Building elements made from binders hardening by combined hydration and carbonation

Abstract

A method of manufacturing building elements has the steps: providing a binder comprising at least 8% by weight ternesite, at least 15% by weight dicalcium silicate and at least 5% by weight ye'elimite, each with respect to the total binder, as hydraulically reactive phases; mixing the binder with water to form a paste; casting the paste into a desired shape for the building element; reacting the paste hydraulically to form calcium-silicate-hydrates, calcium-aluminium-silicate-hydrates, portlandite, brucite, strätlingite, hydrotalcite-like phases and ettringite/AFm and capillary pores, and carbonation hardening to provide the building element and to building elements obtainable by the method.

Claims

1. A method of manufacturing building elements comprising the steps: providing a binder comprising at least 8% by weight ternesite, at least 15% by weight dicalcium silicate and at least 5% by weight ye'elimite, each with respect to the total binder, as hydraulically reactive phases mixing the binder with water to form a paste casting the paste into a shape for the building element reacting the paste hydraulically to form hydrated phases and to create additional capillary pores, and carbonation hardening to provide the building element.

2. The method according to claim 1, wherein the binder contains at least 28% by weight hydraulically reactive phases relative to the total binder weight.

3. The method according to claim 1, wherein in addition to ternesite, dicalcium silicate, and ye'elimite at least one additional hydraulically reactive phase selected from the group consisting of ellestadite, ferritic phases, and amorphous hydraulic phases is contained.

4. The method according to claim 1, wherein the water-to-binder ratio with respect to the sum of hydraulically reactive phases in binder is set from 0.2 to 1.2.

5. The method according to claim 1, wherein the hydrated phases of the hydraulically reactive phases form a major part of the phases hardening by carbonation.

6. The method according to claim 1, wherein periclase or free lime hardening by carbonation are present in the provided binder in an amount of up to 15% by weight each and up to 30% combined.

7. The method according to claim 1, wherein at least one of water reducing agents, plasticizers and/or super plasticizers are added to adjust consistency while keeping the water-to-binder ratio in the range suitable for self-desiccation.

8. The method according to claim 1, wherein air entraining agents are added to the binder.

9. The method according to claim 1, wherein additives are added, selected from the group consisting of fillers, pigments, reinforcing elements, and self-healing agents.

10. The method according to claim 1, wherein the binder contains 8 to 75% by weight ternesite, 15 to 80% by weight dicalcium silicate, 5 to 70% by weight ye'elimite, 0 to 50% by weight C.sub.6A.sub.xF.sub.y with x+y=3 and both x and y≥0 and x≤y, 0 to 20% by weight reactive aluminates 0 to 30% by weight hydraulic X-ray amorphous phase, 0 to 30% by weight minor phases, all with respect to the total amount of binder.

11. The method according to claim 1, wherein the paste is subjected to hydraulic hardening within an atmosphere of 40 to 99% relative humidity and having a temperature from 10 to 80° C.

12. The method according to claim 1, wherein carbonation takes place in an atmosphere rich in CO.sub.2 that has a pressure of CO.sub.2 ranging from of 0.005 to 2 MPa, and a temperature in the range from 15° C. up to 100° C.

13. The method according to claim 12, wherein CO.sub.2 rich exhaust gas is used to provide the atmosphere rich in CO.sub.2.

14. A building element obtained from a binder comprising at least 8% by weight ternesite, at least 15% by weight dicalcium silicate and at least 5% by weight ye'elimite as hydraulically reactive phases, by a method according to claim 1.

15. The building element according to claim 14 in the form of a pre-cast concrete element.

16. The method according to claim 1, wherein the binder contains at least 50% by weight hydraulically reactive phases relative to the total binder weight.

17. The method according to claim 1, wherein the water-to-binder ratio with respect to the sum of hydraulically reactive phases in the binder is set from 0.25 to 0.8.

18. The method according to claim 1, wherein the water-to-binder ratio with respect to the sum of hydraulically reactive phases in the binder is set from 0.35 to 0.6.

