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Research ArticleExperimental Study on Hygrothermal Deformation of ExternalThermal Insulation Cladding Systems with Glazed Hollow Bead

Houren Xiong,1,2 Jinming Xu,1 Yuanzhen Liu,3 and Shimeng Wang3

1Department of Civil Engineering, Shanghai University, Shanghai 200444, China2Building Energy Efficiency Technology Laboratory, Jiaxing University, Jiaxing 314001, China3College of Architecture and Civil Engineering, Taiyuan University of Technology, Taiyuan 030024, China

Correspondence should be addressed to Houren Xiong; [email protected]

Received 30 July 2016; Accepted 16 October 2016

Academic Editor: Doo-Yeol Yoo

Copyright © 2016 Houren Xiong et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This research analyzes the thermal and strain behavior of external thermal insulation cladding systems (ETICS) with GlazedHollow Beads (GHB) thermal insulation mortar under hygrothermal cycles weather test in order to measure its durability underextreme weather (i.e., sunlight and rain).Thermometers and strain gauges are placed into different wall layers to gather thermal andstrain data and another instrument measures the crack dimensions after every 4 cycles. The results showed that the finishing coatshrank at early stage (elastic deformation) and then the finishing coat tends to expand and become damaged at later stage (plasticdeformation). The deformation of insulation layer is similar to that of the finishing coat but its variation amplitude is smaller.Deformation of substrate expanded with heat and contracted with cold due to the small temperature variation. The length andwidth of cracks on the finishing coat grew as the experiment progressed but with a decreasing growth rate and the cracks stoppedgrowing around 70 cycles.

1. Introduction

Due to the rapid economic development, there has beena constant increase in the building energy consumptionin China. According to the relevant statistics, the buildingenergy consumption accounts for about 30% of the totalenergy consumption of the society at large [1]. As for a build-ing, according to the statistics, the external walls of a build-ing, or the barriers between the internal and the externalparts, roughly account for 45% of the total building externalarea. The energy dissipated through the walls from thestructure enclosure accounts formore than 60% of the energyloss of the entire building [2]. Accordingly, the most effectiveway of reducing the energy dissipation through the walls is toimprove the thermal insulation of its external walls.

Many approaches have beenmade referred to the thermalinsulation systems for the peripheral structures of buildings.Dozens of thermal insulation systems for the external wallsof buildings were developed [2–4]. Specifically, by using aninsulating layer made of porous inorganic materials, the

external thermal insulation composite systems with GlazedHollow Bead thermal insulation mortar (ETICS GHB) arecharacterized by the high thermal insulation and fireproofperformances. The ETICS GHB have been widely applied inChina and many researchers investigated this system in thepreparation and molding [5–7], thermal insulation propertyand shrinkage deformation [8–10], mechanical property [11,12], and antifrost property [13]. However, only the functionalanalyses were focused on the GHB mortar or concrete andsingle material was concerned in most approaches. Littlewas taken accounted for the ETICS GHB, a system madeof laminated composite materials, from their hygrothermalproperties [10], especially from durability in a hygrothermalenvironment.

In practice, due to the heat blocking action of theinsulating layer, heat is usually stored in the finishing coatof the ETICS. For instance, in the summer, the temperatureof the ETICS finishing coat may reach 70∘C. On the otherhand, if a rainstorm occurs after several sunny days, thesurface temperature may suddenly drop to 50∘C [14]. This

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2016, Article ID 3025213, 14 pageshttp://dx.doi.org/10.1155/2016/3025213

2 Advances in Materials Science and Engineering

temperature change caused by sunshine and rain will reducethe strength and the thermal insulation effect of the materialsin the ETICS. The temperature change may also causehygrothermal deformation of the materials and thereafterresult in the damage in the structure (such as cracking of theinsulating layer, separation of the insulating layer from thebase, and falloff of the finishing coat). These damage affectthe normal service of ETICS [15–17]. For this reason, a hightemperature-rain simulation test on ETICS, in the currentstudy, was conducted in order to determine the hygrothermaldeformation and hygrothermal mechanical properties of thefinishing coat material. The test may provide vital scientificand engineering information both in evaluating the reliabilityand service life of the ETICS and in formulating guidelines fora safe ETICS design.

