- Email: [email protected]
Nanostructured zonolite–cementitious surface compounds for thermal insulation
Available online at www.sciencedirect.com
Construction and Building
MATERIALS
Construction and Building Materials 23 (2009) 515–521
www.elsevier.com/locate/conbuildmat
Nanostructured zonolite–cementitious surface compounds for thermal insulation M.S. Morsy a, H.A. Aglan b
a,*
, M.M. Abd El Razek
b
a Mechanical Engineering Department, Tuskegee University, AL, USA Housing and Building National Research Center, P.O. Box 1770, Cairo, Egypt
Received 15 June 2007; received in revised form 21 October 2007; accepted 22 October 2007 Available online 20 February 2008
Abstract This paper investigates the effect of zonolite loadings on the thermal resistivity and indirect tensile strength of nanostructured cementitious compounds. The main objective of this research is to develop a structural lightweight compound that can be used on building skins and cores for pre fabricated structural insulated panels (SIPs). The application of this compound is intended to improve the thermal resistivity of the building envelope with suitable mechanical performances. The zonolite dosage was added to the cement-nano clay blend at different dosages up to 40% by weight. The nano clay reinforcement used is montmorillonite clay (Hydrated sodium calcium aluminum silicate). The mixes were prepared using water of consistence. The wet compounds were molded in PVC cylindrical molds, having 50 mm inside diameter and 27 mm height, and left for 24 h, then demolded and cured in humid air (20 ± 1 C&100% RH) for 28 days. The samples were then dried at 105 ± 5 C for 24 h before testing using a forced convection oven. The thermal resistivity and indirect tensile strength of the different compounds were evaluated. Results demonstrate that the thermal resistivity at 40% zonolite loading enhanced by about 2.9 folds compared to the control samples. An increase of more than 30% in the indirect tensile strength was also achieved when a 0.5% by weight of polycarboxylate superplasticizer was used. 2007 Elsevier Ltd. All rights reserved. Keywords: Thermal resistivity; Zonolite; Nano clay; Portland cement; Indirect tensile strength
1. Introduction Thermal insulation is a major contributor towards achieving energy efficiency in residential and commercial buildings. The knowledge of thermal transport properties of construction materials is essential in predicting the temperature profile and heat flow through building envelopes. Thermal conductivity of cementitious construction compounds is much higher than the thermal conductivity of air. Introducing holes or air-gaps in these materials will reduce their thermal conductivity or increase their thermal resistivity. The use of lightweight aggregate with low thermal conductivity in the production of lightweight cementi-
*
Corresponding author. E-mail address: [email protected] (H.A. Aglan).
0950-0618/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2007.10.018
tious material can provide enhanced thermal insulation and hence energy savings. Although, lightweight cementitious materials have desirable properties such as low density and good thermal insulation, they have low mechanical properties [1–5]. Zonolite, vermiculite, perlite and expanded polystyrene beads, can be easily incorporated with different contents in cementitious material to produce lightweight mortar with a wide range of densities [6–9]. Zonolite masonry insulation is used to insulate masonry wall cores and cavities. Vermiculite is a mica – like mineral that is heated to about 700 C during processing. This causes the particles to expand in volume, which increases their internal surface area. This expanded (exfoliated) product is used as lightweight aggregate in concrete and plaster for building applications. Recently, we have developed a nanostructured cementitious surface compound with 70% by weight
516
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
loading of perlite particulates [10]. The compound possesses superior thermal resistivity and workability. For the last decade or so nano clay has been incorporated in polymer composites to improve their mechanical and barrier performance. The use of nanofiller in polymer increases the matrix tortuosity, better scratch resistance even for very modest clay loadings (1–5%), and increased heat deflection temperature [11–13]. Nano clay can also provide enhancements in the properties of other materials such as cementitious composites [14,15]. Due to their high surface to volume ratio nano clay can retain water during the mixing of cementitious materials. After dispersion, between cement particles, this water will be available to enhance the hydration process and hence the strength of the cement binder [10]. This finding was established using microstructural analysis of the nanostructured cementitious compounds. Superplasticizers are sometimes used to improve the workability and the mechanical performance of cementitious materials. They allow the production of concretes with special flow properties like self-compacting concrete. In addition, superplasticizers allow the formulation of concrete mixes with very low water/cement ratios. Thus, high performance concretes with very high strength and durability can be achieved. Lightweight thermally resistant cement composites can benefit more from using superplasticizer as well as nano clay. The current research addresses some of the issues associated with such technologies. 2. Materials and experimental 2.1. Materials The starting materials used in this investigation are ordinary Portland cement (OPC) (type I/II) produced by Quikrete Portland Cement Co., Zonolite Masonry Insulation treated with hydrophobic coating produced by GRACE construction products, Cambridge, MA, nano clay produced by Southern Clay Products and Sokalan HP 80 polycarboxylate ether provided by BASF Chemical Company. The chemical compositions of the OPC and zonolite are summarized in Table 1. The particle size
