Slide 1 of 47 Fahim Al-Neshawy (2014) Sensors and systems for non-destructive testing of facade...

Slide 1 of 47Fahim Al-Neshawy (2014)

Sensors and systems for non-destructive testing of facade structures: Humidity and temperature monitoring

Fahim Al-Neshawy10.2.2014

Rak-43.3312 Repair Methods of Structures II


OUTLINES

PART IConcrete

facade

PART IIHeat and moisture transfer

PART IIIMonitoring

systems

PART IVCase studies


Table of contents

• PART I: Concrete facade structures– History of the concrete facades– Classifying of concrete facades– Examples of the concrete facades defects– Repairing methods for concrete facades

• PART II: Heat and moisture transfer in concrete facades– Heat transfer mechanisms– Moisture transfer mechanisms– Deterioration of concrete facades caused by heat and moisture


Table of contents

• PART III: Monitoring systems– Measurement devices– Monitoring networks– Development of RHT-MS monitoring system

• RHT-MS sensor network and monitoring data analysis software• Field monitoring of relative humidity and moisture for repaired concrete

facades

• PART IV: Case studies - Results– Monitoring data analysis– Effectiveness of different repairing methods– Prediction of deterioration of concrete facades

• Summary


PART I: Concrete facade structures

Photo:Jukka Piironen


Building facades: general

• On of the basic function of the facade of a building is to protect the conditioned interior spaces from the surrounding environment.

• In general, the facade of a building has to provide: – (i) structural resistance to wind and gravity loads; – (ii) environmental protection from the elements, including moisture and

temperature, and– (iii) architectural appearance and aesthetics.


Concrete building facades: history

• 1840 – 1895 era– Heavy massive stone or brick supporting

structures – Building facades with natural stone – Decorations were made from gypsum and

were painted with oil paints• 1895 – 1920 era

– Cladding with natural stone was often used – Building facades with smooth, coarse, or

splash rendering systems – Building facades with red bricks

• 1920 – 1940 era– Staring of using the concrete as building

material in supporting structures– Mostly facades with red bricks, air bricks

Photos:Piritta Hannula and Marja Salonen


• 1940 – 1960 era– Staring of using the industrial prefabricated

concrete elements and thermal insulation– Building facades with coarse or splash

rendering systems – Starting of the concrete façades with

sandwich-element

• 1960 – 1980 era– Staring of the concrete elements frame

systems (columns – slab systems)– Building facades with exposed-aggregate

concrete surfaces – Building facades with cladding materials like

brick and clinker slabs – Building facades with dark brown bricks or

painted surfaces




• 1980 – present– Different types of prefabricated sandwich

elements with ventilation gaps – Concrete facades with cladding such as

metal sheets, boards, bricks or concrete panels

– Industrial building with glass and steel double facades


Hannula, P., Salonenin, M. (2007). Buildings tell – basic information for habitants (in Finnish: Rakennukset kertovat – perustietoa asukkaille). Helsingin Kaupunginosayhdistysten Liitto ry. Yliopistopaino, Helsinki, Finland. 52 pages.



Classifying of concrete facades

Wall typeFramework construction

Surface materials

Cross-section

Concrete wall with rendered lightweight concrete block cladding

Massive concrete cast-in-situ

Lime cement rendering

Cast-in-situ massive concrete

Fibre cement boards or profiled metal sheet cladding

Concrete wall with cladding of concrete panels


Prefabricated concrete panels

Concrete wall of prefabricated sandwich panels

Prefabricated concrete units

Prefabricated sandwich panels

Concrete wall with cladding of brick, board or metal sheeting


Brick


Classifying of concrete facades

+- +-

1. External concrete panel (75 – 100 mm)

2. Insulation (100 – 200 mm)

3. Internal concrete panel (120 – 150

mm)

1. External concrete panel (75 – 100 mm)

2. Ventilation gap (20 – 40 mm)

3. Wind protection insulation (25 mm)

4. Insulation (100 – 200 mm)

5. Internal concrete panel (120 – 150

mm)