Many approaches have been made on the hygrothermaldeformation of ETICS, Zirkelbach et al. [18] conducted afive-year hygrothermal coupling analysis on themineral woolETICS in three European countries with various climaticconditions. He compared the temperature and humidity datafrom southern Portugal and northern Finland with thosemeasured in central Germany. Zhang et al. [19] used a finitedifference method to analyze the temperature stresses in theinternal and external thermal insulation walls. Collina andLignola [20] combined stress-strain to analyze the influenceof various stresses (such as shear stress and thermal stress)on the durability of ETICS. Balocco et al. [21] used the finiteelement software ANSYS to conduct a thermal fatigue studyon ETICS. Passa et al. [22] conducted the thermal straintest on various structural layers of EPS thermal insulationsystems in oven heating and analyzed the influence ofexternal temperature on the deformation of various structurallayers. Yiu et al. [23] used a simple equipment to conductthe hygrothermal cycle test on the small-scale wall testspecimens pasted with strain gauges in order to obtain thedeformation curves of the concrete, rendering, and tiles.Griciute and Bliudzius [24] conducted the contrast tests inthe indoor and natural ageing on ETICS made of threefinishing coat materials (i.e., acrylic, silicone, and silicate).They analyzed the change features in the microstructures,ingredients, and water contents of these materials. Daniottiet al. [25] used six cameras to monitor the finishing coatof the ETICS in the accelerated ageing test and recordedthe degradation failure phenomena at different deformationstages.

However, the degradation features of various structurallayers in the ETICS GHB under hygrothermal cycle are ofgreat importance; few of the existing studies, as we know,focused on these features. In this study, referring to the testmethod as described in the European standard ETAG 004[26], a high temperature-rain periodic test was conducted onlarge-scale ETICS GHB. The temperature sensors and straingaugeswere embedded in various structural layers tomeasurethe temperature and strain of various structural layers underhygrothermal cycles. The changes in temperature and strainin various structural layers of the ETICS GHB were alsoexamined. The degradation characteristics of the finishingcoat with the number of cycles were thereafter quantitativelyinvestigated.

Table 1: Properties of GHB.

Properties ValuesParticle size (mm) 0.5–1.5Cylindrical compress strength (kPa) ≥150Bulk density (kg/m3) 80–130Thermal conductivity (W/(mK)) 0.032–0.045Surface vitrified close cell content (%) ≥95Volatile water absorption (%) 20–50Volume floating rate (%) ≥98

Figure 1: Glazed Hollow Bead dimension (mm).

2. Materials and Experimental Procedure

2.1. Glazed Hollow Bead. Glazed Hollow Beads were pro-duced by Henan Xinyang Yongxin Perlite Plant (China). TheGHB particle sizes dimensions are shown in Figure 1. Theproperties of GHB particles are shown in Table 1.

2.2. Preparation of Rig for Test. The substrate of the rigwas prepared in accordance with the dimensions in [26],which is 3.0m (width) × 2.0m (height) concrete wall with0.6mm (height) × 0.4m (width) aluminum alloy window(see Figure 2). The structure of the rig from inside tooutside is formed by substrate, bonding layer, insulation layer,reinforced base coat, and finishing coat (see Figure 3). Thethermal parameters of the rig wall are detailed in Table 2.

The preparation procedure was described as follows. Thesubstrate base was first cleaned and moisturized. The adhe-sion agent was then brushed. After drying the adhesion agentfor at least 24 h, two layers of the GHB thermal insulationmortar were applied. The second layer was applied aftersetting the initial conditions of the system and completing thefirst layer. After curing the insulating layer in three days, twolayers of the anticrack mortar were applied on and pressedin the alkali-resistant glass fiber mesh between the first andsecond layers which were set. Then, the anticrack layer wascured for three days and the flexible putty was applied twiceafter being cured for at least one day.The external wall water-proof priming coatwas sprayed and the top layerwas finished.Furthermore, the system was cured at laboratory for 28 days.After completing the curing stage, the weathering test wasconducted. To monitor the distribution of the temperature atdifferent positions and structural layers along the horizontal

Advances in Materials Science and Engineering 3

Table2:Teste

dwalls:

layersandtheirtherm

alcharacteris

tics.

