METHODS FOR THE RETRIEVAL OF AGGREGATE FROM WASTE CONSTRUCTION MATERIAL BY GRINDING

Abstract

Methods for the retrieval of aggregates from waste construction material by grinding in a ball mill or on a compressive grinder, which are useful in the recycling of waste construction material, especially in the recycling of concrete or mortar. Also, cleaned aggregates obtained from waste construction material by grinding and their use on the production of new construction materials.

Claims

1. A method for the retrieval of aggregates from waste construction material, the method comprising a step of grinding the waste construction material, wherein the grinding is done in a semi-autogeneous mill or on a compressive grinder.

2. A method as claimed in claim 1, wherein the grinding is done in a ball mill or in an agitation mill, and the filling degree of the mill is not higher than 60%, based on the volume of the mill.

3. A method as claimed in claim 1, wherein the grinding is done in a ball mill or in an agitation mill, and the mass ratio of waste construction material to grinding media is 0.2 to 3.

4. A method as claimed in claim 1, wherein the grinding is done in a ball mill or an agitation mill, and the grinding media is selected from balls, rods, pebbles, or pieces of steel, zirconium oxide, aluminum oxide, ceramics, natural stone, concrete, or mortar.

5. A method as claimed in claim 1, wherein the grinding is done in a ball mill or an agitation mill, and the grinding media has a minimum size which is larger than the maximum particle size of the aggregate to be retrieved.

6. A method as claimed in claim 1, wherein a grinding aid is added before and/or during the grinding of the waste construction material.

7. A method according to claim 6, wherein the grinding aid is selected from the group consisting of polycarboxylate ethers, alkanolamines, sugars, sugar acids, hydrogenated sugars, super absorbent polymers, glycols, glycerine, calcium formiate, and mixtures thereof.

8. A method as claimed in claim 6, wherein the grinding aid is added in an amount of 0.01-10 w %, relative to the total dry weight of the waste construction material.

9. A method as claimed in claim 1, wherein the method additionally comprises a step of carbonation of the waste construction material.

10. A method as claimed in claim 9, wherein the carbonation of the waste construction material is effected during the grinding of the waste construction material.

11. Aggregates obtained in a method as claimed in claim 1.

12. Aggregates according to claim 11, wherein the difference between the water absorption of an aggregate obtained in a method comprising a step of grinding the waste construction material, wherein the grinding is done in a semi-autogeneous mill or on a compressive grinder and the water absorption of the same fresh aggregate is not more than 300% of the water absorption of the same fresh aggregate.

13. A construction material comprising the aggregates as claimed in claim 11.

14. A construction material comprising at least a binder and an aggregate as claimed in claim 11, wherein the aggregates make up at least 30 w % of the total weight of aggregates.

15. A method of reducing the water demand of construction materials, the method comprising a step of replacing fresh aggregate by aggregates as claimed in claim 12.

16. A method of reducing the content of binder in construction materials while keeping a constant strength, the method comprising a step of replacing fresh aggregate by aggregates as claimed in claim 12.

17. A method as claimed in claim 15, wherein the replacement level of fresh aggregate by aggregates is at least 30 w % of the total weight of aggregates.

Description

EXAMPLES

[0129] The following table 1 shows an overview of chemicals used.

TABLE-US-00001 TABLE 1 Raw materials used PCE-1 Co(poly-acrylate-poly-methacrylate) with Mn = 5000 g/mol and methoxy- terminate dpolyethylenoxide side chain (Mn = 3000 g/mol); molar ratio carboxylate:side chain = 4.5 PCE-2 Co(poly-acrylate-poly-methacrylate) with Mn = 5000 g/mol and methoxy-terminated polyethylenoxide side chain (Mn = 1000 g/mol); molar ratio carboxylate:side chain = 0.8 PCE-3 Co(poly-acrylate-poly-methacrylate) with Mn = 5000 g/mol and methoxy-terminated polyethylenoxide side chain (Mn = 500 g/mol); molar ratio carboxylate:side chain = 1.0 PCE-4 Copolymer of methallylalcohol started polyethylenoxide (Mn = 2400 g/mol), acrylic acid, and 2-hydroxyethylacrylate with a molar ratio of 0.625:0.416:2.80 Ca(HCOO).sub.2 Calcium formiate; Sigma-Aldrich (>99%) Melasse Untreated melasse from sugar production from raw sugar (solid content appr. 80 Gew.-%; pH = 5.5) TIPA Triisopropanolamine, Sigma-Aldrich (95%)

Trial 1Aggregate Retrieval

[0130] The waste construction material used was a pre-crushed concrete from demolition (with primary aggregate sand and gravel 0-32 mm).

