Accelerator

Abstract

A hardening accelerator for mineral binder compositions, in particular for cementitious binder compositions, including at least one phosphoric acid ester of a polyvalent alcohol and at least one alkali metal carbonate.

Claims

1. A composition comprising at least one mineral binder and at least one hardening accelerator for mineral binders comprising at least one phosphoric acid ester of a polyhydric alcohol, at least one calcium compound, and at least one alkali metal carbonate; wherein the hardening accelerator is in the form of an at least two-component hardening accelerator, with the at least one calcium compound being present in a first component, while the at least one phosphoric acid ester of a polyhydric alcohol and the at least one alkali metal carbonate are present together in a second component or are present separately from one another as further individual components.

2. The composition as claimed in claim 1, comprising, based in each case on the weight of the binder: a) the at least one phosphoric acid ester of a polyhydric alcohol in an amount of 0.001 to 2 wt %, b) the at least one alkali metal carbonate in an amount of 0.001 to 6 wt %, c) the at least one calcium compound with a fraction of 0.001 to 10 wt %.

3. A method for reducing an influence of magnesium carbonate on accelerating admixtures, in a mineral binder composition comprising magnesium carbonate, and/or for improving an effect of an accelerating admixture in a mineral binder composition comprising magnesium carbonate, said method comprising addition of a hardening accelerator for mineral binders comprising at least one phosphoric acid ester of a polyhydric alcohol and at least one alkali metal carbonate to said mineral binder composition.

4. The method as claimed in claim 3, wherein the at least one phosphoric acid ester is a partial ester of a polyhydric alcohol.

5. The method as claimed in claim 3, wherein the at least one alkali metal carbonate comprises sodium carbonate (Na.sub.2CO.sub.3) and/or potassium carbonate (K.sub.2CO.sub.3).

6. The method as claimed in claim 3, wherein the at least one phosphoric acid ester comprises glycerol phosphate, disodium glycerol phosphate and/or a hydrate thereof and in that the at least one alkali metal comprises sodium carbonate (Na.sub.2CO.sub.3) and/or potassium carbonate (K.sub.2CO.sub.3).

7. The method as claimed in claim 3, wherein a weight ratio of the at least one phosphoric acid ester of a polyhydric alcohol to the at least one alkali metal carbonate is in the range of 1:1-10:1.

8. The method as claimed in claim 3, wherein the hardening accelerator additionally comprises at least one calcium compound.

9. The method as claimed in claim 8, wherein the at least one calcium compound comprises calcium oxide and/or calcium hydroxide.

10. The method as claimed in claim 8, wherein a weight ratio of the at least one calcium compound to the at least one phosphoric acid ester of a polyhydric alcohol is in the range of 100:1-1:1.

11. The method as claimed in claim 8, wherein the hardening accelerator is in the form of an at least two-component hardening accelerator, with the at least one calcium compound being present in a first component, while the at least one phosphoric acid ester of a polyhydric alcohol and the at least one alkali metal carbonate are present together in a second component or are present separately from one another as further individual components.

Description

WORKING EXAMPLES

1. Substances and Methods

1.1. Substances

(1) Substances used for the working examples were as follows:

(2) TABLE-US-00001 TABLE 1 Substances used Abbreviation Substance PCE Polycarboxylate ether plasticizer (e.g., Sika Viscocrete 20 HE, available from Sika Schweiz AG); solids content: 40 wt % GPD Glycerol phosphate, disodium salt, pentahydrate (available from Sigma Aldrich Schweiz); 10 wt % in H.sub.2O NaCt Sodium carbonate; 10 wt % in H.sub.2O KCt Potassium carbonate; 10 wt % in H.sub.2O MgCt Magnesium carbonate; 10 wt % in H.sub.2O CaOx Calcium oxide (Nekafin 2 from Kalkfabrik Netstal AG, Switzerland, having a specific surface area (BET) of 1.9 m.sup.2/g)

(3) Sodium carbonate, potassium carbonate, and magnesium carbonate are available commercially from various suppliers in pure form (purity >97%). They were each dissolved in water in the quantity specified in table 1, and used in the form of aqueous solutions.

1.2 Mortar Mixtures

(4) The mortar mixture M1 used has the dry compositions described in table 2.

(5) TABLE-US-00002 TABLE 2 Dry composition of mortar mixture Component M1 Portland cement of type CEM I 52.5 N 750 g (Normo 5R; available from Holcim Schweiz) Limestone filler 141 g Sand 0-1 mm 738 g Sand 1-4 mm 1107 g Sand 4-8 mm 1154 g

(6) To prepare the mortar mixtures, the sands, the limestone filler, the cement, and optionally calcium oxide (CaOx) were mixed dry in a Hobart mixer at a temperature of 20 C. for 1 minute. Over the course of 30 seconds, the mixing water (water/cement ratio or w/c=0.4), admixed beforehand with the polycarboxylate ether plasticizer (PCE; 1 wt % based on cement) and optionally further substances (GPD, NaCt, KCt, MgCt), was added and mixing was continued for 2.5 minutes more. The total wet mixing time lasted 3 minutes in each case.

1.3 Test Methods

(7) To determine the activity of the hardening accelerators of the invention, a determination was made of the compressive strengths of different mortar mixtures at different times after the preparation of the mortar mixtures. The test for determining the compressive strength (in N/mm.sup.2) took place on prisms (4040160 mm) in accordance with standards EN 12390-1 to 12390-4.

