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.

Composites: Part B 55 (2013) 221–233 Contents lists available at SciVerse ScienceDirect Composites: Part B journal homepage: www.elsevier.com/locate/compositesb Porosity, pore structure and water absorption of polymer-modified mortars: An experimental study under different curing conditions Mahyuddin Ramli, Amin Akhavan Tabassi ⇑, Kwan Wai Hoe School of Housing, Building and Planning, Universiti Sains Malaysia, Malaysia a r t i c l e i n f o Article history: Received 20 June 2012 Received in revised form 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 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 Ó 2013 Elsevier Ltd All rights reserved Introduction The corporation of synthetic polymers in Portland cement mortars 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 polymer latexes, such as styrene–butadiene rubber (SBR) latex in a Portland 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 improves 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 distributions 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 ⇑ Corresponding author Tel.: +60 174709240 E-mail address: akhavan.ta@gmail.com (A.A Tabassi) 1359-8368/$ - see front matter Ó 2013 Elsevier Ltd All rights reserved http://dx.doi.org/10.1016/j.compositesb.2013.06.022 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, not contribute to permeability Porosity, on the other hand, is a measure of the proportion of the total volume occupied by pores, and is usually expressed in a percent If the porosity is high and the pores are interconnected, the permeability 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 characteristics of the material In this regard, porosity and pore size distribution 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 applied as waterproof renders, floor topping and also structure repair materials The PMM system also use to build structures that are exposed 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 parameters, including porosity, pore size distribution, and water absorption can help tremendously in assessing the effect of polymer additions and curing conditions on the durability properties of cement 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 222 M Ramli et al / Composites: Part B 55 (2013) 221–233 within different curing conditions In addition, this paper also elaborates 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 Table Details of mix design Experimental set-up 2.1 Polymer materials Polymer-modified mortar (PMM) is normally prepared by mixing 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–butadiene 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] Polyacrylic ester emulsion (PAE) has been reported to improve various engineering properties of mortars and concrete [2] Vinyl acetate–ethylene (VAE) copolymer re-dispersible powders are commercially 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 styrene 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 temperatures 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 sulfonated 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 shows the details of different mixes designed for the study 2.4 Specimens The mortar prisms were cast in steel moulds at dimension of 100 Â 100 Â 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 in Table Quartzite sand was used as fine aggregate for all mixes a Type of mix OPCa (kg/ m3) Polymer solids (%) Superplasticiser (%) Sand (kg/ m3) Water– cement ratio Slump (mm) CON1 SBR1 SBR3 CON2 PAE VAE 506 506 506 506 506 506 6.75 15.0 15.0 15.0 0.65 0.3 9.0 0 1518 1518 1518 1518 1518 1518 0.400 0.400 0.273 0.273 0.281 0.320 130 145 150 140 150 150 OPC: Ordinary Portland cement 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 ± °C water for six days and then laboratory air conditions cured at 27 ± °C and 80 ± 5% relative humidity until the test age; Curing II: The specimens were kept in the laboratory air conditions at 27 ± °C and 80 ± 5% relative humidity for seven days after de-moulding, followed