GB2268174A - Lightweight aggregate - Google Patents
Lightweight aggregate Download PDFInfo
- Publication number
- GB2268174A GB2268174A GB9212075A GB9212075A GB2268174A GB 2268174 A GB2268174 A GB 2268174A GB 9212075 A GB9212075 A GB 9212075A GB 9212075 A GB9212075 A GB 9212075A GB 2268174 A GB2268174 A GB 2268174A
- Authority
- GB
- United Kingdom
- Prior art keywords
- pellets
- polystyrene beads
- lightweight aggregate
- mix
- cement
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000008188 pellet Substances 0.000 claims abstract description 55
- 239000011324 bead Substances 0.000 claims abstract description 42
- 239000004793 Polystyrene Substances 0.000 claims abstract description 33
- 229920002223 polystyrene Polymers 0.000 claims abstract description 33
- 239000000203 mixture Substances 0.000 claims abstract description 29
- 239000004568 cement Substances 0.000 claims abstract description 24
- 239000000446 fuel Substances 0.000 claims abstract description 19
- 239000004794 expanded polystyrene Substances 0.000 claims abstract description 8
- 238000002156 mixing Methods 0.000 claims abstract description 7
- 238000004519 manufacturing process Methods 0.000 claims abstract description 6
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 5
- 239000007788 liquid Substances 0.000 claims abstract description 5
- 239000002245 particle Substances 0.000 claims abstract description 5
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims abstract description 4
- 239000000920 calcium hydroxide Substances 0.000 claims abstract description 4
- 229910001861 calcium hydroxide Inorganic materials 0.000 claims abstract description 4
- 235000011116 calcium hydroxide Nutrition 0.000 claims abstract description 4
- 238000009835 boiling Methods 0.000 claims abstract description 3
- 238000000034 method Methods 0.000 claims description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 14
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 10
- 239000000945 filler Substances 0.000 claims description 7
- 239000001569 carbon dioxide Substances 0.000 claims description 5
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 4
- 239000004094 surface-active agent Substances 0.000 claims description 3
- 238000005245 sintering Methods 0.000 claims description 2
- 239000007787 solid Substances 0.000 claims description 2
- 230000036571 hydration Effects 0.000 claims 1
- 238000006703 hydration reaction Methods 0.000 claims 1
- 239000002956 ash Substances 0.000 description 14
- 239000010881 fly ash Substances 0.000 description 8
- 239000004567 concrete Substances 0.000 description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 239000003245 coal Substances 0.000 description 4
- 239000011505 plaster Substances 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- 239000011398 Portland cement Substances 0.000 description 2
- 239000004566 building material Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000003546 flue gas Substances 0.000 description 2
- 239000008187 granular material Substances 0.000 description 2
- 150000004677 hydrates Chemical class 0.000 description 2
- 239000004615 ingredient Substances 0.000 description 2
- 239000004576 sand Substances 0.000 description 2
- 238000009736 wetting Methods 0.000 description 2
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000010882 bottom ash Substances 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 239000011872 intimate mixture Substances 0.000 description 1
- 239000003562 lightweight material Substances 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 239000000375 suspending agent Substances 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/02—Agglomerated materials, e.g. artificial aggregates
- C04B18/027—Lightweight materials
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Civil Engineering (AREA)
- Ceramic Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Processing Of Solid Wastes (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
A method of making a lightweight aggregate comprises mixing together less than 80% by weight of pulverized fuel ash, greater than 20% by weight of cement and an amount of expanded polystyrene beads having a particle size of less than 2.5 millimetres, such that the volume of polystyrene beads is from 15% to 80% of the total volume of the final mixture, to form a pelletisable mix, forming the mix into pellets having a diameter less than 15 millimetres and curing the pellets in a moist atmosphere at a temperature below the boiling point of any expanding agent within the polystyrene beads. Building blocks prepared from this lightweight aggregate, in which liquid or powdered fuel, or hydrated lime, may replace some of the cement.
Description
LIGHTWEIGHT AGGREGATE
The present invention relates to a lightweight aggregate in the form of pellets or granules and, in particular, to a lightweight aggregate in the form of pellets or granules for use in the building industry.
The pellets of aggregate are suitable, for example, for making structural or non-structural building blocks, for lightweight fill and as a filler for lightweight concrete, for example lightweight concrete screeds.
