RETARDING MIXTURE FOR ALKALI-ACTIVATED BINDING AGENTS

Abstract

The invention relates to a retarding mixture comprising sodium gluconate and alkali hydrogen carbonate, an alkali-activated binding agent containing sodium gluconate and alkali hydrogen carbonate and a method for adjusting the strength development, wherein sodium gluconate and alkali hydrogen carbonate are added to an alkali-activated binding agent.

Claims

1. Retarding mixture for alakali-activated binding agents, characterised in that it contains a mixture of sodium gluconate and alkali hydrogen carbonate.

2. Retarding mixture according to claim 1, characterised in that the alkali hydrogen carbonate is a sodium hydrogen carbonate, a potassium hydrogen carbonate or a mixture thereof.

3. Retarding mixture according to claim 1, characterised in that the weight ratio of sodium gluconate to alkali hydrogen carbonate ranges from 9:1 to 1:4, preferably from 3:1 to 1:1.

4. Retarding mixture according to claim 1, characterised in that additional retarders based on lignosulphonates, sulphonated naphthalene, melamine or phenol formaldehyde condensates; or based on acrylic acid acrylamide mixtures or polycarboxylate ethers or based on phosphated polycondensates; based on phosphated alkyl carboxylic acids and salts of these; based on (hydroxy)carboxylic acids and carboxylates, in particular citric acid, citrates, tartaric acid, tartrates; borax, boric acid and borates, oxalates; sulfanilic acid; aminocarboxylic acids; salicylic acid and acetylsalicylic acid; dialdehydes and mixtures thereof are contained.

5. Retarding mixture according to claim 4, characterised in that the additional retarders are present in a weight proportion of 10% to 50%, with regard to the retarding mixture.

6. Retarding mixture according to claim 4, characterised in that borax, boric acid and borates are used as additional retarders.

7. Alkali-activated binding agent comprising latent hydraulic and/or pozzolanic component(s) which provide aluminosilicates and/or silicates and aluminosilicates and/or calcium (alumino)silicates, characterised in that a retarding mixture according to claim 1 is contained.

8. Alkali-activated binding agent according to claim 7, characterised in that the latent hydraulic and or pozzolanic component(s) are selected from the group consisting of calcined clay, calcium-rich and/or siliceous fly ash, granulated blast furnace slag, slag and mixtures thereof.

9. Alkali-activated binding agent according to claim 7, characterised in that it contains at least 40% latent hydraulic components and/or calcium-rich, pozzolanic components.

10. Alkali-activated binding agent according to claim 7, characterised in that the latent hydraulic and/or pozzolanic component(s) together have a CaO content of at least 10 wt %.

11. Alkali-activated binding agent according to claim 7, characterised in that from 0.1 to 10 wt % retarding mixture with regard to the binding agent, preferably from 0.5 to 5 wt % and most preferably from 1 to 3 wt % are contained.

12. Alkali-activated binding agent according to claim 7, characterised in that the activated is selected from alkali silicates, hydroxides, alkali carbonates, alkali sulphates, Portland cement, Portland cement clinkers and mixtures of two or more thereof.

13. Alkali-activated binding agent according to claim 7, characterised in that the activator has a weight ratio SiO.sub.2/Na.sub.2O.sub.equivalent of at least 1.0, preferably of at least 1.25.

14. Alkali-activated binding agent according to claim 7, characterised in that it contains aluminosilicates, silicates and aluminates and/or calcium (alumino)silicates made of calcined clay, calcium-rich and/or siliceous fly ash, granulated blast furnace slag and/or slag.

15. Alkali-activated binding agent according to claim 7, characterised in that concrete liquefier and/or plasticizer and/or additional retarder are contained, preferably based on lignin sulphonates; sulphonated naphthalene, melamine or phenolformaldehyde condensate; or based on acrylic acid acrylamide mixtures or polycarboxylate ethers or based on phosphated polycondensates; phosphated alkyl carboxylic acid and salts of these; (hydroxy)carboxylic acids and carboxylates, in particular citric acid, citrate, tartaric acid, tartrates; borax, boric acid and borates, oxalates; sulfanilic acid; aminocarboxylic acids; salicylic acid and acetylsalicylic acid; dialdehydes and mixtures thereof.

16. Method for adjusting the strength development of alkali-activated binding agents, characterised in that sodium gluconate and alkali hydrogen carbonate are added to the alkali-activated binding agent as a retarding mixture.

17. Method according to claim 16, characterised in that a sodium hydrogen carbonate, a potassium hydrogen carbonate or a mixture thereof is used as an alkali hydrogen carbonate.

