Influence of the Design Materials on the Mechanical

8/2/2019 Influence of the Design Materials on the Mechanical

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O R I G I N A L A R T I C L E

Influence of the design materials on the mechanical

and physical properties of repair mortarsof historic buildings

P. Manita T. C. Triantafillou

Received: 15 March 2009 / Accepted: 15 March 2011 / Published online: 26 March 2011

RILEM 2011

Abstract Historic buildings are subjected to dete-

rioration by natural weathering or by corrosion due to

polluted atmosphere and the materials more suscep-

tible are the mortars used. This study examines the

influence of the type and quantity of design materials

on compressive strength, creep, water absorption and

length change of repair mortars produced. The design

materials used were lime, natural pozzolan, sand and

brick fragments in order to obtain the compatibility

required between historic and repair mortars; differ-

ent quantities of Portland cement were also used inorder to quantify his influence. Nine mixtures were

then designed and produced considering as parame-

ters two binder: aggregates ratios, three pozzolan:

cement ratios and three sand: brick fragments ratios.

The experimental measurements continued until the

age of 3 years or the stabilization of the test values.

The results indicate that compressive strength is

strongly affected by cement content and aggregates

dosage and type. It appears that the increase of

cement as well as brick fragments leads to confine-

ment of creep deformation, while the mixtures with

high pozzolan and sand content experience consider-

ably high creep values. Water absorption reaches

higher values when pozzolan or aggregate dosage

arises and brick is in excess. Shrinkage increases

when binder or brick quantity arise and is consider-

ably influenced by cement content.

Keywords Repair mortars of historic buildings

Lime

Pozzolan

Compressive strength

Creep coefficient Water absorption

Length change Long-term measurements

1 Introduction

During human history, masonries made up of stones or

bricks and mortar are widely used. The art of mortars

and masonries is especially developed in the Mediter-

ranean basin from the most ancient times until our

days. The Phoenicians used brick dust in order to givehydraulicity to the air lime mortars (tenth century BC).

The Greeks added Santorinian earth (a natural pozzo-

lan of volcanic origin) to the mixtures leading to the

production of mortars with hydraulic properties and

water-resistance (ninth century BC). The Romans also

used hydraulic mortars; they achieved a great knowl-

edge about their production and applications and they

spread their use throughout their empire. The Byzan-

tines, during the 1000 years of their empire, used

P. Manita (&)

Laboratory of Building Materials, Department of Civil

Engineering, Democritus University of Thrace,

P.O. Box 252, 67100 Xanthi, Greece

e-mail: [email protected]

T. C. Triantafillou

Structural Materials Laboratory, Department of Civil

Engineering, University of Patras, 26500 Patras, Greece

Materials and Structures (2011) 44:16711685

DOI 10.1617/s11527-011-9726-9


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extensively the hydraulic mortars and they added

crushed bricks in order to improve its performance [1].

The majority of historic mortars in Greece and

generally in the Mediterranean basin have as binding

material lime with natural pozzolan and/or brick dust;

the last two possess hydraulic properties. The aggre-

gates used are inert materials like silicate, carbonateor dolomite sand and/or gravel or porous aggregates,

physico-chemically active, like crushed brick, etc.

Usually, crushed brick is added in order to ameliorate

the performance of mortar towards better adhesion or

workability. Sometimes, a component could derive

either from the binder or the aggregates used [2, 3].

The aggregate quality, the composition of binding

material and the use, sometimes, of additives such as

straw fibres, milk or egg, in order to improve the

characteristics of mortar, determined the mechanical

strength and the durability of the mortar produced.A lot of mechanical, physical, biological and

chemical reasons lead to historic mortars deterioration.

The design of repair mortars for historic buildings

depends on the type and use of historic mortar, the

width of alteration, the reason of damage and, of

course, the financial resources. The research about the

ideal repair mortar occupies a lot of scientists [48].

For the first time, the characteristics of an ideal repair

mortar were presented by Peroni et al. [9] as follow:

(i) easy workability, (ii) rapid and reliable setting in

both dry and wet environments, (iii) slow shrinkageduring setting, (iv) mechanical and thermal character-

istics and porosity similar to those of the components

(natural stones, bricks, etc.) of the masonry and

(v) soluble salts content as low as possible. The last

two points indicate that an ideal repair mortar must be

harmless and in order to obtain this scope scientists

concluded that repair mortars must have characteristics

as similar as possible to those of the materials to be

repaired [10, 11]. However, the traditional lime

pozzolansand mortars, extensively used in ancient

masonry in Europe, can sometimes give unsatisfactoryresults due to their low workability, their poor and slow

setting in humid environments and their incomplete

carbonation beneath the surface [12]. In order to

anticipate these problems, an extensive use of cement

in repair mortars started at the beginning of the past

century, which gave unsatisfactory results because of

the high content of soluble salts and the limited

compatibility between cement and the original com-

ponents of the masonry. However, it must be pointed

out that, a lot of the present mistrust to the use of

cement in restoration of historic buildings is basically

due to its uncontrolled application without directed

research [12]. Consequently, the controlled use of

cement improves mechanical strength of repair mortar

and eliminates its influence on microstructure [13, 14].

The addition of cement in limepozzolancementmortar allows for the development of bond strength at

early age of the mortar, whereas the pozzolanic

reaction contributes to further enhancement of the

mechanism mainly after the age of 28 days [15].

