NZ515494A

NZ515494A - Carbon loaded concrete products

Info

Publication number: NZ515494A
Application number: NZ515494A
Authority: NZ
Inventors: Stephen John Bloomer; John Griffiths; Jaqueline Lander
Original assignee: Mantle & Llay Ltd
Priority date: 1999-05-14
Filing date: 2000-05-15
Publication date: 2003-10-31
Also published as: EP1187795A1; CA2373436A1; NO20015553D0; AU5082600A; NO20015553L; WO2000069789A1; EE200100602A; GB9911165D0

Abstract

A concrete or cementicious product having one or more forms of carbon dispersed therethrough so as to reduce thermal conductance across the product. The one or more forms of carbon are dispersed therethrough in small clusters and/or agglomerates that are wholly or substantially isolated from each other. The carbon(s) have a BET surface area of less than 550 m2/g and include(s) carbon black. Also provided is a method of forming such a concrete or cementicious product.

Description

515494 1 CARBON LOADED CONCRETE PRODUCTS 2 3 This invention relates to carbon loaded concrete and 4 cementicious products having reduced thermal conductance. 6 7 Heat transfer through a composite material occurs via a 8 combination of convection, conduction and radiation. 9 in practice, composite thermal conductivity depends, in part, on the volume of the solid(s) versus pore volume, 11 and the conductivity of the bulk solid. 12 13 In general terms, for a porous material, the greater 14 the porosity (lower density) , the more significant is convection through pores and radiation from cell walls. 16 The relative importance of convection depends on the 17 degree and type of porosity, for example, the pro- 18 portion of open to closed porosity, pore diameter and 19 shape. Below a certain pore size, in-pore gases are effectively static and convection is drastically 21 reduced. 22 2 1 Conversely, heat transfer by convection increases with 2 moisture content of the concrete. 3 4 An additional effect of pore size is that when there are many very small pores, as against a few larger 6 ones, there are a greater number of narrow, solid, 7 heat-bridges, thus constricting thermal conduction 8 through the solid. 9 Further, the greater number of solid barriers through a 11 given volume in a system of small pores, results in a 12 higher impedance to thermal transfer by radiation. 13 This is due to the fact that heat energy must be 14 absorbed and re-radiated many times for heat transfer to occur. 16 17 According to one aspect, of the present invention, there 18 is provided a concrete or cementicious product having 19 one or more forms of carbon dispersed therethrough so as to reduce thermal conductance across the product. 21 22 In another view of the present invention, there is 23 provided a concrete or cementicious product having one 24 or more forms of carbon dispersed therethrough in small clusters and/or agglomerates that are wholly or 26 substantially isolated from each other. 27 28 Particulate loadings, especially carbons, may be used 29 to reduce heat transfer by any or a combination of the following, depending on the other components in the 31 matrix and the processing methods: 32 3 PCT/GBOO/01845 1 Increase irtpedance to heat transfer by radiation 2 because certain carbons are good infra-red 3 absorbers. . 4 Provide particles with a chosen porosity to 6 influence convection. 7 8 Depending on other components and processing 9 methods,they may influence the size and form of a proportion of the porosity, other than their own 11 porosity, as has been observed for carbon and/or 12 silica composite systems other than concrete. 13 14 Carbons suitable for use in the present invention will typically have a BET surface area of < 550 m2/g. 16 17 One typical form of carbon for use with the present 18 invention is carbon black. 19 Carbon blacks are composed of spheroidal primary 21 particles which partially coalesce during manufacture 22 to form interlinked clusters and chains of carbon 23 spheres. The structure of a carbon black is defined in 24 terms of the growth of the clusters and chains. The carbon black industry defines a "low structure" black 26 as consisting of small clusters of spheroids, whereas a 27 "high structure" black contains extensive chains and 28 clusters, which tend to interlock further to form large 29 agglomerates. 31 The form(s) of carbon black suitable for use with the 32 present invention preferably have a medium to low 4 PCT/GB00/Q1845 1 "structure" and a high intrinsic electrical 2 resistivity. 3 4 Also preferred in some cases are forms of carbon with a low pH in dry dispersion in cement, and/or a small 6 particle size. 7 . 