injection grouts for ancient masonry adherence study · the grout injection is a technique used for...

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INJECTION GROUTS FOR ANCIENT MASONRY – ADHERENCE STUDY

André Filipe Melo de Almeida Figueiredo

Civil Engineering Department, Instituto Superior Técnico, Universidade Técnica de Lisboa, Portugal

1. Introduction

The consolidation of ancient masonry buildings has recently emerged as a need, due not only to

urban factors but also to architectural and historical ones. In fact, a great part of the memory of a city

is contained in ancient buildings and these are the ones that make it unique.

The grout injection is a technique used for the consolidation and strengthening of ancient masonry

buildings. The grout, once injected into the internal structure of the walls, enhances the cohesion of

the structure by filling in the empty spaces and small cracks in the masonry walls. Thus, the

mechanical behavior of the building is enhanced without affecting its appearance (Binda et al, 1999)

In the present work four grouts, two pre-mixed and two hydraulic lime grouts were selected with the

objective of studying the adherence to different types of substrate: ancient brick and mortar. It should

be noted that the substrates have been previously prepared to present characteristics similar to the

ancient materials used in masonry buildings.

2. Grout Requirements

The choice of grout injection depends on the characteristics of the ancient masonry. Therefore it is

important to evaluate the chemical properties of the chosen grouts in order to ensure its compatibility

with the masonry, namely with the mortar, to avoid future problems as a consequence of chemical

reactions . When choosing the pattern for injection several other factors, such as the grout fluidity,

injectability, stability, mechanical and physical properties should be taken into account (Valluzzi,

2005).

The choice of the grout to inject depends on the degradation state of the entire masonry structure as

well as on the characteristics of the ancient masonry wall that is intended to consolidate.

3. Adherence study

The accuracy of the grouts injection technique on the consolidation of ancient masonry walls

depends mainly on the adherence between the injected grout and the masonry materials. Studies

carried out prove that the final result depends more on the grout-substrate adherence properties than

on the mechanical properties of the grout (Toumbakari, 2002).

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The bond strength is due to two mechanisms – a chemical and a mechanical one. The chemical

bond results from the reaction among the different materials in contact along the bond interface. The

chemical bond usually decreases when the slip process begins, getting close to zero . (Adami et al,

2007; Binda, et al, 1993)

On the other hand the mechanical bond depends on the substrate characteristics, above all on its

roughness and porosity and also, in a lower scale, on its retaining water capacity. The greater the

substrate porosity is, the higher the failure tensions are, thus resulting in higher bond strength values

along the interface. This mechanical strength is verified even for higher slip levels, which is an

important characteristic to be considered in structures subject to the effects of earthquakes and

differential settlements (Adami et al, 2007; Climaco 2001 ).

The bond strength between the grout and the substrate along the interface can be evaluated through

different experimental tests, presenting a wide variety of values, accordingly to the used method

(Momayez, et. al., 2004).

Studies carried out show that, in general, the highest adherence values are registered in the Slant

Shear Testn (SST), while the lowest values occur in the Pull-off Test. Some researchers indicate the

Slant-Shear test as being particularly appropriated to evaluate the bond compressive strength, as it

introduces a combined state of shear and compressive stress, which is found in a real structure

(Austin et al, 1999). In the experimental study, the specimen used to perform SST, was produced

with an angle of 30º to the vertical, according to the procedures used in previous studies (Saldanha

et al, 2012).

As concerns the adherence tests, it is equally important to analyse the type of failure mode

observed. The failure mode is called adhesive or cohesive when it occurs along the interface or

within the grout or substrate, respectively. Whereas the adhesive failures indicate the value of the

bond failure strength, the cohesive failures only indicate an inferior limit value for the same bond

strength. In fact, when the failure mode is cohesive, it depends on the strength to compression of the

weakest materials and not on the interface characteristics.

