How Do I Protect a Slab Made of Cellular Lightweight Concrete (CLC)

Plan ahead next time.

I'd coat it with clear, two-part epoxy.

Thanks. Why it has to be "clear" and not colored? Could this epoxy coating on the slab be thick and strong enough to sustain the weight of a passenger car without breaking? Greetings

It doesn't have to be clear.

I can't answer the question of weight support. Too many unknowns. Concrete is sometimes referred to by it's load bearing strength. What's yours?

I may be wrong but from what I know epoxy is not suitable for continuous exposure in the open air. It is adversely affected by UV radiation of the sun. It will crack and degenerate quite soon. Do you agree with these statements?

Let me give you some more information so that I may help you help me. The CLC slab in question is not meant to be structural. All it is required is to sustain its own and be in place without absorbing water and without failing in case a lighter vehicle runs over it.

Its purpose in life is to serve as a safety truck arresting bed installed on the sides of a winding highway where many accidents happen each year when heavy trucks veer off their normal course.

Therefore it is going to be a repeated construction of a standardized slab no taller than 1 foot (35 cm). CLC was selected because we want the cellular concrete to crush under the weight of the oncoming runaway truck, thus creating drag force that decelerates and stops the truck.

Specifications imposed by the state authority: a)Water absorption is to be avoided as it will affect the physical characteristics and safety performance of the truck arresting bed (slab). b) Exterior hard coating is necessary in order to sustain the weight of a passenger car.

My problem boils down to how to go about doing a) and b) above.

Have a great month of June. Regards, Chris

Thanks Lyn. Very good remarks. Are u a believer in extraterrestrial intelligence? I am too.

I believe that with a universe as large as the one we inhabit, it would be arrogant to think that we are the only organisms who display intelligence.

Unfortunately, many times this "intelligence" seems to allow completely un-intelligent things to occur.

I guess intelligence and logic are not directly related, as intelligence and ethics seem to have parted ways, as well.

The original "The Day The Earth Stood still" is a good example of where we have come. "Klaatu barada nikto"

We are nothing more than a dust spec.......

So would I.

From what I know epoxy is not suitable for continuous exposure in the open air. It is adversely affected by UV radiation of the sun.

http://www.durabond.com/Products/protective_coatings/dur-a-hard_em.htm

Where I made my living (Canada) this class of material was considered OBSOLETE when I last looked, about a decade ago. The moisture absorptive properties were impossible to mitigate, even when 'encapsulated'. My Industrial Roofing Firm installed some in the 1960's but we removed it (failed) all within a year. In subsequent years we removed many acres of the stuff, always after it had failed. Failures sometimes involved the collapse of structural decks. The contained-moisture caused premature wastage of adjoining structural concrete reinforcement in many buildings - shortening building life. On one memorable project 13000 square feet of structural cellular slabs deformed the building structure. Our contract to remove the failed material ended prematurely with the collapse of a large part of the 20 year old building.

Maybe your southern latitude will help - I can't say. If I were in your shoes, I would not count on it.

I can say tell you with certainty that if the stuff is already 'placed' then it is too late to start looking for coatings to save this installation. It is cheapest and best to tear it out and re-specify. Get rid of it. It is nothing but trouble.

Thank you. Let me give you some more information so that I may help you help me. The CLC slab in question is not meant to be structural. All it is required is to sustain its own and be in place without absorbing water and without failing in case a lighter vehicle runs over it.

Its purpose in life is to serve as a safety truck arresting bed installed on the sides of a winding highway where many accidents happen each year when heavy trucks veer off their normal course.

Therefore it is going to be a repeated construction of a standardized slab no taller than 1 foot (35 cm). CLC was selected because we want the cellular concrete to crush under the weight of the oncoming runaway truck, thus creating drag force that decelerates and stops the truck.

Specifications imposed by the state authority: a)Water absorption is to be avoided as it will affect the physical characteristics and safety performance of the truck arresting bed (slab). b) Exterior hard coating is necessary in order to sustain the weight of a passenger car.

Greetings. Chris

how about a 2 part system:

1) Epoxy, urethane or similar coating for waterproofing

2) Asphalt paving on top, which will also aid in the waterproofing. Select the grade and thicknesses to carry a given point load that will carry a passenger vehicle but not a truck (lorry). Have fun figuring out how to compact it though.