by continuous exposure to 22 ± °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 ± °C) for six days initially, followed by ambient air conditions (RH 80 ± 5% and temperature of 27 ± °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 Chemical composition of cement according to manufacturer’s detail Constituent Percentage by weight (%) Lime (CaO) Silica (SiO2) Alumina (Al2O3) Iron oxide (Fe2O3) Magnesia (MgO) Sulphur trioxode (SO3) Nitrogen oxide (N2O) Loss of ignition Lime saturation factor C3S C2S C3A C4AF 64.64 21.28 5.6 3.36 2.06 2.14 0.05 0.64 0.92 52.82 21.45 9.16 10.2 223 M Ramli et al / Composites: Part B 55 (2013) 221233 Correction factor ẳ Volume mm ị surface area ðmm2 Þ Â 12:5 ð1Þ INTRUSION VOLUME, mL/g 0.06 0.05 CON1 0.04 CON2 0.03 SBR1 0.02 SBR3 PAE 0.01 VAE 28 days mths 12 mths 18 mths AGE OF CURING Fig Intrusion pore volume of specimen under prolonged water curing 0.06 INTRUSION VOLUME, mL/g 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 0.0043 lm For all mortar specimens, the penetrometer with a maximum measurable volume of 1.057 cc was selected The size of mortar samples 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 h at a temperature of 105 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 specimen was then weighed and immediately immersed in water for a period of 30 0.5 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 expressed as a percentage of dry specimen multiply by a correction factor derived from the BS 1881:Part 122:1983 as follows: CON1 0.05 CON2 0.04 SBR1 0.03 SBR3 0.02 PAE 0.01 VAE 28 days mths 12 mths 18 mths AGE OF CURING Results and discussion Fig Intrusion pore volume of specimen exposed to cyclic water and air curing 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 1–3 show 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 following sections 3.1.1 Effect of polymer modification The effect of polymer addition on the total porosity of cement mortars are shown in Figs 4–6 According to Fig 4, initial water cur- ing followed by prolonged air curing 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 values were nearly 10.5% At the age of months, all specimens exhibited much closer porosity values with one another with an average value of 8.81% After 12 months of air curing, a significant improvement was observed in all cement 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 cement hydration to take place, and subsequent air drying allows the 12 CON1 0.05 CON2 0.04 SBR1 0.03 SBR3 0.02 PAE 0.01 VAE TOTAL POROSITY, % INTRUSION VOLUME, mL/g 0.06 10 28 days mths 12 mths 18 mths SBR3 SBR1 VAE CON1 CON2 0 PAE 50 100 150 200 250 300 350 400 450 500 550 600 AGE, days AGE OF CURING Fig Intrusion pore volume of specimen under prolonged air curing Fig Effect of polymer modification on total porosity-initial days water curing followed by air curing 224 M Ramli et al / Composites: Part B 55 (2013) 221–233 TOTAL POROSITY, % 12 10 PAE SBR3 SBR1 VAE CON1 CON2 0 50 100 150 200 250 300 350 400 450 500 550 600 AGE, days Fig Effect of polymer modification on total porosity-initial days air curing followed by water curing TOTAL POROSITY, % 12 10 PAE SBR3 SBR1 VAE CON1 CON2 100 150 200 0 50 250 300 350 400 450 500 550 600 AGE, days Fig Effect of polymer modification on total porosity-cyclic water/air curing 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 cement 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 modified 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 shows almost a similar trend of porosity development for samples subjected to seven days of initial curing in air, followed 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%) Accordingly, all samples subjected to prolonged water curing were slightly better than those exposed to prolonged air curing, except of SBR3 and PAE mixes, which showed higher porosity results 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 faỗade where it is exposing to the weather condition Fig indicates that the total porosity of SBR1, CON1 and CON2 reduced gradually with