Porosity, pore structure and water absorption of polymer-modified mortars: An experimental study under different curing conditions

The porosity and pore size distributions are pore structure parameters which have a direct effect on the permeability of cement paste as well as its durability. This paper is based on laboratory programs comparing the porosity, pore size distributions and water absorption with varying ageing processes of three commercial polymer-modified mortars (SBR, PAE and VAE) as well as unmodified conventional mortar mixes exposed to different curing conditions. It was found that an increase in polymer loading has resulted in a significant reduce in porosity and water absorption in polymer-modified mortars. Furthermore, the SBR3 mix exhibited the most superior properties of the study in all conditions at different ages of curing.

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Porosity, pore structure and water absorption of polymer-modiﬁed

mortars: An experimental study under different curing conditions

School of Housing, Building and Planning, Universiti Sains Malaysia, Malaysia

Article history:

Received 20 June 2012

Received in revised form 8 May 2013

Accepted 12 June 2013

Available online 25 June 2013

Keywords:

A Polymer–matrix composites (PMCs)

B Porosity

E Cure

Water absorption

a b s t r a c t

The porosity and pore size distributions are pore structure parameters which have a direct effect on the permeability of cement paste as well as its durability This paper is based on laboratory programs com-paring the porosity, pore size distributions and water absorption with varying ageing processes of three commercial polymer-modified mortars (SBR, PAE and VAE) as well as unmodified conventional mortar mixes exposed to different curing conditions It was found that an increase in polymer loading has resulted in a significant reduce in porosity and water absorption in polymer-modified mortars Further-more, the SBR3 mix exhibited the most superior properties of the study in all conditions at different ages

of curing

1 Introduction

The corporation of synthetic polymers in Portland cement

mor-tars and concrete, such as polyvinyl acetate (PVAC) and polyacrylic

ester (PAE) began in the 1950s[1] Since then, a greater interest on

the use of synthetic polymer latex weighed over the use of natural

rubber latex in polymer-modiﬁed cement systems Synthetic

poly-mer latexes, such as styrene–butadiene rubber (SBR) latex in a

Port-land cement system, has gained acceptance in many applications

[2] As a result, various types of synthetic polymer latexes have

been widely applied in the construction industry[3,4] The main

reason may be due to the fact that normal air-entrained concrete

is relatively porous Furthermore, moisture, oxygen and chlorides

from de-icing salts can migrate through the surface and reach the

reinforcing steel causing corrosion and subsequent spalling [5]

Polymer-modiﬁed mortar (PMM) and concrete seal the pores and

microcracks developed during hardening of the cement matrix by

dispersing a polymer phase throughout the concrete[6] Apart from

improving chemical resistance, polymer modiﬁcation also

im-proves the workability at low water–cement ratios This reduction

in water also contributes to the increase strength and durability

characteristics[7] In this regard, porosity and pore size

distribu-tions are of paramount importance and cannot be considered as

insigniﬁcant when determining the durability performance of a

PMM system The porosity and pore size distributions are pore

structure parameters which have a direct effect on the permeability

of cement paste However, permeability is directly related to the ﬂow of ﬂuids through continuous pores with a diameter of at least

120 or 160 nm[8] Furthermore, discontinuous pores whether in cement paste or in aggregate, do not contribute to permeability Porosity, on the other hand, is a measure of the proportion of the to-tal volume occupied by pores, and is usually expressed in a percent

If the porosity is high and the pores are interconnected, the perme-ability is relatively high Conversely, if the pores are disconnected, then the permeability tends to be low, regardless if its porosity is high[9] The pore structure of a PMM system, perhaps more than any other characteristic, inﬂuences the behaviour and other charac-teristics of the material In this regard, porosity and pore size distri-bution are important pore structure parameters due to their affects

on the strength, durability and permeability of the materials[10– 12] The PMM system that is well-known with its reﬁned pore structure and durable performance is therefore excellent to be ap-plied as waterproof renders, ﬂoor topping and also structure repair materials The PMM system also use to build structures that are ex-posed to the aggressive weathering effects like freezing/thawing, marine environment and, etc or apply in thin sections (10–

30 mm) which serve as coating layers to the structures

In view of the aforementioned, measuring pore structure param-eters, including porosity, pore size distribution, and water absorp-tion can help tremendously in assessing the effect of polymer additions and curing conditions on the durability properties of ce-ment mortars This is therefore becomes the major concern of this paper which describes the analysis and discussion of the porosity, pore size distribution and water absorption of Portland cement mortars and their modiﬁcations with various polymer emulsions 1359-8368/$ - see front matter Ó 2013 Elsevier Ltd All rights reserved.

⇑ Corresponding author Tel.: +60 174709240.

E-mail address: akhavan.ta@gmail.com (A.A Tabassi).

