lecture 2. sustainable design, material variability, and ... · 3) efficient: products in...

CIV-E1010 Building Materials Technology (5 cr) (1/18)

Lecture 2. Sustainable design, Material variability, and Nature of materials

Prepared by: Fahim Al-Neshawy, D.Sc. (Tech.) Aalto University School of Engineering Department of Civil Engineering A: P.O.Box 12100, FIN-00076 Aalto, Finland


Table of Contents Lecture 2. Sustainable design, Material variability, and Nature of materials ..................................... 1

2.1 Sustainable design ...................................................................................................................... 3

2.1.1 Phases of building materials ............................................................................................... 3

2.1.2 Features of sustainable building materials ......................................................................... 5

2.2 Material variability ..................................................................................................................... 6

2.2.1 Variance of sampling ........................................................................................................... 7

2.2.2 Normal distribution ............................................................................................................. 9

2.2.3 Control charts ...................................................................................................................... 9

2.2.4 Experimental error and uncertainty ................................................................................. 10

2.3 Nature of materials - Basic materials concepts ....................................................................... 11

2.3.1 Electron configuration ...................................................................................................... 12

2.3.2 Bonding ............................................................................................................................. 13

2.3.3 Material classification by bond type ................................................................................. 18


2.1 Sustainable design (1)

Sustainable development: is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs. The five basic principles of sustainable product design are:

1) Cyclic: Products are made from compostable organic materials or from minerals which are continuously recycled in a closed loop.

2) Solar: Products in manufacture and use consume only renewable energy that is cyclic and safe 3) Efficient: Products in manufacture and use require 90% less energy, materials and water than

equivalent products did in 1990 4) Safe: All releases to air, water, land or space are safe. 5) Social: Product manufacture and use supports basic human rights and natural justice

2.1.1 Phases of building materials

A material’s life cycle can be organized into three phases:

i. Pre-Building; ii. Building; and

iii. Post-Building.

These stages parallel the life cycle phases of the building itself. The evaluation of building materials’ environmental impact at each stage allows for a cost-benefit analysis over the lifetime of a building, rather than simply an accounting of initial construction costs.

Figure 1. Three phases of the building material life cycle (1)

2.1.1.1 Pre-Building phase The Pre-Building Phase describes the production and delivery process of a material up to, but not including, the point of installation.

1 Jong-Jin Kim, (1998). Sustainable Architecture Module: Qualities, Use, and Examples of Sustainable Building Materials. Available online at:http://www.umich.edu/~nppcpub/resources/compendia/ARCHpdfs/ARCHsbmIntro.pdf


• This phase has the most potential for causing environmental damage. • Understanding the environmental impacts in the pre-building phase will lead to the wise

selection of building materials through the design process. • Raw material procurement methods, the manufacturing process itself, and the distance from

the manufacturing location to the building site - all have environmental consequences. • The extraction of raw materials, whether from renewable or finite sources, is in itself a source

of severe ecological damage. • These materials exist in finite quantities, and are not considered renewable and each of these

processes produces a large amount of toxic waste. • A material is only considered a renewable or sustainable resource if it can be grown at a rate

that meets or exceeds the rate of human consumption. • The ecological damage related to the gathering of natural resources and their conversion into

building materials includes loss of wildlife habitat, erosion, and water and air pollution.

2.1.1.2 Building phase The building phase refers to a building material’s useful life.

• It begins at the point of the material’s assembly into a structure, includes the maintenance and repair of the material, and extends throughout the life of the material.

• Construction: - The material waste generated on a building construction site can be considerable. - The selection of building materials for reduced construction waste. - Waste that can be recycled is critical in this phase of the building life cycle.

• Use/Maintenance: - Long-term exposure to certain building materials may be hazardous to the health of a

building’s occupants.

2.1.1.3 Post-Building phase The post-building phase refers to the building materials when their usefulness in a building has expired.

• At this phase, old materials may be reused in its entirety, have its components recycled back into other products, or waste to be returned to nature.

• The sustainable design strategy focuses on reducing construction waste by recycling and reusing packaging and excess material.


2.1.2 Features of sustainable building materials (2)

Three groups of criteria are identified, based on the material life cycle, which can be used in evaluating the environmental sustainability of building materials. The presence of one or more of these features in building materials make it environmentally sustainable.

(i) In Pre-Building Phase: Manufacture

• Pollution prevention: measures taken during the manufacturing process can contribute significantly to environmental sustainability.