4. Experimental Program

4.1. Introduction

In the present work four grouts, two pre-mixed grouts (PM) and two hydraulic lime grouts (HL), were

selected with the objective of studying the adherence to two different types of substrate: ancient brick

and mortar. The studied grouts were characterized in fresh and hardened states with the objective of

comparing its performance. It should also be noted that the mortar used in the present experimental

study was produced in the laboratory trying to obtain similar characteristics to the mortars present in

ancient masonry buildings.

The bricks were taken from a demolished ancient building located in the center of Lisbon, and

previously prepared in order to ensure physical and mechanical characteristics similar to the original

ones.

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4.2. Mixing procedure, tested grouts, cure conditions and test methods

The grout production was carried out using a power drill and a coupled mixer, being the assembly

fixed to a support drill column. The production of grout was made by adding water to the product,

previously placed into the mixing vessel, which was followed by homogenization of the constituents

for 3 minutes, with a power drill speed of 2700 rpm.

The water/binder ratio was set up according to the procedures included in the grouts data. Fluidity,

using the cone method, measured 10 1 seconds for the four grouts.

Table 1 shows the characteristics of the studied grouts

Table 1 –Grouts studied

Manufacturer Grout Type Designation Water/binder

ratio

Secil Martingança Hydraulic lime NHL5 HL NHL5 0.60

Lafarge Ciments Chaux Blanche NHL3.5-Z HL Lafarge 0.75

MAPEI Mape-Antique I PM MAPEI 0.38

BASF The Chemical Company Albaria Iniezione PM BASF 0.40

The test procedures used in the characterization of grout in fresh and hardened state were based on

the standards applicable to grout injection in pre-stressing cables, NP EN 445:2008, NP EN

446:2008, NP EN 447:2008 and, EN 1015, LNEC E 393, LNEC E 398, EN 12390-6, and RILEM

procedures, including Test No. I.1, Test No. I.2 and Test No. II.5.

The chosen cure conditions , T=20 2oC; Hr=100%, were adapted from the cure conditions, outlined

in NP EN 445:2008, which were intended to cementitious grouts injection.

The specimens were demolded after 48 hours.

The characterization of fresh grout was performed immediately after production (t=0min) and after 30

minutes, based on the standards applicable to grout injection, the NP EN 447:2008. According to this

standard, the grout fluidity is not expected to differ more than 20%, between time measurement t0 to

t30. During the test the grout was continuously mixed.

The characterization of the grouts in the hardened state was based on mechanical and physical

tests. This characterization was performed on prismatic (40x40x160 mm3) and cylinder (h=100mm e

Ø=50mm) specimens. The mechanical tests were preceded by ultrasound velocity tests. The

specimens were submitted to some physical tests: water absorption by capillarity, porosity and mass

and length retraction.

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4.3. Adherence – specimens and test procedures

Regarding the compressive stress tests involving the four grouts and the two types of substrate,

mortar and ancient brick, four different specimens were used in the performance of Slant Shear and

Pull-off Tests. The amount of specimens produced, using each of the different grouts, and the

corresponding tests are presented in Table 2.

Table 2 – Specimens used in the study of adherence

Designation

Dimensions

Test

Figure

Mixed specimens

40x40x160 (mm3)

Flexure

Joint specimens

40x40x160 (mm3)

Flexure

Slant Shear specimens

40x40x160 (mm3)

Slant Shear

Concrete slabs

grout-to-brick

grout-to-mortar

30x30x10 (mm3)

Pull-off

Mixed specimens are formed by half prismatic specimens made of mortar or brick(40x40x80 mm3),

added with grout. Regarding the joint specimens, two halves formed by the same material are

separated by a layer of grout 4 mm thick. The Specimens used in Slant Shear tests were produced

with an interface defining an angle of 30º with vertical. The paving slabs contain a basis of concrete,

added with mortar or brick and a layer of grout approximately 1, 5 thick.

