Systematization of common cracking patterns in buildings€¦ · Systematization of common cracking...

Systematization of common cracking patterns in buildings

Case studies

Sara Freitas Novais Ferreira de Almeida

Extended Abstract

Supervisors: Professora Doutora Inês dos Santos Flores Barbosa Colen

Professora Doutora Maria Cristina de Oliveira Matos Silva

May 2015

1

Abstract

The cracking phenomenon has been, over the years, one of the most common pathologies in buildings, concerning not only

the external façades but also the interior elements. This phenomenon occurs due to imperfect design or execution, or simply

due to accidental actions over which it’s almost impossible to predict their consequences.

This work intends to study the most common cracking patterns in buildings, through an inspection that will be conducted over

6 case studies. The analysis of these cases intends to give a practical application to what was referred in the literature review,

regarding cracking characteristics, cracking patterns and diagnosis of the main causes.

To conduct the inspection, it’s developed a methodology focused on the cracking phenomenon, which includes the elaboration

of an inspection sheet to gather data concerning the building and its pathologies.

The data analysis will allow to create a cracking patterns catalogue that intends to represent the patterns observed and its

main characteristics.

Keywords: Cracking patterns; Façades; Inspection; Diagnosis

1. Introduction

The cracking phenomenon has been, over the years, one

of the most common pathologies in buildings, concerning

not only the external façades but also the interior

elements. This phenomenon occurs due to imperfect

design or execution, or simply due to accidental actions

over which it’s almost impossible to predict their

consequences.

Characterizing cracks based on its width, orientation,

location or their extension on the façade can help to

diagnose the causes of their appearance. To understand

the cracking phenomenon completely, it’s important to

look for mechanisms (physical, chemical, among others)

that explain it. These mechanisms may need to be

continuously questioned or validated, until we come up

with a cause-effect relationship that justifies why the

cracks were formed. The quest for this relationship poses

the biggest obstacle when it comes to study this

phenomenon.

2. Cracking in buildings

2.1. Definition and general cracking conditions

Crack can be defined as a physical discontinuity on an

element or material. Structures have loads applied that

lead to displacements and volume variations, causing

stress that can affect all the building or its components

individually. Cracks appear when stress is bigger than the

strength of the material (BONSHOR, et al., 1996) and

(PAIVA, et al., 2006).

When it comes to buildings, cracking can take a double

role, as cause and effect, because it can be a secondary

effect of another pathology or can be the one leading to

other consequences (worst case scenario, it can lead to

the buildings collapse). Apart from the structural safety of

buildings, cracks should be limited for other reasons, per

example, the aesthetics or to maintain the durability of

constructions (BONSHOR, et al., 1996), (BONE, 1989)

and (VEIGA, 1998).

2.2. Elementary cracking mechanisms

As stated by (BONSHOR, et al., 1996), the stresses that

appear on the materials and lead to its cracking are normal

and shear stresses. These stresses are the result of axial

forces (traction or compression) and shear forces that are

applied, which create uniform stress distribution. To

calculate it, we can use Equation 1 and Equation 2:

𝜎 =𝑃

𝐴

𝜏 =𝐹

𝐴

Where:

𝜎 – normal stress (MPa); 𝜏 – shear stress (MPa); P – axial force (kN); F

– shear force (kN); A – area (m2)

Equation 2

Equation 1

2

The relative displacement of parallel sections causes

strain that can be extension or distortion according to the

axis in which the displacement occurs. In case of uniform

axial strain, stress can be calculated with the Equation 3:

𝜎 = 𝐸𝜀

Where:

𝜎 – normal stress (kPa); E – modulus of elasticity (MPa); 𝜀 – strain (m/m)

The volume range of the materials is the result of its free

expansion or shrinkage. In case this range is restricted,

there will appear stress on the material. In the special case

of temperature difference, this stress can be obtain using

the Equation 4:

𝜎 = 𝐸 𝛼𝑡 ∆𝑇

Where:

𝜎 – normal stress (kPa); E – modulus of elasticity (MPa); 𝛼𝑡– coefficient

of linear thermal extension (m/m ºC); ∆𝑇 – temperature difference (ºC)

2.3. Types of cracking

2.3.1. According to its width

Cracks can be classified according to their width.

