Stabilized solidification and setting accelerator for hydraulic binders

Abstract

A solidification and setting accelerator for hydraulic binders, in particular for shotcrete/gunite or sprayed mortar, comprises sulfate, aluminum and at least two chemically distinct organic acids, each of which contains at least one hydroxy group in addition to at least one acid group, the combined maximum content of the at least two organic acids being 1 wt % in relation to the total weight of the accelerator.

Claims

1. A solidification and hardening accelerator for hydraulic binders, comprising sulfate, aluminum, and at least two chemically different organic acids, each having at least one hydroxyl group as well as at least one acid group, the combined maximum fraction of the at least two organic acids being 0.95 wt % based on the total weight of the accelerator, wherein at least one of the two organic acids is a hydroxycarboxylic acid.

2. The accelerator as claimed in claim 1, wherein the hydroxycarboxylic acid has a weight fraction of 0.05-0.8 wt % based on the total weight of the accelerator.

3. The accelerator as claimed in claim 1, wherein at least one of the two organic acids contains as acid group an enol group, an enediol group or a reductone group.

4. The accelerator as claimed in claim 3, wherein the organic acid having an enol group, an enediol group or a reductone group has a weight fraction of 0.05-0.8 wt % based on the total weight of the accelerator.

5. The accelerator as claimed in claim 1, wherein a first of the two organic acids is a hydroxycarboxylic acid and in that a second of the two organic acids contains as acid group an enol group, an enediol group or a reductone group.

6. The accelerator as claimed in claim 1, wherein a first of the two organic acids is citric acid and a second of the two organic acids is ascorbic acid.

7. The accelerator as claimed in claim 1, wherein a weight ratio of the at least two different organic acids is in the range of 5:1-1:5.

8. The accelerator as claimed in claim 1, wherein it comprises 17 to 35 wt % of sulfate, 3.2 to 9.5 wt % of aluminum, and 0.001 to 1 wt % of the at least two organic acids, based on the total weight of the accelerator.

9. The accelerator as claimed in claim 1, wherein 0.1 to 10 wt % of magnesium hydroxide, magnesium oxide, magnesium oxyhydroxide, magnesium carbonate and/or the corresponding amount of another magnesium compound, based on the total weight of the accelerator, are present.

10. The accelerator as claimed in claim 1, wherein a fraction of further acids is less than 0.1 wt % based on the total weight of the accelerator.

11. A method for accelerating the solidification and hardening of hydraulic binders, concrete comprising hydraulic binders, or mortar comprising hydraulic binders, wherein a mixture which comprises hydraulic binders is admixed with a solidification and hardening accelerator as claimed in claim 1 in an amount of 0.1 to 15 wt %, based on the weight of the hydraulic binder.

12. A method of making a hydraulic binder-comprising mixture, comprising adding the solidification and hardening accelerator as claimed in claim 1 to a hydraulic binder.

13. A binder-comprising mixture comprising a hydraulic binder and the accelerator as claimed in claim 1.

14. A cured shaped article obtained by curing a binder-comprising mixture as claimed in claim 13, tempered with water.

Description

WORKING EXAMPLES

(1) 1. Production of Accelerators

(2) Various accelerators A1-A2 (inventive) and B1-B11 (comparative tests) were produced, with the compositions described in table 1. In each case the water was introduced at room temperature (about 20 C.), the magnesium hydroxide was slurried in this water, and the acid or acids identified in table 1 (quantity figure based in each case on pure acid(s) or active substance) were added, producing an increase in the temperature of the solution. Thereafter the aluminum sulfate (17% Al.sub.2O.sub.3) and the aluminum hydroxide (amorphous) were added and dissolved at elevated temperature. The solution was then stirred until, after about an hour, the temperature had dropped to about 40 C. The accelerators thus are present in the form of clear solutions with in some cases finely dispersed particles.

(3) TABLE-US-00001 TABLE 1 Accelerator compositions (all amounts in wt %) Al(OH).sub.3 Acid(s)/ No. H.sub.2O (amorphous) Al.sub.2(SO.sub.4).sub.314 H.sub.2O Mg(OH).sub.2 Fraction(s) A1 45.70 15.60 37.00 1.00 Citric acid/0.50 Ascorbic acid/0.20 A2 45.45 15.60 37.00 1.00 Citric acid/0.50 Ascorbic acid/0.20 Formic acid/0.25 B1 45.90 15.60 37.00 1.00 Citric acid/0.50 B2 45.10 15.60 37.00 1.00 Citric acid /1.30 B3 44.75 15.60 37.00 1.00 Citric acid/0.50 Ascorbic acid/1.15 B4 44.70 15.60 37.00 1.00 Citric acid /1.02 Ascorbic acid/0.68 B5 45.95 15.60 37.00 1.00 Ascorbic acid/0.20 Formic acid/0.25 B6 45.66 15.60 37.00 1.00 Ascorbic acid/0.43 Formic acid/0.31 B7 46.20 15.60 37.00 1.00 Ascorbic acid/0.20 B8 45.65 15.60 37.00 1.00 Citric acid/0.50 Formic acid/0.25 B9 45.51 15.60 37.00 1.00 Citric acid/0.61 Formic acid/0.28 B10 46.40 15.60 37.00 1.00 B11 44.58 15.60 37.00 1.00 Phosphoric acid/1.82
2. Properties and Effect of the Accelerators