This invention also importantly incorporates pulverized fuel ash, which is a waste product from coal-fired power stations.
It has previously been shown that the incorporation of expanded polystyrene beads in lightweight concrete, cement and plaster mixes can result in lightweight building materials.
JP-60176976 teaches the production of lightweight building material from mixtures of an inorganic binder, a lightweight aggregate such as polystyrene beads and reinforcing fibres.
GB-1118621A relates to cement or plaster mixes comprising cement or plaster, expanded polystyrene, filler and a suspending agent.
GB-2095227A teaches a method of making lightweight concrete comprising cement, expanded polystyrene, sand, water and a surfactant.
US-3764357A teaches the preparation of lightweight concrete and plaster by a method comprising several steps to ensure that the lightweight aggregate is uniformly mixed with the cementaceous material and other relatively heavy ingredients of the mixes.
GB-2100244A teaches the production of insulating building blocks comprising.a cement, a filler and a lightweight material, for example polystyrene, comprising up to 25% of the volume of the block.
It is also known to produce a lightweight aggregate in the form of pellets from pulverised fuel ash and a relatively small proportion of lime or cement, calculated on the content of fuel ash.
It has never previously, however, been considered feasible to incorporate large quantities of expanded polystyrene beads in such pellets because it has been thought that the presence of polystyrene would interfere with the pelletising or granulating process by preventing compaction of the fuel ash/cement mixture and that the polystyrene would migrate towards the surface of the pellets during formation thereof, so that the pellets would consist of a core of solid material and a soft surface layer mainly of polystyrene beads.
It has now been found that a lightweight aggregate containing large quantities of expanded polystyrene beads can be successfully produced.
Accordingly, the present invention provides a method for forming a lightweight aggregate comprising mixing together less than 80% by weight of pulverised fuel ash, greater than 20% by weight of cement and an amount of expanded polystyrene beads having a particle size of less than 2.5 millimetres, such that the volume of polystyrene beads is from 15% to 80% of the total volume of the final mixture, to form a pelletisable mix, forming the mix into pellets having a diameter of less than 15 millimetres and curing the pellets in a moist atmosphere at a temperature below the boiling point of any expanding agent within the polystyrene beads.
The preferred proportion of cement in the mixture is from greater than 20% too35% by weight, the preferred size of the polystyrene beads is less than 1 millimetre and the preferred diameter of the pellets is from 3 to 9 millimetres.
The pellets are preferably cured at a temperature which is not above 500C and hardened sufficiently in 1 to 2 days, depending on the curing temperature.
The rate of curing of the pellets can be increased if pulverised fuel ash, which retains heat from the power station in which it is produced, is utilized in the process. The rate of curing can also be increased by using rapid hardening cement and/or standard hardening accelerators.
Fuel ash which is preferred for use in the preparation of the lightweight aggregate of the present invention is produced as waste from coal fired power stations which burn hard coal, for example coal fired power stations found in the United Kingdom. The form of fuel ash preferred is either as dry ash or a sticky mix comprising approximately 12 to 15% water.
Where the fuel ash for use in preparing the aggregate is already moist, for example in the form of a sticky mix, additional water to form a pelletisable mix may not be required. Where the fuel ash is used is in the form of dry ash or does not contain sufficient water to form a pelletisable mix, additional water is required during the mixing of the solid batch components and polystyrene beads. The cement used in the process is preferably Portland cement. The pulverised fuel ash used in the process is preferably fly ash.
It is also possible to add an inert filler in an amount of up to 20% by weight of the material forming the pellets (other than the polystyrene). Such fillers should be very fine material, preferably of particle size of less than 20 micrometres. Examples of such inert fillers are furnace bottom ash, ground slag, sand or finely ground quarry waste, such as rock dust.
During curing, the cement in the pellet hydrates. To reduce shrinkage, pellets which have been at least partially cured are placed in an atmosphere which includes carbon dioxide which reacts with the hydrates in the pellet. The resulting pellets have increased strength and have undergone reduced drying shrinkage.
Commonly, the source of carbon dioxide is the atmosphere. Other sources include carbon dioxide produced from "burnt out" polystyrene beads or from flue gases from coal fired power stations. In addition to the carbon dioxide in the flue gases, heat for the curing process is also usually present, providing an economical method for curing the pellets.
If desired, after curing and hardening the pellets may be modified by heating. At temperatures from between approximately 100 C to 3000C the polystyrene beads exposed on the pellet face collapse from their expanded form to their unexpanded form.
