Ultrasonic Pulse Velocity Testing for Monitoring the Degradation of

Infill Masonry Walls and Access Their Impact on the Durability of the

Envelope of Buildings with Reinforced Concrete Structure

JOSÉ MIRANDA DIAS

Department of Buildings,

National Laboratory of Civil Engineering (LNEC),

Av. do Brasil 101, Lisboa,

PORTUGAL

Abstract: - Buildings with reinforced concrete structure (RCS buildings), including unreinforced masonry

(URM) infill walls, can be negatively affected by anomalies in their envelope, such as cracking and water

penetration, which worsen the aesthetic aspect and reduce the safety and level of comfort of those buildings. To

access the relevance of these anomalies and their evolution along service life, a corresponding survey and

monitoring during service life are essential. Non-destructive test methods (NDT), in particular ultrasonic pulse

velocity (UPV) testing, are currently used in that survey and monitoring. In the context of monitoring the

degradation of the URM infill walls and access their impact on the durability of the RCS building envelope,

UPV testing can be a type of NDT method to be used, considering that it can contribute to the evaluation of the

state of conservation of the construction elements, such as masonry and concrete.

It is intended here to access the potential use of UPV testing in the monitoring of anomalies related to the

degradation of building facades due, particularly, to cracking and to water penetration associated with WDR

(wind driven-rain). The preliminary assessment of the use of UPV testing is made through the previous analysis

of the results of the application of UPV testing for the detection of sub-surface and surface cracking in

compression tests of masonry specimens. Following that analysis, an evaluation is made of the conditioning

aspects of the use of UPV testing to access durability problems of the building envelope. Particularly, the main

characteristics of cracking with interest for the assessment of the potential use of UPV testing are generally

discussed. And, finally, an evaluation is made of the risk of water penetration through the cracks, for potential

use of UPV testing in monitoring the presence of humidity in the cracks.

Key-Words: Ultrasonic pulse velocity testing; Infill masonry walls; Buildings; Service life; Durability

Received: April 15, 2023. Revised: July 7, 2023. Accepted: September 4, 2023. Published: September 21, 2023.

1 Introduction

Buildings with reinforced concrete structure (RCS

buildings), including unreinforced masonry (URM)

infill walls, can be negatively affected by anomalies

in their envelope, such as cracking and water

penetration, which worsen the aesthetic aspect and

reduce the safety and level of comfort of those

buildings. To access the relevance of these

anomalies and their evolution along service life, a

corresponding survey and monitoring during service

life are essential. Non-destructive test methods

(NDT), in particular ultrasonic pulse velocity (UPV)

testing, are currently used in that survey and

monitoring, especially in the case of heritage

buildings, which can be justifiable, due to their

cultural/historical importance and public utility, to

use these methods. In the context of monitoring the

degradation of the URM infill walls and access their

impact on the durability of the RCS building

envelope, UPV testing can be a type of NDT

method to be used, considering that it can contribute

to the evaluation of the state of conservation of the

construction elements, such as masonry and

concrete. The use of UPV testing for monitoring

building envelope, along their service life, could be

based on the determination of the rate of spread of

ultrasonic waves through their construction

elements (particularly, URM infill walls and RCS

elements), for a possible estimation of the respective

compactness and stiffness.

It is intended here to access the potential use of

UPV testing in the monitoring of anomalies related

to the degradation of building facades due,

particularly, to cracking and to water penetration

associated with WDR (wind-driven rain). The

preliminary assessment of the use of UPV testing is

made through the previous analysis of the results of

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the application of UPV testing for the detection of

sub-surface and surface cracking in compression

tests of masonry specimens. Following that analysis,

an evaluation is made of the conditioning aspects of

the use of UPV testing to access durability problems

of the building envelope. Particularly, the main

characteristics of cracking with interest for the

assessment of the potential use of UPV testing for

their monitoring are generally discussed. Finally, an

evaluation is made of the risk of water penetration

through the cracks, for potential use of UPV testing

in monitoring the presence of humidity in the

cracks.

2 Need for Improved Knowledge

about the Use of UPV Testing for

Monitoring the Degradation of URM

Infill Walls and the Methodology of

the Present Study

The durability of the RCS building envelope can be

significantly affected by degradation agents related

to the current external environmental conditions,

[1], mainly associated with normal actions of

temperature, rain, wind, air pollutants, and

biological action, as well as related to climate

changes, [2], [3]. The potential use of UPV testing

in the monitoring of anomalies of the RCS building

envelope should deal with the assessment of the

impact of those degradation agents in that envelope.

Their common adverse impact on the RCS building

envelope is particularly related to the degradation of

the facades, which mainly are due to the cracking

and detachment of renders and paintings of the

URM infill walls and to water penetration through

that cracking, associated with WDR (wind-driven

rain), as well as the deterioration of externally

exposed concrete elements. Water penetration in

buildings can decrease their internal conditions of

health and comfort.

Cracking of masonry walls of building

envelope can occur due to diverse causes, which one

of the more relevant are related to deformations of

URM infill walls and confining structural elements

due to temperature and moisture variations and to

vertical loads of the structural elements that support

the walls, [1], [4].

Masonry is a composite material made with

bricks and mortar adjusted in many different

bonding. Usually, the wall section can be

correspondent to a single leaf or two leaves of

different thicknesses, which can be connected or

separated by an internal layer, filled with insulation

material, or not filled at all (void space). The

knowledge of characteristics of the URM infill walls

and the respective technique of construction is

essential to analyze the anomalies that occur in the

RCS building envelope, but, sometimes, these

characteristics are not fully known. The use of non-

destructive testing techniques (NDT), such as

ultrasonic pulse velocity (UPV) testing, has been

used currently in the survey of anomalies to obtain a

better knowledge of the constitution of the URM

infill walls and to investigate more profoundly their

anomalies, considering that different causes of

cracking are possible, [5]. UPV testing could

attempt to be used for capturing the signs of

degradation of the envelope along service life,

particularly of relevant sub-surface and superficial

cracking that can occur mainly associated with any

of these referred causes.

Therefore, UPV testing can be an option for

monitoring the degradation and durability of infill

masonry walls, but there is a need to improve the

knowledge about the conditions of their use,

particularly to access the advantages and

disadvantages of the use of UPV testing for

monitoring the anomalies in facades related to their

cracking.

The main motivation behind this work is to study

more deeply the characteristics of cracking as well as

the assessment of the risk of water penetration through

the cracks, for the assessment of the potential use of

UPV testing for monitoring the cracking and the

presence of humidity in the cracks.

Taking into account the referred need for

improved knowledge on the application of UPV

testing in RCS buildings, the methodology of the

present study will consist of the evaluation of the

potential use of UPV testing in monitoring the

degradation and accessing the durability of URM

infill walls of RCS building envelope. The referred

degradation is due, particularly, to cracking and

water penetration associated with WDR (wind-

driven rain), including climate change effects on

buildings. That assessment will be made through the

previous analysis of the results of the application of

UPV testing for the detection of sub-surface and

surface cracking in compression tests of masonry

specimens. Following that analysis, an evaluation

will be made of the conditioning aspects of the use

of UPV testing to access the durability problems of

the building envelope. The main characteristics of

cracking with interest for the assessment of the

potential use of UPV testing for their monitoring are

generally discussed. Finally, the evaluation of the

risk of water penetration through the cracks, for

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potential use of UPV testing in monitoring the

presence of humidity in the cracks will be made.

3 Basic Characteristics of UPV

Testing and Their Ability for

Monitoring the Degradation of

Construction Elements as Infill

Masonry Walls and Concrete

Elements

The ultrasonic pulse velocity (UPV) testing consists

of the analysis of the relation between the velocity of

elastic waves that propagate in a solid medium and

the properties of that medium. For the specific case

of construction materials, such as concrete and

masonry, higher frequency waves are used in the

ultrasonic range (20 kHz to 150 kHz). The device

more commonly used consist on a central module,

which emits waves, and two transducers (an emitter

of pulses of ultrasonic longitudinal waves and a

receiver), being the central module to processes the

reading and recording of the transmission time.

Other type of device, specifically used to obtain

improved measuring accuracy, is the ultrasound

tomography, where a multi-head antenna equipped

with many independent ultrasonic transducers

induces the elastic waves.

The use of UPV testing in the mechanical

characterization of materials, such as masonry and

concrete, is based on the assumption of a relation

between the parameters of propagation of ultrasonic

waves and the elastic properties of these materials,

[6], [7], [8], [9]. Particularly, the wave speed was

found dependent on the elastic properties of the

transmitting medium, its density and Poisson's ratio,

[7]. Concerning the use of UPV testing for the

identification of deterioration in materials, some of

the parameters that characterize the elastic waves,

such as wave speed, generally, are influenced by the

existence of damage in the materials, [10]. The

propagation velocities of longitudinal waves

generally decrease for a damaged material and,

particularly, the amplitude of these waves and the

speed of propagation of ultrasound are significantly

influenced by the presence of surface and subsurface

cracks in the material.

The heterogeneity of the material or large voids

result in rapid wave attenuation and eventual

restriction of the waves from passing through the

material, [9]. Flaws, voids, and other type of similar

defects increase the transit time of the ultrasonic

pulses, [11]. Applied to buildings, these

characteristics of UPV testing can help in monitoring

the degradation of construction elements, especially

due to their sub-cracking and surface cracking.