Structurelayer

Materials

Thickn

ess(mm)Con

ductivity

(W/(mK)

)Density(kg/m3)Specifich

eat(J/(

kgK)

)Sketch

ofstr

ucture

Substrate(Sub)

Con

cretew

all

150

1.740

2500

862

Sub

BL IL RBC

FC

Bond

inglayer(BL

)Ad

hesio

nagent

10.760

1500

1050

Insulatio

nlayer(IL)

GHBthermalinsulatio

nmortar

300.068

325

1170

Reinforced

base

coat(RBC

)Anticrack

mortar

40.750

1937

780

Glassfib

ermesh

Finishingcoat(FC)

Putty

+prim

ecoat+

topcoatwith

acrylic

bind

er3

0.58

1420

1000


2200

200

4 8 10 12 14 16

123456789

10

6 18

1112

00 2

Strain gauges (S)Thermometer (T)

I: bonding layer

II: insulation layerIII: finishing coat

Window

400400

1000

400

600

T-I-1T-II-1T-III-1S-I-1

S-II-1S-III-1

T-I-2T-II-2T-III-2

S-I-2S-II-2S-III-2

T-I-3T-II-3T-III-3

S-I-3S-II-3S-III-3

T-I-4T-II-4T-III-4

S-I-4S-II-4S-III-4

T-I-5T-II-5T-III-5

S-I-5S-II-5S-III-5

T-I-6T-II-6T-III-6

S-I-6S-II-6S-III-6 T-III-7

S-I-7S-II-7S-III-7

12×150

20 × 150

Figure 2: Schematic graph of measuring points (mm).

Strain gauge/temperature sensorin the bonding layer

Strain gauge/temperature sensorin the insulating layer

Strain gauge/temperature sensorin the finishing coat

Figure 3: Strain gauges and temperature sensors profiles in thevertical section.

and vertical directions of the test wall surface, the straingauges and temperature sensors in preparing ETICS GHBshould be installed at the same positions as the concretebase, the insulating layer (outer surface), and the finishingcoat. Seven strain gauges and six temperature sensors wereinstalled in each layer (see Figures 2–4).

2.3. Test Apparatus. (1) The weathering test chamber cansimulate the effect of hot and rainy summer weather withevaporators and fans on the ceiling and spraying system setup by the two sides of the chamber near the testing rigs(see Figure 5). Altogether the test chamber can reproducethe damage to ETICS in a few weeks that occur over manyyears outdoors, where the range of simulated temperature isfrom −25∘C to 100∘C and the range of simulated rainwatertemperature is 10∘C to 20∘C with the precision of ±1.0∘C.

(2) INV2312N wireless bus static strain test system: thesystem is characterized by high sampling rate and highstability with a temperature drift less than 1 𝜇𝜀/∘C, a time drift

less than 3 𝜇𝜀/4 h, and the measurement precision of ±0.3%FS ± 2 𝜇𝜀.

(3) KON-FK (N) crack width detector: the detector mayautomatically and quickly record the width of a crack with aprecision of 0.01mm.

(4) GM eight-channel temperature acquisition system: inconnecting to the DS18B20 waterproof copper sensor probe,the systemmay simultaneously record temperature signals at32 points within the temperature from−55∘C to 125∘C and theresolution of 0.0625∘C.

(5) Scanning electron microscopy (SEM) micrographs ofthe top coat and GHB mortar were obtained, respectively,using the types of SU-1510 and JSM-6700 (Hitachi, Japan) atvarious cycles.

(6) KFG/KFW-5-120-D16-11L1M2S strain gauge: the biax-ial overlapping configuration was used in the strain gaugein substrate combining with polyimide resin. The straintemperature drift in this arrangement may show by itselfwithout connecting to a compensating plate. It is noted thatthe KFG series strain gauges were mainly laid out in theinternal structures of the ETICS tomake high waterproof andmoisture-resistant performance.The series of strain gauges inKFW were mainly laid on the outdoor surface of the ETICS,even in the underwater or rainy environments. Table 3 showsthe performance indexes of the strain gauges.

