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Design and evaluation of polyester fiber and SBR latex compound-modified perlite mortar with rubber powder
Construction and Building Materials 127 (2016) 751–761
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Design and evaluation of polyester fiber and SBR latex compound-modified perlite mortar with rubber powder Fang Xu a,⇑, Chao Peng a, Jing Zhu b, Jianping Chen a a b
Faculty of Engineering, China University of Geosciences, Wuhan 430074, PR China Hubei Communications Technical College, Wuhan 430079, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A new kind of perlite mortar (FPMP)
was proposed. The effect of the major mix design
parameters on the properties was studied. The microstructure of FPMP were studied by Optical Microscope, XRD and SEM.
The micrographs (SEM) of EP
The micrographs (SEM) of FPMP matrix
a r t i c l e
i n f o
Article history: Received 20 July 2016 Received in revised form 26 September 2016 Accepted 6 October 2016
Keywords: Perlite mortar Rubber powder Polyester fiber SBR latex Mix design Mechanical performance Thermal property
a b s t r a c t This paper proposed a new kind of perlite mortar modified by rubber powder, polyester fiber and SBR latex. The orthogonal experiment design method was employed to study the mix design of this new kind of perlite mortar. The influence of the major mix design parameters on the working performance, mechanical and thermal properties of the perlite mortar was studied. Furthermore, X-ray diffraction, Optical Microscope and Scanning Electron Microscope were employed to study the microstructure and failure mechanism of the perlite mortar. The results indicated that SBR latex/cement ratio had a significant influence on the fluidity and unit dry weight of the perlite mortar. Expanded perlite/cement ratio and rubber powder/cement ratio were the major influence factors on the compressive and flexural strength. Furthermore, the addition of SBR latex and polyester fiber can effectively improve the softening coefficient and frost resistance of the perlite mortar. The compressive strength and thermal conductivity coefficient was nearly linearly proportional to the unit dry weight of the perlite mortar. The internal microscopic matrix of the perlite mortar showed the porous structure and a large amount of unhydrated expanded perlite. SBR latex reinforced the interfacial transition zone between cement hydrates and rubber particles. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Perlite is an amorphous volcanic glass, which is produced from crude perlite rock and comprised of mainly alumina and silicon ⇑ Corresponding author. E-mail address: [email protected] (F. Xu). http://dx.doi.org/10.1016/j.conbuildmat.2016.10.060 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
dioxide [1–3]. The numerous micropores in the perlite ensure lightweight properties while providing the properties of thermal and sound insulation [4]. Therefore expanded perlite (EP) has been widely used in the building industry as an aggregate in the manufacturing of lightweight mortars, concretes and insulation products, etc [5]. However, normal perlite mortars usually have some problems in the practical application. Firstly, because of high
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F. Xu et al. / Construction and Building Materials 127 (2016) 751–761
Table 1 P.C 32.5 physical and mechanical properties of cement. Fineness (%)
Setting time (min) Initial setting
Final setting
1.21
75
210
Stability
Flexural strength (MPa) 3d
7d
28 d
3d
7d
28 d
Qualified
3.6
5.3
8.1
13.8
23.6
38.9
brittleness and direct exposure in external environment, cracks are easily formed in the matrix of perlite mortars under dry-wet circulation and freeze-thaw cycles. Secondly, a large number of irregular harmful pores, which lead to the poor durability and weak long-term application of insulation construction, are often existed inside normal perlite mortar. How to solve these problems of normal perlite mortar, has become a very attractive topic in the practical application. Nowadays, polymers have been vastly used in construction industry as modifiers, especially for the purpose of improving service performance of both cement concrete and mortar [6,7]. In fact, polymer latexes are used most widely in the different types of polymeric substances [8]. Tang et al. [9] studied mechanical and drying shrinkage properties of graded polystyrene aggregate concrete modified by polymer latex. Chen and Liu [10] investigated mechanical properties of polymer-modified concretes containing expanded polystyrene beads. Besides, different kinds of short organic fibers, including polypropylene fiber, polyester fiber, carbon fiber and basalt fiber, were used as reinforcement additions to improve mechanical properties since fibers could increase cracking resistance and fracture toughness of the brittle matrix [11,12]. It was reported that the addition of polypropylene fiber in perlite mortar improves its flexural strength and toughness. The reason is that the fibers will withstand the load until the interfacial bonding between the matrix and the fibers in the concrete was failed after cracking of matrix [13,14]. Furthermore, the properties of cement based materials can be further improved by the addition of organic polymer and fibers. Xu et al. [15] studied the influence of SBR latex and polypropylene fiber on the mechanical performances of crumb rubber mortar. The test results showed that the flexural toughness index of the rubber mortar was improved by 50–100% with the addition of SBR latex and polypropylene fiber. Cao [16] reported that the mechanical performance of cement mortar modified by short carbon fibers was improved by adding acrylic dispersion in the amount of 15% by mass of cement. As to the application of recycled tyre rubber in construction industry, many studies have been carried out on concrete and mortars modified by used tyre rubber [17–19]. The literature about the use of tyre rubber powders in cement-based materials mainly focuses on the use of tyre rubber powders as aggregates and evaluates the mechanical properties of the matrix. Relative research results have indicated that rubberized concrete mixtures show lower density, lower compressive and splitting tensile strength, higher impact resistance, and better sound insulation [20–23]. A major merit of adding tyre rubber powders into cement based materials is that cement based materials become more flexible and ductile [24–26]. Pelisser [27] reported that the compressive strength of concrete with the addition of 10 wt.% tyre rubber powders decreased by only 14% comparing with that of normal concrete. Similar studies confirmed that the proper addition of tyre rubber powders leads to minor changes in the mechanical performances of cement based materials [28,29]. As to the weak bonding between tyre rubber powders and cement, Segre [30] uncovered that alkaline-treated tyre rubber powders had a better bonding strength to cement particles. Other researchers found that tyre rubber powders can be externally modified to improve their compatibility of cement and polymer mixtures [31,32]. Moreover, investigations were conducted about the influences of tyre rubber
Compressive strength (MPa)
powders on the thermal properties of cement based materials [33]. It was reported that the addition of rubber particles reduces the thermal conductivity and density of cement composites. As mentioned above, in order to improve the performances of normal perlite mortar, this paper proposed a new kind of perlite mortar modified by rubber powder (RP), SBR latex (SBR) and polyester fiber (PF). This mortar is called fiber and polymer compoundmodified perlite mortar with rubber powder (FPMP). The orthogonal experiment design method was employed to study the mix design of FPMP. The influence of the main mix design parameters on the working performance, mechanical and thermal properties of FPMP were studied. In order to better understand the mechanical behavior, X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) were employed to investigate the microstructure and failure mechanism of FPMP.
2. Experimental 2.1. Materials The physical and mechanical performances of P.C 32.5 Portland cement used in this paper were measured according to ASTM C150, which were shown in Table 1. The appearance of expanded perlite (EP) used in this research was shown in Fig. 1. The bulk density of EP is 61 kg/m3. The water absorption ratio is 120% 300% and the particle size is 0.1 mm 2.5 mm. The bulk density of rubber powder (RP) used in this research is 310 kg/m3, the particle size of the RP is 0.75 mm 2.36 mm. The specific technical parameters and physical properties of polyester fiber (PF) were obtained from the fiber producer, which were listed in Table 2. The physical and mechanical properties of PF were tested according to ASTM C1557 and ASTM D7138. The properties of SBR latex was provided by BASF company, which were shown in Table 3. The performance experiments of SBR latex were performed by ASTM D4026. The water used in this research was the tap water.
Fig. 1. The appearance of EP.
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F. Xu et al. / Construction and Building Materials 127 (2016) 751–761 Table 2 The physical and mechanical properties of PF. Crimp degree
Length (mm)
Nominal diameter (mm)
Density (g/cm3)
Melting temperature (°C)
Ignition temperature (°C)
Flexural strength (MPa)
Broken elongation (%)
–
6 ± 0.5
0.014 ± 0.005
1.36
520
560
540
42
Table 3 The performance of SBR latex. Latex type
Main chemical components
Solid content (%)
pH
SBR
Butadiene, styrene
50
7 10
2.3.2. The fluidity test The fluidity of FPMP was evaluated by the index of consistency, which refers to the flow performance of the mortar by the external force or gravity. The consistency was measured by the mortar consistency tester. After mixing, the consistency of the fresh mortar was immediately determined by the immersing depth of the cone in the consistency tester.
2.2. The design of orthogonal experiment The orthogonal experiment design method was employed to study the mix design of FPMP in this paper. RP/cement ratio (A), SBR/cement ratio (B), PF dosage (C) and EP/cement ratio (D) were considered as the four major mix design parameters. In this experiment, RP/cement ratio is between 0 and 18%. SBR/cement ratio is between 0 and 15%. PF dosage is between 0 and 0.15%, which is the volume fraction of FPMP composite. EP/cement ratio is set in the range of 30–45%. Five factors and four levels of orthogonal test design scheme, including the fifth factor for blank columns, were carried out. The water/cement ratio was fixed to 0.9 for each group of the orthogonal experiment. The design table of the orthogonal experiment was shown in Table 4.
