Category Archives: Tips & Tricks

Tips and tricks for building in Queensland.

Why do Industrial Concrete Pavements Crack

Why do industrial concrete pavements cracks and degrade? Join our #StructuralWhyFile to find out how to improve your chances of a top quality industrial concrete slab in #Australia.

Shrinkage Cracks

G’day. It’s Matt Cornell from Cornell Engineers. Today we’re going to have a quick look at an external concrete slab – a driveway slab – and have a look at some failures that are pretty common and I’ll give you a couple pointers on how to avoid them.

So here we are let’s start with this one. This crack looks like a shrinkage crack and shrinkage cracks occur in the early days of a concrete slabs life – probably in the first one to four days and they occur when the concrete shrinks, loses volume and gets smaller in volume, before the concrete has enough strength to resist the tensile forces.

So the crack forms at at stressed locations, in this case there was another piece of concrete against it and would have propagated over its life. It isn’t going to get any worse.

The best way to avoid these types of cracks is to place extra reinforcement at stress locations. So a couple of extra bars across the perpendicular to the direction of the crack would have kept that crack closed or at least a little bit more controlled.

Abraded Concrete from Weak Surface

So moving on now and we’re looking at some abraded concrete. See how the stones in the cement matrix of the concrete matrix have been exposed which probably means that the surface has been abraded away by the wheel traffic or weathering or both leaving the fine stones and exposing them to so that you can see them.

So probable cause of this is either a weak surface the cement matrix was water soft or had too much water in the in the cement matrix at the surface and that decreased the strength of the concrete layer on top and allowing it to be abraded by the wheel traffic.

Crack Beside Sawn Joint

Moving back up to here so this next crack is an interesting one.

See how it’s right beside a sawn line that – the straight line is a saw cut line in the concrete and there’s a crack right beside it.

So in this case this is still a shrinkage crack the purpose of that sawn joint was to avoid this crack forming or to relieve the stresses in the concrete that caused this crack to form.

So what has actually happened is the sawn joint has been placed way too late. Even if it had been placed the next day after the concrete was poured it’s likely that the sawn joint had have been placed way too late so it really should have been placed in the first six to eighteen hours after the concrete was poured.

So now we see some more abraded concrete – the surface layer is lost and the stones are very well exposed.

Shrinkage Cracks Again

Coming up now to a different kind of crack again so, well actually, it’s the same kind of crack because it’s another shrinkage crack.

So cracks that propagate from changes in shape of concrete or corners where cutouts were placed in the concrete for the grated are prime examples for concrete to shrink in two directions away and the stress buildup is accentuated at the corner of the grated and causes it to crack in another location where extra reinforcement should have been placed in the concrete.

Moving on and you can just make out a pattern of rectangular shaped things on that patch of concrete back there but we’ll come back to that. So across another control joint.

Shrinkage Cracking in the Middle of a Slab Panel

This crack in the middle of the driveway right down the centre of the driveway is again another example of shrinkage cracking.

So this tells us that perhaps this is where the concreters should have put another control joint – another sawn joint where the crack was positioned.

In this case, unlike the front crack which was right beside a control, a control joint hasn’t been placed in this location in the middle of the driveway and a crack has formed there anyway.

Some more control joints more control joints and more cracks just in the middle of slab panels.

Plastic Shrinkage Cracks

So this rectangular section of straight line cracks is again another sample of cracks but these are not shrinkage cracks. Well in actual fact they are shrinkage cracks they actually known as plastic shrinkage cracks.

So in this case the concrete has actually settled, maybe been under-compacted around these locations.

The cracks are formed as the concrete slumped and hung over the top of the reinforcement so the cracks have opened up again in the early days of the concrete slab so hasn’t really affected the extra life for long age or the longevity of the concrete but nevertheless this concrete has got these cracks showing up and that’s why in this case.

Failed Concrete Corner Joint

And then finally we come to a failed corner joint and I say it’s failed because there’s cracks in each corner – just about each corner on three of the four corners so this is not so much a concreting error as it is an error by the engineer the design engineer the concrete inspector perhaps to instruct the concreter on how to locate dowels – reinforcement across these joints.

The cracks have probably formed after the sawn joints in this case so there has been shrinkage after the concrete was placed after the saw joints were placed across these joints. In industrial to light commercial slabs, there are often dowels. They help keep the concrete slabs level as they open up as the control joints do what they’re supposed to do concrete opens up at those joints if you don’t have dowels there you don’t have load transfer and the slabs can misalign. So these slabs are nicely aligned but the concrete the two-many dowels across the corner in both directions have locked up the concrete.

