METHOD FOR PRODUCING SUPPLEMENTARY CEMENTITIOUS MATERIAL

Abstract

A method for producing a supplementary cementitious material from concrete waste and similar materials includes the steps of i) providing a starting material comprising hydrated cement and aggregate comprising silicate and/or alumino-silicate, ii) hydrothermal treatment of the starting material provided in step i) to obtain a hydrothermally activated material, and iii) carbonation of the hydrothermally activated material of step ii) to provide the supplementary cementitious material, as well as supplementary cementitious material obtainable by the method, hydraulic binder comprising the supplementary cementitious material and use of the supplementary cementitious material and of the hydraulic binder for making hydraulic building materials.

Claims

1: A method for producing a supplementary cementitious material comprising the steps: i) providing a starting material comprising hydrated cement and aggregate comprising silicates and/or alumino-silicates, ii) hydrothermal treatment of the starting material provided in step i) to obtain a hydrothermally activated material, and iii) carbonation of the hydrothermally activated material of step ii) to provide the supplementary cementitious material.

2: The method according to claim 1, wherein the hydrated cement and the aggregate is obtained from waste concrete.

3: The method according to claim 1, wherein the aggregate comprises crystalline or amorphous silicates, alumino-silicates or mixtures thereof.

4: The method according to claim 3, wherein the aggregate comprises quartz, basalt, granite, olivine and/or skarn.

5: The method according to claim 1, wherein water is added to the starting material obtained in step i), wherein a water-solid weight ratio is equal to or larger than 0.1.

6: The method according to claim 1, wherein the starting material provided in step i) has a particle size distribution determined by laser granulometry with a D.sub.90500 m.

7: The method according to claim 1, wherein the hydrothermal treatment in step ii) is carried out at a temperature in the range from 25 C. to 400 C. and/or at a pressure in the range from 1 bar to 25 bar and/or at a water-solid ratio from 0.2 to 4 and/or for 30 minutes to 48 hours.

8: The method according to claim 1, wherein the carbonation in step iii) is carried out at a temperature in the range from 20 C. to 200 C. and/or at a pressure in the range from 0.5 bar to 100 bar.

9: The method according to claim 1, comprising an additional step iv) of sulfurization of the supplementary cementitious material obtained in step iii).

10: A supplementary cementitious material obtained by the method defined in claim 1.

11: A method of manufacturing a hydraulic building material comprising producing a supplementary cementitious material by the method defined in claim 1.

12: A hydraulic binder comprising the supplementary cementitious material obtained by the method defined in claim 1 and a cement.

13: The hydraulic binder according to claim 12 comprising, based on the total weight of the hydraulic binder, 1 to 88% by weight supplementary cementitious material and 22 to 99% by weight cement.

14. (canceled)

15: The hydraulic binder according to claim 12, wherein the cement is selected from the group consisting of Portland cement, calcium sulfoaluminate cement and calcium aluminate cement.

16: The method according to claim 11, wherein the hydraulic building material is a composite binder, a concrete, a mortar, a screed or a tile adhesive.

17: The method according to claim 3, wherein the hydrated cement and aggregate is obtained from recycled concrete fines.

18: The method according to claim 4, wherein the hydrated cement and aggregate is obtained from recycled concrete fines.

19: The method according to claim 17, wherein the starting material provided in step i) has a particle size distribution determined by laser granulometry with a D90200 m.

20: The method according to claim 5, wherein the hydrated cement and aggregate is obtained from recycled concrete fines and the starting material provided in step i) has a particle size distribution determined by laser granulometry with a D90500 m.

21: The hydraulic binder according to claim 13, wherein the aggregate comprises crystalline or amorphous silicates, alumino-silicates or mixtures thereof and wherein the hydrated cement and aggregate is obtained from recycled concrete fines.

22: The hydraulic binder according to claim 15, wherein the aggregate comprises crystalline or amorphous silicates, alumino-silicates or mixtures thereof, wherein the hydrated cement and aggregate is obtained from recycled concrete fines, and wherein the starting material provided in step i) has a particle size distribution determined by laser granulometry with a D90200 m.