Moreover, the replacement of a part of traditional lime

by cement permits the reduction of a potential source of

damage ions, especially calcium. The free calcium

dissolves in water present in the stone and then reacts

with sulphates from the environment to form mainly

gypsum, which is the most common and most damag-

ing form of hydrated calcium sulphate; it is revealed aclear correlation between building areas of damaged

granite and sources of calcium, such as lime mortars

[16].

The importance of the repair and rehabilitation of

historic mortars is recognized but the available exper-

imental results are limited. Moreover, a large number

of reported data concern an experimental investigation

with a limited scope. In this study a systematic research

of repair mortars is carried out in a general framework,

without the artificial bounds placed by the problems of

a given monument. During the design an effort wasmade to connect the available experimental evidence

with the demands of the practical application. The

objective of the research was to extract conclusions

about the main factors affecting the mechanical and

physical behaviour of repair mortars, to quantify the

influences induced and to characterize the way and the

degree of the influence of each parameter. Thus, in this

research is studied the influence induced by the design

parameters to compressive strength, creep, water

absorption and length change of repair mortars, in

order to extract conclusions that can served to select asuitable repair mortar for historic buildings.

2 Experimental program

2.1 Design materials

The constituents of the binder (B) used in the

mixtures of repair mortars were hydrated lime as

1672 Materials and Structures (2011) 44:16711685


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dry powder (L), a Greek natural pozzolan (P) and

cement (C). The pozzolan used was a natural

pozzolan of volcanic origin from Milos island, milled

Milos earth (M.e.) with maximum grain size 0.5 mm.

The cement used was a CEM I 42.5 N according to

EN 197-1, i.e. ordinary Portland cement. The aggre-

gates (A) were natural silicate sand (S) and brickfragments (Bf), both with maximum grain size 4 mm

and their gradation was selected to be even and

similar to those used in historic mortars of Mediter-

ranean basin [4]. According to researchers the

influence of aggregate composition on lime mortars

is significant. For example, Pavia et al [17] evidence

that the best graded sands (containing a wide range of

particle sizes) improve the mechanical strength of a

lime mortar simultaneously lowering porosity and

water absorption. The aggregates were used after

testing their suitability.In order to obtain the above mentioned purpose,

the experimental program realized used as parameters

the mixing proportions of design materials.

(i) A considerable variable is the binder: aggregate

ratio, which controls the main properties of the

mortar. The two ratios studied were 1:2 and 1:4

by weight.

(ii) It is important to study the contribution of each

hydraulic material of the binder to the mechan-

ical properties of the repair mortar. By includ-ing as parameter the pozzolan: cement ratio, the

three ratios selected were 4:1, 1:1 and 1:4 by

weight. It must be noticed that, the addition of

cement in mixtures was decided for quantifying

the degree of its influence to repair mortars

characteristics. Moreover, it is considerable the

great number of historical buildings where

repair mortars with significant cement quantity

have been used and where cement still affect the

performance of the mortar. In order to provide

further evidence on these, different percentagesof cement participation have been designed,

even a large one.

(iii) Each type of aggregate used provides different

special surface area, surface shape and surface

texture. According to Ozol [18], surface texture

is the most important aggregate property influ-

encing strength, followed by modulus of elas-

ticity and shape. Concerning the shape of the

aggregate grains used, each type of aggregate

contributes in a different way. Sand, made with

rounded grains, improves the workability but

hinders the adherence and the consequent good

packed structure. Brick fragments provide good

packing due to its angular shapes. Moreover,

during mixing brick fragments as a porous

aggregate absorb immediately part of themixing water and render it during hydration.

It is also noticed that, microscopical observa-

tions confirm the presence of reaction products

at the binderbrick interface, dispersed in the

form of veins along the matrix, filling the

vacancies and discontinuities of its structure.

The presence of calcium and silica in the

reaction products supports the hypothesis of a

pozzolanic reaction [1, 19]. In order to provide

further data for the above mentioned and

estimate the influence of each aggregate typeon the mortars properties, three sand: brick

fragments ratios were studied, i.e. 1:3, 1:1 and

3:1 by weight.

For the study of the previously mentioned vari-

ables nine mixtures were designed, as presented in

Table 1.

2.2 Mixing, curing and testing procedure

As it was expected, the two different aggregates,having different porosity and specific surface area,

required different water content. Usually, the purpose

is to ensure that all mortars included the correct

amount of water that would provide a good work-

ability and final quality. The quantity of the tap water

used in each mixture has been adjusted in order to

provide to all mortars prepared a constant workabil-

ity, corresponding to an initial flow diameter equal to

165 5 mm, measured according to EN 1015-3

[20].

A total of 296 specimens were produced and allspecimens were prepared in accordance with EN

1015-11 [21]. The mortars were molded in the

appropriate casts, according to the test requirement

and then slightly compacted on a vibration table for

2 min. Compaction, although is not prescribed as

necessary in relevant regulations, is considerable in

the case of lime mortars, especially when produced

with coarse aggregates, as resulting from the study of

Stefanidou et al. [22]. The specimens were demolded

Materials and Structures (2011) 44:16711685 1673


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after 48 h. The mortars were cured in laboratory

conditions, at 20 2C and 5565% RH, until the

test day; the curing conditions were selected in order

to simulate the exposure conditions of repair mortarin historic buildings.

The mechanical and physical characteristics mea-

sured were compressive strength, creep coefficient,

water absorption and length change. The compressive

strength was measured at the ages of 7, 28, 90, 180,

365, 730 and 1095 days. The samples used were

cubes of 50 mm edge; these specimens were selected

in an effort to eliminate the effect of dimensions ratio

on the fracture. The reported results are the average

value of three specimens prepared in the same mold.

