PRODUCTION OF AGGREGATES

Abstract

An improved process for the preparation of aggregates for use with mixtures of various carbonatable substances, in particular mixtures comprising pulverised fuel ash and/or steel slag. The mixtures also comprise a carbonatable binder. The process comprises the steps of a. blending a combination of two carbonatable wastes, b. mixing the blended carbonatable waste with a carbonatable binder, c. mixing the blended carbonatable waste and binder with water, and d. carbonating the damp blended carbonatable waste in the presence of carbon dioxide.

Claims

1. A process for the preparation of aggregates, the process comprising: a. blending a first carbonatable waste with a second carbonatable waste to form a blended carbonatable waste; b. mixing the blended carbonatable waste with water to form a damp blended carbonatable waste mixture; and c. carbonating the damp blended carbonatable waste mixture in the presence of carbon dioxide; wherein the process further comprises mixing the blended carbonatable waste with a carbonatable binder; and wherein the first carbonatable waste is steel slag or pulverised fuel ash and/or the second carbonatable waste is steel slag or pulverised fuel ash.

2. A process according to claim 1, wherein the first carbonatable waste is air pollution control residue, cement bypass dust, or biomass ash and/or wherein the second carbonatable waste is air pollution control residue, cement bypass dust, or biomass ash.

3. A process according to claim 1, further comprising initially sieving the first carbonatable waste and/or the second carbonatable waste before blending.

4. A process according to claim 3, wherein the first carbonatable waste and/or the second carbonatable waste are initially sieved to obtain an average particle size of less than around 0.1 mm before blending.

5. A process according to claim 1, wherein the carbonatable binder is cement kiln dust or ordinary portland cement.

6. A process according to claim 5, further comprising initially sieving the carbonatable binder before blending with the first and second carbonatable wastes.

7. A process according to claim 1, wherein a weight ratio between the first carbonatable waste and the second carbonatable waste is approximately 1:2 to approximately 2:1.

8. A process according to claim 1, wherein a weight ratio between the first carbonatable waste, second carbonatable waste, and carbonatable binder is approximately 1:2:2 to approximately 2:1:2.

9. A process according to claim 1, wherein the blended carbonatable waste is mixed with around 15-30% w/w of water to form the damp blended carbonatable waste.

10. A process according to claim 9, further comprising mixing the damp blended carbonatable waste mixture.

11. A process according to claim 1, further comprising sieving the damp blended carbonatable waste mixture.

12. A process according to claim 11, wherein the damp blended carbonatable waste mixture is sieved to obtain an average particle size of less than around 0.1 mm.

13. A process according to claim 11, wherein the blended carbonatable waste comprises any number of additional carbonatable wastes blended into the mixture.

14. A process according to claim 1, wherein the process further comprises mixing the blended carbonatable waste with a third carbonatable waste.

15. A process according to claim 14, wherein the third carbonatable waste is pulverised fuel ash or steel slag.

16. A process according to claim 1, further comprising pressing the damp blended carbonatable waste mixture into a form or shape that resembles the shape of aggregate used in concrete.

17. A process according to claim 16, wherein a force of around 100 N is used to cast each form or shape.

18. A process according to claim 1, wherein the damp blended carbonatable waste mixture is carbonated in a carbon dioxide-rich gaseous environment.

19. A process according to claim 1, wherein the carbonating takes place in a fully or partially enclosed carbonation chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0054] In order that the invention may be more clearly understood an embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

[0055] FIG. 1 is a schematic block diagram of a process according to an embodiment of the present invention;

[0056] FIG. 2 is a graph showing the strength of carbonatable wastes and combinations of carbonatable wastes produced by the process shown in FIG. 1, with a carbonation time of 10 minutes;

[0057] FIG. 3 is a graph showing the strength of carbonatable wastes and combinations of carbonatable wastes produced by the process shown in FIG. 1, with a carbonation time of 20 minutes;

[0058] FIG. 4 is a table showing the sources of various carbonatable wastes that are described herein;

[0059] FIG. 5 is a table showing the % weight compositions of various carbonatable wastes that are described herein.

