Essay: COMPARATIVE BETWEEN LIGHTWEIGHT CONCRETE & TRADITIONAL CONCRETE

ABSTRACT

We visited one site for our Project Report of “Comparative between traditional concrete & Lightweight concrete” We study about lightweight concrete and normal concrete and collect various test report. We had inspected the whole about our project. Lightweight concrete as a type of concrete which includes an expanding an agent in that is increases the volume of the mixture while giving additional qualities such as lessened the dead weight. It is lighter than the conventional concrete. We found various test report on both concrete and inspected the people which type of concrete is better for the construction.

1. INTRODUCTION

Fig.1 lightweight concrete fig.2 traditional concrete

Nowadays, the use of lightweight concrete is increasing, not only for rehabilitation or pavement filling. The application of lightweight concrete on pavements is increasing, mainly due to the lower self

Weight compared to the ordinary concrete, making possible the decrease of loading in the structure. However, one of the major problems that concrete has is the time that it takes to dry

Out, meaning, the time that the water takes to come out of the concrete, delaying the coating and causing anomalies on this one. Since, the drying process is slow, it is necessary to know the water content that is acceptable in the concrete so there isn’t any problem when a coating, that is sensitive to humidity, is applied.

This dissertation has the aim of knowing the water content of concrete, throughout time, in order to estimate how long it does take to dry depending on the lightweight aggregate used.

The usage of lightweight materials, such as pumice-stone, comes far away back since the Romans, when they mixed these aggregates with binders made of volcanic ashes and lime to get a concrete with low density.

Throughout history, several constructions were built using lightweight concrete. Many of them are, to this present day, in very good conditions, mostly for its durability, as for example, the Roman Pantheon that was built between 110 and 125 D.C. [2]. Lightweight concrete was used, throughout time, on different applications, for example naval construction. But today this material is used in all kinds of structures as bridges; buildings, oil

Platforms, among others. The usage of lightweight concrete goes beyond structural function. This material is used to improve the already existing structures, namely pavements, due to its lightness and thermal and

Acoustic isolation characteristics.. Nowadays, many buildings are built using lightweight

Concrete to fill up floors. It is this type of usage that this dissertation is about.

2. DEFINITION

Lightweight concrete

Lightweight concrete is defined according to NP EN 206-1 [1] as a concrete that has a density, after oven drying, that isn’t larger than 2000 kg/m3, total or partially produced with porous structure aggregate.

Traditional concrete

Traditional concrete is that pourable mix of cement, water, sand, and gravel that hardens into a super-strong building material. Sidewalks, foundations, and highways are all made of concrete.

The main difference between lightweight concrete and normal concrete is the lower density

Mass, besides its distinguishable thermal and durability characteristics. In addition, the standard NP EN 13055-1 defines lightweight aggregate as having a particle

density not exceeding 2000 kg/m3 or a loose bulk density not exceeding 1200 kg/m3 .

Fig.3 No-fines concrete

3.2Lightweight aggregate concrete

3.3 Aerated concrete

Fig.5 Aerated concrete

• Aerated concrete is made by introducing air or other gas into a cement slurry and fine sand.

• It is used in precast concrete factories in order to produce concrete with a reasonable high strength and low drying shrinkage.

3.5 High Strength concrete

• Compressive strength of high strength concrete mix is usually greater than 6,000 pounds per square inch.

• High strength concrete is made by lowering the water cement (W/C) ratio to 0.35 or lower.

• Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement, which might reduce the strength at the cement aggregate bond.

3.6 High Performance concrete

• High strength concrete mix can be prepared with careful selection of ingredients and optimization of mix design.

• High workability is attained by super plasticizers, they lower the water cement ratio to 0.25 which is the amount required only for hydration process.

• The admixtures are 20-25% fly ash of partial replacement of cement and rest 70% is Ordinary Portland Cement.

3.7 Self-Compacting concrete

• The concrete where no vibration is required. The concrete is compacted due to its own weight. It is also called self-consolidated concrete or flowing concrete.

• It can be also categorized as high performance concrete as the ingredients are the same, but in this type of concrete workability is increased.

3.8 Pervious concrete

• Pervious concrete contains a network of holes or voids, to allow air or water to move through the concrete. This allows water to drain naturally through it, and can both remove the normal surface water drainage infrastructure, and allow replenishment of groundwater when conventional concrete does not.

• It is formed by leaving out some or the entire fine aggregate (fines), the remaining large aggregate then is bound by a relatively small amount of Portland cement.

• When set, typically between 15% and 25% of the concrete volumes are voids, allowing water to drain.