This process is known as "melt-out". Higher temperatures may be used to remove the exposed polystyrene beads on the surface of the pellets, a process known as "burn out". The hardened pellets are strong enough to withstand the internal forces produced by any further expansion of the polystyrene beads on such heating. Pellets which have had the exposed polystyrene beads removed from their surface or collapsed on their surface have reduced size by the removal of the projected polystyrene and the bulk densities are increased. The pellets may also have increased thermal properties.
It may be that pellets which have undergone "burn out" or "melt out", i.e have had the polystyrene beads removed from the surface or collapsed on the surface thereof are more popular in the building industry than those pellets where the polystyrene beads remain because of their external appearance.
A further embodiment of the present invention is a method of preparing a lightweight aggregate wherein up to 15% by weight of liquid of powdered fuel is used to replace the same amount of cement in the mixture.
Pellets which have been prepared with the inclusion of liquid or powdered fuel are hardened by sintering at a temperature in the range of from 8000C to 14000C.
This heating further increases the porosity of the pellets by burning out the combustable (organic) components of the pellets. At these temperatures, the moisture in the polystyrene beads contained within the pellets vaporizes and forms voids, the silica within the pulverized fuel ash melts, vitrifies and on cooling forms a coating around the pellet. During the preparation of any embodiment of the present invention from 1 to 6% by weight of hydrated lime may be used to replace the same amount of cement in the mixture.
The pelletisable mix according to the present invention is preferably made by weighing out the desired quantities of fuel ash and cement, or fuel ash, liquid or powdered fuel and cement, measuring out the desired relative voluRepof polystyrene beads, wetting the surface of the beads and mixing the beads with the weighed components. Wetting the beads encourages the pulverized fuel ash and/or other components of the mix to stick to the polystyrene beads and destroys the electrostatic properties of the beads. Only a proportion of the total water needed is required to wet the beads initially.
Pretreatment of the polystyrene beads with surfactants or other surface treating agents may be carried out to aid compatibility with the other ingredients of the pellets. The pellets are preferably formed on a pan pelletiser with a water spray, if additional water is required.
The pellets produced according to the present invention have a bulk dry density in the range of from 200 to 750 kilograms per cubic metre. Those pellets with a bulk dry density of 350 kilograms per cubic metre, or below, are suitable for use in preparing thermal building blocks and those pellets with a bulk dry density above 350 kilograms per cubic metre may be used to prepare "standard" building blocks.
The pellets produced according to any embodiment of the invention may be used for the manufacture of building blocks by adding them to a matrix and moulding them in the standard fashion. The preferred matrix mix is formed from cement, pulverized fly ash, hydrated lime and water. Building blocks prepared with the pellets of the present invention have performances closely approaching those of aerated concrete blocks.
In addition, discrete polystyrene beads, coated with cement and/or fuel ash can be incorporated into the building blocks. Such coated beads may be "left over" from the process of making the pellets according to the present invention. Use of such coated beads reduces the quantity of matrix mix required. The resulting blocks are stronger and have increased thermal properties.
As used herein, the term "thermal building block" is intended to cover building blocks with a bulk dry density of 550 kilograms per cubic metre, or below and the term "standard building block" is intended to cover building blocks with a bulk dry density above 550 kilograms per cubic metre.
The present invention is further described by reference to the following Examples;
Example
A batch comprising 35% by weight of Portland cement and 65% by weight of fly ash (source: West
Burton) was weighed out and the bulk volume of the batch assessed. For each 100 parts by volume of the batch 337 parts by volume of polystyrene beads of diameter less than 1 millimetre were measured out.
The polystyrene beads were moistened with water and mixed with sufficient material taken randomly from the batch to produce a thin adherent coating on the beads. The remainder of the batch and a small amount of water was then added and mixing was continued to produce an intimate mixture of flyash, cement and polystyrene beads, the polystyrene beads comprising 77% by volume of the mixture.
The mixture was fed into a 1 metre pan pelletiser with a water spray. The angle of tilt of the pan, the pan speed and depth and the water spray were adjusted until the pellets leaving the pan were hard enough to withstand handling and the major proportion were in the size range 3 to 9 millimetres.
The pellets were passed to storage in a high moisture atmosphere and allowed to hardened at ambient temparature for two days.
