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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
Slide 2 of 47Fahim Al-Neshawy (2014)
OUTLINES
PART IConcrete
facade
PART IIHeat and moisture transfer
PART IIIMonitoring
systems
PART IVCase studies
Slide 3 of 47Fahim Al-Neshawy (2014)
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
Slide 4 of 47Fahim Al-Neshawy (2014)
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
Slide 5 of 47Fahim Al-Neshawy (2014)
PART I: Concrete facade structures
Photo:Jukka Piironen
Slide 6 of 47Fahim Al-Neshawy (2014)
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.
Slide 7 of 47Fahim Al-Neshawy (2014)
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
Slide 8 of 47Fahim Al-Neshawy (2014)
• 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
Photos:Piritta Hannula and Marja Salonen
Concrete building facades: history
Slide 9 of 47Fahim Al-Neshawy (2014)
• 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
Photos:Piritta Hannula and Marja Salonen
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.
Concrete building facades: history
Slide 10 of 47Fahim Al-Neshawy (2014)
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
Cast-in-situ massive concrete
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
Cast-in-situ massive concrete
Brick
Slide 11 of 47Fahim Al-Neshawy (2014)
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
Slide 12 of 47Fahim Al-Neshawy (2014)
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
Slide 13 of 47Fahim Al-Neshawy (2014)
Thermal and moisture exposure classes
Slide 14 of 47Fahim Al-Neshawy (2014)
Concrete facades: repairing methods
Thermal insulation, ventilation
gap and cladding
bricks
Thermal insulation
and rendering
coat
Thermal insulation
and cladding
panels
Slide 15 of 47Fahim Al-Neshawy (2014)
PART II: Heat and moisture transfer in concrete facades
Slide 16 of 47Fahim Al-Neshawy (2014)
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
Slide 17 of 47Fahim Al-Neshawy (2014)
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.
Slide 18 of 47Fahim Al-Neshawy (2014)
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
Slide 19 of 47Fahim Al-Neshawy (2014)
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.
Slide 20 of 47Fahim Al-Neshawy (2014)
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
Slide 21 of 47Fahim Al-Neshawy (2014)
PART III: Monitoring systems
Slide 22 of 47Fahim Al-Neshawy (2014)
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
Slide 23 of 47Fahim Al-Neshawy (2014)
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
Slide 24 of 47Fahim Al-Neshawy (2014)
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
Slide 25 of 47Fahim Al-Neshawy (2014)
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
Slide 26 of 47Fahim Al-Neshawy (2014)
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
Slide 27 of 47Fahim Al-Neshawy (2014)
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)
Slide 28 of 47Fahim Al-Neshawy (2014)
• 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
Slide 29 of 47Fahim Al-Neshawy (2014)
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
Slide 30 of 47Fahim Al-Neshawy (2014)
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
Slide 31 of 47Fahim Al-Neshawy (2014)
Monitored field (3)
PART IV: Case studies - Results
Monitored field (1)
Monitored field (2)
Slide 32 of 47Fahim Al-Neshawy (2014)
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.
Slide 33 of 47Fahim Al-Neshawy (2014)
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.
Slide 34 of 47Fahim Al-Neshawy (2014)
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.
Slide 35 of 47Fahim Al-Neshawy (2014)
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
Slide 36 of 47Fahim Al-Neshawy (2014)
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.
Slide 37 of 47Fahim Al-Neshawy (2014)
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
Slide 38 of 47Fahim Al-Neshawy (2014)
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
Slide 39 of 47Fahim Al-Neshawy (2014)
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)
Slide 40 of 47Fahim Al-Neshawy (2014)
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)
Slide 41 of 47Fahim Al-Neshawy (2014)
Effect of the repairing mouthed on the hygrothermal behavior of the facade wall
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
Slide 42 of 47Fahim Al-Neshawy (2014)
Effect of the repairing mouthed on the hygrothermal behavior of the facade wall
Drying of the original outer panel of the concrete facade
• 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)
Slide 43 of 47Fahim Al-Neshawy (2014)
Effect of the repairing mouthed on the hygrothermal behavior of the facade wall
Drying of the original outer panel of the concrete facade
• 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)
Slide 44 of 47Fahim Al-Neshawy (2014)
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
Slide 45 of 47Fahim Al-Neshawy (2014)
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.
Slide 46 of 47Fahim Al-Neshawy (2014)
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.
Slide 47 of 47Fahim Al-Neshawy (2014)
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.