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Samenvatting 7LY6M0 Materials panorama (7LY6M0)
Summary / Complete overview of the content of the lectures. Information is detailed and includes pictures for better understanding.
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Door: jcmvheeswijk • 1 jaar geleden
Voorbeeld van de inhoud
7LY6M0 – Materials PanoramaLecture 1 – Mineral resources for building materials
. Raw material: a basic, unprocessed material from which a product is made
. Inorganic raw material: the opposite of organic, not derived from living matter
. Virgin raw materials: not recycled, previously unused
Raw materials are the basis for everything we build and determine the properties of the resulting
building materials. Humans require massive quantities and extracted them from the earth’s crust.
Content earth’s crust: Oxygen O 46.4% Calcium Ca 4.15%
Silicon Si 28.2% Sodium Na 2.36%
Aluminum Al 8.3% Magnesium Ma 2.33%
Iron Fe 5.63% Potassium K 2.09%
These materials together with Carbon C, Sulphur S and Phosphor P form the basis for all inorganic
building materials. Building with natural building materials has been done a long time. From oldest to
youngest:
Mudbrick (7500 BCE) – Natural stone (4800 BCE)– Fired brick (4400 BCE, industrially 19th century) –
Gypsum/Lime (2500 BCE, boards/dry wall in 1916 CE) – Concrete (300 BCE, reinforced 1849 CE) – Glass
(2000 BCE, in buildings 100 CE) – Steel (1800 BCE, modern steel 1855 CE) – Aluminum (1825 CE)
Mudbrick – Natural stone – Fired brick – Gypsum/Lime – Concrete – Glass – Steel – Aluminium
Mudbrick is not used anymore; the other materials are all still used. Natural stone is the only element
that was used early in the history and is still used nowadays. Concrete is used in the highest quantities:
16 billion tons a year and responsible for 4-7% of global CO2 emissions.
Concrete Water (1) – Cement (2) – Sand/Gravel (10)
Cement = Clinker (95%) + Gypsum (5%) Heated to 1500 °C
Clinker = mostly Limestone + Clay
i. Limestone (CaCO3) is the source for most of the CO2 emissions, since CaCO3 converts to CaO + CO2.
Even with 100% green energy, pollution cannot be avoided.
ii. The sand used in concrete should be rough and angular. Sand in deserts or on beaches are too
smooth or not angular enough (respectively), therefore presenting unsuitable options and a sand
scarcity. Removal of sand from rivers or beaches has disastrous effects on the environment.
Steel Blast furnace: Iron ore + Coke = pig iron
Heated to 1500 °C
Pig iron + limestone/dolomite = steel
i. In the production of pig iron (2 FeO + C = 2Fe + CO2), a lot of CO2 is produced. A potential solution
would be to execute the steel reaction with Hydrogen: 2FeO + H2 = 2Fe + H2O. The question is how
to produce and store extremely large amounts of hydrogen.
ii. Mountains are crushed and harvested, damaging the environmental aestatics and polluting the
rivers and nature surrounding it. Again, this has disastrous effects on the environment.
Brick Mix of water with raw materials: Sand (50-60%), Clay (20-30%) Lime (5%) and Fe2O3
(5%), fired at 1000 °C.
, Gypsum Gypsum (CaSO4 x H2O) is a very soft material which used to be mined but is also a side
product in many industrial processes.
Free Lime Free lime is a very soft sediment: burned limestone/calcite (CaCO3) into CaO. In this
process CO2 comes free.
Glass Glass consists in many different types of glass with different compositions and
applications. 90% of glass is Soda-Lime glass (SiO2), which melts at 1700 °C.
Na2O/Na2CO3 lowers this temperature to 500-600 °C. This process is: 2 NaCl + CaCO3 =
Na2CO3 + CaCl2.
Aluminium Aluminium is produced in two steps:
I. Bayer process: Bauxite is converted into C using caustic soda (NaOH2). The residue is red mud, which
is highly alkaline and damages the environment.
II. Hall-Heroult process: Al(OH)2 is melted into metallic Al, which requires CaF and Cryolite Na3AlF6,
which is industrially produced. This step is very energy intensive.
Most important inorganic raw materials in the build environment: Calcite (CaO), Sand/Gravel
(SiO2/Al2O3/CaO/Na2O/K2O), Clay (Al2O3/SiO2), Gypsum (CaO/SO4), Bauxite (Al2O3), Iron Ore (Fe2O3),
Coal/Coke (C).
Problems concerning the harvest of these inorganic raw materials can be found in (I) The availability
(geology, engineering and economics), (II) Environmental problems and (III) Social problems.
I. The reserves of a material should be economically and geologically feasible. In Figure 1 an overview
can be seen with different aspects that influence the reserves of a material. To explain: exploration
efforts increase the degree of geological assurance and an increase in prices or technological
improvement can increase the degree of economic feasibility.
II. Environmental impacts as a result of material mining and production are: CO2 emissions/global
warming, pollution of ground water, destruction of habitats, dust, acid mine drainage (for coal and
metals) and mine tailings (material left over after the extraction of ore from its host material).
III. Social impacts relate to the question: Who bears the costs? (e.g. of these environmental damages)
Solutions can be found in a circular economy, where material reuse is maximised, and new material
production is minimised. This, however, can also pose some challenges.
Figure 1: Overview of economical and geological feasibility of material
,Lecture 2 – Bio-based materials
Definition of Bio-based materials
. Bio-degradable: Fast degradation of a product by the means of bacteria in the nature,
converting it in simple molecules
. Bio-compatible: Also known as tissue compatibility: Ability of a material to be used in a living
system without being toxic nor physiologically reactive
. Bio-sourced: Material partially or entirely made from a biological origin/biomass (e.g. plants).
Also called bio-based.