(GASPAR, et al., 2006) considers 5 levels:

- Level 0 (<0,1 mm): Hair strand;

- Level 1 (0,1-0,25 mm): Visibility threshold;

- Level 2 (0,25-1 mm): Visible;

- Level 3 (1-2 mm): Well defined;

- Level 4 (>2 mm): Structural effects.

2.3.2. According to its evolution

According to (LAPA, 2008) and (SILVA, 1998), cracks can

be passive (also called dead or stabilized) or active (also

called alive or not stabilized). What distinguishes these

two types of cracks it’s their movement, i.e., in case there’s

no movement or this can be considered negligible, then

the crack is passive.

When it comes to active cracks, it’s important to

distinguish them according to their evolution. These type

of cracks can suffer aggravation of its causes over time or

just suffer from cyclical or random variations (LUCAS,

1987).

2.4. Causes and cracking patterns

According to (CEB, 1992), the occurrence of cracking can

be related with two different periods on the life of the

structure – before and after concrete hardening. Listed

below are the main causes associated with each of these

periods.

Before concrete hardening:

- Plastic cracks: Plastic shrinkage in concrete (i); Plastic

settlement of concrete (ii).

- Cracks that occur due to displacements during

construction: Incorrect reinforcement setting (iii);

Premature removal of formwork (iv).

After concrete hardening:

- Physical cracks: Concrete shrinkage (v); Plaster

shrinkage (vi).

- Structural cracks: Creep of concrete (vii); Differential

settlements (viii); Accidental overload (ix); Excessive

deformation of the structural elements (x); Excessive

compressive loads on masonry walls (xi); Seismic action

(xii).

- Hygrothermal cracks: Thermal actions (xiii); Fire action

(xiv); Freeze thaw (xv); Moisture-induced size changes

(xvi).

- Chemical cracks: Reinforcement corrosion (xvii); Alkali

silica reaction (xviii); Salt crystallization (xix).

These causes induce different cracking patterns. In Table

3.1 are listed the most common cracking patterns related

to the causes referred.

3. Fieldwork

3.1. Applied methodology

The applied methodology on the case studies inspection

is represented on Figure 3.1. This methodology can be

divided in 3 phases:

i. Data gathering

ii. Data organization

a. General analysis of cracking

b. Analysis per façade

iii. Critical analysis of results

Equation 4

Equation 3

3

Table 3.1 – Cracking patterns, elements affected and possible

causes

Cracking pattern Elements Causes

Horizontal

On walls MW xvi

On walls next to the upper slab

MW v, xiii

On walls next to the bottom slab

MW x

On columns CS ix

Vertical

On walls MW xi, xvi


MW x

On the center of beams and making a 45 degree angle next to the supports

CS ix

On columns CS ix

Diagonal

Making a 45 degree angle on walls

CS, MW viii, x, xi

On walls next to the upper slab

MW xiii


MW x

On the concrete surface

CS i, v, xiii

Making a 45 degree angle on both directions on beams

CS ix

On beams next to the supports

CS ix

Diagonal on

windows

On walls next to windows or other openings

MW, C viii, x, xi,

xvi

Mapped On walls CS, C vi, xviii

Interface

between

different

materials

On horizontal joints MW xiii

On vertical joints MW xiii, xvi

Variable

Along with the reinforcement

CS ii, iii, xiv,

xvii

On the limits of the formwork

CS iv

Parallel to the direction of the force

CS vii, ix

Perpendicular to the direction of the force

CS ix

Irregular CS, MW xii

Parallel to the surface

CS xv, xix

Elements: CS – concrete structure; MW – masonry wall; C – coating

Figure 3.1 – Systematization of the applied methodology

Data gathering – Using inspection sheets, where the case

study and cracks are characterized (using schemes,

photos and measurements) and the possible causes are

diagnosed. Data is collected using different instruments,

namely: hygrometer, crack ruler, tape measure, level,

compass and thermographic camera.

Data organization – Using photos, schemes and

descriptions. Data organization includes the following

steps:

General analysis of cracking – General analysis

of all cracks observed on the case study, granting a global

perspective on cracking location. This analysis is done

over the building’s plan view and for each observed

façade, presenting the following information:

- Area’s percentage of the façade affected by

cracking;

- Maximum width;

- Cracking patterns.