Contents lists available atSciVerse ScienceDirect Composites: Part B

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / c o m p o s i t e s b

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within different curing conditions In addition, this paper also

elab-orates the relationships between the water absorption with total

porosity and maximum continuous pore diameter of PMMs and

unmodiﬁed mortar, respectively This information is scarce in the

body of knowledge

2 Experimental set-up

2.1 Polymer materials

Polymer-modiﬁed mortar (PMM) is normally prepared by

mix-ing either a polymer or monomer in liquid form or a dispersible

powder with fresh cement mortar and concrete mixtures [13]

Among the most common synthetic polymers available in the form

of latexes, emulsions and re-dispersible powders are

styrene–buta-diene rubber (SBR), polychloroprene rubber (CR), polyvinyl acetate

(PVA) latexes, polyacrylic ester (PAE), styrene–acrylic and ethylene

vinyl acetate (EVA) emulsions, and vinyl acetate–ethylene (VAE)

re-dispersible powder Among these polymers, the SBR latex shows

a simpliﬁed application in the construction industry[14]

Polyacry-lic ester emulsion (PAE) has been reported to improve various

engineering properties of mortars and concrete [2] Vinyl

ace-tate–ethylene (VAE) copolymer re-dispersible powders are

com-mercially used as admixtures in hydraulic cement formulations

[15] Accordingly, in the tests reported here, three types of latexes,

SBR with the trade name of Resibond SBR, PAE, which is known as

Mowilith VDM 758, and VAE were used together with an ordinary

Portland cement mortar SBR is a water-based emulsion of a

sty-rene acrylic copolymer containing 45% polymer solids by weight

Mowilith VDM 758 is also a water-based dispersion of a copolymer

based on acrylic esters containing 60% polymer solids by weight

However, VAE known as Vinnapas RE545Z is a copolymer powder

which re-disperses readily in water VAE is white powder resin

having relatively high ethylene content with glass transition

tem-peratures below freezing point

2.2 Super-plasticizer

Super-plasticizers (SP) are admixtures that reduce water and

are also known to improve the workability properties of concrete

and mortars The two most common types of super-plasticizers

are sulfonated melamine–formaldehyde condensates and

sulfo-nated naphthalene-formaldehyde condensates The latter of the

two, sulfonated naphthalene-formaldehyde condensate known as

Cormix SP6, was used in this experimental investigation, because

of its availability in the country

2.3 Mixes

The mortar mix proportions used in this study were cement:

sand: 1:3, all by weight with a water–cement (w/c) ratio of 0.40

for the initial mixes Irrespective of the ﬁnal w/c ratio used, all

the mixes were designed to have ﬂowability of 130–150 mm which

was determined from ﬂow table test The SP was also used as and

when necessary.Table 1shows the details of different mixes

de-signed for the study

2.4 Specimens

The mortar prisms were cast in steel moulds at dimension of

100 100 500 mm, and compacted in three layers using an

internal vibrator The Portland cement (PC) used in the tests was

a typical ASTM Type I PC conforming to the British Standard BS

12:1991 and the chemical composition of cement was illustrated

inTable 2 Quartzite sand was used as ﬁne aggregate for all mixes

as it constitutes the major ingredient of polymer-modiﬁed mortar

To ensure that the batches of ﬁne aggregates used were consistent and complied with the grading zone, a sieve analysis was carried out in accordance with the British Standard BS 882:1983 The water used for the preparation of the mortar was ordinary tap water, complying with the British Standard B.S 3148:1980 All sample mixes were tested for porosity and pore size distributions

at the following ages; 28 days, 6, 12 and 18 months after exposing them to three different curing regimes

2.5 Curing regimes

To investigate the effects of different curing conditions on the parameters of the study, mortar prisms were subjected to three curing regimes as follows:

Curing I: Immediately, after de-moulding, the specimens were immersed in 22 ± 2 °C water for six days and then laboratory air conditions cured at 27 ± 2 °C and 80 ± 5% relative humidity until the test age;

Curing II: The specimens were kept in the laboratory air condi-tions at 27 ± 2 °C and 80 ± 5% relative humidity for seven days after de-moulding, followed by continuous exposure to

22 ± 2 °C water (RH 100%) for the rest of curing period until the time of test; and

Curing III: After de-moulding, the specimens were kept in a water tank (RH 100% and temperature 22 ± 2 °C) for six days initially, followed by ambient air conditions (RH 80 ± 5% and temperature of 27 ± 2 °C) for seven days, and subsequently placed in water and air cyclically for seven days each until the time of test

2.6 Test procedure The porosity and pore size distribution of all specimens were determined from mercury intrusion porosimetry (MIP) technique using a Micromeritics Poresizer model 9320 This equipment is

Table 1 Details of mix design.

Type

of mix OPC a

(kg/

m 3 )

Polymer solids (%)

Super-plasticiser (%)

Sand (kg/

m 3 )

Water–

cement ratio

Slump (mm)

a OPC: Ordinary Portland cement.

Table 2 Chemical composition of cement according to manufacturer’s detail.