Creep test was realized on cylinders 30 9 60 mmand reported results present the average value of two

specimens. Creep is the result of a gradual arrange-

ment of the solid phase to a more stable settlement of

lower energy [23, 24]. As mentioned in Valluzzi [25],

high compression loads, often characterizing massive

brick masonry structures such as towers, curtain walls

and heavily loaded pillars, can lead to critical

conditions due to activation of creep. Typical dam-

agevertical and sub-vertical; thin, but very diffuse

cracksis worsened by cyclic stresses (due to

thermal and hygroscopic strains) or low dynamicforces (wind action or bell ringing). This type of

damage, generally disregarded in such structures, can

induce sudden, unexpected brittle collapse, as

observed in several cases, even at stress values

4060% lower than the strength of the masonry under

short-term static loads [26]. The researchers use

different design parameters in order to calculate the

applied load [27]. In this research, the design value

for the load applied was equal to 30% of the 28 days

compressive strength of the repair mortar; further-

more, a load level equal to 60% of the 28 days

compressive strength was applied in representative

mixtures of mortars. The compressive load wasapplied through a roller in order to provide axial

stress only. The axial deformation measurements

were taken by digital calliper of high accuracy, using

as reference points two very small metal plates

installed on the cylindrical surface of the specimen, at

mid-height. All specimens were loaded at the age of

28 days in an effort to minimize the shrinkage

influence; as illustrated in length change test results

the shrinkage effect was stabilized at this age. The

duration of the test was 90 days, when a slight

stabilization of the values was observed. During theperiod of testing, the curing conditions of the

specimens were stable (20 2C and 5565% RH).

The measurement of water capillary absorption of

mortars was based on RILEM TC 167-COM Rec-

ommendations. The samples used were prismatic

with dimensions 100 9 100 9 50 mm. The lateral

surfaces of the specimens were sealed by self-

adhesive tape, the weights of the prepared specimens

m0 were measured and then the molded bottom sides

were immersed in tap water up to a depth of

approximately 3 mm. They were removed andweighed at time intervals of 10, 45, 60 and

120 min. The test was realized at the ages of 28,

90, 180 and 365 days. The measurement of each

specimen was referred to the surface immersed and

the reported value resulted as the average value of

three specimens.

Length changes were measured in three samples of

40 9 40 9 160 mm, in accordance with DIN 52450

[28]. The samples were kept in a room of the

Table 1 Composition of

repair mortars (proportions

by weight)

Mixture

number

L, Lime P (Me), Pozzolan

(Milos earth)

C, Cement S, Sand Bf, Brick

fragments

W, Water

1 1 0.8 0.2 2 2 1.29

2 1 0.8 0.2 2 6 2.08

3 1 0.8 0.2 4 4 1.86

4 1 0.8 0.2 6 2 1.825 1 0.5 0.5 2 2 1.29

6 1 0.2 0.8 2 2 1.29

7 1 0.2 0.8 2 6 1.90

8 1 0.2 0.8 4 4 1.80

9 1 0.2 0.8 6 2 1.73



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laboratory where the curing conditions were stable

(20 2C and 5565% RH). The length change

values were daily measured up to 29 days, where a

stabilization of the values was noticed. The measure-

ments of the length change were continued period-

ically for almost 6 months; the results of these

measurements showed that the dimensions did notconsiderably change but they were significantly

affected by the variations of the relative humidity.

3 Test results and discussion

3.1 Compressive strength

The results of the compressive tests of repair mortars

specimens, at different ages, are plotted in Fig. 1. In

the tested specimens, no cracks owing to shrinkagewere observed. The results suggest an increment in

strength between 7 and 365 days. After this age the

development of strength is not regular: some mixtures

presented fluctuations or stabilization of the values

and others mixtures showed a slight downward trend.

This behaviour of lime mortars concerning long-term

strength agrees with the references of other research-

ers, for example Karaveziroglou-Weber and Papayi-

anni [29] and Lanas and Alvarez [30]. In order to give

an explanation for this fact, Lanas and Alvarez [30]

studied the compressive strength of lime-based mor-tars and give a hypothesis: mortars exhibit the highest

strength value when a certain amount of portlandite

stays uncarbonated. The decrease of this small amount

produces a slight drop in mortar strength.

3.1.1 Influence of the binder: aggregates ratio

Studying the effect of binder: aggregates ratio (B:A)

in compressive strength of repair mortars, different

results appeared according to the pozzolan: cement

ratio (P:C) of the mixtures compared. In the mixtureswith more pozzolan content (P:C = 4:1), the mixture

with the larger binder amount (No 1) reached higher

strength values. Other researchers agree with this,

evidencing that binder decrease in the lime-based

mortars reduces its strength and mortars with more

binder content show the highest compressive strength

and this fact can be proved at any time and

irrespective of the type of aggregate used [30, 31].

The mixture with the larger binder amount (No 1)

presented a 28 and 56% increment in compressive

strength at the ages of 28 and 1095 days, respec-

tively, when compared to the mortar with the lower

binder content (No 3). A regular development of

strength characterized the mortar No 1, while the No

3 presented a less regular development of strength

after the age of 365 days, when a strength loss of11% was computed. The mortars presented a

150160% increment of strength from the 7th to the

1095th day.

Mosquera et al. state that cement-based mortars

also develop higher strength values when binder

amount arises. Mortars produced with lime, pozzolan

and cement present the same behaviour [16]. Here,

the results of the mixtures with increased cement

content (P:C = 1:4) showed that the high content of

aggregates in the mixture does not significantly affect

the values of compressive strength; in some agesleads to a slight increment of compressive strength.