However, the results of UPV testing can be affected

by minor defects of the surface or their roughness,

due to the restriction, from passing voids, of the

short wavelength of the signal, between the surface

and the receiver, even in case of minor voids. That

leads to the importance of a careful study of the

interaction between subsurface cracks and wave

parameters. This NDT method has been currently

employed to determine the strength of concrete and

masonry, to detect voids and discontinuities in the

concrete structure, and to test crack depths.

Combined with this use of ultrasound testing,

thermography and photogrammetry has been used

for detection of surface and internal cracks, [5].

UPV testing can be used, particularly, for the

primary assessment of the masonry constituent’s

material’s condition, in order to take the adequate

intervention, [12]. NDT can be especially helpful in

finding hidden features, such as internal voids and

flaws and characteristics of the wall section, which

cannot be known otherwise than through destructive

tests, [5], [12]. UPV testing can be also considered a

potential NDT for the detection of significant

variations in the moisture content of masonry wall

constituents and their rendering, [1].

4 Laboratory Tests

UPV tests were made on masonry specimens

subjected to axial compression, aiming to assess, in

a laboratory-controlled setting, the advantages and

limitations of their use for detection of sub-surface

and surface cracking in URM infill of buildings, [5].

Two specimens were tested: Specimen A1 made of

vertically perforated ceramic blocks (Figure 1);

Specimen A2 made of massive concrete blocks of

expanded clay aggregates (Figure 2). These two

masonry specimens were subjected to axial

compression, until they reached a state of significant

cracking, but without reaching a global collapse.

Due to the different dimensions of Specimen A1 and

Specimen A2, the tests were made in two different

compression press machines, which were, for each

of the specimens, considered more suitable (Figure

3, Figure 4, Figure 6 and Figure 8).

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a) Schematic view of

the block

b) Top view of the block

Fig. 1: Type of vertically perforated ceramic blocks

used in the Specimen A1 (compression test of the

specimen)

During the test of both specimens, for each

loading step, after reaching the corresponded

maximum load level, the specimen was discharged.

Immediately after that discharge, the horizontal and

vertical deformations were measured with

alongameter (registering, after unloading, the

deformations in the face A of the specimen – Figure

5 and Figure 7). Horizontal deformations

measurements, were made in the upper course of the

specimen (dh1 (A1-A2), dh2 (A3-A4)) and in the

lower course of the specimen (dh3 (A5-A6), dh4

(A7-A8)).

a) Schematic view

of the block

b) Partial lateral view of the

block

Fig. 2: Type of massive concrete blocks of

expanded clay aggregates used in the Specimen A2

(compression test of the specimen)

a) Specimen A1

(perforated ceramic

blocks)

b) Specimen A2 (massive

concrete blocks of expanded

clay aggregates)

Fig. 3: General view of compression test of

masonry specimens (view of the face A of the

specimens)

a) Specimen A1

(perforated ceramic

blocks)

b) Specimen A2 (massive

concrete blocks of

expanded clay aggregates)

Fig. 4: UPV testing in the compression test of

Specimen A1 and Specimen A2

Vertical deformations measurements, were made

between the upper and lower course, in the left part

of the specimen (dv1 (A1-A5), dv2 (A2-A6) and in

the right part of the specimen (dv3 (A3-A7), dv4

(A4-A8). In addition, the vertical absolute

displacement of central point D1 in Face B of the

two specimens was measured for check control of

the specimen tests.

In addition, the ultrasound velocity

measurements (direct and indirect measurements;

for distance of 100 mm; 200 mm, 300 mm and 400

mm) were made during these tests breaks (3

readings for the measurements in each distance).

Then, after the conclusion of the UPV

measurements, a new phase load was initiated.

During the loading phase of the specimens,

UPV testing was used in the tests for the evaluation

of their ability for detection of initial sub-surface

cracking in the masonry specimens, and of the

evolution of that cracking during the referred axial

compression test. Particularly, it was evaluated the

degree of sensitivity of UPV testing to detect, with

the progressive increment of applied vertical load,

the increased opening of the cracks in the masonry.

5 Description of the Test Setup of the

Specimens

In the following the description of the test setup of

the Specimen A1 and Specimen A2 is made.

5.1 Description of the Test Setup of

Specimen A1

Specimen A1 (Figure 3a) was built with vertically

perforated ceramic blocks (Figure 1), with two

courses of bricks linked between them thorough

cement mortar joints (bed joints) as well as the

vertical joints. The average dimensions of the blocks

were, approximately, 296 mm (length) x 137 mm

(thickness) x 193 mm (height). The average

percentage of voids of the blocks was approximately

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51%. The value of the compressive strength of

blocks was near 21.4 N/mm2. The average

dimensions of Specimen A1 were approximately,

600 mm (length) x 137 mm (thickness) x 415 mm

(height).

During the test of Specimen A1, a gradual axial

compression load was applied, with loading steps of

50 kN (applied vertical stress of 1.23 MPa), 100 kN

(2.47 MPa), 200 kN (4.93MPa), 300 kN (7.40 MPa),

400 kN (9.86 MPa)), and final load of 470 kN

(11.59 MPa); then ended this loading phase.

Face A

Face B

Fig. 5: Schematic representation of the frame

points for horizontal and vertical deformations

measurements (points A1 to A8) in face A, and

ultrasound measurements in face A and Face B of

Specimen A1 in the compression test

Face A

Face B

Fig. 6: The phase of preparation of Specimen A1

for the compression test (view of the face A and B

of the specimen)

5.2 Description of the Test Setup of

Specimen A2

Specimen A2 (Figure 3b) was built with massive

concrete blocks of expanded clay aggregates (Figure

2b), with four courses of blocks linked thorough

cement mortar joints (bed joints) as well as the

vertical joints. The average dimensions of the blocks

were approximately 490 mm (length) x 145 mm

(thickness) x 190 mm (height). The value of the

compressive strength of blocks was near 10.1

N/mm2. The average dimensions of Specimen A1

were, approximately, 750 mm (length) x 145 mm

(thickness) x 810 mm (height).

In the loading phase of Specimen A2, a gradual

axial compression load was applied, with loading

steps of 50 kN (applied vertical stress of 0.54 MPa),

100 kN (1.07 MPa), 200 kN (2.15 MPa), 300 kN

(3.22 MPa), 400 kN (4.30 MPa), and final load of

490 kN (13.98 MPa); then ended this loading phase.

Face A

Face B

Fig. 7: Schematic representation of the frame

points for horizontal and vertical deformations

measurements (points A1 to A8) in face A, and

for ultrasound measurements in face A and face

B of Specimen A2 in the compression test

Face A

Face B

Fig. 8: Phase of preparation of Specimen A2 for the

compression test (view of specimen face A and B)

6 Results of the Tests

The results of the compression test of both

specimens (Specimen A1 and Specimen A2), in

terms of the measurement of horizontal and vertical

deformations with alongameter, and of the UPV

tests, are following presented.

6.1 Test Results of Specimen A1

The results of the measurement of vertical

deformations (dv1 to dv4) and horizontal

deformations (dh1 to dh4), in the face A of the

specimen, for each loading step after the discharge of

the specimen, are presented in Table 1 (vertical

deformations) and Table 2 (horizontal deformations).

The results of UPV tests on Specimen A1 are

presented in Tables 3 (indirect method), Table 4

(direct method), Table 5 (Appendix) and Table 6

(Appendix). During the test, with the increasing of

the load, the specimen was gradually showing signs

of surface cracking, and fragmentation (Figure 9).

At the end the specimen was extensively damaged

(Figure 10, Figure 11, Figure 12, Figure 13 and

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Figure 14), especially in the left part of face A of the

specimen (Figure 10 and Figure 11), with

fragmentation of the top of corner zone. The right

part of face B of the specimen (Figure 12 , Figure 13

and Figure 14) was also severely damaged, with

fragmentation of almost the entire corner zone of the

specimen and with a near vertical crack of the of the

upper brick near the referred corner zone.

Table 1. Vertical deformations in the test of

Specimen A1

Load

(kN)

Vertical deformations

εVm

/(MPa)

dv1

mm/m

dv2

mm/m

dv3

mm/m

dv4

mm/m

0/0

942

1069

1110

818

50/1.23

947

-0.025

1070

-0.005

1115

-0.025

819

-0.005

100/2.47

945

-0.015

1067

0.01

1111

-0.005

818

200/4.93

949

-0.035

1073

-0.02

1115

-0.025

817

0.005

300/7.40

951

-0.045

1074

-0.025

1124

-0.07

819

-0.005

400/9.86

950

-0.04

1084

-0.075

1148

-0.19

823

-0.025

Unity=0.001 mm; Base of measurement = 200 mm

Table 2. Horizontal deformations in the test of

Specimen A1

Load

(kN)

Horizontal deformations

A1-

εHm

A3-

εHm

A5-

εHm

A7-

εHm

/(MPa)

dh1

dh2

mm/m

dh3

mm/

dh4

mm/

0/0

940

981

960

852

50/1.23

932

0.04

980

0.005

955

0.025

853

-0.0025

100/2.47

926

0.07

978

0.015

957

0.015

855

-0.0075

200/4.93

918

0.11

960

0.105

955

0.025

851

0.0025

300/7.40

892

0.24

890

0.455

955

0.025

820

0.08

400/9.86

870

0.35

842

0.695

954

0.03

788

0.16

After reaching the maximum load of 470 kN

(Applied vertical stress of 11.59 MPa), with the

collapse of the specimen (Figure 9, Figure 10,

Figure 11 and Figure 12), the test was halted and the

specimen was discharged.

