Building MaterialsBuilding MaterialsBuilding MaterialsBuilding Materials

Lecture 4

M h i l tiM h i l tiMechanical propertiesMechanical properties --continuationcontinuationcontinuationcontinuation

Abrasion resistanceAbrasion resistance• ability of a surface to resist being worn away y g y

by rubbing or friction• coatings paints floor surfaces pipescoatings, paints, floor surfaces, pipes

Abrasion resistance testsAbrasion resistance tests

• usually measured as a loss percentage based on original weight g g

Taber abraderTaber abrader• thickness loss after definedthickness loss after defined

number of rotations using standardized wheel andstandardized wheel and defined load

Amsler/Böhm testAmsler/Böhm testi i bj t d• a specimen is subjected

to stress by grinding • the abrasive grit

accumulating from this is indicated as loss of volume or thickness (abrasive loss) per test area 50 cm2

7,07 x 7,07 cm

Abrasion resistance (Amsler / Böhm)

• EN 1338, 1339, 1340 – concrete pavings• EN 14157 – natural stones• EN 13 892-3 – screeds

Adh i d h iAdhesion and cohesion

• adhesion – state in which two surfaces are held together by interfacial effectsinterfacial effects

• cohesion – ability of a material to i t i it t th h fi dmaintain its strength when unconfined

adhesion < cohesion

AdhesionAdhesion• between two materials - in compositesbetween two materials in composites

(steel + concrete, cement + aggregates )aggregates…)

Adhesive strengthAdhesive strength• between the upper layer and basebetween the upper layer and base

(plasters, coatings..)

Pull-off testPull-off test

• the circular pull-head plates are glued to the test material and upper layer is pp ycut around them

FPULL-HEADCUT

F

TESTED LAYER

GLUE

SUBSTRATE

TESTED LAYER

SUBSTRATE

Pull-off test equipmentPull-off test equipment Adhesive strength fAdhesive strength fa

F• test results: AFf u

u

f f f ffa fu fa fu

fa = fu

Moisture Moisture (hygric)(hygric) propertiesproperties( yg )( yg ) p pp p

DefinitionsDefinitions

• Moisture content - amount of watercontained in a material

• Dampness - presence of unwanted moisture in the structure of a buildingmoisture in the structure of a building,

• Humidity - amount of water vapor in the air

• Hygric - relating to moisture• Hygric - relating to moisture

Moisture contentMoisture content

• amount of water contained in a material, which can be removed bymaterial, which can be removed by drying

• any porous i l i hmaterial in the

construction is not quite dry !

Moisture typesMoisture types• production (wet• production (wet

manufacturing process)groundwater intrusion• groundwater intrusion

• rainwater leaks• diffusion through walls,

roofs, and floors • indoor moisture

(breathing, perspiration, (b ea g, pe sp a o ,cooking, bathing, and washing )g )

Water-vapor productionWater-vapor production

••

human metabolism (based on activity

50 - 250 g of water vapor/h• vapor/h

bathrooms 700 - 2600 g

•kitchens 600 -1500 g

f tlaundry drying 200 - 500 g of water vapor/h/5 kg

Moisture typesMoisture typesA di iAccording time:• initial moisture (natural, manufacturing)initial moisture (natural, manufacturing)• storage moisture• stabilized moisture (constant - after

longer period – ca 2 - 7 years)

Moisture content during time period Gravimetric water contentGravimetric water content

)(*mmmw DWOH 1002

)(mm

wDD

m 100

mD mass of dry materialmD …. mass of dry materialmW …. mass of wet materialmH2O …. mass of water in material

Volumetric water contentVolumetric water content

)(*mmVw DWOH 1002

)(V*V

wOH

V 1002

mD ..... mass of dry materialD ymW ..... mass of wet materialV l f t i t i lVH2O … volume of water in materialV ....... volume of materialV ....... volume of material

SorptivitySorptivity

• amount of water taken in by a material when immersed

• maximum amount of water, which can be in the materialcan be in the material

• volumetric sorptivity: 0 - 100 %• gravimetric sorptivity: can be higher than• gravimetric sorptivity: can be higher than

100 %

Sorptivity of materialsSorptivity of materials350

300300

350y

[%]

gravimetric sorptivity

200

250

sorp

tivity gravimetric sorptivity

volumetric sorptivity

150

100

150

80

2297

6040 45

2050

100

9 07 00

CapillarityCapillarity• ability of a liquid to flow in narrow ab y o a qu d o o a o

spaces without the assistance of, and in opposition to external forces like gravityopposition to external forces like gravity

Capillarity in practiceCapillarity in practice•

CapillarityCapillarity

MaterialBulk density in dry state

Gravimetric capillarity [kg/m3]aftery

[kg/m3] 2 hours 8 hours 24 hours

Foamed 16 1 1 1 2 1 2polystyrene 16 1,1 1,2 1,2Foamed polyurethane 35 0,3 0,4 0,4polyurethane , , ,

