15th International Brick and Block Masonry Conference

Florianópolis – Brazil – 2012

USE OF POZZOLAN IN REINFORCEMENT MORTAR FOR NON-

STRUCTURAL MASONRY

Mota, João Manoel de Freitas1; Oliveira, Romilde Almeida

2

1 MSc, Doctorate Student, Federal University of Pernambuco, Civil Engineering Department,

joão@vieiramota.com.br 2D.Sc., Permanent Professor, Federal University of Pernambuco, Graduate Program Civil Engineering,

Professor, Catholic University of Pernambuco, Civil Engineering Department,

romildealmeida@gmail.com

In the metropolitan area of Recife (Brazil), the existence of several buildings known as

“caixão” with up to four floors and built with non-structural block is perceived. These non-

structural masonries have been used for structural purposes and were designed without

technological basis and relevant technical standards. The materials used, basically the blocks,

do not have satisfactory performance. Several surveys were carried out in order to better

understand the behavior of these buildings and establish a way of strengthening aiming at an

adequate performance in service, and ensuring conditions for durability. It was verified that

the mortar coating contributes to the hardness of the walls. This suggests the use of mortar

with addition of pozzolan with steel as reinforcement, due to substantial increases in the

mechanical properties and related durability. This study evaluates the influence of the

metakaoline pozzolan in mortars through experimental studies. The mechanical properties and

other related durability at 28 days and 90 days were evaluated. The results indicate that the

addition of metakaoline mortars improves the properties studied.

Keywords: non-structural masonry, reinforced mortar, pozzolan.

INTRODUCTION

In the Metropolitan Region of Recife-Brazil, masonry buildings were widely used since

colonial times, due to the abundance of materials combined with the Portuguese culture

regarding the use of ceramic masonry.

From the 1970s, there was a great raise in the construction of affordable housing on a large

scale. Buildings of up to four stories started to be built using blocks characterized as non-

structural blocks that nevertheless were used for a structural purpose. These constructions

were executed in an empirical way without following specific technical standards and without

any technical scientific basis to allow the establishment of acceptable structural reliability

standards, which in turn resulted in the emergence of a number of pathologies and accidents.

So far, 12 buildings have collapsed, resulting in 11 fatalities and many injured. In addition, a

large number of buildings have been interdicted, for they do not provide safe conditions to

their users.

It is known that these buildings were built without any technical basis and that materials and

processes that did not meet structural requirements were used (MOTA, 2006).

It is estimated that around 6.000 “caixão” buildings, are in use in the Recife Metropolitan

Region, housing approximately 250.000 people (OLIVEIRA, 2004). These high numbers of

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buildings using non-structural masonry made of ceramic blocks with no structural function

were conceived due to their low cost when compared to concrete buildings (OLIVEIRA;

SOBRINHO, 2006).

In addition, several pathologies were identified in these buildings so that about 160 buildings

have been interdicted. Surveys of the buildings showed that the most loaded walls do not meet

the safety requirements established by the relevant technical standards, mainly because the

blocks do not meet strength requirements and resistance concerning to environmental agents.

Nevertheless, buildings with over 30 years of existence are still in use (MOTA; OLIVEIRA,

2007).

Generally, the most important cause of collapse of the so called “caixão” buildings was the

brittle rupture of the foundation walls above the concrete slabs due to the deterioration of the

foundation materials (OLIVEIRA, 2004). Figure 1 shows the generic scheme that well

characterizes these buildings.

In this context, reinforcement models for these buildings were developed by several

researchers. Initially in Recife, Mota (2006) presented studies of prisms of ceramic blocks

with the objective of analyzing the influence of coating mortar on stiffness. The author

concluded that the best result (sample P6) increases axial compressive strength up to 322% in

relation to the reference sample (P1), see Fig. 1.

