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Polymer modified alkali treated jute fibre as a reinforcing agent, substantially improves the physical and mechanical properties of cement mortar with a mix design cement:sand:fibre:water::1:3:0.01:0.6. The workability of the mortar is found to increase systematically from 155 ± 5 mm (control mortar) to 167 ± 8 mm (0.2050% polymer modified mortar). The density of the mortar is increased from 2092 kg/ m3 to 2136 kg/m3 with a concomitant reduction of both water absorption and apparent porosity. Optimal polymer content in emulsion (0.0513%) is found to increase the compressive strength, modulus of rupture and flexural toughness 25%, 28%, 387% respectively as compared to control mortar. Based on the X-ray diffraction and infra-red spectroscopy analyses of the mortar samples a plausible mechanism of the effect of modified jute fibre controlling the physical and mechanical properties of cement mortar has been proposed.
Construction and Building Materials 49 (2013) 214–222 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat Polymer modified jute fibre as reinforcing agent controlling the physical and mechanical characteristics of cement mortar Sumit Chakraborty, Sarada Prasad Kundu, Aparna Roy, Basudam Adhikari, S.B Majumder ⇑ Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302, India h i g h l i g h t s Methodology to disperse polymer modified jute fibre homogeneously into the mortar Significant improvement of CCS, MOR, and FT in jute fibre reinforced mortar Substantial improvement in TI as well as the PCRE in modified mortar Plausible mechanism to explain the improvement in mechanical properties a r t i c l e i n f o Article history: Received September 2012 Received in revised form 26 July 2013 Accepted 18 August 2013 Available online 10 September 2013 Keywords: Cement Polymer Fibre reinforcement Mechanical properties Interfacial bonding a b s t r a c t Polymer modified alkali treated jute fibre as a reinforcing agent, substantially improves the physical and mechanical properties of cement mortar with a mix design cement:sand:fibre:water::1:3:0.01:0.6 The workability of the mortar is found to increase systematically from 155 ± mm (control mortar) to 167 ± mm (0.2050% polymer modified mortar) The density of the mortar is increased from 2092 kg/ m3 to 2136 kg/m3 with a concomitant reduction of both water absorption and apparent porosity Optimal polymer content in emulsion (0.0513%) is found to increase the compressive strength, modulus of rupture and flexural toughness 25%, 28%, 387% respectively as compared to control mortar Based on the X-ray diffraction and infra-red spectroscopy analyses of the mortar samples a plausible mechanism of the effect of modified jute fibre controlling the physical and mechanical properties of cement mortar has been proposed Ó 2013 Elsevier Ltd All rights reserved Introduction Natural fibres as reinforcing agent in cement matrix are nowadays being considered as effective alternative to steel and other inorganic synthetic fibres [1,2] Natural fibres such as sisal, coconut, sugar-cane bagasse, hemp, jute are reported to yield improved mechanical strength of the cement based composites [3–7] Additionally they also enhance the post-cracking resistance, yield high-energy absorption characteristics and improve the fatigue resistance of cement based composites [8–10] Reviewing the literature, it remains difficult to disperse the natural fibre into cement matrix and also their long term durability in cement matrix is yet to be investigated [11–14] The potential application of natural fibre reinforced cement composites are limited to those area where energy must be absorbed or the areas prone to impact damage Accordingly, natural fibre reinforced cement composites are most suitable for shatter and earthquake resistant construction, foundation floor for machinery in factories, fabrication of light weight ⇑ Corresponding author Tel.: +91 3222 283986; fax: +91 3222 282274 E-mail address: subhasish@matsc.iitkgp.ernet.in (S.B Majumder) 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd All rights reserved http://dx.doi.org/10.1016/j.conbuildmat.2013.08.025 cement based roofing and ceiling boards, wall plaster, and construction materials for low cost housing [15] Variety of factors influences the physical and mechanical properties of natural fibre reinforced cement composites These factors may be grouped according to (i) the type and characteristics of reinforcing fibres, (ii) nature of the cement based matrix and mix design, and (iii) way of mixing, casting and curing of the composites [15] Among these parameters, the compatibility between the fibre and cement based matrix leading to a homogeneous distribution of the reinforcing fibres remains one of the most