Lecture 1- Light Weight Construction Materials by Brig. S.K. Sharma

LECTURE - 1

LIGHT WEIGHT CONSTRUCTION MATERIALSThe Northcap University, Gurgaon1UNIT-1LECTURE - 1Brig. S.K. Sharma (Retd.) Pro Vice Chancellor and Professor Department of Civil Engineering, The Northcap University, Gurgaon

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INDEXThe Northcap University, Gurgaon2LIGHT WEIGHT CONCRETEFOAMED OR AERATED CONCRETEMETHOD OF MANUFACTUREPROPERTIES OF LIGHTWEIGHT FOAMED CONCRETE

LIGHT WEIGHT CONCRETE The Northcap University, Gurgaon3NEED FOR: The conventional cement concrete is a heavy material having a density of 2400 kg/m3 and high thermal conductivity. The dead weight of the structure made up of this concrete is large compared to the imposed load to be carried. In highrise buildings Light Weight Concrete can save money and manpower considerably. The improvement in thermal insulation is of great significance to the conservation of energy. The reduction in dead weight is normally achieved by cellular construction by entraining large quantities of air.

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LIGHT WEIGHT CONCRETEThe Northcap University, Gurgaon4There are many advantages of having low density of concrete. It helps in reduction of dead load, increases the progress of building, and lowers haulage and handling costs. The weight of a building on the foundation is an important factor in design, particularly in the case of beams and columns which have to carry load of floors and walls.

METHOD OF MANUFACTUREThe Northcap University, Gurgaon5Basically the main method for making concrete light is by the inclusion of air in concrete. This is achieved in actual practice by three different ways:-By replacing the usual mineral aggregate by cellular porous or light-weight aggregate.By introducing gas or air bubbles. This is known as aerated concrete.By omitting sand from the aggregate. This is called no-fines concrete.Video YouTube, Autoclaved Aerated Concerete blocks installation, 6:26 minVideo YouTube, Foam Concrete House, 18:23 minVideo YouTube, Shobha Home Truths Demo Block Work, 02:55 min

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FOAMED OR AERATED CONCRETEThe Northcap University, Gurgaon6Foamed concrete is a type of porous concrete is a highly workable low-density material which can incorporate up to 50 per cent entrained air. It is generally self-leveling, self-compacting and can be pumped.

METHOD OF MANUFACTURING (Continued..)The Northcap University, Gurgaon7The traditional method of making lightweight aerated or cellular concrete involves the addition of a gas-forming admixture like aluminum powder to a wet mortar mix followed by autoclave curing. Foamed concrete is made from mechanically mixing preformed stable foam to the slurry of cement and water. This action incorporates small air bubbles distributed uniformly within the mortar thereby making low density concrete. The foam is made by a simple foaming generator where air, water, and foaming chemicals are mixed and stable foam is formed.Foamed (or cellular) concrete is obtained by foamed concrete technology which is environment friendly, as there are no waste products in its production and all the ingredients are non-hazardous. Due to its good mechanical strength, low thermal conductivity, simple yet highly technological processing foam concrete has become popular as an environment friendly alternative.

PROPERTIES OF LIGHTWEIGHT FOAMED CONCRETEThe Northcap University, Gurgaon8

1. STRENGTHS:Compressive strength: The compressive strength of foamed concrete is influenced by many factors such as density, age, moisture content, the physical and chemical characteristics of constituent materials and mix proportions. The increase in strength with age is virtually linear over the first 12 months unlike dense-weight concrete which levels out much earlier. The rate of development of strength in foamed concrete is higher than that in the dense weight concrete.

PROPERTIES OF LIGHTWEIGHT FOAMED CONCRETE (Continued..)The Northcap University, Gurgaon9Tensile Strength: Depending on the method of curing, the tensile strength of foamed concrete can be as high as 0.25 times its compressive strength. Shear Strength: The shear strength generally varies between 6 and 10 percent of the compressive strength. Shear reinforcement may be required in flooring and roofing units.

PROPERTIES OF LIGHTWEIGHT FOAMED CONCRETE(Continued)The Northcap University, Gurgaon10

2. SHRINKAGE: Like all cement products, foamed concrete shrinks during the setting stage. The shrinkage depends upon the type and amount of cement in the mix; water-to-cement ratio type of curing process, size of element, quality of sand and density of foamed concrete. The most shrinkage occurs during the first 28 days, after this time it is negligible. During the first 28 days, if the conditions of manufacture of the foamed concrete are well controlled, shrinkage can be kept below 0.1 per cent.

PROPERTIES OF LIGHTWEIGHT FOAMED CONCRETE(Continued)The Northcap University, Gurgaon113. EXPANSION: The coefficient of linear expansion for foamed concrete is or the same order of magnitude as for normal concrete, i.e 0.00001 per degree centigrade. This factor becomes important in the applications where the concrete elements are exposed to extreme heat and cold variations, in case of large areas of roof slabs.


4. Acoustic insulation: Foamed concrete has a high sound absorption capacity. In general, dense-weight concrete tends to reflect sound whereas foamed concrete absorbs the sound. This slight disadvantage is in most cases academic, since most walls are either rendered, painted or both. This in turn will make a wall reflect sound as does dense-weight concrete.


5. Thermal insulation: Thermal insulation is one of the extremely important characteristics of foamed concrete. Due to its cellular structure, it offers a very low transmission of heat resulting in high energy conservation. The thermal conductivity increases with the increase in the density of concrete. The thermal conductivity of foam concrete is very low varying from 0.1 to 0.38.


6. Fire resistance: Foamed concrete is fire resistant and thus is suited to fire rated applications. Furthermore, the application of intense heat such as an oxy-torch held close to the surface of foamed concrete does not make it burn, spall or give off toxic gases, fumes or smoke as is the case with normal dense-weight concrete. The reinforcing steel remains cool and protected for a much longer period.

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