However, this trend is not clear due to the similarity

of the values of the mixtures compared and to the

fluctuations of strength values of the mortar with the

high content of aggregates, after the age of 180 days.

The mortar with the larger binder content (No 6)

showed a 14% decrease in strength compared to the

mortar with low binder dosage (No 8), at the age of

28 days, while a same level value (3% increase for

the No 6) was observed at the age of 1095 days. The

development of strength was similar: an 88% incre-ment was calculated in both mortars between 7 and

28 days. However, the mortar with the higher binder

amount showed a regular strength development,

while the other presented an 11% strength loss from

the 365th to the 1095th day.

The results suggest that the increase of aggregates

in the mixture (B:A = 1:4) leads to a strength

decrease, after the age of 365 days. On the contrary,

when the dosage of aggregates is lower (B:A = 1:2),

a stabilization of the values is noticed after the

365 days and a new increment in strength is showedat the age of 1095 days. These results agree with the

results of other researchers [30] who studied the

development of lime mortars until the age of

365 days.

3.1.2 Influence of the pozzolan: cement ratio

As it was expected, the mortars with the higher

amount of cement showed the higher strength values.



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The hydration of both pozzolan and cement leads to

the formation of similar hydraulic compounds (CSH)providing consistency to mortar paste, which hardens.

However, the hydration process of the two materials

has a different development rate. Pozzolan presents a

significantly slower hydration than cement and,

consequently its contribution to the compressive

strength of the mixture is lower than the cement,

especially at early ages. Here, the results agree with

the above remarking that the values of compressive

strength of mortars have shown a difference accord-

ing to the binder: aggregates ratio used: the trend is

more pronounced when the mixture contains largebinder amount.

In the case of mortars with larger amount of binder

(B:A = 1:2), the mixture where pozzolan is in excess

(No 1) presented considerable lower values of

compressive strength compared to the mixtures with

high cement content (No 6). The mortar made with

the higher pozzolan dosage (No 1) also showed lower

compressive strength than the mortar with the equal

dosage of pozzolan and cement (No 5). The No 5

presented 33% strength increment compared to No 1,

at the age of 28 days, while, the respective percent-age was 28%, at the age of 1095 days. The difference

in compressive strength is considerably higher when

No 1 is compared to the mixture where cement is in

excess (No 6). The No 6 showed 105% increase in

strength compared to No 1, at the age of 28 days,

while, the respective percentage was 64%, at the age

of 365 days. The differences in strength between the

mortar with equal dosage of pozzolan and cement and

the mortar where cement is in excess are lower,

especially after the age of 365 days. However, it is

noticeable the regular development of strength whenpozzolan is in excess in the binder, as in mortar No 1.

In the other case, where B:A = 1:4, the results are

proportional to the above mentioned but the differ-

ences in values of compressive strength are higher.

The mixture made with the higher pozzolan content

(No 3) presented significantly lower strength com-

pared to the mixture where cement is in excess (No 8).

The compressive strength of No 8 was 206 and 148%

increased compared to No 3, at the ages of 28 and

1095 days, respectively.

Therefore, it appears that repair mortars made withequal dosage of pozzolan and cement or with large

cement amount showed significantly higher strength

values, at all ages. This is due, as mentioned, to the

faster production of CSH during cement hydration

when compared to the pozzolan hydration. Mosquera

et al. evidence that cement mortars obtained higher

compressive strength values compared to the mortars

where lime and pozzolan were added; they relate the

reduction of strength to the higher porosity of the

latter binder type [16]. However, the high content of

pozzolan in the binder provides a regular develop-ment of compressive strength and without consider-

able fluctuations, while, the excess of cement in the

binder produces a mixture without regular strength

development.

3.1.3 Influence of the sand: brick fragments ratio

As before mentioned, each type of the aggregate

contributes to the compressive strength of mortars in

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0 90 180 270 360 450 540 630 720 810 900 990 1080 1170

Compressivestre

ngth(MPa)

Age (days)

MORTARS 1-9

No 1

No 2

No 3

No 4

No 5

No 6

No 7

No 8

No 9

Fig. 1 Compressive

strength values (MPa) of

repair mortars, at different

ages



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a different way. Brick is a porous material and have

the property to retain mixing water, leading to an

internal water supply for continuous hydration of

cement and pozzolan [32]. Brick fragments allow the

binderbrick interface reactions with consequent new

formations, thus eliminating any breaks in continuity

between the binder and the brick. In addition, brickfragments present angular shapes due to the crashing

brick process, allowing a better packed structure.

Sand provides to the mixture stiffness and high

special surface area. It is obvious that the influence of

the type of aggregate on the compressive strength of

mortars is significant. From the results of compres-

sive strength, it is evident that the mortars with equal

amount of sand and brick fragments have developed

an improved strength, probably due to the combined

contribution of brick properties and sand stiffness.

In the mortars with larger amount of pozzolan, themixture with the equal content of sand and brick

fragments (No 3) presented the higher values of

strength at all ages and a regular development of

strength. The No 3 showed 0 and 25% increased

strength values when compared to the mortar made

with higher quantity of brick fragments (No 2), at the

ages of 28 and 1095 days respectively. The mortar

made with higher quantity of sand (No 4) obtained 21

and 15% increment in strength when compared to the

No 2, at the ages of 28 and 1095 days respectively.

