PERKEMBANGAN TEKNOLOGI BETONPertemuan 13

Matakuliah : S0793 – Teknologi Bahan KonstruksiTahun : 2009

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Learning outcomes

• Mahasiswa dapat menyebutkan perkembangan teknologi beton di dunia dan di Indonesia

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Outline Materi

• Perkembangan Teknologi Beton• Beton Pracetak• Beton Fiber• Self Compacting Concrete

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Perkembangan Teknologi Beton

• Seiring dengan berkembangnya teknologi bahan dan komputer. Penemuan material baru yang lebih ekonomis dan tahan lama.

• Penggunaan bahan lain misalnya fiber, semen komposit, polimer dan sebagainya.

• Perkembangan teknologi komputer yang dapat membuat pengujian secara virtual sehingga lebih cepat dan akurat dilakukan oleh National Institute of Standard and Testing (NIST).

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Jenis Beton Lain

• Beton Berat (berat isi lebih besar, menahan radiasi, benturan)

• Beton Massa (bendungan besar, kanal, pondasi jembatan, agregat yang digunakan lebih besar, slump rendah)

• Ferro-Cement (beton dengan kawat anyam, kuat tarik tinggi, waterproofing, struktur tipis dan ringan, memungkinkan untuk di fabrikasi, kemudahan pengerjaan, penghematan bahan cetakan

• Beton Siklop (agregat besar hingga 20 cm, digunakan untuk beton massa)

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Beton Pra Cetak (Precast Concrete)

• Precast concrete is a form of construction, where concrete is cast in a reusable mould or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place.

• In contrast, standard concrete is poured into site specific forms and cured on site. Precast stone is distinguished from precast concrete by using a fine aggregate in the mixture so the final product approaches the appearance of naturally occurring rock or stone.

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Precast Concrete

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Fiber Concrete

• Fiber reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers. Within these different fibers that character of fiber reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation and densities. (wikipedia)

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Effect Fiber in Concrete

• Fibers are usually used in concrete to control plastic shrinkage cracking and drying shrinkage cracking.

• They also lower the permeability of concrete and thus reduce bleeding of water.

• Some types of fibers produce greater impact, abrasion and shatter resistance in concrete.

• Generally fibers do not increase the flexural strength of concrete, so it can not replace moment resisting or structural steel reinforcement.

• Some fibers reduce the strength of concrete.• The amount of fibres added to a concrete mix is measured as

a percentage of the total volume of the composite (concrete and fibres) termed volume fraction (Vf).

• Vf typically ranges from 0.1 to 3%. Aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d).

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• Fibres with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio.

• Some recent research indicated that using fibers in concrete has limited effect on the impact resistance of concrete materials

• This finding is very important since traditionally people think the ductility increases when concrete reinforced with fibers. The results also pointed out that the micro fibers is better in impact resistance compared with the longer fibers

• The High Speed 1 tunnel linings incorporated concrete containing 1 kg/m³ of polypropylene fibres, of diameter 18 & 32 μm, giving the benefits noted below. Polypropylene fibres can:– Improve mix cohesion, improving pumpability over long distances – Improve freeze-thaw resistance – Improve resistance to explosive spalling in case of a severe fire – Improve impact resistance – Increase resistance to plastic

Effect Fiber in Concrete

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Fiber Reinforced Concrete

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Self-Compacting Concrete

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The Important Properties

• Self-compactability• Avoidance of bleeding and segregation• Low shrinkage• Low permeability• Strength as needed

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The Benefits

• Less dependent on skill on site• Safer, quieter sites (no vibration)• Better appearance• Better durability• Strength as needed

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What’s Different?

• Segregation resistance from mortar viscosity, not aggregate grading

• Workability through admixtures, not water content

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What’s The Snag?

• Higher cost – especially if high strength not needed

• Plant control has to be better

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Will it happen?

• My guess is that 50% of concrete will be self-compacting within 10 years

• In USA a very large proportion of precast concrete is already SCC

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What is the secret?

Paste Viscosity! Attained by one of three means:• High cement content• High content of Fly Ash, Silica Fume etc• Use of Viscosity Modifying Admixture

Plus low water content using HRWR

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How to Check Suitability?

• There are many new tests: V-funnel, L-box, U-box, Fill-box, Orimet, GTM Screen + Slump Flow and J-ring

• While several of these may be used in mix development, only the latter will find site use

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What is Slump Flow Test?

Measuring spread rather than height plus:• Speed of flow outwards• Ability to pass through J-ring• Observation of edge during flow• Interesting to note that it works better with the

cone upside down!

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Why Does It Look Better?

• Perfect compaction

• No bleeding

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Conclusion

• We are going to expect concrete that is a little more expensive per cubic metre to buy

• BUT• It will require less skill and effort to place• It will look better with no appearance defects• It will be more durable• It will require more skill at the batching plant