the age of curing However, more significant reduction in porosity values were observed for SBR3, PAE and VAE mixes, particularly between 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 progressive 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 improved pore structure of modified mortars by the formation of polymer films around the cement hydrates, filling the voids, sealing the micropores, and resulting 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 characteristic 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 microstructure of the cement system The strength, durability and permeability 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 in Figs 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 performance 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 continuous 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 differences in the porosity values at the age of year were quite significant, but these values began to merge into a unified value at the age of 18 months Furthermore, the behaviour of the cement 225 mortar modified with 15% poly-acrylic ester, PAE, was quite unique Unlike the SBR3 mix, the PAE mix seems not to benefit from the cyclic water and air curing condition; instead it exhibited better porosity development under either water curing or air curing alone These two curing conditions produced lowest porosity values 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 curing period, all three curing regimes showed a very low porosity of about 1% A similar trend of porosity development was also observed 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 CUMULATIVE PORE VOLUME, mL/g M Ramli et al / Composites: Part B 55 (2013) 221–233 0.045 0.04 M12-CON1[7W+A] 0.035 M12-CON1[7A+W] 0.03 M12-CON1[7W/A] 0.025 0.02 0.015 0.01 0.005 10 100 1000 10000 PORE DIAMETER, nm 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 distribution 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 intrusion pore volume, dV/d log D, and differential intrusion pore volume, dV/dD; each parameter was plotted against pore diameter 3.2.1 Unmodified control mortars The cumulative pore volume versus pore diameter for unmodified control mortar, CON1 are presented in Figs 7–10 According to the figures, CON1 mix under cyclic wetting and drying condition showed superior performance by exhibiting the lowest cumulative CUMULATIVE PORE VOLUME, mL/g Fig Cumulative pore volume curve of the unmodified [CON1] at year 0.045 0.04 M18-CON1[7W+A] 0.035 M18-CON1[7A+W] M18-CON1[7W/A] 0.03 0.025 0.02 0.015 0.01 0.005 10 100 1000 10000 PORE DIAMETER, nm CUMULATIVE PORE VOLUME, mL/g Fig 10 Cumulative pore volume curve of the unmodified [CON1] at 18 months 0.06 M28-CON1 [7W+A] 0.05 M28-CON1 [7A+W] 0.04 M28-CON1 [7W/A] 0.03 0.02 0.01 10 100 1000 10000 PORE DIAMETER, nm CUMULATIVE PORE VOLUME, mL/g Fig Cumulative pore volume curve of the unmodified [CON1] at 28 days 0.045 0.04 M6-CON1[7W+A] 0.035 M6-CON1[7A+W] 0.03 M6-CON1[7W/A] 0.025 0.02 0.015 0.01 0.005 10 100 1000 10000 PORE DIAMETER, nm Fig Cumulative pore volume curve of the unmodified [CON1] at months 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 to Fig 8, at the age of 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 year, the cumulative volume was found to decrease with the increasing age of curing, but at year, there was only a marginal decrease in cumulative pore volume as shown in Fig It is clear from Figs 7–10 that 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 conditions, 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 specimens 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 and 12 months, as shown in Figs 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 continuous hydration of the cement paste, thus, prevented further development of dense microstructure in CON2 mix Furthermore, comparisons of Log differential pore volume curves of CON1 under the three curing conditions are presented M Ramli et al / Composites: Part B 55 (2013) 221–233 0.05 0.045 0.04 dV/d(log D), mL/g-nm CUMULATIVE