The concrete has still shrunk but it’s the shrinking forces and the dowels have caused the corners to crack.

Quite A Few Examples of Pavement Failure

So there you have it in quite a small section of concrete really we’ve seen quite a few different types of concrete failure. We’ve seen scabbling of the concrete from a weak concrete surface.

We’ve seen control joints failing because they are either placed too late or dowels being placed across them in both both directions.

We’ve seen plastic shrinkage cracks which were those parallel sort of rectangular cracks that where the concrete was hung over the top of the concrete and we’ve seen that this concrete slab really didn’t have enough control joints in it because of the cracks that are formed in the middle of the concrete panels.

Conclusion – How to Prevent Concrete Slabs Cracking

So that concludes our session on industrial concrete slabs light commercial and light industrial concrete slabs, how they crack and what can be done to prevent that cracking and some of the other failures that we observed.

A lot of the blame has been placed on the concreters but in actual fact construction, concrete construction is a combined effort. Concreters obviously have a large part to play in it but the design engineer, the inspector that inspects the concrete all these people play a part and need to work together to provide top quality concrete slabs.

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3 Surprisingly Simple Ways to Only Hire Quality Engineering Consultants

Looking at the consulting engineering market right now, I see that there’s two qualities of engineering firms out there at the moment.

Too Cheap Engineering Consultants

There’s the way under-priced engineering consultant working for the big building companies.

They’re sending their technical work overseas and/or getting it done in the equivalent of engineering sweatshops right here in Australia. They’re cutting corners on their designs. They’re missing the mark on quality in exchange for way too cheap prices. They are missing or allowing serious issues to develop unchecked.

Is there a consequence of cost-cutting? We’re yet to see the outcomes of these two recent engineering failures:

Distressed Residents Confront Opal Tower Builder
Signature Bridge design had key mistake

But are there more engineering failures on our horizon?

Quality Engineering Consultants are Under-Priced

Then there’s the quality engineering consultants.

They’re doing a great job. They’re doing the hard yards for consumers. They’re really making sure that good designs are going out the door and that engineering is being done properly in a economical way.

The good news is, the quality engineering is being quoted and charged out at unbelievably cheap rates too.

Let me say that again: The really good engineering is unbelievably cheap right now and these guys are doing a really great job for really low engineering fees.

The Winner is the Consumer

It just doesn’t seem right – but in any case the real winner is the consumer and society in general because really good engineering is really cheap.

Those companies that are doing a great job and presenting quality engineering solutions are really easy to find, quite easy to engage and very competitive on price.

Super-Cheap Engineering is a Rip Off

So, when you look at what you get with the really cheap, under-priced engineering companies, you’re really actually getting ripped off in a way.

The companies that are doing work from overseas or sweatshops or are doing mass-market type of jobs for really, really cheap rates are doing so much less work for their money that the consumer is totally getting ripped off.

Cheap Engineers doing Residential Engineering

For example, in the residential structural engineering market, the really cheap guys:

  • Aren’t doing quality soil tests.
  • Aren’t giving enough consideration to the way a building is built.
  • Aren’t visiting sites or getting enough local knowledge for a decent design.
  • Aren’t being chosen for their willingness to deliver quality engineering.
  • Aren’t supervising and mentoring their engineers and drafters to ensure a supply of quality smarts for the next generation. 
The formal investigation into the failure of the FIU bridge has not yet been released but too-cheap engineering could be to blame.

Quality Engineering is So Good There is Absolutely No Reason Not to Use It

The stark reality is: the quality and consistency of the engineering coming from the quality companies is such good value right now that there is absolutely no reason not to seek out and use those companies that deliver value engineering.

Now don’t get confused.

There’s even some larger, better known engineering companies that are so over-worked and so far behind their work schedule that they’re letting down clients too. They’re still talking the big game and selling like they need every job but I’m not talking about them today.

The smart, quality engineering companies are right there to be found and there’s just three questions to ask to make sure you’re dealing with one of them.

3 Questions to Ask to find a Quality Engineering Consultant

Question 1: Can I speak to the engineering manager?

The engineering manager in a consulting engineering firm is the person that determines the quality of the work going out the door.

There’s a big difference between the office manager or sales person or company director or scheduler or whatever other positions there are in the company that you can get to speak to easily.

