Additive for internal post treatment of mineral binder compositions

Abstract

An admixture for mineral binder compositions, in particular an after-treatment agent for mineral binder compositions, including at least one water-absorbing substance and at least one shrinkage reducer.

Claims

1. A method of treating a mineral binder composition, the method comprising: treating the mineral binder composition with an admixture comprising at least one water-absorbing substance and at least one shrinkage reducer by adding the admixture to mineral binder composition, wherein the water-absorbing substance is a modified starch, and a weight ratio of the modified starch to the shrinkage reducer is in a range of 1:99 to 50:50.

2. The method according to claim 1, wherein the modified starch is a hydroxyalkyl starch.

3. The method according to 1, wherein the shrinkage reducer is selected from among alcohols, monoalcohols, glycols, diols, alkanediols, alkenediols, polyols, alkanolamines and polyalkylene oxides.

4. The method according to claim 3, wherein the shrinkage reducer is selected from among alkanediols.

5. The method according to claim 4, wherein the shrinkage reducer comprises at least one of hexylene glycol and neopentyl glycol.

6. The method according to claim 1, wherein the shrinkage reducer comprises neopentyl glycol and the water-absorbing substance comprises at least one of vermiculite and a modified starch.

7. The method according to claim 1, wherein a weight ratio of the shrinkage reducer to the water-absorbing substance is in a range of 5:95 to 99:1.

8. The method according to claim 1, wherein the admixture further comprises an additive selected from the group consisting of antifoams, dyes, preservatives, flow improvers, plasticizers, accelerators, retarders, air pore formers, shrinkage reducers, and corrosion inhibitors.

9. A mineral binder composition containing a mineral binder and the admixture as claimed in claim 1.

10. A shaped body obtained by curing a mineral binder composition as claimed in claim 9 which has been mixed with water.

11. A process for producing a mineral binder composition, wherein the admixture as claimed in claim 1 is mixed with a mineral binder.

12. The method according to claim 2, wherein the hydroxyalkyl starch is a hydroxypropyl starch.

13. The method according to claim 1, wherein a weight ratio of the modified starch to the shrinkage reducer is in a range of 7.5:92.5 to 12.5:87.5.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The figures used for explaining the working examples show:

(2) FIG. 1: at left: cuboidal shuttering filled with a mortar mixture and having an L-shaped steel bar running centrally along the entire width; at right: a detailed view of the steel bar;

(3) FIG. 2: a side view of a crack in the cured mortar mixture of FIG. 1 above the steel bar. The arrow marks the position of the crack;

(4) FIG. 3: a plan view of the crack of FIG. 2. The arrow again marks the position of the crack;

(5) FIG. 4: the shrinkage over time of mortar mixtures without (diamonds) and with an admixture based on vermiculite or neopentyl glycol (squares and triangles, respectively).

WORKING EXAMPLES

(6) 1. Substances Used

(7) The following substances were used for the working examples:

(8) TABLE-US-00001 TABLE 1 Designation Substance mS Hydroxypropyl starch (Emset KH 6; Emsland Stärke GmbH, Germany) SSV Vermiculite NPG Neopentyl glycol V1 Conventional external after-treatment agent based on paraffin (Antisol ® E-20, Sika Schweiz AG) V2 Conventional internal after-treatment agent based on cellulose (Hidratium ®, Cemex Research Group AG, Switzerland)

(9) Vermiculite (SSV) and neopentyl glycol (NPG) are commercially available from various suppliers and are used in pure form (purity >97%).

(10) 2. Provision of the Admixtures

(11) The admixtures Z1-Z3 according to the invention shown below in Table 2 were produced:

(12) TABLE-US-00002 TABLE 2 Water-abs. Shrinkage Designation substance/proportion reducer/proportion Z1 mS/8.16% by weight NPG/91.84% by weight Z2 SSV/66.7% by weight NPG/33.3% by weight Z3 mS/11.7% by weight NPG/88.3% by weight

(13) In all the mortar experiments described below, a modified polycarboxylate in the form of Sika® ViscoCrete®-3081 S was used as flow improver. Sika® ViscoCrete®-3081 S is a comb polymer having a polycarboxylate backbone and polyalkylene oxide side chains attached via ester groups. The flow improver was used in a concentration of 1.0% by weight, based on the binder, and was added beforehand to the tempering water.

(14) 3. Mortar Mixtures

(15) The effectiveness of the admixtures according to the invention was tested in mortar mixtures. Mortars as specified in Table 3 were used for this purpose.