Analysis per façade – Detailed analysis of each

façade selected to fill an inspection sheet. All of cracks and

pathologies are listed and fully characterized.

Critical analysis of results – Diagnosis of the most likely

causes to each pattern, trying to find a connection

between the cracks mentioned on chapter 2 and cracks

observed on case studies. Finally, it’s created a cracking

pattern catalogue that intends to be easy to use and

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allowing to determinate the most probable cause to each

type of crack.

3.2. Suggested inspection sheet

Inspection sheets used in this work intend to fully

characterize the inspected buildings, analysing each

façade separately. In case of interior cracking, inspection

sheets are filled for each interior room observed.

In each façade is characterized the widest or biggest crack

of each type.

The organization of the inspection sheets is the following:

building ID; used instruments and available documents;

main characterization of the façades; cracking

characterization.

3.3. Characterization of the case studies

Table 3.2 shows the total number of buildings, façades

and interior rooms visited on each case study, as well as

the number of inspection sheets filled on each of them.

Table 3.2 – Total of building, façades and interior rooms on

each case study

CS NB

Number of exterior façades

Number of interior rooms

Observed IS Observed IS

A 9 9 4 0 0

B 12 14 3 0 0

C 2 0 0 14 6

D 4 11 6 0 0

E 1 2 4 0 0

F 1 2 2 0 0

29 38 19 14 6

CS – case study; NB – number of observed buildings; IS –

inspection sheet

Case study A – 2 condos with 41 houses, gardens and a

common pool. Each house has two floors and no

basements. The buildings have a reinforced concrete

structure and its foundation consists in shallow foundation

connected by beams.

Case study B – Neighbourhood with 11 building blocks,

each one with 4 floors and no basements. The buildings

have a reinforced concrete structure with fungiform slabs.

The foundation consists in shallow foundation connected

by beams.

Case study C – 14 buildings, with residential floors on the

top floors and shops on the ground floor, making a total of

276 flats and 6612 m2 of commercial area. Each building

has 8 floors on the west façade and 11 floors on the east

façade. It also has an underground park made for 170

vehicles. The buildings have a reinforced concrete

structure.

Case study D – Rehabilitated high school, consisting on

the erection of three new buildings. Two of these buildings

are an extension of existing ones – the main and gym

buildings.

Case study E – Historical convent from the XVII century,

located on Bairro Alto. It was rehabilitated, being now used

as a complex of luxury apartments. The convent has a

stone masonry and wood structure. It has 4 floors and no

basements.

Case study F – Hotel next to Avenida da Liberdade, with

3 floors and 4 basements. The main façade was kept from

the original building and the rest of the hotel was built

posteriorly. This façade is made of stone, and the rest of

the building has a reinforced concrete structure.

4. Analysis and discussion of the results

4.1. Patterns and causes observed on each case

4.1.1. Case study A

The main causes of cracking are differential settlements

that occurred all over the condo. These ground

movements lead to diagonal (Figure 4.1 (a)) and vertical

cracks, affecting both coating and masonry walls.

Mapped cracks (Figure 4.1 (b)) appear due to plaster

shrinkage. However, these kind of cracks became wider

due to foundation movements, mostly the cracks with a

most diagonal orientation.

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Figure 4.1 – Diagonal (a) and map (b) cracking

4.1.2. Case study B

The main causes of cracking are differential movements

of the structure. Because the concrete structure and the

masonry walls have a different structural behaviour, the

values of displacement of the structural elements are not

compatible with the ones of the masonry walls, inducing

cracking. Most common cracks are the ones next to

windows (Figure 4.2 (a)) and horizontal cracks on corners

(Figure 4.2 (b)).

Figure 4.2 – Cracks next to windows (a) and horizontal cracks

on corners (b)

4.1.3. Case study C

The main causes of cracking are structural movements.

This conclusion goes along with a study made by the

company, on which, using a finite elements program, they

concluded that the structure was having excessive

deformations on some parts of the slabs. These excessive

deformations may be due to errors during the design

phase where these values might not have been calculated

to be under acceptable limits.

Most observed cracks were vertical (Figure 4.3 (a)) and

diagonal (Figure 4.3 (b)) ones.

Figure 4.3 – Vertical (a) and diagonal (b) cracking

4.1.4. Case study D

The main causes of cracking are differential movements

of the structure and the most common cracks are the ones

on the interface between different materials (Figure 4.4

(a)).