18. Method according to claim 16, characterised in that from 0.1 to 10 wt % of retarders with regard to the binding agent, preferably from 0.5 to 5 wt % and most preferably from 1 to 3 wt %, are used.

19. Method according to claim 16, characterised in that sodium gluconate and alkali hydrogen carbonate are used in a weight ratio sodium gluconate to alkali hydrogen carbonate in the range from 9:1 to 2:8, preferably from about 3:1 to 1:1.

Description

EXAMPLE 1

[0059] An alkali-activated binding agent comprising 64 wt % fly ash 1, 21 wt % granulated blast furnace slag 1 and 15 wt % activator with regard to the solid content of the binding agent was produced by mixing the aforementioned components. The SiO.sub.2/Na.sub.2O ratio in the activator solution, consisting of a 40% NaOH solution and a commercial water glass by the company PQ (product name: C0265) in the mixing ratio of about 1:1.7, here amounted to 1.0. Before bringing together the aforementioned components, fly ash 1 was here ground down to a fineness of 2850 cm.sup.2/g, granulated blast furnace slag to a fineness of 4920 cm.sup.2/g. The chemical composition of fly ash 1 and granulated blast furnace slag 1 is stated in Table 3. For the binding agent system, a CaO content of 15.1 wt % in terms of the solid content of the binding agent results.

TABLE-US-00003 TABLE 3 Granulated Granulated blast blast furnace furnace slag 1 slag 2 Fly ash 1 Fly ash 2 Fly ash 3 LOI at 0.13 1.67 0.45 0.33 3.20 1050 C. SiO.sub.2 32.91 36.65 55.55 33.60 56.73 Al.sub.2O.sub.3 13.66 11.60 23.14 17.98 21.07 TiO.sub.2 0.47 0.90 1.35 1.52 0.94 MnO 0.34 0.37 0.05 0.02 0.06 Fe.sub.2O.sub.3 1.22 0.46 5.12 5.74 7.71 CaO 41.01 38.89 10.14 27.46 4.07 MgO 5.17 7.83 1.86 6.21 1.91 K.sub.2O 0.35 0.66 0.95 0.38 1.78 Na.sub.2O 0.11 0.17 0.10 2.06 0.88 SO.sub.3 2.72 2.79 0.31 1.87 0.10 P.sub.2O.sub.5 0.02 0.00 0.10 1.32 0.40 Sum 98.11 101.99 99.12 98.58 98.85

[0060] Different substances that have been suggested as retarders and the retarder according to the invention were added to the binding agent in a quantity of 4%. Bringing together the components mentioned above in a homogeneous mixture here took place in the following order: 1) fly ash, 2) granulated blast furnace slag, 3) diverse retarders or the retarding mixture according to the invention, 4) activator solution, consisting of sodium hydroxide solution and water glass, 5) mixing water (demin. water). 20 g of binding agent were stirred in by hand at 20 C. and W/B=0.40 in a single-use plastic beaker for two minutes with a spatula, transferred to a small plastic bag that can be sealed to be airtight and then the setting and hardening properties of the paste were observed, tested by bending and finger pressure and assessed according to a number system. The assessment of the solidification takes place according to an empirically developed system of a total of 6 numbers. Numbers 0-3 here describe the properties of the sample before hardening up to a setting that is roughly in the region of the setting end according to DIN 1164. Numbers 4-6 describe the subsequent hardening properties. Number 6 generally points to a mortar compressive strength in the region of about 4 MPa. The numbering of the effects observed obviously includes a subjective, personal component, however, from experience that becomes fairly uniform with increasing practice. The numbering enables the comparison of samples by tabular and graphic depiction. The depiction in curves provides an additional plausibility check. The method is particularly well suited to the relative assessment of solidification processes before and during the setting of binding agents as part of series samples that are changed systematically and in steps. It presents a meaningful precursor to standard tests in which the effect tendency of certain additives or binding agent mixtures, where necessary also by means of a large number of individual attempts, can be seen while using small amounts of material. The time t.sub.ini up to a slight but noticeable stiffening (leathery) was determined. The frequency of the test of a sample was thus determined according to the character of the binding agent, with a rapidly setting and/or rapidly hardening binding agent it proved to be appropriate to check at intervals of about 5 minutes at the start or even more regularly. The results are summarised in Table 4.