PORE VOLUME, mL/g 226 0.035 0.03 0.025 0.02 0.015 M6-CON2[7W+A] 0.01 M6-CON2[7A+W] M6-CON1[7W+A] 0.04 M6-CON1[7A+W] M6-CON1[7W/A] 0.03 0.02 0.01 M6-CON2[7W/A] 0.005 0 10 100 1000 10000 10 100 1000 10000 PORE DIAMETER, nm PORE DIAMETER, nm Fig 11 Cumulative pore volume curve of the unmodified [CON2] at months Fig A.2 Log differential pore volume curve of the unmodified control [CON1] at months 0.05 0.04 M12-CON2[7W+A] 0.035 M12-CON2[7A+W] 0.03 M12-CON2[7W/A] 0.025 0.02 0.015 0.01 0.005 dV/d(Log D), mL/g-nm CUMULAATIVE PORE VOLUME, mL/g 0.045 0.04 M12-CON1[7W+A] 0.04 M12-CON1[7A+W] 0.03 M12-CON1[7W/A] 0.03 0.02 0.02 0.01 0.01 10 100 1000 0.00 10000 10 PORE DIAMETER, nm 100 1000 10000 PORE DIAMETER, nm in Fig A.1–A.4 in 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 conditions 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 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 Fig A.3 Log differential pore volume curve of the unmodified control [CON1] at 12 months 0.04 M18-CON1[7W+A] 0.04 dV/d(log D), mL/g-nm Fig 12 Cumulative pore volume curve of the unmodified [CON2] at 12 months M18-CON1[7A+W] 0.03 M18-CON1[7W/A] 0.03 0.02 0.02 0.01 0.01 0.00 10 100 1000 10000 PORE DIAMETER, nm Fig A.4 Log differential pore volume curve of the unmodified control [CON1] at 18 months 0.05 dV/d(log D), mL/g-nm M28-CON1[7W+A] 0.04 M28-CON1[7A+W] M28-CON1[7W/A] 0.03 0.02 0.01 0.00 10 100 1000 10000 PORE DIAMETER, nm Fig A.1 Log differential pore volume curve of the unmodified control [CON1] at 28 days distribution of specimens in the other curing conditions remains unchanged Figs A.3 and A.4 (Appendix A) show pore size distributions of the CON1 at 12 and 18 months of curing Lesser number of fine pores was noticed in specimens treated under curing I compared 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 divided 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 between Figs 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 227 M Ramli et al / Composites: Part B 55 (2013) 221–233 3.2.2 Polymer-modified cement mortars 3.2.2.1 Sbr1 The cumulative pore volume curves of SBR1 are presented in Figs 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 prolonged water curing and air curing, whereas, cyclic curing shows 1.80 M12-CON1[7W+A] 1.60 M12-CON1[7A+W] dV/dD, mL/g-nm 1.40 M12-CON1[7W/A] 1.20 1.00 0.80 0.60 0.40 0.20 0.00 10 100 1000 10000 PORE DIAMETER, nm Fig A.7 Differential intrusion volume of the unmodified control [CON1] at 12 months CUMULATIVE PORE VOLUME, mL/g 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 hydrated 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 occurs in a dV/dD – D curve From dV/dD – D plots, Fig A.5, the threshold diameter for CON1 mix at 28 days of curing was about 30 nm Similar threshold values were found in specimens cured for 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 in Fig A.6 This phenomenon was getting more significant after 12 months of curing as presented in Fig A.7 The CON1 with prolonged 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 process of cement hydration However, in long term air drying due to insufficient water for hydration, the resulting cement paste became slightly more porous, and hence, a lower volume of small pores and larger volume of coarse pores were recorded 0.06 M28-SBR1[7W+A] 0.05 M28-SBR1[7A+W] 0.04 M28-SBR1[7W/A] 0.03 0.02 0.01 10 100 1000 10000 PORE DIAMETER, nm Fig 13 Cumulative pore volume curve of SBR1 mix at 28 days 3.50 M28-CON1[7W+A] 3.00 M28-CON1[7W/A] 2.00 1.50 1.00 0.50 0.00 10 100 1000 10000 PORE DIAMETER, nm Fig A.5 Differential intrusion volume of the unmodified control [CON1] at 28 days CUMULATIVE PORE VOLUME, mL/g dV/dD, mL/g-nm M28-CON1[7A+W] 2.50 0.05 M6-SBR1[7W+A] 0.04 M6-SBR1[7A+W] M6-SBR1[7W/A] 0.03 0.02 0.01 10 100 1000 10000 PORE DIAMETER, nm 2.50 Fig 14 Cumulative pore volume curve of SBR1 mix at months M6-CON1[7W+A] dV/dD, mL/g-nm 2.00 M6-CON1[7A+W] M6-CON1[7W/A] 1.50 1.00 0.50 0.00 10 100 1000 10000 PORE DIAMETER, nm Fig A.6 Differential intrusion volume of the unmodified