CHAPTER 1

Fundamentals of materials

1.1 Composition and structure

1.1.1 Composition
1.1.1.1 Chemical composition
The chemical composition of a material can be defined as the distribution
of the individual components that constitute the material.
The material can be a pure substance, which contains only one chemical
component; in this case, the chemical composition corresponds to the
relative amounts of the elements constituting the substance. Normally, it
can be expressed with a chemical formula. For an example, the chemical
formula for water is H2O, thus the chemical composition of water may be
interpreted as a 2:1 ratio of hydrogen atoms to oxygen atoms.
For a mixture, the chemical is equivalent to quantifying the concen-
tration of each component. Component responds to chemically recog-
nizable species (Fe and C in carbon steel, H2O and NaCl in salted water).
There are different ways to define the concentration of a component, and
there are also different ways to define the composition of a mixture. It may
be expressed as molar fraction, volume fraction, mass fraction, molality or
normality or mixing ratio.

1.1.1.2 Phase composition

Phase, in thermodynamics, refers to chemically and physically uniform or
homogeneous quantity of a matter that can be separated mechanically from
a nonhomogeneous mixture, and that may consist of a single substance or a
mixture of substances. The concept of phase is also introduced to charac-
terize the composition of materials containing more than one component.
A phase in a material has uniform physical and chemical characteristics, and
different phases in a material are separated from one another by distinct
boundaries. In materials, a phase may contain one or more components. In
other words, a multicomponent material can exist as a single phase if the

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2 Civil Engineering Materials

different chemical components are intimately mixed at the atomic length

scale. In the solid state, such mixtures are called solid solution.
The components or phases in inorganic materials can be minerals.
Minerals are naturally occurring, inorganic substances with quantifiable
chemical composition and a crystalline structure. Portland cement clinker is
man-made, and contains mainly four phases: Alite, belite, aluminate, and
ferrite; however, we also called these phases as minerals.

1.1.2 Structure
Generally, the term structure for materials refers to the arrangement of
internal components of materials. The structure of materials can be classified
by the general magnitude of various features being considered. The three
most common major classifications of structure are as follows: ①Atomic
structure, which includes features such as the types of bonding between the
atoms, and the way the atoms are arranged; ②Microstructure, which
includes features that can be seen using a microscope, but seldom with the
naked eye; ③Macrostructure, which includes features that can be seen with
the naked eye.
Actually, most properties are highly structure sensitive and the structure
virtually determines everything about a material: its properties, its potential
applications, and its performance within those applications. Therefore, it is
very important to understand the basis for the structure of materials to be
able to control the properties and reliability of engineering materials.

1.1.2.1 Atomic structure

All materials are made of atoms. There are only about 100 different kinds of
atoms in the entire universe. However, these same 100 atoms form thou-
sands of different substances ranging from the air we breathe to the metal
used to support tall buildings. It is the interaction between atoms and
atomic bonding, to hold these atoms together and form different substances.
According to their nature, the bonds can be categorized into two classes
based on the bond energy. The primary bonds (>100 kJ/mol) are ionic,
covalent, and metallic. The secondary bonds are of the van der Waals, or
hydrogen.
Ionic bonding occurs between metal atoms and nonmetal atoms. To
become stable, the metal atom tends to lose one or more electrons in its
outer shell, thus becoming a positively charged ion (aka cations). Since
electrons have a negative charge, the atom that gains electrons becomes a
negatively charged ion (aka anion). As a result, the atoms in an ionic
compound are held together since oppositely charged atoms are attracted to
one another.
 Fundamentals of materials 3

