Figure 1. Traditional diagram of cast in-situ foamed concrete production (Sequential Addition of Materials)
This paper gives an introduction to a new form of concrete called foam concrete which is manufactured by mixing a cement paste or slurry with a manufactured foam material. It is a revolutionary new cementing material which is both lightweight and strong. Here the technique of cast in-situ foam concrete preparation, use of fly ash as a filler material in foam concrete and a comparative study of heat insulation capacity of foam concrete to other commonly used construction materials has been presented. The paper discusses the changes in the property of foam concrete because of the use of different graded sands and different water-solid ratios. Its uses and advantages over other construction materials have also been enlisted.
Concrete is one of the most important building construction materials. The modest concrete is a combination of coarse and fine aggregates, sand, cement and water. Because of the ongoing researches on new types of concrete having various admixtures and additives the quality, durability and strength of concrete is improving rapidly. Nowadays, concrete of compressive strength 200 N/mm2 , is achievable which is comparable to the yield strength of mild steel. There are various types of concrete available having different and unique properties other than just the strength to resist load.
Concrete is now replacing bricks in walls, even the door panels and window panels are being made of concrete. As concrete is extensively used for construction work, these days, it becomes worthy to explore new variants of concrete which are not only high in strength and durability but are also of light weight. In this regard, a recent name in concrete technology is foam concrete. Foam concrete is a type of porous concrete. According to its features and uses, it is similar to aerated concrete. The first comprehensive review on aerated concrete was presented by Valore [1,2] and detailed treatment by Rudnai [3] and Short and Kinniburgh [4]. Foam can be prepared with the help of a foam generator or in a baroplant. In foam concrete, it is possible to achieve air void content up to 25% or more of the concrete volume, and dry density/ compressive strength combination ranging from (1.20 kg/dm3) / (30 N/mm2 ) to (0.70 kg/dm3 ) / (5 N/mm2 ).
This high void percentage makes the foam concrete a very light weight material compared with ordinary concrete. This foam concrete may be used for heat insulation, acoustics and fire resistance. Other light weight constructions can also be carried out by foam concrete.
Any locally available foaming agent, diluted with potable water in the ratio of 1:3 by weight and aerated to produce foam to a density of approximately 50 kg/m3, can be used. To this, fifty three grade Ordinary Portland Cement, coarse river sand (specific gravity = 2.66), pulverized river sand finer than 300 lm (specific gravity = 2.52) and class F fly ash conforming to ASTM C 618 should be mixed.
The following diagrams (Figures 1 and 2) give an idea about the formation of Foam concrete.
The first diagram shows the traditional cast in-situ production and the second diagram shows the advanced version of concrete production unit.
Figure 1. Traditional diagram of cast in-situ foamed concrete production (Sequential Addition of Materials)
Figure 2. Advanced diagram of cast in-situ foamed concrete production (Sequential Addition of Materials)
As foam is added to the wet foam concrete mix, the consistency of the wet mix is very important to get the design density. It is observed that at lower water–solid ratios, i.e., at lower consistency, the density ratio is higher than unity. The mix is too stiff to mix properly thus causing the bubbles to break during mixing resulting in increased density. At higher water–solid ratios, there is also an increase in density ratio as higher water contents make the slurry too thin to hold the bubbles resulting in segregation of the foam from the mix along with segregation of the mix itself thus causing an increase in measured density. Therefore, density ratio of unity or nearly unity is achieved only at a particular consistency. This consistency requirement for the mix before adding foam to it can be expressed in terms of water–solid ratio. It is also observed that the water–solid ratio required to obtain a density ratio value of one, depends on the filler type. Due to higher surface area, foam concrete mixes with fly ash require relatively higher water–solid ratios compared to mixes with sand. At the same time, mixes with fly ash require less foam volume due its low specific gravity (2.09) compared to fine sand (2.52). The water–solid ratio requirement reduces only marginally with an increase in density, but the foam requirement reduces steeply. These observations show that the consistency requirement is mainly affected by the filler type and foam volume to be added in the mix has only a marginal influence.