Or maybe,

2a) find someone to make a UV and weather resistant plastic or other material sheet that can be overlaid to carry the load of a passenger vehicle but rupture under the weight of a truck.

Interesting remarks indeed. Thank you. Epoxy, urethane, asphalt are good candidate materials provided they could be overlaid on top AND sides, would not deteriorate over time and that are not combustible.

Plastic or other material in sheet form sounds good if I only knew the supplier…

Have a great month of June.

Good luck with this, Chris. The specification is demanding that a(n intensely) hygroscopic material not absorb water. Which means that the project is getting off on the wrong foot. This tendency to defy the laws of physics is a well-known hallmark of government specifications here in Canada too.

You NEED a lawyer-engineer to come through this.

Whatever you do, do not compete on warranty. This installation should be at the risk of the specifying authority and they should sign off on the materials and workmanship at every step during construction.

If these are to be used 'often' by trucks, then why use something that gets broken by deployment?

So-called 'run-out' lanes are common in mountainous areas in Canada and the USA. The common Canadian version consists of untamped pea-gravel aggregate which cannot support the weight of a loaded transport truck. Sometimes, where space is limited the run-out lane looks like a shallow ski-jump. The normal scenario when these are used by trucks is that the brakes overheat and the truck is in danger of overspeeding downhill.

For obvious reasons, cars are forbidden to drive on or park on these...

These lanes can bring a 100,000 lb transport truck to a halt in only a few hundred feet from speeds of over 60 miles per hour. And the lanes are not crushed into uselessness by having been used once or twice. The highways department has a machine regrade the safety 'run-out' lanes on a regular schedule to a 'like new' condition.

Does the Greek Highways authority plan to re-pour the lightweight concrete and re-encapsulate it to their mythical high standard of waterproofness after it is broken by the FIRST runaway vehicle? Not likely!

Even if they plan to, what are the chances that the repaired section will perform to the same standard as the original 'perfect' installation?

Make sure that you limit your warranty exposure from that 'maintenance' contract too.

<rant ends>

Sincerest best wishes on this project

All you remarks and comments are valid and worth noting. However current specs are fixed and we have to live with that. My belief is that technically everything is possible nowadays, especially when cost is not an issue. Yes, they will have us maintain, re-pour and repair the safety CLC bed after an exit incident. I envision that any water that might have encroached into the bed system, from the damaged area, will be drained out by drilling a hole at the lowest grade point at the base of the bed. Then the hole will be carefully plugged in and repaired. On second thought the hole might even be left open since no rain water can pass through it towards the interior of the bed (because of the down grade).

Best regards, Chris

What I'm curious about is how there can be "cost is no object" projects in Greece, given the state of their economy. EU bailout money subjected to "shovel-ready" marketing?

Thank you. Let me give you some more information so that I may help you help me. The CLC slab in question is not meant to be structural. All it is required is to sustain its own and be in place without absorbing water and without failing in case a lighter vehicle runs over it.

Its purpose in life is to serve as a safety truck arresting bed installed on the sides of a winding highway where many accidents happen each year when heavy trucks veer off their normal course.

Therefore it is going to be a repeated construction of a standardized slab no taller than 1 foot (35 cm). CLC was selected because we want the cellular concrete to crush under the weight of the oncoming runaway truck, thus creating drag force that decelerates and stops the truck.

Specifications imposed by the state authority: a)Water absorption is to be avoided as it will affect the physical characteristics and safety performance of the truck arresting bed (slab). b) Exterior hard coating is necessary in order to sustain the weight of a passenger car.

Greetings. Chris

Here in the U.S. it may not be a great system, but I like it, is the run away ramps for steep grades.

I believe the highway departments commonly use rough sand and pea sized gravel. I have not had the need to use the ramps, but have seen evidence they are quite effective.

No, a car is not able to use this surface, but they shouldn't be there in the first place. Should a passenger vehicle become stuck in the ramp material, they have to pay to be removed, and possibly have to pay to have the material spread back out.

The pea gravel is reusable multiple times, is very effective at slowing and stopping large commercial vehicles, sheds rainwater with no special treatment, and I'm sure is at a much lower cost being simply pea gravel. Once the surface is disturbed it takes less than a day to put back into "service" and can save another life and more property.

Thanks. The run away ramps for steep grades is a good system but not applicable in our case. Let me give you some more information so that I may help you help me. The CLC slab in question is not meant to be structural. All it is required is to sustain its own and be in place without absorbing water and without failing in case a lighter vehicle runs over it.