8 The "structure" of the carbon black can be defined by 9 its DBP Index. This is the amount of di-butyl phthalate which a carbon can take up to form a paste of 11 a prescribed consistency. A low DBP index indicates a 12 "low structure". DBP Index values for carbons for use 13 with the present invention range typically from 35 to 14 170 ml/lOOg and more preferably have a DBP index in the range of 40 - 105 mls/lOOg. 16 17 An aim of the present invention is to disperse a carbon 18 through the concrete or a cementicious material so that 19 clusters, chains and small agglomerates are largely isolated and do not form linked pathways through the 21 block. In this way, use is made of the carbon's 22 ability to absorb radiant heat, without creating 23 additional routes for convection and/or conduction. 24 The concrete or cementicious products of the present 26 invention can be of any form, size, shape and design. 27 One typical example is concrete blocks, from which 28 structures can be formed and/or built. Furthermore 29 blocks of the Autoclaved Aerated Concrete (AAC) type are suitable for the application of this invention. 31 PCT/G B00/01845 1 According to another aspect of the present invention, 2 there is provided a method of forming a concrete or 3 cementicious product having one or more forms of carbon 4 dispersed therethrough so as to reduce thermal conductance across the product, wherein cement or other 6 cementicious material, water and the or each form of 7 carbon are admixed, cast and cured. 8 9 The carbon is preferably added as a percentage of the cementicious material in the range 0.2 to 3.0 wt%, 11 preferably 0.5 to 2.0 wt%. 12 13 Cementicious material can be: Portland Cement; Calcium 14 Aluminate Cement; Pozzolanic materials such as Pulverised Fuel Ash (PFA), volcanic ash etc; finely 16 ground silica; Latent Hydraulic materials such as 17 Ground Granulated Blastfurnace (GGBS) and other slags 18 etc,- Microsilica; Metakaolin; or mixtures thereof. 19 This list is not-exhaustive. 21 An embodiment of the present invention will now be 22 described by way of example only and with reference to 23 the accompanying Figures as referred to in the text: 24 Suitable forms of PFA comply with BS3892: Part 1: 1993 26 or BS EN 450 : 1995. A suitable source of PFA is from 27 Drax power station (UK). Other forms and sources of 28 PFA may also be used. 29 A suitable Plasticiser for use in this invention is 31 Sikament 10. Other types of plasticiser may also be 32 used. 6 1 2 Suitable types of Coated Aluminium Powder are Higas 100 3 and Higas 220. .Other types of aluminium powder may 4 also be used. 6 (I) Formation of Blocks 7 8 The trials were based on the following dry weight 9 standard formulation: 11 PFA 71.82% 12 Plasticiser 0.54% 13 Ordinary Portland Cement 17.44% 14 Calcium Sulfate Anhydrite 1.54% Hydrated Lime 8.21% 16 Coated Aluminium Powder 0^45% 17 18 Water at ambient temperature was used to make the 19 wet mix at between 40-50% of the dry weight of the ingredients. 21 The following carbon blacks were used: 22 23 BET Surface Area DBP Index 24 (m2/g) (g/lOOml) 26 Carbon 1 40 48 27 Carbon 2 60 64 28 Carbon 3 82 102 29 Carbon 4 525 98 7 PCT/GBOO/O1845 1 Carbon was added as a percentage of cementicious 2 material (PFA + Ordinary Portland Cement) in the 3 range 0.5 to 2.0 wt.%. 4 Components were mixed as follows: 6 7 a. Carbon and approximately 10% of the PFA were 8 dispersed in approximately 15% of the mixing 9 water containing approximately half the plasticiser in a high shear mixer. 11 12 b. Cement, Calcium Sulfate Anhydrite, the rest 13 of the PFA, Plasticiser and mixing water were 14 vigorously agitated to form a slurry with a). 16 (For mixes without carbon addition step a) 17 was omitted) 18 19 c. Lime and the Aluminium Powder were combined and were then added to the slurry with 21 further vigorous agitation to obtain an 22 homogenous mixture. 23 24 The mixing regime should be chosen such that substantially discrete particles of carbon are 26 evenly dispersed throughout the mix. Overmixing 27 of some forms of carbon may lead to agglomeration 28 of the carbon particles and result in poor 29 performace of the blocks. 8 PCT/GBOO/Ol 845 1 Moulds were coated with release agent. The slurry 2 was immediately poured into the mould. The mix 3 rises typically between 80 to 100%. 4 (II) Autoclaving 6 7 Blocks were put in the autoclave up to 12 hours 8 after casting. 9 System was ramped to temperature over 4 hours 11 maintained at 180°C for 8 hours, and cooled down 12 over a period of 4-8 hours. 13 14 The following are examples of autoclaved blocks: 16 Carbon Type Addition 17 18 1 19 2 3 21 Standard Block 22 23 (III)Non-autoclaved blocks 24 In addition the following block was also produced 26 for comparative purposes without autoclaving: 27 28 Carbon Type Addition 29 4 0.5% 31 1.0% 0.5% 1.0% 0% 9 PCT/GB0O/O1845 1 (IV) Drying of Samples 2 3 According to BS 874 Part 2 : Section 2.2 1988, 4 samples must not lose more that 4% weight during thermal measurements for the k-valve to be valid. 6 All blocks were oven dried at 100 to 150°C and 7 weighed before and after measurement. 8 9 (V) Thermal Measurement 11 A "plain unguarded hot plate" apparatus was set up 12 according to BS 874 Part 2 : Section 2.2 1988. 13 14 (VI)Results k-Values Density/kgm"3 k/Wm^K"1 Standard - no carbon 505 0.150 Carbon No4, 0.5% 579 0.115.