Diagonal cracks (Figure 4.4 (b)) that occurred both on the

existing buildings and on the recent ones are caused by

foundation movements.

The main building were quite cracked, especially on the

cantilever and on the east façade. These cracks can be

caused by the use of one floor as a library whose loads

might not have been considered during the design phase.

Figure 4.4 – Cracks on the interface between different materials

(a) and diagonal cracking (b)

4.1.5. Case study E

Most cracks appear on the external wall (Figure 4.5). After

visiting the interior of the convent, it was possible to see

that there were interior gardens next to the external wall.

Cracks appear due to the excessive earth pressure that

led to the walls failure by bending. This pressure was due

to the excessive water in the back of the wall, since the

ground was not drained correctly.

Another cause of cracking might have been foundation

movements as suggested by diagonal cracks on the wall.

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Figure 4.5 – Horizontal (a) and vertical (b) cracking

4.1.6. Case study F

The cracks observed are quite similar along the building,

and are mostly caused by differential movements of the

structure. Main cracks appear on the interface between

different materials (Figure 4.6 (a)) and next to windows

(Figure 4.6 (b)).

The presence of a vertical crack along the transition

between two blocks of the building suggests that there

might have been a relative movement between them,

maybe caused by differential settlements of the structure.

Figure 4.6 – Cracks along the interface between different

materials (a) and cracks next to windows

4.2. Comparison with theoretical literature

Most causes mentioned on theoretical literature are not

easily diagnosed. For that reason, it’s important to know

the story of the building (next to engineers, architects,

blueprints, and others) as well as performing an in situ

analysis in order to get a more accurate diagnosis.

4.3. Statistical analysis

4.3.1. General analysis on cracking phenomenon

Analysing Figure 4.7, it’s possible to conclude that the

most common cracks are vertical cracks on walls (24%),

followed by cracks on the interface between different

materials (17%), mapped cracks and cracks next to

windows or other openings (both with 14%).

Figure 4.7 – Cracking patterns on the case studies

On Figure 4.8, we can see that most part of the cracks

appear on the walls (34%). Next, the most common part

affected by cracking are corners (16%) and interfaces

between different materials (15%). The least common

parts affected by cracking are the platbands (3%) and next

to the roof slab (1%).

Figure 4.8 – Parts of the building affected by cracking

4.3.2. Correlation between cracking pattern and

cracks characteristics

MP – “fissuras mapeadas” (mapped cracks); JA – “fissuras junto a

janelas/aberturas” (cracks next to windows); TM – “fissuras na transição de

materiais” (cracks on the interface between different materials); HE – “fissuras

horizontais em esquinas” (horizontal cracks on corners); DG – “fissuras diagonais”

(diagonal cracks); HZ – “fissuras horizontais” (horizontal cracks); VT – “fissuras

verticais” (vertical cracks); VC – “fissuras horizontais em varandas/consolas”

(cracks on balconies or cantilevered elements)

Figure 4.9 – Correlation between cracking pattern and possible

causes

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Analysing Figure 4.9, we can see that causes like

excessive deformation of the support elements, moisture-

induced size changes and differential settlements are

related with the most part of the cracking patterns, i.e.,

these causes can lead to different cracking patterns. The

other causes are related with fewer cracking patterns, as

it happens with plaster shrinkage that only lead to mapped

cracks.








Figure 4.10 – Correlation between cracking pattern and

average crack width

On Figure 4.10, it’s possible to see that, apart from cracks

on balconies or cantilevered elements, most cracks have

small to moderate widths. Cracks with big or very big

widths are only a small percentage of the cracks observed.

However, these widths are observed on every type of

crack, with the exception of mapped and horizontal cracks

on corners that only have small and moderate widths.

Analysing Figure 4.11, we can see that the most affected

element with cracking is the coating, with more than half

of the cracks observed. Vertical cracks are the only kind of

cracks that we can find on stonework and ceramic coating.

On Figure 4.12, it’s possible to see that all kinds of cracks

appear associated with moisture, and this pathology is

possible to observe in every case study. Detachments also

appear associated with many kinds of cracks, with the

exception of horizontal cracks on corners and diagonal

cracks.








