A mixture for use in the processing of aerated concrete recyclate, an aerated concrete element produced using this mixture and a process for production thereof

Abstract

A mixture for the recycling of an aerated concrete recyclate comprising 60 to 90 wt. % of a cement component; 4 to 35 wt. % of a lime component, and 0.5 to 5.0 wt. % of an expander component. The use of this mixture for the production of an aerated concrete element from an aerated concrete recyclate and the method of production of this element.

Description

[0001] A MIXTURE FOR USE IN THE PROCESSING OF AERATED CONCRETE RECYCLATE, AN AERATED CONCRETE ELEMENT PRODUCED USING THIS MIXTURE AND A PROCESS FOR PRODUCTION THEREOF Fiel d of the invention

[0002] The present invention relates to a mixture for use in the processing of an aerated concrete recyclate, to a building element made from the aerated concrete recyclate and to a process for production the same.

[0003] Prior art

[0004] An aerated concrete or an autoclaved aerated concrete (AAC) is a type of a lightweight concrete with good thermal and sound insulation properties. Today, this material has been widely used, for example, in the production of blocks such as Ytong* produced by Xella, or various aerated concrete shaped elements. In addition to the already mentioned good insulating properties, the advantage of the aerated concrete blocks is their relatively low weight and the fact that their size can be easily adjusted during construction, for example by cutting, either by a machine or simply by using a hand saw. These modifications generate a large amount of waste on construction sites, the use of which depends not only on its purity but also on the size of the particles forming it. Large fragments of the aerated concrete are now used to replace aggregates or are ground up and recycled to the production of the aerated concrete, together with the dust particles of aerated concrete that are produced during cutting. The possibility of returning the aerated concrete to the production is conditional on its purity. This is relatively easy to ensure for the waste produced from new aerated concrete blocks on construction sites. It is somewhat more difficult and costly to meet this condition in the case of recycling the aerated concrete from demolition waste, which must first be thoroughly sorted and stripped of all other materials that could adversely affect the properties, either aesthetic or mechanical, including strength characteristics, of the aerated concrete products, in the manufacture of which part of the raw material would be replaced by recycled aerated concrete.

[0005] The aerated concrete dust has been used for decades to produce a new aerated concrete. Depending on the product, the proportion of the aerated concrete dust in new products is currently up to 15 percent. Another option for recycling the aerated concrete is its use in cement production, where it can partially replace traditional raw materials such as limestone or clinker.

[0006] The disadvantage of all the known ways of using the aerated concrete recyclate so far is still the relatively low proportion of the recyclate in the new products. Other disadvantages Include the need for thorough sorting of the aerated concrete from the construction rubble to get rid of all other materials, which is associated with considerable costs for the operation and maintenance of the sorting stations. Also not negligible are the additional costs associated with the treatment of the recyclate, such as grinding and possibly drying, which are very energy-consuming processes.

[0007] Given the large quantities of the aerated concrete waste generated, whether In the production, on the construction sites or during the demolition of old buildings, there is therefore a constant need to develop technologies to enable a greater proportion of the recycled aerated concrete to be used in new products. At the same time, such technologies should eliminate in the maximum extend the above-mentioned disadvantages of the state of the art. Summary of the invention

[0008] According to the first aspect, the present invention relates to a dry mixture comprising a cement component, a lime component, an expander component, and a mixing water. More particularly, said mixture comprises 60 to 90 wt. % of a cement component, 4 to 35 wt. % of a lime component and 0.5 to 5.0 wt. % of an expander component, always based on the total weight of the mixture.

[0009] As the cement component, preferably a common Portland cement CEM 142.5 R can be used, for example, as the lime component, a white lime CL 90-Q can be used, for example, and as the expander component, a specially treated aluminium powder such as Expandit 10, produced by Grimm Metallpulver GmbH, Roth, Germany, is used. All of the above materials are mentioned herein as the specific examples only, without limiting the scope of the present invention in any way.