Table 2 Particle size distribution US mesh size Aperture (mm) Cumulative % retained
16 1.19 0.5
50 0.3 60–98
100 0.15 90–100
distribution of the zonolite is given in Table 2. The nano clay (Hydrated sodium calcium aluminum silicate) is Cloisite 30B natural montmorillonite modified with an ammonium salt. Sokalan HP 80 polycarboxylate ether was used as a superplasticizer in the current investigation. The superplasticizer was added to the mixed water in ratios of 0.5, 1, 1.5 and 2% by weight of nano clay cement binder. 2.2. Compound preparation and identification The nano clay cement binder (NCB) was prepared by partial substitution of OPC by 2% nano clay [10]. The dry OPC and nano clay were shear mixed for 5 min. Then the zonolite was added to NCB at different weight ratios based on a unit weight of NCB as illustrated in Table 3. The superplasticizer was added to the higher loaded blends of zonolite as shown in Table 3. The blended compounds were prepared by slow mixing for 3 min using the standard water of consistency (optimum amount of water for workability of the mix). The compound was molded in a PVC mold for mechanical and thermal conductivity tests. The samples were kept in molds for 24 h, and then demolded. The specimens were cured at 100% relative humidity and 20 ± 1 C for 28 days. The specimens were dried at a temperature of 105 C for 24 h in an oven. Mechanical and thermal conductivity tests were performed on dried specimens. 2.3. Thermal conductivity tests The thermal conductivity of the nanostructured zonolite–cementitious surface compounds (NZCSC) was deterTable 3 The dry mixes composition of blended binder and compound (mass (%)) Mixes ratio per unite weight of nano clay cement binder (NCB)*
Table 1 The chemical composition of starting material Oxide composition
Portland cement (%)
Zonolite (%)
CaO SiO2 Al2O3 Fe2O3 MgO SO3 Na2O K2O TiO2 Cr2O3 Ignition loss
63.9 20.5 5.4 2.6 2.1 3.0 0.61 – – – 1.4
1–3 38–46 11–16 8–13 – – 0.1–0.3 4–6 1–3 0.05–0.2 –
Mixes
NCB
Zonolite
Superplasticizer
W/C (%)
M0 M1 M2 M3 M4 M5 M6 M7 M8 GS1 GS2 GS3 GS4
1 1 1 1 1 1 1 1 1 1 1 1 1
0 0.025 0.05 0.075 0.1 0.15 0.2 0.3 0.4 0.4 0.4 0.4 0.4
0 0 0 0 0 0 0 0 0 0.005 0.01 0.015 0.02
0.28 0.35 0.375 0.45 0.525 0.675 0.825 1.125 1.425 1.25 1.15 1.1 1.075
*
98% OPC + 2% nanoclay.
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
mined according to ASTM E-1530; guarded heat flow meter method. An axial load of 140 KPa was applied on the test sample to insure good contact. The thermal resistivity is the reciprocal of the conductivity.
517
where rt is the indirect tensile strength, Pmax is the maximum applied load, D is the diameter and t is the thickness of the specimen, was reported for each mix. 3. Results and discussion
2.4. Water absorption and apparent porosity measurements Water absorption was measured according to ASTM C140-01. The specimens were immersed in water at room temperature (22 C) for 24 h and then weighed while they were completely submerged. The immersed weight, Wi was recorded. The specimens were then removed from the water and allowed to drain for 1 min by placing them on a wire mesh. Visible surface water was removed with a damp cloth. The new weight was recorded as Ws (saturated weight). The specimens were then dried in a ventilated oven at 105 C for not less than 24 h and until two successive weights at intervals of 2 h show an increment of loss not greater than 0.2%. This final weight of dried specimens was recorded as Wd (oven-dry weight). The absorption is calculated as Absorption% ¼ ½ðW s W d Þ=W d 100 Apparent porosity was determined from water absorption of the sample. Apparent porosity was determined by dividing volume of absorbed water by the apparent volume of the sample [16]. 2.5. Indirect tensile strength tests The indirect tensile tests were performed on a Sintec-5D MTS machine using the 50 · 27 mm cylindrical samples. Five samples per batch were tested, and the average value was reported. The loading rate on the specimen was 1.27 mm/min. The indirect tensile strength, determined as rt ¼ 2P max =pDt
3.1. Effect of zonolite loading on the mechanical properties and fracture behavior of NZCSC The variations of indirect tensile strength with zonolite loading for the nanostructured zonolite–cementitious surface compounds (NZCSC) hydrated for 28 days are shown in Fig. 1. The indirect tensile strength of the NZCSC decreases as the zonolite loading increases. The NZCSC with 40% zonolite loading possesses about 15% of the indirect tensile strength of the control nanostructure cementitious binder (NCB) after 28 days of hydration (mix M0 in Table 2). Therefore, addition of zonolite to the NCB as a lightweight aggregate leads to weakness of the nanostructured zonolite–cementitious surface compounds’ bonds due to its filler effect. Also by increasing the zonolite ratio; the adsorbed water increases leading to high water to binder ratios. The increased water/binder ratio increases the formed structure porosity leading to a decrease of the indirect tensile strength. The stress-strain behavior of the NZCSC, containing 0, 10, 20, 30 and 40% zonolite hydrated for 28 days is shown in Fig. 2. It is observed that at lower zonolite loading 0% (M0) and 10% (M4), the NZCSC displays brittle behavior. This is characterized as a sudden drop of the stress after a maximum was reached. The fracture surface is very smooth and the strain is small. However, for the NZCSC M8-40%, the stress strain behavior is different from the NZCSC M0 and M4. While testing for indirect tensile strength, the failure mode of NZCSC specimen containing higher ratio of zonolite did not exhibit the typical brittle failure normally observed in lower ratio of zonolite. The failure observed
Fig. 1. Variation of indirect tensile strength of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
518
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
Fig. 2. Variation of indirect tensile strength of nanostructured zonolite–cementitious surface compounds (NZCSC) with strain.
