COMPOSITE CEMENT CONTAINING RECYCLED CEMENT PASTE AND CALCINED CLAY

Abstract

Composite cement containing from 5 to 70 wt.-% cement clinker and from 30 to 95 wt.-% mixture of carbonated or not carbonated recycled cement paste and calcined clay with a weight ratio carbonated or not carbonated recycled cement paste to calcined clay from 4 to 0.1, method for manufacturing it as well as method for manufacturing hydraulically hardening building materials using the composite cement or blending from 5 to 70 wt.-% ground cement clinker with from 30 to 95 wt.-% of a mixture of carbonated or not carbonated recycled cement paste and calcined clay with a weight ratio carbonated or not carbonated recycled cement paste to calcined clay from 4 to 0.1 during mixing.

Claims

1. A composite cement containing from 5 to 70 wt.-% cement clinker and from 30 to 95 wt.-% mixture of carbonated or not carbonated recycled cement paste and calcined clay with a weight ratio carbonated or not carbonated recycled cement paste to calcined clay from 4 to 0.1.

2. The composite cement according to claim 1 containing from 10 to 65 wt.-% cement clinker blended with from 90 to 35 wt.-% mixture of carbonated or not carbonated recycled cement paste and calcined clay, one or more other supplementary cementitious materials than calcined clay and carbonated or not carbonated recycled cement paste, and admixtures and/or additives, wherein the weight ratio between carbonated or not carbonated recycled cement paste and calcined clay in the mixture ranges from 3 to 0.2 and a particle size distribution of the carbonated or not carbonated recycled cement paste has a d.sub.90<100 m.

3. (canceled)

4. The composite cement according to claim 1, wherein the carbonated recycled cement paste has a carbonation degree from 5 to 50 wt.-% and/or a particle size distribution of the carbonated or not carbonated recycled cement paste has a d.sub.90<110 m.

5. The composite cement according to claim 1, wherein the calcined clay is obtained from a raw clay containing from 20 to 100 wt.-% kaolinite and/or a particle size distribution of the calcined clay has a d.sub.90<110 m.

6. The composite cement according to claim 1, wherein the composite cement contains admixtures and/or additives.

7. The composite cement according to claim 1, wherein the composite cement contains one or more other supplementary cementitious materials than calcined clay and carbonated or not carbonated recycled cement paste, selected from the group consisting of ground granulated blast furnace slag and/or other latent-hydraulic or pozzolanic slag, fly ash, burnt oil shale, and natural pozzolans.

8. A method for manufacturing a composite cement wherein from 5 to 70 wt.-% cement clinker is blended with from 30 to 95 wt.-% mixture of carbonated or not carbonated recycled cement paste and calcined clay with a weight ratio carbonated recycled cement paste to calcined clay from 4 to 0.1 in the mixture.

9. The method according to claim 8, wherein from 10 to 65 wt.-% cement clinker are blended with from 90 to 35 wt.-% mixture of carbonated or not carbonated recycled cement paste and calcined clay, wherein one or more other supplementary cementitious materials than calcined clay and carbonated or not carbonated recycled cement paste are added, wherein admixtures and/or additives are added, and wherein the weight ratio between carbonated or not carbonated recycled cement paste and calcined clay in the mixture is adjusted to range from 3 to 0.2, and the carbonated or not carbonated recycled cement paste is ground to a particle size distribution having a d.sub.90<100 m.

10. (canceled)

11. The method according to claim 8, wherein the composite cement is obtained by co-grinding of at least two components or by separate grinding of all components.

12. The method according to claim 8, wherein recycled cement paste is carbonated by a wet, a semi dry or a dry method and/or naturally carbonated recycled cement paste is used.

13. The method according to claim 8, wherein the carbonated recycled cement paste is carbonated to a carbonation degree from 5 to 50 wt.-% and/or the carbonated or not carbonated recycled cement paste is ground to a particle size distribution having a d.sub.90<110 m.

14. The method according to claim 8, wherein the calcined clay is obtained from a raw clay containing from 20 to 100 wt.-% kaolinite and/or the calcined clay is ground to a particle size distribution having a d.sub.90<110 m.

15. The method according to claim 8, wherein admixtures and/or additives are addedindependently from each otherto a carbonation of the recycled cement paste; during a grinding of the cement clinker, carbonated or not carbonated recycled cement paste, calcined clay or any mixture thereof; and/or while blending the cement components.