[0060] FIG. 6 is a table showing the strength of pellets of individual carbonatable wastes produced by the process shown in FIG. 1, with no second carbonatable waste and no carbonatable binder, with a carbonation time of 10 minutes; and

[0061] FIG. 7 is a table showing the strength of pellets of individual carbonatable wastes produced by the process shown in FIG. 1, with no second carbonatable waste and no carbonatable binder, with a carbonation time of 20 minutes.

[0062] Referring to FIG. 1, a first carbonatable waste 1 and a second carbonatable waste 2 are initially selected. In this embodiment, the first carbonatable waste 1 is cement bypass dust from cement production in the Midlands, UK, and the second carbonatable waste is biomass ash from biomass power generation in Picardie, France. The sources of the first and second carbonatable wastes 1, 2, are shown in FIG. 4. The compositions of the first and second carbonatable wastes 1, 2 are shown in FIG. 5.

[0063] A carbonatable binder 3 is then selected. In this embodiment, the carbonatable binder is ordinary portland cement (52.5 N), supplied by Cemex (RTM) Ltd. The composition of the carbonatable binder 3 is shown in FIG. 4.

[0064] At step 104, approximately 2.5 grams of the first carbonatable waste 1 is sieved to obtain a particle size of less than 0.1 mm.

[0065] At step 105, approximately 2.5 grams of the second carbonatable waste 2 is sieved to obtain a particle size of less than 0.1 mm.

[0066] At step 106, approximately 5 grams of the carbonatable binder is sieved to obtain a particle size of less than 0.1mm.

[0067] At step 107, the sieved first carbonatable waste 1, second carbonatable waste 2 and carbonatable binder 3 are combined into a 25 ml beaker and the mixture is thoroughly blended by hand to ensure homogeneity. The dry mixture thus weighs 10 grams.

[0068] At step 108, the blended carbonatable wastes 1, 2 and carbonatable binder 3 mixture is wetted with 2.5 grams (25% w/w) of deionised water using a dropping pipette.

[0069] At step 109, the damp blended carbonatable wastes 1, 2 and carbonatable binder 3 mixture is hand mixed for a second time to ensure that the water in the mixture is evenly distributed. The mixture is then sieved to ensure a particle size of less than 0.1 mm.

[0070] At step 110, the damp blended carbonatable wastes 1, 2 and carbonatable binder 3 mixture is pressed into pellet form using a customised pellet press. The pellet press comprises a 30 mm10 mm nylon split mould with an 8 mm aperture to enable removal of pressed samples; a 32 mm7.5 mm cast resin plunger and a 230 mm160 mm reinforced nylon retaining collar with an aperture of 100 mm.

[0071] In use of the pellet press during step 110, the nylon split mould is inserted into the reinforced nylon retaining collar and placed onto a clean stainless steel dish. The damp mixture of blended carbonatable wastes 1, 2 and a carbonatable binder 3 is carefully placed into the nylon split mould and the cast resin plunger is readied into position. A load of approximately 100 N is applied to the resin plunger to cast the pellet, measured by a Mecmesin (RTM) BFG500N force gauge, to an accuracy of 0.1 N. The resin plunger is then removed carefully by hand and the nylon mould is removed from the reinforced nylon retaining collar. The nylon mould is split open using a spatula so that the pressed pellet can be removed for the mould. Five cylindrical pellets are typically produced for each mixture of blended carbonatable wastes 1, 2 and carbonatable binder 3.

[0072] At step 111, the pellets of blended carbonatable wastes 1, 2 and carbonatable binder 3 are transferred to a five litre carbonation chamber containing carbon dioxide, where they begin to carbonate and harden/set. The chamber operates at a pressure of 2 bar, which is slightly above atmospheric pressure to ensure that a sufficient supply of carbon dioxide is available for carbonation of the pellets, but is not so high as to unduly impact on strength development.

[0073] At step 112, after a period of 10 minutes, the pellets are removed from the chamber. The dimensions of each pellet are measured using a Mitutoyo (RTM) CD-6 CP measuring callipers, to an accuracy of 0.01 mm. Each pellet has a diameter of approximately 7.7 mm and thus a radius of approximately 3.85 mm. The length ratio of each pellet is around 1.0 and thus the length of each pellet is around 7.7 mm.