• Waste reduction: indicates that the manufacturer has taken steps to make the production process more efficient, by reducing the amount of scrap material that results. Reducing waste in the manufacturing process increases the resource efficiency of building materials.

• Recycled content: has been partially or entirely produced from post-industrial or post-consumer waste. The incorporation of waste materials from industrial processes or households into usable building products reduces the waste stream and the demand on virgin natural resources.

• Embodied energy of a material: refers to the total energy required to produce that material, including the collection of raw materials

• Natural Materials: are generally lower in embodied energy and toxicity than man-made materials. They require less processing and are less damaging to the environment.

(ii) In Building Phase: Use

• Minimal construction waste: during installation reduces the need for landfill space and also provides cost savings.

• Locally produced building materials: when used shortens transport distances, thus reducing air pollution produced by vehicles.

• Energy efficiency: is an important feature in making a building material environmentally sustainable. The ultimate goal in using energy- efficient materials is to reduce the amount of generated energy that must be brought to a building site. Depending on type, the energy-efficiency of building materials can be measured using factors such as R-value (building envelopes insulating value), shading coefficient, luminous efficiency, or fuel efficiency and system efficiency (Electrical and Mechanical systems).

• Water treatment/conservation: either increase the quality of water or reduce the amount of water used on a site. This involves reducing the amount of water that must be treated by municipal septic systems, with the accompanying chemical and energy costs.

• Non- or less-toxic materials: are less hazardous to construction workers and a building’s occupants.

2 Sahar Salah Badr, (2013). Building Materials and Techniques applied to achieve Sustainability. Available online at: https://www.academia.edu/8852821/Building_Materials_and_Techniques_applied_to_achieve_Sustainability


• Renewable energy systems: can be used to supplement or eliminate traditional heating,

cooling, and electrical systems through the utilization of this natural energy. • Longer life materials: designed for the same purpose need to be replaced less often. Durable

materials that require less frequent replacement.

(iii) In Post-Building Phase: Disposal

• Reusability: is a function of the age and durability of a material. • Recyclability: measures a material’s capacity to be used as a resource in the creation of new

products. • Biodegradability: of a material refers to its potential to naturally decompose when discarded.

2.2 Material variability (3)

It is essential to understand that engineering materials are inherently variable. For example,

• Steel properties vary depending on chemical composition and method of manufacture. • Concrete properties change depending on type and amount of cement, type of aggregate, air

content, slump, method of curing, etc. • The properties of asphalt concrete vary depending on the binder amount and type, aggregate

properties and gradation, amount of compaction, and age. • Wood properties vary depending on the tree species, method of cut, and moisture content. • Some materials are more homogeneous than others, depending on the nature of the material

and the method of manufacturing. For example, the variability of the yield strength of one type of steel is less than the variability of the compressive strength of one batch of concrete.

When materials are tested, the observed variability is the cumulative effect of three types of variance:

i. The inherent variability of the material [MATERIAL],

ii. Variance caused by the sampling method [SAMPLING], and

iii. Variance associated with the way the tests are conducted [TESTING].

The concepts of precision and accuracy are fundamental to the understanding of variability.

• Precision refers to the variability of repeat measurements under carefully controlled conditions. • Accuracy is the conformity of results to the true value or the absence of bias. • Bias is a tendency of an estimate to deviate in one direction from the true value. In other words, bias is

a systematic error between a test value and the true value. 3 Mamlouk and Zaniewski, (2011)..Materials for civil and construction engineers, third edition. Prentice Hall. ISBN-13: 978-0-13-611058-3


A simple analogy to the relationship between precision and accuracy is the target shown in Figure 2. When all shots are concentrated at one location away from the center, which indicates good precision and poor accuracy (biased) [Figure 2(a)]. When shots are scattered around the center, which indicates poor precision and good accuracy [Figure 2(b)]. Finally, good precision and good accuracy are obtained if all shots are concentrated close to the center [Figure 2(c)]

Figure 2. Exactness of measurements: (a) precise but not accurate, (b) accurate but not precise, and (c) precise and accurate.

2.2.1 Variance of sampling

Typically, samples are taken from a lot or population, since it is not practical or possible to test the entire lot. By testing sufficient samples, it is possible to estimate the properties of the entire lot. In order for the samples to be valid:

• They must be randomly selected. Random sampling requires that all elements of the population have an equal chance for selection.

• Another important concept in sampling is that the sample must be representative of the entire lot. For example, when sampling a stockpile of aggregate, it is important to collect samples from the top, middle, and bottom of the pile and to combine them, since different locations within the pile are likely to have different aggregate sizes.