[0010] Surprisingly, it has been found that if the aerated concrete recyclate is mixed with water in a suitable proportion by weight to the solids and the above mixture is added to the resulting slurry, after thorough mixing of all the components and approximately 40 minutes, a material can be obtained which has parameters similar to those of the aerated concrete. Said water to solids ratio is commonly referred to in the art as the 'water coefficient' and expresses the ratio by weight of water to all the solids in the resulting mixture. According to the present invention, the value of the water coefficient should be in the range from 0.50 to 0.55, preferably from 0.52 to 0.53. The amount of the mixture according to the present Invention which is added to the aerated concrete recyclate is selected so that the weight ratio of the aerated concrete recyclate itself, i.e. without added water, and the mixture according to the present invention is in the range from 1:3 to 3:1.

[0011] The advantage of the above described process compared to the conventional technology, in which finely ground sand is mixed with cement, lime, aluminium powder and water, the resulting mixture is left to solidify and then cured with steam in an autoclave at 200 *C, is that the whole process is selfexpanding and that this process eliminates the need of use the energy-consuming step of autoclave curing, which brings a significant reduction in production costs. Last but not least, the process described herein solves the problem of further use of the aerated concrete recyclate. In addition, the technology described here is essentially waste-free, since even the waste generated by this technology can be reused in the next production cycle.

[0012] A further advantage of the process according to the present invention is that it works with a liquid mixture which is poured into moulds from which a building element of the desired shape is removed after the mixture has solidified. Compared to the present practice, whereby a block of the aerated concrete is first made from which a building element of the desired shape is cut out after solidification, this process is advantageous in that the step of cutting the body out of the block of the aerated concrete is eliminated. Omitting the step of cutting the body from the manufactured aerated concrete block not only reduces production costs, but also eliminates the aerated concrete waste (in the form of cuttings and dust particles) that is necessarily generated during the cutting process.

[0013] In one preferred embodiment, said mixture may further comprise 3-15 wt. % of a filler, such as ground limestone, and up to 1 wt. % of refining component, such as a viscosity reducing agent, such as (superplasticizer) Peramin 149 S, for example.

[0014] Another aspect of the present invention relates to the use of the mixture according to the first aspect of the invention in the processing of the aerated concrete recyclate.

[0015] In this context, it should be noted that the 'aerated concrete recyclate' in this text is intended to mean both the aerated concrete waste from the actual production of the aerated concrete or from working with the aerated concrete products on the construction sites and the aerated concrete obtained by sorting it from demolition rubble. In addition, the aerated concrete recyclate may arise during the production of the aerated concrete such that the product produced has not reached the required parameters and has not passed a quality control. In other words, the term aerated concrete recyclate includes non-conforming pieces from production of the aerated concrete, regardless they are come from the products that do not meet shape or accuracy requirements, or the products that do not meet strength requirements, etc.

[0016] The actual processing of the aerated concrete recyclate is therefore carried out by crushing the aerated concrete recyclate, e.g. in a hammer or jaw crusher, to a grain size of less than 1 mm. If necessary, separation of unwanted construction waste components such as paper, wood, metal, glass, etc. can be ensured during the crushing process.

[0017] Subsequently, the crushed aerated concrete recyclate is gradually added to the water in the mixing device. Last, the mixture according to the first aspect of the present Invention is added. The resulting mixture is mixed until a homogeneous mass is formed. The mixing device is turned off, a sample is taken and a spillage test is performed on a PVC pad to determine the exact amount of water to be used, which is dependent on the moisture content of the starting recyclate. The spillage test shall be carried out in accordance with EN 12706 using a spillage cylinder with an internal diameter of 30 mm and a height of 50 mm. The homogeneous mass should have such a spillage that it fills the mould completely after pouring into the mould. In other words, the mixture should flow into all the 'nooks and crannies' of the mould, including the comers, without the need of use of a vibrating equipment, etc On the other hand, the mixture should not be too diluted, otherwise it would take an unreasonably long time to cure and dry the mixture. For this reason, the spillage value of the prepared homogeneous mass should be between 7.5 and 8.5 cm. If the measured spillage value is within this range, then no water needs to be added to the prepared mixture. If the spillage value is less than 7.5 cm, then the prepared mass should be diluted by adding more water. If, on the other hand, the spillage value is higher than 8 cm, then the ready-mixed mixture should be thickened by adding an additional quantity of the aerated concrete recyclate. In both cases, the mixture is again mixed thoroughly to obtain a homogeneous mass, and the spillage is checked again and, if necessary, readjusted using the above procedure. Once the desired spillage value is achieved, the liquid mixture is poured into the prepared moulds. The processing time of the prepared mixture is 5 to 10 minutes, followed by the spontaneous expansion process which takes 100 to 120 minutes. After the mixture sets, it is advisable to use a suitable tool, such as a saw or wire, to remove the excess mass. Curing the mixture takes approximately 24 hours, after which time the exact dimensions of the product can be adjusted by cutting, If necessary.