Fig. 9: Aspect of the face A of the Specimen A1 in

the compression test, with signs of local

fragmentation of the top part of specimen (left side

of the specimen)

Fig. 10: Aspect of the face A of Specimen A1 at

the end of the test after discharge of a load of 470

Fig. 11: Aspect of the face A of Specimen A1 at

the end of the test with the collapse of the specimen

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Fig. 12: Aspect of the face B of Specimen A1 at

the end of the test

Fig. 13: Aspect of the face B of Specimen A1 at

the end of the test

Fig. 14: Aspect of the face B of Specimen A1 at the

end of the test

Table 3. Results of ultrasound test of specimen A1

by indirect method for zero load (0 kN - 3 readings

for each measurement between two points)

Method

Indirect method

Time (microseconds)

U1-

U6-

Distance

100

200

300

400

100

300

400

Readi

ngs

95.1

199.4

306.2

313.1

78.9

418

506.2

95.1

199.4

305.5

314.1

79.5

357.6

509.2

95.1

199.4

306.6

314.5

79.7

418.3

574.9

Mean

95.1

199.4

306.1

313.9

79.4

398.0

530.1

Table 4. Results of ultrasound test of specimen A1

by direct method for zero load (0 kN - 3 readings for

each measurement between two points)

Method

Direct method

Time (microseconds)

U1-

U2-

U4-

U5-

U6-

U7-

U8-

-U9

Distance

150

Readings

87,8

84,8

89,1

87,3

82,2

82,7

87,4

84,6

88,8

87,3

87,8

82,9

82,7

95,1

87,4

84,6

89,1

87,3

82,9

Mean

95,0

87,5

84,7

89,0

87,3

87,5

82,7

82,8

6.2 Test Results of Specimen A2

The results of the measurement of vertical

deformations (dv1 to dv4) and horizontal

deformations (dh1 to dh4) with alongameter in the

face A of the specimen, for each loading step after

the discharge of the specimen, are presented in

Table 7 (vertical deformations) and Table 8

(horizontal deformations). The results of UPV tests

on Specimen A2 are presented in Table 9, Table 10,

Table 11 (Appendix) and Table 12 (Appendix).

During the test, with the increasing load, the

specimen was gradually showing signs of slight

surface cracking in mortar joints (Figure 13,

Appendix) and, at the end of the test, signs of local

fragmentation of the base of the face B of Specimen

A2 were evident.

After reaching the maximum load of 490 kN

(Applied vertical stress of 5.26 MPa), with the slight

cracking and local fragmentation of the base of the

face B of the specimen (Figure 15, Figure 16, and

Figure 17), the test was halted and the specimen was

discharged.

Table 7. Vertical deformations in the test of

Specimen A2

Load

(kN)

Vertical deformations

A1-

εVm

A2-A6

εVm

A3-

εVm

A4-

εVm

/(MPa)

dv1

mm/m

dv2

mm/

dv3

mm/m

dv4

mm/m

0/0

913

945

851

778

50/0.54

925

-0.06

980

-0.18

882

-0.16

788

-0.05

100/1.07

942

-0.15

1010

-0.33

900

-0.25

794

-0.08

200/2.15

944

-0.16

1063

-0.59

935

-0.42

798

-0.1

300/3.22

986

-0.37

1093

-0.74

959

-0.54

802

-0.12

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400/4.30

1004

-0.46

1130

-0.93

1000

-0.75

821

-0.22

490/5.26

918

-0.03

936

0.05

848

0.02

778

Unity=0.001 mm; Base of measurement = 200 mm

Table 8. Horizontal deformations in the test of

Specimen A2

Load

(kN)

Horizontal deformations

A1-A2

εHm

A3-

εHm

A5-

εHm

A7-

εHm

/(MPa)

dh1

dh2

dh3

mm/

dh4

mm/

0/0

957

970

1010

970

50/0.54

942

0.08

965

0.03

1009

0.01

967

0.02

100/1.07

924

0.17

964

0.03

997

0.07

967

0.02

200/2.15

432

2.63

964

0.03

492

2.59

982

-0.06

300/3.22

175

3.91

954

0.08

190

4.1

994

-0.12

400/4.30

128

4.15

933

0.19

140

4.35

987

-0.09

490/5.26

297

3.3

525

2.23

250

3.8

530

2.2

Unity=0.001 mm; Base of measurement = 200 mm

Fig. 15: Aspect of the Specimen A2 in the

compression test, with signs of slight surface

cracking in mortar joints

Fig. 16: Aspect of the face A of Specimen A2 at

the end of the test

Fig. 17: Aspect of the face B of Specimen A2 at the

end of the test, with evident signs of local

fragmentation of the base of specimen

Table 9. Results of ultrasound test of Specimen A2

by indirect method for zero load (0 kN - 3 readings

for each measurement between two points)

Method

Indirect method

Time (microseconds)

U1-

U6-

Distance

100

200

300

400

100

300

400

Readings

93,1

182,9

236,2

291,8

47,4

143,7

221,9

92,9

182,7

237,6

291,5

46,6

143,2

221,3

91,8

182,4

238,3

293,1

47,5

143,7

221,5

Mean

92,6

182,7

237,4

292,1

47,2

143,5

221,6

Table 10. Results of ultrasound test of Specimen A2

by direct method for zero load (0 kN - 3 readings for

each measurement between two points)

Method

Direct method

Time (microseconds)

U1-

U2-

U4-

U5-

U6-

U7-

U8-

-U9

Distance

150

Readings

58,5

57,8

59,1

59,9

60,3

60,8

60,4

58,5

57,7

57,8

58,6

59,9

60,0

60,6

60,4

59,3

57,7

58,5

58,6

59,9

60,2

61,1

60,4

Mean

58,8

58,0

58,8

59,9

60,2

60,8

60,4

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7 Analysis of Test Results of Specimen

The results of the Specimen A1, related to the

measurement of horizontal and vertical

deformations with alongameter (Figure 18 and

Figure 19) and UPV testing are analyzed in the

following, to access the potential use of UPV testing

in the detection of sub-surface cracking in the

corresponding type of masonry walls. The analysis

of the results of the Specimen A1 test is carried out

in the following, according to their relevant phases,

and particularly with emphasis on the results of

UPV testing. Three phases of the test are

considered: load between 0 kN and 100 kN (2.47

MPa); load between 100 kN and 300 kN (7.40

MPa); and load between 300 kN (7.40 MPa) and the

final load of 470 kN (11.59 MPa).

Fig. 18: Results of deformations measurements in

the compression test of Specimen A1, for

increasing levels of vertical applied stress - vertical

deformations (dv1, dv2, dv3, dv4) in the left

vertical axis; horizontal deformations (dh1, dh2) in

the right vertical axis

The results of the measurement of deformations

in Specimen A1 show that, after the initial phase of

the test (initial phase between 0 and 50 kN) until a

load of near 300 kN, the overall variation of

horizontal and vertical deformations corresponded,

respectively, to a gradual horizontal expansion and

vertical contraction of the specimen. These

measured deformations are presented in Figure 18

and Figure 19. These variations of the vertical and

horizontal measured deformations during the test of

Specimen A1 are relevant to help in the analysis of

the UPV testing results, and their detailed analysis is

developed in the following sub-chapters 7.1 to 7.3.

Fig. 19: Results of deformations measurements in

the compression test of Specimen A1, for

increasing levels of vertical applied stress -

horizontal deformations (dh1, dh2, dh3, dh4) in the

left vertical axis; vertical deformations (dv1, dv2)

in the right vertical axis

7.1 Range of Load between 0 kN and 100 kN

(2.47MPa)

In this phase of load between load zero and 100 kN

(2.47MPa), the vertical and horizontal deformations

did not reveal an appreciable change of values

(Figure 18 and Figure 19), and no significant signs

of visible surface cracking were detected. The

variation of the vertical deformations (dv1, dv2,

dv3, and dv4), in the test of Specimen A1, show an

initial phase of slight contraction of the specimen,

from load zero to 50 kN (1.23 MPa), with increasing

negative moderate values (Figure 18). That was

followed by a vertical expansion, from 50 kN (1.23

MPa) to 100 kN (2.47 MPa), with a reduction of the

negative values (expansion) and a positive value

being reached for 100 kN of load (Figure 18), in the

particular case of dv2 measurement (left side of face

A, in the upper course of bricks).

For this range of load between load zero and

100 kN, horizontal deformations in the upper

course, dh1 and dh2 (Figure 19), show increasing

positive values (expansion), since the start of the

test. In the lower course, dh3 (A5-A6: right side of

face A) only show increasing positive values until a

50 kN of load, after which it reduced the positive

value (contraction). For a load of 50 kN and 100 kN,

dh4 registered a constant positive low value

(expansion), since the start of the test until a 50 kN

of load (Figure 19).