This suggests that, the increment of sand in themixtures leads to higher strength. This is probably

due to the sand stiffness that improves the slow

strength development owned to the pozzolanic reac-

tion. However, it is evident that the mixtures with

larger amount of brick fragments present more

regular development of strength; for example, when

a strength loss was expected after 365 days, a

stabilization of values was noticed. Therefore, this

indicates that the water supply that bricks provide

during hydration allow to a slower and more regular

hydration process.The above conclusion is also resulting from the

mixtures where cement is in excess. The mixture with

the equal content of sand and brick fragments (No 8)

obtained the higher strength values, almost at all

ages. The No 8 reached a slight increment of strength

values when compared to the mortar made with

higher quantity of brick fragments (No 7), at the ages

of 28 and 1095 days respectively. The mortar made

with higher quantity of sand (No 9) showed 36%

decrease in strength when compared to the No 7, at

the 28th and 1095th day. The influence of sand can be

attributed to the enlargement of the aggregates

binder interface surface area that quantifies the weak

mortar mass in tension; the compression failure is

caused from lateral tensile strains [33]. In contrary,

concerning the brick fragments in terms of strength,the lower modulus of brick aggregate may have be

compensated by their high angularity and rougher

surface texture, which improved strength develop-

ment by better mechanical interlocking and better

adhesion. This trend is also reported from other

researchers, referring lime mortars mixtures [31] or

even concrete mixtures, where the influence of brick

and granite aggregate was examined [34].

There seems to be a contradiction: the mixtures

made with cement in excess showed higher strength

when brick fragments increased, while the mixturesmade with pozzolan in excess obtained higher

strength when sand increased. This may be due to

the different effect of the main ingredient of the

binder. However, the contribution of brick fragments

was again underlined: the mixtures with larger

amount of brick fragments present a more regular

development of strength.

3.2 Creep

As before mentioned, the main design value for thecreep load was equal to 30% of the compressive

strength, at the age of 28 days. The load was applied

in all specimens at the age of 28 days, in order to

eliminate the shrinkage influence (drying creep), as

suggested in Neville [27]. Figure 2a illustrates the

creep coefficient values of repair mortars tested under

load equal to 30% fcm,28.


In the mixtures with high quantity of pozzolan, themortar with the higher binder amount (No 1)

experienced significantly higher creep coefficient

values, at all ages. This mixture showed a 218%

increment in creep coefficient when compared to the

mortar with the lower binder amount (No 3), at the

age of 90 days. The No 3 presented low creep

coefficient values. Both repair mortars showed a

normal rate and a slope decrease was noticed after the

56th day. The creep coefficient of No 1 and No 3 was



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increased 439 and 466% respectively, from the 3rd to

the 90th day.

In the mixtures with high amount of cement, the

mortar with the higher binder content (No 6) as well

as the mortar with the lower binder content (No 8)showed a slow development of creep coefficient and

low rate values. The values of two mortars were

similar until the age of 21 days, but after then, the

mixture with the higher binder dosage (No 6) differs

and its value is 131% increased compared to No 8, at

the 90th day. The increment of creep coefficient value

of No 6 and No 8 was 1664 and 970% respectively,

from the 3rd to the 90th day. However, both mixtures

reached low creep coefficient values comparatively to

all the others. This is due to the high content of

cement in the mixtures which controls and restrains

creep leading to low creep values.

Note that, independently the main ingredient of the

composition of the binder (pozzolan or cement), thehigher dosage of aggregates leads to increase of slope

of creep coefficient curve, nearly at the age of

56 days (2 months). This conclusion agrees with the

results of Li et al. [35], who studied the creep of

concrete in early ages. The measurements are realized

from the age of 3 to 120 days (T= 30 2C and

RH = 65 5%) and concluded that concrete mix-

tures with high aggregate dosage obtained low special

compressive creep values until about the 50th day,

0.00

2.00

4.00

6.00

8.00

10.00

12.00

Creepcoefficient

Age (days)

MORTARS 1-9

No 1

No 2

No 3

No 4

No 5

No 6

No 7

No 8

No 9

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

22.00

0 7 14 21 28 35 42 49 56 63 70 77 84 91

Creepcoefficient

MORTARS 1, 5, 7, 9

No 1

No 5

No 7

No 9

Age (days)

0 7 14 21 28 35 42 49 56 63 70 77 84 91

a

b

Fig. 2 Creep coefficient values of repair mortars tested at compressive load equal to a 30% fcm and b 60% fcm of 28 days, at different

ages



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after then the contrary effect was observed and later,

after the 120th day, the aggregate quantity influence

was negligible.


Evaluating the effect of pozzolan: cement ratio increep, it is evident the cement property (when

contained in considerable amount) to confines creep

and to controls creep deformation, at all ages

measured.

In the case of mixtures produced with high binder

content (B:A = 1:2), the lower creep coefficient

values are obtained by the mixture with high cement

quantity (No 6). The mixture where pozzolan is in

excess (No 1) presented significantly higher creep

coefficient values, at all ages; a 300% increment was

noticed compared to No 6, at the age of 90 days. Themixture with equal pozzolan and cement quantity (No

5) illustrated creep coefficient values within those of

No 1 and No 6, approaching the values of No 1. The

No 6 and No 5 showed 73 and 19% reduction of

creep coefficient values compared to No 1, at the age

of 90 days.

In the case of mixtures with lower binder amount

(B:A = 1:4), the same trend was apparent. The

mixture with high pozzolan quantity (No 3) noticed

creep coefficient values 3 times more than the

mixture with high cement content (No 8), at all ages.The mortar No 8 resulted to 62% lower creep

coefficient value compared to No 3, at the 90th day.