The hardened pellets had a bulk density of 280 kg/m3 air dried and an average crushing strength in excess of 82N/cm2 as measured on a Schleuniger tablet test machine between filter paper linings to avoid point loading on the pellets.
Claims (18)
1. A method of making a lightweight aggregate comprising mixing together less than 80% by weight of pulverized fuel ash, greater than 20% by weight of cement and an amount of expanded polystyrene beads having a particle size of less than 2.5 millimetres, such that the volume of polystyrene beads is from 15% to 80% of the total volume of the final mixture, to form a pelletisable mix, forming the mix into pellets having a diameter less than 15 millimetres and curing the pellets in a moist atmosphere at a temperature below the boiling point of any expanding agent within the polystyrene beads.
2. A method as claimed in claim 1 wherein the polystyrene beads have a particle size of less than 1 millimetre.
3. A method as claimed in claim 1 or claim 2 wherein the mix is formed into pellets having a diameter in the range of from 3 to 9 millimetres.
4. A method as claimed in any one of the preceding claims wherein prior to mixing with the solid components of the mix, the polystyrene beads are treated with a surfactant, or other surface treating agents, or combinations of two or more thereof.
5. A method as claimed in any one of the preceding claims further including the addition of water to form the pelletisable mix.
6. A method as claimed in any one of the preceding claims wherein up to 20% by weight of the material (other than the pellets) is an inert filler.
7. A method as claimed in any one of the preceding claims wherein the pellets are formed using a pan pelletiser.
8. A method as claimed in any one of the preceding claims further including when the pellet is at least part hardened allowing the products of hydration in the pellet to react with carbon dioxide.
9. A method as claimed in any one of the preceding claims further including after curing treating the pellet to a temperature from 1000C to 1300C.
10. A method as claimed in any one of the preceding claims further including, after curing, heating the pellets to temperatures above 2500C.
11. A method as claimed in any one of the preceding claims wherein up to 15% by weight of liquid or powdered fuel is used to replace the same amount of cement in the mixture.
12. A method as claimed in claim 11 further including sintering the pellets at a temperature in the range of from 8000C to 14000C.
13. A method as claimed in any one of the preceding claims wherein from 1 to 6% by weight of hydrated lime is used to replace the same amount of cement in the mixture.
14. A lightweight aggregate whenever prepared by a method as claimed in any one of claims 1 to 7.
15. A lightweight aggregate as claimed in claim 11 having a bulk dry density of from 200 to 750 kg/m3.
16. A lightweight aggregate as claimed in claim 11 preferably having a bulk dry density of 350 kg/m3 or below.
17. A building block whenever prepared from the lightweight aggregate as claimed in any one of claims 12 to 14.
18. A building block as claimed in claim 15 having a block density of above 350 kg/m3.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9212075A GB2268174A (en) | 1992-06-08 | 1992-06-08 | Lightweight aggregate |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9212075A GB2268174A (en) | 1992-06-08 | 1992-06-08 | Lightweight aggregate |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9212075D0 GB9212075D0 (en) | 1992-07-22 |
| GB2268174A true GB2268174A (en) | 1994-01-05 |
Family
ID=10716702
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9212075A Withdrawn GB2268174A (en) | 1992-06-08 | 1992-06-08 | Lightweight aggregate |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2268174A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008052753A3 (en) * | 2006-10-30 | 2008-07-31 | Michael C Faas Gmbh Dr | Process for producing lightweight rock particles, lightweight rock particles which can be obtained by this process and use of these for producing building materials |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3834751A1 (en) * | 1988-10-12 | 1990-04-19 | Manfred Ackermann | Process for producing light-weight aggregates having a low density |
| WO1992010438A1 (en) * | 1990-12-07 | 1992-06-25 | National Power Plc | Lightweight aggregate |
-
1992
- 1992-06-08 GB GB9212075A patent/GB2268174A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3834751A1 (en) * | 1988-10-12 | 1990-04-19 | Manfred Ackermann | Process for producing light-weight aggregates having a low density |
| WO1992010438A1 (en) * | 1990-12-07 | 1992-06-25 | National Power Plc | Lightweight aggregate |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008052753A3 (en) * | 2006-10-30 | 2008-07-31 | Michael C Faas Gmbh Dr | Process for producing lightweight rock particles, lightweight rock particles which can be obtained by this process and use of these for producing building materials |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9212075D0 (en) | 1992-07-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |