GB2195328A

GB2195328A - Concrete admixture compositions

Info

Publication number: GB2195328A
Application number: GB08721701A
Authority: GB
Inventors: John W Brook
Original assignee: Sandoz AG
Current assignee: Sandoz AG
Priority date: 1986-09-19
Filing date: 1987-09-15
Publication date: 1988-04-07
Anticipated expiration: 2007-09-15
Also published as: FR2604170B1; ES2005013A6; IT1211786B; AU7848087A; AU592013B2; GB2195328B; JPS6389445A; FR2604170A1; CH675716A5; CA1278797C; BE1002419A4; ATA235987A; DE3730527A1; AT393498B; IT8748397A0; GB8721701D0

Description

1 GB2195328A 1

SPECIFICATION

Concrete admixture compositions This invention relates to concrete admixtures for use as cold weather concrete set accelerators. 5 Low or freezing temperatures (e.g. 5'C to -7'C) present special problems in the mixing, pouring and curing of concrete. Concrete may freeze while saturated and subsequently be of low strength, or there may be a slow development of strength.

The American Concrete Institute (ACI) Report 306R-78 on Cold Weather Concreting, sets forth standard practices to prevent freezing and assure the safe development of concrete strength during curing at ambient freezing conditions. Heating of materials, including mix water and aggregates is mandatory. Protective insulating coverings, heated enclosures and proper curing conditions are described.

An additional factor (not often reported) associated with freezing temperatures, is the distress of the concrete worker operating under adverse conditions. Even if dressed warmly, the conrete 15 worker wishes to finish a pour or complete the finishing as fast as possible, and move indoors out of the wind and cold. Thus, an accelerated set time is an important aspect of cold weather concreting.

While the prior art has addressed the problems of using concrete in cold weather (e.g. the use of calcium chloride as the principle accelerating admixture), it has not successfully developed 20 admixtures which are, (1) non-corrosive, and (2) meet or exceed at - 1 O'C to 5'C the rate-of hardening and compressive strength performance of a plain concrete mix at 10'C.

It has now been found that set accelerating admixtures in specific proportions can be obtained which combine two beneficial effects:

(1) They depress the mix water and pore water freezing point, so that a concrete mix will 25 not freeze during the first few critical hours of curing at temperatures below O'C and (2) They reduce the quantity of mix water necessary for curing, which improves early con crete strength development. The reduction in mix water also has an effect on freezing point depression, because it allows for a more concentrated solution of the admixture.

Accordingly, the present invention provides a chloride-free admixture for use as a cold weather 30 concrete set accelerator which comprises (A) 100 parts by weight of at least one soluble inorganic salt having freezing point depres sant properties (B) from 13.3 to 30 parts by weight of at least one superplasticizer (C) from 3 to 30 parts by weight of at least one inorganic early set and strength accelerator, 35 and (D) from 0 to 10 parts by weight of at least one organic set accelerator.

Preferably the quantity of component B should be greater than 15 parts by weight.

Preferably the quantity of component C is from 5 to 10 parts by weight.

Preferably component D is present in an amount of from 1.3 to 6 parts by weight.

The proportions given above are parts by dry weight of the total dry weight of components A-D, neglecting any water which may be present. The admixture of the invention may be added as a solid direct to the concrete mix water, or may be used in aqueous solution for addition to the mix water. Preferably the admixture is in the form of an aqueous solution.

Component A is preferably selected from ammonium, alkali and alkaline earth nitrates and 45 nitrites, more preferably from calcium and sodium nitrate and nitrite. Calcium nitrate is particularly preferred. Up to 50% of the inorganic salt of component A may be replaced by urea.

Component B is preferably an alkali or alkaline earth salt of a naphthalene sulphonate/formai dehyde condensate or a sulphonated melamine/formaldehyde condensate, more preferably a sodium or calcium salt, or an acrylic copolymer for example poly(hydroxyethyl methacrylate/ac- 50 rylic acid). Particularly preferred is naphthalene sulphonate/formaldehyde condensate in sodium salt form.