AAC 540 12,7 19,9 29,7

Sorption behaviorSorption behavior• ability of a hygroscopic material toability of a hygroscopic material to

absorb or release water vapor from or into the air until a state of equilibriuminto the air until a state of equilibriumis reached

adsorption(uptake of water vapor)( p p )

x desorptiondesorption

(water vapor release)

Equilibrium moisturecontent

Depends on:• air temperature pressure and humidityair temperature, pressure and humidity • pores sizes and shapes

Sorption hysteresisSorption hysteresis Sorption hysteresisp y

Sorption hysteresisSorption hysteresis Water permeabilityWater permeability

Water permeabilityWater permeability

• roofing (ceramic and concrete tiles))• depends on the amount of capillary pores p p y p

and cracks (size 0,01 – 0,5 mm)

Roof tiles are always permeable– space under roof has to be ventilated !p

Permeability testing• measuring the time taken for a drop of water

Permeability testing• measuring the time taken for a drop of water

to appear on the underside of the roofing tile when a 6 cm thick water head is applied onwhen a 6 cm thick water head is applied on the opposite side

• measuring the volume of water that passes through a saturated roofing tile under a 10through a saturated roofing tile under a 10 cm thick water head

Diffusion propertiesDiffusion propertiesDiffusion propertiesDiffusion properties

DiffusionDiffusion• gases, vaporg , p• spread of particles through random motion

from regions of higher concentration to g gregions of lower concentration

• Important for: – vapor barriersp– radon barriers– rehabilitation renders– paints– passive houses

Water vapor transportWater vapor transport

Important properties:• the water vapor diffusion coefficient δthe water vapor diffusion coefficient δ• the resistance to water vapor diffusion

f tfactor μ• the water vapor diffusion equivalent air t e ate apo d us o equ a e t a

layer thickness Sd

Water vapor diffusion -- coefficient δ

• the amount of water vapor [kg] which diffuses through a layer of material which is 1 m thick and has an area of 1 m² at a partial water vapor pressure difference of 1 Pa in 1 hour

• units: [kg/m.h.Pa]units: [kg/m.h.Pa]

Resistance to watervapor diffusion - factor μ

• the ratio of the water vapor diffusion coefficient of the air δL to the value δmat of the building material

a measure for the vapor• a measure for the vapor tightness of a material (h ti t th(how many times greater the resistance to transmission of a layer of building material isa layer of building material is compared to a static layer of air of the same thickness)

Equivalent air layer thickness Sd

Sd = μ · s [m] d μ [ ]• the thickness of a static layer of air in meters,

which displays the same resistance to waterwhich displays the same resistance to water vapor transmission as the building material in the thickness s with the resistance to waterthe thickness s with the resistance to water vapor transmission value μ

• Sd ≤ 0.5 m => diffusion-open materials

• 0.5 m < Sd => diffusion-blocking materials

• Sd ≥ 1500 m => diffusion-proof materials

Diffusion of coatingsDiffusion of coatings Künzel’s facade protection theory:Künzel s facade protection theory:• protection and breathability of coating are influenced by water absorptionare influenced by water absorption capacity w (sorptivity) and the water vapor permeability Spermeability Sd

Soil permeabilitybili f il i d i• ability of soil to transmit water and air

• important in the areas with radon riskimportant in the areas with radon risk

Thermal propertiesThermal propertiesThermal propertiesThermal properties

Interaction heat - materialInteraction heat - material

• If the surroundings of the material has different temperature than the pmaterial, the thermal energy is transferredtransferred

1. The properties of material influence the transmission of heatthe transmission of heat

2. Thermal energy influences the ti f t i lproperties of material

Heat transportHeat transport• conduction – solid materials

– the transfer of heat within a substance, molecule by molecule

• convection - gases, liquids – heat transfer by the mass movement of a fluid in– heat transfer by the mass movement of a fluid in

the vertical direction

• radiation gases• radiation – gases– heat is transfered

through wavethrough wave energy

Heat transportHeat transport

Depends on:

• porosity• porosity• structure• temperature• material typematerial type

I th t i l th h t i• In the porous materials the heat is transferred by combination of all types f h t t tof heat transport

Thermal conductivityThermal conductivity

• a material's ability to conduct heat

λcoefficient of thermal conductivityλ• coefficient of thermal conductivity

Coefficient of thermal conductivity

• or k-value• or k-value• the quantity of heat transmitted, due to

unit temperature gradient in unit timeunit temperature gradient, in unit time under steady conditions in a direction normal to a surfacenormal to a surface

•units SI: [ W/m.K]imperial units: [Btu/hr.ft.F] (1 Btu/hr.ft.F = 1.730735 W/m·K)

•the lower λ, the better insulator (thermal insulating materials λ < 0,15 W/m.K)•range λ : 10-2 - 102 W/m.K

Material λ [W.m-1.K-1]• Copper ……………………..... ~370• Aluminium …………………... ~200• Carbon steel ………………… ~50• Concrete ~1 4Concrete …………………..... 1,4• Glass …………………………. ~0,75• Brick ~0 7• Brick …………………….. ~0,7• Water (20° C, quiet)………... ~0,60