Where a compound only contains nonmetal atoms, a covalent bond is

formed by atoms sharing two or more electrons. Nonmetals have four or
more electrons in their outer shells (except boron). With these many
electrons in the outer shell, it would require more energy to remove the
electrons than would be gained by making new bonds. Therefore, both the
atoms involved share a pair of electrons. Each atom gives one of its outer
electrons to the electron pair, which then spends some time with each
atom. Consequently, both atoms are held near each other since both atoms
have a share in the electrons.
Metallic bonding is a type of chemical bonding that rises from the
electrostatic attractive force between conduction electrons (in the form of
an electron cloud of delocalized electrons) and positively charged metal
ions. It may be described as the sharing of free electrons among a structure
of positively charged ions (cations). Metallic bonding accounts for many
physical properties of metals, such as strength, ductility, thermal and elec-
trical resistivity and conductivity, opacity, and luster.
van der Waals bonding includes attraction and repulsions between
atoms, molecules, and surfaces, as well as other intermolecular forces. van
der Waals bonding differs from covalent and ionic bonding in that they are
caused by correlations in the fluctuating polarizations of nearby particles.
van der Waals force is a distance-dependent interaction between atoms or
molecules and comparatively weak.
When the atoms, ions, or molecules have an opportunity to organize
themselves into regular arrangements, or lattices by the bonds mentioned
above in a solid, the solid is classified as a crystalline material. Hence, a
crystalline solid possesses long range, regularly repeating units.
If there is no long-range structural order throughout the solid, the
material is best described as amorphous. Quite often, these materials possess
considerable short-range order over distances of 1e10 nm or so. However,
the lack of long-range translational order (periodicity) separates this class of
materials from their crystalline counterparts. Examples of amorphous solids
are glass and some types of plastic. They are sometimes described as
supercooled liquids because their molecules are arranged in a random
manner somewhat as in the liquid state. As shown in Fig. 1.1, silicon and
oxygen are bonded by covalent bond to form regular unit, siliconeoxygen
tetrahedron, when the siliconeoxygen tetrahedrons are arranged in regular
way, the solid is called quartz, crystalline SiO2, whereas siliconeoxygen
tetrahedrons are arranged in a random way, they form glass (amorphous
SiO2).
The atomic structure primarily affects the chemical, physical, thermal,
electrical, magnetic, and optical properties.
4 Civil Engineering Materials

Figure 1.1 Schematic comparison between crystalline SiO2(quartz) and amorphous

SiO2(glass).

1.1.2.2 Microstructure
The term “microstructure” is used to describe the arrangement of phases
and defects within a material, the appearance of the material on the nme
mm length scale. A complete description of microstructures involves
describing the size, shape, and distribution of grains and second-phase
particles and their composition.
Microstructure can be observed using a range of microscopy techniques.
The microstructural features of a given material may vary greatly when
observed at different length scales. For this reason, it is crucial to consider
the length scale of the observations you are making when describing the
microstructure of a material.
Microstructures determine the mechanical, physical, and chemical
properties of materials. For example, the strength and hardness of materials
are determined by the number of phases and their grain sizes. The electrical
and magnetic properties and also the chemical behavior (corrosion) are
determined by the grain size and defects (vacancies, dislocations, grain
boundaries, etc.) presented in the material. As a consequence, the behavior
of such multiphase material is determined by the properties of the indi-
vidual phases and the fashion in which these phases interact. As a general
rule, the mechanical properties such as ductility, strength, resistance to creep
and fatigue of engineering materials are determined by their (micro)struc-
ture at different geometric scales.
 Fundamentals of materials 5

Figure 1.2 The BSE and particles packing images of cement-based materials.

The microstructure of cement-based materials is controlled by their

constituents, the mixture proportions, processing (e.g., mixing, consolida-
tion, and curing), and degree of hydration. The properties of the hardened
cement-based materials are dependent on their microstructure; the capillary
pore structure (black areas in Fig. 1.2), which includes the interface tran-
sition zone between the cement paste and aggregates usually governs the
transport properties of concrete, while larger voids reduce the strength of
concrete.

1.1.2.3 Macrostructure
Macrostructure describes the appearance of a material in the scale milli-
meters to meters, it is the structure of the material as seen with the naked
eye. The term macrostructure is sometimes used to refer to the largest
components of the internal structure. Grain flow, cracks, and porosity are
all examples of macrostructure features of materials. Macrostructure also
determines properties of materials, especially the mechanical properties.