19. The method according to claim 10, wherein the water-to-binder ratio with respect to the sum of hydraulically reactive phases in the binder is set from 0.25 to 0.8.

20. The method according to claim 10, wherein the paste is subjected to hydraulic hardening within an atmosphere of 40 to 99% relative humidity and having a temperature from 10 to 80° C.

21. The method according to claim 12, wherein the atmosphere rich in CO.sub.2 has pressure of CO.sub.2 ranging from 0.05 to 0.5 MPa and a temperature ranging from 15° C. up to 50° C.

22. The method according to claim 21, wherein the binder contains 8 to 75% by weight ternesite, 15 to 80% by weight dicalcium silicate, 5 to 70% by weight ye'elimite, 0 to 50% by weight C.sub.6A.sub.xF.sub.y with x+y=3 and both x and y≥0 and x≤y, 0 to 20% by weight reactive aluminates 0 to 30% by weight hydraulic X-ray amorphous phase, 0 to 30% by weight minor phases, all with respect to the total amount of binder, and the water-binder ratio with respect to the sum of hydraulically reactive phases in the binder is set from 0.35 to 0.6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the hardening mechanism of the binder according to the invention:

(2) FIG. 2 shows a graph of the compressive strength of the samples

(3) FIG. 3 shows the results of TG measurements of the hardened paste and mortar:

(4) FIG. 4 shows a graph of the compressive strength and density measured on the mortar samples;

(5) FIGS. 5a and 5b show the result of differential gravimetric analysis;

(6) FIG. 6 shows the XRD spectra; and

(7) FIGS. 7a and 7b show the strength and thermogravimetric behavior measurements of mortars and pastes made according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) The invention will be illustrated further with reference to the examples that follow, without restricting the scope to the specific embodiments described. If not otherwise specified any amount in % or parts is by weight and in the case of doubt referring to the total weight of the composition/mixture concerned.

(9) The invention further includes all combinations of described and especially of preferred features that do not exclude each other. A characterization as “approximately”, “around” and similar expression in relation to a numerical value means that up to 10% higher and lower values are included, preferably up to 5% higher and lower values, and in any case at least up to 1% higher and lower values, the exact value being the most preferred value or limit.

(10) The term “substantially free” means that a particular material is not purposefully added to a composition, and is only present in trace amounts or as an impurity. As used herein, unless indicated otherwise, the term “free from” means that a composition does not comprise a particular material, i.e. the composition comprises 0 weight percent of such material.

EXAMPLE 1

(11) A TBF cement with the oxide composition presented in table 1 was used. It contained, according to XRD Rietveld, 23.6% by weight ternesite, 23.3% by weight dicalcium silicate, 11.8% by weight ye'elimite, 6.1% by weight C.sub.4AF, 3.7% by weight C.sub.2F, 19.2% by weight amorphous hydraulic phase, and 12.3% by weight minor phases, including anhydrite, lime, periclase, quartz, hematite, Ca-langbeinite, maghemite, akermanite each in an amount below 2% by weight. The density was 3.16 g/cm.sup.3, the fineness according to Blaine 2020 cm.sup.2/g.

(12) TABLE-US-00001 TABLE 1 LOI 1050° C. 0.31% by weight SiO2 18.42% by weight Al2O3 8.42% by weight TiO2 0.38% by weight MnO 0.11% by weight Fe2O3 10.38% by weight CaO 49.33% by weight MgO 2.01% by weight K2O 0.57% by weight Na2O 0.3% by weight SO3 9.34% by weight P2O5 0.39% by weight Sum 99.96% by weight

(13) Mortar samples were made from water, cement and sand in a weight ratio 0.5:1:1.3 and pastes from water and cement in a ratio 0.5:1. Mixing was carried out in a Hobart mixer, 15 sec. slow and 15 sec. fast as specified in EN 196. All samples were initially hydrated for 18 h in sealed containers at 50° C. Afterwards, the samples were dried in an oven at 50° C. and either stored under ambient air at 20° C. and relative humidity of about 55% (reference sample) or under 2.5 bar CO.sub.2 at 20° C. (carbonated sample). Paste samples were crushed to <2 mm before storage in ambient air or under CO.sub.2 pressure. The compressive strength of hardened mortar samples was determined according to the procedure specified in EN 196 and hardened pastes and mortars were examined with thermogravimetry in Netzsch Jupiter STA 449 device.