Figure 4.11 – Correlation between cracking pattern and affected

elements








Figure 4.12 – Correlation between cracking pattern and other

pathologies

4.4. Cracking patterns catalogue

All the information collected is compiled under the form of

a catalogue, where every pattern cracking is entirely

characterized. To make it easier to consult, this catalogue

is divided in two parts: a catalogue for cracks that appear

on exterior walls (Table 4.1) and cracks that appear on

interior walls (Table 4.2).

This catalogue intends to serve as a guide to the

observation and diagnosis of cracks in situ, making it

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possible to determinate the main causes of the observed

cracks, as well as an indicate of characteristics that can be

expected for each cracking pattern.

Table 4.1 – Cracking patterns catalogue – Exterior walls

Ele

men

t

Cra

ckin

g

des

crip

tio

n

Po

ssib

le

cau

ses

Exp

ecte

d

wid

th

Aff

ecte

d

elem

ents

Wal

ls

Irregular mesh covering most part of the façade.

PS TA MC

Small (0,1-0,25 mm) to medium (0,25-1 mm)

C

Horizontal and continuous cracks.

DS Variable MW, C

Vertical cracks with variable width and similar spacing between them.

AO Variable MW, C,

OE

Vertical and horizontal cracks with very large widths on retaining walls.

AO MC

Very large (>2 mm)

SE, C

Win

do

ws

or

oth

er o

pen

ing

s

Cracks formed from the corners of windows or other openings.

DS DM MC

Medium (0,25-1 mm)

MW, C

Nex

t to

th

e ro

of

slab

Linear cracks next to the roof slab, usually on the interface between the masonry wall and the concrete structure.

TA MC

Small (0,1-0,25 mm)

C

Pla

tban

ds

Linear cracks next to platbands.

TA MC

Small (0,1-0,25 mm)

C

Nex

t to

th

e g

rou

nd

Horizontal cracks next to the ground.

DS Medium (0,25-1 mm)

MW, C

Diagonal cracks forming a 45 degree angle, with similar spacing between them, next to the ground.

DS Variable SE,

MW, C

Co

rner

s

Horizontal cracks with similar spacing between them, on the corner of buildings.

DM

Small (0,1-0,25 mm) to medium (0,25-1 mm)

MW, C

Vertical cracks with variable width formed from corners.

DS Variable MW, C

Table 4.1 – Cracking patterns catalogue – Exterior walls (cont.)

Ele

men

t

Cra

ckin

g

des

crip

tio

n

Po

ssib

le

cau

ses

Exp

ecte

d

wid

th

Aff

ecte

d

elem

ents

Bal

con

ies

Horizontal cracks on balconies, formed perpendicularly to the façade.

AO DM

Large (1-2 mm)

MW, C

Diagonal cracks with similar spacing between them, next to the upper part of a cantilevered element.

AO DM

Large (1-2 mm)

MW, C

Inte

rfac

e b

etw

een

dif

fere

nt

mat

eria

ls

Linear cracks along the interface between the masonry wall and the concrete structure.

DM TA MC

Small (0,1-0,25 mm)

SE/MW

Orn

amen

tal

elem

ents

Vertical cracks along stonework joints.

AO Large (1-2 mm)

OE

Causes: PS – plaster shrinkage; DS – differential settlements; AO –

accidental overloads; ED – excessive deformation of the structural

elements; DM – differential movements of the structure; TA – thermal

actions; MC – moisture-induced size changes

Elements: SE – structural element; MW – masonry wall; SE/MW –

interface between structural elements and masonry wall; C – coating; OE

– ornamental elements

5. Conclusions

The objectives of this dissertation were fulfilled. In order to

relate what was mentioned on theoretical literature and the

reality of Portuguese buildings, there were analysed six

case studies. The case study buildings provide a

diversified base to study cracking patterns, as well as the

elements affected and the main causes that originates

them.

It was applied a methodology that allowed a full

characterization of the buildings and their pathologies.

This methodology consisted on the creation of an

inspection sheet that intends to be quick and easy to fill

and that provides all the information needed to diagnose

the pathologies observed.

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Table 4.2 – Cracking patterns catalogue – Interior walls E

lem

ent

Cra

ckin

g

des

crip

tio

n

Po

ssib

le

cau

ses

Exp

ecte

d

wid

th

Aff

ecte

d

elem

ents

Wal

ls

Diagonal cracks forming a 45 degree angle.