2.4. Artificial Weathering Tests. The cured ETICS GHB testspecimens were placed inside the large-scale weathering testchamber. The strain gauges and temperature sensors shouldbe properly connected Figure 6 shows the assembled testspecimens. During a hygrothermal cycle test, the temperaturerange of hygrothermal cycle was set from 15∘C to 70∘C, andthe number of cycles was set at 80 with each cycle lasting for6 h.Theheating process consists of raising the air temperatureto 70∘C in approximately 60 minutes and then maintainingthe temperature at 70 (±5)∘C for 120minutes.The rain processconsists of spraying water continuously for 60 minutes andthen resting for 120 minutes. Both strain and temperaturewere recorded at an interval of 10min. A shutdown surfaceobservation of the test wall was carried out at an intervalof once in every four cycles to monitor the effect exertedby the thermal fatigue damage (i.e., crack, detachment, andswell). In order to quantitatively compare the surface damageresults of the test specimen after different number of cycles,the surface of the test specimen was subdivided by a gridspacing of 15 cm (i.e., 20 grids in the horizontal direction and13 grids in the vertical direction), as shown in Figure 2.

3. Results and Analysis

3.1. Temperature Field. To analyze the effect of tempera-ture changes on various structural layers, it is necessaryto determine the temperature features in various layersin the weathering test chamber. Taking 80 cycles in thehygrothermal conditions as an example, the data recordedat the fifth cycle were selected to examine the local changefeatures in temperature at each point. Figure 7(a) showsthe temperature changing curves at the measuring points T-I/II/III-4, T-I/II/III-5, and T-I/II/III-6 on the wall surface in


b

c

(a)

(b) (c)

Figure 4: (a) The rig wall during construction phase and instrumented with temperature sensors and strain gauges between GHB mortarand reinforced base coat. (b) Temperature sensor. (c) Strain gauge.

Table 3: Performance indexes of KFG/KFW.

Series Self-compensatingtemperature range/∘C

Self-compensating expansioncoefficient/10−6/∘C Strain limit/% Fatigue life/number of times

KFG 10–100 11.0 5.0 1.2 × 107

KFW 0–80 10.8 2.8 3.0 × 104

Test wall

Sprayingsystem

Evaporators and fans

Figure 5: The weathering test chamber.

the vertical direction. Figure 7(b) shows the related curvesat the measuring points T-I/II/III-2, T-I/II/III-5, and T-III-7 on the wall surface in the horizontal direction. Figure 8shows the variations in temperature at the measuring pointsT-I/II/III-1, T-I/II/III-2, T-I/II/III-5, and T-I/II/III-6 alongthe wall thickness direction.

(1) As shown in Figure 7, the temperature changing trendat different measuring points on the surfaces of thefinishing coat and the insulating layer are similar andhave a shape of a rectangular wave. However, thechanging trend on the surface of the bonding layerhas a shape of a triangular wave. The results implythat the GHB insulating material has an excellentthermal insulation effect in reducing the temperaturetransferred from the external temperature on thesubstrate wall; the temperature change rate of thebonding layer would slow down during the risingphase and raining phases and improve the indoorthermal comfort.

(2) As shown in Figure 7(a), the test chamber causeda progressively top-down decline in the temperatureof the finishing coat, insulating layer, and bondinglayer along the vertical direction of the wall surface.In this case, the largest temperature differences areamong the upper and lower parts (i.e., 30∘C for thefinishing coat, 26∘C for the insulating layer, and 12∘Cfor the bonding layer). These temperature differences


Figure 6: Data acquisition system of temperature and strain.

resulted in the deformation on the wall surface alongthe vertical direction and of the cracks along the hori-zontal direction. Figure 7(b) displays the temperaturedifference between the bonding layers and insulatinglayer is only about 1∘C along the horizontal directionof the wall surface. Furthermore, the fluctuations atthe measuring point T-III-7 of the finishing coat aremore significant than those at the other points in themiddle part, indicating that there is an unbalance inthe local temperature in the test chamber.