The mortar produced is characterized by a proportion (0,5 ; 0,5; 8) - (aerial lime ; hydraulic lime ; dry

river sand ) and a spread of 165 5 mm using the spread method. The curing of grout test specimens

was performed as follows: the samples were stored in laboratory environment at a temperature of

T=23 5oC; Hr=70 10%, from their production until 60 days of age. It was then object of physical

and mechanical assessment. Meanwhile, the physical and mechanical characteristics of the brick

were also evaluated. These tests were performed with prismatic specimens (40x40x160 mm3).

(1)

(2) (1) (2)

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5. Results and discussion

5.1 Characterization of grouts

Fresh state

The study of fluidity was done through cone and spread methods, measured at t0 and at t30, as can

be seen in figures 1-2.

Figure 1 - Cone method Figure 2 - Spread test

Figure 1 exhibits an increase of the drainage time, when testing the fluidity through cone method,

which is bigger with grouts HL (≈12% a 15%) than with grouts PM (≈6%).Regarding grouts HL the

bigger fluidity may be due to more loss of water, as the water/binder ratio is higher than the one of

grouts PM, as well as due to the different composition of these grouts.

When comparing the two tests it was predictable that all the grouts had similar performance, which

means that as its fluidity time increases, the spread decreases. However, Figure 2 shows that PM

grouts performance is different, spread increases over time. This behavior can be explained as the

tests are meant to assess different features of fluidity. Thus, the cone method evaluates the grout

viscosity, the spread method reflects the yield strength.

It was verified that the mass density of the analyzed grouts increased slightly between the measured

times.

Hardened state

The characterization of the grouts in the hardened state was performed through flexural strength

tests, compressive strength tests, traction by splitting strenght and the coefficient of ductility,

determined by the ratio between flexural and compressive failure strengths.

The results of the tests are presented in Table 3 and Figures 3-4

10.1 10.1

10.6 10.7

11.8

11.4

11.2

11.5

9

10

11

12

NHL5 Lafarge BASF MAPEI

flu

idit

y (s

)

154 160

198 187

148 143

209 197

0

50

100

150

200

250


Spre

adin

g (m

m)

t = 0 minutes

t = 30 minutes

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Table 3 – Flexural , compressive strength and tensile splitting strenght tests

Grout

Flexural strength (MPa)

Compressive strength (MPa)

Tensile splitting strenght (Mpa)

NHL5 1.08 0.09 1.97 0.12 0.17 0.01 0.55

Lafarge 0.68 0.03 1.56 0.06 0.16 0.01 0.44

BASF 3.42 0.21 10.37 0.19 0.75 0.05 0.33

MAPEI 7.03 0.28 21.03 0.55 1.06 0.11 0.33

Figure 3 – Flexural and Compressive strength Figure 4 – Tensile spliting strenght

The results show considerable differences concerning the two types of grout, HL and PM.

When comparing, grouts PM exhibit higher tensile strength values than grouts HL. Moreover, it is

verified that the tensile strength values in grout MAPEI double the values obtained with grouts BASF.

Ductility is a property that measures the deformability capacity of a material before its failure.

It was verified that grouts BASF and MAPEI exhibit similar values concerning the coefficient of

ductility. Grouts HL present higher values, which means that it can endure, without failure, the

imposed strains.

Regarding the physical characterization, the following factors were taken into account: variation of

length and mass, water absorption capacity and porosity of each grout. Figures 5-6 present,

respectively, the mass and lenght variation of the mass and length verified in the retraction test.

Figure 5 – Mass variation Figure 6-Shrinkage

0

5

10

15

20

25


Stre

ngh

t (M

Pa)

Flexural strenght Compressive strenght

0

0,2

0,4

0,6

0,8

1

1,2

1,4


Stre

ngh

t (M

Pa)

Tensile splitting strenght

0

5

10

15

20

25

30

35

0 50 100 150

ΔM

ass

(x-1

)

(%

)

Time (days)


0

1

2

3

4

5

6

0 50 100 150

Sh

rin

kage

(%

)

Time (days)


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It can be observed that the mass values for grouts HL decreased about 25-30% whereas for grouts

PM these values decreased between 15% and 20%. Moreover, grout MAPEI was the one, which

showed a lower value of variation concerning length and mass.

