Lightweight Concrete

                                                                                     

Concrete has been a prominent construction material for centuries due to its versatility, making it a preferred choice over wood or steel. It is composed of coarse and fine aggregates, cement, and water.
Lightweight Concrete is a versatile building material with unit loads ranging from 80 to 120 pounds per cubic foot and compressive strengths varying from 2,600 psi to over 8,500 psi. Being approximately 15% to 45% lighter than normal weight concrete, it offers several advantages. It reduces a structure's dead load, leading to lower foundation costs and decreased requirements for concrete and reinforcement. Moreover, structural lightweight concrete exhibits better fire resistance compared to normal weight concrete due to its lower thermal conductivity and coefficient of thermal expansion.

Principle of LWC:

The essential standard behind the creation of lightweight cement is by actuating the air in concrete. To accomplish the above rule basically, there are 3 different ways.

• Replacement of the ordinary aggregates by cell-permeable aggregates (Lightweight concrete)

• By joining the air or gas rises in concrete (Aerated cement).

• By overlooking the sand from the solid (No-fines concrete).

Classification of Lightweight Concrete

Lightweight concrete classification can be as indicated by their creation. For example,

• For instance, below 2.5, penetrable light aggregates with a specific gravity below clear can be utilised to make solid mortar. Lightweight concrete is this type of concrete.
• Different enormous voids may be found in mortar mass or concrete bland; these voids should be distinguished from the exceedingly fine voids transmitted by air entrainment. Cellular, foamed or gas concrete is the name for this type of concrete.
• The fine particles in concrete can be removed with the goal of creating a large number of interstitial spaces; standard weight coarse aggregate is often employed. As sturdy as unfinished concrete.

Types of Lightweight Concrete

1.   Lightweight Aggregate Concrete:- 
   

In lightweight aggregate concrete, unique low-specific-gravity aggregates with a porous and lightweight nature are incorporated into the concrete mix, deviating from conventional concrete. The distinctive characteristic of this lightweight concrete lies in its high porosity, which contributes to its reduced density.

Lightweight aggregate concrete can be further categorized into two types based on its specific applications.

 

Structural lightweight aggregate concrete

 The structural lightweight concrete, similar to regular reinforced concrete made from dense aggregates, is meticulously compacted. It exhibits a strong bond with steel bars, making it suitable for use in steel-reinforced concrete structures. The concrete ensures adequate protection against the corrosion of steel reinforcement.

The compressive strength of structural lightweight concrete typically ranges from a minimum of 28 days up to a maximum of 18 MPa, with densities varying between 1500 to 1850 kg/m3. Its practical density range lies within 1500 to 1850 kg/m3.

Partially compacted lightweight aggregate concrete;

There are primarily two applications for lightweight aggregates that employ partial compaction: the first is in precast panels or concrete blocks, and the second is in cast-in-situ walls and roofs. The main requirements for this form of concrete are that it has to be strong enough and have a low density to have the optimum heat protection, as well as a low drying shrinkage to avoid splitting or cracking.

Types of Lightweight aggregates suitable for SLWC are below:

• Foamed Slag

• Pumice

• Sintered Pulverised

• Expanded Clays and Shales

        2. Aerated Concrete:-

It is viewed as an aerated mortar does not have any coarse aggregate in it. This concrete is made by bringing different gas or air into a concrete slurry and fine sand. This concrete has the lowest thermal conductivity, density and strength. In industry, traditionally fuel ash or other siliceous material used instead of sand and maybe cement replaced with lime.

 

Aerated concrete is prepared in two ways:

• The principal technique is to infuse the gas into the blending during its plastic condition by methods for a synthetic response. 
• The subsequent technique, the is presented either by blending in stable froth or by whipping-in air, utilizing an air-entraining operator. 

Aerated concrete of air-restored is used where minimal quality is required for instance pipe slacking and housetop outbursts. Full quality improvement depends on the reaction of lime with the siliceous aggregates, and for the comparable densities the quality of high-pressure steam diminished concrete is about twice that of air-re-established concrete and shrinkage is only a solitary third or less. 

     3.  No Fines Concrete:-

As the term, no fine shows it is concrete that composed of only coarse aggregate and binder with no filler aggregates and in the resultant concrete, there are several regularly dispersed voids throughout in concrete blend.

No-fine concrete is mainly given in situ, which plays the role of load-bearing and non-load-bearing walls, mainly in surrounding structures, but in some cases, concrete is used as the ground floor-filling and roof tear. Quality strength of no fine solid increments with the expansion of cement. However, it is tangent to the water system Deficient water can cause an absence of union between the particles and in this manner, ensuing misfortune in quality of the solid. Moreover, an excess of water can cause a concrete film to run off the total to shape laitance layers, leaving the heft of the solid lacking in concrete and consequently debilitates the quality.

 

Advantages and disadvantages 

of using lightweight concrete

Advantages

Lightweight concrete speeds up the construction and make it simple.

• It reduces the dead load of the structure.
• It can reduce the workload, need for manpower and ease the transportation work.
• As the Lightweight concrete minimizes the overall weight of the structure, as a result, the structure frames, footings or piles bear a less or safe load.
• The vast majority of the lightweight concrete has preferable nailing and sawing properties over heavier and more grounded ordinary concrete.

Disadvantages

• Lightweight concrete is very sensitive to water content, so proper measurements should be taken in water-cement ratio.
• Difficult to place and finish as a result of the porosity and precision of the aggregate. In some blends, the concrete mortar may isolate the total and buoy towards the surface.
• Mixing time is longer than ordinary cement to guarantee legitimate blending.

Lightweight Aggregates:

Lightweight Aggregates can be classified into two major categories:

Natural Aggregates

1.      Pumice

2.      Tuff

3.      Volcanic Cinders

4.      Scoria

5.      Diatomite

Except for diatomite, all other types are volcanic:

Artificial Aggregates

1.      Expanded clay, shale, slate

2.      Diatomaceous shale

3.      Vermiculite

4.      Obsidian

5.      Perlite