Description

[0100] The products (SCM) and hardened pastes as well as the hydrothermally activated materials were analysed with TG, FT-IR, and XRD. The PSD was measured for the SCM and for the starting materials. The results are illustrated in the figures and discussed below. In the figures:

[0101] FIG. 1 shows the pH evolution measured for samples of the autoclaved and carbonated samples mixed with water at a w/s (water/solid) of 10.

[0102] FIG. 2 shows FT-IR spectra of two starting materials, the hydrothermally activated material of them and the SCM obtained by carbonation,

[0103] FIG. 3 shows the particle size distribution of the ground starting material and the SCM obtained by autoclaving and carbonation,

[0104] FIG. 4 shows calorimetry data of pastes from the SCM and cement, and

[0105] FIG. 5 shows FT-IR spectra of the SCM and hardened pastes from the SCM and cement for two SCM.

[0106] FIG. 1 indicates that the reactions occurring during autoclaving had impact on the carbonation reaction. For the samples Q and G the early increase of the pH was significantly lower when compared to the comparative L mortars. The increase of the pH is associated with the dissolution of calcium rich hydrates and a fast consumption of CO.sub.2 dissolved in the solution. The lower increase resulted from the formation of lower Ca/Si hydrates in Q and G binders that are known to react slower with carbonates.

[0107] One notes that the evolution of the pH of the remaining hydrothermally treated samples is similar to the cements hydrated at normal conditions indicating that the wet carbonation mechanisms are universal.

[0108] After the autoclaving, the composition of the materials changed considerably. The composition is summarized in table 2. Most of the hydrates are decomposed and new phases are formed. These include mainly the partially crystalline hydrothermal CSH phases like -C.sub.2SH, Tobermorite, Scawtite, Dellaite, Hillebrandite. Still, the content of the XRD amorphous phase is significant. Furthermore, a formation of hydrogarnets (Katoite) is observed. This phase binds alumina, iron and small amounts of silica. Note that at the conditions applied, no asbestos was supposed to form. This was confirmed by the analyses, where no traces of this phase were found. It is noticeable that portlandite was consumed during hydrothermal activation (autoclaving) in the case of the starting materials from mortars Q and G with quartz and granite aggregate, respectively. These aggregates reacted with calcium ions to form hydrates. Analysing the changes of the mineral composition of the aggregates indicates that especially Feldspars and Quartz are hydrothermally reactive at the conditions used in the example, as illustrated by the formation of Tobermorite that is characterized by low Ca/Si ratio equal to 0.8. In the case of the mortar with limestone aggregate (L) a smaller amount of portlandite consumption is observed. Thus, limestone did not react, the observed change in portlandite content was negligible and can be assigned to a crystallization of other phases causing an increase in total mass.

TABLE-US-00002 TABLE 2 bound Ca(OH).sub.2 CaCO.sub.3 H.sub.2O (%, (%, (%, sample TG) TG) TG) Main Phases (QXRD) Q 8.9 4.2 Quartz (from aggregates), Hydrothermal CSH (Scawtite and Tobermorite), Amorphous, Katoite, Vaterite L 8.6 10.5 46.7 Calcite, Hydrothermal CSH (mainly -C.sub.2SH, Dellaite, Killalaite and Hillebrandite), Amorphous, Katoite Portlandite G 7.0 7.0 Muscovite (from aggregates), Hydrothermal CSH (mainly Scawtite and Tobermorite -C.sub.2SH, Dellaite, Killaite, Hillebrandite and Rosenhahnite), Amorphous, Katoite, Calcite, Aragonite

[0109] After the carbonation, the composition had changed again. Most of the CSH phase and the remaining portlandite were decomposed while XRD amorphous phases formed. Furthermore, significant amounts of calcium carbonate precipitated indicating the high carbonation degree of the hydrothermally activated material. The carbonation degree was similar among the investigated samples, indicating that the hydrothermal treatment has little impact on the extent and progress of the carbonation reaction. The compositions of the SCM are summarized in table 3.