control [CON1] at months 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 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, irrespective 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 cumulative 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 respectively This could be explained by the initial air curing for days 0.045 0.04 M12-SBR1[7W+A] 0.035 M12-SBR1[7A+W] 0.03 M12-SBR1[7W/A] 0.025 0.02 0.015 0.01 0.005 10 100 1000 10000 CUMULATIVE PORE VOLUME, mL/g M Ramli et al / Composites: Part B 55 (2013) 221–233 CUMULATIVE PORE VOLUME, mL/g 228 0.035 M12-SBR3 [7W+A] 0.03 M12-SBR3 [7A+W] 0.025 M12-SBR3 [7W/A] 0.02 0.015 0.01 0.005 10 PORE DIAMETER, nm 0.04 0.035 M18-SBR1[7W+A] 0.03 M18-SBR1[7A+W] M18-SBR1[7W/A] 0.02 0.015 0.01 0.005 10 100 1000 10000 Fig A.9 Cumulative pore volume curve of SBR3 mix at 12 months CUMULATIVE PORE VOLUME, mL/g CUMULATIVE PORE VOLUME, mL/g Fig 15 Cumulative pore volume curve of SBR1 mix at 12 months 0.025 100 PORE DIAMETER, nm 1000 10000 0.01 M18-SBR3 [7W+A] M18-SBR3 [7A+W] 0.008 M18-SBR3 [7W/A] 0.006 0.004 0.002 10 PORE DIAMETER, nm 100 1000 10000 PORE DIAMETER, nm Fig 16 Cumulative pore volume curve of SBR1 mix at 18 months Fig A.10 Cumulative pore volume curve of SBR3 mix at 18 months which enables coalescence of polymer particles to form the polymer film, which in turn helps to seal the pores [27] From the dV/d log D – D curves, as shown in Fig 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 months, there was no significant difference in the maximum continuous pore diameters between SBR1 and unmodified control, CON1 at about 20 nm However, at the age of 12 and 18 months, smaller maximum continuous 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, 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 prolonged 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 decreases 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 months, the 0.06 M28-SBR1[7W+A] 0.04 M28-SBR1[7A+W] M28-SBR1[7W/A] 0.03 0.02 0.01 dV / d(log D), mL/g-nm dV/d(log D), mL/g-nm 0.05 M28-SBR3[7W+A] 0.05 M28-SBR3[7A+W] 0.04 M28-SBR3[7W/A] 0.03 0.02 0.01 0 10 100 1000 10000 PORE DIAMETER, nm Fig A.8 Log differential pore volume curve of SBR1 mix at 28 days 10 100 1000 10000 PORE DIAMETER, nm Fig 17 Log differential pore volume curve of SBR3 mix at 28 days 229 M Ramli et al / Composites: Part B 55 (2013) 221–233 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 in Figs 17 and 18 However, at the age of 12 months, the maximum continuous pore diameter dV / d(log D), mL/g-nm 0.1 M6-SBR3[7W+A] 0.08 M6-SBR3[7A+W] M6-SBR3[7W/A] 0.06 0.04 0.02 10 100 1000 10000 PORE DIAMETER, nm Fig 18 Log differential pore volume curve of SBR3 mix at months 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 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 exhibited 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 prolonged air curing after an initial days water curing dV/d(log D), mL/g-nm 0.40 0.35 M12-SBR3[7W+A] 0.30 M12-SBR3[7A+W] M12-SBR3[7W/A] 0.25 0.20 0.15 0.10 0.05 0.00 10 100 1000 was reduced significantly to a value of less than 10 nm, whereas, the coarse pore size remained unchanged as shown in Figs 19 and 20 shows a pronounced right shift in the curves’ peaks when the maximum continuous pore diameter value increased from below 10 nm to approximately 100 nm This may be due to the breaking up of open pores in the specimen under prolonged air curing as a result of intrusion pressure from mercury The results of the threshold diameter for the SBR3 mix at the ages of 28 days, and 12 months in the form of dV/dD - D plots are presented in Table The threshold diameter for SBR3 specimens 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 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 latex 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] 10000 PORE DIAMETER, nm CUMULATIVE PORE VOLUME, mL/g Fig 19 Log differential pore volume curve of SBR3 mix at 12 months dV/d(log D), mL/g-nm 0.030 M18-SBR3[7W+A] 0.025 M18-SBR3[7A+W] M18-SBR3[7W/A] 0.020 0.015 0.010 0.005 0.000 