ED Small (0,1-0,25 mm)

C

Vertical cracks along the full height of the wall.

ED Medium (0,25-1 mm)

MW, C

Win

do

ws

or

oth

er o

pen

ing

s

Cracks formed from the corners of windows or other openings.


MW, C

Co

rner

s

Vertical cracks next to corners and along the full height of the wall.


MW, C

Diagonal cracks that cross two adjacent masonry walls, along the masonry joints.


MW, C

Inte

rfac

e b

etw

een

dif

fere

nt

mat

eria

ls

Horizontal cracks next to the window frames.


C

Orn

amen

tal

elem

ents

Vertical cracks on stonework elements, crossing them completely.


OE

Vertical cracks on ceramic coatings, along their joints.

ED Small (0,1-0,25 mm) to medium (0,25-1 mm)

MW, OE

Causes: PS – plaster shrinkage; DS – differential settlements; AO –

accidental overloads; ED – excessive deformation of the structural

elements; DM – differential movements of the structure; TA – thermal

actions; MC – moisture-induced size changes

Elements: SE – structural element; MW – masonry wall; SE/MW –

interface between structural elements and masonry wall; C – coating; OE

– ornamental elements

The diversity of results obtained made it possible to

elaborate a cracking patterns catalogue, with all types of

cracks observed on the case studies. The statistical

analysis served as base for this catalogue, with a total of

59 cracks analysed.

Thanks to the inspections conducted, it was possible to

conclude that:

- the most common cracks were the vertical ones, with

24% of the totality of cracks observed. This type of cracks

were observed on walls, corners and ornamental

elements, as stonework;

- the part of the building that was most affected by cracking

were the walls, where 34% of the cracks appeared;

- the most recent buildings, with year of construction after

2010, showed the lower area’s percentage of the façade

affected by cracking, never exceeding 50% of the area;

- the main causes of cracking were structural, namely,

differential settlements and differential movements of the

structure. These two kinds of movements led to cracks

with different orientations, widths and patterns, showing,

once again, the difficulty behind searching for a cause-

effect relationship;

- the most affected elements were the coating and the

masonry walls, consisting in 49% and 26% of the affected

elements, respectively. It was possible to see that, most of

the times, structural cracks affected both coating and

masonry walls;

- cracks with width superior to 2 mm were normally

associated with structural phenomena and, on a long-

term, can be responsible to the instability of walls.

References

BONE, S. 1989. Defects in Buildings. Department of

Environment : London, 1989.

BONSHOR, R. B. and BONSHOR, L. L. 1996. Cracking

in Buildings. BRE : Garston, 1996.

CEB. 1992. Durable Concrete Structures. Design Guide.

Comité euro-international du béton : s.n., 1992.

GASPAR, Pedro Lima, FLORES-COLEN, Inês and

BRITO, Jorge de. 2006. Técnicas de diagnóstico e

classificação de fissuração em fachadas rebocadas. s.l. :

IST, Lisboa, 2006.

LAPA, José Silva. 2008. Patologia, recuperação e reparo

das estruturas de concreto. Monografia para obtenção de

título de especialização em Construção Civil :

Universidade Federal de Minas Gerais, 2008.

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LUCAS, J. A. Carvalho. 1987. Revestimentos para

paramentos interiores de alvenaria de blocos de betão

celular autoclavado - VOL. II: Betão celular autoclavado -

Fissuração de paredes de alvenaria em geral; Fissuração

de paredes de alvenaria de betão celular autoclavado no

nosso País. Relatório 109/87-NCCt : LNEC, Lisboa, 1987.

PAIVA, J., AGUIAR, J. and PINHO, A. 2006. Guia

Técnico de Reabilitação Habitacional. s.l. : LNEC, Lisboa,

2006.

SILVA, José António Raimundo Mendes. 1998.

Fissuração das alvenarias - Estudo do comportamento

das alvenarias sob acções térmicas. Dissertação de

Doutoramento em Engenharia CIvi, especialidade de

Construções : Coimbra, 1998.

VEIGA, R. 1998. Comportamento de argamassas de

revestimento de paredes. Contribuição para o estudo da

sua resistência à fendilhação. Teses e Programas de

Investigação : LNEC, Lisboa, 1998.

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