(16) TABLE-US-00003 TABLE 3 Dry composition of the mortar mixtures used (maximum particle size 8 mm) Component Mixture M1 Mixture M2 CEM I 750 g — CEM II A-LL — 750 g Limestone filler 141 g 141 g Sand 0-1 mm 738 g 738 g Sand 1-4 mm 1107 g  1107 g  Sand 4-8 mm 1154 g  1154 g 

(17) For mixture M1, Schweizer CEM I 42.5 N (=mixture of cements Normo 4 [Siggenthal/Holcim AG], Vigier CEM I 42.5N [Vigier Ciment AG] and CEM I 42.5 N [Wildegg/Jura cement] in a weight ratio of 1:1:1) having a Blaine fineness of 3600 cm.sup.2/g was used as cement. The sands, the limestone filler and the cement were mixed dry in a Hobart mixer for 1 minute. The tempering water in which the flow improver (1.0% by weight based on cement) and optionally the admixture Z1-Z3 or V2 had been dissolved or dispersed was added over a period of 30 seconds and the mixture was mixed for a further 2.5 minutes. The total mixing time in each case was 3 minutes. The water/cement value (w/c value) was in the range 0.49-0.55 (see Table 4).

(18) Mixture M2 was produced in the same way but Schweizer CEM II A-LL (Wildegg/Jura cement) was used as cement. The water/cement value (w/c value) was 0.58 (see Table 5).

(19) The proportion of any admixture present based on cement was 0.17% by weight for admixture V2, 0.5% by weight for the admixtures Z1 and Z3 and 1.35% by weight for the admixture Z3. This corresponded to the optimal added amounts for the respective admixtures.

(20) 4. Test Methods

(21) To determine the effect of the admixture, cuboidal shuttering (31 cm×16 cm×4 cm) having an L-shaped steel bar running centrally along the entire width (see FIG. 1) was provided in laboratory experiments. The steel bar here served as intended fracture position. The shuttering was then filled with the freshly made up mortar mixtures and stored under defined conditions in an air conditioned chamber having a wind tunnel. Here, the temperature, the relative atmospheric humidity and the wind velocity could all be controlled during storage. After two days, the specimens produced in this way were examined visually for any crack formation (cf. FIGS. 2 and 3).

(22) The shrinkage behavior was tested by a method based on the Swiss standard SIA 262/1 using prisms (120 mm×120 mm×360 mm) at 20° C. and 65% relative atmospheric humidity after 1, 2, 3 and 7 days. The length changes of the prisms observed were accordingly measured in parts per thousand (0/00) relative to the zero specimen (value after 1 day).

(23) The effect of the admixture on the setting behavior of the mortar mixtures was likewise examined by measuring the temperature change over time at an ambient temperature of 20° C. The temperature measurement was carried out in a manner known per se using a thermocouple as temperature sensor. All specimens were measured under the same conditions. In the present case, the time elapsed from mixing the mortar mixture with water to attainment of the maximum temperature occurring after the induction phase or rest phase was employed as measure of the setting time.

(24) In addition, the compressive strengths of the mortar mixtures at various times (1, 7 and 28 days) after mixing of the mortar mixtures with water were determined. The test to determine the compressive strength (in N/mm.sup.2) was carried out on prisms (40×40×160 mm) in accordance with the standards EN 12390-1 to 12390-4.

(25) Immediately after mixing of the mortar mixtures with water and also 30 minutes and 60 minutes thereafter, the respective slump flow (SF) was measured. The slump flow (SF) of the mortar was measured in accordance with EN 1015-3.

(26) The air content was determined in accordance with the standard EN 1015-7 (air content) immediately after mixing of the mortar mixture with water.

(27) 5. Results

(28) 5.1 Crack Formation

(29) Table 4 shows the effect of the admixtures in respect of the avoidance of crack formation under various conditions and use of mortar mixture M1. It is desirable for no cracks to be formed if possible. The experiments were carried out as described above in chapter 4.

(30) In the experiments A-G, admixtures according to the invention were used. For comparative purposes, the reference experiments R1-R8 without or with admixtures which are not according to the invention were additionally carried out. In experiments R4 and R5, the admixture V1 was in each case not added to the mortar mixture but instead used subsequently for external after-treatment as envisaged by the manufacturer.