(4) The accelerators were evaluated by eye for their stability. This stability represents the time (measured in days) during which an accelerator solution remains substantially unchanged in terms of viscosity and phase structure when viewed at room temperature (about 20 C.) in a tightly sealed container. This means that within this period there is no significant sedimentation, and the water-like flow behavior present at the start is retained. Table 2 lists the stabilities thus determined of the accelerators from table 1. Values of more than 145 days are considered very good. Values below 145 days or less than 5 months may already entail massive restrictions; from production through delivery to distribution centers, delivery to customers, and the processing of an accelerator, the time may be scarce.

(5) The activity of the accelerator compositions (A1-A2 and B1-B11) was determined using a sprayed concrete-equivalent cement paste. The cement paste consists of 8000 g of Portland cement (hydraulic binder), 1600 g of finely ground limestone, 0.7 wt % of Sika ViscoCrete SC-500 (superplasticizer; available from Sika Deutschland GmbH; percentage based on the amount of the hydraulic binder) and water (w/c=0.42).

(6) The cement pastes were subsequently applied to an ultrasound measuring cell, using a miniaturized sprayed concrete apparatus, with admixing of 6 wt % (based on the amount of the hydraulic binder) in each case of accelerator in the nozzle region. The development of the solidification and hardening process of the applied cement paste was then measured by the ultrasound measurement method as described in chapter 3 of the publication by L. Oblak et al. (L. Oblak, B. Lindlar, and D. Lootens Kontinuierliche Messung der Festigkeitsentwicklung von Spritzbeton [8 Continuous measurement of development of strength in sprayed concrete], Sprayed concrete conference 2012 Alpbach). The parameter determined in each case was the development in the shear modulus G over time. During the ultrasound measurements, the temperature was measured in each case directly on the applied cement paste and on the ultrasound spread section, and the temperature dependence of the ultrasound measurement results was included in the considerations. As set out in the publication referred to above, the ultrasound measurement method correlates very well with common measurement methods such as, for example, Proctor meter, Hilti fired bolt, and compressive strength. The results of the ultrasound measurements are directly comparable, accordingly, with results determined by these methods.

(7) Table 2 shows the results of the spraying tests. Indicated in each case are the shear moduli G at times 2 minutes, 6 minutes, and 200 minutes after application. These are particularly relevant times for sprayed concrete applications in particular.

(8) TABLE-US-00002 TABLE 2 Stabilities of the accelerators and results of the spraying tests Shear modulus G after x Stability minutes [MPa] Accelerator [Days] x = 2 min x = 6 min x = 200 min A1 155 1.9 32 230 A2 159 0.9 20 178 B1 140 1.2 20 177 B2 55 0.5 18 245 B3 179 1.6 21 128 B4 180 0.6 14 124 B5 123 B6 119 B7 107 B8 80 B9 77 B10 54 3.4 33 887 B11 124 2.3 31 544

(9) From table 2 it is apparent that the inventive accelerators A1 and A2 exhibit very good stabilities of 155 and 159 days respectively. Similarly, at all of the times investigated, after 2 minutes, 6 minutes, and 200 minutes, high values are achieved for the shear modulus G and respectively for the strengths which correlate with it. This is so in particular for accelerator A1, which in comparison to accelerator A2 contains no formic acid.

(10) While it is possible to obtain even higher values with the shear modules G using accelerators without acid (B10) or accelerators containing phosphoric acid (B11), such accelerators nevertheless score poorly for stability.

(11) With the accelerators B3 and B4, which possess a noninventive fraction of ascorbic acid (B3; 1.15 wt %) and citric acid (B4; 1.02 wt %), respectively, very high stability values are achieved. In comparison with accelerator A1, however, for example, these accelerators are clearly inferior in terms of shear modulus G and/or strength development.

(12) Ascorbic acid alone (B7) or citric acid alone (B2; 0.5 wt % and B2, 1.3 wt %) on their own produce clearly poorer to very poor stability values. The accelerator with 0.5 wt % of citric acid alone (B1), moreover, scores much more poorly, in terms of the development of the shear modulus at all times, than the comparable accelerator with citric acid and ascorbic acid (A1). When using 1.3 wt % of citric acid alone (B2), a higher shear modulus G is achieved than with accelerator A1 at later times (200 min), but at earlier times particularly relevant for sprayed concrete applications (2 min and 6 min) the corresponding values are very much lower.

(13) The embodiments described above should, however, be understood merely as illustrative examples, which may be modified as desired within the scope of the invention.