dominating factors that influences the mechanical properties of these composites [16] The fibre–matrix compatibility is dominated by the chemical composition of the reinforcing fibre together with their surface properties Due to the parametric dependence of so many factors, the wide scattering in the mechanical properties of natural fibre reinforced cement composites as tabulated in Table seem to be obvious In the present work, we aim to investigate the effect of jute fibre as a reinforcing agent to cement mortar For homogeneous distribution of jute fibre into the cement matrix we have modified both the chemical composition as well as surface properties of jute fibre 215 S Chakraborty et al / Construction and Building Materials 49 (2013) 214–222 Table Comparative study of mechanical behavior of different fibre reinforced cement composites Fibre type Type of modification Mechanical properties a Eucalyptus Hemp Jute Kraft banana E grandis Kenaf (1.2, %) Kraft Coconut husk Bagasse fibre Jute a b c d e f – – – – – APTS CaCl2 SBR, Vinyl ester Carboxylated SBR Reference b d e f CCS (MPa) MOR (MPa) MOE (GPa) FT (kJ/m ) TI 31.1 32.65 27.97 – 3.87 4.62 4.44 21.7 22.2 4.7 12.1 2.2 14.5 9.1 – – – 6.7 – 16.3 1.1 6.8 0.5 0.53 0.73 0.62 0.59 1.5 1.3 0.82 – – 1.86 – – – – – – – – – – – – – – 0.63 1.69 0.102 33.4 – 4.1 35.4 PCRE (J) [2] [6] [7] [10] [17] [18] [12] [13] [14] Present research Compressive strength Modulus of rupture Flexural modulus Fracture toughness Toughness index Post cracking resistance energy by a combined dilute alkali and polymer emulsion treatment The effect of fibre modification on the physical and mechanical properties of cement mortar has been investigated Moreover, the effect of chemical treatment of the reinforcing fibres on their durability in highly alkaline cement environment has also been investigated Finally, the plausible mechanism of such fibre treatment controlling the physical and mechanical properties of cement mortar is elucidated Experimental 2.1 Preparation of alkali and polymer modified jute fibre reinforced cement mortar Portland pozzolana cement confirming with IS 1489-1991 (reaffirmed 2005) (Ambuja cement) [19] was used as the binder material for the preparation of cement mortar The oxide composition of this cement is shown in Table The local river sand was used for the preparation of cement mortar This sand did not contain any organic substances which might affect cement hydration reaction To evaluate grading zone and average particle size of sand, sieve analysis was performed From the sieve analysis (Fig 1), it was confirmed that the used sand is in grading zone II with average particle size 0.3 mm TD-4 grade jute fibres were used as reinforcing agent As received jute fibres, being long enough, could not be used as reinforcing Table The oxide composition of Portland pozzolanic (Ambuja) cement a c Composition SiO2 CaO MgO Fe2O3 Al2O3 C L.I.a Weight (%) 27.28 50 1.96 6.18 9.20 0.76 2.66 Loss of ignition agent in cement Therefore to use the jute fibre as reinforcement in cement composite, the long jute fibres were chopped into mm length The average diameter of used jute fibre was 0.062 ± 0.014 mm The treatment composition of jute with alkali and polymer latex is shown in Table First the requisite amount of jute as mentioned in Table was soaked with the 0.5% alkali solution following which the spent alkali solution was decanted out after 24 h of soaking Next the respective amounts of Sika latex containing 41% solid (carboxylated styrene butadiene (SBR)) was diluted with 1000 ml of water and added to the alkali soaked wet jute The cement mortar was prepared following the composition shown in Table In the mix design the weight fraction of cement:sand:fibre:water was kept 1:3:0.01:0.6 The total alkali and polymer treated jute (as shown in Table 3) were mixed with half part of the cement required to make the mortar A mechanical mixer was used to make uniform slurry after 10–15 mixing The required amount of sand, rest of the cement and additional amount of water was mixed thoroughly with the slurry for another 10–20 The fresh mortar thus prepared was cast immediately in 110 mm (length (l)) Â 20 mm (breadth (b)) Â 20 mm (depth (d)) mould for flexural specimen and 70.6 mm cubic mould for compressive specimen The mortar samples were allowed to set in the moulds for 24 h at ambient temperature (30 ± °C) The samples after setting were removed from the mould and water cured for 7, 28, 42, and 90 days After curing, the mortar specimens were dried under ambient condition For the characterization of polymer modified jute fibre reinforced mortar, minimum six samples of each batch were tested As shown in Table 4, nine different formulations (viz., 1–9) were used for the preparation of the mortar samples In these mortar samples, the