was more gradual and the specimens did not separate into two pieces in NZCSC containing 20, 30 and 40% zonolite. However, the higher loading of zonolite in NZCSC increases the strain capacity. This gradual failure and higher strain capacity were significant in cementitious compounds made with high zonolite contents. This indicates that NZCSC with high loadings of zonolite can resist the formation and propagation of microcracks. 3.2. Effect of zonolite loading on thermal resistivity The thermal resistivity of the NZCSC as a function of zonolite loading is presented in Fig. 3. It is clear that, the
thermal resistivity increases with the increasing zonolite ratios. The variation of the thermal resistivity shows that the compound containing 40% zonolite by weight has a thermal resistivity 2.9 times higher than the compound with no zonolite (control). The improvement in thermal resistivity is due to the high porosity of the zonolite particles coupled with the pores network formed during hydration of the cementitious compound. Zonolite particles contain capillary pores formed by the internal surface area during expansion. However, the NZCSC consists of a continuous binder phase in which a discontinuous aggregate is dispersed. Also, drying shrinkage is a natural property of all calcium silicate hydrate (CSH)-based materials. The
Fig. 3. Variation of thermal resistivity of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
519
Fig. 4. Variation of water absorption of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
pure hardened CSH paste undergoes very high drying shrinkage, whereas the reinforced material shows significantly less shrinkage due to the presence of zonolite lightweight aggregate. The non-shrinking reinforcement may form a high resistance to shrinkage and as a result the shrinkage force generated by the CSH paste opens up the pores. The shrinkage induced pores opening disconnects the originally compact binder and creates the disconnected solid phase. Simultaneously, the disconnected solid phase is parallel with the air volume represented by the total porosity. Physically, the heat flow through NZCSC in two parallel paths, one through the connecting binder layers and the other through a path consisting of aggregate and cement paste in series. Thus, the thermal resistivity of NZCSC increases as the zonolite loaded increases.
3.3. Effect of zonolite loading on water absorption of NZCSC The variation of water absorption of nanostructured zonolite–cementitious surface compound with zonolite ratio is shown in Fig. 4. It shows that the water absorption of NZCSC increased as zonolite ratio increased. Therefore, the increase of water absorption is due to the nature of zonolite particles. Basically, water is held in the capillary pores formed by the internal surface area of expanded particles. The adjoining layers of zonolite are held together by a combination of electrostatic and van der Waals forces. At lower level of zonolite loading up to 20% in NZCSC (M6); the water absorption is about 50% which is suitable for application without the use of a vapor barrier but at the higher
Fig. 5. Variation of porosity of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
520
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
Fig. 6. Variation of indirect tensile strength of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of superplasticizer ratio.