10 100 1000 0.006 M18-PAE [7W+A] 0.005 M18-PAE [7A+W] M18-PAE [7W/A] 0.004 0.003 0.002 0.001 10 10000 100 1000 10000 PORE DIAMETER, nm PORE DIAMETER, nm Fig A.11 Cumulative pore volume curve of the PAE mix at 18 months Fig 20 Log differential pore volume curve of SBR3 mix at 18 months Table Maximum continuous and threshold diameters of SBR3 mix Curing conditions 7W+A 7A + W W/A Max continuous pore diameter from dV/d(log D) – D curve (nm) Threshold diameter from dV/dD – D curve (nm) 28 days months 12 months 28 days months 12 months 20 20 25 20 20 25 10 15 20 25 25 25 20 20 20 15 15 15 230 M Ramli et al / Composites: Part B 55 (2013) 221–233 Table Maximum continuous and threshold diameters of PAE mix 7W+A 7A + W W/A Max continuous pore diameter from dV/d(log D) – D curve (nm) Threshold diameter from dV/dD –D curve (nm) 28 days months 12 months 28 days months 15 15 15 15 15 15 10 12 15 15 15 10 10 dV/d(log D), mL/g-nm Curing conditions 0.05 M6-VAE[7W+A] M6-VAE[7A+W] M6-VAE[7W/A] 0.04 0.03 0.02 0.01 0.00 dV/d(log D), mL/g-nm 0.05 M28-VAE[7W+A] 0.04 M28-VAE[7A+W] M28-VAE[7W/A] 0.03 0.02 0.01 0.00 10 100 1000 10000 PORE DIAMETER, nm Fig A.12 Log differential pore volume curve of VAE mix at 28 days 100 1000 10000 Fig A.13 Log differential pore volume curve of VAE mix at months 0.04 M12-VAE[7W+A] 0.04 M12-VAE[7A+W] 0.03 M12-VAE[7W/A] 0.03 0.02 0.02 0.01 0.01 0.00 3.2.2.4 VAE The cumulative pore volume of the VAE at 28 days and months was between 0.045 and 0.055 mL/g, which is quite similar 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 process 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 months of curing, the maximum continuous pore diameters of VAE specimens were divided into fine and large pores The maximum continuous diameter of fine pores was about 20 nm, whereas the coarse pores had a diameter ranging from 2000 to 3000 nm as shown in Figs 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, 10 PORE DIAMETER, nm dV/d(log D), mL/g-nm The Log differential pore volume also revealed that the maximum continuous pore diameters for the PAE mix were approximately 15 nm each for 28 days and 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 diameters 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 in Table At 28 days, the minimum 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 months were 10 nm, each for prolonged air curing, and cyclic wet/dry curing condition, and nm for specimen under prolonged water curing 10 100 1000 10000 PORE DIAMETER, nm Fig A.14 Log differential pore volume curve of VAE mix at 12 months without carefully considering the magnitude of the peak of curve Based on Fig 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 volumes 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 in Figs 21–23 From Fig 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 days curing in water was essential because it allowed the hydration of Portland cement to take place and develop cementing properties Subsequent air drying 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 days appears to have no significant improvement 231 M Ramli et al / Composites: Part B 55 (2013) 221–233 WATER ABSORPTIONS, % 3.6 3.2 2.8 CON1 CON2 SBR1 SBR3 PAE VAE 2.4 1.6 1.2 0.8 0.4 3.4 Relationship between water absorption and total porosity 0 50 100 150 200 250 300 350 400 450 500 550 600 AGE, days Fig 21 Water absorption of cement mortars – days in water + air 3.6 WATER ABSORPTIONS, % PAE mix was seen after ageing for 18 months At this stage, the PAE mix showed superior performance by exhibiting zero water absorption while the SBR3, VAE and SBR1 mixes were of approximately 0.1%, 0.3%, and 0.2%, respectively Although water absorption cannot be used as a measure for quality of mortar and concrete, it is an indicative judgement because most good mortars and concretes normally have absorption well below 10 percent by mass [32] 3.2 CON1 CON2 2.8 SBR1 SBR3 2.4 PAE VAE 1.6 1.2 0.8 0.4 The relationship between water absorption and the total porosity of the polymer-modified and unmodified cement