The existence of major differences are due to the fact that hydraulic limes have a higher water/binder

ratio, since to obtain more fluidity they need, comparing to pre-mixed grouts, the addition of a higher

amount of water. During the test, this water is released by evaporation, thus decreasing the mass

and the specimens’ size.

Figure 7shows water absorption by capillarity curves for studied grouts. It was possible to determine

the capillarity coefficient and asymptotic value of each grout, illustrated in Table 4.

Figure 7 – Water absorption by capillarity curves

Table 4 – Capillarity coefficients and asymptotic values


Capillarity coefficient (Kg/m2.s-0,5) 0.38 0.03 0.07 0.09

Asymptotic value (Kg/m2) 82.6 81.7 67.3 47.5

The internal structure, namely the size of the voids, can be an explanatory factor for the high

capacity of water absorption in the initial part of the test. Thus the larger voids are the first ones to be

filled in.

When comparing the studied grouts, the capillarity coefficient of grout NHL5 is by far the highest one,

achieving more rapidly the saturation state, which indicates that grout NHL5, is the one who contains

larger voids. On the other hand, grout Lafarge shows the lowest capillarity value, which means a

slower absorption capacity.

Grout MAPEI presents the lowest asymptotic value of capillarity, due to the existence of a less thick

capillary network. This value is totally consistent with the porosity coefficient values and the

maximum water content, as shown in Table 5.

Grouts HL present the same asymptotic value of water absorption and the porosity coefficient values

are very similar. These values are higher than the ones presented by pre-mixed grouts, which was

0

10

20

30

40

50

60

70

80

90

0 200 400 600 800 1000 1200 1400

ΔM

/S (K

g/m

2 )

TTime (s0.5)


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expectable, considering the results of the mechanical tests, in which grouts PM have always

presented higher strength values.

Table 5 – Porosity and maximum water content


Porosity (%) 50.8 53.3 43.6 32.2

Wmáx (%) 40.6 50.0 29.9 20.0

5.2. Adherence

Four different types of specimen were used to perform the following tests: flexural resistance,

compressive and traction tests, as shown in table 2. The analysis was made taking into account not

only the registered failure strength values, but also the observed type of failure mode.

The failure can be adhesive, in case it is related to a detachment along the bond interface or

cohesive when it occurs within the substrate or grout.

5.2.1. Mixed specimens

In the present test four different types of failure were analysed, two adhesive and two cohesive

failure modes.

Failure A: adhesive failure showing evident segregation of the materials, Figure 8

Failure B: adhesive failure showing partial adhesion of the materials, Figure 9

Failure C: cohesive failure within the grout, Figure 10

Failure D: cohesive failure within the substrate, Figure 11

Figure 8 – Failure A Figure 9 – Failure B Figure 10 – Failure C Figure 11 – Failure D

When the failures are type A or B, the results present a reliable value concerning the adhesion

strength along the bond interface. However, when the failures are type C or D, the values of flexural

strength are a lower limit of the interface bond strength.

This test was preceded by a measurement of the ultrasonic velocity, being the corresponding values

presented in Table 6. These values are shown in a graph, Figure 12, as well as the values

concerning ultrasonic velocity previously obtained in grout and brick specimens.

The flexural strength values, obtained through this test, can be seen in Table 7, also mentioning the

type of failure observed. Figure 13 shows the values obtained with the flexural strength tests on

brick-to-grout and mortar-to-grout specimens. These values are compared with the mortar and brick

flexural strength, previously determined.