[0131] A ball mill with a diameter of 60 cm and a length of 50 cm was used.

[0132] For milling operations, waste construction material was introduced into the mill together with the grinding media as indicated in below tables. Grinding was effected for 30 min at medium speed. Grinding was done at 20? C. and a relative humidity of the process air of 75%.

[0133] Additional grinding aids, where present, were dosed with a total amount of 0.125 w % relative to the waste construction material. Carbonation, where used, was effected by introducing CO.sub.2 into the mill with the process air (6% CO.sub.2 in process air).

[0134] Sieve line of aggregates was determined as described in standard EN 933-1.

[0135] The following table 2 shows an overview of the examples done.

TABLE-US-00002 TABLE 2 Examples (all examples according to the present invention) Grinding Mass Filling Example media ratio*.sup.2 degree*.sup.3 Additional 1 Steel balls 1 17% None 2 Ceramic 1 17% None balls 3 Concrete*.sup.1 1 17% None 4 Concrete*.sup.1 1 25% None 5 Concrete*.sup.1 1 33% None 7 Concrete*.sup.1 0.5 25% None 8 Concrete*.sup.1 2 25% None 9 Concrete*.sup.1 1 33% carbonation 10 Concrete*.sup.1 1 25% carbonation PCE-1 & PCE-3 (weight ratio 1:1) 11 Concrete*.sup.1 1 25% carbonation PCE-1 & PCE-3 & TIPA (weight ratio 1:1:0.4) 12 Concrete*.sup.1 1 25% carbonation PCE-4 & Ca(HCOO).sub.2 13 Concrete*.sup.1 1 25% carbonation molasse & PCE-2 (weight ratio 2:1) 14 Concrete*.sup.1 1 25% PCE-3 & PCE-1 (weight ratio 1:1) *.sup.1pieces of fully cured concrete (irregular shape, appr. 20 cm diameter) *.sup.2mass ratio of waste construction material: grinding media in the mill *.sup.3% of total mill volume

[0136] The following table 3 shows an overview of the results obtained.

TABLE-US-00003 TABLE 3 Results (examples 1-14 according to the present invention) Specific Sieve line of aggregate*.sup.6 [% passing] Cleaning powder 0.063 0.125 0.5 1 2 4 8 16 Expl. efficiency*.sup.4 abrasion*.sup.5 mm mm mm mm mm mm mm mm 1 58% 74 21 31 41 42 43 46 70 78 2 56% 41 11 17 24 26 29 35 63 72 3 54% 38 8 16 24 28 32 41 55 82 4 43% 27 9 12 19 23 30 39 66 74 5 37% 23 6 9 15 19 26 36 65 73 7 58% 46 12 17 28 33 40 49 72 80 8 37% 19 6 9 13 16 22 31 63 72 9 63% 30 5 9 19 24 31 39 64 68 10 75% 54 12 17 33 39 45 51 60 74 11 75% 49 12 17 31 37 43 50 60 75 12 70% 53 11 15 29 35 42 49 58 72 13 77% 59 11 16 31 36 42 48 58 71 14 73% 49 11 16 30 36 42 49 59 73 *.sup.4cleaning of aggregate determined as water absorption; water absorption of aggregate determined according to EN 1097-6. The percentages given are relative to untreated waste construction material which was set at 0%. *.sup.5in w %/hour *.sup.632 mm maximum particle size in all cases (100% passing)

[0137] The circularity of aggregates retrieved by the inventive method was between 0.73-0.80 when measured according to the method of Cox as described in the paper by Blott cited above. The circularity of the aggregate retrieved from pre-crushing and not treated in a method by the present invention was 0.68. The circularity of the same type of aggregate but never used to make a construction material was 0.8.

[0138] A comparison of examples 1-3 shows that the use of steel balls as grinding media leads to especially high cleaning efficiency and specific powder abrasion. However, there is a risk of contamination with abraded steel of the aggregates obtained when using steel balls as grinding media. In addition, a larger amount of small particles with a size <0.063 mm resulted. The use of ceramic balls also leads to satisfying results. The amount of very small particles was significantly lower and the particle size distribution steadier as compared to the grinding with steel balls which is beneficial. Surprisingly, the use of concrete pieces as grinding media also led to very satisfying results that are comparable to the use of ceramic balls (cf examples 2 and 3). However, in case of concrete pieces used as grinding media, there is no risk of unwanted contamination of the aggregates obtained.

