Reactivating cement stone

Abstract

The invention relates to a method and a device for reactivating cement stone (2a), wherein the method comprises at least the following steps: - providing starting material (1) which comprises at least a proportion of cement stone (2a) (S1); - irradiating the starting material (1) with light (3) such that the cement stone (2b) at least partially forms at least one hydraulically binding phase (4) (S2). The invention also relates to reactivated cement which is produced in accordance with the method according to the invention.

Description

[0001] Reactivation of cement stone

[0002] The present invention relates to a method and a device for reactivating cement stone and reactivated cement.

[0003] Cement production is currently the largest single source of CO2 emissions. With 2.4 billion tons of cement produced, China is the largest CO2 emitter from this source. Germany produces approximately 35 million tons of cement. Typically, approximately 0.6 tons of CO2 are produced per ton of cement. Overall, global CO2 emissions from this source have tripled since 2000.

[0004] To reduce CO2 emissions into the atmosphere, the cement industry is currently promoting the direct use of CO2 produced during cement production as a carbon source. Recycling old materials (concrete and mortar) is, in turn, a CO2-free source of cement. This difference is due to the primary source of calcium for clinker production (sintered preform of cement, which is calcined and sintered at approximately 1450°C), which is present in the lime mineral as CaCO3. 70% of the CO2 emissions for primary cement production come from the decomposition of CaCO3 into CaO, the remainder from providing the high temperatures and electrical energy required for grinding the raw materials and clinker. In old concrete and mortar, the calcium is present in the form of calcium silicate hydrate phases (CSH phases), which form the hydrated binder.When these calcium silicate hydrates decompose back into active, hydraulically binding phases, particularly calcium silicate oxides, only water is released. This decomposition is referred to below as reactivation.

[0005] A suspension of cement and water initially forms the cement paste and, after hardening through hydration, the cement paste. The calcium silicate hydrate phases formed during hydration form the cement gel.

[0006] The decisive factor for the properties of the cement stone, such as strength and durability, is the structure created by the hydration products of the cement.

[0007] If the cement paste is mixed with sand with a grain size of up to 4 mm, the resulting mixture is called mortar. If it also contains coarser aggregate, the mixture is called concrete.

[0008] Portland cement is the most commonly used cement, although the teachings described here are not limited to Portland cement. There are four essential bonding phases that enable Portland cement's functionality:

[0009] 1 . C3S is the mineral 3 CaO*SiO2 (alite), which determines the early strength of the set cement after hydration. C3S typically forms during cement production at temperatures above approximately 1300°C.

[0010] 2. C2S is the mineral 2 CaO*SiO2 (belite), which largely determines strength in old age. C2S typically forms during cement production at temperatures above approximately 600°C.

[0011] 3. C2(A,F) is 2 CaO*(Al2O3,Fe2O3) (aluminum ferrite)

[0012] 4. C3A is 3 CaO'AhOs (calcium aluminate)

[0013] Overall, the composition of a common Portland cement before hydration is given in the following table (from the dissertation of Gustave Semugaza, original data from “Cement and Technology”):

[0014] Table

[0015] Concrete and mortar are made from cement, aggregate, and sand. The final product contains approximately 20% cement by mass.

[0016] For recycling, the aggregate, sand, and cement paste must be separated. There are simple mechanical processes for separating the aggregate from the mortar (sand-cement paste mixture), including various impact crushers or the SmartCrusher, which are so advanced that the aggregate is essentially undamaged during the process.

[0017] It is known from the literature that thermal treatment of cement paste enables reconversion or decomposition into hydraulically binding phases (reactivation). Fully reactivated cement paste thus corresponds to cement. The calcium silicate hydrates are converted back into active, hydraulically binding calcium silicate oxides, releasing only water. A corresponding thermal treatment is described, for example, in "Dehydration and Rehydration of Blast Furnace Slag Cement," August 2019, Journal of Materials in Civil Engineering 31 (8).

[0018] (DOI: 10.1061 / (ASCE)MT.1943-5533.0002725).