1 2 3 1 2 3 4 5


Examples thermal and moisture defects of concrete facades

• Reinforcement corrosion• Carbonation• Salt weathering• Alkali-aggregate reactivity• Cracking of concrete• Damage due to fire• Attack due to micro-

organisms• Freezing-thawing

deterioration of concrete


Thermal and moisture exposure classes


Concrete facades: repairing methods

Thermal insulation, ventilation

gap and cladding

bricks

Thermal insulation

and rendering

coat

Thermal insulation

and cladding

panels


PART II: Heat and moisture transfer in concrete facades


Sources of the moisture in the building wall materials

• Liquid water – from precipitation (rain and melting snow)

or plumbing leaks;• Water vapour

– from the exterior and from activities and processes within the building;

• Liquid and vapour – from the soil adjoining the building

• Moisture built-in – with the materials of construction or

brought in with goods and people Holm, A., Künzel, H.M. (2000). Non-isothermal moisture transfer in porous building materials. Proceedings of the materials week 2000, International congress on advanced materials, their processes and applications, 25-28 September, 2000. Munich, Germany


Moisture transfer

Moisture as vapour• Diffusion from higher into

lower vapour pressure• Convection via gas phase

movement

Moisture as liquid• Capillarity suction …..• Gravity flow …….

through porous materials, cracks, and openings.


Moisture transfer in concrete facades

Adapted from Straube, J., (2002), "Moisture in buildings", ASHRAE Journal, January, pp. 15-19.

Ambient environment

Ambient environment

Materials

transfer

transfer


Heat transfer

• Heat transfer can occur in:– Conduction,– convection and– radiation

• Heat transfer by conduction will occur in any situation where molecules with different temperature can touch. It’s the only heat transfer mode that occurs in a solid.

• Convection is a heat transfer mode that occurs in a gas or a fluid.

• Thermal Radiation is heat transfer by emission and absorption. Objects will emit thermal radiation dependent on their temperature. The higher the temperature the greater the rate of radiation.


Deterioration of concrete facades caused by heat and moisture

Deterioration causes Defects / damage

Physical

Freezing and thawing Cracking, scalling

Moisture changes Shrinkage cracking, delamination

Temperature changes and gradients Curving of elements and plates

Chemical

Carbonation Reinforcement corrosion(spalling )

Alkali-aggregate reaction Delamination, Cracking

Salt crystallization Cracking, spalling

Biological Biological growth Mould problems


PART III: Monitoring systems


Thermal and moisture measurement methods

1. Resistance-based methods measure moisture levels in the materials in terms of their electric resistance, which varies as a function of moisture content

2. voltage-based methods Sensors using voltage-based methods measure moisture in terms of the direct current (DC) voltage across the resistor. The output voltage varies only with changes in wetness meaning that the voltage increases as the wetness increases and vice versa.

3. Surface moisture methods measuring electrical properties, such as conductivity from the surface of a material. The meters are usually equipped with conversion tables for different material groups in order to present the measurement results as moisture value


Relative humidity and temperature measurement devices

RH & T sensor selection criteria are:o Accuracy and uncertainty.o Application and function.o Reliability and quality.o First cost and life-cycle costs.

RH & T sensor categories:o Sensors that provide a record of

conditions at a specific period of timeo Sensors that provide a continuous record

of the conditions.

Data acquisition:o Recording hygrothermo-graph o Data-loggers


Why monitoring of relative humidity and temperature of concrete facades?

• to provide data showing climate conditions• to document condition changes and the

response of the concrete facades to them• to evaluate the effect of temperature and

relative humidity on the damage of concrete facades

• to act as an early warning system to ensure appropriate renovation and maintenance of concrete facades


Type of monitoring systems

• The data logging networko relative humidity and temperature sensors

connected via cable to data logger. o The data loggers are battery-powered

instruments use a computer chip to record data at intervals determined by the user.

o Data is transferred between the data logger and a personal computer by a cable.

• The wireless sensing systemo consists of sensor units and a base stationo The sensors measure input temperature,

relative humidity values and transmit the measured data over a secure wireless link to the base station

o Measurement and transmission intervals are set by user


RHT-MS monitoring system

The aim of the RHT-MS monitoring system is to provide a tool for:– monitoring and quantifying the main environmental parameters affecting the

deterioration of concrete facades,– analysis of the environmental hygrothermal data and the response of the concrete

facade to it, and– predicting the deterioration of concrete facades on the basis of hygrothermal

behaviour.