• The sample size needed to quantify the characteristics of a population depends on the variability of the material properties and the confidence level required in the evaluation.


Figure 3. Sample from the population or lot.

Two commonly used statistical parameters describe the material properties are:

i. The mean: - The arithmetic mean is simply the average of test results of all specimens tested - It is a measure of the central tendency of the population

ii. The standard deviation: - The standard deviation is a measure of the dispersion or spread of the results.

iii. Coefficient of Variation: - A way to combine ‘mean’ and ‘standard deviation’ to give a more useful description of

the material variability.

Figure 4 Basic statistical parameters that describe the material properties.

It is important to understand that the Total Variability of a particular material is a sum of several definable variables. These are sampling, testing, production, and actual material variability. What is important is actual material variability. Variation of construction materials is inevitable and unavoidable. If you can assign the variability to a specific cause – such as segregation of the mix or a problem with a cold feed belt it should be fixed and eliminated.


2.2.2 Normal distribution

In statistical analysis procedures, the symmetrical grouping of data around the mean (or average) is defined as the normal distribution, shown in Figure 5. The normal probability distribution is completely described if the average (mean) and the variation of the data (standard deviation) are known. The normal distribution curve is bell-shaped with a single peak at the centre and tails out symmetrically on each end. There is not a single normal distribution curve, but a family of distributions with the same shape or mathematical form. Two terms are used to describe the normal distribution curve:

i. the mean or average and ii. the standard deviation.

Expressing the results in terms of mean and standard deviation, it is possible to determine the probabilities of an occurrence of an event. For example, the probability of occurrence of an event:

• between the mean and ±1 standard deviation is [34.1 + 34.1] 68.3% • between the mean and ±2 standard deviations is [34.1 + 13.6 + 34.1 + 13,6] 95.5%, and • between the mean and ±3 standard deviations is [2*34.1 + 2*13.6 + 2*2.2] 99.7%.

If a materials engineer tests 20 specimens of concrete and determines the mean (average) as 22 MPa and the standard deviation as 3 MPa, the statistics will show that 95.5% (i.e. 2σ) of the time the true mean of the population will be in the range of 22 ± (2x3) or 16 to 28 MPa.

Figure 5. A normal distribution.

2.2.3 Control charts

• A control chart (also called process chart or quality control chart) is a graph that shows whether a sample of data falls within the common or normal range of variation, shown in Figure 6.


• A control chart has upper and lower control limits that separate common from assignable

causes of variation. • The common range of variation is defined by the use of control chart limits. We say that a

process is out of control when a plot of data reveals that one or more samples fall outside the control limits.

Control charts have many benefits, such as

• detect trouble early • decrease variability • establish process capability • reduce price adjustment cost • decrease inspection frequency • provide a basis for altering specification limits • provide a permanent record of quality • provide basis for acceptance • instil quality awareness

Figure 6. Statistical control charts.

2.2.4 Experimental error and uncertainty

No physical quantity can be measured with perfect certainty; there are always errors in any measurement. This means that if we measure some quantity and, then, repeat the measurement, we will almost certainly measure a different value the second time. How, then, can we know the true value of a physical quantity? The short answer is that we cannot. However, as we take greater care in our measurements and apply ever more refined experimental methods, we can reduce the errors and, thereby, gain greater confidence that our measurements approximate ever more closely the true value.


Error analysis is the study of uncertainties in physical measurements, and to learn some basic principles of error analysis, we can:

• Understand how to measure experimental error, • Understand the types and sources of experimental errors, • Clearly and correctly report measurements and the uncertainties in those measurements, and • Design experimental methods and techniques and improve our measurement skills to reduce

experimental errors.

For example, Figure 7 shows a stress–strain curve in which a toe region (AC) that does not represent a property of the material exists. This toe region is an artefact caused by taking up slack and alignment or seating of the specimen.

In order to obtain correct values of such parameters as modulus, strain, and offset yield point, this artefact must be compensated for in order to give the corrected zero point on the strain axis. This is accomplished by extending the linear portion of the curve backward until it meets the strain axis at point B. In this case, point B is the corrected zero strain point from which all strains must be measured. In the case of a material that does not exhibit any linear region, a similar correction can be made by constructing a tangent to the maximum slope at the inflection point and extending it until it meets the strain axis.

Figure 7. Correction of toe region in stress–strain curve

2.3 Nature of materials - Basic materials concepts

To a large extent, the behaviour of materials is dictated by (i) the structure and (ii) bonding of the atoms that are the building blocks for all matter. Knowledge of the bonding and structure of materials at the molecular level allows us to understand their behaviour.