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Table 6 – Ultrasonic velocity – mixed specimens

Grout

Ultrasonic velocity (m/s)

Grout Brick Mortar

Average Average SD Average SD

NHL5 2000 2760 67 2640 107

Lafarge 1890 2540 39 2510 128

BASF 2430 3090 45 3020 83

MAPEI 3040 3490 78 3420 80

Table 7 – Flexural strength – mixed specimens

Grout NHL5

Grout Lafarge

Grout BASF

Grout MAPEI Flexural strength

Failure mode

Flexural strength

Failure mode

Flexural strength

Failure mode

Flexural strength

Failure mode

Average SD (MPa)

Average SD (MPa)

Average SD (MPa)

Average SD (MPa)

Brick 1.83 0.13 1B + 5C 0.47 0.05 6A 1.34 0.14 3A + 3B 2.51 0.18 3A + 3B

Mortar 0.28 0.02 6D 0.37 0.04 1B + 5D 0.37 0.02 6D 0.28 0.03 6D

Figure 12 – Ultrasonic Velocity – Mixed specimens Figure 13 – Flexural strenght – Mixed specimens

In all grout-to-mortar specimens cohesive failures occurred within the grout, which means that the

failure was always determined by the flexural strength of the mortar (0.39MPa), whose value is

inferior to the bond strength. Thus it can be concluded that the value of bond strength in these

specimens is superior to the ones obtained in the test.

Grout NHL5 is the only grout, which has a grout-to-brick flexural resistance superior to the flexural

resistance of the grout itself. This fact indicates good adhesion properties at the bond interface

NHL5-to-brick. This good adherence is confirmed by the type of failure observed during the test,

most of them being type C.

Grout Lafarge presented tensile strength values very similar, in all specimens. The adhesive failure

observed in the bond Lafarge-to-brick prove its low adhesion level and allow to conclude an

approximate value for the interface tensile strength.

0

500

1000

1500

2000

2500

3000

3500

4000


Ult

raso

nic

vel

oci

ty (m

/s)

Grout Brick - grout Mortar - grout

0

1

2

3

4

5

6

7

8

9

10 Fl

exu

ral s

tre

ngh

t (M

Pa)

Grout Brick - grout Mortar - gout

NH

L5

Lafa

rge

BA

SF

MA

PE

I

Mortar

Brick Brick

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The flexural tensile strength in the bond grout-to-brick was, in grouts PM, lower than the tensile

strength of both materials, which was an explanatory fact for the existence of adhesive failures in all

specimens used in the tests.

The results of the ultrasonic tests, previously performed, present a strong correlation regarding to

the flexural strength values.

5.2.2. Joint specimens

In the flexural strength test, using joint specimens, it was also considered the existence of four

different failure modes, as shown in figures 14 to 17. Table 8 and the graph in Figure 19 present the

values obtained in this test. The table also refers to the amount of times each failure mode occurred.

The graph in Figure 19 also includes the mortar and brick flexural strength previously determined.

Figure 14 – Failure mode A Figure 15 – Failure mode B Figure 16 – Failure mode C Figure 17 – Failure mode D

Table 8 – Flexural strength values and failure modes observed in joint specimens

Grout NHL5

Grout Lafarge

Grout BASF

Grout MAPEI

Flexural strength

(MPa)

Failure mode

Flexural strength

(MPa)

Failure mode

Flexural strength

(MPa)

Failure mode

Flexural strength

(MPa)

Failure mode

Brick 2.46 0.21 3A + 3B 1.51 0.19 2A + 4B 3.82 0.23 2A + 4C 3.46 0.29 6C

Mortar 0.25 0.03 6D 0.30 0.04 6D 0.40 0.04 6D 0.30 0.01 6D

The graph in figure 18 shows the result of the ultrasonic velocity test applied to these specimens.

Figura 18 – Ultrasonic test – joint specimens Figura 19 – Flexural test results - joint specimens

0

500

1000

1500

2000

2500

3000

3500

4000


Ult

raso

nic

vel

oci

ty (m

/s)


Mortar

0

1

2

3

4

5

6

7

8

Flex

ura

l str

en

ght (

MP

a)


NH

L5

Lafa

rge

BA

SF

MA

PE

I

Mortar

Brick

Brick

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In all the joint specimens with mortar substrate the failure was always cohesive within the grout, as it

had occurred with the mixed specimens. The resulting values always depended on the grout tensile

strength and, consequently, were always lower than the bond strength of the interface.