[0019] The article “Reactivation of hydrated cement powder by thermal treatment for partial replacement of ordinary Portland cement” by Semugaza, G., Mielke, T., Castillo, ME et al., published in Mater Struct 56, 48 (2023) (https: / / doi.org / 10.1617 / s11527-023-02133-9) also describes a corresponding thermal treatment of cement.

[0020] The thermal reactivation of cement paste described in the prior art has the disadvantage that, of the hydraulically binding phases, virtually only C2S (2 CaO*SiO2, belite) is formed. Furthermore, thermal reactivation is energy-intensive and therefore costly.

[0021] It is therefore the object of the present invention to provide an efficient and powerful method and a device for reactivating cement stone, wherein preferably higher proportions of hydraulically binding phases are formed, as well as additional hydraulically binding phases are formed.

[0022] This object is achieved according to the invention by a method for reactivating cement stone according to claim 1 and by a device according to claim 15.

[0023] A further object is to provide reactivated cement that has a similar composition to cement before hydration. This object is achieved according to the invention by reactivated cement according to claim 16.

[0024] According to the invention, the process for reactivating cement stone comprises at least the following steps: - Providing starting material which at least partially comprises cement stone,

[0025] - Irradiating the starting material with light so that the cement paste at least partially forms at least one hydraulically binding phase.

[0026] As already described at the beginning, cement stone is formed after hardening as a result of hydration from cement paste, which in turn is a suspension of preferably cement and water.

[0027] The starting material contains at least a portion of cement paste, with the calcium present in the cement paste in the form of, for example, calcium silicate hydrate phases. The decomposition of these calcium silicate hydrate phases back into active, hydraulically binding phases, particularly calcium silicate oxides, corresponds to reactivation.

[0028] The starting material can, for example, be in the form of old concrete and / or mortar, which means that additional substances such as sand and / or gravel are present in the starting material.

[0029] The starting material is preferably placed on a support on which the light is irradiated.

[0030] The starting material is irradiated with light in such a way that the cement paste at least partially forms at least one hydraulically binding phase. Thus, for example, the calcium silicate hydrate phases present after hydration (hardening) are at least partially converted back into at least one active, hydraulically binding phase by the irradiated light, thus reactivating them.

[0031] The starting material treated according to the process of the invention represents the product of the process of the invention. Preferably, the reactivation of the cement paste is complete, resulting in cement. Irradiation of the starting material with light represents a particularly efficient form of reactivation of cement paste and thus of cement recycling.

[0032] The light heats up the starting material, which provides a thermal contribution to the reactivation.

[0033] The thermal contribution can in principle be achieved through a variety of heating processes, such as electrical heating, heating by means of exothermic reactions, in particular the combustion of gases, or the absorption of radiation, preferably light.

[0034] Energy consumption is a particularly relevant factor for the efficient design of heating processes. Heating by absorbing radiation, preferably light, is particularly advantageous in terms of efficiency.

[0035] The photons of light irradiated onto the starting material influence the course of the chemical reactions occurring during the reactivation of cement stone, which provides a photochemical contribution to the reactivation.

[0036] The combination of thermal and photochemical contributions to the reactivation of cement paste has the advantage that the reactivation is very fast and therefore efficient, especially energy-efficient.

[0037] A further advantage is the possibility of processing not only almost pure cement paste as the starting material, but also mixtures such as mortar. Due to the high specificity of the process, sand is virtually unaffected by the light. The introduced light energy can thus be used primarily for the reactivation of cement paste and, unlike conventional heating, does not heat the sand component.

[0038] The irradiation of the starting material with light can be carried out in a variety of ways and is explained in more detail below in various embodiments of the method, wherein the corresponding features are also applicable to the device according to the invention.

[0039] The object described above is also achieved by a device according to the invention for reactivating cement stone, wherein the device is designed to carry out the method according to the invention.

[0040] The device according to the invention for carrying out the method according to the invention has at least one process zone for receiving starting material and at least one light source, wherein the light source is designed to radiate light into the process zone.

[0041] Preferably, the device is designed for continuous operation, for which purpose, for example, conveying options for supplying and removing the starting material can be provided.

[0042] The light source may be a spectrally specific light source, preferably corresponding to one or more lasers and / or LEDs.