1.2 Physical properties

Properties of a material refer to the features we can sense, measure, or test.
For example, if we have a sample of metal in front of us, we can identify
that the material is gray, hard, or shiny. Testing shows that the material is
able to conduct heat and electricity and it will react with an acid. These are
some of the metal’s properties.
Physical properties are those that can be observed without changing the
identity of the substance. The general properties of matter such as density,
specific gravity, fineness, thermal conductivity, heat capacity, etc., are ex-
amples of physical properties.
6 Civil Engineering Materials

1.2.1 Density and specific gravity

Mass (m) is a fundamental measure of the amount of matter. The space the
mass occupies is its volume, and the mass per unit of volume is its density.
Hence, it is simple to calculate density of an object by dividing its mass by its
volume. However, this is pretty complicated in the case of building materials.
A lot of building materials, such as wood, cementitious materials, and
ceramics, are porous. For porous particles, the mass is a finite value, but
how about the volume? As shown in Fig. 1.3, a stack of porous particles
contains a lot of pores, and these pores can be divided into two groups, i.e.,
open pores and closed pores. When the particles are immersed in water,
water can enter open pores, but it cannot enter closed pores. Hence,
different volumes of the porous particles can be defined. For a particulate
solid, it additionally includes the space left void between particles.
Envelope volume: The volumes of the solid and the voids within the
particle, that is, within close-fitting imaginary envelopes completely sur-
rounding the particle.
Apparent volume or skeletal volume: The volumes of the solid in the
particles and closed (or blind) pores within the particle. This volume
definition excludes volumes of open pores.
True or absolute volume: The volume of the solid in the particle, which
excludes volumes of all pores.
Accordingly, we can define different densities for porous materials as
follows:
Apparent density: The mass of a particle divided by its apparent (skeletal)
volume.
Envelope density: The ratio of the mass of a particle to the envelope
volume of the particle.
True density: The mass of a particle divided by its true (absolute)
volume.
For a collection of discrete particles of solid porous material, the bulk
density is the ratio of the mass of the collection of discrete pieces of solid
material to the sum of the volumes of the solids in each piece, the voids
within the pieces, and the voids among the pieces of the particular
collection. For powder materials, bulk density is also called bulk powder
density.
Weight (w) is a measure of the force exerted by a mass and this force is
produced by the acceleration of gravity. Therefore, on the surface of the
earth, the mass of an object is determined by dividing the weight of an
 Fundamentals of materials
Figure 1.3 A schematic picture well illustrates the physical meaning of these density definitions.

7
8 Civil Engineering Materials

object by 9.8 m/s2 (the acceleration of gravity on the surface of the earth).
Since we are typically comparing things on the surface of the earth, the
weight of an object is commonly used rather than calculating its mass.
Specific gravity is the ratio of the density of a substance compared to the
density of freshwater at 4
C. At this temperature, the density of water is at
its greatest value and equals 1 g/cm3. Since specific gravity is a ratio, it has
no units. Specific gravity values for a few common substances are as follows:
Au, 19.3; mercury, 13.6; alcohol, 0.7893; benzene, 0.8786. Note that since
water has a density of 1 g/cm3, the specific gravity is the same as the density
of the material measured in g/cm3.

1.2.2 Fineness
Fineness indicates the fineness or coarseness degree of powdery materials. It
is often expressed as standard sieve percentage or specific surface area.
Fineness can also be expressed by percentage of particles of various sizes
or average value of unit weight material. The population of particles of
various sizes is termed as particle size distribution. D50 is usually used to
represent the particle size of group of particles, which characterizes the
median diameter or medium value of particle size distribution. For instance,
if D50 ¼ 5.8 mm, then 50% of the particles in the sample are larger than
5.8 mm and 50% smaller than 5.8 mm.
The specific surface area is the surface area of the powdery material per
unit weight. There are many methods to determine the specific surface
area, such as gas adsorption, organic molecular adsorption, and air perme-
ability. Blaine’s air permeability apparatus is commonly used for cementi-
tious materials, which consists essentially of a means of drawing a definite
quantity of air through a prepared bed of cement of definite porosity.
Fineness, PSD, and specific surface area are fundamental characteristics
of cementitious materials, they affect the properties of building materials in
many important ways. Taking cement for an example, the finesses affects its
hydration rate, water demand, workability of fresh concrete prepared with
the material.