(31) TABLE-US-00004 TABLE 4 Cracks after Experiment Admixture Mortar mixture w/c T [° C.] Humidity [%] Wind [km/h] 2 d? R1 — M1 0.55 20 40 0 NO R2 — M1 0.49 20 40 3-7 Yes R3 — M1 0.49 20 40 10-12 Yes R4 V1 M1 0.49 20 40 3-7 NO R5 V1 M1 0.49 20 40 10-12 NO R6 V2 M1 0.55 20 40 0 NO R7 V2 M1 0.49 20 40 3-7 NO R8 V2 M1 0.49 20 40 10-12 NO A Z1 M1 0.55 20 40 0 NO B Z1 M1 0.49 20 40 3-7 NO C Z1 M1 0.49 20 40 10-12 NO D Z2 M1 0.55 20 40 0 NO E Z2 M1 0.49 20 40 10-12 NO F Z3 M1 0.55 20 40 0 NO G Z3 M1 0.49 20 40 3-7 NO

(32) The results in Table 4 clearly show that the admixtures Z1-Z3 according to the invention perform at least as well in respect of the avoidance of cracks as do known external after-treatment agents (V1) or conventional internal after-treatment agents (V2).

(33) Table 5 shows the results using mortar mixture M2. In experiments H-K, admixtures according to the invention were used. For comparative purposes, reference experiments (R9-R14) without or with admixtures which are not according to the invention were once again carried out. In the case of experiments R11 and R12, the admixture V1 was in each case not added to the mortar mixture but, as prescribed by the manufacturer used subsequently for external after-treatment.

(34) TABLE-US-00005 TABLE 5 Experiment Admixture Mortar mixture w/c T [° C.] Humidity [%] Wind [km/h] Cracks ? R9 — M2 0.58 20 40 0 Yes R10 — M2 0.58 20 40 3-7 Yes R11 V1 M2 0.58 20 40 0 NO R12 V1 M2 0.58 20 40 3-7 NO R13 V2 M2 0.58 20 40 0 NO R14 V2 M2 0.58 20 40 3-7 Yes H Z2 M2 0.58 20 40 0 NO I Z2 M2 0.58 20 40 3-7 Yes J Z3 M2 0.58 20 40 0 NO K Z3 M2 0.58 20 40 3-7 NO

(35) It can be seen from the data in Table 5 that the admixtures according to the invention also function without problems in other types of cement and sometimes perform even better than the known after-treatment agents. Thus, admixture Z3 effectively prevents crack formation even at wind velocities of 3-7 km/h (see experiment K). However, cracks are present under the corresponding conditions when the conventional agent V2 is used (see experiment R14).

(36) 5.2 Shrinkage Behavior

(37) The shrinkage behavior was examined using a mortar mixture of the type M2 and an admixture of the type Z2. The mortar mixtures were produced as described in chapter 3. FIG. 4 shows the corresponding results. The upper curves with the data points in the form of squares and triangles here correspond to two series of measurements using admixtures according to the invention of the type Z2. It can be seen from FIG. 4 that the shrinkage behavior is influenced in a positive way compared to a reference specimen without admixture for the after-treatment (curve with the data points in the form of diamonds).

(38) 5.3 Workability, Strength and Setting Behavior

(39) To test the influence of the admixtures on the workability, strength and setting behavior, the slump flow (SF), the air content, the point in time of the temperature maximum t(T.sub.M) and the compressive strength were examined as set forth in chapter 4. Table 6 gives an overview of the experiments carried out and the results. Mortar mixture M1 was used for all experiments.

(40) TABLE-US-00006 TABLE 6 Compressive SF [mm] strength [MPa] Experiment Admixture w/c 0′ 30′ 60′ Air content [%] t (T.sub.M) [h] 1 d 7 d 28 d R15 — 0.44 195 173 163 2.9 16.3 27.3 58.0 63.0 R16 V2 0.49 192 172 163 2.8 17.8 20.0 49.6 58.2 M Z1 0.49 189 195 199 2.9 20.2 14.3 43.6 50.2

(41) As can be seen from the data in Table 6, the admixtures of the invention barely impair, or do not at all impair, the workability, the strength and the setting behavior of mortar compositions.

(42) It has thus been shown, in particular, that the admixtures of the invention are suitable as efficient and extremely effective agents for the internal after-treatment or internal curing of mineral binder compositions. In particular, the shrinkage behavior of the mineral binder compositions is influenced in a positive way and formation of cracks can be reduced significantly. Undesirable drying-out of mineral binder compositions can thus be avoided effectively. At the same time, the admixtures of the invention only insignificantly impair, or do not at all impair, the workability, the setting and the strength of the binder compositions.

(43) However, the above-described embodiments should be considered to be merely illustrative examples which can be modified as desired within the scope of the invention.