(3) As shown in Figure 8, the maximum temperaturedifferences between the upper points T-I-1 and T-III-1, the middle points T-I-2 and T-III-2 near thewindow, the middle points T-I-5 and T-III-5 near thecenter, and the lower points T-I-6 and T-III-6 were30.9∘C at 60min, 22∘C at 120min, 22∘C at 120min,and 17.3∘C at 180min, respectively. These results indi-cate that the surface temperatures at various pointswere affected by the local positions along the wallthickness direction. However, the differences in thetemperatures from the top to lower parts are smallerwith the largest one happening later.

3.2. Strain Field. In the test, the data recorded by the straingauges are the total strain in each structural layer of the wall.The data in a total of 80 hygrothermal cycles were analyzedhere. For the purpose of comparison, the measured tempera-tures near eachmeasuring point, the strain-time-temperaturerelationship curves of the finishing coat, insulating layer, andbonding layer at different positions were depicted in Figures9, 10, and 11.

(1) As shown in Figure 9, for each period at the tem-perature rising and maintaining phases, the strain of thefinishing coat changes synchronously with the temperaturein the external layer. This indicates that the material of thefinishing coat tended to expand with heat and to contractwith cold surroundings at these two phases. At the rainingphase, the temperature and strain of the finishing coat dropabruptly with a slight lag in the later curve (see Figures 9(b),9(d), and 9(f)). At the resting phase, the temperature of thefinishing coat continues to fall at a slower rate. On the otherhand, the strainwould increase followed by an initial decreaseas the temperature reaches that at the rising phase in the next

period. These results are consistent with those obtained byYiu et al. [23]. Therefore, the increase in strain during theresting phase may be caused by the hygroscopic expansionof the finishing coat material. For the entire cycle process, themaximumvertical and horizontal strains at the upper point S-III-1 and the lower point S-III-4 on the surface of the finishingcoat are 9469 𝜇𝜀 and 1752 𝜇𝜀 at N = 80, 1379 𝜇𝜀 at N = 78, and682 𝜇𝜀 at N = 5, respectively (N stands for the hygrothermalcycle). However, the vertical and horizontal strains at themiddle point S-III-6 rapidly drop to failure at N = 60 and atN = 70, respectively. These results indicate that the thermaldeformation of the wall surface caused by the temperaturedifference in the vertical direction is two to four times of thedeformation in the horizontal direction; in the finishing coatof the large-scale ETICS, the temperature gradient generatedby the heat blocking action of the insulating layer results inan inconsistent overall hygrothermal deformation in differentdirections.These deformation gradients would accelerate thecracking of the finishing coat material and thereby shortenthe durability of the material, as verified in Figures 15 and 16.

The finishing coat shrinks at early stage and expands aftera number of cycles. The reason is that the micropores onthe surface of the finishing coat are gradually blocked by thecarbonized crystals at early time while the macropores maybe generated between the crystals regions under the cycleload [24]. Figure 12 shows the scans electronic microscopyof the top parts of the finishing coat, respectively, before andafter the test.Themacropore structures appeared between thecrystals in Figure 12(b). These pores resulted from the water-loss and shrinkage of the finishing coat. In the late stage ofthe 20th cycle, there is insignificant change in the structuralporosity of the finishing coating material. As a consequence,the expansion with heat and the contraction with coldoccurred in most positions, especially as in the maintainingphases. At this stage, an irreversible temperature-dependentcreep deformation in the finishing coating material mightbe generated and accumulated with the cyclic temperaturefluctuations. The continuous expansion would cause thecoating material to split.

