AND MATERIALS
FOR
HISTORIC HERITAGE
NOTES
MATERIALS PART
, Contents
01 Materials in Architecture Module ������������������������������������������������������������������ 1
Chemical Properties �����������������������������������������������������������������������������������������������2
Physical Properties ������������������������������������������������������������������������������������������������2
Thermal Properties �������������������������������������������������������������������������������������������������3
Optical Properties ���������������������������������������������������������������������������������������������������3
Mechanical Properties �������������������������������������������������������������������������������������������3
02 The Interaction Between Built Heritage and Environment ���������������������������� 5
03 Degradation and Conservation of Stones ���������������������������������������������������� 7
Binders and Mortars �����������������������������������������������������������������������������������������������8
Decay �������������������������������������������������������������������������������������������������������������������10
04 Types and Reasons for Decay ������������������������������������������������������������������� 11
Action of water ����������������������������������������������������������������������������������������������������� 11
Biodeterioration �����������������������������������������������������������������������������������������������������14
05 Aim and Phases of the Conservation Project ���������������������������������������������� 15
Innovative research: nanotechnology ������������������������������������������������������������������19
06 Approach to Knowledge of Historical Buildings ������������������������������������������ 20
07 Degradation and Deterioration of the Metals ���������������������������������������������� 23
Metals for Restoration and in Historic Building �����������������������������������������������������24
08 Durability of Reinforced Concrete Structures of XXth Century ������������������� 27
Cement �����������������������������������������������������������������������������������������������������������������27
Sulphatic attack �����������������������������������������������������������������������������������������������������29
Corrosion of rebars ����������������������������������������������������������������������������������������������29
Repair of reinforced concrete structures ��������������������������������������������������������������30
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22. 9. 2021.
Materials in Architecture Module
PLACE FOR SUMMARY
How are basic properties of materials relevant with the respect to durability?
Durability -> concept of the time and environment; how materials perform over the exposure of
environmental circumstances over the time.
Compatibility -> materials are compatible if they work together in harmony; similar things go
together with similar things.
It is always important to distinguish symptoms and cause of deterioration. Deterioration mechanism is
reason why damages happen. Materials are solid components, and they are defined as the aggregates
of atoms and molecules bonded together by chemical and physical bonds.
What is the property of material? Property of material is not property of object or element. Property of
material represents the materials reactions to external chemical and physical actions. The property is
always constant and unchangeable, but performance of the material can vary. It could be also presented
as a distinctive quality of each material. Properties could be examined on the three different scales:
• MACRO - STRUCTURE
• MICRO - STRUCTURE
• ATOMIC – MOLECULAR STRUCTURE
Macro-structure is observed by naked eye and it is considered as a whole. Properties can be directly
measured through experimental test carried out on the sample. Its characteristics are: mechanical
strength, weight, dimensions, surface features and durability.
Micro-structure is observed by microscopy so that single phases could be identified. Such phasis
contribute to overall behaviour of the material, such as: geometry, characteristics of the phasis and
interface bonds.
Atomic-molecular structure indicates the state of conservation, materials’ reactivity and thus durability.
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, Material properties that are particularly relevant in the field of historic building conservation include:
• CHEMICAL (relevant to durability, compatibility)
• PHYSICAL (thermal and optical properties)
• MECHANICAL (compressive and tensile strength, hardness)
Chemical Properties
Chemical properties: chemical bonds are derived from the sharing of electrons among two or more
atoms. They can be strong or weak depending on the bond energy. Strong bonds = high resistance to
stresses
Examples of strong bonds: covalent; ionic; metallic
Examples of weak bonds: Van der Waals; hydrogen
Covalent bond: materials with covalent bonding share electrons among two or more atoms. It is a
directional bond -> very strong bonds but no ductility and low thermal conductivity.
Ionic bond: between atoms with remarkable differences in EN, thus exchange of electrons occurs.
Characteristics of this bonds: non directional bond, ionic crystals, soluble salts, water solubility.
Metallic bond: metallic elements due to low electronegativity give up their valence electrons to form
a diffuse ‘electronic cloud’. Positively charged atom cores are held together by the mutual attraction
of the nearby diffused electrons producing a strong bond. Its characteristics are following: strong non
directional bond, thermal conductivity, ductility, high density due to regular and highly packed structures.
Solid materials are composed of atoms and molecules which may be grouped with different levels of
order -> different structures; crystalline = metal; amorphous = glass; semicrystalline = polymers.
Physical Properties
Physical properties: describe the behaviour of a materials subjected to physical actions, such as:
temperature variations, electric or magnetic fields, presence of water or light.
Density is one of the key aspects that is defined as weight per unit volume. Density (ρ) is the mass of
a unit volume of homogeneous materials measured in [g/cm3]. Material density highly correlates to the
structure! For example metals have high density (high atomic number and compact structure) whereas
polymers have low density.
Bulk density is the mass of a unit volume of material in its natural state (with pores and voids). For the
most materials bulk density is less than density, however for liquids and materials like glass and metals,
these parameters are practically the same. Properties like strength and heat conductivity are greatly
affected by their bulk density.
Hygroscopicity: a property of a material to absorb water vapour from the air. It is influenced by air
temperature and relative humidity; pored – their number, type and size.
Water absorption: denotes the ability of a material to absorb and retain water. It is expressed as
percentage in weight or of the volume of dry materials. Ww=((Ms-M))/M [Ms – mass of saturated
material; M – mass of dry material in grams].
Water permeability: is a capacity of a material to allow water to penetrate under the pressure. Materials
like glass, steel or bitumen are impervious.
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