W d 0 15• Wood ………..…………......... ~0,15• Mineral fibers ….……………. ~0,05 m

altio

ns

• Polystyrene foamed …….. ~0,035• Air (dry, quiet) ……….……. 0,025 th

erm

insu

la

• Argon (quiet) …………….... ~0,015

Thermal conductivity - comparisonThermal conductivity comparison Thermal conductivityO i t i l b tt

Thermal conductivity• Organic materials are better

insulators than anorganic m.Cr stalline mat are better• Crystalline mat. are better conductors than amorphous m.Mat with lower bulk density are• Mat. with lower bulk density are usually better insulators.Metals are very good• Metals are very good conductors.Anisotropic mat have different• Anisotropic mat. have different conductivity in different directionsdirections.

Coefficient of thermal conductivity

Depends on:• chemical composition• structure• structure • porosity (bulk density)p y ( y)• moisture• temperature

Porosity influencePorosity influence

• AIR = 0,025 W/m.K

• the higher the amount of air in the material (porosity), the lower bulk (p y),density and thermal conductivity is

• size of pores is limited (best 0,1 – 1 mm)

Moisture influenceMoisture influence app 25 x higher than water app. 25 x higher than air

i t i ifi tl d th th l• moisture significantly reduces the thermal insulating ability of materials

• very small pores are liable to wetting (capillarity) – the best size of pores in ( p y) pinsulating materials: 0,1 – 1 mm

Temperature influenceTemperature influence• increases with rising temperature increases with rising temperature

t0025,00t (for t = 0-100C)

Thermal insulating materialsThermal insulating materials• fibrous - mineral and glass fibersfibrous mineral and glass fibers

- wood wool (excelsior) cellulose fibers- cellulose fibers

- recycled paper fiberst (b l l )- straw (bales, loose)

• porous particles- expanded clay aggregate e pa ded c ay agg egate- expanded perlite- ash- cinders

Thermal insulating materials

shaped li ht i ht t ( ith

Thermal insulating materials

• shaped - lightweight concretes (with lightweight aggregates,

i t d t )pervious c., aerated concretes)- insulating brick blocks- diatomite

• foamed - foamed polymers (PU,PS, h li f )phenolic foam)

- cellular glass

Thermal insulating materialsThermal insulating materials

• other - cork (expanded)- wood- wood-based materials (fiber board particle board)(fiber board, particle board)- lamb wool

Best insulation?Best insulation?

• vacuum• „VIP“ = Vacuum Insulated Panel„VIP Vacuum Insulated Panel• a nearly gas-tight enclosure surrounding a

rigid core from which the air has beenrigid core, from which the air has been evacuated

0 007 W/ K• = 0.007 W/m·K

Thermal conductivity ymeasuring

• steady-state methods - the temperature of the measured material does not change with timewith time

• transient (non steady-state) methods -( y )a measurement during the process of heating up

Steady state - a situation in which all variables are constant in spite of ongoing

th t t i t h th Fprocesses that strive to change them. For an entire system to be at steady state, i.e. for all state variables of a system to be constantstate variables of a system to be constant, there must be a flow through the system

Thermal conductivity ymeasuring

Steady-state methods:• Guarded hot plate• Guarded hot plate• Divided bar

Hot box• Hot box

Transient methods:• Hot wire• Plane source• Needle probeNeedle probe• Laser flash method

Thermal conductivity imeasuring

Thermal conductivity determination

• Steady state method:

dq Q T-Td q

21

AQq

T T 21 Aq….. of heat passing through a unit area of the

sample in unit time [W/m2]sample in unit time [W/m ]d …. average thickness of sample [m]T1 .... temperature of warm side of the sample [K]1 p p [ ]T2 … temperature of cold side of the sample [K]Q .... quantity of heat passing through a base area of y g g

the sample [W]A ..... base area of the sample [m2]

Guarded hot plateGuarded hot plate• placing a solid sample of fixed dimension

between two temperature-controlled plates • one plate is heated while the other plate is

cooled, and their temperatures are monitored until they are constant

Thermal resistanceR-value

• directly proportional to the thickness ofR = d / [(m2 .K) / W]

directly proportional to the thickness of the materialf i i l• for construction, not material

• can be used for masonry blockscan be used for masonry blocks

R = 0 65 (m2 K)/W

• the reciprocal of R-value is thermal

R = 0,65 (m2.K)/W

the reciprocal of R value is thermal conductance [W/m2.K]

Thermal resistance• multi-layered construction : the R-

Thermal resistancemulti layered construction : the Rvalues of the individual layers are addedadded

Rtotal = Routside air film + Rrender + Rinsulationtotal outside air film render insulation+ Rbrick + Rplaster + Rinside air film

Thermal transmittanceU-value

• the measure of the rate of heat loss through a materialthrough a material

• incorporates the thermal conductance of a structure along with heat transfer due tostructure along with heat transfer due to convection and radiation

U-value = 1/R[ W / m2 .K ]

U-value in EuropeU-value in Europe Heat lossesHeat losses