Binders

Question 1

What is a binder?

Answer 1

A material that joins together two elements

Question 2

What is organic and inorganic binders?

Answer 2

Organic binders can be natural or synthetic
Natural: polysaccharides (cellulose, starch), proteins
Synthetic: Epoxy, acrylic, polyacrylic

Inorganic binders can be hydraulic or non-hydraulic
Hydraulic: Hardens with water, hydraulic lime, cement
Non-hydraulic: hardens with air, gypsum, lime

Question 3

Explain some details about inorganic binders

Answer 3

Firing a rock and obtaining it i fine powder.
When this powder is mixed with water, it forms a plastic mass that is moldable. It is basically a Mixtures of inorganic oxides, silicone oxides, magnesium oxide etc.

Setting: Setting is the phase during which the binder paste loses its plasticity and moldability, the ability to be shaped. It takes a few minutes

Hardening: Phase transformation during which the binder paste gets it mechanical properties, forming its stone like material. The duration of this is infinite.

Question 4

What is produced from binders?

Answer 4

1. Binder paste: water + binder
2. Mortar (murburk) : water + binder + fine aggregates
3. Concrete: water + binder + fine aggregates + coarse aggregates. This one is only cement based.

Question 5

Why is mortar preferred before “simple” paste (binder+water) ?

Answer 5

Since mortar has:
* Higher mechanical properties
* Lower shrinkage: Pure binder pastes (like those made with hydraulic lime or cement) undergo significant shrinkage as they set and harden, which can lead to cracking and reduced structural integrity. The sand is incompressible which reduces the shrinkage and also risk of cracks.
* Mortar is cheaper: sand is cheap
* Setting time is lower which is not good

Question 6

What is gypsum?

Answer 6

An inorgnaic binder that has a special process of forming.

Can be of two forms: Gypsum stone or selenite

Question 7

Briefly describe the firing process of gypsum

Answer 7

1. Raw Material:
   Natural Gypsum Stone (CaSO₄·2H₂O): This stone contains two water molecules chemically bound to each calcium sulfate molecule.
2. Heating:
   Temperature: The stone is typically heated to around 130-150°C.
   Duration: Lasts until sufficient water is removed.
3. Dehydration Reaction:
   Chemical Process: When heated, gypsum loses part of its water content and transforms into plaster of Paris (calcium sulfate hemihydrate - CaSO₄·½H₂O).

4.1: Formation of Hemihydrate Gypsum
Plaster of Paris (CaSO₄·½H₂O): This is the primary product of the firing process, which is highly soluble and can be rehydrated to form a hard, stone-like material.
OR
4.2: Formation of Alpha-Anhydrite:
Alpha-Anhydrite (CaSO₄): In regions of the furnace where the temperature is higher, a small amount of alpha-anhydrite forms. This form is less soluble compared to the hemihydrate.

Question 8

Explain the setting process of gypsum

Answer 8

The setting process occurs where water evaporates or adsorps.

Question 9

Explain the hardening process of gypsym

Answer 9

• At the end all the water has been removed, either by absorption by the substrate or by incorporation.
• The solution becomes oversaturated with respect to the poorly soluble dihydrate gypsum that then precipitates and crystallizes.
• Then, new hemihydrate gypsum and alpha-anhydrite pass in solution
• The new bi-hydrate gypsum precipitates and continues to crystallize in form of fine needle-like crystals
• Moldability of the gypsum paste decreases
• Increasement of the mechanical strength

Question 10

Explain some important considerations about gypsum

Answer 10

• The hard part of firing is controlling the temperature
• The lower amount of water the finer final product - less pores
  *Higher amount can lead to better mouldability
• The water of the crystallization if very good fire resistance

Question 11

Use of gypsum?

Answer 11

Paste or mortar
Patch
Temporary fixation
Vault
Decorations, radnering, stuccowork and final touches

Question 12

What is plasterboard?

Answer 12

Plasterboard = wallboard = gypsum board
Grypsum plaster pressed between two thick sheets of paper
Gypsum is micropourus, which makes it to a good moisture absorber, but gets problem wiht fungi and bacteria - add products to the mixture

Question 13

What are some things to think about when using gypsum?

Answer 13

• Hemihydrate calcium sulfate (gypsum) has a solubility in water - dont use gypsum outside
• Cannot be in contact with steel - gypsum will solubilise and the steel will rust
• Cannot be used in ammonia containing environments since it can react with ammonia and carbon dioxide and form ammonium sulfate
• Cannot be near cement an concrete - delayed ettringite

There is an unavoidable potential incompatibility between gypsum and:
Carbonatic stone based walls
Cementitious products
Don’t use gypsum in contact with cement - you will have problems!!

Question 14

What is lime?

Answer 14

Is prepared by firing carbonatic rocks.
Calcination: Limestone is fired at temperatures above 900°C to produce quicklime (CaO).
Lime Slaking: Quicklime is mixed with water to form calcium hydroxide (Ca(OH)2).

Lime is a non-hydraulic binder, meaning it requires contact with air to harden.
Hardening occurs through carbonation, where calcium hydroxide reacts with carbon dioxide to form calcium carbonate.

Question 15

What are som differences and similarities between lime and gypsum?

Answer 15

Calcium carbonate from the rock, fire the rocks calcination, mixing with water, setting and hardening and we get calcium carbonate again.
Gypsum: selentie, calcium, obtained harbenade calcium calcite dehyfrated

Question 16

What are some problems during setting of lime?

Answer 16

During setting the water evaporates which leads to shrinkage, to overcome this you add mortar (siliceous or calcareous sand)

Question 17

Hardening of lime?

Answer 17

Lime hardens in the air
Hardening lime is microporus

Due to the reaction of re-carbonation: CO2 from the air forming calcium carbonate and water.

Calcite crystals occurs. Surface carbonation is a relatively fast process, whereas in the core it is quite slow and is favoured by the porosity of the system (entrance of CO2 from the outside)  degradation analogous to calcite-based stones

Question 18

What is special about lime formation?

Answer 18

we started from CaCO3 and at the end obtain CaCO3 again; the difference is the very smaller size of the final calcite crystals

Question 19

What is lime mortar?

Answer 19

Lime mortar is a mixture of lime, sand, and water.

Lime mortar is made by mixing quicklime with sand and often additional additives like pozzolans (volcanic ash). The specific type of lime used and the ratio of ingredients can influence the properties of the final mortar.

The thing is to avoid the shrinkage problem by adding mortar to the lime.

Question 20

What is important for lime mortar?

Answer 20

Before use, lime in the mortar MUST be completely slaked (15 days for
wall mortar; 3 months for lime plaster); contact with air (hardening) must be
also avoided. If lime is only partially slakedlocalized swelling in lime
plaster due to late hydration

Question 21

what weathering mechanisms can lime mortar get?

Answer 21

MEchanical erosion
Localized expansion: due to late hydration
Crystallization of soluble salts —> efflorescences, sub-florescences
Washing away: calcite dissolution due to rain and othe water based percipitations.
Acids attack with subsequent formation of soluble salts

Question 22

What is hydraulic lime?

Answer 22

Hydraulic lime is a type of lime that can set and harden under water.