The application of UPV testing in this phase of

the test of Specimen A1 reveals an acceptable

correlation between mean time and the distance of

measurement in the upper course, U1 to U5 (mean

time of U1-U2, U1-U3, U1-U4, U1-U5), for the

readings made in the start of the test. These

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readings were made after the discharge of 0 kN of

load (Figure 20a); the first load step of 50 kN

(Figure 20b); and the load step of 100 kN (Figure

20c). The correspondent correlation for the lower

course was also acceptable with the exception of the

meantime of U6 to U9 related to the readings made

in the first load step of 50 kN (Figure 18b) due to

the significant deviation of U6-U7 reading (distance

of 300 mm – reading that include the central vertical

joint – Figure 5). In the horizontal deformations

measurements h3 and h4, which were made in the

zone common to the U6-U7 reading (lower course),

it was detected, at 50 kN of load, a contraction that

also constitutes some type of deviation face to the

others zones that were in expansion.

a) U1-U5: Applied vertical load = 0 kN

b) U1-U5: Applied vertical load = 50 kN (1.23 MPa)

c) U1-U5: Applied vertical load = 100 kN (2.47 MPa)

Fig. 20: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U1-U2 (distance of 100 mm); U1-U3 (200 mm);

U1-U4 (300 mm); and U1-U5 (400 mm)), for levels

of 0 kN, 50 kN and 100 kN of vertical applied stress

in the compression test of Specimen A1

a) U6-U9 - Applied vertical load = 0 kN

b) U6-U9 - Applied vertical load = 50 kN (1.23

MPa)

c) U6-U9 - Applied vertical load = 100 kN (2.47 MPa)

Fig. 21: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U6-U7 (distance of 100 mm); U6-U8 (300 mm); and

U6-U9 (400 mm)), for levels of 0 kN, 50 kN and

100 kN of vertical applied stress in the compression

test of Specimen A1

Concerning the UPV testing, in this phase of test,

with the application of the first load step of 50 kN

(1.23 MPa), the ultrasound velocity (direct method),

registered a slight change in relation to that

registered for 0 kN of load (Figure 21, Figure 22,

Figure 23, Figure 24 and Figure 25). A decrease in

U1-U1, U4-U4, U5-U5, U7-U7 and U8-U8 readings

and an increase in U2-U2, U6-U6, and U9-U9

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readings was registered. That type of slight change,

with no dominant trend in variation of the

ultrasound velocity, is considered not relevant in

this initial phase of load, where the effects of

accommodation of the specimen to the initial load

could be relevant. In the subsequent step load of 100

kN (2.47 MPa), there was a slight decrease of

ultrasound velocity in all readings, which could

indicate that the effects of vertical expansion

occurred between these two steps of load (50 kN-

100 kN) did not change significantly the wave

transmission across the thickness of the specimen.

The ultrasound velocity in the direct method, in

this phase of load, had light decrease of values for

50 kN and 100 kN in relation to the value for 0 kN,

indicating a minor change of the internal material

structure of the specimen. In respect of values of the

calculated ultrasound velocity in the face A (indirect

method), with the application of the first load step of

50 kN (1.23 MPa), there was an appreciable

decrease of the ultrasound velocity measured after

discharge of that load, relatively to the

correspondent value for 0 kN. That decrease was

registered for all the readings, except for U6-U7 (as

referred before this zone was in contraction, in

opposite to other zones of the specimen that were in

expansion) and U6-U9 readings. During this range

of load between 0 kN and 100 kN, no signs of

surface cracking were detected in the specimen.

Fig. 22: Results of UPV testing in the compression

test of Specimen A1, in terms of

Meantime/Distance of measurement (Indirect

method, Mean time of 4 readings U1- U2 (100

mm); U1-U3 (200 mm); U1-U4 (300 mm); U1-U5

(400 mm))

Fig. 23: Ultrasound velocity (direct method) for

increasing levels of vertical applied stress in the

compression test of Specimen A1

Fig. 24: Ultrasound velocity (indirect method:

U1/U5 and direct method: U1-U1, U5-U5) in the

compression test of Specimen A1

Fig. 25: Mean ultrasound velocity (indirect

method: U6/U9 and direct method: U6-U6, U8-U8

U9-U9 ) in the compression test of Specimen A1

7.2 Range of Load between 100 kN (2.47

MPa) and 300 kN (7.40 MPa)

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After discharge of a load level of 200 kN (4.93

MPa), the registered vertical deformations dv1, dv2

and dv3 show negative values associated to

contraction (for load 100 kN (2.47 MPa), these

deformations values were positive), while dv4

increased their positive value (expansion). Between

the levels of load of 200 kN (4.93 MPa) and of 300

kN (7.40 MPa), vertical deformations dv1, dv2 and

dv3 follow the increase of negative values

(contraction), especially deformation dv3 which

show a stronger increase, meanwhile vertical

deformation dv4 reduced their positive value

(contraction) and reached a negative value (Figure

18).

For this range of load between 100 kN and 300

kN, horizontal deformations in the upper and lower

course, (Figure 19), show increase positive values

(expansion), although especially moderate in case of

lower course when compared with that of upper

course, which suggests that micro sub-surface

cracking in the face A of the Specimen was

growing. That micro sub-surface cracking could be

spreading in the face A, especially in the upper

course, although still not very relevant and not

clearly visible.

a) U1-U5: Applied vertical load = 200 kN

b) U1-U5: Applied vertical load = 300 kN

Fig. 26: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U1-U2 (distance of 100 mm); U1-U3 (200 mm);

U1-U4 (300 mm); and U1-U5 (400 mm)), for levels

of 200 kN and 300 kN of vertical applied stress in

the compression test of Specimen A1

a) U6-U9 - Applied vertical load = 200 kN

b) U6-U9 - Applied vertical load = 300 kN

Fig. 27: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U6-U7 (distance of 100 mm); U6-U8 (300 mm); and

U6-U9 (400 mm)), for levels of 200 kN and 300 kN

of vertical applied stress in the compression test of

Specimen A1

About the UPV testing, in this phase of the test

of Specimen A1, the correlation between mean time

and the distance of measurement in the upper

course, U1 to U5, was not as straight as in the

previous phase (Figure 10). That correlation refers

to the mean time of U1-U2, U1-U3, U1-U4, and U1-

U5: correlation for 200 kN and 300 kN, respectively

in Figure 26a and Figure 26b. That could be due to

alterations of surface integrity related to early micro

sub-surface cracking in the face A of specimen A1.

That agrees with the above indication, revealed by

horizontal deformations measurements in the upper

course, of a micro sub-surface cracking upsurge in

this phase of load.

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The correspondent correlation for the lower

course (U6 to U9) was better than that obtained for

upper course, either for 200 kN and for 300 kN

(respectively in Figure 27a and Figure 27b). That

corroborates with the results of the moderate

horizontal deformations measurements h3 and h4, in

this loading phase, which were made in the zone

common to the U6-U9 reading.

The values of ultrasound velocity (direct

method), in this phase of load of the Specimen A1

test, generally, decreased relatively to the previous

values. The exception is the U6-U6´ reading (for

200 kN had an increase followed by a decrease for

300 kN; and U7-U7´ (for 200 kN the value of 100

kN of load maintained, followed by an increase for

300 kN). That increase was notorious, especially

after 200 kN, which is a sign that substantial change

of the internal material structure of the specimen

was in course in this phase of load, above 200 kN.

In respect of values of mean ultrasound velocity

in the face A (indirect method), the readings for the

load of 200 kN, with the exception of U1-U4

reading, registered a considerable decrease in

relation to the previous readings (for 100 kN of

load). That could be associated to a substantial

change in the surface integrity related to early micro

sub-surface cracking in face A.

7.3 Range of Load between 300 kN (7.40

MPa) and Final Load of 470 kN (11.59 MPa)

Between the level of load of 300 kN (7.40 MPa) and

of 400 kN (9.86 MPa), the registered vertical

deformations, dv2, dv3 and dv4, show increasing

negative values associated to contraction (especially

dv4, which show a stronger increase - Figure 18),

while dv1 reduced their negative value (expansion).

Horizontal deformations in the upper and lower

course, in this phase of load (Figure 19), follow the

increase of positive values (expansion) of the

previous phase, particularly accentuated in case of

upper course when compared with that of lower

course (dh3 had a moderate increase). That could

indicate a significant process of sub-surface

cracking of the bricks in the face A of the Specimen,

especially of their upper part. That part of the

specimen, at the end of the test, showed more signs

of extensive surface cracking (Figure 11, Figure 12,

Figure 13 and Figure 14), mainly in the left upper

part of face A (and right upper part of Face B).

In the US measurements of Specimen A1 test,

for 400 kN of load, the correlation between mean

time and the distance of measurement, in the upper

course, was solely correspondent to the readings

from U1 to U4 (mean time of U1-U2, U1-U3, U1-

U4: correlation in Figure 28). That was due the

difficulty of obtaining the U1-U5 reading, which

restricted the full application, in the left and central

part of Face A, of the US readings. Although

limited to U1 to U4, that correlation can be

considered satisfactory. The correspondent

correlation for the lower course was possible from

U6 to U9, but was not as fair as the previous one

(Figure 29), which could be in correspondence with

the results of the moderate horizontal deformations

measurements h3 (common zone to the U6-U9

reading), when compared to the h4 measurement.

a) U1-U5: Applied vertical load = 400 kN

Fig. 28: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U1-U2 (distance of 100 mm); U1-U3 (200 mm);

U1-U4 (300 mm); and U1-U5 (400 mm)), for levels

of 400 kN of vertical applied stress in the

compression test of Specimen A1

a) U6-U9 - Applied vertical load = 400 kN

Fig. 29: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U6-U7 (distance of 100 mm); U6-U8 (300 mm); and

U6-U9 (400 mm)), for levels of 400 kN of vertical

applied stress in the compression test of Specimen

The values of ultrasound velocity (direct

method), in this phase of load of the Specimen A1

test generally decreased, with the exception of U4-

U4´ and U6-U6´. That increase was particularly

relevant for U1-U1´ and U2-U2´, which is a sign

that extensive surface cracking of the upper left part

of the face A of the Specimen was in course which

was evident at the end of the test (Figure 10 and

Figure 11).