[0074] Each pellet is then destructively tested to determine its compressive strength. Each pellet is placed beneath a force gauge and load is applied to the force gauge until the pellet fails under compression. A Mecmesin (RTM) BFG500N force gauge was used, to an accuracy of 0.1 N.

[0075] The above embodiment is described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Examples

[0076] FIG. 4 shows the sources of the carbonatable wastes discussed below and FIG. 5 shows the compositions of the carbonatable wastes shown in FIG. 4.

[0077] The examples described below were formed using the process as described in the Detailed Description of the Invention, except that in some examples there was no carbonatable binder added to the blend of carbonatable wastes. Five samples of each combination of carbonatable wastes were formed and carbonated in the carbonation chamber for a period of either 10 minutes or 20 minutes. Each cylindrical sample had a diameter of approximately 7.7 mm (thus a radius of 3.85 mm) and a length of approximately 7.7 mm.

[0078] The compressive strength in Newtons of each sample was determined by using a Mecmesin (RTM) BFG500N force gauge in the manner as described in the Detailed Description of the Invention. The strength in MPa was determined by the following formula:

[00001]$\mathrm{Strength}\left(\mathrm{MPa}\right)=\frac{\mathrm{Strength}\left(N\right)}{r^2}$

[0079] FIGS. 6 and 7 show the average strength in MPa of five samples of each individual carbonatable waste. These reference samples were all prepared using the process described above in the Detailed Description of the Invention, except that there no second carbonatable waste and no carbonatable binder were added to the blend.

[0080] FIGS. 2 and 3 show the average strength in MPa of five samples of each example composition described below, together with the average strength of five samples of each individual carbonatable waste. As can be seen, after carbonating for a given period of time (10 minutes or 20 minutes) the aggregate comprising a combination of carbonatable wastes is typically stronger than the aggregate comprising only ordinary portland cement or the aggregate comprising only a single carbonatable waste.

Example 1

[0081]

TABLE-US-00001 First Carbonatable Waste: 5 g Air Pollution Control Residue Second Carbonatable Waste: 5 g Biomass Ash Carbonatable Binder: NONE Carbonation Time: 10 mins Strength: 1.842 MPa

Example 2

[0082]

TABLE-US-00002 First Carbonatable Waste: 5 g Cement Bypass Dust Second Carbonatable Waste: 5 g Biomass Ash Carbonatable Binder: NONE Carbonation Time: 10 mins Strength: 1.748 MPa

Example 3

[0083]

TABLE-US-00003 First Carbonatable Waste: 5 g Biomass Ash Second Carbonatable Waste: NONE Carbonatable Binder: 5 g Portland Cement Carbonation Time: 10 mins Strength: 2.503 MPa

Example 4

[0084]

TABLE-US-00004 First Carbonatable Waste: 5 g Cement Bypass Dust Second Carbonatable Waste: NONE Carbonatable Binder: 5 g Portland Cement Carbonation Time: 10 mins Strength: 4.255 MPa

Example 5

[0085]

TABLE-US-00005 First Carbonatable Waste: 2.5 g Cement Bypass Dust Second Carbonatable Waste: 2.5 g Biomass Ash Carbonatable Binder: 5 g Portland Cement Carbonation Time: 10 mins Strength: 4.397 MPa

Example 6

[0086]

TABLE-US-00006 First Carbonatable Waste: 2.5 g Pulverised Fuel Ash Second Carbonatable Waste: 2.5 g Steel Slag Carbonatable Binder: 5 g Portland Cement Carbonation Time: 10 mins Strength: 4.427 MPa

Example 7

[0087]

TABLE-US-00007 First Carbonatable Waste: 5 g Air Pollution Control Residue Second Carbonatable Waste: 5 g Cement Bypass Dust Carbonatable Binder: NONE Carbonation Time: 10 mins Strength: 3.377 MPa

Example 8

[0088]

