Concrete and Sugar

[mzaitz]

Hello all,

A mezzanine I looked at shows some major problems. The mezzanine is 4" total concrete on composite deck (though whether it is a composite deck is now suspect), supported by composite beams framing to noncomposite girders. According to the drawings there are #3@10" ew in top of the slab. If the field, you can see cracking in a square pattern that would be about 10" on center. In high traffic areas, where a lift truck is utilized, there are areas that the concrete has been reduced to rubble which is mainly the coarse aggregate, dust and the rebar. There is no cement paste sticking to the rebar or the aggregate. I suspected a chemical reaction and had cores taken and petragraphic and chemical tests done. The findings indicated a poor concrete with a w/c around 0.60 but no chemical reactions to explain the disintigration of the cement paste. A few articles I have read indicate there is an issue with concrete and soluble sugar. Anyone have any suggestions for more information on this? At the moment, we are looking at removing the concrete and leaving the existing deck in place and then pouring new concrete that does not utilize the deck other than as a form. The concern I have with this approach is that the deck and weld studs may have residue that could just start the same problem. Any ideas on this? We would like to leave the deck in place to minimize the issues with the space below. Anything we do will require that the ceiling plenum below and the area of work be cleaned to remove any sugar dust from the area. Being able to reuse the deck and weld studs would also minimize the amount of hot work in the area which is prefered.

Thanks,

Mike

 

[msquared48]

I get the sense that this is a slab in a sugar refining plant?

Contractors do use sugar to retard concrete from setting, sprinkling it on the surface so they can hose it off later when the concrete below has set. I don't know that that would be the circumstance here though as it is likely the concrete cured completely before seeing any surag dust.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[mzaitz]

Mike

This is in the packaging side of the plant.

MZ

 

[hokie66]

Sugar as a retarder on concrete surfaces is prohibited in most specifications. I don't know how sugar affects hardened concrete, but there are probably some chemical reactions involved.

What I do know is that a 4" slab on deck is not a place for lift trucks to operate.

 

[mzaitz]

Hokie66

I did a check of the deck (using SDI) and with a 4 ft span the deck will work compositely. Now that it is not working compositely there will be additional steel plates and load limits on the mezzanine until repaired.

According to a 1975 paper I found titled "Chemical Attack on Hardened Concrete", sugar and sugar products in solution attacks concrete. In dry form sugar has no effect on hardened concrete.

MZ

 

[MiketheEngineer]

Just add water - like high humidity and you got problems

 

[msquared48]

If that were the case, I would think that the floor would be very sticky.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MiketheEngineer]

Sounds good to me.... I have done worse things on my knees

 

[wannabeSE]

If I remember correctly, forklifts and composite decks are not a good combination. The vibrating/moving loads can affect the bond between the concrete and metal deck. The metal deck can be used as a form, but the structural strength should come from reinforced concrete alone.

 

[Ron]

Essentially any carbohydrate or hydrocarbon will retard the strength of concrete. In sufficient quantity, either will destroy the strength of concrete as well. For instance, alcohol (sugar-like substance) is used to stop the hydration process for wet sieving concrete mixes.

You were correct to get petrography done; however, keep in mind that determining the water-cement ratio after the fact is not very accurate, so your 0.60 could easily be 0.70 or higher (it is easy to underestimate). Did your petrographic examination show water gain voids? Did it show bleeding? Did it show "shadowing" under the coarse aggregate that could indicate upward water migration and a retempering.

 

[mzaitz]

Ron,

The report indicted that the concrete was porous and also that the surface was weak and porous which would indicate bleeding.

I beleive that the deterioration of the slab is due to the high w/c ratio of the concrete combined with a reaction to the sugar (the chemical analysis did not show any)combined with the possible lack of composite action with the deck. I still beleive that sugar is a suspect. We had a contractor remove a test section and he was amazed at how easily the concrete was to remove from the weld studs, rebar and deck.

MZ

 

[Ron]

What chemical tests were run on the materials?

The typical tests done for cement and concrete chemistry will not detect sugar. Most often x-ray diffraction or x-ray fluorescence are used for cement and concrete chemistry (inorganic chemistry methods). You will need to have a test run such as FT-IR or SEM with EDS or similar that will detect organic chemicals.

I would bet that the w-c ratio is more of a culprit than the sugar.

 

[Ron]

....also...this is an elevated slab....any chance the concrete was pumped through an aluminum pipe?

 

[mzaitz]

The chemical testing was x-ray diffraction and gas chromatography/mass spectrometry pyrolysis. The report indicates that calcium saccharate was not found but it was possible that the concentration may be too low for the testing to find. What are FT-IR or SEM with EDS?

As for pumping thru aluminum hose... it was definitely pumped which I beleive helped lead to the high w/c ratio. It was 20 years ago and no one at the plant was around at the time so it is not known if aluminum was used.

 

[concretemasonry]

There also the possibility of sugar mixed into to the concrete.

At the time of the construction, many trucks were required to carry bags of sugar in case of a breakdown and the sugar was dumped in to prevent the mix from hardening in the drum (many of the trucks had a separate motor for the drums and not a power take-off) since it was cheap insurance. A tuck may have had a problem, sugar was dumped in, but not fully cleaned before being put back in service. This could contaminate a load.

When I took a concrete class in engineering we had a 3 credit concrete lab class (one of the luxuries of a 5 year curriculum). The professor encouraged altering concrete before or as cylinder were made to understand the effects and variables. We did controlled mixes with variable amount of sugar to determine the effects. Near our area, there were trucks that hauled both sugar beets and aggregates depending on the weather and the chain of contamination is very similar to trucks carrying fertilizer or salt.

We also did sneak sugar into other teams mixes and also added rebar to the cylinders as childish pranks and the professor just smiled when things were tested because he knew we would figure out the cause as a part of the education.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[charliealphabravo]

I agree with hokie. The tow motor is beating the life out of the composite concrete deck with impact, deflection, stress reversals, and friction. I think the chemistry is a red herring.

 

[StructDave]

I have heard the bag of sugar story as concretemasonry said; my dad had one of the earliest ready-mix operations back in the forties and fifties. Breakdowns were more common. As of the late sixties and on, I don't remember seeing bags of sugar in any of the trucks.