• Atoms are the basic building blocks of all materials. Atoms consist of three subatomic particles:

I. Protons at the centre of the atom, positively charged, and with mas II. Neutrons at the centre of the atom, no charge, but with almost equal mass to the

proton III. Electrons - electrons travel about the nucleus in paths or shells, have discrete

energy states, tend to occupy the lowest available state, negatively charged, and negligible mas.

• The atomic number is the number of protons in the nucleus of the atom. • The atomic mass of an atom is the number of protons plus the number of neutrons in the

centre of the atom. • An element is an atom or group of atoms with the same atomic number.


• Isotopes are elements with different numbers of neutrons in the nucleus.

2.3.1 Electron configuration (4)

The electron configuration of an atom is the representation of the arrangement of electrons distributed among the orbital shells and subshells. Many of the physical and chemical properties of elements can be correlated to their unique electron configurations.

• According to the Niels Bohr Model, electrons (e-) can only orbit the nucleus in specific, allowed

pathways. • They move toward and away from the nucleus by “steps” or discrete amounts of energy (a

quantum) that are released or absorbed. • Electrons farther from the nucleus have more energy. • Electrons e- closer to the nucleus have less energy.

The electrons are located in rings or what are called energy levels. The energy levels are called: 1st energy level, 2nd energy level, 3rd energy level and so forth. Each energy level can contain only a certain number of electrons. Electrons always try to fill the lowest energy location first. Figure 8 shows different energy levels as follow:

• Ground state level: the lowest energy of an atom • Excited state level: higher potential energy state • Energy absorbed e- moves to higher state • Energy emitted e- moves to lower state

Figure 8. Energy levels in an atom.

4 http://chemwiki.ucdavis.edu/Core/Inorganic_Chemistry/Electronic_Structure_of_Atoms_and_Molecules/


2.3.2 Bonding

Atoms tend to arrange themselves in the most stable patterns possible, which means that they have a tendency to complete or fill their outermost electron orbits. They join with other atoms to do just that. The force that holds atoms together in collections known as molecules is referred to as a chemical bond.

As two atoms are brought together, both attractive and repulsive forces develop. The effects of these forces are additive, as shown in Figure 9, such that:

• once the atoms are close enough to interact, they will reach a point at which the attractive and repulsive forces are balanced and an equilibrium is reached.

• Energy is required either to bring the atoms closer together (compression) or to separate them (tension).

• The distance at which the net force is zero corresponds to the minimum energy level, and is called the equilibrium spacing.

• The minimum energy is represented by a negative sign. The largest negative value is defined as the bonding energy.

Figure 9. (a) Attractive and repulsive forces, and (b) attractive and repulsive energies between atoms.

There are two basic categories of bonds (5), shown in Figure 10:

i. Primary bonds, which form when atoms interact to change the number of electrons in their outer shells so as to achieve a stable and nonreactive electron structure similar to that of a noble gas. Three types of primary bonds are defined:

1. ionic bonds—transfer of electrons from one elemental atom to another

5 P. Eyland, (2015). Physics for Civil Engineering. Available online at: http://www.insula.com.au/physics/1279/index.html


2. covalent bonds—sharing of electrons between specific atoms 3. metallic bonds—mass sharing of electrons among several atoms

ii. Secondary bonds, which are formed when the physical arrangement of the atoms in the molecule results in an imbalanced electric charge; one side is positive and the other is negative. Secondary bonds are much weaker than primary bonds, but they are important in the formation of links between polymer materials. Two types of secondary bonds are defined:

1. van der Waal’s bond: the attraction of intermolecular forces between molecules 2. Hydrogen bond: is a weak type of force that forms a special type of dipole-dipole

attraction which occurs when a hydrogen atom bonded to a strongly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons.

Figure 10. The classification of chemical bonds.

2.3.2.1 Primary (strong) bonds Ionic bonding (6)

An ionic bond is formed when valence electrons are transferred from one atom to the other to complete the outer electron shell. Ionic bonding occurs between metal atoms and non-metal atoms.

• Metals usually have 1, 2, or 3 electrons in their outermost shell. • Non-metals have 5, 6, or 7 electrons in their outer shell. • Atoms with outer shells that are only partially filled are unstable. • To become stable, the metal atom wants to get rid of one or more electrons in its outer shell. • Losing electrons will either result in an empty outer shell or get it closer to having an empty

outer shell. • It would like to have an empty outer shell because the next lower energy shell is a stable shell

with eight electrons.

