Pumicite concrete?


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Old 03-22-08, 08:18 PM
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Pumicite concrete?

Hello,

I'm building my own house and the time has come to

a) Apply the stone veneers to the exterior walls and
b) Lay the concrete underfloor over the gravel that covers the foundations.

When trying to lay the normal concrete stone veneer blocks I was making, I realized that it was next to impossible to lay them with mortar due to their heavy weight so I looked for some lightweight aggregate. The only available one on this area is pumicite (not quite pumice but the finer grain material of the same composition) and I managed to get a truckload of pumicite at almost no cost.

The granulometry of this material is as follows: around 30% passes the #200 sieve, around 20-25% is retained by the 2mm sieve, a portion of it being stone gravel and the rest pumice gravel.

The stone veneers I've made with this material look nice, weigh much less and seem to be pretty solid. I use 50% gravel between 2mm and 20mm and 50% of the remaining very fine pumicite sand mixed with cement in a 1/4 ratio. I also add some fiberglass cuttings to try to strengthen the concrete.

I have read that pumice concrete works fine for stone veneers and also has good insulative properties so I'm planning to use my pumicite truckload for the veneers and the subfloor. However, I'm concerned about pumicite and pumice having different properties. I haven't found much on the net. One thing that I notice is that my pumicite mix requires a large amount of water to become workable, so I wonder if this high w/c ratio will not weaken the concrete in the long term. Also, will this concrete subfloor be strong enough to support a wooden floor just over it?

Any advice will be most welcome.

Thanks!
 
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Old 03-22-08, 09:05 PM
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Pumicite concrete?

Where are you located and do you have any idea of where the pumice originally came from? - where it was mined.

There are many sources of pumice in the world and there is a wide range of properties. Because it is a volcanic material much depends on the way it was deposited.

I would imagine that "pumicite" was a name given by someone to the fine pumice that ocurs naturally or is a result of the breaking down of pumice during handling. I am familiar with the geologic term for pumice and it properties, but have never heard of "pumicite" in 40 years.

For many years the pumice that was most commonly used in the U.S. was from a Greecian island in the Aegean? (Yali, I believe). Othe pumice was available in the U.S., but the quality was lower and the shipping and handling cost was no as low as ocean shipping. There is also Italian pumice and there was also some small deposits in Germany. I also saw a deposit of pumice in one of the Canary Islands. I would imagine there is some in Asia and possibly Russia.

Based on the gradation you gave, the excessive amount of fines would make the concrete heavier and weaker than lightweight concrete made whith coarser pumice. Strength could be obtained with the use of more cement, but the weight and shrinkage would increase. For building materials, a large use of pumice is in concrete block where the coarse pumice is used with concrete sand to get a loadbearing block of 85 to 105 pounds per cubic foot. Normal weight concrete block are abot 135-140 pounds per cubic foot.

Because some pumice is very dry due to being directly loaded into ships in an arid climate, users will "pre-wet" the aggregate before batching to be more consistant and to prevent the mix from drying as the pumice absorbs the mixing water.

Because of the light color some pumice is used in non-structural products that are pigmented.
 
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Old 03-23-08, 09:05 AM
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There is also product (called hadite?) which is basically an artificial pumice. It is a lightweight aggregate for concrete made from byproducts from coal fired power plants. It is wetted then baked in a kiln. The stuff is about the size of pea gravel and contains many small air voids like pumice.
It is soaked in water for 24 hours prior to mixing it in the concrete as Dick said. Also, to make concrete more workable (wetter) without compromising strength, there are products called superplasticizers which you can use. Good luck.

Pecos
 
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Old 03-23-08, 09:19 AM
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Thanks a lot for your reply, Concretemasonry. From Wikipedia: "When larger amounts of gas are present, the result is a finer-grained variety of pumice known as pumicite".

I'm actually in Western Argetina. Pumicite pits originated from volcanoes are more or less commonplace here. They are referred to as "pumicita", "pomacita", "pomaza" and sometimes "puzolana". People make a living extracting the material which is mainly used (AFAIK) as a stabilizer bed in roads. I've also heard that some cement companies extract puzzolanic material from it. It's white/yellowish in color.

From the gradation, I immediately saw that this wasn't the normal pumice lightweight aggregate I've read about in the US. Hence my post.

Do you think that using my 50% gravel (2-20mm)
+ 50% pumicite sand (below 2mm) would make the concrete harder? Or should I rather discard the finer stuff? Can you think of any use for the discarded fines (~30% under #200)?

Another couple of questions: when you say pre-wet the aggregate, do you mean mixing the wet/saturated aggregate with cement and then adding the water for the concrete mix? Would the water used to pre-wet the aggregate not count on the w/c ratio? How about using a plasticiser in order to reduce this ratio?

I'd really love to use this local, cheap material but perhaps the end-result will not make it worthwhile. Changing the stone venners would not be much of an issue but replacing the subfloor would. The climate here is sunny and benign.

Again, any advice will be most welcome. Thanks a lot.
 
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Old 03-23-08, 09:53 AM
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Pumicite concrete?

The pumice (from Greece) I described is some of the best in the world. Unfortunately is does not have the particle strength necessary for the high strength demands for structural lightweight concrete (115 pcf max.).

Your veneer strength demands are not a great as those required for block or structural concrete. The best way to find out whether the pumicite is usable for your puposes is to makes several controlled batches, make cylinder sample and test at 7 and 28 days for compressive strength.

Almost all structural concrete in the U.S. is made using shale or clay that is pelletized and burned at over 2000 degrees F in a rotary kiln to produce an expanded shale or clay aggregate. It is then crushed to the correct size gradation. Because it is a pelletized, the absorption is low and it frequently has to be prewetted by soaking for days before use or under pressure. The reason is to make sure the aggregate is saturated and it does not absorb the mixing water that is necessary for pumping, placing or finishing. Some of the quality manufactured lightweight aggregates have been known as Gravelite, Arkalite, Livlite and Haydite. Some aggregates use waste products from power plants that are more variable, heavier and may have impurities that can stain. The use of "bottom ash" or other by-products will usually produce and heavier, lower quality finished product.

Pumice does not have to be prewetted, but it is usually very economical to do it well before batching since the cement is more efficient and is not sucked into the aggregate instaed of coating the aggregate and forming tight bonds. Pumice can range is moisture from 5% to as high as 40%, so you can see prewetting gives a uniform saturated moisture content results in much higher uniformity, better quality, higher strengths and lower cost. When I was responsible fot the use of the pumice, we sprayed the converors transporting the pumice from the ship to the stockplies to increase the moisture and allow the water to be absorbed over the months it was in a stockpile.

I saw some pumice (Greek and other) used in coastal Brazil, but it never went beyond testing. This was for block and not structural concrete. - Probably due to taxes and duties.

If you are considering it for veneer, your pumice could be an adequate raw material, but coarser pumice may be cheaper in the end even though it will cost more. Because of the larger, low density particles, you get more aggregate (volume) in a ton of material. It is also less likely to bulk up when moist and give a false density. Prewetting eliminates the moisture variation. Nothing will beat test mixes and tesing.
 
 

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