(2) Figures 9 and 10 show the results of the strains on thesurfaces of the finishing coat and insulating layer.The changetrends in these two figures are basically similar to each other,implying that the strain in the insulating layer may effectivelyillustrate the deformation of the insulating layer.However, themeasured strain in the insulating layer is much smaller thanthat in the finishing coat due to the less influences of the exter-nal temperature and humidity on the GHB material of theinsulating layer. FromFigures 9 and 10, it can be also seen thatmost of the drying-shrinkage deformation occurred in theearly stage and some of the thermally expansion deformationoccurred at the later stage. During the hygrothermal cycle,the maximum/minimum vertical and horizontal strains were495/−962 𝜇𝜀 and 1072/−188 𝜇𝜀, respectively. As shown inFigure 11, the strain in the bonding layer decreases abruptlydue to the protection effect of the insulating material. Noneof the deformation exceeds the elastic limit in the concretesubstrate regions. Hence, the safety is guaranteed for theinternal concrete enclosure structure; the service life of theconcrete might be lengthened. The maximum/minimum


Tem

pera

ture

(∘C)

Time (min)0 50 100 150 200 250 300 350

T-I-4T-I-5T-I-6T-II-4T-II-5

T-II-6T-III-4T-III-5T-III-6

15

20

25

30

35

40

45

50

55

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T-III-2T-III-5T-III-7

15

20

25

30

35

40

45

50

55

60

65

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75

(b) Along the horizontal direction of wall surface

Figure 7: Temperature changing curves at various measuring points.

32.932.6

34.1

32.4

56.9

56.637.9

61.968.8

64.6

69

42 43.641.5 53.4

43.641.5 53.4

40.5

34.2

37.2

36.8

36.3

36.6

35.635.3

35.3

Tem

pera

ture

(∘C)

Time (min)0 30 60 120 180 210 240 300 360

T-I-1T-II-1T-III-1

0

20

40

60

80

(a) T-I/II/III-1

29.329.1

30.4

29.3

42.150.5

32.9

47.454.3

52.6

58.5

36.5 38.3

54.460.2

35

25.1

23

31

22.6

30.5

23

29.1

29.2

30.430

30

Tem

pera

ture

(∘C)

Time (min)0 30 60 120 180 210 240 300 360

T-I-2T-II-2T-III-2

0

20

40

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(b) T-I/II/III-2

29.329.1

30.9

28.9

41.450.1 33.5

47.255

51.958.8

36.838.5

53.560.3

34

24.3

22.6

30.3

22.8

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29.1

29.2

30.329.8

29.8

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(∘C)

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T-I-5T-II-5T-III-5

0

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(c) T-I/II/III-5

2827.6

29.3

27.6

37.843.8 31.6

44

48

48.6

5234.9

36.6

50.5

53.9

33.8

24.7

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30.1

21.6

29

21.5

27.3

27.2

28.828.3

28.2

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pera

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(∘C)

Time (min)0 30 60 120 180 210 240 300 360

T-I-6T-II-6T-III-6

0

20

40

60

80

(d) T-I/II/III-6

Figure 8: Temperatures at various instants for different measuring points along the direction of wall thickness.


Stra

in (𝜇

𝜀)

Time (h)0 50 100 150 200 250 300 350 400 450480

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S-III-1-HS-III-1-VS-II-1-V

T-III-1S-I-1-HS-I-1-V

(a) In upper part

Stra

in (𝜇

𝜀)

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S-I-1-HS-I-1-VT-III-1

(b) Local amplifications of (a)

Time (h)0 50 100 150 200 250 300 350 400 450480

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in (𝜇

𝜀)

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100020003000400050006000700080009000

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Figure 9: Strain-time-temperature relationship of three surfaces.

vertical and horizontal strains on the surface of the bondinglayer are 359/−181 𝜇𝜀 and 330/−120 𝜇𝜀, respectively.

The different thermal deformation modes demonstratethat the hygrothermal resistance property of the bonding

layer is better than that of the insulating layer. The improve-ment in hygrothermal resistance of the bonding layer can beexplained by the influence of GHB particles. From Figure 13,it can be seen that the microstructure of GHB mortar did


Stra

in (𝜇

𝜀)10b

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Figure 10: Strain-time-temperature relationship of insulating layer.

not change obviously under various hygrothermal cycles,the internal honeycomb pores were relatively smooth, andno significant deterioration was observed. Hence, GHB canimprove hygrothermal behavior of the GHBmortar in reduc-ing thermal deformation of the concrete substrate surface.