The identification of the samples are given as follows: P1 (reference – single prisms); P2

(prisms with rough cast on both sides, ratio 1:3 – cement and coarse sand); P3 (prisms with

rough cast and plaster on both sides, the thickness of the coating of 2.0 cm and the use of a

weak proportion 1:2:9, cement, lime and coarse sand); P4 (prisms with rough cast and coating

on both sides, the thickness of the coating of 2.0 cm and the use of a medium proportion

1:1:6, cement, lime and coarse sand); P5 (prisms with rough cast and coating on both sides,

the thickness of the coating of 3.0 cm and the use of a weak proportion) and P6 (prisms with

roughcast and coating on both sides, the thickness of the coating of 3.0 cm and the use of a

medium ratio).

13,78

26,42

72,45

176,2

131,12

267,77

79,08

218,94

137,76

322,94

0

50

100

150

200

250

300

350

P2 P2 P3 P3 P4 P4 P5 P5 P6 P6

Figure 1 – Increase in resistance due to the influence of the coating

Oliveira et. al (2008) tested masonry prisms of ceramic blocks and non-structural concrete

blocks used for structural purpose. Prisms with and without coating, and prisms with steel

INCREASES IN AVERAGE VALUE

(%)

PRISMS SAMPLES

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mesh embedded in the interior of the rendering mortar with and without connectors that

interconnect the coating layers on both sides of the prisms were used.

The authors obtained results on ceramic blocks prisms where the coating contributed to

increase the load-bearing capacity of up to 335%. Several types of rupture were identified. It

was found that the rupture of the blocks occur due to the side traction in the horizontal

partitions of the blocks, leading to unbalance in the state of confinements of the laying mortar.

No significant load increases were observed when prisms with steel mesh without connectors

were tested. In concrete blocks masonry prisms, an increase of up to 72% was observed due to

the coating layer. However, the increase occurred at levels of up to 159% when steel mesh

was used; the steel mesh equalizes the load distribution inside the coating with a subsequent

influence on the rupture; when a double layer of reinforced mortar was used, the increase in

load bearing achieved almost 300%; the connectors increased axial load bearing capacity

65%, prisms with 3.0 cm of reinforced coating with connectors increased the load bearing

capacity 180%.

Pires Sobrinho et al (2009) tested 145 masonry small walls with the following characteristics:

dimensions 0.09 m × 0.60 m × 1.20 m, hollow ceramic blocks with eight holes (dimensions:

9×19×19 cm each), a mixture of cement, lime and sand mortar with a volumetric mixture ratio

of 1:1:6. In this study, it was concluded that the mortar coating increases the stiffness of the

walls proportionally to the thickness and to the elasticity modulus of the mortar; the coating

does not change the rupture pattern of the masonry, which occurs in a brittle mode. However,

it was found that the coating does have an effective participation in the compressive behavior

of the walls; the steel mesh reinforcement, with the locking of the reinforcement inside the

coating, increases the load bearing capacity of the walls, and, basically, produces significant

change in the rupture pattern, leading to a plastic behavior, below the rupture level, allowing

for a redistribution of strains and deformations between the elements of a structure.

Therefore, nowadays a reinforcement model suitable for the use of reinforced mortar with the

addition of pozzolan is being researched in order to increase mechanical properties, as well as

those related to durability, thus this can be one of the reinforcement models recommended for

constructions with these characteristics i.e., buildings with resistant masonry (walls with non-

structural ceramic blocks).

In this case, the refinement of the pores in materials with a cementitious matrix, provides a

greater barrier to the reinforcement inside the mortar, preventing: sulfate attack, salt spray

(chloride ions), carbon dioxide, and humidity among other aggressive agents increasing as

well the mechanical resistance (MOTA; OLIVEIRA; DOURADO, 2011). Neville (1997)

states that the pozzolans added to the mortars and concretes, promote a higher density of the

mix generating a natural porosity reduction from the interface to the surface (due to the wall

effect).

Galvão (2004) observed that mortars with addition of metakaolin considerably increased

mechanical properties when compared to mixed mortars with no metakaolin. It is known that,

in a number of cases, mortars with metakaolin exceeded in terms of bonding properties.

It was concluded that in research with pozzolan, the addition of this material to mortars tends

to increase mechanical performance up to 2.75 times, especially in bonding strength of

inorganic mortars (TAHA, 2001).