In the mixtures with high pozzolan content (P:C =

4:1), the mortar made with high brick fragments

quantity (No 2) as well as the mortar made with equal

quantity of two aggregates (No 3) obtained similar

and low creep coefficient values. The mixture with

the higher pozzolan dosage (No 4) illustrated a veryfast development of creep coefficient and showed

considerable increased creep values. This is probably

due to the low percentage of cement in the binder

and to the high amount of sand in the dosage of

aggregates. The sand has large special surface area

and leads to high interfacial transition zone which

facilitates the development of creep deformation. It is

evident that the mixtures with low cement and brick

fragments percentages reached enormous creep

coefficient values and fast creep development also.

The No 3 and the No 4 presented 3 and 326%

increased creep coefficient compared to No 2, at the

age of 90 days.

The above mentioned trend is not apparent in the

mixtures produced with high quantity of cement. This

is probably due to the large cement amount thatcontrols the behaviour of mixtures. The mixture with

equal percentage of aggregates (No 8) and the

mixture with the higher sand quantity (No 9) noticed

66 and 14% increment in creep coefficient compared

to the mixture with the higher brick fragments

content (No 7), at the 90th day. The mortars produced

with higher amount of the one aggregates type

showed similar creep development and values,

whereas the No 8 resulted to lower values. This

indicates that the contribution of cement is higher

when the angular shapes and the water supply ofbrick fragments as well as the stiffness of sand are

provided by an equal dosage of the aggregates.

3.2.4 Creep provided by compressive load equal

to 60% fcm,28

Moreover, in order to provide further results, the

creep development of repair mortars was studied

when the compressive load applied was equal to 60%

of the 28 days compressive strength. This load was

applied in four representative mixtures. The mixturestested were selected considering their behaviour

during compressive strength measurements: the

mortar No 1 (representing the group of 14), the

mortar No 5, the mortar No 7 (representing the group

of 68) and the mortar No 9. The reported results are

showed in Fig. 2b. The production, curing and testing

conditions of specimens remained as mentioned,

excepting the load value. The results extracted agree

to those mentioned above: here, the trends were the

same but more pronounced.

The results suggest that the mixtures made withconsiderable pozzolan amount have shown a vast

increment in creep, at all ages and the major part of

cement content contribution occurs until the age of

60 days, with maxima values at early ages. The

mixture made with high pozzolan content (No 1)

showed 86% increment in creep coefficient value

compared to the mixture with equal pozzolan and

cement dosage (No 5), at the age of 3 days, but the

respective percentage was 6%, at the age of 90 days.



10/15

It is noticeable that the mortar No 1 developed an

outstanding increment in creep compared to the other

mixtures, at early ages. This is probably due to the

fact that No 1 contained low cement percentage

allowing an uncontrolled deformation. The develop-

ment of creep coefficient of No 1 was enormous until

the 28th day, when a slope decrease was noticed. Thecreep coefficient value was 94% increased from the

3rd to the 90th day; note that, the 48% of the final

measured creep coefficient value (at 90 days) was

already reached at the 3rd day. Concerning the mortar

No 5, it showed a 240% increment in creep coeffi-

cient from the 3rd to the 90th day of testing.

However, the increment of aggregates and cement

amount in the mixtures leads to considerably lower

creep values. The mortar No 1 showed 521%

increment in creep coefficient value compared to

the mixture with higher cement dosage (No 7), at90 days; the respective percentage was 322% when

No 1 was compared to the mortar with larger

aggregates amount (No 9).

The difference between No 7 and No 9 is the

percentage of each aggregate types participation: No

7 contained S:Bf= 1:3 and No 9 contained S:Bf=

3:1. Both mixtures obtained low values of creep

coefficient and their development was regular. Con-

cerning the aggregates types influence, it appeared

that the values of No 7 where brick was in excess are

lower. The creep coefficient value of the mixturemade with sand in excess (No 9) was 47% increased

compared to No 7, at the age of 90 days. The No 7

presented 1584% increment in creep coefficient from

the 3rd to the 90th day of testing. The creep coeffi-

cient of No 9 showed 371% increment between 3 and

90 days.

Note that, in the case of mixtures with pozzolan in

excess, as in No 1, the reduction of cement acts as

critical factor leading to extremely high creep coef-

ficient values. This influence diminishes when the

mixture contained equal quantities of cement andpozzolan (No 5). In the case of mixtures with cement

in excess and high aggregates amount (No 7, No 9) a

significant restrain of creep occurred and considerably

decreased creep coefficient values are calculated.

3.3 Water absorption

The water absorption was evaluated at the ages of 28,

90, 180 and 360 days. The specimens were measured

at specific time intervals of 10, 45, 60 and 120 min.

The results of the water absorption measurements are

included in Fig. 3ad. During the discussion of

results, is considered that the measurement at

10 min shows the initial value of water absorption

and the measurement at 120 min provides the final

value of water absorption.


In the mortars made with high pozzolan content, the

mixture with low binder proportion (No 3) presented

slightly higher water absorption values compared to

the mixture with high binder proportion (No 1), at

all ages. The No 3 showed 16% increased final

water absorption value compared to No 1, at the age

of 28 days; the relative percentage was 12%, at the

age of 365 days. The mixture No 1 showed initialand final water absorption value 9 and 3%

decreased, respectively, between 28 and 365 days.

The initial and final absorption values of No 3 were

65 and 5% decreased, respectively, between 28 and

365 days. The results suggest that in the case of

mortars with large pozzolan amount, the mixture

made with large amount of aggregates reaches the

higher water absorption values. This is probably due

to the fact that the larger amount of aggregates

causes discontinuities in the structure and provides

higher quantity of brick fragments, a considerablyporous aggregate that increases the total porosity of

the mortar.