zonolite loading; it can be used to insulate masonry wall cores and cavities. 3.4. Effect of zonolite loading on porosity of NZCSC Fig. 5 shows the variation of porosity of nanostructured zonolite–cementitious surface compounds hydrated for 28 days with zonolite loading. It is clear that, the porosity of the NZCSC increases as the zonolite loading increases. The thermal treatment of zonolite particles during expansion process causes the particles to expand in volume which increases their internal surface area. This allows zonolite to improve its porosity. Furthermore, the water adsorbed by zonolite particles during mixing leads to formation of excess pores in the network matrix. However, lightweight zonolite particles lead to increase in the network porosity as well as the pore system of cementitious material. This is in addition to the gel pores and capillary pores which are formed during hydration process. The increase of porosity in the NZCSC leads to an increase in the thermal resistivity. Therefore, the NZCSC can be applied with low loading of zonolite on structural elements and also provide an enhancement to the thermal performance of the building envelope. 3.5. Effect of superplasticizer loading on indirect tensile strength of NZCSC Fig. 6 illustrates the variation of the indirect tensile strength of NZCSC containing 40% zonolite (hydrated for 28 days) as a function of superplasticizer ratio. The relative indirect tensile strength was calculated as the indirect tensile strength with superplasticizer divided by the indirect tensile strength of the control material, i.e. without superplasticizer. As seen, the relative indirect tensile strength increases as the superplasticizer ratio increases. The loading of 0.5% superplasticizer in NZCSC enhanced the indirect tensile strength by 32% compared to the control sample M8 (0% superplasticizer). However, the addition of superplasticizer to NZCSC can modify the suspending
liquid and control particle charge. A repulsion force is created when the polymer layer is present at the surface of particles. This happens whenever the polymer molecules become more compacted. The surface potential of the cement phase becomes negative and the particles start repelling each other. As a result of this, the hydration of cement is delayed. In concentrated suspensions, individual solid particles can be completely separated from each other and can form loosely bonded clusters. This can affect the texture formed of the hardening body of the cement mixes. Since increasing the ratio of the superplasticizer has not considerably increased the indirect tensile strength of the material, and has caused delay in the hydration, 0.5% is the recommended dosage of superplasticizer for the mixture with 40% zonolite. 4. Conclusions Nanostructured zonolite cementitious compound, NZCSC has been formulated. The intended applications of these compounds are building skins and cores for pre fabricated structural insulated panels (SIPs). A balance between strength and thermal resistivity has been achieved at 40% zonolite loading. The use of developed NZCSC can reduce heat loss and heat gain through building envelopes and aide in achieving thermal comfort inside the building. Specific findings derived from the current study are as follows: The use of nano clay particles (Cloisite 30B) in blended cement pastes enhances the indirect tensile strength of the NZCSC. The loading of zonolite in the nanostructured zonolite– cementitious surface compounds (NZCSC) up to 40% by weight of nano clay cement binder increases the thermal resistivity by 2.9 fold compared to the control sample (0% zonolite). The use of zonolite in NZCSC increases the strain capacity leading to resistance in the formation and propagation of microcracks and increases the toughness.
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
The addition of 0.5% polycarboxylate ether superplasticizer to the NZCSC recovered more than 30% of indirect tensile strength of the NZCSC containing 0% superplasticizer (control specimen). Acknowledgments Partial support for this project came from USDA/ CSREES. The BASF Chemical Company and GRACE Construction Products, Cambridge, MA are acknowledged for providing materials used in this study. References [1] Demirboga R, Gul R. The effects of expanded perlite aggregate, silica fume and fly ash on the thermal conductivity of lightweight concrete. Cement Concrete Res 2003;33:723–7. [2] Unala O, Uygunoglu T, Yildizb A. Investigation of properties of lowstrength lightweight concrete for thermal insulation. Build Environ 2007;42:584–90. [3] Demirboga R. Influence of mineral admixtures on thermal conductivity and compressive strength of mortar. Energ Buildings 2003;35:189–92. [4] Babu KG, Babu DS. Performance of fly ash concretes containing lightweight EPS aggregates. Cement Concrete Comp 2004;26:605–11. [5] Nambiar EKK, Ramamurthy K. Models relating mixture composition to the density and strength of foam concrete using response surface methodology. Cement Concrete Comp 2006; 28(9):752–60.
521
[6] Babu DS, Babu KG, Tiong-Huan W. Effect of polystyrene aggregate size on strength and moisture migration characteristics of lightweight concrete. Cement Concrete Compo 2006;28:520–7. [7] Nambiar EKK, Ramamurthy K. Influence of filler type on the properties of foam concrete. Cement Concrete Comp 2006;28(5): 475–80. [8] Nambiar EKK, Ramamurthy K. Air void characterisation of foam concrete. Cement Concrete Res 2007;37:221–30. [9] Babua DS, Babub KG, Weea TH. Properties of lightweight expanded polystyrene aggregate concretes containing fly ash. Cement Concrete Res 2005;35:1218–23. [10] Morsy M, Aglan H. Development and characterization of nanostructured-perlite-cementitious surface compounds. J Mater Sci 2007;42(24):10188–95. [11] Cotterell B, Chiaa JYH, Hbaieba K. Fracture mechanisms and fracture toughness in semicrystalline polymer nanocomposites. Eng Fract Mater 2007;74:1054–78. [12] Siddiquia NAR, Wooa SC, Kima J-K, Leungb CCK, Munir A. Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nano clay-filled epoxy matrix. Composite Part A: applied science and manufacturing 2007;38:449–60. [13] Tong Z, Deng Y. Synthesis of water-based polystyrene-nanoclay composite suspension via mini emulsion polymerization. Ind Eng Chem Res 2006;45:2641–5. [14] Li G. Properties of high-volume fly ash concrete incorporating nanoSiO2. Cement Concrete Res 2004;34:1043–9. [15] Kuo W-T, Lin K-L, Chang W-C, Luo H-L. Effect of nano-materials on properties of waterworks sludge ash cement paste. J Ind Eng Chem 2006;12:702–9. [16] Canakcia H, Demirbog R, Karakoc MB, S ß irin O. Thermal conductivity of limestone from Gaziantep (Turkey). Build Environ 2007;42:1777–82.