(8) Immediately after the preparation of the mortar mixtures, measurements were also made of the respective slump (ABM). The slump (ABM) of the mortar mixtures was measured in accordance with EN 1015-3.

2. Mortar Test

(9) Table 3 shows the negative influence of magnesium carbonate on the effect of hardening accelerators. The greater the amount of magnesium carbonate present, the lower the compressive strengths after 6 and 8 hours and the lower the accelerating effect of GPD and CaOx.

(10) TABLE-US-00003 TABLE 3 Effect of magnesium carbonate Compressive strength ABM.sup.+ [MPa] No. CaOx* GPD* MgCt* [mm] 6 h 8 h A1 3.00 1.50 192 4.0 10.3 A2 3.00 1.50 0.27 187 1.8 5.7 A3 3.00 1.50 0.53 180 1.3 4.1 A4 3.00 1.50 0.80 175 1.3 4.1 A5 3.00 1.50 1.07 142 1.1 2.3 *wt % based on cement content .sup.+slump immediately after preparation

(11) In the case of experiments B1-B6, shown in table 4, the effect of sodium carbonate in binder compositions comprising magnesium carbonate was investigated.

(12) TABLE-US-00004 TABLE 4 Effect of sodium carbonate Compressive strength ABM.sup.+ [MPa] No. CaOx* GPD* MgCt* NaCt* [mm] 6 h 8 h B1 3.00 1.50 196 9.9 19.8 B2 3.00 1.50 0.26 225 4.8 11.7 B3 3.00 1.50 0.26 0.60 196 8.2 19.2 B4 3.00 1.50 0.26 0.70 168 9.9 20.3 B5 3.00 1.50 0.26 0.80 151 8.9 19.0 B6 3.00 1.50 0.26 0.90 122 8.8 20.6 *wt % based on cement content .sup.+slump immediately after preparation

(13) From table 4 it is evident that the use of sodium carbonate (NaCt), is able to eliminate and/or neutralize the negative effects of magnesium carbonate (MgCt). Particularly advantageous in this case are concentrations of 0.06 and 0.07 wt % of sodium carbonate (or 0.6 and 0.7 wt % of the 10% NaCt solutions) (see experiments B3 and B4). Here, on the one hand high compressive strengths and at the same time good workabilities (high slump value) are achieved.

(14) In the case of experiments C1-C6, presented in table 5, the effect of sodium carbonate in binder compositions comprising magnesium carbonate was investigated.

(15) TABLE-US-00005 TABLE 5 Effect of potassium carbonate Compressive strength ABM.sup.+ [MPa] No. CaOx* GPD* MgCt* KCt* [mm] 4 h 6 h 8 h C1 3.00 234 0.7 2.5 6.1 C2 3.00 1.50 211 2.8 10.2 20.4 C3 3.00 1.50 0.26 218 1.1 3.0 8.5 C4 3.00 1.50 0.26 0.30 185 1.7 7.7 18.0 C5 3.00 1.50 0.26 0.60 187 1.9 7.6 18.3 C6 3.00 1.50 0.26 1.20 144 2.4 10.4 21.8 *wt % based on cement content .sup.+slump immediately after preparation

(16) Table 5 shows that potassium carbonate as well is able to very largely eliminate or to neutralize the negative effects of magnesium carbonate (MgCt). Particularly advantageous here are concentrations of 0.06 wt % of potassium carbonate (or 0.6 wt % of the 10% KCt solutions) (see experiment C5). Concentrations higher than in experiment C6 do produce better compressive strengths, but result in a less good workability (slump at 144 mm). A comparison of experiments C1 and C2 further demonstrates the accelerating effect of GPD.

(17) Experiments D1-D4, presented in table 6, were all carried out without magnesium carbonate, and illustrate the interaction of alkali metal carbonates and phosphoric acid esters of polyhydric alcohols.

(18) TABLE-US-00006 TABLE 6 Interaction of sodium carbonate with GPD Compressive strength ABM.sup.+ [MPa] No. CaOx* GPD* MgCt* NaCt* [mm] 6 h 8 h D1 3.00 234 0.5 0.6 D2 3.00 1.50 165 0.9 1.5 D3 3.00 0.60 232 0.5 0.6 D4 3.00 1.50 0.60 190 1.6 4.5 *wt % based on cement content .sup.+slump immediately after preparation

(19) What table 6 shows, among other things, is that sodium carbonate as such has no accelerating effect (compare experiment D3 vs. experiment D1). From a comparison of experiments D2 and D3, however, it is apparent that through the interaction of sodium carbonate and GPD the accelerating effect of GPD is further greatly increased. This shows that alkali metal carbonates and phosphoric acid esters of polyhydric alcohols interact synergistically.

(20) The above-described embodiments, however, are to be understood merely as illustrative examples, which may be modified as desired within the bounds of the invention.

(21) Hence in the examples it is possible, for example, to leave out calcium oxide (CaOx) as additional component. This results in lower compressive strengths. In qualitative terms, however, there is no change to the activities and effects described.

(22) It is likewise possible, for example, to replace the cement at least partially by a latent hydraulic and/or pozzolanic binder. It is also possible, additionally to or instead of the aggregates described (sands, limestone filler), to use larger aggregates, to obtain a concrete composition, for example. This does not result in any change to the activities and effects described above.