TABLE-US-00004 TABLE 4 Retarder t.sub.ini [min.] without ZnO NaP.sub.2O.sub.7 NaAlO.sub.2 C.sub.18H.sub.35NaO.sub.2 NaHCO.sub.3 30 C.sub.6H.sub.8O.sub.7 40 Na.sub.2HPO.sub.42H.sub.2O + 45 C.sub.6H.sub.11NaO.sub.7 + NaHCO.sub.3 Lignin sulphonate + NaHCO.sub.3 55 Na.sub.2HPO.sub.42H.sub.2O 60 Na.sub.2HPO.sub.42H.sub.2P + C.sub.6H.sub.11NaO.sub.7 65 Borax 65 C.sub.6H.sub.11NaO.sub.7 90 C.sub.6H.sub.11NaO.sub.7 + NaHCO.sub.3 120 ( = not able to be checked, immediate setting)

[0061] It is apparent that many substances lengthened the open time, however the mixture according to the invention showed the greatest effect.

EXAMPLE 2

[0062] The binding agent of example 1 and an analogously composed binding agent with fly ash 2 were mixed with 1% of different retarders and, as in example 1, the time until the noticeable stiffening of the paste samples was determined. Furthermore, as described in [00019], mortar prisms were produced and, in addition, the compressive strength was measured after 28 days (stored at 20 C., 100% rel. air humidity). Table 5 summarises the results.

TABLE-US-00005 TABLE 5 Fly ash 1 Fly ash 2 average CaO content high CaO content 28 days 28 days compressive compressive Retarder t.sub.ini [min] strength [MPa] t.sub.ini [min] strength [MPa] without 40 45 NaHCO.sub.3 40 42 Na.sub.2HPO.sub.42 H.sub.2O 45 33 15 28 C.sub.6H.sub.11NaO.sub.7 70 45 45 57 C.sub.6H.sub.11NaO.sub.7 + 95 51 65 62 NaHCO.sub.3 Lignin sulphonate + 50 48 20 58 NaHCO.sub.3 C.sub.6H.sub.11NaO.sub.7 + 55 36 20 35 Na.sub.2HPO.sub.42 H.sub.2O Borax 50 46 25 55

[0063] With fly ash 1 that produces a binding agent with a CaO content of about. 15.1 wt % with regard to the solid content of the binding agent, it turned out again that indeed many comparison substances caused a retardation, but not as significantly as according to the invention. The 28 day compressive strength was here impaired or not changed by most substances, however with the retarder according to the invention, it significantly increased.

[0064] The binding agent with fly ash 2 had a higher CaO content of about. 26.2 wt % with regard to the solid content of the binding agent and, without retarders, could not be mixed in at all. Adding sodium hydrogen carbonate alone also did not help. With the measurable systems, there was a useful open time and a high compressive strength only for the additive according to the invention.

EXAMPLE 3

[0065] To illustrate the problem underlying the invention, FIG. 1 a shows the spreading capacity measured in mortar samples according to DIN/EN1015-3, and FIG. 1 b shows the compressive strength measured in mortar samples according to DIN/EN 1015-11.

[0066] The binding agents used to produce the mortar samples in each case contained fly ash 3 (FA3) and granulated blast furnace slag 2 (S2) in variable mixing ratios (FA3/S2=7.31.0), comprising 85 wt % (total) with regard to the solid content of the binding agent. The CaO content with regard to the solid content of the respective binding agent thus increased from about 7.0 wt % (FA3/S2=7.3) to about 18.0 wt % (FA3/S2=1.0) successively. The chemical composition of fly ash 3 and granulated blast furnace slag 2 is stated in Table 3. The SiO.sub.2/Na.sub.2O ratio in the activator used equally for all binding agents, consisting of 40% NaOH solution and a commercial water glass by the company PQ (product name: C0265) in the mixture ratio of about 1:1.7, here amounted to 1.0. The W/B was set to 0.40 for all mortar mixtures. Before bringing together the aforementioned components, fly ash 3 was there ground to a fineness of 4360 cm.sup.2/g, granulated blast furnace slag 2 to a fineness of 4450 cm.sup.2/g.

[0067] It can be easily seen in FIG. 1 a that binding agents with successively increasing CaO content (about 7.0-18.0 wt % with regard to the solid content of the binding agent) respectively increasing granulated slag portion (FA3/S2=7.31.0), are worse in processability. In mortar samples, the spreading capacity already significantly decreases after 30-45 min with significantly increased CaO content of >10.0 wt %, accompanied by a clear stiffening of the samples. With an increasing CaO content, the open time reduces to such an extent that a processing is no longer possible. Thus, for such geopolymer binding agents, retarding admixtures are necessary.

[0068] FIG. 2 clarifies the ambivalent character of variable CaO contents already described in [00020]. While the binding agent FA3/S2 described in [00060] with a low CaO content of <10 wt % indeed showed a good processability, though a poor strength development, with the binding agent systems based on fly ash/granulated blast furnace slag, FA3/S2 with a significantly higher CaO content>10 wt %, a poorer processability in the sense of a very short open time was generally associated with high strengths.