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Figure 2 shows the metakaolin positioned between the cement particles, filling the gaps

(physical effect – filler) and reacting with the calcium hydroxide turning into C-S-H

(chemical effect). This physical phenomenon explains the decrease of gaps, for it takes place

before the pozzolanic reactions start, when the finer inert metakaolin particles fill the existing

spaces that would otherwise be occupied by air.

Figure 2 – Metakaolin – Electronic Microscopy – magnified 3000 X

(Source: www.metacaulim.com.br)

Figure 3 shows pozzolan particles in the cement interstitial spaces.

Figure 3 – Metakaolin pozzolan particles in the cement interstices

(Source: www.metacaulim.com.br)

Figures 4A and 4B show the electronic microscopy of the region located between the

reference paste with pure cement (left) and the paste with an 8% metakaolin content (right)

replacing cement, both at 28 days. The darker regions represent porosities or interstices.

A B

Figure 4 – Metakaolin pozzolan particles in the cement interstices

(Source: www.metacaulim.com.br)

This study aims to evaluate the increase in mechanical properties of reinforced mortar with

addition of metakaolin.

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METHODOLOGY AND MATERIALS

The study was conducted on four samples of mortar mix consisting of cement, hydrated lime

and sand, with percentages of 0 %, 10 %, 15 % and 20 % addition of metakaolin in relation to

the cement volume. Cylindrical specimens were prepared for each case in order to investigate

mechanical properties (axial compressive strength, traction by diametral compression and

tensile bond strength).

All studies were performed at the Civil Engineering Laboratory (LEC), of Vale do Ipojuca

College – FAVIP (Caruaru, Pernambuco), which is part of the developed research.

During the preparation of the samples, mortar workability was kept constant, measured from

the flow table at a value of 200 mm + 20 mm. The quantities of materials used are listed

below:

sample 1 (reference - 0% metakaolin) – 1:1:6:1.5 (cement:lime:sand:water/cement ratio);

sample 2 (10% metakaolin replacing cement) – 1:1:6:1.5;

sample 3 (15% metakaolin replacing cement) – 1:1:6:1.5;

sample 4 (20% metakaolin replacing cement) –1:1:6:1.5.

To evaluate the influence of metakaolin on the mechanical performance of the mortars, tests

were performed at 28 and 90 days, using the same amount of samples in both cases. 15

replicas per sample for each age – 28 days and 90 days, were used. For all tested specimens,

cylinder surfaces were capped with sulfur on both sides.

The tensile bond strength test was accomplished by cutting the mortar into a 10 cm × 10 cm

square shape. After bonding the metal plates with epoxy, rupture of the sample was carried

out after 24 hours. Both sides of the wall were used for the test, one with conventional

roughcast in a 1:3 ratio (cement and sand) and the other side with roughcast with replacement

of 5% metakaolin.

Statistical analysis was performed by calculating the standard deviation of all results,

eliminating values more than three times the standard deviation away from the mean, for each

side. Afterwards, a new mean value, standard deviation and variation coefficient were

calculated, according to the table.

MATERIALS

Binders - CP II-F-32 cement and CH-II hydrated lime were used, both are widely used in

the region;

Additions – The metakaolin used is industrialized in the Recife Metropolitan Region,

originating from high reactivity kaulinitic clay, with the following basic characteristics

(informed by manufacturer): White color; specific mass density 2.49 g/cm3

and apparent mass

density 0.43 g/cm3;

Fine aggregates – Natural quartz sand widely found in the region of the city of Caruaru

(PE), was used. This material is characterized by specific and apparent mass density, and

determination of the granulometric curve and coefficient of uniformity according to the Allen-

Hazem method. This method relates C = d60/d10, meaning the equivalence of percent passing

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of material.

Table 1 shows the features of the natural sand.

Table 1 – Features of the sand used in the research

Maximum characteristic dimension 2.36

Fineness module 2.15

Apparent density (g/cm³) 1.63

Specific mass (g/cm³) 2.56

Uniformity coefficient 1.20

Blocks: The masonry base executed with non-structural ceramic blocks was built next to the

laboratory and had the following features: average length, height and width measurements

(19.0 cm; 9.5cm and 19.1cm); mass 2.510 g; IRA (Initial Rate Absorption) 12.2 g/200

cm2/min and total absorption 12.3 %;

Water: The water used came from the water supply system of the Pernambuco Sanitation

Company (COMPESA). It was verified that the pH of the water used, was close to 6.5.

