2 binders material

DEFINITION

11/02/14HAILEMARIAM GIRMA2

Binders are substances that are used to bind inorganic and organic particles and fibers to form strong, hard and/or flexible components.

THE BINDING ACTION

The binding action is generally due to chemical reactions which take place when the binder is heated, mixed with water and/or other materials, or just exposed to air.

TYPES OF BINDERS TO BE DISCUSSED

Binders

Gypsum Plasters

Asphalt Cement

Portland Cement

MAIN GROUPS OF BINDERS

There are three main groups of binders: -

1. Mineral binders 2. Bituminous (Asphalt)binders 3. Synthetic binders

1. MINERAL BINDERS

Mineral Binders

Non-hydraulic binders Hydraulic binders

E.g. Lime, Gypsum plasters E.g Portland cement

1.1 NON-HYDRAULIC BINDERS

Non-hydraulic binders are only harden in the presence of air

The most common non-hydraulic binder is:-

A. Lime. B. Gypsum

Hardening of non-hydraulic binder/lime depends on its combination with carbon dioxide from the air (carbonation), by which it again becomes calcium carbonate (limestone).

Cont’d

Gypsum is a non-hydraulic binder which occurs naturally as a soft crystalline rock.

The chemical name is calcium sulfate anhydrate (CaS04.2H20).

Cont’d

By gentle heating up to about the boiling point of water, calcium sulfate hemi-hydrate (CaSO4.1/2H2O) is produced, more commonly known as "Plaster of Paris", which when mixed with water sets in 10 minutes.

The common name for calcium sulfate hemi-hydrate is known as Plaster of Paris

1.2 HYDRAULIC BINDERS

Hydraulic binders require water to harden and develop strength.

The most common hydraulic binder is Portland cement.

Hydraulic binders are usually available in the form of a fine powder. Why?

Cont’d

On account of their affinity to water, hydraulic binders must be stored in absolutely dry conditions.

Why? Answer:- to avoid premature setting and

hardening (pre- hydration and carbonation). Even humid air can cause hydration.

2. BITUMINOUS BINDERS/ASPHALT

"Asphalt" is a dark brown to black, highly viscous, hydrocarbon produced from petroleum distillation residue.

This distillation can occur naturally, resulting in asphalt lakes, or occur in a petroleum refinery.

3. SYNTHETIC BINDERS

Synthetic binders are generally produced by industrial processes.

They can either be used as adhesives or as surface coatings and are either applied hot, or as an emulsion, or with a solvent.

Cont’d

Synthetic admixtures which bind loose particles together are mainly resins derived from plant materials or mineral oil.

Adhesives are used to stick larger particles, components, membranes, sheets, boards, tiles, etc. on another surface.

General

Lime is one of the oldest known cementing material

Lime is found in many parts of the world in its natural form as a rock of varying degree of hardness.

Lime is mainly composed of calcium oxide (CaO).

Cont’d

Lime in its pure form associates with CO2 to give white CaCo3.

Lime deposits are generally found mixed with impurities such as CO2, Fe2 O3, and MgCO3.

Depending on the impurities, lime deposits acquire different colors.

Production of lime

Lime is produced by burning the raw material limestone CaCO3.

Chalk , shell and coal can have CaCO3 content

exceeding 98 %

Dolomite mineral has as low as 54 %

Burning process

A. VERTICAL SHAFT KILN

Raw materials are fed in at the top & the finished product drawn off through an opening at the bottom.

Limestone

~10000c

B. ROTARY KILN

The raw materials fed in at the top & the finished product is drawn off at the bottom continuously.

Limestone

CLASSIFICATION OF LIME

Commercial lime is classified into three groups:-

1.Quick lime (Caustic lime) 2.Hydrated lime (Slaked lime)3.Hydraulic lime

1. QUICK LIME

The manufacture of quick lime consists in burning the limestone in some form of vertical kilns to a temperature of 10000c.

CaCO3 CaO+CO2

Quick Lime:

Is obtained by calcining (burning) the purest available calcium carbonate

Gives out considerable heatSwells two to three times of its original

volume upon addition of waterTakes much time in hardeningIs used for plastering and white washingIs not suitable for being used as mortar

because of its poor strength and slow hardening

2. HYDRATED LIME (SLAKED LIME)

Quick lime can never be used as such for construction purposes but must be mixed with water.

CaO+H2O Ca (OH)2 + heat

This process is called slaking and the product (calcium hydroxide) is called slaked lime or hydrated lime.