4. APPLICATION

4.1 Lightweight concrete

4.2 Traditional concrete

4.1 LIGHTWEIGHT CONCRETE

• This material is used in concrete blocks and panels for outer leaves of buildings as well as partition walls, concrete slabs for roofing and floor screeds.

• 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.

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

4.2 TRADITIONAL CONCRETE

• Concrete application include dams, bridges, swimming pools, homes, streets, patios, basements, balustrades, plain cement tiles, mosaic tiles, pavement blocks, kerbs, lamp-posts, drain covers, benches and so on….

• Concrete is specific to different applications like rebuilding, mending and construction.

• Concrete building components in different sizes and shapes are also made before hand and later applied.

• They include wall panels, doorsills, beams, pillars and more. Post-tensioned slabs is a preferred method for industrial, commercial and residential floor slab construction.

5. CHARACTRISTICS

5. LIGHTWEIGHT CONCRETE

5.1 Thermal insulation

5.2 Fire insulation

5.2 Durability

5.3 Rain penetration

5.4 Acoustic properties

5.5 Water absorption

5.1 Thermal insulation

• Thermal insulation efficiency is defined as resistance to heat flow either through conduction, or radiation.

• Lightweight concrete has a high heat insulation resistance.

• such as porous concrete walls 150mm to provide four times better insulation than 225mm thick brick wall.

5.2Fire insulation

FIg.6 Fire insulation

Fire prevention is associated with thermal insulation

Two types of fire protection

a) Combustible materials – such as organic wood

b) A non-combustible materials – such as non-organic materials such as stone, bricks, rocks and other.

5.3Durability

• It is defined as the ability to bear the effects of environment such as the effects of chemical, physical stress and mechanical effects. The intended effect of the chemical, including ground water containing sulphate, air pollution and reactive liquid spills.

• Physical stress is the shrinkage, the stresses of temperature, cooled, and others. If all the physical stress will cause cracks in the structure of lightweight concrete

• Mechanical effect is the impact and costs are excessive. The situation in the steel structure unit should be protected from rusting.

5.4Penetration of rain water

Fig.7 Rain water penetration

It is an important element to the wall.

5.5 Acoustic properties

Fig.8 Acoustic properties

• The key factor is the density of the sound insulation material. Therefore, for sound insulation, lightweight concrete can not show the desired characteristics.

5.6 Water absorption

Fig.9 Water absorption

Absorption water by the concrete is high and more than that found in solid concrete. This is because the lightweight concrete has holes in it

6. PROPERTIES

Lightweight concrete

• STRENGTH

a) Compressive strength

b) Tensile strength

c) Shear strength

• WATER ABSORPTION

• SHRINKAGE

• EXPANSION

• FIRE RESISTANCE

7. PRODUCTION

Lightweight concrete

CEMENT + LIGHTWEIGHT AGGREGATE + FOAM

• The lightweight matrix formed by the mixture of cement, water and foam, lightweight aggregates can be used without the tendency to float when the mix is vibrated.

• Aggregates which are used are:- expanded shale or clay, scoria, pumice, vermiculite or fly ash.

• It is often increasing the overall density for a given strength, since simply a higher foam content can achieve better results.

• The mixture is then ready for discharging into the moulds or wherever it is to be placed.

7.1 WATER : CEMENT RATIO

• The amount of water to be added to the mix depends upon the moisture content of the sand, 40-45 litres of water is used for every 100 kilograms of cement.

• When the amount of foam is increased, as for lighter densities, the amount of water can therefore be decreased.

• The water: cement ratio should be kept as low as possible in order to avoid unnecessary shrinkage in the moulds.

7.2 BATCHING OF MATERIALS

• Appropriate quantities of sand & cement are batched, and an amount of water required for the mix to be flowable is added.

• Materials are mixed thoroughly in a mixing plant fitted with foam-generating plant and pumping units.

• Water to be added is adjusted for moisture content of sand. The foam is injected into mix rather than added on to mix.

7.3 MIXING AND TRANSPORTATION

Ready mix concrete agitator is used for mixing.

All the raw materials are metered into the agitator and with the agitator turning at a high speed, a predetermined batched volume of foam is introduced into the agitator.

Batching of both of the raw materials and foam are done at the ready mixed concrete batching plant, it will be possible trip to transport at the site.

7.3 PLACING

Properly designed foam concrete has a stable burble structure and can be pumped to normal heights without loss of entrained air.

A squeeze-type pump is referred over a screw-feed pump.

Foam concrete produced and delivered at the site can be pumped up to height of 60 m and placed like SCC.