1.2.3 Thermal conductivity and heat capacity

Thermal conductivity is the ability of a material to transfer heat. Thermal
conductivity is quantified using the unit of W/(m$K), and is the reciprocal
of thermal resistivity, which measures the ability of materials to resist heat
transfer. Thermal conductivity can be calculated as the following equation:
k ¼ Q  L=AðT2  T1 Þ (1.1)
 Fundamentals of materials 9

where Q is heat flow, W; L is length or thickness of the material, mm; A is

surface area of material, m2; T2  T1 is temperature gradient, K.
The thermal conductivity of a specific material is highly dependent on a
number of factors, including the temperature gradient, the properties of the
material, and the path length that the heat follows. The thermal conduc-
tivity of the materials around us varies substantially, from those with low
conductivities such as air with a value of 0.024 W/(m$K) at 0
C to highly
conductive metals like copper, 385 W/(m$K).
The thermal conductivity of materials determines how we use them, for
example, those with low thermal conductivities are excellent at insulating
our homes and businesses, while high thermal conductivity materials are ideal
for applications where heat needs to be moved quickly and efficiently from
one area to another, as in cooking utensils and cooling systems in electronic
devices. By selecting materials with the thermal conductivity appropriate for
the application, we can achieve the best performance possible.
Heat capacity describes how much heat must be added to a substance to
raise its temperature by 1
C:
C ¼ Q=DT (1.2)
where C is heat capacity; Q is energy (usually expressed in joules); DT is the
change in temperature (Celsius or in Kelvin).
Specific heat and heat capacity are related by mass:

C ¼m  S (1.3)
where C is heat capacity; m is mass of material; S is specific heat.

1.2.4 Linear coefficient of thermal expansion

The average amplitude of the atoms’ vibration within the material increases
when heat is added to most of the materials. This, in turn, increases the
separation between atoms and causes materials to expand. It is usually
expressed as a fractional change in length or volume per unit temperature
change; a linear expansion coefficient is usually used in describing the
expansion of a solid. The linear coefficient of thermal expansion (a) de-
scribes the relative change in length of a material per degree temperature
change.
Dl
a¼ (1.4)
li $DT
where li is initial length; Dl is the change in length; DT is change in
temperature.
10 Civil Engineering Materials

Thermal expansion (and contraction) must be taken into account when

designing structures. The phenomena of thermal expansion can be chal-
lenging when designing bridges, buildings, aircraft, and spacecraft, but it can
be put to beneficial uses.

1.2.5 Wetting and capillarity

Wetting is the ability of liquid to form interfaces with solid surfaces, or
refers to describe how a liquid deposited on a solid (or liquid) substrate
spreads out. To determine the degree of wetting, the contact angle (q) that
is formed between the liquid and the solid surface is measured. The smaller
the contact angle and the smaller the surface tension, the greater the degree
of wetting.
As shown in Fig. 1.4, a wetting liquid is a liquid that forms a contact angle
with the solid which is smaller than 90 degrees. A nonwetting liquid creates a
contact angle between 90 and 180 degrees with the solid. Assuming that
there are no other factors involved (e.g., roughness), when the contact angle
formed between water and a solid surface is smaller than 90 degrees, the solid
is hydrophilic. On the contrary, water creates a contact angle between 90
and 180 degrees with a solid, which means that water cannot spread on the
solid surface autogenously, then the solid is hydrophobic.
Capillarity is the ability of a substance to draw another substance into it.
It occurs when the adhesive intermolecular forces between the liquid and a
substance are stronger than the cohesive intermolecular forces inside the
liquid. The effect forms a concave meniscus where the substance is
touching a vertical surface. The same effect is what causes porous materials
to soak up liquids. Capillary forces pull a wetting liquid toward a low
contact angle with the surface and wets the surface. A completely wetting
liquid forms a zero-contact angle into a capillary by creating a curved
meniscus at the rising liquid front. This phenomenon can be described with
the YoungeLaplace equation and the Laplace pressure inside a capillary.

Figure 1.4 Schematic illustration of contact angle of both hydrophobic surface and
hydrophilic surface.
 Fundamentals of materials 11

1.3 Mechanical properties

1.3.1 Loading and strength
The application of a force to an object is known as loading. Materials can be
subjected to many different loading scenarios and a material’s performance is
dependent on the loading conditions. There are five fundamental loading
conditions: tension, compression, bending, shear, and torsion (Fig. 1.5).
If material is subjected to a constant force, it is called static loading. If the
loading of the material is not constant but instead fluctuates, it is called
dynamic or cyclic loading. The way material is loaded greatly affects its
mechanical properties and largely determines how, or if, a component will
fail; and whether it will show warning signs before the failure actually
occurs.
In mechanics of materials, the strength of a material is its ability to
withstand an applied load without failure or plastic deformation. According
to different loading conditions, the strength includes tensile strength,
compressive strength, flexible strength, shear strength, and others.