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The values of mean ultrasound velocity in the

face A (indirect method), namely the reading from

U1 to U5, for the load of 400 kN, showed a

considerable decrease in relation to the previous

reading (for 300 kN of load). The exception was

U1-U4 and U6-U8 readings, which had an increase

of mean US velocity. That agrees with the findings

of the direct method, that extensive surface cracking

of the specimen was in course, especially in the

upper left part of the face A of the Specimen. At the

end of the test, the situation of extensive surface

cracking of the upper left part of face A of

Specimen A1 was fully revealed (Figure 11).

8 Analysis of Test Results of Specimen

The results of the Specimen A2, related to the

measurement of horizontal and vertical

deformations with alongameter and ultrasound tests

are analyzed in the following, according to their

relevant phases, particularly with emphasis on the

results of UPV testing, aiming the access of their

potential use in the detection of sub-surface and

surface cracking. Three phases of the test, similarly

as made for specimen A1, were here considered:

load between 0 kN and 100 kN (1.07 MPa); load

between 100 kN (1.07 MPa) and 300 kN (3.22

MPa); and load between 300 kN (3.22 MPa) and the

final load of 490 kN (5.26 MPa). The results of the

measurement of vertical deformations in Specimen

A2 show that, during the test, until a load of near

400 kN (4.30 MPa), the overall variation

corresponded to a gradual vertical contraction of the

specimen.

These vertical and horizontal measured

deformations during the test of the specimen A2 are

presented in the Figure 30 and Figure 31, and are

relevant to help in the analysis of the UPV testing

results. Their detailed analysis is developed in the

following sub-chapters 8.1 to 8.3.

Fig. 30: Results of deformations measurements in

the compression test of Specimen A2, for

increasing levels of vertical applied stress - vertical

deformations (dv1, dv2, dv3, dv4) in the left

vertical axis; horizontal deformations (dh1, dh2) in

the right vertical axis

Fig. 31: Results of deformations measurements in

the compression test of Specimen A2, for

increasing levels of vertical applied stress -

horizontal deformations (dh1, dh2, dh3, dh4) in the

left vertical axis; vertical deformations (dv1, dv2)

in the right vertical axis

8.1 Range of Load between 0 kN and 100 kN

(1.07 MPa)

For a load level of 100 kN (1.07 MPa), the

registered vertical deformations dv1, dv2, dv3, and

dv4 show negative values associated with

contraction (Figure 30). For this range of load

between load zero and 100 kN, horizontal

deformation in the upper course, dh1, and the lower

course, dh3 (Figure 31), show increasing positive

values (expansion), since the start of the test.

The UPV testing results in this phase of the test

of Specimen A2 reveal an acceptable correlation

between mean time and the distance of

measurement in the upper course, U1 to U5, for the

readings made before the start of the test (0 kN of

load - Figure 32a); in first load step of 50 kN

(Figure 32b); and the load step of 100 kN (Figure

32c), indicating a constant decrease of ultrasound

velocity. The correspondent correlation for the

lower course, U6 to U9, was also acceptable (Figure

33). With respect to the results of UPV testing in

this phase of the load until the step load of 100 kN

(1.07 MPa), there was not a clear tendency for the

evolution of ultrasound velocity in the readings of

the direct method and indirect method (Figure 34,

Figure 35, Figure 36 and Figure 37).

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a) U1-U5: Applied vertical load = 0 kN

b) U1-U5: Applied vertical load = 50 kN (1.23 MPa)

c) U1-U5: Applied vertical load = 100 kN (2.47 -MPa)

Fig. 32: Correlation between mean time and

distance of measurement in UPV testing (indirect

method: U1-U2 (distance of 100 mm); U1-U3 (200

mm); U1-U4 (300 mm); and U1-U5 (400 mm)), for

levels of 0 kN, 50 kN and 100 kN of vertical applied

stress in the compression test of Specimen A2

a) U6-U9 - Applied vertical load = 0 kN

b) U6-U9 - Applied vertical load = 50 kN (1.23 MPa)

c) U6-U9 - Applied vertical load = 100 kN (2.47 MPa)

Fig. 33: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U6-U7 (distance of 100 mm); U6-U8 (300 mm); and

U6-U9 (400 mm)), for levels of 0 kN, 50 kN and

100 kN of vertical applied stress in the compression

test of Specimen A2

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Fig. 34: Results of UPV testing in the compression

test of Specimen A2, in terms of Mean

time/Distance of measurement (Indirect method,

Mean time of 4 readings U1- U2 (100 mm); U1-U3

(200 mm); U1-U4 (300 mm); U1-U5 (400 mm)

Fig. 35: Ultrasound velocity (direct method) for

increasing levels of vertical applied stress in the

compression test of Specimen A2

Fig. 36: Ultrasound velocity (indirect method:

U1/U5 and direct method: U1-U1, U5-U5) in the

compression test of Specimen A2

Fig. 37: Mean ultrasound velocity (indirect

method: U6/U9 and direct method: U6-U6, U8-U8

U9-U9 ) in the compression test of Specimen A2

8.2 Range of Load between 100 kN (1.07

MPa) and 300 kN (3.22 MPa)

Between the levels of the load of 100 kN (1.07

MPa) and of 300 kN (3.22 MPa), vertical

deformations dv1, dv2, and dv3 follow the increase

of negative values (contraction). The horizontal

deformations in the upper course, dh1, and lower

course, dh3, (Figure 30 and Figure 31), show a

constant increase of positive values (expansion),

which suggests that micro sub-surface cracking in

the face A (left part) of the Specimen A2 was

growing in this phase of the test.

The UPV testing results in this phase of the test

of Specimen A2 reveal fair correlation between

mean time and the distance of measurement in the

upper course, U1 to U5, for the readings made in the

load step of 200 kN (Figure 38a) and load step of

300 kN (Figure 38b), indicating a constant decrease

of ultrasound velocity. The correspondent

correlation for the lower course, U6 to U9, was not

so fair (Figure 39) indicating that some alterations in

the integrity of the specimen were occurring. The

values of ultrasound velocity (direct method and

indirect method), in this phase of load of the

Specimen A2 test, generally, decreased relatively to

the previous values (Figure 34, Figure 35, Figure 36

and Figure 37) presumably indicating the onset and

progression of sub-surface cracking of the

specimen.

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a) U1-U5: Applied vertical load = 200 kN

b) U1-U5: Applied vertical load = 300 kN

Fig. 38: Correlation between mean time and distance

of measurement in UPV testing (indirect method:

U1-U2 (distance of 100 mm); U1-U3 (200 mm);

U1-U4 (300 mm); and U1-U5 (400 mm)), for levels

of 200 kN and 300 kN of vertical applied stress in

the compression test of Specimen A2

a) -U6-U9 - Applied vertical load = 200 kN

b) U6-U9 - Applied vertical load = 300 kN

Fig. 39: Correlation between mean time and

distance of measurement in UPV testing (indirect

method: U6-U7 (distance of 100 mm); U6-U8 (300

mm); and U6-U9 (400 mm)), for levels of 200 kN

and 300 kN of vertical applied stress in the

compression test of Specimen A2

8.3 Range of Load between 300 kN (3.22

MPa) and Final Load of 470 kN (5.26 MPa)

Between the level of load of 300 kN (3.22 MPa) and

final load of 470 kN (5.26 MPa), the registered

vertical deformations, dv1, dv2, dv3 and dv4

(Figure 30), progress their contraction till the load

level of 400 kN (4.30 MPa), after which decreasing

negative values were recorded, associated probably

to sub-surface cracking of the blocks and mortar

joints in face A. Horizontal deformations in the

upper and lower course, in this phase of load, follow

the increase of positive values (expansion) of the

previous phase till the load of 400 kN (Figure 31),

after which changed and reduced the positive

values, indicating possibly a process of slight sub-

surface cracking of the blocks and mortar joints in

the face A of the Specimen 2.

In the US measurements of Specimen A1 test,

for 400 kN of load, the correlation between mean

time and the distance of measurement, in the upper

course, was correspondent to the readings from U1

to U5 (mean time of U1-U2, U1-U3, U1-U4, U1-

U5: correlation in Figure 40), which can be

considered satisfactory. The correspondent

correlation for the lower course, from U6 to U9

(Figure 41), can be also considered satisfactory.

Concerning of values of mean ultrasound velocity in

the face A (direct method and indirect method), the

readings for the load of 470 kN, generally,

registered a decrease in relation to the previous

readings which could be associated to slight

cracking of blocks and mortar joints of the face A.

a) U1-U5: Applied vertical load = 400 kN

Fig. 40: Correlation between mean time and

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distance of measurement in UPV testing (indirect

method: U1-U2 (distance of 100 mm); U1-U3 (200

mm); U1-U4 (300 mm); and U1-U5 (400 mm)), for

levels of 400 kN of vertical applied stress in the

compression test of Specimen A2

a) U6-U9 - Applied vertical load = 400 kN

Fig. 41: Correlation between mean time and

distance of measurement in UPV testing (indirect

method: U6-U7 (distance of 100 mm); U6-U8 (300

mm); and U6-U9 (400 mm)), for levels of 400 kN of

vertical applied stress in the compression test of

Specimen A2

9 Global Analyses of the Results of the

Tests of Specimen A1 and of Specimen

Based on the results of the measurement of

deformations with alongameter and the results of the

UPV testing, in compression tests of Specimen A1

and Specimen A2, it can be inferred a general

tendency, with the increase of loading in these tests,

to a gradual horizontal expansion (an increase of

positive values) and vertical contraction (an increase

of negative values) of the specimens (Figure 42 and

Figure 43) and a reduction of ultrasound velocity

(direct and indirect measurements). An almost

constant decrease of the values of the ultrasound

velocity (indirect measurements (U1-U2), and direct

measurement (U1-U1´)) appears to follow that

variation trend of horizontal/vertical deformation

measurements, for increasing levels of load (Figure

42 and Figure 43).