Construction and Building
MATERIALS
Construction and Building Materials 23 (2009) 515–521
www.elsevier.com/locate/conbuildmat
Nanostructured zonolite–cementitious surface compounds for thermal insulation M.S. Morsy a, H.A. Aglan b
a,*
, M.M. Abd El Razek
b
a Mechanical Engineering Department, Tuskegee University, AL, USA Housing and Building National Research Center, P.O. Box 1770, Cairo, Egypt
Received 15 June 2007; received in revised form 21 October 2007; accepted 22 October 2007 Available online 20 February 2008
Abstract This paper investigates the effect of zonolite loadings on the thermal resistivity and indirect tensile strength of nanostructured cementitious compounds. The main objective of this research is to develop a structural lightweight compound that can be used on building skins and cores for pre fabricated structural insulated panels (SIPs). The application of this compound is intended to improve the thermal resistivity of the building envelope with suitable mechanical performances. The zonolite dosage was added to the cement-nano clay blend at different dosages up to 40% by weight. The nano clay reinforcement used is montmorillonite clay (Hydrated sodium calcium aluminum silicate). The mixes were prepared using water of consistence. The wet compounds were molded in PVC cylindrical molds, having 50 mm inside diameter and 27 mm height, and left for 24 h, then demolded and cured in humid air (20 ± 1 C&100% RH) for 28 days. The samples were then dried at 105 ± 5 C for 24 h before testing using a forced convection oven. The thermal resistivity and indirect tensile strength of the different compounds were evaluated. Results demonstrate that the thermal resistivity at 40% zonolite loading enhanced by about 2.9 folds compared to the control samples. An increase of more than 30% in the indirect tensile strength was also achieved when a 0.5% by weight of polycarboxylate superplasticizer was used. 2007 Elsevier Ltd. All rights reserved. Keywords: Thermal resistivity; Zonolite; Nano clay; Portland cement; Indirect tensile strength
1. Introduction Thermal insulation is a major contributor towards achieving energy efficiency in residential and commercial buildings. The knowledge of thermal transport properties of construction materials is essential in predicting the temperature profile and heat flow through building envelopes. Thermal conductivity of cementitious construction compounds is much higher than the thermal conductivity of air. Introducing holes or air-gaps in these materials will reduce their thermal conductivity or increase their thermal resistivity. The use of lightweight aggregate with low thermal conductivity in the production of lightweight cementi-
*
Corresponding author. E-mail address: [email protected] (H.A. Aglan).
0950-0618/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2007.10.018
tious material can provide enhanced thermal insulation and hence energy savings. Although, lightweight cementitious materials have desirable properties such as low density and good thermal insulation, they have low mechanical properties [1–5]. Zonolite, vermiculite, perlite and expanded polystyrene beads, can be easily incorporated with different contents in cementitious material to produce lightweight mortar with a wide range of densities [6–9]. Zonolite masonry insulation is used to insulate masonry wall cores and cavities. Vermiculite is a mica – like mineral that is heated to about 700 C during processing. This causes the particles to expand in volume, which increases their internal surface area. This expanded (exfoliated) product is used as lightweight aggregate in concrete and plaster for building applications. Recently, we have developed a nanostructured cementitious surface compound with 70% by weight
516
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
loading of perlite particulates [10]. The compound possesses superior thermal resistivity and workability. For the last decade or so nano clay has been incorporated in polymer composites to improve their mechanical and barrier performance. The use of nanofiller in polymer increases the matrix tortuosity, better scratch resistance even for very modest clay loadings (1–5%), and increased heat deflection temperature [11–13]. Nano clay can also provide enhancements in the properties of other materials such as cementitious composites [14,15]. Due to their high surface to volume ratio nano clay can retain water during the mixing of cementitious materials. After dispersion, between cement particles, this water will be available to enhance the hydration process and hence the strength of the cement binder [10]. This finding was established using microstructural analysis of the nanostructured cementitious compounds. Superplasticizers are sometimes used to improve the workability and the mechanical performance of cementitious materials. They allow the production of concretes with special flow properties like self-compacting concrete. In addition, superplasticizers allow the formulation of concrete mixes with very low water/cement ratios. Thus, high performance concretes with very high strength and durability can be achieved. Lightweight thermally resistant cement composites can benefit more from using superplasticizer as well as nano clay. The current research addresses some of the issues associated with such technologies. 2. Materials and experimental 2.1. Materials The starting materials used in this investigation are ordinary Portland cement (OPC) (type I/II) produced by Quikrete Portland Cement Co., Zonolite Masonry Insulation treated with hydrophobic coating produced by GRACE construction products, Cambridge, MA, nano clay produced by Southern Clay Products and Sokalan HP 80 polycarboxylate ether provided by BASF Chemical Company. The chemical compositions of the OPC and zonolite are summarized in Table 1. The particle size
Table 2 Particle size distribution US mesh size Aperture (mm) Cumulative % retained