1.3.2 Elasticity and plasticity

Elasticity is the property of solid materials to return to their original shape
and size after the forces deforming them have been removed. When a force
is applied to a certain cross-sectional area of an object, that object will
develop both stress and strain as a result of the force.

Figure 1.5 The fundamental loading conditions and illustration.

12 Civil Engineering Materials

Stress is the force carried by the member per unit area;

L  L0 d
ε¼ ¼ (1.5)
L0 L0
where F is the applied force; A is the cross-sectional area over which the
force acts.
Strain is the ratio of the deformation to the original length of the part:
L  L0 d
ε¼ ¼ (1.6)
L0 L0
where L is the deformed length; L0 is the original undeformed length; d is
the deformation (the difference between the two).
Stress is proportional to strain in the elastic region of the material’s
stressestrain curve (below the proportionality limit, where the curve is
linear). The coefficient that relates a particular type of stress to the resulted
strain is called an elastic modulus (plural, moduli).
E ¼ s=ε (1.7)

Elastic moduli are properties of materials, not objects. The elastic

modulus, also known as the modulus of elasticity, or Young’s modulus, is
essentially a measurement of the stiffness of a material. As a result, it is
commonly used in design and engineering applications.
Plasticity, ability of solid material to flow or to change shape perma-
nently when subjected to stresses of intermediate magnitude between those
producing temporary deformation, or elastic behavior, and those causing
failure of the material, or rupture. Plasticity enables a solid under the action
of external forces to undergo permanent deformation without rupture.
Plastic deformation is a property of ductile and malleable solids.
Most of the building materials are not pure elastic materials. Some
materials only have elastic deformation if the stress is not large, but plastic
deformation will happen to them when the stress is beyond a limit, such as
low-carbon steel. Under external forces, some materials will have elastic
deformation and plastic deformation at the same time, but elastic defor-
mation will disappear and plastic deformation still maintains when the stress
is removed, such as concrete.

1.3.3 Brittleness and toughness

Brittleness is a property of materials which enables it to withstand per-
manent deformation. Cast iron and glass are examples of brittle materials.
They will break rather than bend under shock or impact. Generally, the
brittle materials have high compressive strength but low in tensile strength.
 Fundamentals of materials 13

Toughness means the ability of a material to deform plastically and to

absorb energy in the process before fracture occurs. The emphasis of this
definition should be placed on the ability to absorb energy before fracture.
Ductility is a measure of how much something deforms plastically before
fracture, but note that a material is ductile does not make it tough. The key
to toughness is a good combination of strength and ductility. A material
with high strength and high ductility will have more toughness than a
material with low strength and high ductility. Therefore, one way to
measure toughness is by calculating the area under the stressestrain curve
from a tensile test. This value is simply called “material toughness” and it
has the unit of energy per volume. Material toughness equates to slow
absorption of energy by the material.
It is the property of a material which enables it to withstand shock or
impact. Toughness is the opposite condition of brittleness. The toughness
may be considering the combination of strength and plasticity. Manganese
steel, wrought iron, mild steel, etc., are examples of toughness materials.
There are several variables that have a profound influence on the toughness
of a material. These variables are strain rate (rate of loading), temperature,
and notch effect.

1.3.4 Hardness
Hardness is the resistance of a material to localized deformation. The term
can apply to deformation from indentation, scratching, cutting, or bending.
In metals, ceramics, and most polymers, the deformation considered is
plastic deformation of the surface. For elastomers and some polymers,
hardness is defined as the resistance to elastic deformation of the surface.
Hardness measurements are widely used for the quality control of materials
because they are quick and considered to be nondestructive tests when the
marks or indentations produced by the test are in low-stress areas. There are
a large variety of methods used for determining the hardness of a substance.
Historically, it was measured on an empirical scale, determined by the
ability of a material to scratch another, diamond being the hardest and talc
the softer. There are a few different hardness tests: Mohs, Rockwell, Bri-
nell, Vickers, etc. They are popular because they are easy and nonde-
structive (except for the small dent).
14 Civil Engineering Materials