As an example of this trend, the results of the

tests of Specimens A1 and A2 reveal an almost

constant increase of the values of horizontal

measurements (dh1 and dh3), in the left part of Face

A (Figure 42 and Figure 43), of specimens, between

the level of load of 50 kN (1.23 MPa (A1) and 0.54

MPa (A2)) and 300 kN (7.40 MPa (A1) and 3.22

MPa (A2)), which generally are higher (in absolute

values) than the vertical measurements (more

expansion in horizontal direction than contraction in

vertical direction, at the left side of face A of the

specimens). The values of dh1 (path with one

vertical mortar joint, in the upper part of the left side

of face A of both specimens) are higher or

approximately equal, relative to the dh3 values (path

with no mortar joint), which suggests that the

influence of the presence of vertical mortar joint is

appreciable in the deformation behavior of the

specimen, and that distinctive behavior was also

reflected in the variation of ultrasound velocity.

Ultrasound velocity of the indirect measurements

U1-U2, in that upper part, is generally lower than

the indirect measurements U6-U7, in the

correspondent inferior part, and, probably, that

could be related to the decrease of the propagation

velocities of longitudinal waves, in case of presence

of a mortar joint linking the material of the masonry

units (bricks (A1) or blocks (A2)), and the amplitude

of these waves and the speed of propagation of

ultrasound could be significantly influenced by the

discontinuity / in-homogeneity represented by the

mortar joint.

Moreover, the presence of vertical mortar joints

can change the local pattern of stress and lead to the

up-surge of micro cracking in the mortar joints and

masonry units. The measured horizontal

deformations, for increasing load levels, revealed

that could be sensible (more than the measured

vertical deformations) to the onset and progression

of cracking phenomena observed during the test of

the specimens, which corresponded in the same

loading steps, to significant alterations of values of

ultrasound velocity in the UPV testing. It appears

that the behavior revealed by horizontal

measurements, for load levels above 200 kN, when

the cracking is intensified significantly in both tests

of the specimens, could also be reflected in the UPV

testing. Therefore, the alterations of the ultrasound

velocity in the UPV testing on Specimen A1 and A2

can allow the presumption that, with indirect and

direct measurement of the ultrasound velocity, it can

be possible the detection of the onset and

progression of the micro sub-surface cracking.

In conclusion, the critical discussion made in

this section regarding the results tabulated in the

previous sections appears to make it fully

understandable that the main intention here is to

claim and highlight that, with the measurement of

ultrasound velocity in the masonry specimens, it

could be possible the detection of the onset and

progression of the micro sub-surface cracking

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Fig. 42: Results of deformations measurements in

the compression test of Specimen A1, for

increasing levels of vertical applied stress -

horizontal (dh1, dh3) and vertical (dv1)

deformations in the left vertical axis; Mean

ultrasound velocity (indirect method: U1/U3, U6-

U7 and direct method: U1-U1) in the right vertical

axis

Fig. 43: Results of deformations measurements in

the compression test of Specimen A2, for

increasing levels of vertical applied stress -

horizontal (dh1, dh2) and vertical (dv1)

deformations in the left vertical axis; Mean

ultrasound velocity (indirect method: U1/U3, U6-

U7and direct method: U1-U1) in the right vertical

axis

10 Conditioning Aspects of the Use

of UPV Testing to Access Durability

Problems of Building Envelope

Considering the type of Masonry

Cracking and Climate Factors

URM infill walls of envelope of RCS buildings are

usually subjected to aggressive actions, especially

due to the climate factors, which can lead to

appreciable degradation of these URM infill walls.

That can lead, particularly, to the reduction of

durability of the building envelope, associated

especially to their degradation, in result of cracking

and associated surface erosion of URM infill walls,

as well as, water penetration in these walls due to

wind-driven rain (WDR), particularly across that

cracking. Furthermore, that cracking and associated

water penetration, subsequently, can severely

worsen their weathering characteristics due,

particularly to water infiltration/humidity inside the

building, and may lead to considerable weakening

of the structural building elements, as their

deterioration progress, especially, due to wetting.

Therefore, in the scope, of preventive and/or

corrective actions along the service life of the

buildings, it is important the monitoring of the

durability anomalies, particularly related to cracking

of URM infill walls of the envelope of buildings,

which can occur along their service life, especially

in the case of heritage buildings. As revealed in the

previous sections (section 4 to 9), UPV testing could

possibly help in the evaluation of the state of

conservation of URM infill walls especially in the

detection of sub-surface cracks in these walls. UPV

testing can possibly be used, besides monitoring of

the cracks before an intervention of repair of

previous cracking in the envelope, also for a type of

monitoring, along building service life, the

durability problems in the URM infill walls,

particularly related to their cracking and water

penetration thorough that cracking. In order to use

UPV testing in detection and monitoring of cracks,

as well as in the access of the risk of water

penetration thorough that cracking, it could be

useful to classify the main typologies of cracking to

be analyzed by UPV testing, as well as the relevant

conditions of exposure to WDR of building

envelope.

10.1 Main Characteristics of Cracking

with Interest for the Assessment of the

Potential Use of UPV Testing for Their

Detection and Monitoring

Cracking is a common defect that occurs in facade

cladding and it is observed that cracking defects are

frequently associated with mechanical actions, [13].

Loads applied to the building envelope can lead to

deformations that may cause significant stress that

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affects, particularly URM infill walls, [1], [4], as

well as other confining construction elements and

components. The stresses in URM infill walls,

which lead to its cracking, can be the result of axial

forces (tension or compression) and of applied shear

forces. When normal or shear stress values are

larger than, respectively, the normal or shear

strength of the material, that create the essential

conditions for the formation of a crack, here defined

as a physical discontinuity on an element or

material, [14].

Cracks characterization can be based on its

width, orientation, location, or their extension on the

facade. For the assessment of potential degradation

of the URM infill walls, it is important to define the

characteristics of the cracking, which can lead to

subsequent detachment and/or local degradation.

That assessment can orientate the effort of

monitoring anomalies related to cracking, which are

essentially related to the following main

characteristics: crack orientation; width of the crack;

crack time evolution; crack configuration; a group

of cracks of the same type; and crack depth.

These main characteristics of cracks are

presented in Table 13 (Appendix), for the

assessment of the interest of potential use of UPV

testing for their detection and monitoring. In Table

13 (Appendix), a possible classification of the

cracks, [15], [16], according to their width is

presented: Negligible (0-0.1 mm); Thin (0.1 mm – 1

mm); Medium (2 mm – 3 mm); Large (greater than

3mm). In that Table 13 (Appendix), it is suggested

the estimated potential interest for the use of UPV

for the assessment of the state of conservation of

URM infill walls in relation to these main

characteristics of the cracking and of other types of

anomalies associated to cracking, assuming different

levels of interest: Nupv – Null estimated potential

interest for the use of UPV testing; Lupv Low

estimated potential interest for the use of UPV

testing; Mupv – Medium estimated potential interest

for the use of UPV testing; Hupv – High estimated

potential interest for the use of UPV testing. That

estimation involves the estimation of the importance

of the type of cracks in the process of decision about

the use of UPV testing, aiming at the definition of

corrective intervention.

10.2 Assessment of Potential Use of UPV

Testing for Monitoring the Presence of

Humidity in Walls and for the Evaluation of

the Risk of Water Penetration through Their

Cracking

As referred above (in section 3), UPV testing is an

interesting NDT method that can be explored to

access their potential use for detection of significant

variations in moisture content of a URM infill wall.

For that detection, it is important to identify the

conditioning aspects of the use of UPV testing for

that purpose, which should be, especially, related to

the relevance of water penetration across the

existing cracking, and the consequent risk of

degradation of the building facade, particularly of

their aesthetic aspect and of the infiltration of

humidity inside the building. Therefore, it is

important to identify the critical aspects the of

transfer of moisture within the walls, particularly

related to water penetration inside the walls due to

rainwater. The mechanisms of transfer of moisture

within the walls are very complex and are mainly

related to physical processes of absorption,

condensation and capillarity in the constituent

materials of the walls, which appears to be not

easily identified by UPV testing.

Precipitation accompanied by intense wind is

the principal agent accountable for the wetting of

building envelopes.

Degradation of building vertical envelope due to

micro-cracking of sub-surface and surface of URM

infill wall (associated for example to temperature

and moisture cyclic variations) can lead to a need of

a survey of building envelope, with the use of NDT

methods, particularly UPV testing, aiming possible

maintenance and repair actions. Micro-cracking

upsurge (for example associated with excessive

thermal strain) at the external surfaces of the URM

infill walls and concrete structure elements can

modify the permeability of these external surfaces to

the rain with a horizontal velocity component given

by the wind, which is called wind-driven rain

(WDR). The use of UPV testing could be made

when these cracks are partially or completely filled

with water after a precipitation period (rain) and/or

could be made later, after that precipitation period,

when the wall is almost dried particularly the

cracks, eventually allowing to compare the results of

both readings of UPV testing in different periods.