Component C is preferably selected from ammonium, alkali or alkaline earth thiocyanates and thiosulphates, more preferably from calcium, ammonium and sodium thiocyanates and thiosul phates. Particularly preferred as component C is sodium thiocyanate. - 55 Component D is preferably selected from methyloiglycolurils, dimethylolurea, mono- and di-(N methylol) hydantoin, mono- and di-(N-methylol) dimethylhydrantoin, Nmethylolacrylamide, tri-(N methylol) melamine, Whydroxyethylpiperidine, N,N-bis(2- hydroxyethyi)piperazine, glutaraldehyde, pyruvaldehyde, furfural and water soluble urea-formaldehyde resins. More preferably, component D is selected from methyloiglycolurils, e.g. tri-(N-methylol)giycoluril and tetra (N-methyloi)giycolu- 60 ril, particularly tetra (N-methyloi)giycoluril.

A preferred admixture according to the invention consists of (A) calcium nitrate, (B) sodium salt of naphthalene sulphonate/formaidehyde condensate, (C) sodium thiocyanate and (D) tetra(N methyioi)giycoluril, in the proportions by weight given above. Particularly preferred is a mixture of the above four components in the proportions by weight: 100 parts (A), 20 parts (B), 6.7 parts 65 2 GB2195328A 2 (C) and 4 parts (D). This preferred admixture is preferably used in the form of an aqueous solution containing 40-60% dry weight of components A-D, particularly 50% wt.

The admixtures of the invention may be used over a wide range of temperatures from about 200C to about - 15'C. The amount of admixture which is added to the concrete may be from 0.13 to 5.6 parts (dry weight) per 100 parts dry weight of cementitious material in the concrete 5 (e.g. portland cement plus pozzolanic material such as fly ash) preferably 0.65 to 5.6 parts. For theabove preferred admixture, the dose range is from 1.3 to 4.6 parts/100 parts cement, and the lower the ambient temperature the higher will be the dosage required. Thus a dosage of 2.6 parts/100 parts cement of the preferred admixture will prevent a concrete mix from freezing at temperatures down to about - 1 O'C, while for lower temperatures a dosage of 3.9 parts/ 100 10 parts cement is preferred.

While the admixture of the invention may be used with any of ASTM type 1 to V cements, types 1 and 11 are preferred. The admixtures may'be used in cement mortars as well as in concrete.

The invention also provides a method for accelerating the set of a concrete or cement mortar 15 mix, suitable for use in cold weather conditions, comprising adding to the mix from 0.65 to 5.6 parts (dry weight) of an admixture according to the invention per 100 parts dry weight of cementitious material in the mix. The concrete or cement mortar so obtained will contain the following amounts of components A-D, defined above:

Component parts1100 parts cement A B C 25 D A B C D 0.5 -4.0 0 1 -0.8 0.033-0.6 0.0 -0.16 preferably 0.02 -0.16 Preferred amounts are:

Component parts1100 parts cement 2.0 -3.0 0.4 -0.6 0.1 -0.6 0.04-0.12 Consequently, a similar method which may be substituted for that already described, corn35 prises adding to the concrete or cement mortar (1) 0.5 to 4% by weight of cement of at least one cmponent (A), (2) 0. 1 to 0.8% by weight of cement of at least one component (B), (3) 0.033 to 0.6% by weight of cement of at least one component (C) and (4) 0 to 0.16% of cement of at least one component D.

In the preferred method, at least one component D is added in the amount of from 0.02 to 40 0.16% wt. of cement.

The following Examples illustrate the invention. All parts and percentages are by weight unless indicated otherwise.

EXAMPLES Standard procedure A concrete mix without addition of any admixtures of the invention (herein referred to as plain reference) is prepared according to the following formulation:

component Kg1M3 of concrete 50 Cement of ASTM type 1 307 Aggregate 1900 (Sand to stone ratio of 40:60 to 50:50; the stone used is about 2 em topsided crushed limestone) 55 Water as indicated in Tables Ill to VII.

An air-entraining admixture may also be added. Those used are sold by Master Builders Inc. (Cleveland, Ohio) under the trade marks Micro-Air, and Master Builders Neutralised Vinsol, re- spectively. Both meet the requirements of ASTM C-260, AASHTO M-154 and CR1)-C13.