[0043] The advantages of the device according to the invention for reactivating cement stone arise in an analogous manner to the process.

[0044] The reactivated cement according to the invention is produced according to the method according to the invention, preferably using the device according to the invention. The reactivated cement produced in this way has the advantage that the composition of the reactivated cement, in particular the ratio of the hydraulically binding phases formed, is similar to the composition of the cement before hydration.

[0045] As a result, by using the cement reactivated according to the invention, a cement can ideally be reproduced which is so close to the original cement that it can be used technically on a virtually equal level.

[0046] This is usually not possible with conventional reactivated cement, as the ratio of the resulting hydraulically binding phases differs from the ratio of the cement before hydration. A replica cement formed from conventional reactivated cement does not correspond to the original cement. Therefore, its properties also differ, making it technically unsuitable for use.

[0047] In one embodiment of the method, the light has a power density on the starting material in the range of greater than 7.5 W / cm 2 , preferably greater than 20 W / cm 2 , more preferably greater than 50 W / cm 2 , more preferably greater than 100 W / cm 2, more preferably greater than 200 W / cm 2 on.

[0048] The term power density on the source material refers to the value of the effective light power available on the surface of the source material per cm 2 This can be generated by one or more light sources. The power density has a significant influence on the thermal and photochemical contribution to the reactivation of hardened cement paste described above. The choice of power density can thus, for example, control which and to what extent hydraulically binding phases form. High power densities have proven advantageous, as they enable rapid reactivation and thus short irradiation periods. Furthermore, it can also be advantageous to choose low to medium power densities for efficiency reasons.

[0049] In a further embodiment of the method, the light is in a wavelength range in the range 200 to 600 nm, preferably in the range 350 to 500 nm, preferably in the range 360 ​​to 460 nm.

[0050] Different starting materials absorb light of different wavelengths to varying degrees. By selecting the appropriate wavelength range, it is possible, for example, to ensure that the light affects the cement paste (thermally and / or photochemically) but not, or at least relatively less, the sand. This makes the process particularly efficient, since, for example, only the intended reactivation of the cement paste can be activated in the starting material.

[0051] The wavelength range from 350 to 500 nm is particularly preferred because sufficiently cost-effective light sources with sufficient light output are available in this range. Furthermore, absorption in this wavelength range is particularly efficient.

[0052] In a further embodiment of the method, the light is emitted by a plurality of light sources, wherein a first part of the light sources has a first wavelength range in the range 425 to 600 nm and a second part of the light sources has a second wavelength range in the range 200 to 425 nm.

[0053] By using multiple light sources, for example, it is possible to combine several cost-effective light sources to achieve a high overall light output. Furthermore, by selecting light sources with different wavelength ranges, it is possible to match the output to different absorbing materials.

[0054] In a further embodiment of the method, the method further comprises the step of removing the irradiated starting material, wherein the provision of the starting material, the irradiation of the starting material and the removal of the irradiated starting material take place continuously.

[0055] By removing the already irradiated and thus reactivated cement paste, it is possible to add new material, creating a continuous process. For example, conveyor systems can be provided for the supply and removal of the starting material. A continuous process enables, among other things, high process stability and high throughput.

[0056] In a further embodiment of the process, at least one hydraulically binding phase C2S (2 CaOSiCh, belite) and / or C3S (3 CaO*SiO2Alite) is formed.

[0057] In particular, the formation of the hydraulically binding phase C3S (3 CaO*SiO2, alite) is associated with a high energy expenditure in conventional, exclusively thermal processes, since high temperatures are required for the formation of this phase in an exclusively thermal process.

[0058] Furthermore, the C3S (3 CaO*SiO2, alite) phase is crucial for the early strength of the set cement after rehydration, so the presence of this phase in the reactivated cement paste is desirable.

[0059] Due to the formation of both phases, C2S (2 CaO*SiO2, belite) and C3S (3 CaO*SiO2, alite), it is possible that the composition, especially the ratio of the forming hydraulic phases in the reactivated cement paste, is similar to the composition of the cement paste before hydration.

[0060] In a further embodiment of the process, the proportion of the at least one hydraulically binding phase amounts to at least 50%, preferably at least 80%, preferably at least 100% of the original proportion in the cement paste before hydration.