Its purpose in life is to serve as a safety truck arresting bed installed on the sides of a winding highway where many accidents happen each year when heavy trucks veer off their normal course.

Therefore it is going to be a repeated construction of a standardized slab no taller than 1 foot (35 cm). CLC was selected because we want the cellular concrete to crush under the weight of the oncoming runaway truck, thus creating drag force that decelerates and stops the truck.

Specifications imposed by the highway authority: a)Water absorption is to be avoided as it will affect the physical characteristics and safety performance of the truck arresting bed (slab). b) Exterior hard coating is necessary in order to sustain the weight of a passenger car.

My problem boils down to how to go about doing a) and b) above.

Have a great month of June. Regards, Chris

Thanks but I cannot change the specs. I least I am not under any budgetary constraint. I am just called upon to address this humidity and durability problem. Please read the additional information in the thread. I shall expect your input. Have a great month of June. Regards

Cap it with a slab of reinforced non-cellular heavyweight concrete, designed by CaptMoosie.

Placed, not poured.

--007

Such a concrete coating did not save the structure from catastrophic collapse "13000 square feet of structural cellular slab" in post #5 of this thread. They were factory manufactured and were a structural deck material with approx 1" of hard concrete encasement (imagine a chocolate Aero bar and you have a scale model of the slab)- creating total encapsulation.

These snapped in half as a result of a) weight gain, and b) corroded internal re-bar which had 'wasted' to half of its original size after slowly absorbing ambient humidity for a decade or two.

Total encapsulation of the slabs in 20 mils of epoxy might have been a good solution for that problem. However the AP correctly points out that the concrete for this project will be 'placed', meaning poured in situ.

I had a thread on CR-4 about 3 years ago looking for an admixture for concrete which could render the material non-hygroscopic. There were some tentative suggestions about super-plasticizers. The manufacturers subsequently advised that their products did not greatly alter the hygroscopic nature of cured concrete.

I think that this 'waterproof concrete' is a kind of a Holy Grail item for civils.

Concrete bridges continue to collapse at the halfway point of their design life, and we continue to treat the symptoms. Current good practice is to install a)epoxy coating on all steel encapsulated by concrete, and b) high quality waterproofing on the slab before asphalt paving is placed over the concrete. We have every reason to believe that the service life will be doubled - back to the original projections of 80 to 100 years.

What the OP is looking for is a product that is intended to FAIL predictably, reliably and often.

Chrismaki, can you tell us what the predicted service life of the installation might be in normal service conditions. It could be that you don't need too much moisture protection if these 'events' involving trucks occur on a monthly or even an annual basis.

It is difficult, if not impossible, for a slab to "collapse" as you described, if it is laid on the ground.

Which one of us misses the point?

"What the OP is looking for is a product that is intended to FAIL predictably, reliably and often."

That is the only point!

Ohhh thanks a lot Tornado! Don't get me involved with this can of worms!!! LOL

Why the heck doesn't the state (wherever this is) use vehicle attenuation devices instead of the CLC slab? Seems to me to be ass-backwards thinking from the get-go!

UW-Madison is a leader in Concrete Research and studies...........

Check their website, if they have any information on Cellular concrete studies

Prof. Steven Cramer

Dear Steven,

Thanks for your suggestion. May I ask what is your discipline and field of academic study and teaching? I hold an MBA degree from Stanford.

Best regards, Chris Constantinides

How could we manage for the bed not to retain water

If water can find its way into the arresting bed (AB), it can also find its way out of it. Neither sophistication nor science is required here. Water will follow the inclination of the ground and just drain out from the very bottom of the AB. It is as simple as that. All we have to do is to locate the low points on the AB periphery, drill drainage holes right there, and leave all the rest to the law of gravity.

Caveat: My only reservation is the capillary action (effect). Due to the capillary effect, water can defy gravity and stay into the AB. In case ambient temperature drops to freezing or below, this humidity can turn to ice crystals which could affect bed performance.

Your comments -if any- are of utmost interest to me!

I'm sorry but Steven Cramer is not me, Steven Cramer is the professor at UW-Madison.

Sorry for the mix-up. You are certainly good enough as you are. It would help if I knew your first name. Regards, Chris

Happens to be Steve also ......

You might have luck with a siliconized acrylic sealer.

Check this out.