1. If superplasticizer is being used its dosage should not be more than 0.2 bwc.
2. Ignore the amount of water contained in the foam in the mix design calculation.
3. Determine the amount of air (kg/m3) in the mix from consideration of a unit volume, and from the target density of the foam, estimate the required quantity of foam. Worked out final mix proportion for trials. The easiest way to do this is to use different sized mixing containers; 20 gal, 30 gal, 50 gal, etc. You could use a graduated container if it is easy to determine levels once mixed.
4. Usually the total cement content lie between 300 to 500 kg/m3. The gain in strength is small above cement content of 500 kg/m3.
5. Fly ash is added, at level of up to 100% of the OPC content, to enhance workability and increase long-term strength of foamed concrete. Because of greater surface area of OPC/FA mixes have a greater water demand than OPC/sand mixes. The addition of fly ash to a mix leads to a more uniform bubble structure in the paste, which in turn improve some of the engineering properties of the concrete.
6. Fly ash can be used as a total replacement for sand to produce foamed concrete with a dry density of up to 1400 kg/m3.
7. In all cases trial mixes should be done with proposed materials to determine workability, plastic density, if need be the mix should be modified. Specimens shall be cast and tested for the compliance of required specifications.
8. To minimize shrinkage the W/C or W/C+FA ratio should be kept as low as possible.
9. Total fly ash based foamed concrete products are eco friendly as no sand is used.
10. Foamed concrete should be allowed to dry under shade for a period of 28 days to complete initial curing. In low humidity environments wet burlap is helpful to cover the concrete during the curing process.
The above tables show the density and compressive strength of air-crete using different mixes. Note the large increase in compressive strength over time. Here is more info I gleaned from a few sources and put together.
The air content in the foam is typically between 40 to 80 percent of the total volume. The bubbles vary in size from around 0.1 to 1.5 mm in diameter. Foamed concrete differentiates from (a) gas or aerated concrete, where the bubbles are chemically formed through the reaction of aluminum powder with calcium hydroxide and other alkalis released by cement hydration and (b) air entrained concrete, which has a much lower volume of entrained air is used in concrete for durability. The 28 days strength and dry density of the material vary according to its composition, largely its air voids content, but usually they range from 1.0 to 25.00 N/mm2 and 400 to 1800 kg/m3. The plastic density of the material is about 150 to 200 kg/m3 higher than its dry density. There is at present, no guidance or standard method for proportioning foamed concrete, because the hardened density of foamed concrete depends on the saturation level in its pores. CLC can be produced in a density range of 400 kg/m3 to 1,800 kg/m3, with high insulation value and a 28-day cube crushing strength of up-to 275 kg/cm2.
The high density range from 1200kg/m3 (Crushing strength 65 kg/cm2) to 1800 kg/m3 (Crushing strength 250 kg/cm2) is structural grade material utilized for:
(a) In-situ casting of structural (load-bearing) walls and roofs of low rise individual or group housing schemes.
(b) Manufacture of reinforced structural cladding or partitioning panels.
(c) Making pre-cast blocks (500x250x200/100 mm) for load- bearing walling masonry for low rise buildings. The highest density that can be achieved using only cement and foam is about 700kg/m3 . To reach the densities required to use for building load bearing structures, we will need to add fly ash or sand or both. Tables below show amounts required for desired densities.
This page is dedicated to projects using "Air-crete" which is concrete that is mixed with a stiff foam. It forms a much lighter product than stanard concrete mixes. It has been used extensively in Europe for several decades but is relatively new in the US. Proponents of this material say it is fire proof, insect proof, bullet proof, it floats, and is very inexpensive to produce. A dome structure built with aircrete is very strong and inexpensive to maintain. Many think it will revolutionize home construction. It can be poured in panels or blocks creating modular systems the are expandable and interchangeable. The basic formula starts with Portland cement and water. The water to concrete ratio (W/C) should be 0.45-0.50 by weight. Any increase in water will degrade the final product and is called "Water of convenience". Excess water makes the concrete weaker beacuse the concrete particles can't surround the aggregates in the mix and they come out of solution. Strength improves with lower water cement ratios. A 0.45 water cement ratio can hit 4500 psi (pounds per square inch) or greater. A 0.50 water cement ratio may reach 4000 psi or greater. Sand and or fly ash improves the density of the final product. Typically a sand in the "fine" range is used in aircrete. Ratios used are generally 1:1, 2:1, or 3:1, sand to concrete. The highest densities are attained with the highest ratios. Varying the amount of foam in the mix also affects the final density. The less foam in the mix also reduces the quailties that are desirable in the aircrete. It depends on the use of the material. What are the structural requirements of the material? Other means of reinforcing may be required to achieve structural integrity. The foam used in aircrete is created with a foam generator which injects air into a mixture of foaming agent and water. The finished foam is best with the smallest sized bubbles. It usually resembles a thick shaving cream. Many foaming agents used in the industry are proprietary and unavailable to most of us. Agricultural foaming agents can be used but may contain additional chemicals that need to dissipate or be sealed before the structure could be occupied. Many promote dish soap as an alternative but this makes very large and inconsistent bubbles. Hair shampoo makes adequate foam which lasts a long time and is generally nontoxic. The foam needs to remain intact in the mix long enough for the concrete to set or you will not have aircrete. There is a limitaion on how high you can build your forms before the weight of the concrete collapses the foam in the mix. It is dependent on the foam but generally is 6-9 ft. I will elaborate on all factors as I learn new information or experiment myself.
The above chart shows particle sizes and conversions. Foamed concrete is commercially made using a "fine " sand which corresponds to a sieve size of 60-120. Finding this grade of sand locally is challenging. QUIKRETE® Commercial grade sand is available in, Fine No. 1961 #30 - #70 (0.6-0.2 mm). This would be acceptable for our use if you can get it. It is not available where I live. The last option beyond paying shipping for "sand" is making it yourself. Commercial productions uses giant ball mills to create their own grades of sand. Maybe a smaller version similar to a rock tumble can be utilized for the same purpose. I've also looked into using an expanded clay material which is locally produced here. It would provide a lightweight aggregate alternative.
Copyright © FAB Online LLC. All rights reserved.