In one sense there’s nothing new here. All the points below are the subject of constant discussion and study. This is a broad-brush overview, and you’re probably well educated on most of the details. But maybe we can show you an advanced approach to an old challenge – the durability of concrete.
1. CONTENT AND MIX DESIGN
The research into the ideal mix design for any given situation is extensive, and every premix firm has their particular variations. The factors involved include budget constraints, ease of placement, and available resources – all under an overarching requirement for strong, long-lasting concrete.
We would particularly draw attention to the use of flyash to reduce sorptivity and contaminant permeation. More about these points later.
2. PLACEMENT QUALITY
Here we touch on a pain point. Effective placement involves thorough compaction, to minimize air voids and sufficient coverage of the reinforcing.
Hasty or incompetent placement can introduce serious weakness to the quality of the concrete. Unfortunately, construction or production schedules can pressure teams to sacrifice quality to speed.
3. CURING QUALITY
Curing is a key topic. Concrete must be allowed to cure thoroughly, with minimal thermal differential (i.e. the ambient temperature not too hot or cold), and hydration/evaporation adequately controlled.
Improper curing will lead to plastic or drying shrinkage and resultant cracking. Cracks become the cause of longer-term issues.
This is another pain point, where quality tends to suffer due to the demands of construction schedules.
4. ENVIRONMENTAL CONDITIONS
This refers to the environmental conditions where the structure is situated, and how exposed the structure is to those conditions. Marine splash zones are notoriously challenging for concrete due to the fluctuating moisture levels, and high chloride content of the seawater.
Extreme climates, particularly in cold areas, may cause cracking in the concrete due to significant thermal shrinkage-expansion cycles.
5. CHEMICAL ATTACK AND SITUATIONAL PRESSURES
Concrete structures used to store fertiliser, acids, or bio-waste, are all at risk of a chemical attack. High chlorides, sulphates, or other reactive elements, will pose serious challenges to the concrete.
Other examples include sewage reticulation; aged care floor slabs; or transit areas for reactive chemicals.
Then there are situational challenges such as dynamic loads – transport traffic, wind variations and so on – which test the design engineering of the structure.
Cracking can build up over time. Spectacular failures are thankfully rare, but of course, they do happen, and generally make headlines.
6. INTERNAL REACTIVITY
ASR, DEF and Carbonation are three common examples of reactivity within the concrete. Then there is the potential corrosion of the steel.
- ASR (alkali silica reaction) is driven by non-crystalline silica in certain aggregates when sufficient moisture is available.
- DEF (delayed ettringite formation) is typically caused by precast elements which have been steam cured too hot, leaving some inner material to cure later as water becomes available.
- Carbonation involves the conversion of calcium hydroxide to calcium carbonate over time, which can lower the pH of the concrete, increasing the risk of reinforcement corrosion.
- Steel corrosion is driven by lower pH levels and increased moisture.
Critically, all of these reactions require water to commence and continue.
7. PERMEABILITY
We have arrived at the key point that ties the others together. Notice how sorptivity, cracks, voids, and moisture movement appear through the other factors? There is a direct correlation between concrete permeability and concrete durability.
This is because moisture and the contaminants that it carries through the concrete is a driving force for deterioration. This is called ‘contaminant permeation’, and is the underlying force behind a wide array of concrete issues.
It’s simple:
- If the moisture isn’t already in the concrete, keep it out.
- If the moisture is already in the concrete, immobilize it.
Yes, this is possible: there’s a single treatment which will perform both these tasks, and it’s a concrete hydrogel.
WHAT’S YOUR CONCRETE CHALLENGE?
Whether you’re in the construction industry, civil or structural engineering, or have the care of existing assets, no doubt there are issues you face every day. What’s your field of interest, and what are your pain points?
- New construction?
- Maintenance and repairs?
- Time constraints?
- Cost vs budget?
We’d love to talk to you about your specific concrete industry needs! Get in touch with our friendly team!
