abbas jamani (sd 0510 ) cept university, ahmedabad

Structural Lightweight Concrete

Abbas Jamani(SD0510)

CEPT University , Ahmedabad

Contents

Introduction Properties of LWC Applications of LWC Advantages and disadvantages Case study conclusion References

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Introduction

Lightweight concrete can be defined as a type a type of concrete which includes an expanding agent in that it increases the volume of the mixture while giving additional qualities and lessened the dead weight.

It is lighter than the conventional concrete. The use of lightweight concrete has been

widely spread across countries such as USA, United Kingdom and Sweden.

Structural lightweight concrete

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It was first introduced by the Romans in the second century where ‘The Pantheon’ has been constructed using pumice, the most common type of aggregate used.

The building of ‘The Pantheon’ of lightweight concrete material is still standing eminently in Rome until now for about 18 centuries as shown in Figure . It shows that the lighter materials can be used in concrete .


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structural lightweight concrete

The Pantheon

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Compressive Strength

Compressive strength is the primary physical property of concrete and is the one most used in design.

Fourteen trial mixes had been prepared

during the research and from the results, the mixture with the highest compressive strength was used.


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Compressive strength at different densities

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Compressive strength at different percentage of foam

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Compressive strength at different w/c ratio

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Compressive strength at 28 days

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Compressive strength for different % of foam

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Compressive strength at different w/c ratio

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Water Absorption Water absorption is an important factor

due to the porous structure of the aerated

lightweight concrete. The water absorption test is done using

the samples prepared at the age of 28 days.

The purpose of this test is to identify the capability of the concrete to absorb water.


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Water absorption at different percentage of foam

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structural lightweight concrete

Water absorption at different foam agent and water ratio

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Moisture content at different percentage of foam

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Density of wet and hardened concrete

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Entrained Air

As with normal-weight concrete, entrained air in structural lightweight concrete ensures resistance to freezing and thawing and to deicer applications.

It also improves workability, reduces bleeding and segregation, and may compensate

for minor grading deficiencies in the aggregate.


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The amount of entrained air should be sufficient to provide good workability to the plastic concrete and adequate freeze-thaw resistance to the hardened concrete.

Air contents are generally between 5% and 8%, depending on the maximum size of coarse aggregate used and the exposure conditions.


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SLUMP

Due to lower aggregate density, structural lightweight concrete does not slump as much as normal-weight concrete with the same workability.

It is seldom necessary to exceed slumps of 125 mm (5 in.) for normal placement of structural lightweight concrete.


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VIBRATION

As with normal-weight concrete, vibration can be used effectively to consolidate lightweight concrete; the same frequencies commonly used for normal-density concrete

are recommended. Excessive vibration causes

segregation by forcing large aggregate particles to the surface.


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THERMAL RESISTANCE


Thermal resistance of concrete vs density

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APPLICATIONS

Lightweight concrete has been used since the eighteen centuries by the Romans.

The lightweight concrete was also used in construction during the First World War. The

United States used mainly for shipbuilding. It is widely used as loose-fill insulation in

masonry construction where it enhances fire ratings, reduces noise transmission, does

not rot and termite resistant.


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It is also used for vessels, roof decks and other applications.


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ADVANTAGES


Rapid and relatively simple construction.

Economical in terms of transportation as well as reduction in manpower.

Significant reduction of overall weight results in saving structural frames, footing or piles.

Most of lightweight concrete have better nailing and sawing properties than heavier and stronger conventional concrete.

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DISADVANTAGES

Very sensitive with water content in the mixtures.

Difficult to place and finish because of the porosity and angularity of the aggregate.

Mixing time is longer than conventional concrete to assure proper mixing.


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CASE STUDY

Wellington stadium. Location: New Zealand. Capacity of the stadium : 40000 Architects : Hok-Lobb (brisbane), Warren

& Mahoney. Structure consultants :Holmes

Consulting Group Contractor : Fletcher Construction, Ltd. LWA Supplier :TXI -Pacific Custom

Materials, Inc. (California).Structural lightweight concrete

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History And Layout

The stadium is sited in a prominent location on the harbour edge, in close proximity to the main Wellington railway station, the Parliament buildings.

The site is exposed to wind blown sea spray and is located just a few hundred metres from one of the country's most active and violent

seismic fault lines.Structural lightweight concrete

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continue…. The structural layout consists of an

oval bowl around the playing field (roofed only over the spectator seating) and is connected by a two level open walkway and parking building to the railway station.

At the southern end of the oval there is a four-storey administration building that also forms part of the main stand .


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The completed stadium

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FACTORS FAVOURING

Poor foundation condition. Severe earthquake forces. Durability. Rapid construction. Space utilization. Reduced site work. Innovative spirit.


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DESIGN

The use of lightweight concrete was initially proposed by Stresscrete, the precast concrete supplier.

But it was also readily accepted by the project structural consultants, Holmes Consulting Group, who were impressed by the potential of the product to reduce cost and responded enthusiastically to the challenge of a new material.


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In the final analysis, the choice was between a structure of lightweight concrete, or one of steel. Normal weight concrete was ruled out early in the final design process.


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Failure On Expansive Soils 36

Properties

Compressive strength : 44 MPa. Density : 1845 kg/m^3. Modulus Of Elasticity : 19 GPa. Creep : 2.3.

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CONCLUSION

The initial findings have shown that the lightweight concrete has a desirable strength to be an alternative construction material for the industrialized building system.

The strength of aerated lightweight concrete are low for lower density mixture. This resulted in the increment of voids throughout the sample caused by the foam.


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The foamed lightweight concrete is not suitable to be used as non-load bearing as the compressive strength is 27% less than recommended. The compressive strength is accepted to be produced as non-load bearing structure.


39Structural lightweight concrete

References

Report on research project on lightweight concrete.

Formed Lightweight Concrete. www.pearliteconcreteforrorepair.com

A.M Neville (1985) Properties of concrete Cellular Lightweight Concrete, Plan

City/NCS LLC. www. Neoporsystem.com

Thank you

abbas jamani (sd 0510 ) cept university, ahmedabad

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