16. A method for manufacturing a hydraulically hardening building material from a cement, wherein during mixing of the hydraulically hardening building material from 5 to 70 wt.-% ground cement clinker is blended with from 30 to 95 wt.-% of a mixture of carbonated or not carbonated recycled cement paste and calcined clay with a weight ratio carbonated or not carbonated recycled cement paste to calcined clay from 4 to 0.1 or a composite cement according to claim 1 is used as the cement.

17. The composite cement according to claim 1 containing from 20 to 60 wt.-% cement clinker blended with from 80 to 40 wt.-% mixture of carbonated or not carbonated recycled cement paste and calcined clay.

18. The composite cement according to claim 1, wherein the weight ratio between carbonated or not carbonated recycled cement paste and calcined clay in the mixture ranges from 2 to 0.3.

19. The composite cement according to claim 4, wherein the carbonated recycled cement paste has a carbonation degree from 10 to 75 wt.-% and/or a particle size distribution of the carbonated or not carbonated recycled cement paste has a d.sub.90<100 m.

20. The composite cement according to claim 4, wherein the carbonated recycled cement paste has a carbonation degree from 15 to 100 wt.-% and/or a particle size distribution of the carbonated or not carbonated recycled cement paste has a d.sub.90<90 m.

21. The composite cement according to claim 5, wherein a particle size distribution of the calcined clay has a d.sub.90<100 m.

22. The method according to claim 8, wherein from 20 to 60 wt.-% cement clinker are blended with from 80 to 40 wt.-% mixture of carbonated or not carbonated recycled cement paste and calcined clay.

23. The method according to claim 8, wherein the weight ratio between carbonated or not carbonated recycled cement paste and calcined clay in the mixture is adjusted to range from 2 to 0.3.

24. The method according to claim 8, wherein the carbonated recycled cement paste is carbonated to a carbonation degree from 10 to 75 wt.-% and/or the carbonated or not carbonated recycled cement paste is ground to a particle size distribution having a d.sub.90<100 m.

25. The method according to claim 8, wherein the carbonated recycled cement paste is carbonated to a carbonation degree from 15 to 100 wt.-% and/or the carbonated or not carbonated recycled cement paste is ground to a particle size distribution having a d.sub.90<90 m.

26. The method according to claim 8, wherein the calcined clay is ground to a particle size distribution having a d.sub.90<100 m.

Description

EXAMPLE 1

[0054] The potential for saving CO.sub.2 emissions was calculated based on estimated amounts of carbon dioxide emitted during manufacturing the various components of composite binders shown in table 1. Clinker is a Portland cement clinker made in a state of the art cement plant using limestone as primary CaO source. Such production results in 500 kg CO.sub.2/t clinker of process emissions, 300 kg of CO.sub.2/t clinker coming from fuels and 45 kWh electricity per ton of clinker. Clinker grinding to a Blaine fineness around 4000 cm.sup.2/g consumes another 55 kWh/t clinker totaling at 100 kWh/t of ground clinker in cement, resulting in 26.1 kg CO.sub.2/t of clinker in the cement from electricity. Grinding natural gypsum to a Blaine fineness of about 5000 cm.sup.2/g and its blending with the cement consumes 15 kWh/t. Calcined clay of natural origin, calcined in a state-of-the-art calciner results in fuel emissions of 150 kg CO.sub.2/t calcined clay. An electricity consumption of 50 kWh/t was assumed for grinding to a of D.sub.90=90 m. Limestone quarrying, crushing and grinding in a state-of-the-art ball mill results in an electricity consumption of 15 kWh/t for a Blaine fineness of 3000 cm.sup.2/g. Concrete recycling and separation of RCP with a D.sub.90<125 m in a vibrating cone crusher circuit equipped with a dynamic separator consumes 10 kWh/t RCP assuming physical allocation of emissions among all products from recycling. Another 5 kWh/t RCP are needed for handling of RCP in the cement plant and its blending into the composite cement. Carbonation of RCP in a fluidized bed-type reactor to a carbonation degree of 90% consumes 35 kWh/t RCP and binds 100 kg CO.sub.2/t for RCP1 and 200 kg CO.sub.2/t of RCP2, respectively, assuming a cement paste content of 50% and 100%, respectively. For values in table 1 an electricity emission factor of 261 g CO.sub.2/kWh was assumed, see https://ourworldindata.org/grapher/carbon-intensity-electricity?tab=table

TABLE-US-00001 TABLE 1 Process emissions Fuel and indirect emissions Material [kg CO.sub.2/t material] [kg CO.sub.2/t material] Clinker (PC) 500 326.1 Gypsum (C$) 0 3.915 Calcined clay (cc) 0 163.05 Limestone (LL) 0 3.915 RCP 0 3.915 cRCP1 100 13.05 cRCP2 200 13.05

[0055] Composite cements with differing amounts of calcined clay and either limestone or RCP/cRCP were calculated. Table 2 lists the compositions and compares the emissions for them. Therein, R denotes a reference cement according to the prior art and Inv designates a composite cement according to the invention.