This trend becomes less pronounced in the case of

mortars with high cement content. According to the

results obtained, the values of water absorption

diminished after long-term hydration time: the initial

values noticed a considerable reduction while the

final values were slightly decreased, between 28 and

365 days. This is probably due to the fact that cement

hydration forms a binder with dense structure. The

mixture with the lower binder percentage (No 8)presented similar water absorption values, at all ages.

The water absorption value of No 8 was 1.3%

increased compared to No 6, at the age of 28 days;

the relative percentage was 3.5%, at the age of

365 days. The initial and final absorption values of

No 6 were 26 and 5% decreased, respectively,

between 28 and 365 days. The mixture No 8 showed

initial and final absorption value 71 and 3%

decreased, respectively, between 28 and 365 days.



11/15

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Waterabso

rption(gr/m2)

Age (days)

MORTARS 1-9, 10minutes

No 1

No 2

No 3

No 4

No 5

No 6

No 7

No 8

No 9

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 30 60 90 120 150 180 210 240 270 300 330 360 390

Waterabsorption(gr/m2)

Age (days)


No 1

No 2

No 3

No 4

No 5

No 6

No 7

No 8

No 9

0 30 60 90 120 150 180 210 240 270 300 330 360 390

a

b

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 30 60 90 120 150 180 210 240 270 300 330 360 390

Waterabsorption(

gr/m2)

Age (days)


No 1

No 2

No 3

No 4

No 5

No 6

No 7

No 8

No 9

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Waterabsorption(gr/m2)

Age (days)


No 1

No 2

No 3

No 4

No 5

No 6

No 7

No 8

No 9

0 30 60 90 120 150 180 210 240 270 300 330 360 390

c

d

Fig. 3 Water absorption

values (g/m2

) of repair

mortars at a 10 min,

b 45 min, c 60 min, and

d 120 min measurements



12/15


Evaluating the water absorption of mortars produced

with high binder content, it can be observed that the

values increased when pozzolan quantity rises. The

mixture made with the greater pozzolan quantity

(No 1) presented the higher water absorption valueswhile the mixture with the lower pozzolan content

(No 6) showed the lower values; the values of the

mixtures compared lied close. The No 1 obtained 3

and 5% increased absorption value compared to No 6,

at the ages of 28 and 365 days, respectively. The

mixture with equal amount of pozzolan and cement

(No 5) reached values between those of No 1 and No

6. It seems that cement controls the behaviour of the

mixture No 5 creating a dense structure, which leads

the values of the specimens close to those of No 6.

The absorption value of No 5 was 1% increasedcompared to No 6, at the age of 28 days; the relative

percentage was 2%, at 365 days.

The above results are nearly directly proportional to

those arising from the mixtures with low binder content:

the mixture with high cement quantity (No 8) reached

lower water absorption values compared to the mixture

with high pozzolan quantity (No 3). The No 3 obtained

16 and 14% increased absorption value compared to No

8, at the ages of 28 and 365 days, respectively. It is

evident that, the increment of cement in the mixture

leads to denser structure of mortar, allowing a reductionin water absorption values. This trend is more intense in

the mortars with low binder: aggregates ratio (1:4).


As it was expected, the mixtures with brick fragments

in excess presented the higher water absorption

values, due to the high porosity of brick. The results

obtained from the mortars with high pozzolan

quantity showed that the mixture with high brick

fragments amount (No 2) reached the higher waterabsorption values compared to the mixture with high

sand quantity (No 4) which noticed the lower

absorption values. The values of No 2 were 36 and

38% increased compared to No 4, at the ages of 28

and 365 days, respectively. The values reached by the

mixture with equal percentage of the two aggregates

(No 3) fall within those of No 2 and No 4. The No 3

obtained 20 and 19% increased absorption value

compared to No 4, at the ages of 28 and 365 days,

respectively. The development of the water absorp-

tion was regular; however, the values reached by the

mortars with high pozzolan quantity were compara-

tively high, especially for No 2 and No 3.

The same trend appeared in the mortars made with

high cement content: the mixture with high brick

fragments quantity (No 7) presented the higher waterabsorption values compared to the mixture with high

sand amount (No 9) which showed the lower

absorption values. The water absorption value of

No 7 was 13% increased compared to No 9, at the age

of 28 days; the relative percentage was 19%, at

365 days. The values of the mortar with equal dosage

of sand and brick fragments (No 8) lied between

those of No 7 and No 9. The No 8 obtained 4 and 8%

increased water absorption value compared to No 9,

at the ages of 28 and 365 days, respectively. The

development of water absorption was regular and thevalues reached were similar.

Therefore, this indicates that the increment of brick

fragments percentage in mixture leads to increased

water absorption values, independently of pozzolan:

cement ratio. In case that cement amount in the

mixture is considerable, the trend is less pronounced

and the values of water absorption are reduced.

3.4 Length change

The length change values were daily measured up tothe age of 29 days, where a stabilization of the values

was noticed. The measurements of the length change

were continued periodically for almost 6 months. The

results showed that the latter values did not consid-

erably vary, but they were significantly affected by

the variations of the relative humidity of the labora-

tory: the increase of the relative humidity leads to

higher length change values. The results of the length

change measurements are showed in the Fig. 4.