Among the climatic hazards that are more

influential on buildings, particularly heritage

buildings, wind-driven rain (WDR) is found to be

especially detrimental, as it may cause surface

erosion and facilitate moisture penetration and bio-

deterioration, [17]. Erosion here means the

detachment of material from the masonry of the

building facade due to the physical impingement of

WDR. Water penetration in the building envelope

essentially can occur due to significant absorption of

precipitation water (l/m2) by the vertical surface due

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to wind-driven rain (WDR). Semi-empirical

equations have been proposed in the literature to

compute the amount of wind-driven rain (WDR)

incident on a wall.

The amount of WDR, for a selected rainy

period, could be calculated using a semi-empirical

approach of the ISO model, [18], which is based on

the physical correlation of WDR, wind speed, and

horizontal rain (Rwdr = α. U10 . (Rℎ) 0.88 . cos θ -

where α is the WDR coefficient, U10 is the wind

speed measured 10 m above the ground (m/s), Rh is

the horizontal rainfall intensity (mm) and θ is the

angle between the wind direction and the normal to

the building facade; α, is computed as α

=0.222.CR.CT.O.W - where CR and CT are the

roughness and topography coefficients, respectively,

while O is the obstruction factor and W is the wall

factor. CR is calculated on the basis of height above

the ground (z) and the minimum height (zmin)

parameters).

In another approach the WDR load, IWDR

(kg/m2s), at building facades, can be obtained by

multiplying the horizontal rainfall intensity Ih

(kg/m2 s) by a parameter η (IWDR=Ih× η (θ, Uref, Ih),

where η is a function of the angle θ (°) between

reference wind direction and orientation of the wall,

reference wind speed Uref (m/s) and Ih, all obtained

from meteorological data, [19], [20]. That parameter

η could be obtained from measurements, empirical

relations, or numerical simulations. Moisture

presence caused by WDR can negatively affect the

durability of building facades due to degradation of

surface material, cracking (especially relevant for

larger crack width, and interior damage, [17]. And

considering some of the variables involved in the

computation of WDR, particularly related to

geographical localization of the buildings, it could

be inferred that the local implantation of the

building probably should condition the potential use

of UPV testing, being more useful in case of severe

environmental conditions that propitiates the

formation of cracking, as well as water penetration

through that cracking.

In the evaluation of the risk of water penetration

across the existing cracking in the envelope of a

building, specifically should be assessed the extent

of facade area affected by the cracks, the cracking

patterns and the maximum width of the cracks.

If there are only very slight cracks in the URM

infill wall (crack width less than 0.1 mm), the sheet

of constant and uniform runoff water passes through

them without penetrating them, and the portion to be

absorbed by the walls is foremost due to the

capillarity of the constituent materials of the wall. In

these cases, the wind associated with the incident

rain acts on the wall creating a pressure difference

between the wall and the sheet of runoff water, [16].

Thus, this sheet is, by this effect, forced to penetrate

the wall; the most significant portion of the water

migration to the interior of the wall is then

processed through cracks with significant crack

width (greater than 0.1 mm), through which the

sheet of runoff water passes in its downward

trajectory. These cracks are most often located in

the area of vertical and horizontal mortar joints. It

should be noted that, at the end of the precipitation

period (rain), a considerable part of the moisture

absorbed by the surface layer of the wall evaporates

through a drying process, the speed of which

depends on the climatic conditions (temperature,

wind, relative humidity of ambient air). In case of

elements of the building envelope of solid material

such as solid bricks (non-perforated bricks) or

concrete, generally the presence of humidity in the

very small voids of the solid material, possibly,

increases the speed of propagation of ultrasound in

relation to the correspondent values of the dry

material, considering that the path of longitudinal

waves has less alterations that in case of dry

material. And, regarding the use of UPV testing for

detection of cracks in these solid materials, the

presence of humidity in the cracks can lead to

misleading results in what concern the detection of

these cracks and the estimation of their depth.

Therefore, it is important to study more deeply the

applicability of UPV testing for the accessing the

cracks filled with humidity.

In case of building vertical envelope with

absence of defects or pores larger than 1 mm, the

pressure difference across the facade (difference of

indoor and outdoor wind pressure) is the most

sensitive factor related to water penetration,

regardless of the existing water supply, [21].

However, in case of building vertical envelope with

defects, pores, or larger cracks (>5 mm), water is

able to penetrate the facade, even without high wind

pressure. For facades with defects, pores, and cracks

of less than 1 mm, the influence of wind pressure in

water penetration is dominant, while, in the case of

damaged or poorly maintained facades, the major

influence in the penetration process is the amount of

water falling on the facade, [21]. Experimental

studies, [16] indicated that, for values of incident

water flow (“iwf”) in walls ranging between 100 l/h

and 240 l/h, the infiltrated water flow (“fiw”) in

walls could tend to be higher in horizontal mortar

joints (“hmj”), than in vertical mortar joints (“vmj”).

In vertical joints “fiw” could be, likely, lower for a

crack width of 0,7 mm, when compared to a crack

width of 1 mm to 2 mm, which indicates that UPV

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testing should concentrate on monitoring walls with

cracks above 1 mm. Besides the referred trend, a

general tendency for the increase, with the rise of

differential pressure on the wall, of the ratio

between the infiltrated water flow and the incident

water flow in the wall (assuming a constant value of

240 l/h for “iwf”). And, for the case of “fiw”, it

could be expected that, for a crack width around 0,7

mm, a reduction of that ratio with increase of “iwf”

in walls, regardless of the values of differential

pressure acting on wall, also indicating the tendency

for a more dominant effect of “iwf” on “fiw”, when

compared to the effect of differential pressure on

“fiw”. It could be referred that, as an example, the

value of incident water flow (“iwf”) and of sob-

pressure in the wall could be around respectively,

2,3 l/m2 and 480 Pa, which approximately could

correspond to a value of precipitation of 140 mm/h,

accompanied by the wind speed of 100 km/h (27,8

m/s).

The previewed more intense rain and increase in

temperatures due to climate changes will accentuate

the adversity of present environmental conditions in

terms of water penetration through the cracking in

the walls. Therefore, it could be of convenience for

choosing different intensities (periodicity) of

monitoring the cracking in the URM infill walls

using UPV testing after an intervention of repair,

considering the scenarios correspondent to

assessments of projected future changes using

Representative Concentration Pathways (RCPs) that

can influence durability problems in buildings, [3].

A more intense monitoring could be advised for

scenario of high greenhouse gas emission, about

RCP 8.5, when compared to the monitoring that can

be advised for the scenario of low greenhouse gas

emission, Scenario A, about RCP 4.5, being the first

scenario (RCP 8.5), less favorable, supposed to lead

to predictable greater intensity of rain and higher

increase in temperature variations due to climate

changes, relatively to that previewed for RCP 4.5

scenario.

Taking into account the previous considerations

made in this sub-section, in Table 13 (Appendix), it

is suggested the estimated potential interest for the

use of UPV testing for monitoring the presence of

humidity in walls and for the evaluation of the risk

of water penetration through their cracking, in

parallel to what was suggested in sub-section 10.1,

about the main characteristics of the cracking.

11 Conclusion

An evaluation was here made of the potential use of

UPV testing in the monitoring of the degradation of

the URM infill walls and access their impact on the

durability of the RCS building envelope. The

degradation of URM infill walls of building facades

due, particularly, to cracking and to water

penetration associated to WDR (wind driven rain),

including climate change effects, was here

especially focused.

That assessment was made through the previous

analysis of the results of the application of UPV

testing for the detection of sub-surface and surface

cracking in compression tests of masonry

specimens. Based on the results of the measurement

of deformations with alongameter and the results of

the UPV testing, in the referred compression tests of

Specimen A1 and Specimen A2, it can be inferred a

general tendency, with the increase of loading in

these tests, to a gradual horizontal expansion

(increase of positive values) and vertical contraction

(increase of negative values) of the specimens, and a

reduction of ultrasound velocity (direct and indirect

measurements). An almost constant decrease of the

values of the ultrasound velocity (indirect

measurements, and direct measurement) appears to

follow that variation trend of horizontal/vertical

deformation measurements, for increasing levels of

load.

The results of the tests of Specimens A1 and

A2 reveal that the influence of the presence of

vertical mortar joint is appreciable in the

deformation behavior of the specimen, and that

distinctive behavior was reflected in the variation of

ultrasound velocity.

Moreover, the presence of vertical mortar joints

can change the local pattern of stress and lead to the

up-surge of micro cracking in the mortar joints and

masonry units. The measured horizontal

deformations, for increasing load levels, revealed

that could be sensible (more than the measured

vertical deformations) to the onset and progression

of cracking phenomena observed during the test of

the specimens, which corresponded in the same

loading steps, to significant alterations of values of

ultrasound velocity in the UPV testing. Therefore,

the alterations of the ultrasound velocity in the UPV

testing on Specimen A1 and A2 can allow the

presumption that, with indirect and direct

measurement of the ultrasound velocity, it can be

possible the detection of the onset and progression

of the micro sub-surface cracking.

Following that analysis of compression tests of

masonry specimens, an evaluation was made of the

conditioning aspects of the use of UPV testing to

access durability problems of the building envelope.

