Kuliah 03 Teknologi Bahan,Agregat

8/10/2019 Kuliah 03 Teknologi Bahan,Agregat

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KULIAH-03

Agregat (batuan)

Aggregate is the term used to describe rock used for road making andrefers to an assembly of discrete particles (i.e. pieces of rock).

Suatu bahan yang terdiri dari mineral padat, berupamassa berukuran besar, ataupun berupa fragmen-fragmen. (ASTM 1974)

Agregat merupakan komponen utama perkerasan jalan 90-95% berat, atau 75-85% volume.

Daya dukung, keawetan dan kualitas lapis perkerasanditentukan oleh sifat agregat dan hasil campuranantara agregat dengan material lain.

Klasifikasi agregat: Berdasarkan proses terjadinya Berdasarkan proses pengolahannya Berdasarkan ukuran butirnya.

Melting

Heat andpressure(metamorphism)

SEDIMENTARYROCK

METAMORPHIC

IGNEOUSROCK

Cementation and compaction

Weathering,transport,anddeposition

Sediment

Magma(molten rock)

Cooling andSolidification(crystallization)

Weathering,transport, anddeposition

Rock Cycle

Each type can be formed from any other

volcanoigneous rocksbasalt

igneous rocks granite

Rocks riseto the surface byuplift and erosion.

Weathering breaks downrocks.

metamorphic rocks slate andmarble

sedimentary rocksmudstone

slow solidification

high pressureand temperature

transportationand deposition

Magmarises tothe surfacewhere itcools rapidly.

limestonelimestone chalkchalk

sandstonesandstone sandstonesandstone

…an orangey-coloured rock which looks like lots of sand grains stuck together. Itis quite soft.

Sandstone is … Sandstone is …

…a grey/white rock which is mostly made from crushed sea shells. Limestoneoften contains fossils.

Limestone is … Limestone is …

…a white or grey powdery rock with very fine grains. Chalk often containsfossils.

Chalk is … Chalk is …

Sedimentary rocks consist of lots of small grains. These grainsmay be weakly held together so the rocks are often porousand may be soft and crumbly.

What are the properties of sedimentary rocks?

Sedimentary rocks often have fossils trapped within them.

Sedimentary rocks often have layers showing the deposition

of sediment at different time periods.

Sedimentary rocks consist of layers of lots ofsmall particles and are often porous.

Ciri-ciri batuan sedimen adalah:(1). Berlapis (stratification),

(2) Mengandung fosil,

(3) Memiliki struktur sedimen,

(4). Tersusun dari fragmen butiran hasiltransportasi .

Why are sedimentary rocks near the surface younger than sedimentary rocks deeperdown?

Weathering creates small rock fragments whichare transported to the sea where they aredeposited (sink) and form a sediment.

At this stage, dead creatures may becometrapped within the sediment and give riseto fossils.

Over millions of years, the pressure of layers above and the

effects of salts cement the sediment together. This ishow sedimentary rocks like sandstone,

fast-flowingwater

slowwater

pressure

s e d i m en t a t i on

c em en t a t i on

Some sedimentary rocks are formed by the cementation of sediment.

mudstone and limestone are formed.

These limestone rocks at Punakaiki in New Zealand are known as the Pancake Rocks.How were they formed?

Certain minerals are dissolved in seas andlakes.

Over millions of years these seas or lakes dryup.

As the water disappears, the dissolvedminerals precipitate.

Chalk and limestone, common in the UK,can be formed in this way.

dissolvedminerals

precipitation

a p or a t i on

Sedimentary rocks can also be formed from minerals which are left behindwhen water evaporates.

marblemarble slateslate

...a hard smooth rock made from sedimentary limestone or chalk in conditions ofstrong heat and low pressure.

Marble is … Marble is …

…a grey rock with fine grains made from sedimentary shale in conditions of lowtemperature and low pressure. Slate can be split into thin sheets.

Slate is … Slate is …

How are the properties of metamorphic rocks different from sedimentary rocks?

Metamorphic rocks often have layer structures of crystals caused by the effect ofheat and pressure.