ratio of cement:sand:fibre were kept constant, however, the solid polymer: water (weight to volume) ratio were varied The solid polymer content in emulsion (defined as weight of solid polymer in 100 ml water) was varied in between 0.0257% and 0.205% (w/v) In this experiment, for each formulation samples were fabricated for each test To evaluate the durability of the alkali polymer modified jute fibres in alkaline cementitious medium, the combined alkali polymer modified jute reinforced cement paste was prepared with the mix design cement:alkali treated jute:water 1:0.01:0.6 In this test 100 mm long jute fibres were used Initially the jute fibres were treated with 0.5% NaOH solution for 24 h followed by mixing with polymer Fig (a) A comparative study of cumulative mass (%) passing of fine aggregate (sand) through the equivalent spherical diameter sized sieve with the standard value of grading zone II, (b) retention of fine aggregate on different equivalent spherical diameter sized sieve 216 S Chakraborty et al / Construction and Building Materials 49 (2013) 214–222 Table Treatment composition of jute with alkali and polymer latex Ingredients For modification with alkali and polymer latex Jute fibre (2–5 mm long) (g) Aqueous sodium hydroxide (0.5%) (ml)a Water based Sika latex (41% solid content) (ml) 30 900 0.625 0.257b 1000 Water (ml) a b 30 900 1.250 0.513b 1000 30 900 2.500 1.025b 1000 30 900 5.000 2.050b 1000 After 24 h of soaking in alkali spent alkali solution was decanted Weight of polymer of Sika latex in respective formulations on dry basis Table Composition of jute reinforced cement mortar Components Cement (kg) Sand (kg) Raw/0.5% alkali treated jute Weight of polymer (dry basis) Water (ml) (for polymer emulsion) Additional water (ml) (for mortar mixing) a b c d Formulation No 9 – – – 1800 30a – – 1800 30b 0.257c 1000d 800 30b 0.513c 1000d 800 30b 1.025c 1000d 800 30b 2.050c 1000d 800 30b 0.513c 1000d 740 30b 1.025c 1000d 680 30b 2.050c 1000d 620 Weight of water soaked raw jute (g) Weight of alkali treated jute (g) Weight of polymer of Sika latex in respective formulations on dry basis Added water for making polymer emulsion (ml) emulsion (0.0513% polymer content in emulsion) for 10 The combined alkali polymer modified jute fibres were then dispersed in cement slurry to prepare jute cement paste After waiting for 24 h, the semi-hardened and hydrated jute cement paste was water cured up to 360 days During curing, at least twenty-five single strand jute fibres were isolated in regular intervals (cured for 7, 28, 42, 90, 180 and 360 days), washed sequentially in water and acetone, and oven dried at 105 °C for 24 h Finally, the tensile strength of these fibres was measured using a universal testing machine 2.2 Physical properties and microstructure of jute fibre and fibre reinforced mortar Flow behaviour of the freshly prepared cement mortar (which indicates its workability) is estimated by a flow table test in accordance with IS 1727 standard [20] The bulk density (both wet and dry), water absorption, and apparent porosity of the water cured mortar samples were estimated according to ASTM C 948 [21] standard Fourier transformed infra-red spectroscopy (FTIR) measurements were performed on jute fibre as well as mortar samples using a spectrometer (Nexus 870, Thermo Nicolet Corp USA) Oven dried (at 85 °C for h) jute fibre as well as powdered mortar samples were mixed with KBR to make pellets for FTIR measurements The FTIR spectra were recorded in the wave number range between 4000–400 cmÀ1 after averaging 32 scans The structural characteristics of raw as well as alkali modified jute fibres and the water cured mortar samples were investigated using an X-ray diffractometer (Ultima III, Rigaku Inc Japan) Cu Ka radiation (40 kV, 30 mA) was used to record the X-ray diffractograms of these samples in the rage of 2h between 10° and 60° maintaining at a scanning rate of 1ominÀ1 Fig Load deflection curve of Polymer modified jute reinforced mortar The micrographs of the jute fibre and fractured surface of the mortar specimens were recorded using a scanning electron microscope (Vega-LSV, TESCAN, Czech Republic) A thin gold coating was applied on the surface of the samples to avoid charging 2.3 Mechanical properties of jute fibre and jute fibre reinforced mortar The compressive strength measurements were carried out using a 1000 kN hydraulic universal testing machine (AIM: 31402, S No 091020) Mortar cubes (volume = 3.52 Â 105 mm3) samples were tested (without any preload) using a loading rate 13 kN minÀ1 in compliance with the IS 516 standard [22] The compressive strength or cold crushing strength (CCS in MPa) was calculated measuring the fracture load (F in N) and area of the face of the cube (A in mm2) using the following relation CCS ẳ F=A 1ị