The main characteristics of cracking with interest

for the assessment of the potential use of UPV

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testing for their monitoring were generally

discussed. That assessment can orientate the effort

of monitoring anomalies related to cracking, which

are essentially related to their main characteristics.

Finally, an evaluation was made of the risk of

water penetration through the cracks, for potential

use of UPV testing in monitoring the presence of

humidity in the cracks. Moisture presence caused by

WDR can negatively affects the durability of

building facades due to degradation of surface

material, cracking (especially relevant for larger

crack width, interior damage. And considering some

of the variables involved in the computation of

WDR, particularly related to geographical

localisation of the buildings, it could be inferred that

the local implantation of the building probably

should condition the potential use of UPV testing,

being more useful in case of severe environmental

conditions that propitiates the formation of cracking,

as well as water penetration through that cracking.

Regarding the contributions of this work

concerning to previous works in literature, a

comprehensive analysis of the characteristics of

cracking, as well as the assessment of the risk of

water penetration through the cracks is considered

to have been suitably made in this paper, with

positive repercussions in terms of their better

knowledge. That knowledge could be useful, in

terms of the practical applicability for the

assessment of the potential use of UPV testing for

the monitoring of the cracks and water penetration

through the cracks.

Thus, it is admitted that the present paper can

provide, for future scientific research work, a

helpful reference for UPV testing, considering the

contribution of the paper in revealing the relation

between ultrasound velocity and the upsurge of

micro-cracking in masonry.

As possible future developments of this work, it

is recommendable that should be further studied,

deeply, the benefits and limitations of the use of

UPV testing for monitoring the degradation and

access the durability of URM infill walls of the

RCS building envelope, considering the type of

URM infill walls cracking and the climate factors.

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risk, indoor climate and energy consumption.

Energy Build., 41, 2009, pp. 101-110,

https://doi.org/10.1016/j.enbuild.2008.07.011

[20] Blocken, B.; Carmeliet, J., Spatial and

temporal distribution of wind-driven rain on

low-rise building. Wind and Structure,

Volume 5, Number 55, 2002, pp. 441-462.

https://doi.org/10.12989/was.2002.5.5.441

[21] Pérez-Bella, J. M.; Domínguez-Hernández, J.;

Rodríguez-Soria, B.; Coz-Díaz, J. J.; Cano-

Suñén, E., Combined use of wind-driven rain

and wind pressure to define water penetration

risk into building façades: The Spanish case.

Building and Environment, Volume 64, 2013,

pp. 46-56

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APPENDIX

Table 5. Results of ultrasound test on specimen A1 by indirect method, for each of the loading

steps of the compression test (Mean of three readings for each measurement between two points

- Mean ultrasound velocity (m/s))

Points

Dist.(a)

Mean ultrasound velocity (m/s)

0 kN/

0 MPa

50 /

1.23

100 /

2.47

200 /

4.93

300 /

7.40

400 /

9.86

U1-U2

100

1052

1015

997

716

1113

929

U1-U3

200

1003

789

774

756

628

U1-U4

300

980

680

679

863

465

571

U1-U5

400

1274

548

587

377

171

U6-U7

100

1260

1610

1265

1606

1795

1275

U6-U8

300

754

404

628

739

641

706

U6-U9

400

755

783

630

440

510

435

Table 6. Results of ultrasound test of specimen A1 by direct method for the load steps of the

compression test (Mean of three-time readings for each measurement between two points- Mean

ultrasound velocity (m/s))

Points

Dist.(a)

Mean ultrasound velocity (m/s)

0 kN/

0 MPa

50 /

1.23

100 /

2.47

200 /

4.93

300 /

7.40

400 /

9.86

U1-U1

150

1578

1573

1562

1422

1042

890

U2-U2

150

1714

1720

1705

1684

1660

1053

U4-U4

150

1772

1771

1756

1755

1732

1754

U5-U5

150

1685

1678

1657

1620

1573

1545

U6-U6

150

1718

1728

1708

1744

1703

1743

U7-U7

150

1715

1710

1718

1731

1717

U8-U8

150

1815

1797

1796

1783

1781

1772

U9-U9

150

1812

1836

1824

1821

1809

1804

Table 11. Results of ultrasound test on specimen A2 by indirect method, for each of the loading

steps of the compression test (Mean of three readings for each measurement between two points

- Mean ultrasound velocity (m/s))

Points

Dist.(a)

Mean ultrasound velocity (m/s)

0 kN/

0 MPa

50 /

0.54

100 /

1.07

200 /

2.15

300 /

3.22

400 /

4.30

U1-U2

100

1080

815

800

545

475

423

U1-U3

200

1095

1092

1067

874

762

570

U1-U4

300

1264

1257

1458

700

866

833

U1-U5

400

1369

1348

1620

774

1019

1040

U6-U7

100

2120

2024

2122

1081

1054

1040

U6-U8

300

2090

2091

2440

1202

1112

871

U6-U9

400

1805

1765

1774

741

573

809

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Table 12. Results of ultrasound test of specimen A2 by direct method for the load steps of the

compression test (Mean of three-time readings for each measurement between two points- Mean

ultrasound velocity (m/s))

Points

Dist.(a)

Mean ultrasound velocity (m/s)

0 kN/

0 MPa

50 /

0.54

100 /

1.07

200 /

2.15

300 /

3.22

400 /

4.30

U1-U1

150

2552

2561

2613

2607

2534

2493

U2-U2

150

2588

2514

2545

2551

2501

U4-U4

150

2585

2488

2592

2568

2528

U5-U5

150

2552

2508

2534

2479

2560

2538

U6-U6

150

2504

2528

2510

2467

2456

2444

U7-U7

150

2493

2542

2504

2454

2436

2386

U8-U8

150

2466

2508

2501

2417

2467

2419

U9-U9

150

2552

2520

2500

2496

2466

2423

After reaching the maximum load of 490 kN (Applied vertical stress of 5.26 MPa), with the

fragmentation of the base of specimen (Figure 8, Figure 9, Figure 10 and Figure 11), the test was

halted and the specimen was discharged.

Table 13. Potential use of UPV testing for assessment of cracking in URM infill walls

Classification

of the cracks

- Crack width

Cond

Par.

(1)

SA,

SB,

WTC

Main Characteristics of cracking in URM infill walls

Other types of anomalies

associated to cracking

Vertical,

horiz. or

inclined

crack

orient.

(2)

Width of the crack

(3)

Constant width (C);

Variable cracks (V);

Relative displacements

(R) -

Crack

evolution along

the time

(4)

Living cracks -

actives and cyclical

variable or not

(LC);

Dead cracks-

stabilised (DC)

Crack

configuration

(5)

Discrete cracking:

continuous/

discontinuous,

linear or erratic

cracks (D); Mesh/

Mapped cracking

(M)

Group

cracks

of the

same

type

Crack

depth

Spalling

/peeling /

exfoliation

Cracking

in the

interface

between

masonry

and

concrete

elements

Cracking

close to

openings

(windows

doors)

Negligible (0-

0.1 mm)

Mupv

Lupv

Mupv

Lupv

Mupv

Lupv

Mupv

Lupv

Mupv

WTC

Nupv

Thin (0.1 mm

– 1 mm)

Mupv

Lupv

Mupv

Lupv

Mupv

Lupv

Mupv

Lupv

Mupv

WTC

Lupv

Medium (1

mm – 3 mm)

Mupv

Lupv

Mupv

Lupv

Mupv

Lupv

Mupv

Lupv

WTC

Lupv

Mupv

Lupv

Large (>

3mm)

Mupv

Lupv

Mupv

Lupv

Mupv

Lupv

Nupv

Lupv

Nupv

Lupv

Nupv

Lupv

WTC

Mupv

Estimated potential interest for the use of UPV for the assessment of the state of conservation of masonry walls, aiming the

definition of corrective intervention:

 Nupv - Null estimated potential interest for the use of UPV testing;

 Lupv - Low estimated potential interest for the use of UPV testing;

 Mupv - Medium estimated potential interest for the use of UPV testing;

 Hupv - High estimated potential interest for the use of UPV testing

(1) Conditioning parameters - SB: Sub-surface cracks (Internal cracking across the masonry), flaws, and voids; SC: Superficial

cracks; WTC: water penetration through the cracking

(2) Vertical, horizontal, or inclined crack orientation

(3) Width of the crack: Constant width /stabilized cracks (C); variable cracks - active cracks and cyclical variable (V); Relative

displacements associated to the cracks (R) - Plane displacements/ Displacements along the masonry element in depth

(4) Crack evolution along the time: Living cracks - actives and cyclical variable or not (LC); Dead cracks- stabilized (DC)

(5) Crack configuration: Discrete cracking: continuous/ discontinuous, linear or erratic cracks (D); Mesh/ Mapped cracking (M)

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Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

José Dias had the ideas and was responsible for

formulation of overarching research goals and

aims of this paper; he was responsible for

conducting the research and for the development

of the methodology of the study; he has organized

the experiments referred in the sections 4 to 9,

and was responsible for their execution; he as

carried out the preparation, creation of the

published work.

Sources of Funding for Research Presented in

a Scientific Article or Scientific Article Itself

The Planned Research Programme of the

“National Laboratory of Civil Engineering”

(LNEC) has funded the present study.

Conflict of Interest

The author has no conflict of interest to declare

that is relevant to the content of this article.

Creative Commons Attribution License 4.0

(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

Creative Commons Attribution License 4.0

https://creativecommons.org/licenses/by/4.0/deed.

en_US

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