[0061] This feature represents a criterion for how similar the compositions, in particular the ratio of the hydraulic phases formed, are in the reactivated cement paste and the cement paste before hydration.

[0062] It is desirable that the proportions of all hydraulically binding phases in the reactivated cement paste and the cement paste before hydration match 100%. A proportion of more than 100% of individual hydraulically binding phases in the reactivated cement paste compared to the cement paste before hydration is also possible, for example, if the proportion of other hydraulically binding phases is comparatively lower.

[0063] Furthermore, this characteristic represents a criterion for how completely the cement stone is reactivated. Ideally, the cement stone is completely reactivated.

[0064] With a largely complete reactivation of the cement paste while retaining the phase proportions (100%) as far as possible, the use of the reactivated cement paste according to the invention can produce a cement that is so close to the original cement that it can be used technically on a virtually equal level.

[0065] In a further embodiment of the method, the starting material is irradiated with light over a period of less than 30 seconds, preferably less than 15 seconds, preferably less than 5 seconds, preferably less than 1 second.

[0066] Correspondingly short irradiation times enable a high throughput of starting material. This also facilitates the implementation of the process as a continuous process, for example, by continuously passing the starting material past one or more light sources.

[0067] Irradiating the starting material with light over a limited period of time does not necessarily mean that the irradiation is stopped after the end of the period, but rather that the irradiation of a limited amount of starting material takes place within the specified period of time and then unirradiated starting material is irradiated.

[0068] For example, the starting material can be transported on a conveyor belt past one or more light sources, whereby the respective cement stone to be reactivated is irradiated and reactivated over the corresponding period of time.

[0069] For a large-scale industrial process, periods of less than 1 second are particularly advantageous.

[0070] In a further embodiment of the process, the formation of the at least one hydraulically binding phase is carried out at temperatures below 1300°C, preferably below 1000°C, preferably below 800°C, preferably below 550°C.

[0071] This makes the process particularly efficient. For example, the light power density is selected such that the starting material, especially the cement paste it contains, does not exceed the corresponding temperatures. Selecting appropriate power densities and thus lower temperatures than with conventional thermal processes is possible, since both the thermal and photochemical components contribute to the reactivation of cement paste.

[0072] This means that less energy is required overall than with conventional thermal processes.

[0073] In a further embodiment of the method, the light is generated by a spectrally specific light source, preferably by one or more lasers and / or by LEDs.

[0074] Using a spectrally specific light source, the wavelength range of the light can be adjusted with great precision. This makes it possible, for example, to select wavelengths that are absorbed by the cement paste (thermal contribution) and / or contribute significantly to the photochemical contribution in the reactivation of the cement paste, but do not unnecessarily heat the other substances present in the starting material.

[0075] The use of LEDs is particularly preferred, as they represent a cost-effective and robust alternative to lasers or other optical systems while simultaneously achieving high luminous intensity. The use of LEDs enables particularly energy-efficient and therefore cost-effective light generation. LEDs are also cheaper to purchase than, for example, laser systems.

[0076] In a further embodiment of the process, the starting material is preheated before irradiation, preferably by a gas stream and / or microwave radiation.

[0077] This makes it possible, for example, to further shorten the irradiation time and further increase the process throughput. Furthermore, efficiency can be further increased, for example, by using waste heat to generate energy for the gas stream.

[0078] In a further embodiment of the process, the starting material is selected from the group consisting of: cement paste as granules, cement paste as powder, cement paste in bound form in cement matrix, cement paste in bound form in mortar, cement paste in bound form in concrete.

[0079] The process makes it possible to irradiate different types of starting material and thus reactivate the cement stone contained in the starting material.

[0080] In particular, it is possible to reactivate cement paste that is present in a bound form in the cement matrix. By selecting the wavelength of the light, it is possible to influence the cement paste thermally and photochemically, thus reactivating it. This applies particularly to cement paste in bound form in mortar or concrete.

[0081] In order to reactivate the cement stone according to the process, it is therefore not necessary to completely separate the starting material into its components.