Metamorphic rocks are usually denser and harder than sedimentary rocks.

Metamorphic rocks sometimes show distortions caused by the movements thatled to their formation. This may give rise to wavy or zig-zag patterns within therock.

Metamorphic rocks contain regular layers of crystalsthat sometimes have a wavy or zig-zag arrangement.

basaltbasalt

granitegranite pumicepumice

Granite is…

…a hard grey rock consisting of large crystals that are randomly arranged.

Granite is…

…a pale grey rock made up of very small crystals and is porous and extremelylight.

Pumice is … Pumice is …

Basalt is …

…a dark glassy rock which has very fine crystals and often forms as columns ofrock.

Basalt is …

What are the properties of igneous rocks?

The size of the crystals depends on how quickly the igneous rock solidifies.

The crystals in igneous rocks have a disorderly arrangement.

Igneous rocks contain interlocking crystals which are held together very strongly

and make the rock hard.

Igneous rocks never contain fossils.

Igneous rocks consist of randomly arranged interlockingcrystals.

intrusiveigneous rock

extrusive igneousrock

Igneous rocks are formed when magma cools and solidifies.

How are igneous rocks formed?

Deep in the ground is molten rock called magma. Sometimes, magma bursts through thesurface causing volcanic eruptions.

When magma cools

above the surface,

extrusive igneous

rocks are formed.

When magma coolsbelow the surface,

intrusive igneous

rocks are formed.

How is the size of crystals in igneous rocks determined by the rate at which magmacools and solidifies?

Magma above the Earth’s surface cools quickly. Onlysmall crystals are formed as the magma solidifies.

This is how extrusive igneous rocks like pumice andbasalt are formed.

Magma below the Earth’s surface cools slowly. There istime forlarge crystals to grow as the

magma solidifies.

This is how extrusive igneous rocks like granite areformed.

A mineral is anonliving solid foundin nature.

But, aren’t rocksnonliving and foundin nature too??

Then what is the

difference betweena rock and amineral?

Rocks are made up of one or moreminerals!!!

The reason why some rocks have more

than one color, is because they containmore than one mineral.

Also, some rocks are made of other

things, such as sand and pebbles, inaddition to minerals.

The Mohs Hardness

Scale was designedfor us to use as ascale to determinethe strength of

rocks and minerals.

1. Agregat beku (igneous rock ) Berasal dari magma yang mendingin kemudian

membeku

Dibedakan atas:▪ Agregat beku dalam (intrusive igneous rock ): dibentuk dari

magma yang tidak dapat keluar ke permukaan bumi,mengalami pendinginan dan membeku pelan-pelan di dalambumi. Dapat ditemui di permukaan bumi karena proses erosi.Umumnya bertekstur kasar: granit gabbro, diorit, syenit dll.

▪ Agregat beku luar (Extrusive igneous rock): dari magma yangkeluar ke permukaan bumi ada saat gunung berapi meletus,karena pengaruh cuaca mengalami pendinginan danmembeku. Umumnya bertekstur halus: batu apung,andesit,obsisian, fumice dll.

2. Agregat sedimen (sedimentary rock )

Berasal dari campuran partikel mineral, sisa

hewan dan tanaman yang mengalamipengendapan dan pembekuan dalam waktu lama.

Merupakan lapisan-lapisan di kulit bumi atau hasil

endapan di danau/laut

Contoh: batu lempung, batu gamping, batu bara

3. Agregat metamorfik = batuan malihan(metamorphic rock )

Berasal dari batuan beku atau sedimen yangmengalami perubahan bentuk akibat perubahantekanan atau temperatur tinggi di kulit bumi.