6 https://depts.washington.edu/matseed/ces_guide/bonding.htm


Example of a typical ionically bonded material is NaCl (Salt), shown in Figure 11. The sodium (Na) atom gives up its valence electron to complete the outer shell of the chlorine (Cl) atom. Ionic materials are generally very brittle, and strong forces exist between the two ions.

Figure 11. Example of typical ionically bonded material - NaCl (Salt).

Generally, solid materials with ionic bonds are (7):

• Hard because particles cannot easily slide past one another. • Good insulators because there are no free electrons or ions (unless dissolved or melted). • Transparent because their electrons are not moving from atom to atom and less likely to

interact with light photons. • Brittle and tend to cleave rather than deform because bonds are strong. • Have high melting point because ionic bonds are relatively strong.

Covalent Bonding (6)

A covalent bond is formed when the valence electrons from one atom are shared between two or more particular atoms.

Example: Many compounds have covalent bonding, such as polymers. Nylon rope is an example of a material that is made up of polymers. Polymer structures typically are long chains of covalently bonded carbon and hydrogen atoms in various arrangements.

Figure 12. Example of typical covalently bonded material - Nylon rope.

Some common features of materials with covalent bonds are (7):

• Low enthalpies of fusion and vaporization • Good insulators

7 https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Structure/ionic.htm


• Solids can be soft or brittle • If brittle often transparent and cleave rather than deform Good electrical and thermal

conductors due to their free valence electrons

Metallic bonding

A metallic bond is formed when the valence electrons are not associated with a particular atom or ion, but exist as a "cloud" of electrons around the ion centres. Metallic materials have good electrical and thermal conductivity when compared to materials with covalent or ionic bonding. A metal such as iron has metallic bonding.

In the real and imperfect world, most materials do not have pure metallic, pure covalent, or pure ionic bonding; they may have other types of bonding as well. For example, iron has predominantly metallic bonding, but some covalent bonding also occurs.

Figure 13. Example of typical metallic bonded material.

Some common features of materials with metallic bonds:

• Good electrical and thermal conductors due to their free valence electrons • Opaque • Relatively ductile

2.3.2.2 Secondary (weak) bonds Van der Waals bonds

Van der Waals force is the sum of the attractive or repulsive forces between molecules. The van der Waal bonds occur to some extent in all materials but are particularly important in plastics and polymers. The main characteristics of Van der Waals bonds are:

• Weaker than normal ionic, covalent, or metallic bonds. • Additive and cannot be saturated. • Having no directional characteristic. • Short - range forces and hence only interactions between nearest need to be considered

instead of all the particles. The greater is the attraction if the molecules are closer due to Van der Waals forces.


• Independent of temperature except dipole - dipole interactions.

There are three types of Van der Waals forces, shown in Figure 15:

1. force between two permanent dipoles (Keesom force) (A dipole simply refers to the separation of charges within a molecule)

2. force between a permanent dipole and a corresponding induced dipole (Debye Force) 3. force between two instantaneously induced dipoles (London dispersion force)

(1)

(2)

(3)

Figure 14. Types of Van der Waals forces (8).

Hydrogen Bonding

Hydrogen bonding is the attraction between a hydrogen atoms of a molecule to an unshared pair of electrons in another molecule. Hydrogen bonding occurs in molecules where hydrogen is covalently bonded to a very electronegative element. Hydrogen bonding occurs in molecules containing N, O, F. Hydrogen bonds are responsible for the physical properties of many biological substances and, more importantly, water.

Figure 15. Secondary bond: Hydrogen Bridge (8).

8 http://www.buzzle.com/articles/explanation-of-intermolecular-forces-with-examples.html


2.3.3 Material classification by bond type

Based on the predominant type of bond a material’s atoms may form, materials are generally classified as:

• Metals : (formed by metallic bonds) generally have a crystalline structure, a repeated pattern or arrangement of the atoms

• Organic solids: usually have a random molecular structure. Long chains having molecules of C, H, O, N which are formed by covalent bonding. The chains are bound to each other either by covalent bonds or Van der Waals forces.

• Inorganic solids: Inorganic solids include all materials composed of non-metallic elements or a combination of metallic and non-metallic elements.

• Ceramics: Ceramic materials are mainly aluminosilicates formed by a combination of ionic and covalent bonds.

Figure 16. Classification of the predominant materials used in civil engineering by bond type.

lecture 2. sustainable design, material variability, and ... · 3) efficient: products in...

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