[0082] In a further embodiment of the method, the starting material is thermally decoupled from the environment during irradiation, for example by an insulating base.

[0083] This allows for further increasing energy efficiency, since only the starting material is thermally influenced. In a further embodiment of the method, the starting material is provided in a layer thickness of at most 10 mm, preferably at most 5 mm, more preferably at most 3 mm, and this layer thickness is maintained even during irradiation.

[0084] The provision of the starting material in a corresponding layer thickness can be carried out, for example, by placing crushed starting material as granules or powder in a corresponding amount on a base so that a layer thickness of 10 mm, preferably 5 mm, more preferably 3 mm is not exceeded.

[0085] Appropriately selected layer thicknesses allow for particularly short irradiation times. Furthermore, such layer thicknesses enable particularly complete and homogeneous irradiation of the starting material.

[0086] The invention is explained in more detail below with reference to the accompanying drawings. They show:

[0087] Fig. 1 shows an embodiment of a device for carrying out a process for reactivating cement stone,

[0088] Fig. 2 is a schematic representation of an embodiment of a process for reactivating cement stone,

[0089] Fig. 3 X-ray diffractometric characterization of cement paste powder before and after reactivation.

[0090] Figure 1 describes an embodiment of a device 6 for carrying out a method for reactivating cement stone 2a. The schematic sequence of one embodiment of the method is shown in Figure 2. Starting material 1 is fed from a storage container 8 onto a conveyor belt 9. The starting material 1 contains at least a portion of cement stone 2a. The cement stone 2a is formed during the hardening of cement as a result of hydration.

[0091] The starting material 1 is present in a layer thickness d on the conveyor belt 9, which enables uniform and complete irradiation of the entire starting material 1.

[0092] Preferably, the conveyor belt 9 is designed to be thermally insulating, so that the starting material 1 located on the conveyor belt 9 is thermally decoupled from the environment.

[0093] The conveyor belt 9 continuously transports the starting material 1 into a process zone 7, which corresponds to a step S1 of providing the starting material 1. In the process zone 7, the starting material 1 located there is irradiated with light 3 from the light sources 5a and 5b, which corresponds to a step S2 of irradiating the starting material 1.

[0094] In this process, the cement paste 2a, which contains calcium silicate hydrates, is at least partially reactivated, resulting in reactivated cement paste 2b, in which hydraulically binding phases 4, particularly calcium silicate oxides, have formed. Reactivated cement paste 2b corresponds to cement.

[0095] During the reactivation of cement paste 2a, the calcium silicate hydrates formed during hydration are reactivated into active, hydraulically binding phases 4, particularly calcium silicate oxides. This results in at least partially reactivated cement paste 2b.

[0096] The starting material 1 treated according to the method according to the invention represents the product 10 of the method according to the invention. In the illustrated embodiment, for example, light sources 5 are in the form of LEDs, wherein the first light source 5a emits, for example, in a first wavelength range from 425 to 600 nm, while the second light source 5b emits in a second wavelength range in the range from 200 to 425 nm.

[0097] By selecting suitable wavelength ranges, it can be achieved, for example, that the light 3 acts on the cement stone 2a, 2b (thermally and / or photochemically), but not on sand (not shown). This allows the method according to the invention to be carried out particularly efficiently with the device 6, since, for example, only the intended reactivation of the cement stone 2a in the starting material 1 can be activated, resulting in at least partially reactivated cement stone 2b.

[0098] The irradiation of the starting material 1 with light 3 in step S2 preferably takes place within a short period of time t, for example, less than 1 second. The irradiation period t can be freely selected via the speed of the conveyor belt 9, thus enabling high throughputs.

[0099] By appropriately selecting a power density of the light 3 on the starting material 1 in interaction with the selected wavelengths of the light 3, the process for reactivating cement stone 2a, 2b can be adjusted very specifically.

[0100] For example, high power densities can be selected, as these enable rapid reactivation and thus short irradiation periods t. Furthermore, for efficiency reasons, it may also be advantageous to select low to medium power densities. During the irradiation in step S2, at least one hydraulically binding phase 4 is formed, at least partially, in the cement paste 2a, thus forming reactivated cement paste 2b. The resulting hydraulically binding phase 4 corresponds, for example, to C2S (2CaOSiC, belite) and / or C3S (3CaOSiCh, alite).