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able to perform both low and high pressures with a maximum

intrusion pressure of 207 MPa (30,000 psia) Using a contact angle

of 117° and a mercury surface tension of 0.485 N/m (485 dyn), the

smallest pore that can be intruded by the mercury is 0.0043lm

For all mortar specimens, the penetrometer with a maximum

mea-surable volume of 1.057 cc was selected The size of mortar

sam-ples used with this penetrometer was about 2–3 mm and the

total weight of samples was about 2.50 g Low pressure run and

high pressure operation were also set for the samples

Water absorption is usually measured by drying a specimen to a

constant mass, immersing it in water, and measuring the increase

in mass as a percentage of dry mass For a representative sample,

a set of three core samples were taken from the full thickness of

three mortar prisms at the ages of 28, 91, 182, 364, and 546 days

using a drilling machine with diamond cutting edge The three

cores were put in an oven for 72 2 h at a temperature of 105 5 C

After drying, the cores were removed from the oven, and allowed

to cool in an air-tight container for a period of 24 0.5 h Each

spec-imen was then weighed and immediately immersed in water for a

period of 30 0.5 min On removal from water, the surface of the

specimens was wiped and weighed again The water absorption

was calculated from the increase in mass of the specimen and

ex-pressed as a percentage of dry specimen multiply by a correction

factor derived from the BS 1881:Part 122:1983 as follows:

Correction factor ¼ Volume ðmm

3Þ surface area ðmm2Þ 12:5 ð1Þ

3 Results and discussion

3.1 Porosity

Porosity is considered to be one of the major factors controlling

the durability and strength of cement pastes, mortars or concretes

[11,16] Generally, concrete materials with higher porosity values

are believed to exhibit high permeability properties and hence,

lower resistance to chemical attacks may be achieved[17,10,12]

In this regard, the pore structure of PMM system, perhaps more

than any other characteristics, has inﬂuence on the behaviour of

this material Therefore, the effects of polymer modiﬁcation on

the porosity and pore size distributions of cement mortars, which

were determined from MIP, are discussed through the followings

Figs 1–3show the summary of raw data obtained from MIP test

The data were then plotted in different presentations in order to

examine the speciﬁc parameter as discussed in each of the

follow-ing sections

3.1.1 Effect of polymer modiﬁcation

The effect of polymer addition on the total porosity of cement

mortars are shown inFigs 4–6 According toFig 4, initial water

cur-ing followed by prolonged air curcur-ing shows lower porosity in all PMMs than the unmodiﬁed control mixes The total porosity at

28 days for CON1 was found to be slightly better than that of the modified specimens, except with SBR3, which showed the lowest porosity of all the samples The porosity of CON2, however, was comparable to the modified specimens and their total porosity val-ues were nearly 10.5% At the age of 6 months, all specimens exhib-ited much closer porosity values with one another with an average value of 8.81% After 12 months of air curing, a significant improve-ment was observed in all ceimprove-ment mortars modified with 15% of polymer solids (SBR3, PAE and VAE) However, SBR1 with 6.75% of polymer solids revealed the highest porosity, even higher than that

of the unmodiﬁed control mixes (CON1 and CON2) The lower porosity results recorded by the samples with 15% polymer were

in the expected range Initially, seven days water curing enables ce-ment hydration to take place, and subsequent air drying allows the

0

0.01

0.02

0.03

0.04

0.05

0.06

AGE OF CURING

CON1 CON2 SBR1 SBR3 PAE VAE

0 0.01 0.02 0.03 0.04 0.05 0.06

AGE OF CURING

Fig 2 Intrusion pore volume of specimen under prolonged water curing.

0 0.01 0.02 0.03 0.04 0.05 0.06

AGE OF CURING

Fig 3 Intrusion pore volume of specimen exposed to cyclic water and air curing.

0 2 4 6 8 10 12

AGE, days

Fig 4 Effect of polymer modiﬁcation on total porosity-initial 7 days water curing

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formation of the polymer ﬁlm in the aggregate-cement inter-phase,

partially ﬁlling the pores and hence, resulting in lower porosity and

permeability values of the polymer–cement systems[18–20] The

total porosity of SBR3 and PAE at the age of 18 months was found

to be less than 1%, compared to 3% of the mix VAE, although their

polymer loadings were the same The only difference was that the

VAE mix was made up from polymer powder, whereas SBR and

PAE mixes were made from polymer emulsions As a result, the

polymer emulsion had better ﬁlling properties which formed a

ce-ment matrix of a much smaller pore size compared to that of the

latter However, the unmodiﬁed cement mortars exhibited a total

porosity of about three to four times higher than that of the

modi-ﬁed cement mortars Furthermore, the porosity of the PMM system

has been known to be reduced signiﬁcantly with the age of curing

by other researchers such as Li and Roy[21], Ohama[22]and Wang

and Lee[23]

Fig 5shows almost a similar trend of porosity development

for samples subjected to seven days of initial curing in air,

fol-lowed by prolonged water curing The PAE mix shows the lowest

porosity of 1.10%, followed by mixes from SBR3 (1.61%), VAE

(2.82%), CON2 (5.45%), SBR1 (6.86%) and CON1 (7.33%)