(3) The strain-time relationship changing curve maybe divided into three stages (see Figure 14). Before the20th hygrothermal cycle, the strain of each structural layerdecreases with the increase of𝑁, that is, implying the shrink-age deformation occurs (see Figure 15). The most, second to


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Figure 11: Strain-time-temperature relationship of bonding layer.


0 cycle80 cycle

Figure 12: SEM graphs of top finish on the finishing coat.

30 cycle 60 cycle

Figure 13: SEM graphs of GBH mortar on insulating layer.

Number of hygrothermal cycles/N0 10 20 30 40 50 60 70 80

0123456789

10

Expansion stageShrinkage

stageFailurestage

Finishing coatInsulating layerBonding layer

Stra

in (𝜇

𝜀)

×103

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Figure 14: Accumulating process of fatigue damage.

most, and less significant shrinkage are located in the finish-ing coat, insulating layers, and bonding layers, respectively.On the whole, the deformations in the materials may beregarded at the elastic stage. At 𝑁 = 70, the changing trendsin the strains of various structural layers are not similar. The

horizontal strains in the finishing coat and the total strainsin the insulating and bonding layers increase continuouslywith a relative slowly rate until the end of the test. Conversely,the vertical strains in the finishing coat increase, implyingthat the expansion deformation generated (see Figure 16).Thetensile strain only recovers partially, especially the verticalstrain of the finishing coat behaviors of the plastic deforma-tionmode.These changing trends are consistent with those ofchange features in the temperature shown in Figure 7. Duringthe last ten cycles, there is an abrupt change in the verticalstrain in the finishing coat. To be specific, the changes in thestrains are not significant at the upper position (Figure 9(a))and at the lower position (Figure 9(e)) on finishing coat sur-face; while the strain gauge placed atmiddle position (see Fig-ure 9(c)) damages, the deformation enters the failure mode.

3.3. Surface Crack. Figures 15 and 16 show the sketches of thecracks recorded by the crackwidth detector at𝑁= 20 and𝑁=80. In these two instants, the cracks and swells on the finishingcoat appeared as lines and circles. In all procedure of thetest, the cracks, swells, and other degradation always occurredon the finishing coat. The rules relations between the length,width, and distribution of the cracks on the finishing coat andthe number of cycles are relatively obvious. The degradationcharacteristics of the finishing coat from the perspectives ofcrack length and width will be examined as follows.

(1) On the surface of the finishing coat (see Figure 15),most of the cracks are in the horizontal direction,


(0, 10) (1, 10)

(0, 9) (1, 9)

(9, 10) (10, 10)

(9, 9) (10, 9)

Expansion crack

Expansion crack

Detachment of the finishing coat

Swelling of the finishing coat

Window

1 2 4 8 9 10 11 12 13 14 16 17 19

123456789

10

3 5 6 7 15 18

1112

00

Figure 15: Crack propagations on the finishing coat, the 20 cycles.

Window

1 2 4 8 9 10 11 12 13 14 16 17 19

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10

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1112

00

(0, 10) (1, 10)

(0, 9) (1, 9)

(9, 10) (10, 10)

(9, 9) (10, 9)

Expansion crack

Shrinkage crack

Detachment of the finishing coat

Swelling of the finishing coat

Figure 16: Crack propagations on the finishing coat, the 80 cycles.

the second to most of the cracks are vertical ones,and very few of the oblique cracks appeared. Thereason is that the temperatures on the surface of thefinishing coat in the vertical direction changed moreintensely than those in other directions (see Figures7 and 8). So, the newly generated temperature stressmade it easier for cracks to emerge. As a result, under

the repeated actions of the hygrothermal load, mostof the cracks formed along the horizontal directionand developed relatively quickly. These cracks mayconverge to some extent. To be specific, the horizontaland vertical cracks converged regionally, while theoblique cracks distributed locally. The cracks on thefinishing coat only initially existed on the surface


Table 4: Number, length, and increase magnitude of cracks.