[0018] The product reaches its final strength after approximately 28 days, during which time the product dries out and the associated weight loss occurs.

[0019] As mentioned above, the residues generated during production are subjected to shredding and added to the additional recyclate and recycled into the whole process.

[0020] In addition to the aforementioned wastelessness of the entire technology, another significant advantage of the method according to the invention is that the time- and energy-consuming step of drying the aerated concrete recyclate, which is carried out in the currently used recycling processes, is eliminated.

[0021] Brief description of drawings

[0022] Figure 1 is an image showing the profile structure of a block manufactured by the process of the invention and tested in Example 3

[0023] Figure 2 is the block from Figure 1 indicating the locations from which the samples were cut for testing in Example 3. Example 1

[0024] Production of a porous concrete element from a recycled concrete using a mixture of Portland cement CEM 142.5 R, lime CL 90 and specially treated aluminium powder Expandit 10

[0025] 52 litres of water was charged into the mixing device and the device was put into operation. 60 kg of an aerated concrete recyclate, which had been pre-treated to a grain size of 1 mm, was added in portions to the mixture in the mixing device, while the mixture was continuously stirred. To the resulting slurry was added 40 kg of a mixture containing 85 wt. 96 of cement, 12 wt. 96 of lime, and 3 wt. % of Expandit 10, all based on the total weight of the dry mixture. The resulting mixture was stirred until a homogeneous mass was formed (approximately 60-90 s). The mixing device was switched off and a sample of the mixture was taken from the device in order to carry out a spillage test (according to EN 12706: using the spillage cylinder with an internal diameter of 30 mm and a height of 50 mm, as described above). Based on the test results, where the observed spillage was less than 7.5 cm, additional 100 ml of water were added to the mixture. The mixture was then briefly stirred and poured into prepared moulds of a hardened PVC or steel treated with a separation oil. After a period of approximately 10 minutes, the expansion process started spontaneously and was completed after approximately 110 minutes. After a period of 24 hours from the start of the expansion process, it was possible to remove the manufactured aerated concrete element from the mould, at which time it was possible to walk on the element. The final strength of the element was achieved after 28 days, during which time the product dried out, which also led to a reduction in its weight.

[0026] Example 2

[0027] Production of a porous concrete element from a recycled concrete using a mixture of Portland cement CEM 142.5 R, lime CL 90 and specially treated aluminium powder Expandit 10, ground limestone fraction 0-0.09 and superplasticizer Peramine 149 S

[0028] 26 litres of water was charged into the mixing device and the device was put into operation. 30 kg of an aerated concrete recyclate, which had been pre-treated to a grain size of 1 mm, was added in portions to the mixture in the mixing device, while the mixture was continuously stirred. To the resulting slurry was added 20 kg of a mixture containing 65 wt. % of cement, 4 wt. 96 of lime, 1 wt. 96 of Expandit 10, 13 wt. % of ground limestone, and 1 wt. % of the superplasticizer Peramin 149 S, all based on the total weight of the dry mixture. The resulting mixture was stirred until a homogeneous mass was formed (approximately 60-90 s). The mixing device was switched off and a sample of the mixture was taken from the device in order to carry out a spillage test (according to EN 12706: using the spillage cylinder with an internal diameter of 30 mm and a height of 50 mm, as described above). Based on the test result, where the observed spillage was less than 7.5 cm, additional 100 ml of water were added to the mixture. The mixture was further briefly stirred and poured into prepared moulds made of a steel and pre-treated with a separation oil. After a period of approximately 5 minutes, the expansion process started spontaneously and was completed after approximately 120 minutes. After 24 hours had elapsed from the start of the expansion process, it was possible to remove the manufactured aerated concrete element from the mould, at which time it was possible to walk on the elementn. The final strength of the element was achieved after 28 days, during which time the product dried out, which also led to a reduction in its weight. Example 3