Accord-ingly, all samples subjected to prolonged water curing were

slightly better than those exposed to prolonged air curing,

ex-cept of SBR3 and PAE mixes, which showed higher porosity

re-sults The unmodiﬁed cement mortars seemed to beneﬁt from

the long term exposure to water through cement hydration,

whereas some PMMs (SBR3 and PAE) beneﬁted from long term

air curing, which enabled the continuous formation of polymer

ﬁlm

In cyclic wetting and drying conditions, however, the total

porosity results for all samples were generally better than those

for prolonged air curing and water curing Such exposure condition

is likely to occur especially on the building façade where it is exposing to the weather condition.Fig 6indicates that the total porosity of SBR1, CON1 and CON2 reduced gradually with the age of curing However, more significant reduction in porosity val-ues were observed for SBR3, PAE and VAE mixes, particularly be-tween the ages of 200 and 550 days The results also indicated that the porosity decreased as the age of curing was increased Accordingly, for a given sample mass, the intrusion pore volume was directly related to the total porosity of the sample The pro-gressive reduction in cumulative intrusion pore volume with the increasing age of curing resulted in a decrease in total porosity The significant reduction in total porosity was attributed to the im-proved pore structure of modified mortars by the formation of polymer films around the cement hydrates, filling the voids, seal-ing the micropores, and resultseal-ing in a low porosity cement matrix Furthermore, it was revealed that at the age of 18 months, the intrusion volumes for PMMs with 15% polymer solids, decreased significantly compared to that of the unmodified control mixes The intrusion volumes, which measured the amount of mercury penetrating and filling-up the pores, also explained the kind of pore structure which the materials exhibited The kind or the char-acteristic of pore structure inclusive of its cumulative pore volume

at speciﬁc pore diameter, maximum continuous pore diameter in the matrix would be discussed thoroughly in later sections 3.1.2 Effect of curing conditions

Curing conditions showed a signiﬁcant effect on the hydration

of the cement paste and the overall development of the micro-structure of the cement system The strength, durability and per-meability properties of mortar and concrete seem to be governed primarily by the quality of the matrix and the curing conditions existing during cement hydration The efficiency of curing was controlled mainly by the temperature and relative humidity of the environment, both of which greatly influenced the porosity and pore structure of the cement paste Accordingly, the effect of curing conditions on the total porosity of both unmodified and PMM systems with increasing the age of curing are discussed based on the results which have shown inFigs 4–6

According to the ﬁgures, CON1 shows marginal differences in total porosity between the three adopted curing regimes However, cyclic wetting and drying conditions exhibited a superior perfor-mance compared to the samples exposed to prolonged air curing The long term water curing showed consistent porosity values with that of cyclic curing All the three curing regimes applied to these samples exhibited a gradual decrease in porosity at the end

of the curing period of 18 months The test results also revealed that for the CON1 mix, the initial seven days curing in water was not sufﬁcient to complete the early hydration of the cement paste, and subsequent air drying disrupted further development of the microstructure due to lack of water for a hydration reaction, thus, resulted in a more porous structure of mortar matrix

Furthermore, quite a similar development in total porosity of the SBR1 mix compared to CON1, in different curing regimes, was also observed A gradual decrease in porosity was perceived

in all three different curing conditions with increasing the age of specimens Even then, prolonged water curing and cyclic wetting and drying conditions showed a better effect on porosity than con-tinuous exposure to the air curing regime On the other hand, reduction in total porosity values of the SBR3 mix was much more pronounced after the age of 200 days As a result, cyclic wetting and drying conditions showed a remarkable decrease in porosity compared to that of water curing or air curing alone The differ-ences in the porosity values at the age of 1 year were quite signif-icant, but these values began to merge into a uniﬁed value at the age of 18 months Furthermore, the behaviour of the cement

0

2

4

6

8

10

12

AGE, days

Fig 5 Effect of polymer modiﬁcation on total porosity-initial 7 days air curing

followed by water curing.

0

2

4

6

8

10

12

AGE, days

Fig 6 Effect of polymer modiﬁcation on total porosity-cyclic water/air curing.

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mortar modiﬁed with 15% poly-acrylic ester, PAE, was quite