(14) The compressive strength of the samples is depicted in FIG. 2, it can be seen that carbonation almost doubled compressive strength. The samples gained on average 0.6 g corresponding to about 10% cement mass during carbonation. This mass change includes the CO.sub.2 bound as well as water lost during the carbonation. To distinguish between these two mass changes, a differential thermogravimetric analysis (TG) was made.

(15) FIG. 3 shows the results of TG measurements on the hardened paste and mortar. The weight loss from about 500° C. to about 850° C. shows that a significant amount of calcite was formed during carbonation. Pastes gained about 28% calcite corresponding to about 15% mass gain and mortars gained about 13% calcite corresponding to about 6% of mortar mass corresponding to about 14% of cement mass.

EXAMPLE 2

(16) The same clinker as in example 1 was used, however, ground to a fineness of 2910 cm.sup.2/g according to Blaine. Mortar and paste samples were made analogously to example 1. All samples were initially hydrated for 24 h in sealed containers at 50° C. Afterwards, the samples were treated with one or more of the following: D: dried 24 h in an oven at 50° C. L: stored 24 h under ambient air at 20° C. and relative humidity of about 55% CO.sub.2: stored 24 h under 2.5 bar CO.sub.2 at 20° C.
The compressive strength and density of hardened mortar samples was determined according to the procedure described in EN 196 and hardened pastes and mortars were examined with thermogravimetry in Netzsch Jupiter STA 449 device.

(17) FIG. 4 shows the compressive strength and density measured on the mortar samples. The comparison of the strength for sample C—CO2 that is hydrated and carbonated with C—L that is only hydrated (but hydrated longer than C—CO.sub.2) shows that carbonation improves hardening, higher strength is gained by subsequent carbonation than with prolonged hydration. The drying at elevated temperature enhances hardening in itself by accelerating hydration and improving carbonation. Thus, sample C—D that is only hydrated but longer than sample C—L has a higher strength than that, but carrying out carbonation according to the invention provides much higher strength as shown by sample C—D—CO.sub.2. These findings are confirmed by the measured densities. The gained 0.1 g/cm.sup.3 correspond to the bound CO.sub.2 in the carbonated samples.

(18) The result of differential thermogravimetric analysis is shown in FIGS. 5a and 5b. It can be seen in FIG. 5a that drying does not change the hydrates formed initially, compare sample C only hydrated with sample C—D that was hydrated and dried in an oven. During carbonation under 2.5 bar CO.sub.2 the hydrates partially decompose and form carbonates, compare samples C+CO.sub.2 and C+D+CO.sub.2 with sample C in FIG. 5b. The mass loss between ˜500° C. and ˜850° C. is due to decomposition of CaCO.sub.3 and shows that about 40% of CaO is bound as carbonate during carbonation.

(19) FIG. 6 shows the XRD spectra. The TG result is confirmed, namely that drying does not change the hydrates. Further, carbonation of AFm takes place in all samples carbonated with 2.5 bar CO.sub.2. Carbonation of ettringite only occurs in dried samples.

EXAMPLE 3

(20) Mortars and pastes were made analogously to example 2 from the cement used in example 1. In addition to the treatments in example 2, samples were carbonated by placing them 24 h in the chimney of the operating cement plant. Thus, carbonation took place in cement plant exhaust gas for samples designated PI. Like in example 2 the strength and thermogravimetric behavior were measured. The results are shown in FIGS. 7a and 7b and confirm that cement plant exhaust gas is a very suitable medium for carbonation.

(21) Last but not least, carbonation depth was measured by spraying with 1% by weight thymolphthalein in a mixture of 70 Vol. % ethanol and 30 Vol. % water. All samples carbonated in exhaust gas showed no coloring at all, i.e. were fully carbonated. In contrast, the reference samples that were only dried or stored in ambient air were deeply coloured.