For a given density, the mix with fine sand results in higher strength than the mix with coarse sand and the variation is higher at higher density. Cut sections of the specimens viewed through an optical microscope with magnification factor of 20 shows that there is a comparatively uniform distribution of pores in the case of foam concrete with fine sand, while the pores are larger and irregular for mixes with coarse sand. This indicates that coarse sand causes clustering of bubbles to form irregular large pores. Thus it can be concluded that, fine sand results in uniform distribution of bubbles and hence results in higher strength than coarse sand at a given density. Kearsley and Visagie [5] reported similar observations on the effect of pore size on the strength of foam concrete. For a given density, an increase in fly ash content results in higher strength. Apart from pozzolanicity of fly ash, the lower requirement of foam volume for a given density of foam concrete will also contribute to strength enhancement by reducing the pore volume and facilitating the uniform distribution of pores. Durack and Weiqing [6] observed a similar enhancement in strength due to fly ash and this was attributed to the development of strong inter particle bond between the gel matrix and the fly ash particles. Based on a comparison of strength to density ratio for different mixes, the following conclusions can be drawn:
As the experiments and other researches show, the insulation property of foam concrete is quite good. Compared with ordinary concrete, it has a good insulation (0.05kcal/mh. C), about 20-30 times than that of ordinary concrete. It has very low thermal conductivity and thermal conductivity less than 0.2w/mk.
The quality of foam concrete can be modified and better strength and durability can be achieved by using admixtures like fly ash. Kearsley [7] discusses on how addition of fly ash effects the compressive strength of foam concrete. This variant of foamed concrete is 'Fly ash based filler type foam concrete'.
Pre-formed foam concrete is manufactured by adding foam, prepared by aerating a foaming agent solution, to cement paste or cement mortar. By using fly ash as filler (fine aggregate) instead of sand, the high volume utilization of fly ash becomes possible, thus providing a means of economic and safe disposal of this waste product. Comparison of the strength of air-cured foam concrete made with cement sand and cement–fly ash for masonry shows that for products of comparable density, mixes with fly ash as fine aggregate in place of sand gave relatively higher strength.
Foam concrete is an almost ageless and everlasting material not subject to the impact of time. It does not decompose and is as durable as rock. High compression resistance allows using it with lower volumetric weight while construction, which increases the temperature lag of a wall. On the other hand, ordinary concrete has a design life, so it is more durable than ordinary concrete.
Due to high temperature lag, buildings constructed from foam concrete are able to accumulate heat, which allows minimizing heating expenses by 20-30%.
Foam concrete prevents the loss of heat in winter, is humidity proof, and allows avoiding very high temperatures in summer and controlling air humidity in a room by absorbing and output of moisture, thus helping to create a favorable microclimate.
Small density, and, therefore, lightness of foam concrete, large sizes of blocks compared with bricks, allows increasing the speed of lying by several times. Foam concrete is easy to process and trim – to cut channels and holes for electrical wiring, sockets, and pipes, but the bricks cannot be trimmed easily. The simplicity of lying is reached through high exactness of linear dimensions; the tolerance is ± 1 mm. On the other hand, ordinary concrete wall cannot be penetrated and thus making groove channels st for electrical wiring in concrete wall is impossible. The 1st grade brick wall is also very difficult for wiring work as channel making is troublesome.
Foam concrete has a relatively high property of acoustical absorption. In buildings constructed of porous concrete, the acting requirements for acoustic insulation are met. On the other hand, a brick masonry wall and ordinary concrete wall cannot absorb the sound waves and hence echo problem arises in the building. So, by the use of foam concrete blocks, we can reduce the echo problem considerably. Concrete foam bubbles can form an independent, sound-absorbing capacity of up to 0.09- 0.19%, which is 5 times that of ordinary concrete, leaving space to adequately address the noise problem.