The person in charge of the quality of the actual engineering is the one with the RPEQ registration in Queensland or the experienced NPER registered engineer in other states of Australia.

If you can speak to THAT person, the engineering manager, in person or at the very least on the phone with minimal mucking around, then right there, that’s one fantastic indication that the engineering company that you are dealing with is a quality company.

But you’re going to have to make sure. In the way under-priced, mass-market engineering consultancies you’re going to get the run-around.

  • “Oh the engineering manager just stepped out.”
  • “I’m so sorry the engineering manager is at an appointment.”
  • “The engineering manager is on annual leave today.”

Really???

Don’t accept speaking to anyone less than the engineering manager, in a really simple process, or start looking carefully at the company you are dealing with.

And I’m talking about you too – the big mass market building companies pumping out hundreds of houses a year.

There’s really good quality, cheap engineering consultants out there. They’re right out there and it’s just another couple of phone calls for you.

The quality of the cheap and nasty engineering consultants is so poor you are being ripped off if you can’t speak easily to the engineering manager.

Solution: Have the number of the engineering manager for your engineering consultant on speed-dial. They are the one you need to thank when the job goes well or chase up and hound if you job goes too slow.

Question 2: Who will be working on my job?

It’s a simple question. In residential engineering, just ask “Who will be doing the engineering on my job and who will be doing the drafting for my job?”

  • “Oh. We haven’t allocated anyone to your job just yet….”
  • “The engineer working on your job is away today.”

Bull.

A quality engineering company sets up a job and allocates staff just about as soon as they know about the job.

A too-cheap engineering consultancy doesn’t know the name of the engineer working on your job because they are the “engineers-with-no-name”. I just made that up. I’m talking about the engineers and drafters working in the back room with hardly any supervision, checking, training or enthusiasm.

Solution: Find out the name, phone number and email address of the engineer working on your job. Keep it handy. You may just need it.

Question 3: Can you do inspections during construction?

A quality engineering company backs up their design work with inspections by a local engineer.

It doesn’t matter so much if your consultancy is out of town – a quality engineering firm already has a relationship with a local engineer that will do your inspections during construction.

If your engineering consultant is local, they should have someone available to do the inspections.

Under-priced structural engineering consultants either don’t offer inspection services or they use an inexperienced inspector.

For example, at Cornell Engineers, our inspections are carried out by 4 year degree qualified structural engineers that have worked for us for at least three months. In the first three months they only carry out inspections with a more experienced structural engineer.

Too-cheap engineers are allowing builders to either sign off on their own work, or they send out inspectors for a drive-by inspection. Either that or the inspectors don’t have any training, don’t know exactly what they are looking for and are so over-worked they don’t have time to find problems let alone solve them on site.

Finally too-cheap inspectors are now trying to inspect frames, footings and major structural elements via Facetime or Skype. You cannot verify the bearing capacity of a footing via video. You cannot confirm that all timber connections and members are correctly sized from a video call.

Quality engineering consultants attend site in person, write up notes and either email them or hand deliver them to the builder. Those notes are available for review by the homeowner and the certifier if required. Quality engineering firms take photos during their inspection and keep these on file in case a dispute arises later on.

I’ve been invited by homeowners to attend inspections by other engineering consultants. I’ve arrived on site early and waited for an inspector only to be told “the inspection has already happened.” Now unless the inspector is extremely tiny that inspection probably didn’t happen but the owner still got charged for it.

Solution: Confirm that your engineering consultant can provide an experienced inspector for inspections during construction. Find out the inspector’s qualifications. Attend during the inspection and DO NOT accept an inspection report from an inspector unless you or your independent adviser can verify that the inspection actually happened by an inspector in person.

Really Good Engineering is Really Cheap

So there you have it.

Really exceptional engineering is really cheap and excellent value. It’s way under-priced for what you get and the quality of the assistance you get.

There’s just three surprisingly simple questions to ask to help you find good quality engineering assistance for your next project. Too-cheap engineering just doesn’t stack up. Can you afford not to engage a quality engineering consultant?

Investigating Structural Damage

Mr Rob Hughes, semi-retired director of engineer consultancy heavy-weight Hughes, Beal & Wright, has forgotten more about investigating structural damage than many engineers will ever know.

So when Rob agreed to let Cornell Engineers share his guidelines for investigating structural damage, we were super-excited to take this opportunity to publish his truly exceptional insights.

Structural engineers, forensic engineers and up and coming engineers: please read on. Continue reading Investigating Structural Damage