2.3.3. Mechanical performance tests The specimen dimension for compressive strength tests was 70.7 70.7 70.7 mm. The size of the specimens for flexural strength tests was 40 40 160 mm. The compressive and flexural strength tests were conducted according to ASTM C109 and ASTM C348-97. The specimen dimension for tensile bonding strength tests was 22.2 22.5 78 mm, which was illustrated in Fig. 2. Firstly, the normal cement mortar was casted into one half of the mold and cured for 7 days. Then, the FPMP composites were casted into the other half of the mold. When FPMP specimens were cured for 28 days, the tensile bonding strength was carried out in UTM machine (Fig. 2).
2.3. Experiment procedure 2.3.1. Preparation procedure of FPMP composites The mixing process of FPMP composites was performed by several steps. Firstly, all dry materials such as cement, EP, RP and PF were mixed. Secondly, the water, SBR latex and water reducer were mixed together. Thirdly, the liquid mixture was added gradually to the dry mix. This step should be completed at most 3 min. It is important to mix all dry materials uniformly in order to prevent the agglomeration of PF. FPMP composites were mixed in JJ-5 mortar mixer. When the appearance of the composites existed petal shaped, immediately stop stirring to avoid damaging perlite aggregates. After stirring, the specimens were molded on the vibration table within five minutes.
2.3.4. Softening coefficient tests During the softening coefficient tests, the test specimens having a dimension of 70.7 70.7 70.7 mm were used. The specimens (cured after 28 days) were immersed into the water for 48 h before the compressive strength tests. The water temperature was 23 ± 1 °C. The softening coefficient (Ks) was determined by Eq. (1).
Ks ¼
r1 r0
ð1Þ
where Ks is the softening coefficient, r1 is the compressive strength after water immersion (MPa), r0 is the compressive strength before water immersing (MPa).
Table 4 The design of the orthogonal experiment. NO.
SY1 SY2 SY3 SY4 SY5 SY6 SY7 SY8 SY9 SY10 SY11 SY12 SY13 SY14 SY15 SY16
Mix groups
A1B1C1D1 A1B2C2D2 A1B3C3D3 A1B4C4D4 A2B1C2D3 A2B2C1D4 A2B3C4D1 A2B4C3D2 A3B1C3D4 A3B2C4D3 A3B3C1D2 A3B4C2D1 A4B1C4D2 A4B2C3D1 A4B3C2D4 A4B4C1D3
Factors (%) RP/cement ratio (A)
SBR/cement ratio (B)
PF dosage (C)
EP/cement ratio (D)
0 0 0 0 6 6 6 6 12 12 12 12 18 18 18 18
0 5 10 15 0 5 10 15 0 5 10 15 0 5 10 15
0 0.05 0.1 0.15 0.05 0 0.15 0.1 0.1 0.15 0 0.05 0.15 0.1 0.05 0
30 35 40 45 40 45 30 35 45 40 35 30 35 30 45 40
Fig. 2. The tensile bonding strength test.
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iron, Dt is temperature difference between initial and final temperature. When Qi was calculated, the thermal absorption amount of specimen (Qs) is assumed to be equal to Qi. Then the thermal conductivity coefficient of specimen (k) was determined by the Eq. (3).
k¼
Q sd AðT 2 T 1 Þ
ð3Þ
where Qs is the heat absorption amount of the specimen, A is the contact area of the specimen, d is the depth of the specimen, T1 is the initial temperature before heating, T2 is the final temperature after heating. Fig. 3. The test apparatus for thermal conductivity coefficient.
2.3.5. Frost resistance tests For each group, six specimens of 70.7 70.7 70.7 mm were prepared. After one day of moist curing, specimens were cured into standard curing chamber in a controlled environment of constant 20 °C and 90% humidity. After curing for 28 days, they were exposed to 15 cycles frozen in a ‘‘deep-freeze” state at 18 ± 1 °C and thawed in water at +4 ± 1 °C (specimens were kept in deepfreeze water for 4 h in each cycle). Freezing and thawing tests were conducted according to the ASTM C 666 procedure B. After 15 cycles, samples were tested for unit dry weight and compressive strength. Results of freezing and thawing samples were compared to those of control samples in a standard curing chamber for 28 days. The weight loss and strength loss were calculated from the above results. The average of the three samples was considered as each experimental result.
2.3.7. Optical Microscope observation The film forming process of SBR latex was observed by Zeiss axioskop40 microscope. 2.3.8. Scanning Electron Microscope observation The specimens for Scanning Electron Microscope (SEM) testing were obtained after 90-day curing process. The testing specimens were firstly dried by a vacuum and then coated with a thin layer of platinum before observation, and the microstructure was investigated by a SU8010 Scanning Electron Microscope. 2.3.9. X-ray diffraction test Phase analysis of the test specimens was conducted by D/Max-RB rotating anode XRD equipment. 3. Results and discussion 3.1. Mix design of FPMP composites
2.3.6. Thermal conductivity tests The test apparatus for thermal conductivity coefficient was shown in Fig. 3. The bottom of the specimen was contacted with the heating plate and the surface of the specimen was contacted with a polished iron. Under the condition of steady heat conduction, we assume that the heat absorption amount of specimen is equal to that of the polished iron. The heat absorption amount (Qi) of polished iron was determined by using the following expression:
Q i ¼ cmDt
ð2Þ
where Qi is the thermal absorption amount of the polished iron, c is the specific thermal capacity of iron, m is the weight of the polished
The test results of fluidity, unit dry weight, compressive strength, tensile strength and thermal property in the orthogonal experiment were listed in Table 5. The influence factors of the mix design were analyzed as follows. 3.1.1. Fluidity and unit dry density The fluidity test results were analyzed according to the orthogonal experiment design method. The range analysis of fluidity was shown in Fig. 4. The factors affecting fluidity follow the order of SBR/cement ratio (B) > EP/cement ratio (D) > PF dosage (C) > RP/ cement ratio (A). As to the fluidity of FPMP, the range value of SBR/cement ratio is 2.6, which is much more than those of other
Table 5 The test results of the orthogonal experiment. NO.
SY1 SY2 SY3 SY4 SY5 SY6 SY7 SY8 SY9 SY10 SY11 SY12 SY13 SY14 SY15 SY16
Consistence (cm)
Unit dry weight (g/cm3)
Compressive strength (MPa)
Flexural strength (MPa)
Softening coefficient
Bonding strength (MPa)
Frost resistance Weight loss (%)
Strength loss (%)
6.9 9.1 6.6 7.6 10.2 5.6 8.2 8.9 7.1 8.1 7.9 8.7 7.3 6.6 6.6 6.3
0.85 0.53 0.7 0.83 0.73 0.88 0.48 0.52 0.74 0.76 0.64 0.45 0.79 0.64 0.73 0.76
7.39 4.64 5.16 7.55 6.44 7.18 2.46 2.22 6.45 7.46 4.94 2.21 4.19 3.81 3.73 4.72
1.70 1.16 1.50 2.34 1.55 1.72 0.89 0.69 1.74 2.09 1.58 0.73 1.38 1.22 1.33 1.70
0.65 0.52 0.71 0.99 0.82 0.87 0.95 0.82 0.86 0.85 0.7 0.84 0.93 0.92 0.90 0.86
0.14 0.21 0.26 0.31 0.12 0.20 0.28 0.32 0.11 0.17 0.26 0.31 0.09 0.15 0.19 0.22
4.7 2.49 2.31 3.89 8.17 1.94 3.46 1.61 1.12 2.02 2.13 3.62 1.81 6.6 1.75 13.95
18.3 14.8 7.5 7.4 11.1 14.8 7.6 10.4 9.7 7.5 15.4 10.2 6.9 10.7 12.3 13.6
Thermal conductivity coefficient (W/(mK))
0.142 0.091 0.114 0.119 0.123 0.144 0.079 0.079 0.122 0.125 0.105 0.078 0.123 0.102 0.104 0.105
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Fig. 4. The range analysis of fluidity. Fig. 5. The range analysis of unit dry weight.
three factors including EP/cement ratio, PF dosage and RP/cement ratio. It indicates that SBR/cement ratio and EP/cement ratio have a significant influence on the fluidity of FPMP. The range analysis of unit dry weight was shown in Fig. 5. SBR/cement ratio and EP/ cement ratio are also the major influence factors of the unit dry weight of FPMP. It can be found that SBR latex has good water retention and water reducing effect, which is due to the ‘‘ball” effect of the polymer particles and dispersion effect on the cement particles [34]. To be specific, SBR latex having obvious water reducing property can effectively reduce the surface tension of the water around the cement particles. Therefore the water reducing effect improves with the increase of SBR latex dosage. It can be concluded that the fluidity of FPMP can be adjusted by changing SBR/cement ratio. As to EP, the bulk density of EP is only about one-fiftieth as much of the cement. EP particles contribute to lightweight properties and high water absorption capability of cement. The higher water absorption of EP particles causes a more water requirement in FPMP to obtain the same workability of normal mortar. Thus with the increase of EP/cement ratio, the fluidity and unit dry density decreases obviously. EP with a bulk density of 61 kg/m3 was between 30% and 45% by weight of Portland cement to yield a range of mortars with unit dry weight between 450 and 880 kg/m3. 3.1.2. Mechanical performance (1) Compressive strength The range analysis of compressive strength of FPMP (cured for 28 days) was illustrated in Fig. 6. The factors influencing the compressive strength follow the order of EP/cement ratio(D) > RP/ cement ratio(A) > SBR/cement ratio(B) > PF dosage(C). As to the compressive strength, the range values of the EP/cement ratio is 7.27, which are much more than those of other influence factors including RP/cement ratio, SBR/cement ratio and PF dosage. Therefore, it can be found that EP/cement ratio is the major factor on the compressive strength of FPMP. The more the EP/cement ratio is, the less the compressive strength of FPMP is. Besides, the addition of RP also has an obvious adverse impact against the compressive strength of FPMP. With the increase of RP/cement ratio, the compressive strength of FPMP shows a significant decreasing trend. Furthermore, the relationship between the unit dry weight and compressive strength was shown in Fig. 8. The unary linear regression formula was built and the correlation coefficient is 0.91. Thus it can be seen that the compressive strength is approximately linearly proportional to unit dry weight of FPMP. With the increase of
Fig. 6. Range analysis of compressive strength.