16 1.19 0.5
50 0.3 60–98
100 0.15 90–100
distribution of the zonolite is given in Table 2. The nano clay (Hydrated sodium calcium aluminum silicate) is Cloisite 30B natural montmorillonite modified with an ammonium salt. Sokalan HP 80 polycarboxylate ether was used as a superplasticizer in the current investigation. The superplasticizer was added to the mixed water in ratios of 0.5, 1, 1.5 and 2% by weight of nano clay cement binder. 2.2. Compound preparation and identification The nano clay cement binder (NCB) was prepared by partial substitution of OPC by 2% nano clay [10]. The dry OPC and nano clay were shear mixed for 5 min. Then the zonolite was added to NCB at different weight ratios based on a unit weight of NCB as illustrated in Table 3. The superplasticizer was added to the higher loaded blends of zonolite as shown in Table 3. The blended compounds were prepared by slow mixing for 3 min using the standard water of consistency (optimum amount of water for workability of the mix). The compound was molded in a PVC mold for mechanical and thermal conductivity tests. The samples were kept in molds for 24 h, and then demolded. The specimens were cured at 100% relative humidity and 20 ± 1 C for 28 days. The specimens were dried at a temperature of 105 C for 24 h in an oven. Mechanical and thermal conductivity tests were performed on dried specimens. 2.3. Thermal conductivity tests The thermal conductivity of the nanostructured zonolite–cementitious surface compounds (NZCSC) was deterTable 3 The dry mixes composition of blended binder and compound (mass (%)) Mixes ratio per unite weight of nano clay cement binder (NCB)*
Table 1 The chemical composition of starting material Oxide composition
Portland cement (%)
Zonolite (%)
CaO SiO2 Al2O3 Fe2O3 MgO SO3 Na2O K2O TiO2 Cr2O3 Ignition loss
63.9 20.5 5.4 2.6 2.1 3.0 0.61 – – – 1.4
1–3 38–46 11–16 8–13 – – 0.1–0.3 4–6 1–3 0.05–0.2 –
Mixes
NCB
Zonolite
Superplasticizer
W/C (%)
M0 M1 M2 M3 M4 M5 M6 M7 M8 GS1 GS2 GS3 GS4
1 1 1 1 1 1 1 1 1 1 1 1 1
0 0.025 0.05 0.075 0.1 0.15 0.2 0.3 0.4 0.4 0.4 0.4 0.4
0 0 0 0 0 0 0 0 0 0.005 0.01 0.015 0.02
0.28 0.35 0.375 0.45 0.525 0.675 0.825 1.125 1.425 1.25 1.15 1.1 1.075
*
98% OPC + 2% nanoclay.
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
mined according to ASTM E-1530; guarded heat flow meter method. An axial load of 140 KPa was applied on the test sample to insure good contact. The thermal resistivity is the reciprocal of the conductivity.
517
where rt is the indirect tensile strength, Pmax is the maximum applied load, D is the diameter and t is the thickness of the specimen, was reported for each mix. 3. Results and discussion
2.4. Water absorption and apparent porosity measurements Water absorption was measured according to ASTM C140-01. The specimens were immersed in water at room temperature (22 C) for 24 h and then weighed while they were completely submerged. The immersed weight, Wi was recorded. The specimens were then removed from the water and allowed to drain for 1 min by placing them on a wire mesh. Visible surface water was removed with a damp cloth. The new weight was recorded as Ws (saturated weight). The specimens were then dried in a ventilated oven at 105 C for not less than 24 h and until two successive weights at intervals of 2 h show an increment of loss not greater than 0.2%. This final weight of dried specimens was recorded as Wd (oven-dry weight). The absorption is calculated as Absorption% ¼ ½ðW s W d Þ=W d 100 Apparent porosity was determined from water absorption of the sample. Apparent porosity was determined by dividing volume of absorbed water by the apparent volume of the sample [16]. 2.5. Indirect tensile strength tests The indirect tensile tests were performed on a Sintec-5D MTS machine using the 50 · 27 mm cylindrical samples. Five samples per batch were tested, and the average value was reported. The loading rate on the specimen was 1.27 mm/min. The indirect tensile strength, determined as rt ¼ 2P max =pDt
3.1. Effect of zonolite loading on the mechanical properties and fracture behavior of NZCSC The variations of indirect tensile strength with zonolite loading for the nanostructured zonolite–cementitious surface compounds (NZCSC) hydrated for 28 days are shown in Fig. 1. The indirect tensile strength of the NZCSC decreases as the zonolite loading increases. The NZCSC with 40% zonolite loading possesses about 15% of the indirect tensile strength of the control nanostructure cementitious binder (NCB) after 28 days of hydration (mix M0 in Table 2). Therefore, addition of zonolite to the NCB as a lightweight aggregate leads to weakness of the nanostructured zonolite–cementitious surface compounds’ bonds due to its filler effect. Also by increasing the zonolite ratio; the adsorbed water increases leading to high water to binder ratios. The increased water/binder ratio increases the formed structure porosity leading to a decrease of the indirect tensile strength. The stress-strain behavior of the NZCSC, containing 0, 10, 20, 30 and 40% zonolite hydrated for 28 days is shown in Fig. 2. It is observed that at lower zonolite loading 0% (M0) and 10% (M4), the NZCSC displays brittle behavior. This is characterized as a sudden drop of the stress after a maximum was reached. The fracture surface is very smooth and the strain is small. However, for the NZCSC M8-40%, the stress strain behavior is different from the NZCSC M0 and M4. While testing for indirect tensile strength, the failure mode of NZCSC specimen containing higher ratio of zonolite did not exhibit the typical brittle failure normally observed in lower ratio of zonolite. The failure observed
Fig. 1. Variation of indirect tensile strength of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
518
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
Fig. 2. Variation of indirect tensile strength of nanostructured zonolite–cementitious surface compounds (NZCSC) with strain.