mortars for all types of curing conditions were also considered Accordingly, the relationship between water absorption and total porosity of the PMM mixes existed in the exponential form with a correlation factor of 0.7 The results also showed that the water absorption of the PMM mixes increased exponentially with increasing values of total porosity irrespective of their curing conditions Similar types of correlation with a slightly lower correlation coefficient of 0.6 were observed for the unmodified cement mortars The results also indicated a scatter of test results for both the modified and unmodified cement mortars at the higher curing age This may be due to the breaking-up of soft pores in the cement paste and ruptures as a result of the increase in the intrusion pressure of the mercury See Figs 24–27 0 50 100 150 200 250 300 350 400 450 500 550 600 AGE, days Fig 22 Water absorption of cement mortars, days in air + water 3.5 Relationship between water absorption and maximum continuous pore diameter The water absorption of the cement mortar, W, revealed a direct relationship to the maximum continuous pore diameter, dm The 3.2 CON1 CON2 2.8 SBR1 SBR3 PAE VAE 2.4 1.6 1.2 0.8 0.4 0 50 100 150 200 250 300 350 400 450 500 550 600 WATER ABSORPTION, W [%] WATER ABSORPTIONS, % 3.6 W = 0.067e r = 0.7 0.8 0.18 P 0.6 0.4 0.2 AGE, days 10 12 TOTAL POROSITY, P [%] Fig 23 Water absorption of cement mortars – cyclic curing in water/air on the water absorption properties of PMMs Fig 22 shows that the water absorption of all PMMs was about 50% lower than that of the unmodified cement mortars A much lower value of water absorption was observed in PMMs exposed to cyclic wetting and drying as represented by Fig 23 However, under this curing condition, the VAE did not show similar improvement as that of the other modified mortars The variations of water absorption with age and different curing conditions showed that the water absorption for all the modified and unmodified specimens decreased with the increasing ages of curing At 28 days of cyclic curing, the water absorption of the SBR3 mix showed the lowest value of approximately 0.2% compared to that of the PAE and VAE mixes of nearly 0.5% and 0.7%, respectively After months of ageing, the water absorption of the SBR3 mix was about 0.1% and the PAE mix was approximately 0.15% However, a significant change in water absorption for the WATER ABSORPTION, W [%] Fig 24 Relationship between water absorption and total porosity of the polymermodified cement mortar 3.5 0.20 P W = 0.30e r = 0.6 2.5 1.5 0.5 10 11 12 TOTAL POROSITY, P [%] Fig 25 Relationship between water absorption and total porosity of the unmodified cement mortar M Ramli et al / Composites: Part B 55 (2013) 221–233 WATER ABSORPTION, W [%] 232 0.6 0.5 W = 0.021e 0.12 dm r = 0.95 0.4 0.3 0.2 0.1 10 15 20 25 30 MAXIMUM CONTINUOUS DIAMETER, dm [nm] WATER ABSORPTION, W [%] Fig 26 Regression correlation between water absorption and the maximum continuous pore diameter of the PMM mortars 3.5 W = 0.06e 0.13 dm r = 0.91 2.5 1.5 0.5 18 20 22 24 26 28 30 32 MAXIMUM CONTINUOUS DIAMETER, dm [nm] Fig 27 Regression correlation between water absorption and the maximum continuous pore diameter of the unmodified mortars relationships between water absorption and the continuous pore diameter of the PMM and the unmodified control mixes were calculated A high correlation coefficient of 0.95 and 0.91 for the PMM and unmodified mixes, respectively, indicates that a good relationship existed between the water absorption and the continuous pore diameter of the specimens in the form of exponential Eqs (2) and (3) For the polymer-modified mixes, W ¼ 0:021e0:12 dm ðr ¼ 0:95Þ ð2Þ And for the unmodified mix, W ¼ 0:06 e0:13 dm r ẳ 0:91ị 3ị Both the modied and unmodified mixes were seen to show a decreased scatter result compared to that of the total porosity previously discussed The results have clearly shown that the water absorption depended primarily on the maximum accessible pores through which water can permeate As the maximum