unit dry density, the compressive strength of FPMP increases gradually. As to samples with low unit dry density, the content of cement paste is not enough to fill the gaps between EP and RP particles. As a result, a lot of harmful pores in the gaps lead to the decline of compressive strength of FPMP. For the specimens with high unit dry density, the compressive strength increases due to the internal matrix of FPMP is denser than that with low unit dry weight. (2) Tensile bonding strength The range analysis of tensile bonding strength was shown in Fig. 7. The factors affecting tensile bonding strength follow the order of SBR/cement ratio (B) > EP/cement ratio (D) > RP/cement ratio (A) > PF dosage (C). SBR/cement ratio is the major influence factor on the tensile bonding strength of FPMP. The effect of PF dosage on the tensile bonding strength is not significant. The polymer films are formed due to the water loss of SBR latex. The films can fill harmful pores in the FPMP matrix, and produce continuous mesh structure which improves the tensile bond strength of the FPMP matrix. The excellent tensile bonding strength of FPMP can contribute to the effective bonding between insulation layer and the wall of buildings.
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Fig. 9. Range analysis of rf/rc ratio. Fig. 7. Range analysis of tensile bonding strength.
(3) Flexural strength(rf)/compressive strength(rc) ratio The rf/rc ratio is an index to evaluate the brittleness of cement base material [15,34]. The range analysis of rf/rc ratio was illustrated in Fig. 9. The range value of RP/cement ratio and SBR/cement ratio are 0.96 and 0.74, which are much more than those of other factors. The more RP/cement ratio and SBR/cement ratio are, the less the brittleness of FPMP is. The rf/rc ratio of FPMP increases by 8% 56% compared with that of control sample without FP and SBR. It can be concluded that the addition of RP and SBR is beneficial to reduce the brittleness of FPMP. The high rf/rc ratio (>0.35) of FPMP can provide a good flexibility for constructive applications.
and PF. EP particles have good water absorption and swelling properties. In the process of immersing into water, a great amount of EP particles absorb water and swell. Excessively swelling EP will damage the internal structure of the matrix, which leads to an obvious decrease of soften coefficient. Meanwhile, when the internal structure of the matrix is damaged by the swelling perlite, polyester fiber can inhibit crack expansion and improve the internal structure of FPMP matrix. The softening coefficient of FPMP could be increased by using the proper dosage of polyester fiber. Furthermore, the continuous network of SBR polymer film structure, improving the compatibility between rubber particles and cement, can contribute to the improvement of the whole structure of FPMP. Thus SBR latex also plays an important role in the increase of softening coefficient.
3.1.3. Softening coefficient The range analysis of softening coefficient was illustrated in Fig. 10. The difference of range values for SBR/cement ratio, PF dosage and EP/cement ratio is not significant. As to the softening coefficient of FPMP, the range value of RP/cement ratio is 0.15, which is less than other three factors including SBR/cement ratio, PF dosage and EP/cement ratio. The softening coefficient of SY4 sample (SBR/cement ratio = 15%, PF dosage = 0.15) increases by over 50% than that of SY1 sample without the addition of SBR latex
3.1.4. Frost resistance The weight loss and strength loss are the evaluation indices of frost resistance in this paper. The range analysis of weight loss after 15 freeze-thaw cycles was illustrated in Fig. 11. The factors related to the weight loss follow the order of EP/cement ratio(D) > RP/cement ratio(A) > SBR/cement ratio(B) > PF dosage(C). With respect to the range analysis of weight loss, the range value of EP/cement ratio is 5.6, which is much more than those of other three factors including RP/cement ratio, SBR/cement ratio and PF dosage. In the process of freeze-thaw test, EP absorbs a large
Fig. 8. Relationship between unit dry weight and compressive strength.
Fig. 10. Range analysis of softening coefficient.
F. Xu et al. / Construction and Building Materials 127 (2016) 751–761
amount of water. The water in the EP will freeze and expand, and this phenomenon leads to the damage of the matrix. The components at the edge of the specimens will be broken primarily by the volume expansion, thereby causing the obvious weight loss of the specimens. The range analysis of strength loss after 15 freeze-thaw cycles was illustrated in Fig. 12. The result shows that the range value difference of the four factors is not significant. It could be seen that the mechanism of strength loss after freeze-thaw cycles is determined by the multiple factors. RP is a kind of inert material [15]. The combination between RP particles and cement stone is not tight enough. So the addition of EP and RP into FPMP will lead to the strength loss under the condition of freezing and thawing cycles. Nevertheless, PF can effectively inhibit the generation and development of crack due to volume deformation in the FPMP matrix. Furthermore, SBR films can improve the combination between RP and cement stone. The continuous network structure of polymer films has a good flexibility, which could improve the elastic deformation ability of the matrix in the process of volume deformation. Thus the addition of SBR latex and PF can effectively reduce the strength loss of FPMP under freeze-thaw cycles.
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3.1.5. Thermal conductivity property The thermal conductivity property is defined as a property that measures the response of a material to the application of heat [12]. When a kind of material absorbs energy in the form of heat, its internal temperature rises and its dimension expands. The energy can be transferred to cooler parts of the material if temperature gradients exist [33]. The test result of thermal conductivity performance was shown in Table 5. The relationship between unit dry weight and thermal conductivity coefficient was illustrated in Fig. 13. The unary linear regression formula of the relationship was built and the correlation coefficient is 0.87. Therefore, the thermal conductivity coefficient is nearly linearly proportional to the unit dry weight of FPMP. With the increase of unit dry density, the thermal conductivity coefficient of FPMP increases proportionally. With the increase of SBR latex dosage, the unit dry weight decreases gradually. The addition of SBR latex can lead to a large number of small pores within the matrix of FPMP, resulting in a certain degree decline of the unit dry density in the matrix. The high porosity in the matrix results in the low thermal conductivity coefficient of FPMP. Besides, EP/cement ratio is closely related to the unit dry weight of FPMP. It will lead to more pores in the matrix of FPMP, thus the thermal conductivity performance reduces to a certain extent. The low value of thermal conductivity coefficient (0.070–0.145 W/mK) of FPMP shows great promise for constructive applications as a thermal insulator. Furthermore, the mechanical and thermal insulation performances of FPMP are interacted with each other by the test results mentioned above. If the compressive strength of FPMP is too high, the thermal conductivity coefficient will increase to a high level, and vice versa. In order to ensure good mechanical performance and thermal insulation property, the optimal value of the unit dry weight of FPMP is determined to be between 0.45 and 0.55 g/cm3. According to the above experimental results, the service properties of the FPMP samples improve obviously with the proper addition of RP, SBR, PF and EP. Therefore, further dosage optimization of these materials in FPMP is therefore necessary. It can be concluded that the optimal value range of RP/cement ratio, SBR/cement ratio, PF dosage and EP/cement ratio is 6% 12%, 10% 15%, 0.05% 0.10% and 30% 35%, respectively.
3.2. The cement hydration analysis by X-ray diffraction (XRD) test Fig. 11. Range analysis of weight loss.
Calcium hydroxide(Ca(OH)2) is one of the major cement hydration products in the cementitious materials [34]. In order to study
Fig. 12. Range analysis of strength loss.
Fig. 13. Relationship between unit dry weight and thermal conductivity coefficient.