was more gradual and the specimens did not separate into two pieces in NZCSC containing 20, 30 and 40% zonolite. However, the higher loading of zonolite in NZCSC increases the strain capacity. This gradual failure and higher strain capacity were significant in cementitious compounds made with high zonolite contents. This indicates that NZCSC with high loadings of zonolite can resist the formation and propagation of microcracks. 3.2. Effect of zonolite loading on thermal resistivity The thermal resistivity of the NZCSC as a function of zonolite loading is presented in Fig. 3. It is clear that, the
thermal resistivity increases with the increasing zonolite ratios. The variation of the thermal resistivity shows that the compound containing 40% zonolite by weight has a thermal resistivity 2.9 times higher than the compound with no zonolite (control). The improvement in thermal resistivity is due to the high porosity of the zonolite particles coupled with the pores network formed during hydration of the cementitious compound. Zonolite particles contain capillary pores formed by the internal surface area during expansion. However, the NZCSC consists of a continuous binder phase in which a discontinuous aggregate is dispersed. Also, drying shrinkage is a natural property of all calcium silicate hydrate (CSH)-based materials. The
Fig. 3. Variation of thermal resistivity of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
519
Fig. 4. Variation of water absorption of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
pure hardened CSH paste undergoes very high drying shrinkage, whereas the reinforced material shows significantly less shrinkage due to the presence of zonolite lightweight aggregate. The non-shrinking reinforcement may form a high resistance to shrinkage and as a result the shrinkage force generated by the CSH paste opens up the pores. The shrinkage induced pores opening disconnects the originally compact binder and creates the disconnected solid phase. Simultaneously, the disconnected solid phase is parallel with the air volume represented by the total porosity. Physically, the heat flow through NZCSC in two parallel paths, one through the connecting binder layers and the other through a path consisting of aggregate and cement paste in series. Thus, the thermal resistivity of NZCSC increases as the zonolite loaded increases.
3.3. Effect of zonolite loading on water absorption of NZCSC The variation of water absorption of nanostructured zonolite–cementitious surface compound with zonolite ratio is shown in Fig. 4. It shows that the water absorption of NZCSC increased as zonolite ratio increased. Therefore, the increase of water absorption is due to the nature of zonolite particles. Basically, water is held in the capillary pores formed by the internal surface area of expanded particles. The adjoining layers of zonolite are held together by a combination of electrostatic and van der Waals forces. At lower level of zonolite loading up to 20% in NZCSC (M6); the water absorption is about 50% which is suitable for application without the use of a vapor barrier but at the higher
Fig. 5. Variation of porosity of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of zonolite ratio.
520
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
Fig. 6. Variation of indirect tensile strength of nanostructured zonolite–cementitious surface compounds (NZCSC) as a function of superplasticizer ratio.
