Fixing concrete cancer
by Megan Macpherson
Choosing a Professional
Concrete affected by concrete cancer may not need to be knocked down completely.
It is important for the extent of the problem to be diagnosed by a professional. Tests can be performed to measure the level of alkalines and chlorines at various depths.
Choosing a concrete repairer is the first step to fixing the problem. The Australian Concrete Repair Association has a list of members which comply with the association’s mission. The goal of the association is excellence in the concrete repair field, and members are subject to association scrutiny, education and training. A concrete repairer should diagnose the problem with the building, and propose a solution specific to the individual job.
Cracks need to be filled, and exposed steel needs to be covered and waterproofed. Damaged concrete should be removed, and steel cleaned of rust or replaced and then covered with new concrete.
As concrete draws water, waterproofing is needed to effectively prevent water from corroding steel bars. An inert sealing substance will prevent water from being soaked into the concrete, as well as stop the contaminating chemicals from getting into the pores.
History of concrete cancer in Australia
Ahmad Shayan was the first person in Australia to diagnose the cause of concrete cancer, and from this figured out ways to fix it. Samples of cracked concrete were tested by him, and he found that there was a reaction between the aggregate and the alkaline in the cement which causes the cracking. During the research he learned that waste glass can be mixed in with concrete, and old aggregate from recycled concrete can be used to make new concrete. These recycling factors prolong the life of concrete, and the structures it is used in.
Law of Fives
The Australian Concrete Repair Association explains on its website the Law of Fives, which says that for four phases in concrete cancer, the value of damage in dollar terms increases by a multiplication of five if it is left to deteriorate to the next stage.
“The life of a concrete structure with concrete durability problems can be divided into four phases:
- Design, construction and concrete curing
- Corrosion initiation processes are underway, but propagation of damage has not yet begun.
- Propagating deterioration has just begun.
- Propagation of corrosion is advanced, with extensive damage manifesting.
One dollar extra spent in Phase A is equivalent to saving five dollars remedial expenditure in Phase B, or 25 dollars remedial expenditure in Phase C, or 125 dollars remedial expenditure in Phase D.”