TABLE-US-00002 TABLE 2 a: 25% SCM with 10% cc and 15% LL/RCP/cRCP component R1 Inv1 Inv2 Inv3 PC 70% 70% 70% 70% C$ 5% 5% 5% 5% cc 10% 10% 10% 10% LL 15% RCP 15% cRCP1 15% cRCP2 15% Process emissions 350 350 335 320 Fuel and indirect emissions 245 245 247 247 Total emissions 595 595 582 567 b: 25% SCM with 20% cc and 5% LL/RCP/cRCP component R2 Inv4 Inv5 Inv6 PC 70% 70% 70% 70% C$ 5% 5% 5% 5% cc 20% 20% 20% 20% LL 5% RCP 5% cRCP1 5% cRCP2 5% Process emissions 350 350 345 340 Fuel and indirect emissions 261 261 262 262 Total emissions 611 611 607 602 c: 45% SCM with 35% cc and 10% LL/RCP/cRCP component R3 Inv7 Inv8 Inv9 PC 50% 50% 50% 50% C$ 5% 5% 5% 5% cc 35% 35% 35% 35% LL 10% RCP 10% cRCP1 10% cRCP2 10% Process emissions 250 250 240 230 Fuel and indirect emissions 221 221 222 222 Total emissions 471 471 462 452

[0056] It is readily apparent that composite cements according to the invention will provide significant improvements over composite cements according to the prior art from the same cement clinker and combining calcined clay and limestone as SCM. Mainly, limestone is a valuable natural resource while RCP and cRCP are waste materials. Limestone provides lower or the same compressive strength and higher or the same carbon dioxide footprint as RCP and cRCP, so replacing limestone with RCP or cRCP is able to save natural resources and in many cases also carbon dioxide emissions while achieving the same or in some cases higher strength.

EXAMPLE 2

[0057] Several composite cements were made based on: [0058] Ordinary Portland clinker ground in the laboratory with a Blaine fineness of 3900 cm.sup.2/g as hydraulic cement (C) [0059] Natural limestone with a calcium carbonate content of >90 wt.-% and industrially ground to a fineness of 3470 cm.sup.2/g (L) [0060] Metakaolin of industrial origin with a metakaolin content of >90 wt.-%, a D.sub.90 of 5.5 m as measured by laser granulometry and characterized by a Rosin Rammler Slope n of 1.52 and d (63.2%) of 2.88 as calcined clay (MK) [0061] Synthetic recycled cement paste, ground for deagglomeration and carbonated in a wet reactor using 100 Vol.-% CO.sub.2 for 6 h at 20 C. to a carbonation degree of >90 wt.-%, characterized by a D.sub.90 of 105.5 m as measured by laser granulometry as well as a Rosin Rammler Slope n of 0.55 and d (63.2%) of 17.13 (RCP) Four composite cements containing 60 wt.-% hydraulic cement clinker and 40% SCM were mixed in a laboratory mixer. The SO.sub.3 content was brought to 3.0% by addition of gypsum. Table 3 summarizes the composition of the composite cement without sulfate (in wt.-%) and the strength (in MPa) measured according to DIN EN 197-1. The measured strength is also depicted in FIG. 1.

TABLE-US-00003 TABLE 3 sample C-L C-MK-L C-RCP C-MK-RCP limestone 40% 30% metakaolin 10% 10% cRCP 40% 30% 1 day strength 10.7 11.9 13 13.8 2 day strength 17.1 18.9 21.7 23.3 7 day strength 26 30.5 37.9 41 28 day strength 31.8 40.1 43.2 49

[0062] As is apparent, a composite cement with calcined clay and carbonated RCP provides significantly higher strength than one with calcined clay and limestone at the same level of SCM. At the same time, natural resources (limestone) can be saved and a waste product (RCP) made useful.