We may observe a good correlation between the ultrasonic velocity tests and the results of this test.

In the grout-to-brick based specimens, with pre-mixed grouts, the values of the tensile strength were

higher than the ones with grouts HL, accordingly to the grouts PM and HL behavior, when studied

separately.

MAPEI is the only grout that shows lower tensile strength along the grout-to-brick interface than the

tensile strength of the grout itself. In hydraulic lime grouts the tensile strength is more than the

double of the flexural strength of the grout itself, occurring in all cases, adhesive failures. Thus, these

grouts show good adhesion properties in this test.

5.2.3 Slant Shear Test

In the Slant shear test, when the failure was cohesive, it was necessary to distinguish between

cohesive failure due to shear and to crushing. It was seen that in all grout-to-mortar specimens, the

failure was always cohesive within the mortar, with crushing.

Table 9 and the graph in Figure 20 present the values of compressive strength as well as its

tangential and normal components.

Table 9 – Slant Shear test results – mortar-to-grout specimens (shear cohesive failures)


Compressive strength (MPa) 0.45 0.03 0.41 0.02 0.71 0.03 0.63 0.04

Shear strength (MPa) 0.39 0.02 0.35 0.01 0.61 0.02 0.55 0.04 Normal strength (MPa) 0.23 0.02 0.20 0.01 0.35 0.01 0.32 0.02

Figure 20 –Slant Shear test results – mortar-to-grout specimens

When using grout-to-brick specimens it was verified both adhesive and cohesive failures. In this

situation, the choice was to present the results separately, in order to make clear the difference

between them.

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8


Stre

ngh

t (M

Pa)

Compressive strenght

Shear strenght along the interface

Normal strenght along the interface

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Table 10 – Failure modes


Brick 6 cohesive failures by crushing

6 adhesive failures 3 adhesive + 3 cohesive by crushing

2 adhesive+ 4 cohesive by crushing

Mortar 6 cohesive by shear 6 cohesive by shear 6 cohesive by shear 6 cohesive by shear

Table 11 – Slant Shear test results –brick-to-grout specimens (adhesive failures)


Compressive strength (MPa) ------ 1.29 0.16 7.77 0.55 10.27

Shear strength (MPa) ------ 1.12 0.14 6.73 0.48 8.90

Normal strength(MPa) ------ 0.64 0.08 3.89 0.27 5.14

Table 12 –Slant Shear test results – brick-to-grout specimens (cohesive failures)


Compressive strength (MPa) 2.51 0.17 ------ 7.71 0.61 10.62 1.42

Shear strength (MPa) 2.17 0.23 ------ 6.68 0.53 9.20 1.23

Normal strength(MPa) 1.25 0.14 ------ 3.85 0.31 5.31 0.71

Figure 21–Slant Shear test results: brick-to-grout specimens (adhesive failure)

Figure 22 –Slant Shear test results: brick-to-grout specimenscalda (cohesive failure)

All the NHL5-to-brick specimens experienced cohesive failure by crushing, within the grout, which

indicates a good adhesion along the interface NHL5-to-brick. On the other hand, all the Lafarge-to–

brick specimens were subjected to an adhesive failure, which means that the bond tensile strength

value was lower than the one of the grout itself.

PM grouts presented a very similar amount of adhesive and cohesive failures, showing higher tensile

strength values than the ones related to hydraulic lime grouts.

MAPEI grout is the one that presents higher mechanical strength values, obtained in previous tests,

as well as better adherence performance along the bond interface of the two materials. In this grout

the cohesive failures occurred within the brick by crushing, having been verified some adhesive

failures, too. Thus, it is deductable that the brick tensile strength value and the bond strength along

the interface are close, although lower than the tensile strength value of the grout itself.