un-ique Unlike the SBR3 mix, the PAE mix seems not to beneﬁt from

the cyclic water and air curing condition; instead it exhibited

bet-ter porosity development under either wabet-ter curing or air curing

alone These two curing conditions produced lowest porosity

val-ues of about 2% for a year, compared to about 5% under cyclic water

and air curing regime In contrast, at the end of an 18 months

cur-ing period, all three curcur-ing regimes showed a very low porosity of

about 1% A similar trend of porosity development was also

ob-served in the VAE mix Cyclic water and air curing conditions only

beneﬁted in the long term, but in the short term, prolonged water

and air curing conditions showed signiﬁcant effects on total

porosity

3.2 Pore size distributions

Although MIP has some limitations in determining the pore size

distribution and pore characteristics of cement paste, it has been

generally recognized that the pore structure, which it measures,

is related to the same factors which control permeation of ﬂuids

and ions[21,24] The following sections deal with the pore size

dis-tribution on unmodiﬁed control mixes and PMMs The results of

pore size distribution at the different ages are presented in the

form of cumulative intrusion pore volume, Log differential

intru-sion pore volume, dV/d log D, and differential intruintru-sion pore

vol-ume, dV/dD; each parameter was plotted against pore diameter

3.2.1 Unmodiﬁed control mortars

The cumulative pore volume versus pore diameter for

unmodi-ﬁed control mortar, CON1 are presented inFigs 7–10 According to

the ﬁgures, CON1 mix under cyclic wetting and drying condition

showed superior performance by exhibiting the lowest cumulative

pore volume compared to that of wet or dry curing alone The mix with prolonged air curing, however, showed the highest intrusion volume of about 0.05 mL/g at 28 days of curing (Fig 7) According

toFig 8, at the age of 6 months the cumulative volume curves for the wet/dry curing regime which tended to shift to the right, although the total cumulative pore volume of all samples at this stage were the same and nearly 0.04 mL/g Between 28 days and

1 year, the cumulative volume was found to decrease with the increasing age of curing, but at 1 year, there was only a marginal decrease in cumulative pore volume as shown inFig 9 It is clear fromFigs 7–10that the curves for specimens under cyclic wetting and drying were always below the curves of the corresponding specimens cured under prolonged water or air curing conditions These results also imply that under cyclic wetting and drying con-ditions, the mix showed a better pore size distribution than that of other curing conditions For CON2 the cumulative intrusion pore volume curves for different ages showed similar behaviour to that

of CON1 The specimens under cyclic wetting and drying exposure exhibited superior pore size distribution compared to that under prolonged water curing or air curing In other words, the speci-mens could have a more compacted matrix when treated under cyclic conditions The results also indicated more variations in the pore characteristics of CON2 specimens at 6 and 12 months,

as shown inFigs 11 and 12 This may be due to the breaking-up

of smaller pores as a result of an increase in the intrusion pressure

of the mercury Prolonged air curing obviously disrupted continu-ous hydration of the cement paste, thus, prevented further devel-opment of dense microstructure in CON2 mix

Furthermore, comparisons of Log differential pore volume curves of CON1 under the three curing conditions are presented

0

0.01

0.02

0.03

0.04

0.05

0.06

PORE DIAMETER, nm

M28-CON1 [7W+A]

M28-CON1 [7A+W]

M28-CON1 [7W/A]

Fig 7 Cumulative pore volume curve of the unmodiﬁed [CON1] at 28 days.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

M6-CON1[7W+A]

M6-CON1[7A+W]

M6-CON1[7W/A]

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

M12-CON1[7W+A]

M12-CON1[7A+W]

M12-CON1[7W/A]

Fig 9 Cumulative pore volume curve of the unmodiﬁed [CON1] at 1 year.

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

M18-CON1[7W+A]

M18-CON1[7A+W]

M18-CON1[7W/A]

Fig 10 Cumulative pore volume curve of the unmodiﬁed [CON1] at 18 months.

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inFig A.1–A.4in Appendix A The plot of Log differential intrusion

pore volume versus pore diameter enables the determination of

maximum continuous pore diameter, as deﬁned by its maximum

value on the dV/d log D - D plot The curve of specimen at 28 days

(Fig A.1) reveals that the maximum continuous pore diameter of

all three curing conditions was nearly the same, which was about

30 nm However, the higher peak of the curve was recorded for

specimens subjected to cyclic wetting and drying exposure

condi-tions This also indicates that more ﬁne pores were found in the

specimens under cyclic curing conditions than that in the other

two curing conditions At the age of 6 months, the peak of the

curve for specimens in curing I shifted to the right and was broader

which also indicated that there were more coarse pores present

The maximum continuous pore diameter, as shown in Fig A.2

(Appendix A), was about 40 nm However, the pore size

distribution of specimens in the other curing conditions remains unchanged.Figs A.3 and A.4(Appendix A) show pore size distribu-tions of the CON1 at 12 and 18 months of curing Lesser number of ﬁne pores was noticed in specimens treated under curing I com-pared to the ones treated under curing II and III, as shown in Figs A.3 and A.4 indicates that the pore size distributions was di-vided into ﬁne pores and coarse pores Fine pores had a diameter of about 25 nm, while the diameter of the coarse pores was exceeding

100 nm and these were clearly showed by the specimens in curing

II and III Meanwhile, the Log differential pore volume curve of the specimen in curing I have shifted to the right when comparison was made betweenFigs A.3 and A.4 This indicates that greater number

of coarse pores was found in specimens subjected to prolonged air curing, and their sizes were in the range of 100 nm to 600 nm

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

M6-CON2[7W+A]

M6-CON2[7A+W]

M6-CON2[7W/A]

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

M12-CON2[7W+A]

M12-CON2[7A+W]

M12-CON2[7W/A]

0.00

0.01

0.02

0.03

0.04

0.05

M28-CON1[7W+A]

M28-CON1[7A+W]

M28-CON1[7W/A]

Fig A.1 Log differential pore volume curve of the unmodiﬁed control [CON1] at

0 0.01 0.02 0.03 0.04 0.05

M6-CON1[7W+A] M6-CON1[7A+W] M6-CON1[7W/A]

6 months.