Berdasarkan strukturnya dibedakan atas:

▪ Agregat metamorf yang masif (marmer, kwarsit)

▪ Agregat metamorf yang berlapis (batu sabak)

1. Agregat alam (agregat siap pakai) Agregat yang dapat digunakan dalam bentuk dan

ukuran sebagaimana diperoleh di lokasi asalnya. Bentuk partikelnya ditentukan berdasarkan proses

pembentukannya: Erosi akibat aliran air di sungai: partikelnya bulat-

bulat dengan permukaan licin

Degradasi di bukit: partikelnya bersudut denganpermukaan kasar. Berdasarkan tempat asalnya

Pitrun: diambil dari tempat terbuka di alam

Bankrun: agregat dari endapan sungai

2. Agregat yang melalui proses pengolahan .Agregat besar dari gunung atau sungaiharus dipecah dahulu sebelum digunakan

dengan menggunakan tenaga manusia ataustone crusher ), sehingga diperoleh: Gradasi sesuai dengan yang diinginkan

Bentuk bersudut, diusahakan berbentuksudut. Bertekstur kasar, sehingga punya

gesekan yang baik,

1. Agregat kasar (course aggregate)Butiran yang tertahan di atas saringan no.4(4,75 mm) ASTM

1. Agregat halus ( fine aggregate)Butiran yang lolos saringan mo. 4 dantertahan di atas saringan no.200. ASTM

1. Agregat pengisi ( filler aggregate)bagian dari agregat halus yang minimum75% butirnya lolos saringan no. 200 (0,075mm) ASTM

To provide the good performance for base and sub-basecourse from the traffic loading and ground water.

To prevent the pavement failure due to concentrated

high stress from the wheel loading. To minimize the cost of pavement construction.

Strength & Toughness Particle Shape

Porosity Surface Texture Surface Chemistry Surface Coatings Specific Gravity

Ukuran lubangsaringan menurut

AASHTO

Contohhasil

analisasaringan:

Buat grafik gradasi zone I, II, III, dan IVmenurut BS.

• Cek benda uji berikut, termasuk ke dalamzone berapa.

Catatan:apabila grafik gradasi benda uji berada pada

rentang gradasi zone A, maka benda ujitermasuk agregat zone A

Jenis gradasi agregat:1. Gradasi baik (well graded )

2. Gradasi jelek ( poorly graded )- gradasi seragam = gradasi terbuka (uniform

graded )

- gradasi timpang = gradasi senjang ( gap graded )

Gradasi baik (well graded) disebut juga gradasi rapat

(dense graded )

Ukuran maksimum agregat:Semua lapis perkerasan lenturmembutuhkan agregat yang terdistribusidari besar sampai kecil. Semakin besarukuran maksimum agregat yang digunakan,akan semakin banyak variasi ukuran dari

besar sampai kecil yang dibutuhkan.Batasan ukuran maksimum yang digunakandibatasi oleh tebal lapis yang diharapkan.

Ukuran maksimum agregat:Penggunaan agregat dengan ukuran besarmenguntungkan, (tetapi sifat kurang baik)karena: Usaha pemecahan partikel lebih sedikit,

sehingga biaya lebih murah

Luas permukaan yang harus diselimutiaspal lebih sedikit, sehingga kebutuhanaspal menjadi sedikit.

Ukuran maksimum agregat, dapat dinyatakandengan menggunakan:a) Ukuran maksimum agregat:

- menunjukkan ukuran saringan terkecil

dimana agregat yang lolos saringantersebut sebanyak 100%- merupakan ukuran satu saringan yang lebih

besar dari ukuran nominal maksimumb) Ukuran nominal maksimm agregat:

- menunjukkan ukuran saringan terbesardimana agregat yang tertahan saringantersebut sebanyak < 10%

Tebal lapis perkerasan minimum = 2 x ukuranmaksimum agregat

Jika agregat terlalu besar, maka:

Untuk mendapatkan agregat bergdarasi baikdibutuhkan butir-butir yang terdistribusi dalam

rentang yang lebih besar.

Semakin mudah terjadi segregasi, yaitupemisahan butir-butir berukuran besar dan kecil.

Contoh:

Alat uji abrasiLos Angeles

Tekstur permukaan agregat:

Macam berat jenis (specific graffity)

1. Metcalf

2. Fuller & Thompson

Kuliah 03 Teknologi Bahan,Agregat

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