Cracks in Concrete – That You Should Have an Expert Look At
Following on from our last blog, concrete is a highly durable material but it also has its limits. Under certain circumstances, concrete is especially prone to cracking. If the concrete on either side of the crack is at a different level or if one section is higher than the other – this crack could be the result of subsidence.
Subsidence Crack
While it is true that many parts of Perth are blessed with good quality compatible sand to build upon, there are some sands and related earth working practices which lend themselves to an unacceptable degree of subsidence and or lifting. Also, sand used for foundations which is deemed to contain deleterious materials (such as clay or rock) can have an adverse effect on the structural integrity of a building.
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During the leveling of a site, it is not uncommon for earth workers to import sand from another site. This sand should be clean fill, of the correct clay content, and free of vegetation or any un-compressible or decaying material. If such contaminated fill is used, the rotting or un- compactable material can slowly break down leaving voids under the concrete slab and or footings. The concrete now having no or little support can crack and subside to the degree that it affects the structural integrity of the building.
Any surface vegetation and rubbish which exists on site must be dug out and carted away, and not just turned over and buried in the construction zone.
Another cause of subsidence cracking can be from loss of compaction due to washouts. Washouts are more common than they should be with many builders not installing stormwater systems correctly or in some cases not at all, leaving it up to the Client to do it after hand over.
Yet another factor is when incorrectly backfilling to depths. When backfilling to depths it is paramount that this be compacted in layers so that a uniform density is maintained through the entire body of fill.
Sand Jacking
Sand Jacking is typically when shrinkage cracks appear. Let’s say the crack is on a footpath. When the concrete cools down and contracts, windblown sand or sand from nearby traffic can now fill the crack with fine particles. As temperatures rise during the day, the concrete wants to expand but is unable to because the crack is now full of sand. As pressure mounts on either side of the sand-filled crack, that section of pathway lifts slightly to allow for that expansion. This cycle continues and over time the area adjacent to the crack can lift substantially.
You may see evidence of this where local councils have ground down areas of the footpath to remove trip hazards.
Loss of Compaction Due to Neighbouring Conditions
Sometimes you can be blissfully going about your business, unaware that your neighbour is emptying out his pool just on the other side of your boundary line and causing a loss of compaction of your foundation material without even realising it.
Maybe the neighbour has decided to drop the ground level to a point that undermines your footings. Be vigilant and explore beyond your boundary if you suddenly notice new or changed conditions on your property.
Most builders these days will use Chemical Injection when excavating close to the boundary so as not to adversely affect the neighbouring property.
Cracks Caused by Rusting Steel
If water reaches the rebar (a steel bar used to reinforce concrete), it can cause the steel to rust. Rust is an iron oxide which can expand several times its size. The expanding rust can create further cracks in the concrete and can cause structural problems depending on where it occurs. Over time, this can weaken the area around the crack and lead to structural damage.Any of the above cracks should be checked by a suitably qualified person, an Engineer that can provide a report and recommend a remedy for the repair.Don’t ignore structural cracks, they could get worse and become a safety issue.
Author’s Bio
Alex Morrison has worked with a range of businesses giving him an in depth understanding of many different industries including local locksmiths, financial support and health care. As the owner of Integral Media, he is now utilising his knowledge and experience with his rapidly increasing client portfolio to help them achieve their business goals.