The exural tests were performed using a universal testing machine (Hounsfield H10KS) A three point bending configuration was used to determine the modulus of rupture (MOR) Rectangular water cured mortar specimen (110 mm (l) Â 20 mm (b) Â 20 mm (d)) was used as sample During the flexural tests, the span length (L) = 60 mm and constant loading rate 1.2 mm minÀ1 were maintained as per IS 4332 [23] specification The MOR is determined using the following relation MOR ¼ 3P Á L=ð2 Á b Á d Þ ð2Þ Fig Variation of the density (wet and dry), water absorption and apparent porosity of jute modified mortar samples with the polymer content in emulsion (%) S Chakraborty et al / Construction and Building Materials 49 (2013) 214–222 Table The flow table value of the control and polymer modified jute cement mortar Formulation No Solid polymer content in emulsion (%) Water cement ratio Flow table value (mm) – – 0.0257 0.0513 0.1025 0.2050 0.0513 0.1020 0.2050 0.60 0.60 0.60 0.60 0.60 0.60 0.58 0.56 0.54 155 ± 156 ± 157 ± 161 ± 164 ± 167 ± 156 ± 156 ± 151 ± 217 FT ẳ Absorbed energy during flexural testị=Area of the broken sectionÞ ð3Þ where the numerator is the area under the load deflection curve (shaded region in Fig 2) Flexural modulous (F.M) is estimated using the following relation F Á M ¼ m Á L3 =ð4b Á d Þ ð4Þ where ‘m’ is the slope of the load–deflection curve during elastic deformation (usually in the deflection regime between 0.05 and 2.0 mm) and L is support span length Toughness indices (TI) are defined as ratio of the whole area under the flexural load–deflection curve and the area under the deflection of maximum load This is also termed as peak load toughness indices [6] Finally, the difference between the total absorbed energy during flexural test and absorbed energy up to peak load is known as post cracking resistance energy This is estimated as the difference between the whole area under the flexural load–deflection curve and area under the deflection of maximum load The tensile strength of the jute fibres, isolated from jute reinforced cement paste after curing for specified period in the range of 7–360 days, were measured using a 10 kN universal tensile testing machine (H10KS, Hounsfield, Salfords, UK) A gauge length of 25 mm was employed with a crosshead speed of mm/min in accordance with ASTM D3822-01 (ASTM, 2001) [24] For this test each single fibre was mounted within a cardboard frame (with a rectangular opening of 15 mm in width and 30 mm in height) using adhesive The frame was placed within the jaws of universal testing machine (UTM) equipped with a 100 N load cell At least twenty-five single fibres each randomly drawn from cement paste were tested Result 3.1 Physical, mechanical and microstructure analysis of combined alkali and polymer modified jute fibre reinforced mortar Fig Variation of flexural modulus (FM), compressive and flexural strength of the control and fibre-reinforced mortar samples (cured for 28 days) with the polymer content in emulsion (%) Fig SEM micrographs of the fractured surface of the (a) control, (b) 0.0257%, (c) 0.0513%, and (d) 0.02050% polymer modified jute reinforced mortar specimens where P is the fracture load, ‘L’ is the support span length, ‘b’ is the breadth and ‘d’ is the depth of the mortar samples From the recorded load–deflection curve (Fig 2); flexural modulus (FM), flexural toughness (FT), toughness index (TI), and post cracking resistance energy (PCRE) are estimated as described below: Toughness is the energy absorption capacity of the composite which defines its ability to resist fracture under static, dynamic or impact load The flexural toughness (FT) is determined using the following relation Fig shows the variation of the density (wet and dry), water absorption and apparent porosity of jute modified mortar samples as a function of the polymer content in emulsion (%) used for cement hydration As shown in the figure, the densities are increased, whereas the water absorption as well as apparent porosity is reduced with the polymer content Usually in most of the studies on polymer modified cement composites, the weight ratio of polymer: cement is kept more than 5% [25–28] It is reported that higher polymer: cement affects the cement hydration, however, coherent polymer film retards the propagation of tiny cracks in cement mortar forming an interpenetrating structure with the modified cement mortar with lower rigidity Therefore optimum polymer: cement ratio improves the mechanical properties of cement mortar Unlike all these reports, in the present work, very small amount of SBR based latex is used to make the cement mortar As shown in Table 5, the flow table value of the jute-modified cement mortar is systematically increased with the polymer content in emulsion used for cement hydration The