0.00 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04 0.05

12 months.

0.00 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04

18 months.

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The differential pore volume distributions, as represented by

dV/dD – D plots, enable differentiation between the ﬁnes and

coarse pores much easier The magnitude of dV/dD was high for

ﬁne pores and small for the coarse pores The dV/dD plot enables

determination of ‘threshold diameter’ or minimum pore diameter

and is geometrically continuous throughout all regions of the

hy-drated cement paste, as deﬁned by Winslow and Diamond[25]

Threshold diameter, as explained by Feldman and Beaudoin[26]

is the pore diameter where the initial maximum dV/dD value

oc-curs in a dV/dD – D curve From dV/dD – D plots,Fig A.5, the

thresh-old diameter for CON1 mix at 28 days of curing was about 30 nm

Similar threshold values were found in specimens cured for

6 months, but a greater number of this pore size was distributed

in the specimens under cyclic wetting and drying, and prolonged

water curing compared to that of prolonged air curing as shown

inFig A.6 This phenomenon was getting more signiﬁcant after

12 months of curing as presented inFig A.7 The CON1 with

pro-longed water curing seems to have higher volume of small pores

compared to that of the other curing conditions This also indicates

that in the long term, bigger pores were ﬁlled or sealed by the

pro-cess of cement hydration However, in long term air drying due to

insufﬁcient water for hydration, the resulting cement paste

be-came slightly more porous, and hence, a lower volume of small

pores and larger volume of coarse pores were recorded

3.2.2 Polymer-modiﬁed cement mortars

3.2.2.1 Sbr1 The cumulative pore volume curves of SBR1 are

pre-sented inFigs 13–16 At 28 days of curing, the SBR1 mix exhibited

a cumulative pore volume between 0.05–0.06 mL/g Lower

cumulative intrusion volumes were recorded under both

pro-longed water curing and air curing, whereas, cyclic curing shows

the highest pore volume as shown in Fig 13 This is in contrast with the results obtained for CON1 and CON2 for similar ages of curing At the age of 6 months, although the curve with prolonged air curing was above the curves for other curing conditions (Fig 14), the total cumulative pore volumes of all specimens, irre-spective of their curing conditions, were the same and nearly 0.045 mL/g For long term exposure condition (Figs 15 and 16), the curves emphasize that cyclic wetting and drying and prolonged water curing were ideal conditions for the SBR1 mix Their cumu-lative pore volume at the age of 12 months was about 0.035 mL/g compared to that under prolonged air drying of about 0.04 mL/g, and at 18 months, their values were 0.032, and 0.037 mL/g respec-tively This could be explained by the initial air curing for 7 days

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

M28-CON1[7W+A]

M28-CON1[7A+W]

M28-CON1[7W/A]

Fig A.5 Differential intrusion volume of the unmodiﬁed control [CON1] at 28 days.

0.00

0.50

1.00

1.50

2.00

2.50

M6-CON1[7W+A]

M6-CON1[7A+W]

M6-CON1[7W/A]

Fig A.6 Differential intrusion volume of the unmodiﬁed control [CON1] at

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80

Fig A.7 Differential intrusion volume of the unmodiﬁed control [CON1] at

12 months.

0 0.01 0.02 0.03 0.04 0.05 0.06

M28-SBR1[7W+A]

M28-SBR1[7A+W]

M28-SBR1[7W/A]

Fig 13 Cumulative pore volume curve of SBR1 mix at 28 days.

0 0.01 0.02 0.03 0.04 0.05

M6-SBR1[7W+A]

M6-SBR1[7A+W]

M6-SBR1[7W/A]

Fig 14 Cumulative pore volume curve of SBR1 mix at 6 months.

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which enables coalescence of polymer particles to form the

poly-mer ﬁlm, which in turn helps to seal the pores.[27]

From the dV/d log D – D curves, as shown inFig A.8, a lower

maximum continuous pore diameter of about 20 nm was observed

under cyclic curing condition, compared to about 30 nm of the

unmodiﬁed mixes This also revealed that with 6.75% polymer

addition, the maximum continuous pore diameter of the mix can

be reduced by nearly 50% At the age of 6 months, there was no

sig-niﬁcant difference in the maximum continuous pore diameters

be-tween SBR1 and unmodiﬁed control, CON1 at about 20 nm

However, at the age of 12 and 18 months, smaller maximum

con-tinuous pore diameters of about 15 nm were recorded for the SBR1

specimens, compared to about 20 nm for the unmodiﬁed control

mix In dV/dD curves, however, the threshold diameters of SBR1

at 28 days, 6 and 12 months were similar to that of the unmodiﬁed

control mixes, about 25 nm

3.2.2.2 SBR3 For SBR3, it was observed that the cumulative pore volume curves at 28 days were similar for all curing conditions The results also indicated that cyclic wet/dry curing seems to be the best curing method for SBR-modiﬁed specimens At the age