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the formation of the hydrates of Ca(OH)2, XRD patterns at 2h range of 17–19° were recorded for PMP (cement paste with SBR latex, SBR/cement ratio = 15%) and KBY(control cement paste without SBR latex) cured at different curing ages. The results were shown in Fig. 14. The XRD patterns of Ca(OH)2 was analyzed by the software ‘‘MDI Jade 6.5”. In this way, the integrated results of XRD peak of Ca(OH)2 including the interplanar spacing (d), full-width half-maximum (FWHM), peak height (Imax), integral intensity (Iinteg) and the ratio of Ca(OH)2 content in the modified paste to that of the control paste (R) were listed in Table 6. From the integral intensity (Iinteg), it can be seen that the Ca(OH)2 content is lowest in the PMP sample cured for 6 h, then increased with the hydration time. The R value of the PMP sample was only 0.12 when the curing time is 6 h. Nevertheless, as the curing time extended for 3 days and 28 days, the R value of the PMP sample rose to 0.57 and 0.85, respectively. Thus it can be seen that the SBR latex
A
(a)
slows down the formation of Ca(OH)2, especially at the early curing time. 3.3. Film forming process of SBR latex by Optical Microscopic test Fig. 15 showed the appearance change of SBR latex in the film forming process by Optical Microscopic test. The SBR latex shows light blue at the beginning of the test, as polymer particles leads to the longer wavelength scatter of the light, and the blue light which has shorter wavelength can pass through the latex. With the forming of the polymer films, the intensity of light weakens gradually and the color of light becomes gray from the figures. Furthermore, these figures illustrate the change of blue light with the extension of time. After 200 min, the variation of the blue light became stable, and it can be speculated that the polymer film formation was almost completed. Thus it indicates that the process of
A: Ca(OH) 2
A
(b)
A: Ca(OH) 2
PMP Cured for 6h
PMP cured for 3d
KBY cured for 3d
KBY Cured for 6h
17.0
17.5
18.0
18.5
17.0
19.0
17.5
18.0
18.5
19.0
2 Theta/Deg.
2 Theta/Deg.
A
A: Ca(OH)2
(c) PMP cured for 28d
KBY cured for 28d
17.0
17.5
18.0
18.5
19.0
2 Theta/Deg. Fig. 14. XRD patterns of PMP(cement paste with SBR latex, SBR/cement ratio = 15%) and KBY (control cement paste without SBR latex) cured for different curing time: (a) The samples cured for 6 h; (b) The samples cured for 3 days; (c) The samples cured for 28 days.
Table 6 Integrated results of XRD diffraction peak of crystal surface of Ca(OH)2 for cement pastes with and without SBR latex modification (KBY has no SBR latex addition, PMP has 15 wt.% of SBR latex addition). NO.
Curing time
d/(nm)
FWHM/(°)
Imax/(counts)
Iinteg/(counts)
R
KBY PMP KBY PMP KBY PMP
6h 6h 3 days 3 days 28 days 28 days
0.4938 0.4923 0.4919 0.4915 0.4896 0.4824
0.136 0.153 0.126 0.145 0.121 0.140
11,369 1292 23,695 12,487 48,796 36,968
89,654 10,986 186,935 105,642 389,623 330,684
1.0 0.12 1.0 0.57 1.0 0.85
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Fig. 15. The color variance of SBR polymer film forming process by microscope.
Fig. 17. The micrographs (SEM) of FPMP matrix. Fig. 16. The micrographs (SEM) of EP.
3.4. SEM analysis of FPMP matrix SBR polymer film formation does not need to take a long time. Besides, SBR polymer film can be formed simultaneously when the cement hydration reaction takes place in the matrix of FPMP.
The micrographs (SEM) of EP particles in the matrix were shown in Fig. 16. It can be observed that EP particle has a rough and porous structure. The micrographs (SEM) of FPMP matrix were
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coefficient of FPMP. Thus the thermal insulation performance of FPMP improved to some extent. Besides, a large amount of unhydrated EP exists in the matrix of FPMP. From Figs. 18 and 19, the hydration products observed are ettringite (needle-like crystals), calcium silicate hydrate (gel-like structures), and calcium hydroxide (plant-like crystals, portlandite). From these figures, EP shows nearly inert behavior, and calcium silicate hydrate gel formation is not sufficient to cover the EP particles. The pozzolanic activity is adversely affected by the bigger particle size and the higher water absorption of EP in comparison with cement. However, introducing EP in mortar as aggregate was effective to decrease the unit dry weight due to the lower bulk density of EP when it is compared to cement or sand. Fig. 20(a) displayed the microstructure of interfacial transition zone (ITZ) between the cement hydration and RP particles in the matrix of SY9 sample (SBR/cement ratio = 0). The apparent cracks were found in the ITZ. Fig. 20 (b) showed the SEM micrograph of ITZ between the cement hydration and RP particle in SY12 sample (SBR/cement ratio = 15%). It can be seen that the ITZ in SY12 sample is much denser than that of SY9 sample and the obvious flaws cannot be found in the ITZ. Thus SBR latex can reinforce the ITZ in cement hydrate, RP and EP. Appropriate dosage of SBR latex can optimize the pore distribution and reduce pore size of the mortar matrix with a filling and bonding effect. This partly proves that the softening coefficient and frost resistance of FPMP are better than those of the samples without SBR latex addition.
Fig. 18. Ettringite crystal in FPMP.
4. Conclusion
Fig. 19. Calcium silicate gel in FPMP.
shown in Fig. 17. The internal matrix of FPMP shows porous structure. Porous materials could retain large amount of the air in the internal voids. The thermal conductivity coefficient of the air in normal pressure and temperature is very small (only 0.026 W/mK), which is much less than that of the cement matrix. This will lead to the obvious decrease of the thermal conductivity
(a)
Based on the results obtained in this research, the following conclusions can be drawn: SBR/cement ratio has a significant influence on the fluidity and unit dry weight of FPMP. With the increase of SBR/cement ratio, the consistence increases and the unit dry weight deceases to some degree. EP/cement ratio and RP/cement ratio are the major influence factors on the compressive and flexural strength of FPMP. The more the EP and RP dosages are, the lower the compressive and flexural strength are. Compared with the control sample, the compressive strength of modified samples reduced by 25% 65% and the flexural strength decreased by 17% 45%. However, the rf/rc ratio of modified samples increased by 8% 56% than that of control sample. It can be concluded that the brittleness of FPMP reduces obviously by the addition of SBR latex, PF and RP. Furthermore, the addition of SBR latex and PF can effectively improve softening coefficient and frost resistance of FPMP. The low value of thermal conductivity coefficient (0.070–0.145 W/mK) of FPMP
(b) RP RP
Fig. 20. SEM micrographs of interfacial transition zone (ITZ) between RP and cement hydrates (cured for 90 d): (a) The ITZ in the matrix of SY9 sample (SBR/cement ratio = 0); (b) The ITZ in the matrix of SY12 sample (SBR/cement ratio = 15%).
F. Xu et al. / Construction and Building Materials 127 (2016) 751–761
shows great promise as a thermal insulator. It can be concluded from the test results that the optimal value range of RP/cement ratio, SBR/cement ratio, PF dosage and EP/cement ratio is 6% 12%, 10% 15%, 0.05% 0.10% and 30% 35%, respectively. It indicates that SBR latex slows down the formation of Ca(OH)2, especially at the early curing time. The internal microscopic matrix of FPMP shows porous structure. Besides, a large amount of unhydrated EP exists in the matrix of FPMP. SBR latex can reinforce the ITZ in cement hydrate, RP and EP. Appropriate dosage of SBR latex may optimize the pore distribution and reduce pore size of the FPMP matrix with a filling and bonding effect. Acknowledgements This work was supported by the Natural Science Foundation of China (51308518), the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (CUGL150412 and G1323531606) and the China Postdoctoral Science Foundation (2015M582303). References [1] I.B. Topçu, B. Ißsıkdag˘, Manufacture of high thermal conductivity resistant clay bricks containing perlite, Build. Environ. 42 (10) (2007) 3540–3546. [2] A.G. Celik, A.M. Kilic, G.O. Cakal, Expanded perlite aggregate characterization for use as a lightweight construction raw material, Physicochem. Probl. Miner. Process. 49 (2) (2013) 689–700. [3] I. Demir, M.S. Baspinar, Effect of silica fume and expanded perlite addition on the technical properties of the fly ash–lime–gypsum mixture, Constr. Build. Mater. 22 (6) (2008) 1299–1304. [4] D. Sun, L. Wang, C. Li, Preparation and thermal properties of paraffin/expanded perlite composite as form-stable phase change material, Mater. Lett. 108 (2013) 247–249. [5] M.J. Shannag, Characteristics of lightweight concrete containing mineral admixtures, Constr. Build. Mater. 25 (2) (2011) 658–662. [6] C. Vipulanandan, E. Paul, Characterization of polyester polymer and polymer concrete, J. Mater. Civ. Eng. 5 (1) (1993) 62–82. [7] A.R. Joao, V.A. Marcos, Durability of polymer-modified lightweight aggregate concrete, Cem. Concr. Compos. 26 (2004) 375–380. [8] G. Barluenga, F. Hemandez, SBR latex modified mortar rheology and mechanical behavior, Cem. Concr. Res. 34 (2004) 527–535. [9] W.C. Tang, Y. Lo, A. Nadeem, Mechanical and drying shrinkage properties of structural-graded polystyrene aggregate concrete, Cem. Concr. Compos. 30 (2008) 403–409. [10] B. Chen, J. Liu, Mechanical properties of polymer-modified concretes containing expanded polystyrene beads, Constr. Build. Mater. 21 (2007) 7–11. [11] O.A. Duzgun, R. Gul, A.C. Aydin, Effect of steel fibers on the mechanical properties of natural lightweight aggregate concrete, Mater. Lett. 59 (2005) 3357–3363. [12] O. Sengul, S. Azizi, F. Karaosmanoglu, M.A. Tasdemir, Effect of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete, Energy. Build. 43 (2011) 671–676.