7.4 CURING

Fig.10 Curing

• Air Curing

• This is probably the easiest and most popular method of curing.

• It is a slow, but acceptable system which enables a turn around of moulds every 24 hours on average, depending on the ambient temperature.

7.5 STEAM CURING

When precast Aerated Concrete panels and slabs are made under factory conditions in order to induce an early strength into the concrete by applying heat from steam to the underside of the moulds.

Steam curing is not begun until at least five hours after casting, and even then the increase in temperature is well controlled and should not exceed 70°C (167°F). The extent of steam curing depends upon the climate .

TRADITIONAL CONCRETE

CEMENT + SAND + AGGREGATE + ADMIXTURE + WATER

• The manufacture of concrete is fairly simple. First, the cement (usually Portland cement) is prepared. Next, the other ingredients—aggregates (such as sand or gravel), admixtures (chemical additives), any necessary fibers, and water—are mixed together with the cement to form concrete.

• The concrete is then shipped to the work site and placed, compacted, and cured.

7.6 WATER: CEMENT RATIO

• In the preparation of concrete the water cement ratio it very important.

• For normal construction the water cement ratio is usually 0.5

• Adding to much water will reduce the strength of concrete and can cause segregation.

• For different ratio of concrete the amount of water for 50kg of cement.

Concrete ratio quantity water

1:3:6 34Litre

1:2:4 30 Litre

1:1.5:3 27Litre

1:1:2 25 Litre

7.7 BATCHING OF MATERIALS

Fig.11 BATCHING OF MATERIALS

• It is the process of measuring concrete mix ingredients either by volume or by mass and introducing them into the mixture.

• Traditionally batching is done by volume but most specifications require that batching be done by mass rather than volume

7.8 MIXING AND TRANSPORTATION

Fig.11 mixing machine

• Mixing concrete is simply defined as the “complete blending of the materials which are required for the production of a homogeneous concrete”

• This can vary from hand to machine mixing, with machine mixing being the most common.

• Suitable arrangement of materials and equipment, and correct weighing of the materials are the essential steps that must be completed before any mixing takes place.

Fig.12 transporting machine

• Transporting the concrete mix is defined as the transferring of concrete from the mixing plant to the construction site.

• Keep in mind that not all concrete is mixed on the actual construction site and could require some significant travel. This is most common for ready-mixed concretes.

• The main objective in transporting concrete is to ensure that the water-cement ratio, slump or consistency, air content, and homogeneity are not modified from their intended states.

7.9 CURING

Fig.13 Curing

• Curing is the process in which the concrete is protected from loss of moisture and kept within a reasonable temperature range.

• The result of this process is increased strength and decreased permeability.

• Curing is also a key player in mitigating cracks in the concrete, which severely impacts durability.

8. ADVANTAGES

LIGHTWEIGHT CONCRETE

• 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.

TRADITIONAL CONCRETE

• Ingredients of concrete are easily available in most of the places.

• The durability of concrete is very high.

• It can be cast to any desired shape.

• Maintenance cost of concrete is almost negligible.

• Concrete makes a building fire-safe due to its non combustible nature.

• Concrete can withstand high temperatures.

• Concrete is resistant to wind and water.

• Sound proofing & economical material.

9. DISADVANTAGES

LIGHTWEIGHT CONCRETE

• 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.

• Compressive and flexural strengths of foamed concrete reduce with its density.

TRADITIONAL CONCRETE

• Compared to other binding materials, the tensile strength of concreter is relatively low.

• Concrete is less ductile.

• The weight of compared is high compared to its strength.

• Concrete may contains soluble salts. Soluble salts cause efflorescence.

• Transportation is not easy.

• Dead load very High. Concrete is very costly.

10. CONCLUSION

 Lightweight concrete can be utilized as a normal concrete replacement structure shield.

 Aerated Concrete and Lightweight Aggregate Concrete also can be use as energy absorbent.

 Lightweight aggregate concrete, it depends on the materials used.

 Lightweight concrete can develop to be high strength concrete and good absorbability of impact energy.

 It has a lower modulus of elasticity and higher tensile strain capacity further provides better impact resistance than normal weight concrete.

 In recommendation, more research is required if the capabilities of the material are to be exploited and utilization the reinforcement for enhance the tensile strain capacity of concrete.

Foamed lightweight concrete is not suitable to be used as non-load bearing wall as the compressive strength is 27% less than recommended

11. References

 Report on research project on lightweight concrete.

 Lightweight Concrete

www.slideshare.com

 www.wikipedia.org

 www.google.com

 www.bing.com

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