zonolite loading; it can be used to insulate masonry wall cores and cavities. 3.4. Effect of zonolite loading on porosity of NZCSC Fig. 5 shows the variation of porosity of nanostructured zonolite–cementitious surface compounds hydrated for 28 days with zonolite loading. It is clear that, the porosity of the NZCSC increases as the zonolite loading increases. The thermal treatment of zonolite particles during expansion process causes the particles to expand in volume which increases their internal surface area. This allows zonolite to improve its porosity. Furthermore, the water adsorbed by zonolite particles during mixing leads to formation of excess pores in the network matrix. However, lightweight zonolite particles lead to increase in the network porosity as well as the pore system of cementitious material. This is in addition to the gel pores and capillary pores which are formed during hydration process. The increase of porosity in the NZCSC leads to an increase in the thermal resistivity. Therefore, the NZCSC can be applied with low loading of zonolite on structural elements and also provide an enhancement to the thermal performance of the building envelope. 3.5. Effect of superplasticizer loading on indirect tensile strength of NZCSC Fig. 6 illustrates the variation of the indirect tensile strength of NZCSC containing 40% zonolite (hydrated for 28 days) as a function of superplasticizer ratio. The relative indirect tensile strength was calculated as the indirect tensile strength with superplasticizer divided by the indirect tensile strength of the control material, i.e. without superplasticizer. As seen, the relative indirect tensile strength increases as the superplasticizer ratio increases. The loading of 0.5% superplasticizer in NZCSC enhanced the indirect tensile strength by 32% compared to the control sample M8 (0% superplasticizer). However, the addition of superplasticizer to NZCSC can modify the suspending
liquid and control particle charge. A repulsion force is created when the polymer layer is present at the surface of particles. This happens whenever the polymer molecules become more compacted. The surface potential of the cement phase becomes negative and the particles start repelling each other. As a result of this, the hydration of cement is delayed. In concentrated suspensions, individual solid particles can be completely separated from each other and can form loosely bonded clusters. This can affect the texture formed of the hardening body of the cement mixes. Since increasing the ratio of the superplasticizer has not considerably increased the indirect tensile strength of the material, and has caused delay in the hydration, 0.5% is the recommended dosage of superplasticizer for the mixture with 40% zonolite. 4. Conclusions Nanostructured zonolite cementitious compound, NZCSC has been formulated. The intended applications of these compounds are building skins and cores for pre fabricated structural insulated panels (SIPs). A balance between strength and thermal resistivity has been achieved at 40% zonolite loading. The use of developed NZCSC can reduce heat loss and heat gain through building envelopes and aide in achieving thermal comfort inside the building. Specific findings derived from the current study are as follows: The use of nano clay particles (Cloisite 30B) in blended cement pastes enhances the indirect tensile strength of the NZCSC. The loading of zonolite in the nanostructured zonolite– cementitious surface compounds (NZCSC) up to 40% by weight of nano clay cement binder increases the thermal resistivity by 2.9 fold compared to the control sample (0% zonolite). The use of zonolite in NZCSC increases the strain capacity leading to resistance in the formation and propagation of microcracks and increases the toughness.
M.S. Morsy et al. / Construction and Building Materials 23 (2009) 515–521
The addition of 0.5% polycarboxylate ether superplasticizer to the NZCSC recovered more than 30% of indirect tensile strength of the NZCSC containing 0% superplasticizer (control specimen). Acknowledgments Partial support for this project came from USDA/ CSREES. The BASF Chemical Company and GRACE Construction Products, Cambridge, MA are acknowledged for providing materials used in this study. References [1] Demirboga R, Gul R. The effects of expanded perlite aggregate, silica fume and fly ash on the thermal conductivity of lightweight concrete. Cement Concrete Res 2003;33:723–7. [2] Unala O, Uygunoglu T, Yildizb A. Investigation of properties of lowstrength lightweight concrete for thermal insulation. Build Environ 2007;42:584–90. [3] Demirboga R. Influence of mineral admixtures on thermal conductivity and compressive strength of mortar. Energ Buildings 2003;35:189–92. [4] Babu KG, Babu DS. Performance of fly ash concretes containing lightweight EPS aggregates. Cement Concrete Comp 2004;26:605–11. [5] Nambiar EKK, Ramamurthy K. Models relating mixture composition to the density and strength of foam concrete using response surface methodology. Cement Concrete Comp 2006; 28(9):752–60.
521
[6] Babu DS, Babu KG, Tiong-Huan W. Effect of polystyrene aggregate size on strength and moisture migration characteristics of lightweight concrete. Cement Concrete Compo 2006;28:520–7. [7] Nambiar EKK, Ramamurthy K. Influence of filler type on the properties of foam concrete. Cement Concrete Comp 2006;28(5): 475–80. [8] Nambiar EKK, Ramamurthy K. Air void characterisation of foam concrete. Cement Concrete Res 2007;37:221–30. [9] Babua DS, Babub KG, Weea TH. Properties of lightweight expanded polystyrene aggregate concretes containing fly ash. Cement Concrete Res 2005;35:1218–23. [10] Morsy M, Aglan H. Development and characterization of nanostructured-perlite-cementitious surface compounds. J Mater Sci 2007;42(24):10188–95. [11] Cotterell B, Chiaa JYH, Hbaieba K. Fracture mechanisms and fracture toughness in semicrystalline polymer nanocomposites. Eng Fract Mater 2007;74:1054–78. [12] Siddiquia NAR, Wooa SC, Kima J-K, Leungb CCK, Munir A. Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nano clay-filled epoxy matrix. Composite Part A: applied science and manufacturing 2007;38:449–60. [13] Tong Z, Deng Y. Synthesis of water-based polystyrene-nanoclay composite suspension via mini emulsion polymerization. Ind Eng Chem Res 2006;45:2641–5. [14] Li G. Properties of high-volume fly ash concrete incorporating nanoSiO2. Cement Concrete Res 2004;34:1043–9. [15] Kuo W-T, Lin K-L, Chang W-C, Luo H-L. Effect of nano-materials on properties of waterworks sludge ash cement paste. J Ind Eng Chem 2006;12:702–9. [16] Canakcia H, Demirbog R, Karakoc MB, S ß irin O. Thermal conductivity of limestone from Gaziantep (Turkey). Build Environ 2007;42:1777–82.