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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
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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 binder- brick 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
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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.
3.2.1 Influence of the binder: aggregates ratio
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.
3.2.2 Influence of the pozzolan: cement ratio
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.
3.2.3 Influence of the sand: brick fragments ratio
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.
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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.
3.3.1 Influence of the binder: aggregates ratio
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.
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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)
MORTARS 1-9, 45minutes
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)
MORTARS 1-9, 60minutes
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)
MORTARS 1-9, 120minutes
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
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3.3.2 Influence of the pozzolan: cement ratio
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).
3.3.3 Influence of the sand: brick fragments ratio
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.
3.4.1 Influence of the binder: aggregates ratio
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.
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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.
3.4.2 Influence of the pozzolan: cement ratio
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.
3.4.3 Influence of the sand: brick fragments ratio
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
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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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