[0139] A comparison of examples 3-5 shows that an increase in the filling degree leads to a lower cleaning efficiency and also a lower specific powder abrasion. Lower cleaning efficiency and lower specific powder abrasion is unwanted. Nevertheless, a higher degree of filling in the mill leads to a higher material throughput at the same residence time, thus leading to improved overall process efficiency. The filling degree must thus be chosen to enable a compromise between cleaning efficiency and material throughput. The aggregates obtained tend to be coarser when the filling degree is higher.

[0140] A comparison of examples 4, 7, and 8 shows that an increase in mass ratio of waste construction material to grinding media in the mill reduces the cleaning efficiency and the specific powder abrasion. Reduced cleaning efficiency and reduced specific powder abrasion is unwanted. Nevertheless, if the mass ratio of waste construction material:grinding media becomes too low, material throughput and thus overall process efficiency might be too low. This mass ratio must thus be chosen to enable a compromise between cleaning efficiency and material throughput. The aggregates obtained tend to be coarser when this mass ratio is increased.

[0141] Example 9 shows that carbonation leads to an increase in specific powder abrasion (compare to example 5). Also, the aggregates obtained tend to be finer when grinding is done with carbonation.

[0142] Finally, examples 10-14 show that the method for retrieving aggregates can be additionally improved by the addition of grinding aids. This can be seen for example from the specific powder abrasion which is higher for examples 10-14 as compared to examples 5 or 9.

[0143] The following table 4 shows the results of the water absorption. Water absorption was measured according to standard EN 1097-6:2013-09.

[0144] The gravel used as a reference was fresh crushed gravel used as received.

TABLE-US-00004 TABLE 4 Water absorption of cleaned aggregate (examples 1-14 according to the present invention) Water absorption of aggregate with particle size of Example 0.063-4 mm 4-8 mm 8-16 mm 16-32 mm Gravel 0.9 0.8 0.8 0.7 Untreated waste 12.0 8.0 6.0 3.0 construction material 1 2.30 1.90 2.79 2.48 2 2.82 2.01 2.94 2.29 3 4.58 3.10 2.13 1.87 4 4.95 2.58 2.68 2.85 5 6.09 2.65 2.33 3.31 7 4.52 1.98 1.99 2.36 8 5.60 2.88 3.17 2.57 9 8.49 3.62 2.89 2.41 10 5.92 2.78 1.63 1.19 11 5.20 2.38 1.90 1.30 12 5.70 2.40 1.80 1.68 13 5.62 2.29 1.59 1.27 14 5.57 2.37 1.89 1.47

[0145] Similar observations can be made as discussed for the results of table 3. Especially it can be seen from the results of table 4, that aggregates retrieved from a method of the present invention have much lower water absorption as compared to untreated waste construction material. A lower water absorption of the aggregates is beneficial as this will allow to formulate cementitious materials, especially concrete or mortar, with less mixing water and thus higher strength. It can also be seen that at least for the particle size groups 4/8, 8/16, and 16/32, the cleaned aggregate has a water absorption which is similar to the water absorption of fresh gravel of the same particle size group. For the particle size group 0.063/4 the observed differences are bigger which may be due to the presence of fine ground mineral powder resulting from the binder in this particle size group.

Trial 2Tests in Mortar

[0146] Aggregates retrieved in a method of the present invention were tested in a mortar formulation. The dry mortar was composed of CEM II/B-LL and aggregates in the amounts as indicated in below table 5. Aggregate used was either sand, untreated waste construction material, or aggregate retrieved in a method of the present invention as indicated in below table 5. Dry mortar was mixed with water to realize a water:binder ratio of 0.4. Mixing was done on a Hobart mixer for 3 min. A commercial polycarboxylate superplasticizer (SikaViscoCrete 3088 available from Sika Schweiz AG), was added together with the mixing water tin an amount of 1 w % relative to the binder content.

[0147] All aggregates used were water saturated. The grading curve of any aggregate used was as follows:

TABLE-US-00005 Particle size [mm] 0.063 0.125 0.250 0.50 1.0 2.0 4.0 Vol-% passing 0% 6.7% 15.8 28.2 45.1 68.3 100

[0148] The Blaine fineness of such a coarse grading cannot be measured with meaningful results.

