Hardening accelerator

Abstract

A process for producing a setting and/or curing accelerator for mineral binders is characterized in that a mineral solid is subjected to milling in a liquid medium.

Claims

1. A setting and/or curing accelerator obtained by milling a mineral solid in a liquid medium, wherein the setting and/or curing accelerator is present as suspension and comprises the following constituents: a) 97-99.9 w % of a dispersed inert mineral solid which is rock or rock flour; b) 0.1-3 w % of a dispersed mineral binder which is cement; where both the inert mineral solid and the mineral binder are present in dispersed form or in the form of suspended particles; the mineral solid is milled to particles having an average particle size of <600 nm, and the mineral binder is completely hydrated by the liquid medium during milling.

2. The setting and/or curing accelerator as claimed in claim 1, wherein a proportion of liquid in the setting and/or curing accelerator is 40-85% by weight, based on the total weight of the curing accelerator.

3. The setting and/or curing accelerator as claimed in claim 1, wherein the mineral solid is in the form of a flour before milling and/or the mineral solid has an average particle size of from 0.0001 to 1.0 mm.

4. The setting and/or curing accelerator as claimed in claim 1, wherein the liquid medium contains water and/or alcohol.

5. The setting and/or curing accelerator as claimed in claim 1, wherein the mineral solid is milled to particles having an average particle size of <60 nm.

6. The setting and/or curing accelerator as claimed in claim 1, wherein the mineral solid has a proportion of 5-95% by weight in the liquid medium, based on the total weight of the liquid medium and the mineral solid.

7. A composition containing a setting and/or curing accelerator as claimed in claim 1 and also a component of a mineral binder composition.

8. A shaped body obtainable by curing a composition as claimed in claim 7 after addition of water.

9. A method comprising applying the setting and/or curing accelerator as claimed in claim 1 for accelerating the setting and/or curing of a mineral binder and/or of mineral binder compositions.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a picture recorded by means of a scanning electron microscope of an accelerator produced according to the invention after drying.

(2) FIG. 2 shows the courses of the temperature during curing of various mortar samples containing the curing accelerators produced according to the invention compared to two reference samples.

WORKING EXAMPLES

(3) 1. Production of Curing Accelerators

(4) 1.1 Accelerators Based on Limestone Flour

(5) To produce a suspension, 30% by weight of limestone flour (particle size 0.0-0.09 mm), 1.5% by weight of a polycarboxylate ether (e.g. Sika® Viscocrete® VC 2000, a comb polymer having a polycarboxylate backbone and polyalkylene oxide side chains bound via ester groups) and 68.5% by weight of water were mixed. The suspension was then milled in a stirred ball mill using milling beads (bead mill) to give fractions having various particle sizes (D50 values). After the milling operation, the particle size of each fraction was determined by laser light scattering in accordance with the standard ISO 13320:2009. The following fractions or curing accelerators were obtained: A) KSTM A: D50=625 nm B) KSTM B: D50=310 nm C) KSTM C: D50=140 nm

(6) FIG. 1 shows a representative picture of a curing accelerator which has been produced according to the invention and subsequently dried under reduced pressure. Primary particles having a size of <50 nm can clearly be seen.

(7) 1.2 Accelerators Based on Limestone Flour and Cement

(8) In a further set of experiments, limestone flour was suspended in water in a manner analogous to the process described above in chapter 1.1, dispersed together with a polycarboxylate ether, milled and subsequently admixed with in each case different amounts of cement (type CEM I, in each case identical) and stirred further for at least 30 minutes. The following accelerators were produced: D) KCEM0: pure limestone flour suspension without addition of cement E) KCEM1: limestone flour suspension containing 1% by weight of cement (based on the total weight of the suspension) F) KCEM2: limestone flour suspension containing 2% by weight of cement (based on the total weight of the suspension) G) KCEM3: limestone flour suspension containing 3% by weight of cement (based on the total weight of the suspension)

(9) All curing accelerators KCEM0-KCEM3 each contain, for the purposes of comparability, the same amount of identical limestone flour (20% by weight, based on the total weight), the same amount of identical polycarboxylate ether (2% by weight, based on the total weight) and have the same total weight. The latter was achieved by the water content, which forms the main constituent, of the curing accelerators comprising cement being reduced by the appropriate proportion by weight.