role of the polymer modification in controlling the physical and mechanical properties of jute fibre reinforced concretes are discussed later Fig shows the variation of flexural modulus (FM), compressive strength (CCS) and modulus of rupture (MOR) of the control and fibre-reinforced mortar samples (cured for 28 days) with the polymer content in emulsion (%) Interestingly, both compressive strength and MOR are improved up to the 0.0513% polymer content Thus with polymer modification, the CCS and MOR of the control mortar has increased from 28 MPa and 7.0 MPa to 35 and 9.0 MPa respectively With further increase of polymer content up to 0.2050%, the CCS and MOR of the jute reinforced polymer modified mortars are decreased however, still remains comparable to/better than the control sample In contrast to this, the flexural modulus values are decreased with the increase of the polymer content (%) As expected, the CCS and MOR values increase with curing days, however, the trend of their variation with the polymer content in emulsion remains similar to that presented in Fig for mortar samples cured for 28 days Thus for 90 days cured mortar samples the CCS and MOR values are measured to be 37.9 MPa and 12.8 MPa respectively As presented in Table 5, the flow table values were systematically increased with the increase of the polymer content in emulsion (%) For the polymer content 0.0513%, the 218 S Chakraborty et al / Construction and Building Materials 49 (2013) 214–222 Fig The force-extension curves of control, raw jute reinforced and polymer modified jute reinforced mortar specimens with polymer contents varying from 0.0257% to 0.2050% (six samples of formulation Nos 1–6 as indicated in Table 4) water content required for cement hydration was reduced from 60% to 58% to yield the flow table value (156 ± mm) similar to that of control mortar (155 ± mm) As a result, the CCS and MOR values of the mortar samples were found to increase further up to 36 MPa and 9.3 MPa respectively after 28 days curing Interestingly, when the curing time is increased for 90 days, the CCS and MOR values of these samples are increased to 38.4 MPa and 14 MPa respectively The above results illustrate that by tuning the processing methodologies, the mechanical properties of polymer modified jute reinforced cement mortars may be fine tuned depending on the application needs Fig shows the SEM micrographs of the fractured surface of the (a) control, (b) 0.0257%, (c) 0.0513%, and (d) 0.2050% polymer modified jute reinforced mortar specimens As observed clearly in Fig 5(c) and (d), with the increase of the polymer contents the porosity of the mortar matrix is markedly reduced The rubber like SBR contains both rigid styrene and flexible butadiene chains [29] which help to form coherent polymer film and probably an interpenetrating structure with the mortar matrix Unlike the other literature reports, in this work we have found that a comparatively diluted polymer emulsion is sufficient to yield a coherent polymer film As presented earlier in Fig 4, since the flexural modulus is reduced with the increase in the polymer content, therefore it advantageous to keep the polymer content low enough to form a coherent film and interpenetrating structure with the mortar matrix Fig shows the force-extension curves of control, raw jute reinforced and polymer modified jute reinforced mortar specimens with polymer contents varying from 0.0257% to 0.2050% (6 samples of formulation Nos 1–6 as indicated in Table 4) It is observed Fig Variation of the flexural toughness (FT) and toughness index (TI) with the polymer content in emulsion (%) Fig Variation of the post cracking resistance energy (PCRE) with the polymer content in emulsion (%) from the figure that maximum load is carried by 0.0513% polymer modified jute fibre reinforced cement mortar sample Very small extension is observed for control sample as compared to that of the mortar sample prepared by polymer modified jute fibre reinforcement This is due to the occurrence of sudden failure for control sample (Fig 7(a)), however higher extension for polymer modified jute reinforced cement mortar is due to the gradual failure as envisaged from the Fig 7(b) The mortar specimens were also characterized in terms of their flexural toughness and toughness index characteristics As explained previously (Fig 2) the fracture toughness and toughness index were calculated from this load extension curve As envisaged from Fig 6, initially, the load Fig Failure mode in bending test of the control and polymer modified jute reinforced cement mortar samples S Chakraborty et al / Construction and Building Materials 49 (2013) 214–222 Table Tensile strength retention (%) of raw and alkali polymer (0.0513%) modified jute fibres exposed in alkaline cementitious environment