0

2

4

6

8

10

12

Lafarge BASF MAPEI

Stre

ngh

t (M

Pa)




0

2

4

6

8

10

12

NHL5 BASF MAPEI

Stre

ngh

t (M

Pa)




13

Concerning BASF and MAPEI grouts, in relation to the two failure modes, the results of tensile

strength are much similar.

5.2.4. Pull-off

In this test it was made clear the difference between adhesive failures (A) and cohesive ones (C).

The results are presented in Table 13

Table 13 – Pull-off Test and failure modes

NHL5 Grout

Lafarge Grout

BASF Grout

MAPEI Grout Pull-off

Failure mode

Pull-off Failure mode

Pull-off Failure mode

Pull-off Failure mode Average PD

(MPa) Average PD

(MPa) Average PD

(MPa) Average PD

(MPa)

Brick 0.91 0.32 6A 1.08 0.17 4A + 2C 0.43 0.08 6A 0.52 0.19 6C

Mortar 0.11 0.04 6C 0.30 0.06 6C 0.07 0.02 6C 0.24 0.04 6C

In all mortar specimens, the failure was always cohesive within the mortar and it was achieved to low

tensile strength values. These results are probably due to the fact that the mortar was intended to

reproduce the ancient mortar, having consequently fragile tensile strength characteristics.

It was also verified that for HL grouts used in brick substrate, the tensile strength values are

practically two times more than the ones observed in PM grouts.

6. Conclusions

During the characterization process of the four grouts, it was concluded that the pre-mixed grouts

achieved higher flexural, compressive and traction strength values than the NHL5 and Lafarge

grouts.

In all adherence tests, whenever the substrate was mortar based, there were cohesive failures within

the mortar, to very low tensile strength values. As a consequence, the result obtained was always an

inferior value of the bond tensile strength.

In the flexural test performed in mixed specimens, only the NHL5 grout presented cohesive failures,

with bond strength values similar to the ones registered in the pre-mixed grouts. As it is a cohesive

failure it is possible to state that the bond strength value is higher than the one obtained in the

experimental test, which means, a good adherence between brick and NHL5 grout.

During the flexural test on joint specimens, it was verified adhesive failures in the hydraulic lime

grouts and cohesive failures in the pre-mixed grouts. This means that for the NHL5 and Lafarge

grouts this test provided approximated values of the bond tensile strength. It was also verified that

the bond strength on the brick-to-grout interface, with hydraulic lime grouts, was lower than the one

registered with pre-mixed grouts.

Analyzing the results of the Slant Shear Test, the pre-mixed grouts presented higher values of bond

strength than the hydraulic lime grouts. In this test, in all NHL5 brick-to-grout specimens, cohesive

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failures, by crushing within the grout, were observed. Thus we can conclude that the bond tensile

strength is higher than the tensile strength of the grout itself. All mortar based substract specimens

present shear failures within the mortar, which means that the shear bond resistance between the

mortar and the grout is higher than the shear resistance of the mortar.

During the Pull-off Test the hydraulic lime grouts revealed higher traction tensile strength values,

meaning a better adherence on the grout-to-brick interface, when using NHL5 and Lafarge grouts.

In all tests which were performed with brick and Lafarge grout, this grout presented always adhesive

failures and low values of adherence. In fact, it is the one that shows the worst adherence properties.

7. References

Adami, Chryssi-Elpida; Vintzileou, Elizabeth – Interventions to historic masonries: Investigation of

the bond between stones or bricks and grouts. RILEM, 2007

Austin, S. ; Robins, P.; Pan, Y.– Shear bond testing of concrete repair. Cement and Concrete

Research, Vol. 29, N. 7, pp. 1067-1076, March 1999

Binda, L.; Baronio, G.; Mosena, C. - Strenghtening of masonries by injection technique. The Sixth

North American Masonry Conference, Philadelphia, Pennsylvania, June 1993.

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injection grouts for ancient masonry adherence study · the grout injection is a technique used for...

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