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Design and evaluation of polyester fiber and SBR latex compound-modified perlite mortar with rubber powder Fang Xu a,⇑, Chao Peng a, Jing Zhu b, Jianping Chen a a b
Faculty of Engineering, China University of Geosciences, Wuhan 430074, PR China Hubei Communications Technical College, Wuhan 430079, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A new kind of perlite mortar (FPMP)
was proposed. The effect of the major mix design
parameters on the properties was studied. The microstructure of FPMP were studied by Optical Microscope, XRD and SEM.
The micrographs (SEM) of EP
The micrographs (SEM) of FPMP matrix
a r t i c l e
i n f o
Article history: Received 20 July 2016 Received in revised form 26 September 2016 Accepted 6 October 2016
Keywords: Perlite mortar Rubber powder Polyester fiber SBR latex Mix design Mechanical performance Thermal property
a b s t r a c t This paper proposed a new kind of perlite mortar modified by rubber powder, polyester fiber and SBR latex. The orthogonal experiment design method was employed to study the mix design of this new kind of perlite mortar. The influence of the major mix design parameters on the working performance, mechanical and thermal properties of the perlite mortar was studied. Furthermore, X-ray diffraction, Optical Microscope and Scanning Electron Microscope were employed to study the microstructure and failure mechanism of the perlite mortar. The results indicated that SBR latex/cement ratio had a significant influence on the fluidity and unit dry weight of the perlite mortar. Expanded perlite/cement ratio and rubber powder/cement ratio were the major influence factors on the compressive and flexural strength. Furthermore, the addition of SBR latex and polyester fiber can effectively improve the softening coefficient and frost resistance of the perlite mortar. The compressive strength and thermal conductivity coefficient was nearly linearly proportional to the unit dry weight of the perlite mortar. The internal microscopic matrix of the perlite mortar showed the porous structure and a large amount of unhydrated expanded perlite. SBR latex reinforced the interfacial transition zone between cement hydrates and rubber particles. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Perlite is an amorphous volcanic glass, which is produced from crude perlite rock and comprised of mainly alumina and silicon ⇑ Corresponding author. E-mail address: [email protected] (F. Xu). http://dx.doi.org/10.1016/j.conbuildmat.2016.10.060 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
dioxide [1–3]. The numerous micropores in the perlite ensure lightweight properties while providing the properties of thermal and sound insulation [4]. Therefore expanded perlite (EP) has been widely used in the building industry as an aggregate in the manufacturing of lightweight mortars, concretes and insulation products, etc [5]. However, normal perlite mortars usually have some problems in the practical application. Firstly, because of high
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Table 1 P.C 32.5 physical and mechanical properties of cement. Fineness (%)
Setting time (min) Initial setting
Final setting
1.21
75
210
Stability
Flexural strength (MPa) 3d
7d
28 d
3d
7d
28 d
Qualified
3.6
5.3
8.1
13.8
23.6
38.9
brittleness and direct exposure in external environment, cracks are easily formed in the matrix of perlite mortars under dry-wet circulation and freeze-thaw cycles. Secondly, a large number of irregular harmful pores, which lead to the poor durability and weak long-term application of insulation construction, are often existed inside normal perlite mortar. How to solve these problems of normal perlite mortar, has become a very attractive topic in the practical application. Nowadays, polymers have been vastly used in construction industry as modifiers, especially for the purpose of improving service performance of both cement concrete and mortar [6,7]. In fact, polymer latexes are used most widely in the different types of polymeric substances [8]. Tang et al. [9] studied mechanical and drying shrinkage properties of graded polystyrene aggregate concrete modified by polymer latex. Chen and Liu [10] investigated mechanical properties of polymer-modified concretes containing expanded polystyrene beads. Besides, different kinds of short organic fibers, including polypropylene fiber, polyester fiber, carbon fiber and basalt fiber, were used as reinforcement additions to improve mechanical properties since fibers could increase cracking resistance and fracture toughness of the brittle matrix [11,12]. It was reported that the addition of polypropylene fiber in perlite mortar improves its flexural strength and toughness. The reason is that the fibers will withstand the load until the interfacial bonding between the matrix and the fibers in the concrete was failed after cracking of matrix [13,14]. Furthermore, the properties of cement based materials can be further improved by the addition of organic polymer and fibers. Xu et al. [15] studied the influence of SBR latex and polypropylene fiber on the mechanical performances of crumb rubber mortar. The test results showed that the flexural toughness index of the rubber mortar was improved by 50–100% with the addition of SBR latex and polypropylene fiber. Cao [16] reported that the mechanical performance of cement mortar modified by short carbon fibers was improved by adding acrylic dispersion in the amount of 15% by mass of cement. As to the application of recycled tyre rubber in construction industry, many studies have been carried out on concrete and mortars modified by used tyre rubber [17–19]. The literature about the use of tyre rubber powders in cement-based materials mainly focuses on the use of tyre rubber powders as aggregates and evaluates the mechanical properties of the matrix. Relative research results have indicated that rubberized concrete mixtures show lower density, lower compressive and splitting tensile strength, higher impact resistance, and better sound insulation [20–23]. A major merit of adding tyre rubber powders into cement based materials is that cement based materials become more flexible and ductile [24–26]. Pelisser [27] reported that the compressive strength of concrete with the addition of 10 wt.% tyre rubber powders decreased by only 14% comparing with that of normal concrete. Similar studies confirmed that the proper addition of tyre rubber powders leads to minor changes in the mechanical performances of cement based materials [28,29]. As to the weak bonding between tyre rubber powders and cement, Segre [30] uncovered that alkaline-treated tyre rubber powders had a better bonding strength to cement particles. Other researchers found that tyre rubber powders can be externally modified to improve their compatibility of cement and polymer mixtures [31,32]. Moreover, investigations were conducted about the influences of tyre rubber
Compressive strength (MPa)
powders on the thermal properties of cement based materials [33]. It was reported that the addition of rubber particles reduces the thermal conductivity and density of cement composites. As mentioned above, in order to improve the performances of normal perlite mortar, this paper proposed a new kind of perlite mortar modified by rubber powder (RP), SBR latex (SBR) and polyester fiber (PF). This mortar is called fiber and polymer compoundmodified perlite mortar with rubber powder (FPMP). The orthogonal experiment design method was employed to study the mix design of FPMP. The influence of the main mix design parameters on the working performance, mechanical and thermal properties of FPMP were studied. In order to better understand the mechanical behavior, X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) were employed to investigate the microstructure and failure mechanism of FPMP.
2. Experimental 2.1. Materials The physical and mechanical performances of P.C 32.5 Portland cement used in this paper were measured according to ASTM C150, which were shown in Table 1. The appearance of expanded perlite (EP) used in this research was shown in Fig. 1. The bulk density of EP is 61 kg/m3. The water absorption ratio is 120% 300% and the particle size is 0.1 mm 2.5 mm. The bulk density of rubber powder (RP) used in this research is 310 kg/m3, the particle size of the RP is 0.75 mm 2.36 mm. The specific technical parameters and physical properties of polyester fiber (PF) were obtained from the fiber producer, which were listed in Table 2. The physical and mechanical properties of PF were tested according to ASTM C1557 and ASTM D7138. The properties of SBR latex was provided by BASF company, which were shown in Table 3. The performance experiments of SBR latex were performed by ASTM D4026. The water used in this research was the tap water.
Fig. 1. The appearance of EP.
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F. Xu et al. / Construction and Building Materials 127 (2016) 751–761 Table 2 The physical and mechanical properties of PF. Crimp degree
Length (mm)
Nominal diameter (mm)
Density (g/cm3)
Melting temperature (°C)
Ignition temperature (°C)
Flexural strength (MPa)
Broken elongation (%)
–
6 ± 0.5
0.014 ± 0.005
1.36
520
560
540
42
Table 3 The performance of SBR latex. Latex type
Main chemical components
Solid content (%)
pH
SBR
Butadiene, styrene
50
7 10
2.3.2. The fluidity test The fluidity of FPMP was evaluated by the index of consistency, which refers to the flow performance of the mortar by the external force or gravity. The consistency was measured by the mortar consistency tester. After mixing, the consistency of the fresh mortar was immediately determined by the immersing depth of the cone in the consistency tester.
2.2. The design of orthogonal experiment The orthogonal experiment design method was employed to study the mix design of FPMP in this paper. RP/cement ratio (A), SBR/cement ratio (B), PF dosage (C) and EP/cement ratio (D) were considered as the four major mix design parameters. In this experiment, RP/cement ratio is between 0 and 18%. SBR/cement ratio is between 0 and 15%. PF dosage is between 0 and 0.15%, which is the volume fraction of FPMP composite. EP/cement ratio is set in the range of 30–45%. Five factors and four levels of orthogonal test design scheme, including the fifth factor for blank columns, were carried out. The water/cement ratio was fixed to 0.9 for each group of the orthogonal experiment. The design table of the orthogonal experiment was shown in Table 4.