Studying the mortars produced with high pozzolan

content, it was evident that the mixture with larger

binder amount (No 1) presented higher length change

values compared to the mixture with low binder

dosage (No 3). The No 1 showed 53% increased

length change value compared to No 3, at the

28 days. The development of shrinkage was regular

and the values were stabilized at the age of 9 days.



13/15

In the mortars with high cement quantity, it wasobserved that the mixture with the lower binder

percentage (No 8) noticed the higher length change

values. However, the values obtained by the mortars

No 8 and No 6 were similar, especially after the 12th

day. The mixture with the higher binder amount

(No 6) presented 26% decreased length change value

compared to No 8, at the age of 30 days. As the

results suggest, the length change values of No 6 and

No 8 illustrated close to those of No 1.


In the case of mortars with high binder amount, the

mixtures noticed similar length change development

and values. The mixture with equal pozzolan and

cement percentage (No 5) obtained the lower length

change values. The No 5 and No 6 reached 38 and 25%

decreased length change value compared to No 1,

respectively, at the age of 30 days. The mixture with

the higher pozzolan quantity (No 1) showed a stabil-

ization of values at the 14th day, while the mixtures

with considerably cement amount (No 5 and No 6)were easily affected by humidity and their values

presented a slight fluctuation even after the 14th day.

In the case of mortars with low binder amount, the

mixture with the higher cement quantity (No 8)

showed higher length change values. The No 8

obtained 55% higher length change value compared

to No 3, at the age of 30 days.

Concerning the influence of the components of the

binder on the length change, Mira et al. [36] evidence

that, when lime putty is added in concrete made byOPC, a smooth increase in the length change of the

specimens is observed. However, when pozzolanic

materials are contained in the concrete, a rather

significant decrease in the length change is observed.

The authors suggest that in the latter case, the faster

formation of strength components as a result of the

reaction between lime and pozzolanic materials

improve the total stability of concrete.


The mortars produced with high pozzolan amount

noticed similar rate and values of length change. The

mixture with equal aggregate dosage (No 3) and the

mixture with sand in excess (No 4) reached 21 and 27%

increased length change values compared to the mixtures

with large brick fragments quantity (No 2), at the age of

30 days. The measurements showed that, in the case of

high pozzolan content in the binder, the length change

values are significantly low and the proportion of the

aggregates seems to not affect the shrinkage.

The mortars made with high cement contentshowed higher length change values when compared

to those of the above group. The mixture with the

higher sand quantity (No 9) presented the higher

length change values, while the mixture with the

higher brick fragments quantity (No 7) obtained the

lower values. The mixture with equal quantity of each

aggregate (No 8) and the mixture with large amount

of the sand (No 9) noticed 45 and 50% increment of

length change value compared to No 7, respectively,

0.000

0.050

0.100

0.150

0.200

0.250

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Lengthchange(

%)

Age (days)

MORTARS 1-9

No 1

No 2

No 3

No 4

No 5

No 6

No 7

No 8

No 9

Fig. 4 Length change

values (Dl %) of repair

mortars, at different ages



14/15

at the age of 30 days. The large differences of the

values are probably due to high porosity of the brick

that facilitates the move of the water in the micro-

structure of the mixture.

Thus, the lower length change values are noticed

by the mixtures with the larger brick fragments

quantity. This result is in agreement with otherresearchers who report that brick-aggregate concrete

shrunk less than granite-aggregate concrete; they

state that drying shrinkage in brick-aggregate con-

crete is delayed by continued hydration due to the

presence of internal moisture in the aggregate [34].

Also, Hansen [37] suggests that the reduced shrink-

age of brick-aggregate mixture contradicts the expec-

tation that brick aggregates offer less deformation

resistance to the shrinkage of cement paste due to its

lower modulus of elasticity. As shown here, this trend

is obvious in mixtures where cement is in excess.However, it is not clear in the mixtures with high

pozzolan content, probably because the values

reached lie close.

4 Conclusions

1. It is observed that, in the case of mixtures

produced with high pozzolan content, the incre-

ment of binder in the mixture improves the

compressive strength but also allows to develop a

considerably high creep and leads to slightly

higher length change values.

2. The mixtures with large cement amount noticed

higher compressive strength and lower creep

values; these properties are not significantly

affected by the proportion of the binder. These

mixtures showed lower length change values

when larger binder amount was used.

3. The compressive strength of the mixtures noticed

fluctuations after the age of 12 months. The

increment of pozzolan in the binder allows a

more regular development of strength; the same

effect is obtained when brick fragments quantity

increases. It was observed that, in case of

mixtures with high pozzolan content the incre-

ment of sand leads to improved strength, while,

in the mixtures with high cement amount, this

result is reached when brick fragments rises.

4. Cement as well as brick fragments counteract the

creep deformation. Mortars made with high

pozzolan and sand quantities have noticed

extremely high creep values.

5. Specimens produced with low binder content

showed increased water absorption values, prob-

ably due to the fact that the larger amount ofaggregates causes discontinuities in the structure

and produces a mixture with higher quantity of

brick fragments, a considerably porous aggregate

that increases the total porosity of the mortar. The

water absorption values are higher when the

percentage of brick fragments increased; this trend

is more pronounced when pozzolan content rises.

6. The length change measurements suggest that, the

mixtures made with large brick fragments quantity

present lower values and the trend becomes more

intense when cement percentage increases.7. Further research is in progress in order to

estimate the porosity and the water permeability

of the mortars tested; the pore structure and the

water move considerably affect the properties of

mortars. The compatibility between the repair

mortars and the original components must also

be determined. In addition, the carbonation of the

mortars tested will be studied in order to evaluate

the hardening process.

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