continuous pore diameter increased the more water permeated through the structure of the cement paste and hence, the higher the water absorption Conclusions and recommendations From the experimental tests results and discussions on the pore structure of the polymer modified and unmodified cement systems, the following conclusions and recommendations were extracted: The porosity of PMMs was comparable to that of the unmodified control specimens at the ages of 28 days and months However, at the ages of 12 and 18 months, there was a pronounced reduction in total porosity for the SBR3, PAE and VAE mortars The results also confirmed that by modifying cement mortar with 15% polymer latex, the characteristics of the resulting mix were greatly enhanced The PMMs had a porosity value of at least times smaller than that of the unmodified control At 18 months of air curing, the SBR3, PAE, and VAE mixes had a corresponding porosity of 0.89%, 0.98% and 2.91%, compared to that of the unmodified control, CON1 and CON2, with a porosity of 8.05% and 5.62%, respectively The PMM with 6.75% of SBR solids did not show a significant improvement in porosity The porosity of the SBR1 mix in any curing condition was in fact higher than that of the unmodified controls, CON1 and CON2 at the ages of 6, 12 and 18 months As far as porosity was concerned, prolonged air curing after days, an initial water curing seemed to be the best curing method for PMMs The cyclic wet and dry curing procedure seems to improve the pore structure of the unmodified control specimens However, prolonged water curing was not beneficial to the PMM system The intruded pore volume of the unmodified control mortar, CON1, exhibited decreased pore volumes with increased curing ages between 28 days and year The curves represented by wet and dry curing were always below the corresponding curves of prolonged air or water curing Thus, it implies that in a normal environment, cyclic wet and dry curing can enhance the pore size distribution in unmodified mortars Although, the intruded pore volumes of PAE and VAE modified mortars were initially higher than those of unmodified mortars, their values were significantly reduced after 12 months of age, irrespective of their curing conditions The SBR3 mix exhibited the most superior properties in all conditions compared to the rest of the specimens at different curing ages The maximum average continuous pore diameters for unmodified cement mortars were more than the PMM materials The threshold diameters of the PMMs were comparable to the value obtained by unmodified cement mortars However, it was difficult to determine the threshold diameter at the age of 18 months due to the fact that pore openings increased and broke up into larger pores fairly easily when mercury pressure was applied 10 A good correlation was observed between the water absorption and the maximum continuous pore diameter for both the polymer-modified and unmodified cement mortars, irrespective of their curing conditions and the curing ages 11 Prolonged air curing after the initial water curing enhanced the PMM materials as indicated by low water absorption of less than 1% compared to the unmodified control mortars The increase in polymer loading from 6.75% (in the SBR1 mix) to 15% (in the SBR3 mix) also reduced the water absorption by approximately 60% Acknowledgement All polymer-modified and unmodified cement mortars have shown a reduction in total porosity with the increasing age of curing irrespective of their curing conditions The authors gratefully acknowledge the financial support from Universiti sains Malaysia M Ramli et al / Composites: Part B 55 (2013) 221–233 References [1] Wagner HB Polymer-modified 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of the study of Manmohan and Mehta [28] that the cumulative intrusion volume of pores... age and different curing conditions showed that the water absorption for all the modified and unmodified specimens decreased with the increasing ages of curing At 28 days of cyclic curing, the water