RESULTS AND DISCUSSIONS

The results of mechanical tests regarding compressive strength are presented on Table 2.

Table 2 – Results of compressive strength tests

AXIAL COMPRESSIVE STRENGTH (MPa)

Age

in

days

Samples

1 2 3 4

Avg SD COV

% Avg SD

COV

% Avg SD

COV

% Avg SD

COV

%

28 5.01 0.37 7.39 5.28 0.20 3.79 5.86 0.41 6.99 6.33 0.48 7.58

90 6.25 0.39 6.24 6.50 0.18 2.77 6.94 0.42 6.05 8.46 0.27 3.19

Figure 5 shows the rupture mode of the specimens.

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Figure 5 – Specimen during the compressive strength test

An increase in compressive strength in the samples with addition of metakaolin was observed

when compared to the reference sample and in relation to time, as well.

In regards to traction by diametral compression, Table 3 presents the results of the tests

performed.

Table 3 – Results of traction by diametral compression

TRACTION BY DIAMETRAL COMPRESSION (MPa)

Age

in

days

Samples

1 2 3 4

Avg SD COV

% Avg SD

COV

% Avg SD

COV

% Avg SD

COV

%

28 0.54 0.03 5.56 0.93 0.17 18.28 0.99 0.08 8.08 1.00 0.02 2.00

90 0.78 0.04 5.12 1.07 0.03 2.56 1.15 0.13 11.3 1.38 0.07 5.07

Figure 6 shows a specimen during traction by diametral compression test.

Figure 6 – Traction test by diametral compression test

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Satisfactory results were also observed for the tensile strength test, considering the increase

for the samples with metakaolin in relation to the reference sample. There was also an

increase in the results when compared the 28-days age with 90-days age. Table 4 presents the

results for the tensile bond strength test.

Table 4- Results of tensile bond strength test

Age in days

Samples

1 2 3 4

Avg SD COV

% Avg SD

COV

% Avg SD

COV

% Avg SD

COV

%

ROUGH CAST

WITHOUT

ADDITION

0.28 0.067 23.93 0.29 0.074 25.51 0.36 0.06 16.67 0.38 0.035 9.21

PREDOMINANT

RUPTURE

ROUGH

CAST/BLOCK

ROUGH CAST

/BLOCK

ROUGH CAST

/BLOCK ROUGH CAST

ROUGH CAST

WITH

ADDITION

0.37 0.05 13.51 0.41 0.07 14.89 0.41 0.012 2.93 0.43 0.026 6.05

RUPTURE BLOCK ROUGH CAST

AND BLOCK

ROUGH CAST

AND MORTAR

ROUGH CAST

/BLOCK

It was observed that there was an increase in tensile bond strength as pozzolan was added. It

was also found that bonding increased at 90-day age when compared to 28-day age.

Figures 6a and 6b show the test in loco.

A B

Figure 7 – Tensile bond strength test

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CONCLUSIONS

- It was observed that axial compressive strength of the mortars increased as of addition of

pozzolan increased, and in relation to time, as well. The largest increase was in sample 4 at 90

days in relation to the reference sample at 28 days (69.9%), thus evidencing the effect of

pozzolanic reactions;

- The tensile bond strength by axial compression, with the addition of metakaolin increased in

relation to time. The greatest increase occurred in sample 4 at 90 days in relation to sample 1

at 28 days (155%);

- Concerning to tensile bond strength, it increased when the extraction in the reference sample

was compared to samples with addition, as well as to the side where the rough cast had

pozzolan addition. The most significant increase achieved 53.5%;

- This study indicated that the addition of pozzolan in mortars contributes to the improvement

of mechanical properties, an important fact for the entire universe of mortars, and,

significantly, for the reinforcement of mortars.

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cement modified by polymers and containing mineral additions (in portuguese). Master

Thesis (UFG), 2004.

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Ceramic Blocks Masonry Prisms (in portuguese) Master Thesis. UFPE – Federal University

of Pernambuco. Recife, 2006. PE.

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