2.3.3. Mechanical performance tests The specimen dimension for compressive strength tests was 70.7 70.7 70.7 mm. The size of the specimens for flexural strength tests was 40 40 160 mm. The compressive and flexural strength tests were conducted according to ASTM C109 and ASTM C348-97. The specimen dimension for tensile bonding strength tests was 22.2 22.5 78 mm, which was illustrated in Fig. 2. Firstly, the normal cement mortar was casted into one half of the mold and cured for 7 days. Then, the FPMP composites were casted into the other half of the mold. When FPMP specimens were cured for 28 days, the tensile bonding strength was carried out in UTM machine (Fig. 2).
2.3. Experiment procedure 2.3.1. Preparation procedure of FPMP composites The mixing process of FPMP composites was performed by several steps. Firstly, all dry materials such as cement, EP, RP and PF were mixed. Secondly, the water, SBR latex and water reducer were mixed together. Thirdly, the liquid mixture was added gradually to the dry mix. This step should be completed at most 3 min. It is important to mix all dry materials uniformly in order to prevent the agglomeration of PF. FPMP composites were mixed in JJ-5 mortar mixer. When the appearance of the composites existed petal shaped, immediately stop stirring to avoid damaging perlite aggregates. After stirring, the specimens were molded on the vibration table within five minutes.
2.3.4. Softening coefficient tests During the softening coefficient tests, the test specimens having a dimension of 70.7 70.7 70.7 mm were used. The specimens (cured after 28 days) were immersed into the water for 48 h before the compressive strength tests. The water temperature was 23 ± 1 °C. The softening coefficient (Ks) was determined by Eq. (1).
Ks ¼
r1 r0
ð1Þ
where Ks is the softening coefficient, r1 is the compressive strength after water immersion (MPa), r0 is the compressive strength before water immersing (MPa).
Table 4 The design of the orthogonal experiment. NO.
SY1 SY2 SY3 SY4 SY5 SY6 SY7 SY8 SY9 SY10 SY11 SY12 SY13 SY14 SY15 SY16
Mix groups
A1B1C1D1 A1B2C2D2 A1B3C3D3 A1B4C4D4 A2B1C2D3 A2B2C1D4 A2B3C4D1 A2B4C3D2 A3B1C3D4 A3B2C4D3 A3B3C1D2 A3B4C2D1 A4B1C4D2 A4B2C3D1 A4B3C2D4 A4B4C1D3
Factors (%) RP/cement ratio (A)
SBR/cement ratio (B)
PF dosage (C)
EP/cement ratio (D)
0 0 0 0 6 6 6 6 12 12 12 12 18 18 18 18
0 5 10 15 0 5 10 15 0 5 10 15 0 5 10 15
0 0.05 0.1 0.15 0.05 0 0.15 0.1 0.1 0.15 0 0.05 0.15 0.1 0.05 0
30 35 40 45 40 45 30 35 45 40 35 30 35 30 45 40
Fig. 2. The tensile bonding strength test.
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iron, Dt is temperature difference between initial and final temperature. When Qi was calculated, the thermal absorption amount of specimen (Qs) is assumed to be equal to Qi. Then the thermal conductivity coefficient of specimen (k) was determined by the Eq. (3).
k¼
Q sd AðT 2 T 1 Þ
ð3Þ
where Qs is the heat absorption amount of the specimen, A is the contact area of the specimen, d is the depth of the specimen, T1 is the initial temperature before heating, T2 is the final temperature after heating. Fig. 3. The test apparatus for thermal conductivity coefficient.
2.3.5. Frost resistance tests For each group, six specimens of 70.7 70.7 70.7 mm were prepared. After one day of moist curing, specimens were cured into standard curing chamber in a controlled environment of constant 20 °C and 90% humidity. After curing for 28 days, they were exposed to 15 cycles frozen in a ‘‘deep-freeze” state at 18 ± 1 °C and thawed in water at +4 ± 1 °C (specimens were kept in deepfreeze water for 4 h in each cycle). Freezing and thawing tests were conducted according to the ASTM C 666 procedure B. After 15 cycles, samples were tested for unit dry weight and compressive strength. Results of freezing and thawing samples were compared to those of control samples in a standard curing chamber for 28 days. The weight loss and strength loss were calculated from the above results. The average of the three samples was considered as each experimental result.
2.3.7. Optical Microscope observation The film forming process of SBR latex was observed by Zeiss axioskop40 microscope. 2.3.8. Scanning Electron Microscope observation The specimens for Scanning Electron Microscope (SEM) testing were obtained after 90-day curing process. The testing specimens were firstly dried by a vacuum and then coated with a thin layer of platinum before observation, and the microstructure was investigated by a SU8010 Scanning Electron Microscope. 2.3.9. X-ray diffraction test Phase analysis of the test specimens was conducted by D/Max-RB rotating anode XRD equipment. 3. Results and discussion 3.1. Mix design of FPMP composites
2.3.6. Thermal conductivity tests The test apparatus for thermal conductivity coefficient was shown in Fig. 3. The bottom of the specimen was contacted with the heating plate and the surface of the specimen was contacted with a polished iron. Under the condition of steady heat conduction, we assume that the heat absorption amount of specimen is equal to that of the polished iron. The heat absorption amount (Qi) of polished iron was determined by using the following expression:
Q i ¼ cmDt
ð2Þ
where Qi is the thermal absorption amount of the polished iron, c is the specific thermal capacity of iron, m is the weight of the polished
The test results of fluidity, unit dry weight, compressive strength, tensile strength and thermal property in the orthogonal experiment were listed in Table 5. The influence factors of the mix design were analyzed as follows. 3.1.1. Fluidity and unit dry density The fluidity test results were analyzed according to the orthogonal experiment design method. The range analysis of fluidity was shown in Fig. 4. The factors affecting fluidity follow the order of SBR/cement ratio (B) > EP/cement ratio (D) > PF dosage (C) > RP/ cement ratio (A). As to the fluidity of FPMP, the range value of SBR/cement ratio is 2.6, which is much more than those of other
Table 5 The test results of the orthogonal experiment. NO.
SY1 SY2 SY3 SY4 SY5 SY6 SY7 SY8 SY9 SY10 SY11 SY12 SY13 SY14 SY15 SY16
Consistence (cm)
Unit dry weight (g/cm3)
Compressive strength (MPa)
Flexural strength (MPa)
Softening coefficient
Bonding strength (MPa)
Frost resistance Weight loss (%)
Strength loss (%)
6.9 9.1 6.6 7.6 10.2 5.6 8.2 8.9 7.1 8.1 7.9 8.7 7.3 6.6 6.6 6.3
0.85 0.53 0.7 0.83 0.73 0.88 0.48 0.52 0.74 0.76 0.64 0.45 0.79 0.64 0.73 0.76
7.39 4.64 5.16 7.55 6.44 7.18 2.46 2.22 6.45 7.46 4.94 2.21 4.19 3.81 3.73 4.72
1.70 1.16 1.50 2.34 1.55 1.72 0.89 0.69 1.74 2.09 1.58 0.73 1.38 1.22 1.33 1.70
0.65 0.52 0.71 0.99 0.82 0.87 0.95 0.82 0.86 0.85 0.7 0.84 0.93 0.92 0.90 0.86
0.14 0.21 0.26 0.31 0.12 0.20 0.28 0.32 0.11 0.17 0.26 0.31 0.09 0.15 0.19 0.22
4.7 2.49 2.31 3.89 8.17 1.94 3.46 1.61 1.12 2.02 2.13 3.62 1.81 6.6 1.75 13.95
18.3 14.8 7.5 7.4 11.1 14.8 7.6 10.4 9.7 7.5 15.4 10.2 6.9 10.7 12.3 13.6
Thermal conductivity coefficient (W/(mK))
0.142 0.091 0.114 0.119 0.123 0.144 0.079 0.079 0.122 0.125 0.105 0.078 0.123 0.102 0.104 0.105
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Fig. 4. The range analysis of fluidity. Fig. 5. The range analysis of unit dry weight.
three factors including EP/cement ratio, PF dosage and RP/cement ratio. It indicates that SBR/cement ratio and EP/cement ratio have a significant influence on the fluidity of FPMP. The range analysis of unit dry weight was shown in Fig. 5. SBR/cement ratio and EP/ cement ratio are also the major influence factors of the unit dry weight of FPMP. It can be found that SBR latex has good water retention and water reducing effect, which is due to the ‘‘ball” effect of the polymer particles and dispersion effect on the cement particles [34]. To be specific, SBR latex having obvious water reducing property can effectively reduce the surface tension of the water around the cement particles. Therefore the water reducing effect improves with the increase of SBR latex dosage. It can be concluded that the fluidity of FPMP can be adjusted by changing SBR/cement ratio. As to EP, the bulk density of EP is only about one-fiftieth as much of the cement. EP particles contribute to lightweight properties and high water absorption capability of cement. The higher water absorption of EP particles causes a more water requirement in FPMP to obtain the same workability of normal mortar. Thus with the increase of EP/cement ratio, the fluidity and unit dry density decreases obviously. EP with a bulk density of 61 kg/m3 was between 30% and 45% by weight of Portland cement to yield a range of mortars with unit dry weight between 450 and 880 kg/m3. 3.1.2. Mechanical performance (1) Compressive strength The range analysis of compressive strength of FPMP (cured for 28 days) was illustrated in Fig. 6. The factors influencing the compressive strength follow the order of EP/cement ratio(D) > RP/ cement ratio(A) > SBR/cement ratio(B) > PF dosage(C). As to the compressive strength, the range values of the EP/cement ratio is 7.27, which are much more than those of other influence factors including RP/cement ratio, SBR/cement ratio and PF dosage. Therefore, it can be found that EP/cement ratio is the major factor on the compressive strength of FPMP. The more the EP/cement ratio is, the less the compressive strength of FPMP is. Besides, the addition of RP also has an obvious adverse impact against the compressive strength of FPMP. With the increase of RP/cement ratio, the compressive strength of FPMP shows a significant decreasing trend. Furthermore, the relationship between the unit dry weight and compressive strength was shown in Fig. 8. The unary linear regression formula was built and the correlation coefficient is 0.91. Thus it can be seen that the compressive strength is approximately linearly proportional to unit dry weight of FPMP. With the increase of
Fig. 6. Range analysis of compressive strength.