for 7–360 days Exposure time (days) 28 42 90 180 360 Tensile strength retention (%) of raw and combined alkali polymer modified jute in cement environment Raw jute Modified jute 100.0 98.5 92.8 91.9 82.1 77.6 73.7 100.0 99.8 99.1 98.7 96.7 94.3 93.2 219 of the polymer content Comparing the results presented in Table 1, it is encouraging to note that as compared to other jute fibre reinforcement report, substantial improvement is achieved in CCS, MOR and FT values reported in the present work Fig presents the variation of the post cracking resistance energy (PCRE) with the polymer content in emulsion The PCRE is substantially improved up to 0.0513% polymer content With further increase of the polymer content, the PCRE is reduced, however, up to 0.2050% polymer content the estimated PCRE is found to be far improved as compared to the control mortar sample The results presented above are summarized as follows: Addition of diluted SBR based latex in alkali modified jute-fibre reinforced mortar is found to systematically increase the flow-table value and density, while reducing the water absorption and apparent porosity of the mortar Using optimal polymer content in emulsion (0.0513%) substantial improvement in CCS and MOR values has readily been achieved The flexural toughness is also markedly increased when 0.0513% polymer modifier is used Irrespective of the polymer contents the flexural modulus is decreased with the increase in the polymer content in emulsion (%) We have observed that the toughness index as well as the post cracking resistance energies is substantially improved in polymer modified jute reinforced mortars 3.2 Durability study of jute fibre in cement medium Fig 10 The X-ray diffraction patterns of (i) control mortar and (ii) 0.0513% polymer modified jute reinforced mortar samples cured for 28 days The letters referring to the XRD peaks are (a) Alite, (b) Belite, (c) Calcite, (g) Genite, (p) Portlandite, and (q) Quartz The durability of raw as well as combined alkali polymer (0.0513%) modified jute fibre (in alkaline cement paste) was also investigated by estimating the value of tensile strength retention of respective fibres Table shows the tensile strength retention (%) of raw and combined alkali polymer (0.0513%) modified jute fibres as a function of time for alkaline cementitious environment As shown in Table 6, in cement environment, combined alkali polymer (0.0513%) modified jute fibres have better tensile strength retention (%) as compared to their raw jute counterpart After 360 days exposure in cement paste, almost 93% of tensile strength was retained in combined alkali polymer modified jute fibre as compared to 74% retention for raw jute fibre The main reason of natural fibre degradation in alkaline matrix is attributed to be due to Ca2+ fixation (known as mineralization) on fibre surface [30] When the fibre surface is coated with polymer latex, the Ca2+ fixation seems to be minimized to retard the degradation Discussion Fig 11 Experimental, fitted and the deconvoluted XRD peaks in the 2h range between 15° and 40° of control mortar sample carrying capacity increases up to 0.0513% polymer modified jute fibre reinforced cement sample (formulation code of the sample is 4) With further increase of polymer content load carrying capacity decreases gradually Therefore, optimal polymer content (0.0513%) shows maximum load carrying capacity Fig shows the variation of the flexural toughness (FT) and toughness index (TI) with the polymer content in emulsion (%) As compared to the control specimen, the flexural toughness is substantially increased up to 0.0513% polymer content With further increase of the polymer content the FT values are decreased, however, the values still remain better than the control sample On the other hand, the toughness index increases with the increase In the preceding section we have reported an overall improvement of the physical characteristics and mechanical properties of polymer modified alkali treated jute fibre reinforced cement mortar samples The durability of raw as well as combined alkali polymer (0.0513%) modified jute fibre (in alkaline cement paste) has also been reported In order to find a plausible mechanism controlling these improvements we have performed X-ray diffraction and FTIR analyses of the modified jute fibres and cement mortar samples Fig 10 shows the X-ray diffraction patterns of (i) control mortar and (ii) 0.0513% polymer modified jute reinforced mortar samples cured for 28 days It is known that the major constituents of Portland pozzolana cement are alite (a) [tricalcium silicate C3S (Ca3SiO5)], belite (b) [dicalcium silicate C2S (Ca2SiO4)], tricalcium aluminate [C3A (Ca3Al2O6)], and tetracalcium alumino ferrite [C4AF (Ca4AlnFe2ÀnO7,)] As compared to ordinary Portland