of 12 months,Fig A.9(Appendix A), the cumulative pore volume was about 0.008 mL/g compared to the other curing conditions, which was about 0.03 mL/g At the age of 18 months, prolonged air curing showed a better performance (Fig A.10) However, the cumulative pore-volumes for the cyclic wet/dry curing and pro-longed air curing were 0.005 and 0.004 mL/g respectively, which

is in agreement with the results of the study of Manmohan and Mehta [28] that the cumulative intrusion volume of pores de-creases with increasing age of hydration

The Log differential pore volume curves were also generated by the study Accordingly, at the ages of 28 days and 6 months, the

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

M12-SBR1[7W+A]

M12-SBR1[7A+W]

M12-SBR1[7W/A]

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

M18-SBR1[7W+A]

M18-SBR1[7A+W]

M18-SBR1[7W/A]

0

0.01

0.02

0.03

0.04

0.05

M28-SBR1[7W+A]

M28-SBR1[7A+W]

M28-SBR1[7W/A]

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

M12-SBR3 [7W+A]

M12-SBR3 [7A+W]

M12-SBR3 [7W/A]

Fig A.9 Cumulative pore volume curve of SBR3 mix at 12 months.

0 0.002 0.004 0.006 0.008 0.01

M18-SBR3 [7W+A]

M18-SBR3 [7A+W]

M18-SBR3 [7W/A]

Fig A.10 Cumulative pore volume curve of SBR3 mix at 18 months.

0 0.01 0.02 0.03 0.04 0.05 0.06

M28-SBR3[7W+A] M28-SBR3[7A+W] M28-SBR3[7W/A]

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maximum continuous pore diameters for SBR3 specimens were

about 20 nm for the ﬁne pores, and about 80 nm for the coarse

pores, which was clearly illustrated inFigs 17 and 18 However,

at the age of 12 months, the maximum continuous pore diameter

was reduced signiﬁcantly to a value of less than 10 nm, whereas, the coarse pore size remained unchanged as shown in Figs 19 and 20shows a pronounced right shift in the curves’ peaks when the maximum continuous pore diameter value increased from be-low 10 nm to approximately 100 nm This may be due to the break-ing up of open pores in the specimen under prolonged air curbreak-ing as

a result of intrusion pressure from mercury

The results of the threshold diameter for the SBR3 mix at the ages of 28 days, 6 and 12 months in the form of dV/dD - D plots are presented inTable 3 The threshold diameter for SBR3 speci-mens at 28 days of curing was comparable to that of the SBR1 and CON1 mixes Pronounced changes in the threshold diameter were observed in the SBR3 mix at the ages of 6 and 12 months when the peak of the curve shifted from approximately 20 nm to

a value of less than 10 nm This improvement may be due to filling the pores with polymer films, which in turn, seal the smaller pores and reduce the larger ones resulting in an almost impermeable polymer–cement system The effective pore filling by polymer la-tex has also been reported by Filho et al.[29], on polymer-modified cement mortars by Ohama and Demura[30]and on the Styrene– Butadiene Latex Concrete using the SEM Micrograph by Shaker

et al.[31]

3.2.2.3 PAE The cumulative pore volume curve results of the PAE mix revealed that the cumulative intrusion volumes of specimens

at 28 days and 6 months were between 0.045 and 0.055 mL/g This

is comparable to that of the SBR3, SBR1 and CON1 mixes However, after 12 months of curing, the cumulative intrusion pore volumes were between 0.015 and 0.025 mL/g compared to 0.008, 0.035, and 0.04 mL/g for the SBR3, SBR1 and CON1 mixes respectively With the increasing curing age, the PAE modiﬁed mortars exhib-ited a better pore size distribution The cumulative intrusion pore volume at 18 months, as shown in Fig A.11 (Appendix A), was nearly 0.005 mL/g, which was quite similar to that of the SBR3 mix However, all the results, irrespective of their curing ages, show a beneﬁcial effect on the PAE mix when subjected to pro-longed air curing after an initial 7 days water curing

0

0.02

0.04

0.06

0.08

0.1

M6-SBR3[7W+A]

M6-SBR3[7A+W]

M6-SBR3[7W/A]

Fig 18 Log differential pore volume curve of SBR3 mix at 6 months.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

M12-SBR3[7W+A]

M12-SBR3[7A+W]

M12-SBR3[7W/A]

0.000

0.005

0.010

0.015

0.020

0.025

0.030

M18-SBR3[7W+A]

M18-SBR3[7A+W]

M18-SBR3[7W/A]

Table 3

Maximum continuous and threshold diameters of SBR3 mix.