unit dry density, the compressive strength of FPMP increases gradually. As to samples with low unit dry density, the content of cement paste is not enough to fill the gaps between EP and RP particles. As a result, a lot of harmful pores in the gaps lead to the decline of compressive strength of FPMP. For the specimens with high unit dry density, the compressive strength increases due to the internal matrix of FPMP is denser than that with low unit dry weight. (2) Tensile bonding strength The range analysis of tensile bonding strength was shown in Fig. 7. The factors affecting tensile bonding strength follow the order of SBR/cement ratio (B) > EP/cement ratio (D) > RP/cement ratio (A) > PF dosage (C). SBR/cement ratio is the major influence factor on the tensile bonding strength of FPMP. The effect of PF dosage on the tensile bonding strength is not significant. The polymer films are formed due to the water loss of SBR latex. The films can fill harmful pores in the FPMP matrix, and produce continuous mesh structure which improves the tensile bond strength of the FPMP matrix. The excellent tensile bonding strength of FPMP can contribute to the effective bonding between insulation layer and the wall of buildings.
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Fig. 9. Range analysis of rf/rc ratio. Fig. 7. Range analysis of tensile bonding strength.
(3) Flexural strength(rf)/compressive strength(rc) ratio The rf/rc ratio is an index to evaluate the brittleness of cement base material [15,34]. The range analysis of rf/rc ratio was illustrated in Fig. 9. The range value of RP/cement ratio and SBR/cement ratio are 0.96 and 0.74, which are much more than those of other factors. The more RP/cement ratio and SBR/cement ratio are, the less the brittleness of FPMP is. The rf/rc ratio of FPMP increases by 8% 56% compared with that of control sample without FP and SBR. It can be concluded that the addition of RP and SBR is beneficial to reduce the brittleness of FPMP. The high rf/rc ratio (>0.35) of FPMP can provide a good flexibility for constructive applications.
and PF. EP particles have good water absorption and swelling properties. In the process of immersing into water, a great amount of EP particles absorb water and swell. Excessively swelling EP will damage the internal structure of the matrix, which leads to an obvious decrease of soften coefficient. Meanwhile, when the internal structure of the matrix is damaged by the swelling perlite, polyester fiber can inhibit crack expansion and improve the internal structure of FPMP matrix. The softening coefficient of FPMP could be increased by using the proper dosage of polyester fiber. Furthermore, the continuous network of SBR polymer film structure, improving the compatibility between rubber particles and cement, can contribute to the improvement of the whole structure of FPMP. Thus SBR latex also plays an important role in the increase of softening coefficient.
3.1.3. Softening coefficient The range analysis of softening coefficient was illustrated in Fig. 10. The difference of range values for SBR/cement ratio, PF dosage and EP/cement ratio is not significant. As to the softening coefficient of FPMP, the range value of RP/cement ratio is 0.15, which is less than other three factors including SBR/cement ratio, PF dosage and EP/cement ratio. The softening coefficient of SY4 sample (SBR/cement ratio = 15%, PF dosage = 0.15) increases by over 50% than that of SY1 sample without the addition of SBR latex
3.1.4. Frost resistance The weight loss and strength loss are the evaluation indices of frost resistance in this paper. The range analysis of weight loss after 15 freeze-thaw cycles was illustrated in Fig. 11. The factors related to the weight loss follow the order of EP/cement ratio(D) > RP/cement ratio(A) > SBR/cement ratio(B) > PF dosage(C). With respect to the range analysis of weight loss, the range value of EP/cement ratio is 5.6, which is much more than those of other three factors including RP/cement ratio, SBR/cement ratio and PF dosage. In the process of freeze-thaw test, EP absorbs a large
Fig. 8. Relationship between unit dry weight and compressive strength.
Fig. 10. Range analysis of softening coefficient.
F. Xu et al. / Construction and Building Materials 127 (2016) 751–761
amount of water. The water in the EP will freeze and expand, and this phenomenon leads to the damage of the matrix. The components at the edge of the specimens will be broken primarily by the volume expansion, thereby causing the obvious weight loss of the specimens. The range analysis of strength loss after 15 freeze-thaw cycles was illustrated in Fig. 12. The result shows that the range value difference of the four factors is not significant. It could be seen that the mechanism of strength loss after freeze-thaw cycles is determined by the multiple factors. RP is a kind of inert material [15]. The combination between RP particles and cement stone is not tight enough. So the addition of EP and RP into FPMP will lead to the strength loss under the condition of freezing and thawing cycles. Nevertheless, PF can effectively inhibit the generation and development of crack due to volume deformation in the FPMP matrix. Furthermore, SBR films can improve the combination between RP and cement stone. The continuous network structure of polymer films has a good flexibility, which could improve the elastic deformation ability of the matrix in the process of volume deformation. Thus the addition of SBR latex and PF can effectively reduce the strength loss of FPMP under freeze-thaw cycles.
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3.1.5. Thermal conductivity property The thermal conductivity property is defined as a property that measures the response of a material to the application of heat [12]. When a kind of material absorbs energy in the form of heat, its internal temperature rises and its dimension expands. The energy can be transferred to cooler parts of the material if temperature gradients exist [33]. The test result of thermal conductivity performance was shown in Table 5. The relationship between unit dry weight and thermal conductivity coefficient was illustrated in Fig. 13. The unary linear regression formula of the relationship was built and the correlation coefficient is 0.87. Therefore, the thermal conductivity coefficient is nearly linearly proportional to the unit dry weight of FPMP. With the increase of unit dry density, the thermal conductivity coefficient of FPMP increases proportionally. With the increase of SBR latex dosage, the unit dry weight decreases gradually. The addition of SBR latex can lead to a large number of small pores within the matrix of FPMP, resulting in a certain degree decline of the unit dry density in the matrix. The high porosity in the matrix results in the low thermal conductivity coefficient of FPMP. Besides, EP/cement ratio is closely related to the unit dry weight of FPMP. It will lead to more pores in the matrix of FPMP, thus the thermal conductivity performance reduces to a certain extent. The low value of thermal conductivity coefficient (0.070–0.145 W/mK) of FPMP shows great promise for constructive applications as a thermal insulator. Furthermore, the mechanical and thermal insulation performances of FPMP are interacted with each other by the test results mentioned above. If the compressive strength of FPMP is too high, the thermal conductivity coefficient will increase to a high level, and vice versa. In order to ensure good mechanical performance and thermal insulation property, the optimal value of the unit dry weight of FPMP is determined to be between 0.45 and 0.55 g/cm3. According to the above experimental results, the service properties of the FPMP samples improve obviously with the proper addition of RP, SBR, PF and EP. Therefore, further dosage optimization of these materials in FPMP is therefore necessary. It can be concluded that the optimal value range of RP/cement ratio, SBR/cement ratio, PF dosage and EP/cement ratio is 6% 12%, 10% 15%, 0.05% 0.10% and 30% 35%, respectively.
3.2. The cement hydration analysis by X-ray diffraction (XRD) test Fig. 11. Range analysis of weight loss.
Calcium hydroxide(Ca(OH)2) is one of the major cement hydration products in the cementitious materials [34]. In order to study
Fig. 12. Range analysis of strength loss.
Fig. 13. Relationship between unit dry weight and thermal conductivity coefficient.