Number of cycles/𝑁 Number Total length/m Increase magnitude/% Max. width/mmNumber Total length

12 28 8.51 — — 0.0720 45 12.13 61 43 0.0940 64 18.22 42 50 0.1060 80 22.05 25 21 0.1272 89 24.18 11 10 0.1680 92 24.68 3 2 0.17

of the coating material but subsequently extendedto the inside of the material. However, they did notpenetrate the finishing coat.

(2) As shown in Table 4, the number, the length, andwidth of the cracks on the surface of the finishing coatgradually increase with the increase in the numberof cycles. Specifically, the most significant increase isthe number of cracks, followed by the total lengthof cracks. The increase in the width of cracks is notsignificant. All of these three parameters decreasewith the increasing in 𝑁. In particular, for 𝑁 >20, the cracks on the surface of the finishing coatdeveloped rapidly, also being verified by the strains inFigure 9(c). For𝑁 = 72, only a few new cracks formedand stably propagated. Therefore, after 72 hygrother-mal cycles, the degradation of the ETICS is not signifi-cant, suggesting that setting the number of hygrother-mal cycles at 80 in ETAG 004 [26] is appropriate.

4. Conclusions

In this study, the temperature and strain in three variousstructural layers (i.e., finishing coat, insulating layer, and thebonding layer) of the ETICS GHB under the hygrothermalcycles were investigated. Based on the test results, the follow-ing conclusions were obtained:

(1) Due to the differences in the thermophysical proper-ties, the relations between temperature distributionson the surface and inside the chamber are different forthree structural layers. These differences contributedto the internal stresses in the structural layers. Thetemperature difference between different positions onthe same plane of the finishing coat and the insulatinglayer is 20∘C. On the other hand, for the bondinglayer, the difference is only around 5∘C. The localtemperature difference existing on the surface of thefinishing coat may cause the surface crack openningon the finishing coat.The temperature of the bondinglayer is not excessively high because of the thermalinsulation action of the insulating layer.

(2) Most of the thermal deformation on the surfaceof three layers is moisture expansion and drying-shrinkage one and thermal expansion one, respec-tively, at the early stage and at the later stage. The

surface strain of the finishing coat shows three stagesof deformation with the increasing of𝑁: for𝑁 < 20,the shrinking elastic deformation occurs; for 20 <𝑁 < 70, the expansion-type elastoplastic deformationoccurs; for 𝑁 > 0, the plastic failure deformationoccurs.The change trends of the surface strains in theinsulating and bonding layers with the increase of 𝑁are similar, except that magnitude in the insulatinglayer is smaller. Due to the surface strain of thebonding layer, the elastic deformation occurs.

(3) The cracks on the surface of the finishing coat mostlyconverged into horizontal ones, followed by verticalcracks, and, lastly, locally formed a few of obliquecracks. With increasing 𝑁, the most significantincrease is the number of cracks on the finishing coatand then the length of the cracks. The width of thecracks increased is gradually. However, the increaserate of these parameters (i.e., number, length, andwidth) decreases with the increase in𝑁.The cracks ofthe finishing coat are the generation, expansion, andsaturation modes, respectively, for𝑁 < 20, 20 < 𝑁 <70, and𝑁 > 70.

(4) GHB mortar with internal honeycomb pores andsmooth closed surface has good water retentioncapacity and stable structure. Hence, the special porestructure can reduce the thermal conductivity ofGHBmortar, prevent the moisture migration extensionof concrete substrate, and accordingly alleviate thehygrothermal behavior of the bonding layer.

Competing Interests

The authors declare that they have no competing interests.

Acknowledgments

This work was financially supported by the National Nat-ural Science Foundation of China (no. 41472254 and no.51308371), Jiaxing University School-Class Key Topics ofFunded Projects (no. 70115020), Jiaxing Science and Technol-ogy Project (no. 2016AY13009), and The “Twelfth Five-Year”Key Disciplines in the Universities of Zhejiang Province, Dis-cipline of Building Energy Efficiency Technology (Depart-ment of Education of Zhejiang Province Office Document[2012] no. 80).


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