[0149] The following table 5 shows an overview of the examples realized and the results measured. Slump flow was measured according to standard EN 12350-5:2019-09. The funnel flow time was measured in accordance with standard EN 12350-9:2010-12.

TABLE-US-00006 TABLE 5 Aggregate testing in mortar (examples 2-3 and 2-6 are according to the present invention) CEM II/ Slump Funnel B-LL Aggregate Aggregate flow flow Example [Vol-%] [Vol-%] (type) [mm] time [s] 2-1 56.9 43.1 Sand 218 3.6 2-2 56.7 43.3 CDW*.sup.1 162 4.8 2-3 56.3 43.7 Aggregate*.sup.2 228 3.1 2-4 54.1 45.9 Sand 240 2.8 2-5 53.9 46.1 CDW*.sup.1 198 3.1 2-6 53.9 46.1 Aggregate*.sup.2 276 2.4 *.sup.1CDW: waste construction material, untreated *.sup.2Aggregate: aggregate retrieved in a method of the present invention

[0150] It can be seen from the above table 5, that when aggregates retrieved by a method of the present invention are used in a mortar formulation, this mortar formulation has an increased slump flow and a reduced funnel flow time as compared to the same mortar but where untreated sand or untreated waste construction material is used. This is the case when the grading curve of the respective aggregates are the same. An increased slump flow and/or a reduced funnel flow time are indicative for a lower water demand. The amount of mixing water in a formulation with aggregates retrieved by a method of the present invention can be reduced to adapt this formulation to the same rheology of a formulation using e.g. standard sand. A reduced amount of mixing water is desirable as this will lead to increased strength of the cured formulation. Similarly, the amount of cement and water can be reduced in a formulation using aggregates retrieved by a method of the present invention to achieve the same rheology and strength as a formulation using e.g. standard sand. By this high level of original sand replacement are possible and/or cement savings can be realized.

Trial 3Tests in Mortar

[0151] Tests of aggregates obtained in a method of the present invention were conducted as follows: 750 g cement (CEM I 42.5N), 141 g limestone filler (Nekafill 15 from Netstal AG), and 2999 g aggregates (sand, concrete demolition waste and/or aggregate according to the present invention respectively) were mixed in the dry state for 1 minute in a Hobart mixer. The aggregates added were of the type as indicated in below table 6. The mass ratios of aggregates used are also given in below table 6. Then water was added to realize a water to cement ratio of 0.46. The mixing water contained PCE-1 in an amount of 0.6 w % relative to the cement. Then mixing was continued for 3 minutes. Slump flow was measured according to standard EN 12350-5:2019-09 after the times indicated in below table 6. All aggregates used were water saturated.

[0152] The grading curve of any aggregate used was as follows:

TABLE-US-00007 Particle size [mm] 0.063 0.125 0.250 0.50 1.0 2.0 4.0 8.0 w % passing 0.1 0.4 1.6 6.9 16.2 27.4 43.9 95.7

TABLE-US-00008 TABLE 6 Aggregate testing in mortar (examples 3-3 and 3-5 are according to the present invention) Example 3-1 3-2 3-3 3-4 3-5 Sand 100 70 70 50 50 CDW*.sup.1 0 30 0 50 0 Aggregate*.sup.2 0 0 30 0 50 Slump flow @ 0 min [mm] 205 135 204 121 195 Slump flow @ 30 min [mm] 206 131 202 118 205 Slump flow @ 60 min [mm] 204 128 200 116 196 Slump flow @ 90 min [mm] 202 118 195 110 196 Slump flow @ 120 min [mm] 194 116 191 110 192 *.sup.1CDW: waste construction material, untreated *.sup.2Aggregate: aggregate retrieved in a method of the present invention

[0153] It can be seen from the results in above table 6 that at a replacement level of fresh aggregate of 30 w % by aggregates obtained in a method of the present invention no significant changes in the slump flow are observed (cf examples 3-1 and 3-3). Hence, replacement at such level is possible without taking any further measures. To the contrary, where untreated waste construction material of the same grading is used, a significant loss of slump flow is observed when 30 w % of fresh aggregate are replaced by such untreated waste construction material (cf examples 3-1 and 3-2).

[0154] At a replacement level of fresh aggregate of 50% by aggregates obtained in a method of the present invention, the changes in slump flow observed are acceptable for typical applications (cf example 3-1 and 3-5). When untreated waste construction material of the same grading is used significantly lower slump flow results (cf examples 3-1 to 3-4).