There are many sources of bio-based materials. Cellulosic materials differ in shape and size: from macro
(timber logs) to micro (wood flakes) to nano scale (cellulose).
Natural fibers (NF) properties
A natural fiber is a cellulose fiber reinforced material with 4 main constituents: Cellulose, Hemicellulose,
Pectin and Lignin. Examples are: coir, water hyacinth, bagasse, oils palm and hemp.
Cellulose provides the strength
Hemicellulose acts as a binder between cellulose fibers
Pectin is no constituent of natural fibre
Lignin acts as an outer layer, as a matrix
Natural fiber is highly heterogeneous (diverse), has a high number of defects and porosity and has a
cross-section which is difficult to measure. NF is much lighter than synthetic fibres (E-glass), but has a
comparable (≈) specific modulus/strength as E-glass. Important to not is the uncertainty about the
mechanical properties of NF, because the production process differs due to wheatear differences.
NF is extremely flammable, has a high water uptake, risk of swelling and leaching of composite. The
direction of the cellulose influences the strength. This is called crystallinity; a lower angle is better (e.g.
Hempflax). A high cellulose content can be related to high mechanical properties.
Hydrothermal behaviour of bio-based materials – Alex Koh
a. Hygrothermal properties - Intro
High moisture contents in bio-based materials may reduce the thermal
resistance (λwater 0.6 > λair = 0.025 mK), result in growth of microorganism
(e.g. mould and bacteria), cause salt crystallization (due to water transport
and deposit salts in building element), destroy the cellular structure (or induces oxidation of other
building elements within them) and result in mechanical stresses (due to unaccounted expansion).
Replacing air with water increases the thermal conductivity. When adding water to bio-based materials,
the first 20-25% of water goes inside the ‘wall’, not effecting the thermal conductivity. Only when the
water absorption surpasses 25% air will be replaced by water and the thermal conductivity will go down.
Hygroscopic is the ability of a substance to attract and hold water molecules from the surrounding
environment. Two specific types of sorption contribute to hygroscopic damping: (1) absorption
(incorporation of vapour into material) and (2) adsorption (bonding of vapour onto surface of material).
Desorption is the release of vapour from or through surface of material. For building material in general,
their moisture content is regulated through adsorption and desorption mechanism.
b. Hygrothermal properties
The amount of adsorbed water is related to the RH of air (see image). This relationship can be
established using sorption isotherm (moisture storage function), i.e. mass concentration of water u
, [kg/m3] plotted against relative humidity RH [%] at a fixed temperature. Once sorption isotherm of
material is constructed, by measuring RH of air, we can approximate moisture content of building
material (non-destructive). Specimens can reach equilibrium by conditioning the RH.
Water vapour diffusion is movement of water molecules from region of high vapour pressure to low
vapour pressure. The process is governed by Fick’s first law, and expressed in water vapour diffusion
coefficient D [m2/s]. D (water vapour diffusion) is material dependent.
ꞏ Water vapour resistance factor µ [-]: ratio of D over stagnant air Dair
ꞏ Water vapour permeability δ [kg/m·s·Pa]: ability of material to let vapour through due to difference
in water vapour pressure, where δ= δair/µ
ꞏ Water vapour diffusion-equivalent air layer thickness Sd [m], Sd= µ·d
High µ material (e.g. moisture barrier) is used to protect building material (e.g. bio based) from
moisture, however it can also accumulate moisture at interface. Selection of material µ is depending
on built environment & design. Water vapour transmission properties can be tested using desiccant
method (dry cup) or water method (wet cup). The vapour diffusion is moisture dependent, i.e. apparent
vapour resistance falls with increasing RH.
Thermal conductivity λ [W/m·K] of a material is affected by its moisture content u and temperature.
Typically, the λ of building products is declared as λ23,50 (equilibrium with air at 23°C and 50% RH) or λdry
(dried at 23°C). The built environment is neither dry nor at constant RH. It is recommended to measure
λ using steady state method, i.e. guarded hot plate, heat flow meter or calibrated/guarded hot box.
Specimen should be conditioned as per standards / industrial requirement, or specific test conditions
(e.g. RH & temperature) for characteristic investigation.
Thermal diffusivity α [m2/s] is the ratio of thermal conductivity λ, density ρ and specific heat capacity
cp, i.e. α=λ/ρ·cp. This parameter is used to describe dynamic heat transfer. In steady state heat transfer,
both in and out heat flow rate are equal. Under dynamic heat transfer, both inflow and outflow differ.
Materials with a larger volumetric heat capacity (ρ·cp) will have smaller temperature changes for the
same heat flow rate.
Other parameters affecting the hygrothermal performance of a material: specific heat capacity cp at
constant pressure [J/kg·K], porosity [m3/m3] and bulk density [kg/m3], Built-in moisture [kg/m3], layer
thickness [m], finishing / interfaced building components (plaster/coating, bricks, concrete, timber,
fibreboards, etc.), orientation & inclination of construction, outdoor RH, temperature, driving rain and
indoor RH & temperature.
c. Hygrothermal performance
If characteristics of individual materials are available, instead of mock-up testing (under controlled
environment) or field testing (under actual environment), their hygrothermal performance can be
simulated using validated software, under different assembly designs and environmental conditions.
The typical procedures as following: (1) define material properties, (2) define assembly design, (3)
define climates and locations and (4) define building model (if to investigate energy demand). Moisture
content profiles across building assembly can be simulated, and therefore predict their transient
thermal transmittance and even mould growth potential.
d. Stalk fibres
Straw is the left-over stalk of cereal plants after grain has been harvested. Straw is currently used for
animal food, bedding of livestock or biomass (burning). It might be more beneficial to use straw as
building material to store CO2. After usage in the building it can be replaced or disposed (composted).
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