Forms of hydrated lime

Depending upon the amount of water added during the slaking process, three forms of hydrated lime are commonly produced:-

a) Dry hydrate, a dry, fine powder, formed by adding just enough water (Dry-Slaking) to slake the lime, which is dried by the heat evolved.

b) Milk of lime, made by slaking quicklime with a large excess of water (Wet-Slaking) and agitating well, forming a milky suspension;

c) Lime putty, a viscous mass, formed by the settling of the solids in the milk of lime.

3. HYDRAULIC LIME

Is prepared by burning impure limestone that contains clay, producing compounds similar to those present in Portland cement.

It is stronger but less fat or plastic than non-hydraulic lime.

Hydraulic lime is manufactured in the same way as quick lime, although a somewhat higher temperature is required in burning.

SETTING AND HARDENING OF LIME

Slaked lime hardens or sets by gradually losing the water through evaporation and absorbing carbon dioxide from the air.

Thus changing back from calcium hydroxide, Ca (OH)2 to calcium carbonate, CaCO3 or limestone.

The Lime cycle

CaOCa(OH)2

Burning

Slaking

Drying

USES OF LIME

1. Lime as a construction material As mortar (lime mortar) mixed with sand. Lime is used in cement mortar to make it

more workable As plaster (lime plaster) As a whitewash, when it gives a sparkling

white finished at a very low cost As lime concrete As a stabilizer in soil constructions with clayey

2. Lime as an industrial materialIn industry, lime finds many applications:-

As a flux in the metallurgical industry As a refractory material for lining

metallurgical furnaces; As a raw material for the manufacture of

glasses.

3. Lime as an agricultural input Lime is used for improving the productive

qualities of soils. It is added to the poor soils to enrich their

lime content.

GYPSUM PLASTERS

General

Gypsum is a combination of sulfate of lime with water of crystallization.

Gypsum occurs naturally as: Hydrous sulfate of lime (Ca SO4

2H2O) which is generally 76% CaSO4 and 24% H2O,

Anhydrate (Ca SO4). Pure gypsum is known as alabaster

and it is a white translucent crystalline mineral

Gypsum plasters

Gypsum plasters are used in the arts and in building construction.

Gypsum plasters are manufactured by heating the raw material gypsum at either moderate or high temperatures the results being plaster of Paris or hard-finish plaster respectively.

A. PLASTER OF PARIS

If some of the water of crystallization is driven off by incomplete dehydration at a temperature just above the boiling point of water (1000c), pure finely ground gypsum, a semi-hydrated plaster is obtained which is known as plaster of Paris.

(CaSO4.2H2O)+Moderate Heat (CaSO4 .1/2 H2O) +1/2 H2O

Cont’d

Plaster of Paris:- is a white powder having a specific gravity of 2.57. is also known as low-temperature gypsum derivative

or semi-hydrated plasters (hemi hydrate). When mixed with sufficient water to form a plastic

paste, it sets very rapidly (retarder must be added)

Cont’d

Glue, sawdust or blood can be added to Retard the setting time of the plaster.

Owing to rapidity of setting, its use in structures is limited to ornamental work.

Complete cycle in gypsum used as plaster

CaSo4.2H2O

CaSo4.1/2H2O

Moderate heat Hydration

B. HARD-FINISH PLASTER

Produced by burning gypsum to a considerably higher temperature .

Hard-finish plaster is also known as anhydrous plaster or high-temperature gypsum derivative.

(CaSO4. 2H2O)+High Heat CaSO4+ 2H2O

This plaster is less soluble with consequent reluctance to absorb water in the process of re crystallization.

Other Derivatives of Gypsum

1.Gypsum Ready Mixed PlasterIs calcined gypsum(CaSo4.1/2H2O) mixed at the

mill with mineral aggregate to serve as a base to receive various coats.

Contains about 60% of CaSo4.1/2H2O

2.Gypsum Neat plasterContains about 66% of CaSo4.1/2H2O by weight.The addition of aggregate is made on site.

3.Gypsum Wood fibered plasterComposed of not less than 66% of

CaSo4.1/2H2O and about 1% wood fiber.

4 . Gypsum bond plaster

Used as a bonding scratch -coat over monolithic concrete.

It contains not less than 93% of CaSo4.1/2H2O and not less than 2% or more than 5% of hydrated lime.

5.Gypsum Gauging Plaster Is prepared for mixing with lime putty for the

finish coat.

Contains not less than 66% of

CaSo4.1/2H2O

Thank you !!!

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