TABLE-US-00003 TABLE 3 bound Ca(OH).sub.2 CaCO.sub.3 H.sub.2O (%, (%, (%, sample Tg) Tg) Tg) Main Phases (XRD) Q 7.2 46.9 Quartz (from aggregates), Vaterite and Calcite L 5.3 86.2 Calcite, Hydrothermal CSH, Amorphous, Katoite G 5.4 45.1 Feldspar, Muscovite, Quartz (from aggregates), Calcite, Vaterite, Hydrothermal CSH, Amorphous, Katoite

[0110] FT-IR data (FIG. 2) provide information about the transformations of the calcium silicate phases during the autoclaving and carbonation process. The FT-IR spectra of the SCM (after autoclaving and carbonation) were characterized by a large signal between 800 and 1200 cm.sup.1 which is associated with vibrations of SiO bonds. A peak at about 960 cm.sup.1, corresponding to the asymmetric stretching vibration of SiO bonds in the Q2 units of the CSH gel, was found in the starting material. After the autoclaving, the peak was at 930 cm.sup.1 which is associated with the hydrothermal CSH phase. The position of this peak moved with the progress of carbonation associated with the carbonation-induced decalcification of the CSH phase and the formation of alumina-silica gel. While during carbonation of hydrated cements without prior hydrothermal treatment the position of the peak was close to 1040 cm.sup.1, the position further decreased to 1080 cm.sup.1 here. This indicates some modification of the gel formed from the hydrothermally activated material. Note that the carbonation conditions were the same.

[0111] The particle size distribution of the starting material for the autoclaving process is shown in FIG. 3. All investigated samples were characterized by the same particle size distribution. However, after the autoclaving and carbonation, the particle size distribution was modified for samples Q and G. The origin of this phenomenon is currently not recognized.

[0112] The pozzolanic reactivity of the materials after hydrothermal treatment and after both, hydrothermal treatment and carbonation, was investigated. For this, the autoclaved and/or carbonated materials were mixed with portlandite and an activator (NaOH) to mimic the conditions in a composite cement paste. The pozzolanic reaction occurs according to the simplified equation:

AlSi-gel+CH.fwdarw.CS(A)-H+AFm

[0113] In this reaction the calcium aluminate phases react with portlandite to from mainly CSH phase. Additionally, AFm phases may form if the gel contains significant amounts of alumina. The progress of the reaction is proportional to the portlandite consumption which was measured and is given in table 4.

TABLE-US-00004 TABLE 4 consumed Ca(OH).sub.2 after consumed Ca(OH).sub.2 after sample autoclaving autoclaving and carbonation Q 6% 100% L 4% 58% G 13% 88%

[0114] The autoclaving alone did not promote a significant pozzolanic reaction in all the investigated samples. In the mixes Q and G containing autoclaved and carbonated material, i.e. SCM according to the invention, the consumption of portlandite is about 60% by weight. L was a reference sample in this set of the experiments since the limestone aggregate used cannot improve the pozzolanic properties as the limestone aggregates do not react with CO.sub.2. Samples from starting material containing olivine aggregate had similar consumption of portlandite as the limestone aggregate sample. The consumption of portlandite was slightly higher for basalt and significantly higher in the case of samples with quartz and granite aggregate. This confirms the hydrothermal activation of those aggregates.

[0115] Calorimetry data shown in FIG. 4 indicate that the samples from autoclaved and carbonated materials were reacting rapidly. However, the shape of the curves indicates that the reactions were not complete after 7 days.

[0116] The FT-IR spectra (FIG. 5) indicate the transformation of the AlSi gel into a CSH phase for the hydrated samples. The main position of the SiO vibration moved from 1040-1080 cm.sup.1 to 950 cm.sup.1. This was associated with a binding of significant amounts of the water, typical for hydrates.

[0117] Thus, hydrothermal treatment of waste concrete allows to transform a higher amount of the material into SCM by carbonation and thereby provides more reactive SCM. This enables further saving of natural raw materials and reduction of CO.sub.2 emission for the production of binders. Less effort is needed to detach RCP from aggregate and/or to separate RCF from RCA.