1.3.5 Dynamic mechanical properties

A lot of structures are subjected to dynamic load during their service time
such as bridges, rails. Dynamic mechanical properties refer to the response
of a material to a periodic force. These properties may be expressed in terms
of a dynamic modulus, a dynamic loss modulus, and a mechanical damping
term. Polymers, and particularly rubbers, are often deliberately selected for
products which are to be subjected to dynamic mechanical loading.
Stress analysis involves the use of the frequency-dependent dynamic
moduli of the polymers. Assume, for example, that the polymer is subjected
to a sinusoidal stress s of amplitude so and frequency u, i.e., s ¼ s0sinut.
Stress analysis concerned with the dynamic mechanical properties normally
assumes that polymers are linearly viscoelastic. Hence, the strain response ε
to the imposed sinusoidal stress can be described as ε ¼ ε0sin(wt  d) where
d is the phase angle. This is shown diagrammatically in Fig. 1.6. The
imposed stress and the material response do not coincide, and the phase
angle d is the difference between the two curves.
Note that the strain response lags behind the stress by the phase
angledowing to the viscous component of the material. Some, but not all,
of the energy stored during the deformation of the material is dissipated.
Since the material is assumed to be linear, the stress is proportional to the
strain at all times, i.e., s ¼ Ee, but E is a function of the frequency u.
Because the stress and strain are not in phase, E must be treated as a
complex function:
E * ¼ E0 þ iE 00 (1.8)

Figure 1.6 The sinusoidal stress s and corresponding strain ε response for a linear
viscoelastic material.
 Fundamentals of materials 15

where and E 0 and E00 are the in-phase and out-of-phase components of the
modulus.
From the above definitions of the dynamic moduli and by manipulation
of the linear relationship between the sinusoidal stress and the corre-
sponding strain response, the phase angle d can be expressed as follows:
tan d ¼ E 00 =E0 (1.9)
where tan d is commonly called the loss tangent or damping factor; E00 and
E 0 are the most commonly measured dynamic properties of rubbers, repre-
senting the elastic stiffness and damping or hysteresis properties, respec-
tively. Sometimes the “argument” of the complex modulus jEj is used
instead of E*, and is given by the following equation:
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
jEj ¼ ðE 0 Þ þ ðE 00 Þ
2 2
(1.10)

At very high frequencies (u ¼ 104  108 cycles/s or Hz) rubber is very

stiff with a glass-like modulus. At these frequencies the polymer molecules
do not have time to react in response to the forcing oscillations. The
damping factor is then small but it increases to a maximum value in the
“leathery” transition region between the glassy modulus and the usual (low)
modulus which is characteristic of rubbers that are deformed slowly (u < 1
cycle/s or Hz).

1.4 Durability
For materials, durability is the ability to service for the long term without
significant deterioration by resisting the effects of the heavy use, drying,
wetting, heating, freezing, thawing, corrosion, oxidation, volatilization, etc.
According to the deterioration mechanisms, the deleterious factors
mainly consist of physical actions, chemical reactions. Physical actions
include wetting and drying, change in temperatures, and freeze-and-thaw
cycle.
For cement-based materials, chemical reactions leading to degradation
include acid attack, salt attack, alkali-aggregate reaction, carbonation, and
reinforcement corrosion. Two types of corrosion can be distinguished for
steel and other metals: direct reaction of the corrosive compound with the
metal and corrosion that occurs through the water present at the metal
surface. For asphalt, plastic, rubber, and other organic materials will be
damaged due to aging.
16 Civil Engineering Materials

Durability is one of the major requirements to be considered in the use

of building materials. More knowledge about deterioration mechanisms
and the measures to counteract these are to be provided in other chapters in
this book.

Exercises
1. Please summarize the factors which influence the durability of materials
for civil engineering.
2. Water is easy to spread over the surface of concrete and transport in
concrete because it is a hydrophilic material, how to improve the imper-
meability of concrete without changing its porosity and pore structure?
3. When designing buildings such as airport terminals, why the linear co-
efficient of thermal expansion of used materials should be considered ?
4. State the general relationship between the composition, structure, and
properties of materials.
5. Complete the following form to describe the change in properties of a
materials as its porosity increases. (using [when increasing; Y when
decreasing,  when unchanged, and ? for unclear)

Envelope Water Resistance Thermal

Porosity Density density Strength sorption to frost conductivity
[