(10) 1.3 2-Component Accelerators Based on Limestone Flour and Cement

(11) The following two-component accelerators were produced: H) 2-component KCEM-LL: Component 1: pure limestone flour suspension analogous to KCEM0, but with the water being water reduced by 2% by weight; Component 2: 2% by weight of cement (CEM I, identical to the case of the accelerator in chapter 1.2) was stirred and suspended in water in a separate vessel for the same period of time. The percentage by weight of 2% by weight is for the present purposes based on the weight of the first component (limestone flour and water and polycarboxylate ether) plus cement but without the water present in the second component. Thus, two separate aqueous suspensions are present in the case of the accelerator 2-component KCEM-LL, with one suspension (=component 1) containing suspended limestone flour and the other suspension (=component 2) containing suspended cement. I) 2-Component KCEM-LS: Component 1: pure limestone flour suspension like component 1 of the above-described 2-component accelerator 2-component KCEM-LL; Component 2: 2% by weight of cement (CEM I, identical to the case of the accelerator in chapter 1.2) provided in powder form in a separate vessel. Thus, an aqueous component (=component 1; limestone flour suspension) and a solid component (=component 2; cement powder) are present in the case of the accelerator 2-component K-KCEM-LS.

(12) 2. Production of Mortar Compositions

(13) To produce mortar compositions, portland cement, sand and mixing water, to which one of the fractions or curing accelerators mentioned in chapter 1 had in each case been added, and also a fluidizer were mixed in a mechanical mixer. The fluidizer is a modified polycarboxylate in the form of Sika® ViscoCrete®-3081 S, a comb polymer having a polycarboxylate backbone and polyalkylene oxide side chains bound via ester groups.

(14) 3. Test Methods

(15) To determine the effectiveness of the curing accelerators, the compressive strengths of the mortar mixtures were determined 6, 8 and 24 hours after mixing the mortar mixtures with water. Testing to determine the compressive strength (in N/mm.sup.2) was carried out on prisms (40×40×160 mm) in accordance with the standard EN 196-1.

(16) Furthermore, the course of the temperature of selected mortar mixtures was recorded in order to monitor the hydration or the setting behavior of the mortar mixtures after mixing with water. The temperature measurement was carried out using a thermocouple as temperature sensor in a manner known per se. All samples were measured under identical conditions.

(17) 4. Results

(18) 4.1 Courses of the Temperature in Mortar Samples

(19) FIG. 2 shows the courses of the temperature for various mortar samples during curing using the curing accelerators KSTM A, KSTB B, KSTM C produced according to the invention compared to two reference samples R1 and R2 under comparable conditions. The mortar sample R1 was produced without addition of a curing accelerator but otherwise like the samples containing the curing accelerators KSTM A, KSTB B, KSTM C. In the case of the mortar sample R2, precipitated CaCO.sub.3 having a particle size (D50) of 595 nm was used instead of curing accelerators KSTM A, KSTB B, KSTM C produced according to the invention. The mortar samples essentially have an identical processability.

(20) It is clear from FIG. 2 that the curing accelerators produced according to the invention lead to a temperature increase in the mortar sample significantly earlier than in the case of the reference samples and that the temperature maximum is reached earlier when using the curing accelerators produced according to the invention. The more finely the particles are milled, the more effective, accordingly, are the curing accelerators at the same introduced amount.

(21) It is particularly notable that the reference sample R2 (D50=595 nm) accelerates significantly less strongly than the curing accelerator KSTM A (D50=625 nm) produced according to the invention despite having a smaller particle size. This shows that the curing accelerators produced according to the invention accelerate the setting and curing of mortar compositions and that the process of the invention has a decisive influence on the accelerating effect.

(22) 4.2 Compressive strength of mortar samples

(23) In further experiments, the compressive strengths of various mortar samples containing different cements and different fluidizer concentrations as described in chapter 2 were measured. Here, in a first experiment, conventional curing accelerators B1, B2 and B3 (see table 1) were compared with the curing accelerator of the type KSTM C produced according to the invention. The results are summarized in table 1:

(24) TABLE-US-00001 TABLE 1 Amount of fluidizer introduced [% by weight] based on Compressive strength in MPa Cement cement Time Ref B1 B2 B3 KSTM C CEM I 0.75 6 h 2.6 4.4 3.9 4.1 6.0 52.5 R 8 h 8.8 11.9 10.6 14.7 17.6 24 h 44.3 48.2 48.7 44.1 46.5 0.90 6 h 1.8 3.9 3.9 3.7 4.9 8 h 6.9 12.0 9.9 11.3 14.7 24 h 41.8 43.0 37.6 43.1 43.4 CEM I 0.45 6 h 0.7 1.4 1.6 1.1 2.9 52.5 8 h 2.0 2.0 4.0 1.1 9.8 R-ft 0.90 6 h 0.6 1.1 1.5 1.2 2.8 8 h 1.5 1.2 3.1 1.2 8.7 CEM I 0.70 6 h 0.6 0.9 1.0 0.9 2.1 42.5 R 8 h 1.8 4.6 2.9 3.7 6.6 24 h 31.1 35.1 29.0 33.8 34.6 0.80 6 h n.d. n.d. n.d. n.d. n.d. 8 h n.d. 1.3 1.5 1.4 3.2 24 h 28.9 35.5 28.3 34.1 34.5 n.d. = not determined Ref = blank without addition of a curing accelerator. B1 = commercial accelerator based on Ca(NO.sub.3) and NaSCN. B2 = commercial accelerator based on Ca(NO.sub.3). B3 = commercial accelerator based on Ca(NO.sub.3) and an alkanolamine.

(25) The results show that the curing accelerator KSTM C produced according to the invention gives significant compressive strength increases compared to commercial products, independently of the type of cement used. This is particularly true in the period of time of 6-8 hours after mixing the mortar mixtures with water.

(26) In further experiments, the accelerator suspensions based on limestone flour and cement were tested.

(27) Table 2 shows mortar experiments using the accelerators KCEM0, KCEM1 and KCEM2. The mortar samples were produced as described above in chapter 2 and tested in accordance with the indications in chapter 3. As cement, use was made of the same cement of the type CEM I 52.5 R as in the first experiments. Ref. denotes a reference experiment without addition of an accelerator.

(28) TABLE-US-00002 TABLE 2 (all values in MPa) Accelerator .fwdarw. Ref. KCEM0 KCEM1 KCEM2 Compressive strength 2.6 3.9 4.5 6.5 after 6 hours Compressive strength 8.8 12.3 13.4 17.8 after 8 hours

(29) All three accelerator suspensions KCEM0, KCEM1 and KCEM2 increase both the 6 hour and the 8 hour strengths. Compared to the pure limestone flour suspension (KCEM0), the strengths are increased further when using the accelerators KCEM1 and KCEM2, which additionally contain suspended cement.

(30) In order to verify these results and to rule out the possibility that the higher strengths are attributable to the increased cement content in the mortar system, the mortar experiments shown in table 3 were carried out using the suspensions KCEM0, KCEM1, KCEM2, KCEM3, 2-component KCEM-LL and 2-component KCEM-LS in mortar mixtures containing a different cement of the type CEM I. The suspensions were always in a proportion of 5% by weight, based on the cement content of the mortar composition. In the case of the accelerator 2-component KCEM-LL, the first component (limestone flour suspension) and the second component (cement suspension) were added at the same time to the mortar mixture. In the case of the accelerator 2-component KCEM-LS, the cement was added as powder (=2nd component) simultaneously with the limestone flour suspension (1.sup.st component) to the mortar mixture.

(31) TABLE-US-00003 TABLE 3 (all values in MPa) Accelerator 2-component 2-component Ref. KCEM0 KCEM1 KCEM2 KCEM3 KCEM-LL KCEM-LS Compressive strength 1.0 1.5 2.0 2.5 3.1 1.7 1.5 after 6 hours Compressive strength 4.3 6.5 8.1 9.1 11.7 7.1 6.3 after 8 hours

(32) The results confirm that the accelerators with addition of small amounts of cement to the limestone flour suspension (KCEM1, KCEM2, KCEM3) give higher early strengths than pure limestone flour suspensions (KCEM0). Furthermore, it was able to be shown that the additional acceleration is achieved not only by means of the increased amount of cement in the system (2-component KCEM-LS) or by means of prehydrated cement (2-component KCEM-LL). When the cement is added to the finely milled limestone flour suspension and the entire mixture is then added as accelerator to mortar/concrete mixtures, additional acceleration is achieved and cement and limestone flour act functionally together as constituents in a suspension.

(33) In conclusion, it can be seen that effective setting and/or curing accelerators which do not significantly impair the processability of mineral binder compositions are obtainable in a simple way using the process of the invention. However, the above-described embodiments merely represent illustrative examples which can be modified in any way within the scope of the invention.

(34) Thus, the portland cement can, for example, be replaced at least partly by a latent hydraulic and/or pozzolanic binder.

(35) Furthermore, larger aggregates can be used in addition to or instead of the aggregates described (sands, limestone fillers) in order, for example, to obtain a concrete composition. Likewise, it is possible to use further admixtures, e.g. curing-accelerating substances.