[0101] Due to the formation of the phases 4 C2S (2 CaOSiC, belite) and / or C3S (3 CaOSiCh, alite), it is possible that the composition, in particular the ratio of the forming hydraulic phases 4 in the reactivated cement paste 2b is similar to the composition of the cement paste before hydration.

[0102] After the irradiation step S2, the starting material 1, which now comprises reactivated cement stone 2b with at least one hydraulically binding phase 4, is conveyed out of the process zone 7 by the conveyor belt 9, which corresponds to a step S3 of removing the starting material 1.

[0103] The device 6 according to Figure 1 and the method that can be carried out therewith according to Figure 2 are thus designed for continuous operation, which enables, for example, high process stability and high throughputs.

[0104] The supply and removal of the starting material 1 is possible in many different ways known to the person skilled in the art.

[0105] Figure 3 shows X-ray diffraction (XRD) characterizations of starting material 1 with cement paste 2a before reactivation and product 10 with cement paste 2b after reactivation. The curing time of the respective starting material 1 was 28 days in each case. The different peaks of graphs G1, G2, and G3 represent different phases and compositions, which are labeled with symbols according to the legend given in Figure 3. According to the legend, the following symbol assignment applies:

[0106] T Tri-Calcium Silicate (C3S)

[0107] X Di-calcium silicate (ß-C2S)

[0108] * Calcite (CaCO3)

[0109] * Alpha low di-calcium silicate (a / L-C2S)

[0110] * Portlandite (Ca(OH)2) v Calcium Silicate Hydrate (CSH) Ettringite (AFt)

[0111] The first graph G1 represents an XRD measurement on a starting material 1 with hydrated cement paste 2a before reactivation. Starting material 1 was not subjected to the process according to the invention. Starting material 1 corresponds to a Portland cement with a composition as described in Table 1.

[0112] Graph G1 shows that the hydrated cement paste 2a also contains portions of hydraulically binding phases 4. However, these hydraulically binding phases 4 consist exclusively of C2S (2 CaO*SiO2, belite), whose peaks are marked with an "X" in the XRD measurement. No C3S (3 CaO*SiO2, alite) is present. Instead, calcium silicate hydrates (CSH) are visible; represented by the "v" symbol.

[0113] A second graph G2 represents an XRD measurement on a starting material 1 after undergoing the process according to the invention and thus on the product 10, which comprises partially reactivated cement paste 2b. The starting material 1 corresponded to a Portland cement with a composition as described in Table 1.

[0114] The starting material 1 of graphene G2 was treated according to the method according to the invention with light 3 at a low power density of approximately 10 W / cm 2 irradiated over a period of 20 seconds, and the starting material 1 was converted into the product 10. The selected wavelength corresponded to 440 nm.

[0115] Graph G2 shows the formation of a higher proportion of hydraulically bonding phases 4, especially C2S (2 CaO*SiO2, Belite) phases, whose peaks in the XRD measurement are marked with an “X” and a However, no C3S (3 CaO*SiO2, alite) phase is formed.

[0116] A third graph G3 represents an XRD measurement on a starting material 1 after it has undergone the process according to the invention, and thus on the product 10, which comprises fully reactivated cement paste 2b. This starting material 1 also corresponded to a Portland cement with a composition as described in Table 1.

[0117] The starting material 1 of graphene G3 was treated according to the method of the invention with light 3 at an average power density of approximately 50 W / cm 2 irradiated over a period of 20 seconds, and the starting material 1 was converted into the product 10. The selected wavelength was also 440 nm.

[0118] Graph G3 shows the formation of various hydraulically bonding phases 4, in particular C2S (2 CaO*SiO2, Belite), whose peaks in the XRD measurement are marked with an “X” and a and C3S (3 CaO*SiO2, Alit) phases, whose peaks in the XRD measurement are marked with a “T”.

