakers made presentations on various methods of repair.
Dr Gareth Glass talked on concrete protection using sacrificial anodes. Cassandra van der Merwe presented on crystalline water proofing and Navin Shewani’s presentation dealt with rapid setting repair mortars.
Gareth concentrated on treating corrosion in reinforced concrete structures using galvanic anodes. His presentation was structured around the causes & implications of corrosion, factors influencing corrosion, repair solutions and he finished off by presenting case studies.
The 1st generation of galvanic anode operation involved galvanic anodes in patch repair to stop anodes on steel, while the 2nd generation involved galvanic anodes in parent concrete to stop anodes on steel.
The use of hybrid anode technology will extend the life of a structure by 30 to 50 years; simple installation with less concrete breakout, low maintenance, innovative dual technology, cost-effective, performance can be monitored and the technology conforms to international standard ISO 12696:2012.
Benefits include: Limited disruption during application, targeted to area of need, increased service life, reduced breakout.
Navin Shewani’s presentation focussed on the European Standard for rapid setting repair mortars. He provided background to EN 1504 which consists of 10 main parts covering about 65 standards for test methods for atmospherically exposed, buried and submerged concrete structures.
Navin concentrated his presentation on the requirements, testing and application of a Class R4 structural repair product.
Recommended uses are in columns, piers and cross beams of all bridges, cooling towers and chimneys and other industrial environments, marine structures, water treatment and sewerage facilities and tunnels, pipes, outfalls and all below ground construction especially in harsh ground conditions.
These mortars are easy to mix, based on non-sag rheology, application thickness up to 30mm, are pumpable, sprayable or hand applied with a rapid setting achieving 16 MPa in 3 hours.
Cassandra van der Merwe presented on crystalline waterproofers for application in waterproofing, protection or repair contracts.
Crystalline waterproofers may be added at the time of batching or applied post-construction to a suitably prepared surface from the negative and positive side. Applications include the strengthening and waterproofing of concrete tunnels, harbours, runways, water reservoirs, basements, slabs, and roof gardens.
The water proofer becomes an integral part of the concrete, while penetrating deeply to seal capillary tracts and shrinkage cracks. It can be applied to either the positive or the negative side and is completely effective against high hydrostatic head pressure. Crystalline waterproofers can be applied to moist or green concrete, are nontoxic and thus approved for potable water use.
Deon Kruger and Matthew Scott did a joint presentation on non-destructive assessment of concrete segments using state-of-the-art infrared thermography. Deon set the scene for the need for non-destructive assessment in general, while Matthew proceeded to provide the background on infrared cameras and thermography. He then presented a case study where this technology was used on a cooling tower. This project formed part of his research towards his MSc degree. The use of the infrared concept was supported by ASTM D4788 – 03: Standard Test Method for Detecting Delaminations in Bridge Decks Using Infrared Thermography.
Gordon Mowatt concluded the day with a presentation titled Essential Steps in the implementation and measurement of concrete repair projects. His presentation was based on the fact that given high capital costs of demolition and reconstruction, it makes sound economic sense to upgrade buildings and structures, rather than to knock them down. The success of a repair project could hinge on importance of skill set, correct specification, measurement and itemization during the
pre-tender documentation stage.
Structures are repaired to make it safe, restore structural competence, extend the service life, change of use or to improve the aesthetics.
He stressed that the access scaffolding on a repair contract was usually the most expensive part of the project.
In summary he identified the essential steps to a successful repair job as:
- Health, Safety & Environment
- Definition of the client's objectives
- Assessment of damage or deterioration and diagnosis of its cause
- Specification of the repair work
- Preparation of contract documents including a full specification and bill of quantities.
RepSem 2015 - Photo Gallery
(Click on images to enlarge)