TABLE-US-00008 First Carbonatable Waste: 5 g Air Pollution Control Residue Second Carbonatable Waste: NONE Carbonatable Binder: 5 g Portland Cement Carbonation Time: 10 mins Strength: 1.857 MPa

Example 9

[0089]

TABLE-US-00009 First Carbonatable Waste: Air Pollution Control Residue Second Carbonatable Waste: Pulverised Fuel Ash Carbonatable Binder: Portland Cement Carbonation Time: 10 mins Strength: 2.877 MPa

Example 10

[0090]

TABLE-US-00010 First Carbonatable Waste: 25% Cement Bypass Dust Second Carbonatable Waste: 25% Pulverised Fuel Ash Carbonatable Binder: 50% Portland Cement Carbonation Time: 10 mins Strength: 5.048 MPa

Example 11

[0091]

TABLE-US-00011 First Carbonatable Waste: Biomass Ash Second Carbonatable Waste: Pulverised Fuel Ash Carbonatable Binder: Portland Cement Carbonation Time: 10 mins Strength: 3.509 MPa

Example 12

[0092]

TABLE-US-00012 First Carbonatable Waste: 5 g Air Pollution Control Residue Second Carbonatable Waste: 5 g Biomass Ash Carbonatable Binder: NONE Carbonation Time: 20 mins Strength: 2.001 MPa

Example 13

[0093]

TABLE-US-00013 First Carbonatable Waste: 5 g Cement Bypass Dust Second Carbonatable Waste: 5 g Biomass Ash Carbonatable Binder: NONE Carbonation Time: 20 mins Strength: 1.984 MPa

Example 14

[0094]

TABLE-US-00014 First Carbonatable Waste: 5 g Biomass Ash Second Carbonatable Waste: NONE Carbonatable Binder: 5 g Portland Cement Carbonation Time: 20 mins Strength: 2.942 MPa

Example 15

[0095]

TABLE-US-00015 First Carbonatable Waste: 5 g Cement Bypass Dust Second Carbonatable Waste: NONE Carbonatable Binder: 5 g Portland Cement Carbonation Time: 20 mins Strength: 8.213 MPa

Example 16

[0096]

TABLE-US-00016 First Carbonatable Waste: 2.5 g Cement Bypass Dust Second Carbonatable Waste: 2.5 g Biomass Ash Carbonatable Binder: 5 g Portland Cement Carbonation Time: 20 mins Strength: 5.424 MPa

Example 17

[0097]

TABLE-US-00017 First Carbonatable Waste: 2.5 g Pulverised Fuel Ash Second Carbonatable Waste: 2.5 g Steel Slag Carbonatable Binder: 5 g Portland Cement Carbonation Time: 20 mins Strength: 7.483 MPa

Example 18

[0098]

TABLE-US-00018 First Carbonatable Waste: 5 g Air Pollution Control Residue Second Carbonatable Waste: 5 g Cement Bypass Dust Carbonatable Binder: NONE Carbonation Time: 20 mins Strength: 4.371 MPa

Example 19

[0099]

TABLE-US-00019 First Carbonatable Waste: 5 g Air Pollution Control Residue Second Carbonatable Waste: NONE Carbonatable Binder: 5 g Portland Cement Carbonation Time: 20 mins Strength: 2.580 MPa

Example 20

[0100]

TABLE-US-00020 First Carbonatable Waste: Air Pollution Control Residue Second Carbonatable Waste: Pulverised Fuel Ash Carbonatable Binder: Portland Cement Carbonation Time: 20 mins Strength: 4.561 MPa

Example 21

[0101]

TABLE-US-00021 First Carbonatable Waste: 25% Cement Bypass Dust Second Carbonatable Waste: 25% Pulverised Fuel Ash Carbonatable Binder: 50% Portland Cement Carbonation Time: 20 mins Strength: 6.480 MPa

20 Example 22

[0102]

TABLE-US-00022 First Carbonatable Waste: Biomass Ash Second Carbonatable Waste: Pulverised Fuel Ash Carbonatable Binder: Portland Cement Carbonation Time: 20 mins Strength: 5.110 MPa