Carbon Nol, 1.0% 580 0.136 Carbon No3, 1.0% 483 0.120 Carbon No2, 0.5% 698 0.142 Commercially available aerated block 490 0.140 ■ 16 17 18 As the density of most materials, including 19 aerated concrete, increases so does the k-value.

It can be seen from the above results that where 21 the density has increased compared to the standard 22 block there has been a reduction in the k-value 23 and where the density has reduced the decrease in 1 k-value is greater than that expected from the 2 density reduction alone. 3 4 (VII)Pore Structure 6 Fracture surfaces of autoclaved samples were gold 7 coated and examined in a scanning electron 8 microscope. 9 11 12 13 14 16 17 18 19 21 At low magnification (Figure 4), the standard 22 " formulation appears slightly irregular compared 23 with aerated commercial sample. The size range of 24 blown pores is again 0.1 to 1mm dia., and pore wall thickness is similar. The pore wall 26 structure (Figure 5) is loosely bonded PFA, with a 27 size range similar to the aerated commercial 28 sample. There is considerable "debris" around the 29 PFA particles. Very few acicular crystals were seen. 31 The aerated commercial sample consisted of roughly spherical, blow pores of 0.1 to 1mm diameter (Figure 1). Pores are not completely closed.

Pore walls are relatively smooth (Figure 2) with further irregular, open porosity (up to 0.05^im) between acicular crystals. The matrix between the blown pores consists predominantly of loosely bonded PFA spheres, in the size range 1 to 10 m (Figure 3). with considerable open porosity between.

PCT/GB00/Q1845 11 1 In a carbon black (Nol) loaded sample at 0.5% 2 carbon addition, blown pores were less regular in 3 shape (Figure 6) (size range 0.1 to 2mm dia.). 4 Again, pores were not completely closed. The internal pore surface was much rougher (Figure 7). 6 The matrix was less regular and composed of 7 particles in the range 0.5 to 10/xm. The majority 8 of particles were 0.5 to 1.0/xm, hence the porosity 9 . in the matrix of the carbon black loaded sample contains relatively few larger pores. 11 12 Conclusions 13 14 1. 16 l"7 18 19 2. 21 22 23 24 3. 26 27 28 Brief Description of the Figures 29 Figure 1 shows the pore structure of commercial aerated 31 block magnified x 20. 32 Carbon loaded aerated concretes have been formed with k-values lower than the standard (no carbon) aerated concrete even where the carbon loaded concretes were of increased density.

Carbon influences pore structure as follows : blown pores become less regular and pore surfaces appear rougher than either the standard formula or the aerated sample.

Carbons which give the best results are for example high resistivity carbon blacks, with medium to low structures,(DBP 40 to 105mls/100g). 12 1 Figure 2 shows the pore structure of commercial aerated 2 block magnified x 3000. 3 4 Figure 3 shows the pore structure of commercial aerated block magnified x 3000. 6 7 Figure 4 shows the pore structure in standard 8 formulation x 20. 9 Figure 5 shows the pore structure in standard 11 formulation x 3000. 12 13 Figure 6 shows the pore structure in a carbon black 14 (Nol) loaded sample at 0.5% carbon addition x 20. 16 Figure 7 shows the pore structure in a carbon black 17 (Nol) loaded sample at 0.5% carbon addition x 1500. ■i

Claims

1 CLAIMS 5154 2 3 1. A product having one or more forms of carbon 4 dispersed therethrough so as to reduce thermal 5 conductance across the product, characterised in 6 that the product is a concrete or cementitious 7 product in which the one or more forms of carbon 8 dispersed therethrough are in the form of small 9 clusters and/or agglomerates that are wholly or 10 substantially isolated from each other. 11 12 2. A concrete or cementitious product as claimed in 13 claim 1 wherein the carbon(s) have a BET surface 14 area of less than 550 m2/g. 15 16 3. A concrete or cementitious product as claimed in 17 any of the preceding claims wherein the one or 18 more form of carbon is or includes carbon black. 19 20 4. A concrete or cementitious product as claimed in 21 claim 3 wherein the carbon black has a medium to 22 low structure and a high intrinsic electrical .23 resistivity. 24 25 5. A concrete or cementitious product as claimed in . 26 any of the preceding claims wherein jthe carbon has 27 a low pH in dry dispersion in cements A concrete or cementitious product as claimed in any of the preceding claims wherein the one or more form of carbon has a DBP Index value of from 35 to 170 ml/lOOg. INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 0 MAR 2003 28 29 6. 30 31 32 33 RECEIVED

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6 7 8 9 10 11 12 13 14 15 16 14 51549 4

7. A method of forming a concrete or cementitious product as claimed in any of the preceding claims wherein cement or other cementitious material, water and the or each form of carbon are admixed, cast and cured.

8. A method as claimed in claim 7 where the carbon is added as a percentage of the cementitious material in the range 0.2 to 3.0 wt%.

9. Use of carbon black in the production of a product as claimed in any of claims 1 to 6.

10. Use of carbon black in a method as claimed in claim 7 or 8. INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 o MAR 2003