BASIC PROPERTIES OF BUILDING MATERIALS

Introduction

Properties of (building) material are determined by the type andmagnitude of bonds and forces that take place between atoms, ions,and molecules

• atoms – basic elements of materials

– mass 10–25 – 10–27 kg and diameter ~10–10 m

• molecules – sufficiently stable units of two or more atoms in aspecific arrangement given by chemical bonds

• compounds – combination of two or more molecules

– dimensions between 1 nm to 10 nm or more

– could contain even 1000 atoms or more

– formation of compounds from elements and their transformation – processesknown as chemical reactions

– in chemical reactions bonds are formed between some atoms and destroyedbetween other atoms

Introduction

• States of substances: solids, liquids, gases, and plasma

‒ Fluids = liquids + gases

• Various types of materials

‒ porous materials

‒ homogeneous vs. inhomogeneous materials

‒ isotropic vs. anisotropic materials

‒ etc.

• Heterogeneous materials

‒ not uniform in composition or structure

‒ typical for the most of solid substance (except of some alloys)

‒ a heterogeneous area usually represent pores, composites, and powder substances

• Environmental conditions (temperature, liquid moisture, relative moisture, pressure) may strongly affect material properties

Development of intelligent materials → materials engineering

• Materials that can change their properties in dependence on the change of their external environment

‒ vapor-permeable foils with variable water vapor resistance

‒ smart glasses – change their color

‒ self-cleaning surfaces – coated by a special type of coatings that repel dirt, smear, and water

‒ interior plasters that allows in sunny and hot days accumulation of heat – phase change materials

‒ materials with recovery (in shape)

‒ electrically conductive polymers – antistatic materials

• Progress of intelligent materials = control at the molecular level

Properties of materials

Basic physical properties

Hygric and diffusion properties

Mechanical properties

Thermal properties

Acoustic properties

Radioactivity

Chemical properties

Basic physical properties

• properties whose determination requires only the measurement of the mass and dimensions (or volume)

– bulk density

– matrix density

– relative density

– porosity, pore size distribution

– granularity, grain size distribution

Bulk density, matrix density

• Density is defined as the ratio of the elementary mass to the elementary volume

• Bulk density ρ – the total volume of a body is considered (including the pores), and

‒ the unit = kg/m3

‒ for an inhomogeneous (such as porous) material the definition may be misleading

• Matrix density ρmatrix – the volume without pores is considered

V

m

Experimental determination of bulk and matrix density

• Gravimetric method – from the measured dimensions of the sample and its mass, the bulk density can be calculated

• Pycnometric method – used for measurement of the matrix density – an indirect method

– pycnometer = a special vessel having a stopper with a capillary for the overflowing liquid; hence,

the pycnometer volume is constant

– the matrix density of material is calculated as

– m1 = mass of a dry sample

– m2 = mass of a closed pycnometer with a sample and water

– m3 = mass of pycnometer filled with water

– The mass difference between the situations

[pycnometer + water] vs. [pycnometer + water + sample]

is m3 – m2 = Vmatrix ρwater – Vmatrix ρmatrix → ρmatrix = m1/Vmatrix = a (ρwater – ρmatrix)

with a = m1/(m3 – m2 )

– From this relation we get Eq. (1) above

)1()( 123

1watermatrix

mmm

m

• (Building) materials are mostly not homogeneous

– they are porous, often formed from a mixture of several components

• Therefore, the bulk density is used in technical applications for the basic characterization of building materials

The bulk density depends on the matrix density of the individual components and on the porosity

The bulk density changes due to the moisture content (the porous space can be filled by water)

For loose materials (aggregates, sand, soil) and compressible materials (mineral wool, glass wool, etc.) it depends also on their compressibility

Powder density – involves the whole volume of the grains including the gaps and interspace between the grains

Relative density

• Describes how the material volume is filled with the solid phase (defined only for solids)

• It is the ratio of the solid phase volume Vsolid to the total volume Vtotal

= the ratio of the bulk density to the matrix density:

• It is a dimensionless number between 0 and 1

solid

total matrix

Vh

V

Porosity

• Porosity is the ratio of the pores volume Vpores to the total volume Vtotal of a

porous body,

[–]pores

total

V

V

Porosity

• Open porosity = the part of the total porosity involving the

open pores– open pores = have a direct connection with the surface of a material

• Open pores are usually formed by

‒ gases released during the material production (light-weight materials)

‒ water evaporation from the materials (concrete, ceramics, plasters,

cement based composites)

‒ intentional aerating and foaming (light-weight concretes)

• Closed porosity = the part of the total porosity including

closed pores – closed pores = not connected with the material surface, and so they do

not take part in transport processes

– the closed pores can be formed e.g. by sintering (of ceramics) and do

not allow the air humidity to enter the porous structure

• Pores may have complicated and variable shapes

• Therefore, the porosity of materials is described by pore-size

distribution curve which represents the pore sizes

– an example is on p. 15

• Different methods and approaches are used to measure the pore-

size distribution curve

– mercury porosimetry

– gas adsorption porosimetry

– electron microscopy

– optical microscopy

– water suction

– neutron imaging

• Suitable for micro and mesoporous materials (pore radius < 25 nm)

• Uses adsorption of the inert gases (such as helium) that are forced to enter a

sample under a given pressure

• From the known gas volume inside the sample and the pressure we can

estimate the volume ratio of pores of a given radius

– A higher pressure is needed for a gas to enter smaller pores

Gas adsorption porosimetry

Gas adsorption porosimetry

Mesopores volume distribution of metakaolin:

Mesopores volume:

0.021 cm3 g-1

Mercury intrusion porosimetry

• Suitable for meso and macroporous matters (pore radius > 2 nm)

• Uses mercury rather than a gas

– liquids cannot enter small pores as easy as gases

Material Porosity [%]

Slate 1.5 – 2.5

Marble 2 - 3

Sandstone 1 - 31

Ceramic brick 20 - 37

Cement mortar 31

Limestone 31

Sand 39

Lime mortar 41

Fine aggregates 42

Gypsum 51 - 66