During maintenance, foam concrete does not produce toxic substances and its ecological compatibility is second to wood. The brick manufacturing factories' chimney emits effluents containing a huge amount of SO2 in the atmosphere which causes acid rain in the nearby agricultural fields, thus affecting the growth of crops and make them toxic for human beings. The other effluents coming from these chimneys cause skin diseases and respiratory problems. On the other hand, foam concrete blocks do not contain high amount of chemicals and hence are eco- friendly. They contain a good amount of fly ash as a replacement of fine aggregate and so it is solving the problem of dumping fly ash produced by thermal power plants. As foam concrete can replace wood from door panel, it also prevents the forest reserve of the nation. The coefficient of ecological compatibility of porous concrete is 2; of wood – 1; of brick – 10; of keramzite blocks – 20.
Due to high workability, it is possible to produce various shapes of corners, arches, pyramids, which will attach beauty and architectural expressiveness to your house. In ordinary concrete, to achieve high workability, we have to add chemical admixtures which increase the production cost of concrete and are a threat to ecology. In foam concrete, we achieve this enhanced workability due to the presence of very small air bubbles which reduce the friction between particles.
High geometrical exactness of dimensions of concrete produced allows to lay blocks on glue, to avoid “frost bridges” in a wall and to make inner and outer plaster thinner. Foam concrete weighs from 10% to 87% less than standard heavy concrete. Sufficient reduction of weight leads to smaller foundations for supporting building and thus leads to sufficient economy on basements. 160- 1700kg/m3 density in between are the ordinary concrete 1/5-1/8 which are light-weight products, and can reduce the overall load of the building.
Earthquake resistance is superior with foam concrete products, the formation of numerous independent bubble show pad for external force, and can spread to other parts of the pressure to improve the seismic performance.
Foam concrete provides protection from fire and correspond to the first degree of refractoriness, which is proved by tests. Thus, it is can be used in fire-proof constructions. Under the impact of intensive heat, like blow lamp, on the surface of foam concrete, it does not split or blow, as it happens with heavy concrete. As a result, armature is longer protected from heating. Tests show that foam concrete 150 mm wide can protect from fire for 4 hours. During tests carried out in Australia, an outer side of a foam concrete panel 150 mm wide, was exposed to temperatures up to 12000 C for 4 hours without considerable damage to concrete.
Favorable combination of weight, volume and packaging makes all building constructions convenient for transportation and allow using motor or railway transport. The pre-cast members are light in weight, so it is easy to transport them from casting yard to construction site.
1. Lightweight concrete walls and floor panels on account of having good thermal, acoustic and load bearing properties.
2. Lightweight Blocks which have low water uptake.
3. Foam Concrete Wall Partition that can be casted either vertically or at an angle saving time, labor or space.
4. Foam Concrete Roof Decks- since it permits controlled hydration and has high early and final strength.
Foam concrete is a better option to replace traditional heavy concrete where we want to reduce dead load of structure within the strength limits of foam concrete. It can be used in concrete block wall and acoustic problem is solved. The major drawback is that we cannot produce concrete of compressive strength more than 30 N/mm2 . The conclusions drawn from characteristics of the materials used and the range of parameters investigated: (i) the consistency of pre-formed foam concrete mixtures (defined as the water–solid ratio for achieving the target density) mainly depends on the filler type, i.e., relatively higher for mixes with fly ash as filler compared to mixes with sand; (ii) the flow behavior mainly depends on the foam volume and as the foam volume increases, the flow decreases. For a given density, foam concrete with fly ash as filler showed relatively higher flow values; (iii) an increase in fineness of sand causes an increase in strength of foamed concrete; (iv) for a given density, an increase in fly ash content of the mix results in increased strength; (v) finer filler results in higher strength to density ratio, i.e., foam concrete mixes based on fly ash as filler showed higher strength to density ratios than those based on sand for all density values; (vi) the water absorption of foam concrete, because of its reduced density, should rather be expressed in kg/m3 than as a percentage by weight; (vii) the water absorption of foam concrete is observed to decrease with density. In comparison to cement–sand mixes, cement–fly ash mixes showed relatively higher water absorption.