Sensor network Monitoring and

data analysis software


RHT-MS monitoring system: Sensor network

• The RHT-MS sensor network consists of a controller and nodes where relative humidity and temperature sensors are connected

• The controller provides configuration services and enables communication with computers to take place.

• The sensor network may contain up to 200 nodes connected to a twisted-pair CAT5 cable with a maximum total length of 1000 metres.

• The nodes used in the RHT-MS sensor network are hybrid nodes configured as 12-bit data and analogue-digital AD/state groups.

o Network controller (LIC04)o Network hybrid nodes

o 12-bit data groups o AD/state groups

o RH and temperature sensorso Cabling (CAT15 cable)


• Relative humidity and temperature sensors

1. HMP44 for relative humidity2. SHT15 for relative humidity3. PT100 for temperature

– The calibrations of the relative humidity sensors were confirmed by the manufacturers.

1

2

3

RHT-MS monitoring system: Sensor network


RHT-MS monitoring software

The RHT-MS monitoring software:o communicates between the host computer and the RHT-MS sensor network

controller o collects relative humidity and temperature datao saves the resulting values in an ASCII file and displaying them on the screen.

Monitoring software


RHT-MS data analysis software

1. hygrothermal data analysis (ststistical)

2. Prediction of carbonation-induced corrosion

3. Prediction of frost damage

4. Prediction of the potential mould growth


Monitored field (3)

PART IV: Case studies - Results

Monitored field (1)

Monitored field (2)


Monitored field (1)

• Apartment building of eight-storey built with sandwich elements.

» Demolishing the outer panel and insulation of the sandwich panel.

» Adding 150 mm new mineral wool insulation and

» cladding of 130 mm bricks » with a ventilation gap of 40 mm.


Monitored field (2)

• Six-storey apartment building built with sandwich elements.

• The facade was repaired by adding:» 50 mm external expanded polystyrene

(EPS) insulation» 6 mm rendering system.


Monitored field (3)

• Four-storey apartment building built with sandwich elements. • The facade was repaired by adding:

» 70 mm external mineral wool insulation

» 6 mm rendering system.


Analysis of the outdoor environmentMoisture index

• The moisture index describes the environmental moisture and thermal load.

• The moisture index is a function of two components: – the potential for wetting (wetting index) – the potential for drying (drying index).

• WI = the amount of rainfall (kg/m²)

𝐷𝐼= (𝑤𝑠𝑎𝑡,𝑖 −𝑤𝑎𝑐𝑡,𝑖)𝑡𝑚𝑜𝑖=1

𝑀𝐼=ඥ(𝑊𝐼𝑛𝑜𝑟𝑚2 +ሺ1−𝐷𝐼𝑛𝑜𝑟𝑚ሻ2


Analysis of the facade wall’s responseRelative humidity and temperature index

• The relative humidity and temperature index (RHTI) is a long-term hygrothermal response indicator derived from the relative humidity and temperature conditions inside the building envelope cross-section over a period of time for any specific area of the cross-section.

• The RHTI index is an indicator used to quantify and compare the hygrothermal response of the wall assembly.


Analysis of the facade wall’s responseRelative humidity and temperature index

• The RHTI index is an indicator used to quantify and compare the hygrothermal response of the wall assembly

1. Metal corrosion2. Concrete carbonation3. Biological growth


Analysis of the facade wall’s responseFreezing thawing index

• The freezing and thawing index (FTI) is defined as the number of freezing or thawing oscillations when temperatures oscillate around 0°C for those structures that are almost at the moisture saturation level RHcrit


Effect of the repairing mothed on the hygrothermal behavior of the facade wall

Using ventilated exterior wall

• The drying potential (saturation deficit) at the ventilation gap was higher during the hottest months of the year

• The temperature in the ventilation gap was always higher than the temperature outdoors, which increased the air movement from the ventilation gap outdoors.