cement (OPC), the Portland pozzolana cement contains substantial amount of quartz (q) and minute quantity of gypsum (g) as well The hydration of alite and belite phases produces Ca(OH)2 (p) (portlandite) and amorphous calcium–silica–hydrate (C–S–H) [31] All the 220 S Chakraborty et al / Construction and Building Materials 49 (2013) 214–222 Fig 12 (a) The FTIR spectra of (i) alkali treated jute fibre and (ii) polymer (0.0513%) modified jute fibre, (b) the FTIR spectra of (i) mortar (control) and (ii) 0.0513% polymer modified jute reinforced mortar specimen cured for 28 days, (c) the experimental, fitted and deconvoluted modes for the mortar (control) specimen Table Assignment of the FTIR modes of hydrated cement mortar Peak position (cmÀ1) Assignment 3638 3400–3100 OAH stretching of Ca(OH)2 Symmetric and asymmetric stretching (m1 and m3) of the OAH vibrator of the water molecules The asymmetric stretching of HAC bond present in the organic compound m2 Deformation mode of the molecular water HAOAH absorbed 2928 1644 1477 and 1420 970 m3 of COÀ2 The m3 stretching of SiAO bond of calcium silicate hydrate (CASAH) This mode accounts for the polymerization of the SiO4À units present in C3S and C2S during hydration diffraction peaks corresponding to these phases in the cured mortar specimens are indexed in Fig 10 As noted in Fig 10, the characteristic peak that corresponds to portlandite phase (p) appears at 2h = 18° The diffraction peak of the major reactant alite (a) is identified at 2h = 29.4° Estimation of the ratio of the integrated area of the portlandite (p) and allite (a) peak ratio could therefore be treated as the index of the degree of hydration The XRD pattern of the cured mortar specimen was fitted using a commercial software (Peakfit 4.1, Jandel Scientific) and Fig 11 shows the fitted as well as deconvoluted XRD peaks in the 2h range 15–40° Similar fitting was also performed of the XRD pattern of 0.0513% polymer modified jute reinforced cement mortar sample (not shown) We have found that the integrated peak area ratio of the peaks corresponding to the portlandite (p) and alite (a) phase (Ap/Aa) of the control sample (0.169) is reduced to 0.140 in polymer modified jute reinforced mortar sample This is indicative to two possibilities: first, as compared to the control sample, either the formation of portlandite is less in the polymer modified mortar specimen or the hydrated product (portlandite) (in the polymer modified jute reinforced mortar specimen) is consumed elsewhere To better understand this phenomenon we have performed FTIR analyses of the alkali modified jute fibre and the polymer modified jute fibres Fig 12 (a) compares the FTIR spectra of alkali treated jute fibre with the one after polymer modification As shown in the figure, the absorption band 3559 cmÀ1 is assigned to be due to OAH stretching The mode at 2921 cmÀ1 is assigned to be due to CAH stretching vibration The absorption band at 1739 cmÀ1 is absent in alkali modified fibre and appears only in polymer modified fibre (encircled with dotted mark) The mode is assigned to be due to the C@O stretching of ester linkage [32] The appearance of this band is indicative to some kind of interaction between the polymer additive and alkali modified jute fibres In Fig 12(b) we have compared the FTIR spectra of (i) control mortar and (ii) 0.0513% polymer modified jute reinforced mortar specimen cured for 28 days All the absorption bands are indexed and the assigned modes along with their wave numbers are tabulated in Table [33] As indicated in Table 7, the absorption mode at 3638 cmÀ1 is indexed to be due to OAH stretching of the portandite (Ca(OH)2) phase The mode 2928 cmÀ1 is due to asymmetric stretching of HAC bond from the organic moieties present in the mortar sample Considering the mode 2928 cmÀ1 as an internal standard [34], the change in the intensity of the OAH stretching mode of portandite phase (both in control and polymer modified mortar specimens) is estimated by fitting these modes using commercial software The typical fitting and the deconvoluted modes for the control specimen is shown in Fig 12(c) The ratio of the integrated area of OAH S Chakraborty et al / Construction and Building Materials 49 (2013) 214–222 221 Fig 13 Schematic of the plausible mechanism for the interfacial bonding between the alkali modified jute fibre and cement matrix (see text for details) stretching mode and asymmetric HAC mode (AOAH/AHAC) are estimated from these fit The ratio is estimated to be 0.39 for control and 0.37 for 0.0513% polymer modified jute reinforced mortar samples In line to the XRD analyses presented above, the FTIR analyses also indicate that the formation of portandite is retarded in polymer modified specimens Through these analyses it is clearly demonstrated that the