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the formation of the hydrates of Ca(OH)2, XRD patterns at 2h range of 17–19° were recorded for PMP (cement paste with SBR latex, SBR/cement ratio = 15%) and KBY(control cement paste without SBR latex) cured at different curing ages. The results were shown in Fig. 14. The XRD patterns of Ca(OH)2 was analyzed by the software ‘‘MDI Jade 6.5”. In this way, the integrated results of XRD peak of Ca(OH)2 including the interplanar spacing (d), full-width half-maximum (FWHM), peak height (Imax), integral intensity (Iinteg) and the ratio of Ca(OH)2 content in the modified paste to that of the control paste (R) were listed in Table 6. From the integral intensity (Iinteg), it can be seen that the Ca(OH)2 content is lowest in the PMP sample cured for 6 h, then increased with the hydration time. The R value of the PMP sample was only 0.12 when the curing time is 6 h. Nevertheless, as the curing time extended for 3 days and 28 days, the R value of the PMP sample rose to 0.57 and 0.85, respectively. Thus it can be seen that the SBR latex
A
(a)
slows down the formation of Ca(OH)2, especially at the early curing time. 3.3. Film forming process of SBR latex by Optical Microscopic test Fig. 15 showed the appearance change of SBR latex in the film forming process by Optical Microscopic test. The SBR latex shows light blue at the beginning of the test, as polymer particles leads to the longer wavelength scatter of the light, and the blue light which has shorter wavelength can pass through the latex. With the forming of the polymer films, the intensity of light weakens gradually and the color of light becomes gray from the figures. Furthermore, these figures illustrate the change of blue light with the extension of time. After 200 min, the variation of the blue light became stable, and it can be speculated that the polymer film formation was almost completed. Thus it indicates that the process of
A: Ca(OH) 2
A
(b)
A: Ca(OH) 2
PMP Cured for 6h
PMP cured for 3d
KBY cured for 3d
KBY Cured for 6h
17.0
17.5
18.0
18.5
17.0
19.0
17.5
18.0
18.5
19.0
2 Theta/Deg.
2 Theta/Deg.
A
A: Ca(OH)2
(c) PMP cured for 28d
KBY cured for 28d
17.0
17.5
18.0
18.5
19.0
2 Theta/Deg. Fig. 14. XRD patterns of PMP(cement paste with SBR latex, SBR/cement ratio = 15%) and KBY (control cement paste without SBR latex) cured for different curing time: (a) The samples cured for 6 h; (b) The samples cured for 3 days; (c) The samples cured for 28 days.
Table 6 Integrated results of XRD diffraction peak of crystal surface of Ca(OH)2 for cement pastes with and without SBR latex modification (KBY has no SBR latex addition, PMP has 15 wt.% of SBR latex addition). NO.
Curing time
d/(nm)
FWHM/(°)
Imax/(counts)
Iinteg/(counts)
R
KBY PMP KBY PMP KBY PMP
6h 6h 3 days 3 days 28 days 28 days
0.4938 0.4923 0.4919 0.4915 0.4896 0.4824
0.136 0.153 0.126 0.145 0.121 0.140
11,369 1292 23,695 12,487 48,796 36,968
89,654 10,986 186,935 105,642 389,623 330,684
1.0 0.12 1.0 0.57 1.0 0.85
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Fig. 15. The color variance of SBR polymer film forming process by microscope.
Fig. 17. The micrographs (SEM) of FPMP matrix. Fig. 16. The micrographs (SEM) of EP.
3.4. SEM analysis of FPMP matrix SBR polymer film formation does not need to take a long time. Besides, SBR polymer film can be formed simultaneously when the cement hydration reaction takes place in the matrix of FPMP.
The micrographs (SEM) of EP particles in the matrix were shown in Fig. 16. It can be observed that EP particle has a rough and porous structure. The micrographs (SEM) of FPMP matrix were
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coefficient of FPMP. Thus the thermal insulation performance of FPMP improved to some extent. Besides, a large amount of unhydrated EP exists in the matrix of FPMP. From Figs. 18 and 19, the hydration products observed are ettringite (needle-like crystals), calcium silicate hydrate (gel-like structures), and calcium hydroxide (plant-like crystals, portlandite). From these figures, EP shows nearly inert behavior, and calcium silicate hydrate gel formation is not sufficient to cover the EP particles. The pozzolanic activity is adversely affected by the bigger particle size and the higher water absorption of EP in comparison with cement. However, introducing EP in mortar as aggregate was effective to decrease the unit dry weight due to the lower bulk density of EP when it is compared to cement or sand. Fig. 20(a) displayed the microstructure of interfacial transition zone (ITZ) between the cement hydration and RP particles in the matrix of SY9 sample (SBR/cement ratio = 0). The apparent cracks were found in the ITZ. Fig. 20 (b) showed the SEM micrograph of ITZ between the cement hydration and RP particle in SY12 sample (SBR/cement ratio = 15%). It can be seen that the ITZ in SY12 sample is much denser than that of SY9 sample and the obvious flaws cannot be found in the ITZ. Thus SBR latex can reinforce the ITZ in cement hydrate, RP and EP. Appropriate dosage of SBR latex can optimize the pore distribution and reduce pore size of the mortar matrix with a filling and bonding effect. This partly proves that the softening coefficient and frost resistance of FPMP are better than those of the samples without SBR latex addition.
Fig. 18. Ettringite crystal in FPMP.
4. Conclusion
Fig. 19. Calcium silicate gel in FPMP.
shown in Fig. 17. The internal matrix of FPMP shows porous structure. Porous materials could retain large amount of the air in the internal voids. The thermal conductivity coefficient of the air in normal pressure and temperature is very small (only 0.026 W/mK), which is much less than that of the cement matrix. This will lead to the obvious decrease of the thermal conductivity
(a)
Based on the results obtained in this research, the following conclusions can be drawn: SBR/cement ratio has a significant influence on the fluidity and unit dry weight of FPMP. With the increase of SBR/cement ratio, the consistence increases and the unit dry weight deceases to some degree. EP/cement ratio and RP/cement ratio are the major influence factors on the compressive and flexural strength of FPMP. The more the EP and RP dosages are, the lower the compressive and flexural strength are. Compared with the control sample, the compressive strength of modified samples reduced by 25% 65% and the flexural strength decreased by 17% 45%. However, the rf/rc ratio of modified samples increased by 8% 56% than that of control sample. It can be concluded that the brittleness of FPMP reduces obviously by the addition of SBR latex, PF and RP. Furthermore, the addition of SBR latex and PF can effectively improve softening coefficient and frost resistance of FPMP. The low value of thermal conductivity coefficient (0.070–0.145 W/mK) of FPMP
(b) RP RP
Fig. 20. SEM micrographs of interfacial transition zone (ITZ) between RP and cement hydrates (cured for 90 d): (a) The ITZ in the matrix of SY9 sample (SBR/cement ratio = 0); (b) The ITZ in the matrix of SY12 sample (SBR/cement ratio = 15%).
F. Xu et al. / Construction and Building Materials 127 (2016) 751–761
shows great promise as a thermal insulator. It can be concluded from the test results that the optimal value range of RP/cement ratio, SBR/cement ratio, PF dosage and EP/cement ratio is 6% 12%, 10% 15%, 0.05% 0.10% and 30% 35%, respectively. It indicates that SBR latex slows down the formation of Ca(OH)2, especially at the early curing time. The internal microscopic matrix of FPMP shows porous structure. Besides, a large amount of unhydrated EP exists in the matrix of FPMP. SBR latex can reinforce the ITZ in cement hydrate, RP and EP. Appropriate dosage of SBR latex may optimize the pore distribution and reduce pore size of the FPMP matrix with a filling and bonding effect. Acknowledgements This work was supported by the Natural Science Foundation of China (51308518), the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (CUGL150412 and G1323531606) and the China Postdoctoral Science Foundation (2015M582303). References [1] I.B. Topçu, B. Ißsıkdag˘, Manufacture of high thermal conductivity resistant clay bricks containing perlite, Build. Environ. 42 (10) (2007) 3540–3546. [2] A.G. Celik, A.M. Kilic, G.O. Cakal, Expanded perlite aggregate characterization for use as a lightweight construction raw material, Physicochem. Probl. Miner. Process. 49 (2) (2013) 689–700. [3] I. Demir, M.S. Baspinar, Effect of silica fume and expanded perlite addition on the technical properties of the fly ash–lime–gypsum mixture, Constr. Build. Mater. 22 (6) (2008) 1299–1304. [4] D. Sun, L. Wang, C. Li, Preparation and thermal properties of paraffin/expanded perlite composite as form-stable phase change material, Mater. Lett. 108 (2013) 247–249. [5] M.J. Shannag, Characteristics of lightweight concrete containing mineral admixtures, Constr. Build. Mater. 25 (2) (2011) 658–662. [6] C. Vipulanandan, E. Paul, Characterization of polyester polymer and polymer concrete, J. Mater. Civ. Eng. 5 (1) (1993) 62–82. [7] A.R. Joao, V.A. Marcos, Durability of polymer-modified lightweight aggregate concrete, Cem. Concr. Compos. 26 (2004) 375–380. [8] G. Barluenga, F. Hemandez, SBR latex modified mortar rheology and mechanical behavior, Cem. Concr. Res. 34 (2004) 527–535. [9] W.C. Tang, Y. Lo, A. Nadeem, Mechanical and drying shrinkage properties of structural-graded polystyrene aggregate concrete, Cem. Concr. Compos. 30 (2008) 403–409. [10] B. Chen, J. Liu, Mechanical properties of polymer-modified concretes containing expanded polystyrene beads, Constr. Build. Mater. 21 (2007) 7–11. [11] O.A. Duzgun, R. Gul, A.C. Aydin, Effect of steel fibers on the mechanical properties of natural lightweight aggregate concrete, Mater. Lett. 59 (2005) 3357–3363. [12] O. Sengul, S. Azizi, F. Karaosmanoglu, M.A. Tasdemir, Effect of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete, Energy. Build. 43 (2011) 671–676.
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