[0119] The following table shows the quantitative phase ratios of the starting materials from Figure 3 investigated by XRD:

[0120] Table 2

[0121] For product 10, which is represented by graph G3, it is true that in particular the ratio of the hydraulically binding phases C3S (3 CaO*SiO2, alite) is approximately 100% of the original proportion in the cement paste before

[0122] Hydration corresponds.

[0123] In direct comparison of Table 1 and Table 2, within the measurement uncertainty for the C3S (3 CaO*SiO2, Alit) content of product 10 - corresponding to G3 - a consistent value (65 to 70

[0124] In this case, the product 10 with the reactivated cement paste 2b thus essentially has a composition of Portland cement before hydration. As a result, when using the inventive product 10 with reactivated cement paste 2b, which is represented by graph G3, a cement can be reproduced that is so close to the original cement before hydration that it can be used on an equivalent technical level.

Claims

Patent claims 1 . A method for reactivating cement stone (2a), comprising the following steps: - providing starting material (1 ) which at least partially comprises cement stone (2a) (S1 ), - irradiating the starting material (1) with light (3) so that the cement stone (2b) at least partially forms at least one hydraulically binding phase (4) (S2).

2. Method according to claim 1, wherein the light (3) has a power density on the starting material (1) in the range of greater than 7.5 W / cm 2 , preferably greater than 20 W / cm 2 , more preferably greater than 50 W / cm 2 , more preferably greater than 100 W / cm 2 , more preferably greater than 200 W / cm 2 has.

3. Method according to one of the preceding claims, wherein the light (3) is in a wavelength range in the range 200 to 600 nm, preferably in the range 350 to 500 nm, preferably in the range 360 to 460 nm.

4. Method according to one of the preceding claims, wherein the light (3) is emitted by a plurality of light sources (5), wherein a first part of the light sources (5a) has a first wavelength range in the range 425 to 600 nm and a second part of the light sources (5b) has a second wavelength range in the range 200 to 425 nm.

5. Method according to one of the preceding claims, further comprising the step - removing the irradiated starting material (S3), wherein the provision of the starting material (S1), the irradiation of the starting material (S2) and the removal of the irradiated starting material (S3) take place continuously.

6. Process according to one of the preceding claims, wherein the at least one hydraulically binding phase (4) corresponds to C2S (2 CaOSiC, belite) and / or C3S (3 CaOSiCh, alite).

7. Method according to one of the preceding claims, wherein the proportion of the at least one hydraulically binding phase (4) amounts to at least 50%, preferably at least 80%, preferably at least 100% of the original proportion in the cement stone before hydration.

8. Method according to one of the preceding claims, wherein the irradiation of the starting material with light (3, S2) takes place over a period (t) of less than 30 seconds, preferably less than 15 seconds, preferably less than 5 seconds, preferably less than 1 second.

9. Method according to one of the preceding claims, wherein the formation of the at least one hydraulically binding phase (4) is carried out at temperatures below 1300°C, preferably below 1000°C, preferably below 800°C, preferably below 550°C.

10. Method according to one of the preceding claims, wherein the light (3) is generated by a spectrally specific light source (5), preferably by one or more lasers and / or by LEDs.

11. Method according to one of the preceding claims, wherein the starting material (1) is preheated before irradiation (S2), preferably by a gas stream and / or microwave radiation.

12. Method according to one of the preceding claims, wherein the starting material (1) is selected from the group consisting of: cement stone (2a) as granules, Cement stone (2a) as powder, Cement stone (2a) in bound form in cement matrix, cement stone (2a) in bound form in mortar, cement stone (2a) in bound form in concrete.

13. Method according to one of the preceding claims, wherein the starting material (1) is thermally decoupled from the environment during the irradiation (S2), for example by a thermally insulating base.

14. Method according to one of the preceding claims, wherein the starting material (1) is provided in a layer thickness (d) of at most 10 mm, preferably at most 5 mm, more preferably at most 3 mm, and this layer thickness (d) is also maintained during the irradiation (S2).

15. Device (6) for carrying out a method according to one of the preceding claims, comprising a process zone (7) for receiving starting material (1) and at least one light source (5), wherein the light source (5) is designed to radiate light (3) into the process zone (7).

16. Reactivated cement produced by a process according to any one of claims 1 to 14.

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