Curing conditions Max continuous pore diameter from dV/d(log D) – D curve (nm) Threshold diameter from dV/dD – D curve (nm)

0 0.001 0.002 0.003 0.004 0.005 0.006

M18-PAE [7W+A]

M18-PAE [7A+W]

M18-PAE [7W/A]

Fig A.11 Cumulative pore volume curve of the PAE mix at 18 months.

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The Log differential pore volume also revealed that the

maxi-mum continuous pore diameters for the PAE mix were

approxi-mately 15 nm each for 28 days and 6 months, respectively The

maximum continuous pore diameters for 12 months of curing

were nearly 8, 10, and 12 nm for prolonged air curing, prolonged

water curing, and cyclic water/air curing, respectively These

diam-eters were a little lower than that of the SBR3, SBR1 and CON1

mixes for similar curing ages The threshold diameters for the

PAE-modiﬁed mortar are presented inTable 4 At 28 days, the

min-imum continuous pore diameter was about 15 nm, which was

quite similar to that of specimens previously obtained for similar

age of curing The threshold diameters for the PAE specimens at

the age of 6 months were 10 nm, each for prolonged air curing,

and cyclic wet/dry curing condition, and 5 nm for specimen under

prolonged water curing

3.2.2.4 VAE The cumulative pore volume of the VAE at 28 days and

6 months was between 0.045 and 0.055 mL/g, which is quite

sim-ilar to that of the PAE mix Furthermore, the cumulative intrusion

volumes were between 0.015 and 0.035 mL/g for the age of

12 months and between 0.01 and 0.016 mL/g at the age of

18 months, which was a little higher compared to that of the PAE

mix The test results also revealed that cyclic wet/dry curing was

a better method of curing for the VAE specimens The combination

of wet and dry exposure applied intermittently seems to enhance

polymer–cement systems; wet curing enabled a continuous

pro-cess of cement hydration, and dry curing on the other hand, helped

in the polymer ﬁlm formation, which was also the key factor for

polymer modiﬁcation

The maximum continuous pore diameter of the VAE mix was

determined from the peak of dV/d log D curves as presented in

Figs A.12–A.14(Appendix A) At 28 days and 6 months of curing,

the maximum continuous pore diameters of VAE specimens were

divided into ﬁne and large pores The maximum continuous

diam-eter of ﬁne pores was about 20 nm, whereas the coarse pores had a

diameter ranging from 2000 to 3000 nm as shown inFigs A.12 and

A.13 At the age of 12 months, the distribution of maximum pore

sizes, in fact, occurs throughout the entire range of diameters

Hence, it is difﬁcult to differentiate the ﬁne and coarse pores,

without carefully considering the magnitude of the peak of curve Based onFig A.14, a wider range of maximum pore diameters can

be chosen, and the value of ﬁne pores was ranging from 10 to

20 nm, whereas, the coarse pores were in the range of 200–

1000 nm It was observed that the VAE mix exhibited higher vol-umes of coarse pores compared to that of the SBR1, SBR3 and PAE mixes The results also explained that larger pore sizes were distributed throughout the entire mortar matrix of the VAE mix, which also justiﬁed its higher porosity value compared to that of the SBR3 and PAE

3.3 Water absorption The PMMs have a structure in which the micro-pores and voids normally occurring in Portland cement systems are partially filled with polymers or sealed by continuous polymer film that forms during curing The effect of polymer filling increases with a rise

in polymer content or polymer–cement ratio As a result, the PMMs have improved waterprooﬁng and reduced water absorption over ordinary cement mortars

The results are presented inFigs 21–23 FromFig 21, all PMMs exposed to prolonged air-curing exhibited low water absorption properties of less than 1% compared to the unmodified cement mortars The increase in polymer loading from 6.75% in SBR1 to 15%, by weight of cement, in SBR3 resulted in a reduction of about 60% in water absorption The initial 7 days curing in water was essential because it allowed the hydration of Portland cement to take place and develop cementing properties Subsequent air dry-ing enabled polymer film formation to yield a monolithic matrix phase with a network structure in which the hydrated cement phase and polymer phase interpenetrate into each other[22] This phenomenon also explains the reason for low water absorption capacity in PMM systems Prolonged exposure to water after initial air curing for 7 days appears to have no significant improvement

Table 4

Maximum continuous and threshold diameters of PAE mix.

Curing conditions Max continuous pore diameter

from dV/d(log D) – D curve (nm)

Threshold diameter from dV/dD –D curve (nm)

28 days 6 months 12 months 28 days 6 months

0.00

0.01

0.02

0.03

0.04

0.05

M28-VAE[7W+A]

M28-VAE[7A+W]

M28-VAE[7W/A]

0.00 0.01 0.02 0.03 0.04 0.05

M6-VAE[7W+A]

M6-VAE[7A+W]

M6-VAE[7W/A]

Fig A.13 Log differential pore volume curve of VAE mix at 6 months.

0.00 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04

M12-VAE[7W+A]

M12-VAE[7A+W]

M12-VAE[7W/A]

Fig A.14 Log differential pore volume curve of VAE mix at 12 months.

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