, ( , 100%) , ( , )a a as s gap T RH a outdoor T RHD V V

Monitored field (1)


Effect of the repairing mouthed on the hygrothermal behavior of the facade wall

Adding external insulation with rendering coat

• The minimum temperature in the middle of the original outer concrete was always above 0°C

Monitored field (2)

Monitored field (3)



Drying of the original outer panel of the concrete facade

• The amount of water vapour that can be held by the material depends on saturated water vapour pressure

• The water content inside the facade wall assembly depends of the relative humidity and the saturated water vapour pressure

ps is the saturated vapour pressure, PaT is the temperature, °C

a, b & n for 0 ≤ T ≤ 30°Ca = 288.68 Pa, b = 1.098, and n = 8.02

for -20 ≤ T < 0°Ca = 4.689 Pa, b = 1.486, and n = 12.3

[g/m³]𝑊𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡=𝑝𝑠 (𝑇 )∗ 𝑅𝐻100




• The daily average relative humidity of the outer concrete panel dropped from 80% to 60 % then varies between 40% and 60%.

• The temperature of the original outer concrete panel was most of the time above 0 °C.

• These results indicate that the progress of reinforcement corrosion and frost deterioration of the original concrete facade has strongly decelerated or even stopped.

Monitored field (2)




• The daily average relative humidity of the outer concrete panel dropped from 80% to 60 % then varies between 40% and 60%.

• The temperature of the original outer concrete panel was most of the time above 0 °C.

• These results indicate that the progress of reinforcement corrosion and frost deterioration of the original concrete facade has strongly decelerated or even stopped.

Monitored field (3)


Deterioration prediction on the basis of temperature and moisture monitoring

• The deterioration of concrete typically occurs when the concrete is exposed to ambient outdoor conditions over an extended period– Carbonation -> corrosion– Frost damage– Risk of mould growth

CarbonationFrost damageRisk of mould growth


Summary 1/3

• The function of building facades is to provide (i) structural resistance to wind and gravity loads; (ii) environmental protection (iii) architectural appearance and aesthetics.

• Prefabricated sandwich elements are commonly used as concrete facade walls

• Concrete facade deterioration may occur for two principal reasons: – corrosion of the reinforcement as a result

of carbonation and – internal disintegration of the concrete as a

result of as frost attacks or alkali-aggregate reaction

• the concrete facade repair methods can be classified as:– protective repair methods, – additional thermal insulation and cladding, – demolition of outer layer and rebuilding.

• Moisture problems in the building envelope are usually resulting from water or water vapor migrating from the inside or outside of the building to or into the building envelope, and accumulating on or inside the envelope.

• Heat transfer can occur in conduction, convection and radiation.

• Moisture is transferred as vapour by diffusion and convection and transferred as liquid water by capillarity suction and gravity flow through porous materials, cracks, and openings.

• Thermal and moisture measurement methods are resistance-based methods, voltage-based methods and surface moisture methods

• Monitoring systems are data logging or wireless sensing system.


Summary 2/3

• The RHT-MS monitoring system is to a tool for:– monitoring and quantifying the main

environmental parameters affecting the deterioration of concrete facades,

– analysis of the environmental hygrothermal data and the response of the concrete facade to it, and

– predicting the deterioration of concrete facades on the basis of hygrothermal behaviour.

• Monitoring the thermal and moisture performance of repaired facades is useful providing a better understanding of how the environment and the building interact.

• Effect of the repair techniques on the hygrothermal performance of concrete facades:– The temperature in the ventilation gap was

always higher than the temperature outdoors, which increased the air movement from the ventilation gap outdoors.

– The drying potential at the ventilation gap was higher during the hottest months of the year.

– The advantage of external insulation walls is that they improve the thermal performance of the original wall and transfer the dew-point outside the structural wall element.


Summary 3/3

• Effect of the repair techniques on the hygrothermal performance of concrete facades:– The results of the thermal and moisture

monitoring of facades repaired by adding external wall insulation and rendering system show drying of original outer concrete panel of the repaired facade after one year from repairing.

– The insulation wall thickness has an impact on the drying of the original facade: the thicker the insulation, the faster the drying of the facade wall.

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