polymer coating are chemically interacted with alkali modified jute fibre and retards the formation of the major cement hydration product Viewing in light of the above analyses we are making an attempt to understand the improvement of both physical and mechanical properties in polymer modified alkali treated jute reinforced mortar samples Alkali treatment modifies the fibre composition by removing the amorphous constituents of jute fibres (viz hemicelluloses, wax etc.) and thereby increasing its crystallinity [35] The polymer latex modifies the surface of the fibre as well as the mortar matrix to impart homogeneous distribution of the fibre as well as strong interfacial bonding to the mortar matrix The coherent polymer film and its interpenetrating structure with the mortar matrix improve the density reducing the apparent porosity of the modified mortar The strong interfacial bonding between the uniformly dispersed jute fibre and mortar matrix retard the crack propagation during fracture The main constituent of jute fibre is cellulose which contains large number of inter and intra molecular hydroxyl groups During the alkali (NaOH) treatment, some of these hydroxyl groups in the jute fibre react with Na+ ion to form base exchanged cellulose fibres with OÀNa+ groups (see Fig 13) [36] The carboxylated styrene butadiene rubber (SBR) based polymer latex contains carboxylic acid groups [27] The base exchanged cellulose fibre reacts with the ÀCOOH group of the carboxylated SBR to form an ester linkage forming NaOH as by-product The formation of such ester linkage has clearly been identified in FTIR analyses (Fig 12(a)) To form interfacial bonding to the mortar matrix, some of these ÀCOOH groups of the carboxylated SBR also reacts with the hydrated cement (Ca(OH)2) forming H2O as a byproduct These reactions are also shown schematically in Fig 13 As some part of the hydration product (viz portlandite) is consumed in such reaction, as indicated both in XRD and FTIR analyses (see Fig 10 and Fig 12b) the amount of the hydration product is found to be less in the polymer modified mortar samples Since a much diluted polymer emulsion is used in the present study, it seems to be unlikely that the polymer modification itself would retard the cement hydration Conclusions Jute as a natural fibre is used as a reinforcing agent to improve the physical and mechanical properties of cement mortar The mix design of the mortar was kept, cement:sand:Fibre:water::1:3:0.01:0.6 The chopped jute-fibre (2–5 mm in length) was pre-treated by immersing in 0.5% dilute sodium hydroxide solution overnight prior to disperse in mortar matrix In this investigation the solid polymer content in emulsion (defined as weight of solid polymer in 100 ml water) was varied in between 0.0257% and 0.205% (w/v) A novel processing methodology was developed to homogeneously disperse alkali and polymer modified jute fibre into the mortar matrix The combined alkali and polymer treatment yield mortar where the workability is found to increase systematically from 155 ± mm (control mortar) to 167 ± mm (0.2050% polymer modified mortar) The density of the mortar is increased from 2092 kg/m3 to 2136 kg/m3 with a concomitant reduction of both water absorption and apparent porosity Optimal polymer content in emulsion (0.0513%) is found to increase the compressive strength (CCS), modulus of rupture and flexural toughness 25%, 28%, 387% respectively as compared to control mortar without any jute reinforcement Though the toughness index as well as the post cracking resistance energies are substantially improved with the increase in polymer strength, the flexural modulus is found to decrease as compared to control mortar specimen Based on XRD and FTIR analyses we have identified that the alkali treatment and polymer modification help the reinforcing jute fibre to form strong interfacial bond with mortar matrix A plausible mechanism for such bond formation has been proposed to explain the observed 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Technol 2012;107:222–8 Sreekala MS, Thomas S Effect of fibre surface modification on water-sorption characteristics of oil palm fibres Compos Sci Technol 2003;63:861–9 ... improve the physical and mechanical properties of cement mortar The mix design of the mortar was kept, cement: sand :Fibre: water::1:3:0.01:0.6 The chopped jute- fibre (2–5 mm in length) was pre-treated... etc.) and thereby increasing its crystallinity [35] The polymer latex modifies the surface of the fibre as well as the mortar matrix to impart homogeneous distribution of the fibre as well as strong... ml of water and added to the alkali soaked wet jute The cement mortar was prepared following the composition shown in Table In the mix design the weight fraction of cement: sand:fibre:water was