[0029] Strength tests I

[0030] The pillar block manufactured using the process according to the present invention was subjected to the mechanical tests according to EN 772-1+A1 Compressive strength and EN 772-13 Bulk weight for testing aerated concrete.

[0031] Four sets of 1 specimen each were cut from the block for bulk density testing and another 2 samples were used for compressive strength testing. The sets of specimens marked A and B were cut from the lower (denser) part of the block. Sets C and D were cut from the upper part of the block (see Figure 2).

[0032] The compressive strength specimens were tested in a press in the direction of mass growth (as AAC lintels are tested) and perpendicular to the direction of mass growth (as conventional aerated concrete blocks are tested).

[0033] The results are summarised in Table 1.

[0034] Table 1

[0035] Example 4

[0036] Strength Tests II

[0037] The 40 x 40 x 60 mm prism manufactured using the process according to the present invention was subjected to the mechanical tests according to EN 196. The measured values together with the testing parameters are given below In Table 2. Table 2

Claims

Claims 1. A mixture for recycling an aerated concrete recyclate, characterized In that It includes:- 60 to 90 wt. 96, based on the dry weight of the mixture, of a cement component;- 4 to 35 wt. 96, based on the dry weight of the mixture, of a lime component; and-0.5 to 5.0 wt. 96, based on the dry weight of the mixture, of an expander component.

2. The mixture for recycling an aerated concrete recyclate according to claim 1, characterized In that It further comprises:- 3 to 15 wt. 96, based on the dry weight of the mixture, of a filler and- up to 1 wt. 96, based on the dry weight of the mixture, of a superplasticizer.

3. The mixture for recycling an aerated concrete recyclate according to claim 1 or 2, characterized In that the cement component is CEM 142.5 R Portland cement, the lime component is CL 90 lime, the expander component is an aluminium powder based product, the filler is ground limestone of fraction 0-0.09 mm and the superplasticizer is Peramin 1495.

4. The mixture according to claim 3, characterized in that the aluminium-based product is Expandit 10 or its equivalent.

5. A process for the manufacture of an aerated concrete element, characterized in that it comprises the following steps:(a) charging a mixing device with water and putting the device into operation;(b) stepwise addition of an aerated concrete recyclate to water in the mixing device, with continuous stirring of the resulting mixture;(c) adding the mixture according to any one of claims 1 to 4 to the mixture of step (b) and stirring the mixture to form a homogeneous flowable mass;(d) pouring the mixture from step (c) into the mould;(e) allowing the mixture to cure for at least 24 hours and removing the resulting product from the mould.

6. The process for the manufacture of an aerated concrete element according to claim 5, characterized in that It optionally further comprises between steps (c) and (d) the following steps:(c1) performing a flow test according to EN 12706 - Determination of spill characteristics, on a sample of the mixture from step (c); and optionally(c2) adjusting the flowability of the mixture from step (c) by adding more water or by adding more aerated concrete recyclate.

7. The process according to claim 5 or 6, characterized In that the recyclate : mixture according to any one of claims 1 to 3 weight ratio is in a range between 1:3 and 3:1.

8. The process according to any one of claims 5 to 7, characterized In that the the water coefficient is In a range between 0.52 and 0.

53.

9. The process according to any one of claims 5 to 8, characterized In that the mixing in step (c) is carried out for a period of from 60 to 90 seconds.

10. Use of a mixture according to any one of claims 1 to 4 for the production an aerated concrete building element from an aerated concrete recyclate.

11. An aerated concrete element, characterized In that it is made of an aerated concrete recyclate using the mixture according to any one of claims 1 to 4.

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