Concreteimixes with addition of admixtures of the invention are prepared according to the concrete formulation of the plain reference. Mixing together the concrete component and the admixtures is carried out as follows:

Mix water in the amount of about 80% of that of the plain reference is added to a conven tional cement mixer and the admixture then added to the water. The cement, sand and stone 65 V 3 GB2195328A 3 are further added.

Then the remaining 20% of water is used in part to adjust the slump to the slu.mp of the plain reference.

The concrete is then poured into 10 cm cubes which are covered to prevent moisture loss.

The concrete 'cubes are stored for the time and at the temperature indicated in Examples 1 to VI.5 Properties The following properties are routinely measured:

Slump, i.e. the drop in cm of a 12 inch (30.5 cm) high cone of the fresh mix. (ASTM C 143) 1 Percentage of entrained air Water Reduction i.e. the difference between the amount of water used in the plain reference and the (smaller) amount of water used in the test sample in order to obtain the same slump, expressed as a percentage of the amount of water used in the plain reference.

Compressive Strength, expressed in Kg/CM2 and as a percentage of the compressive strength of the plain reference measured under the same conditions.

Rate of Hardening (ROH), i.e. the time in hours to reach the initial set. (ASTM C 403) Examples 1-26

Tables 1 and 11 list admixture formulations according to the invention, given as parts by weight 30 of components (B), (C) and D per 100 parts by weight of component (A). These formulations are each dissolved in water such that the aqueous solution contained 3 lb (1.36 kg) of compo nent (A) in 90 fluid ounces (2.56 litres) of solution. As the specific gravity of these solutions is approx. 1.39, the solutions of the admixture formulations all contain 1. 36 kg component (A) in 3.56 kg solution, or 38% by wt. component (A). With the other components, the solutions 35 contain a total of approx. 50% wt. active material.

W 4 GB2195328A 4 Table 1

Admixtures 1-1, each containing 100 parts by weight of calcium nitrate (A), and in addition:

parts by weight B) Na salt of naphthalene c) sodiLun Example No. sulphonate/formaldehyde thiocya nate D) tetra (N- 10 methylol) glycoluril 1 2 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 20 20 20 13.3 13.3 13.3 13.3 20 30 30 30 30 20 20 20 20 6.7 20 20 6.7 6.7 20 20 3.3 4 1.6 4 1.3 4 1.3 6.7 4 6.7 16 3 1.3 3.2 6 2 6 2 2 6 2 6 GB2195328A 5 Table 11

Admixtures 19-26 - Formulation (parts by weight) 5 Example No. 19 20 21 22 23 24 25 26 Camponent A) Calcium nitrate 100 100 - 66.7 100 100 100 100 Calcium nitrite - - 10033.3 3) naphthalene sulphonate/ formaldehyde 20 Ca salt 20 20 Na salt - - 20 20 20 20 20 20 C) Sodium thiocyanate 6.7 - - 6.7 6.7 6.7 6.7 6.7 Ammonium thiocyanate - 6.7 6.7 D) tetra(N-methylol) glycoluril 4 4 4 4 - - - - pyruvic aldehyde 4 35 glutaraldehyde N-hydroxyethyl piperidine N,Ell-bis-(2-hydroxy- ethyl)piperazine Sodium acetate 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 f (buffer) In the following Examples, the admixture solutions are added to the test concrete in quantities sufficient to give the indicated dose, given as parts by weight of total admixture (excluding 55 water) per 100 lb of cement.

Example 27

An outdoor experiment was carried out in which all the concrete samples, including the plain concrete reference, were mixed at WC and poured at -7 to -WC. During the curing time, the 6Q outdoor temperature varied from 1WC to + 1WC.

The results are indicated in Table Ill. Trial 1 shows the optimum results which are obtained with the already known corrosive CaCI, admixture while trials 2 and 3 demonstrate that similar results can be obtained when using a non-corrosive admixture of the invention.

6 GB2195328A 6 Exampie 28 Plain concrete is made, poured and cured at 10C while concrete samples of trials 1 to 5 are made at 10T, cured at -8 to -6C for 3 days and then cured at 10T.

In the trials, the admixtures of examples 1 and 4 (of very similar composition) are added in -5 dosage of from approx. 2 to 4.5 parts/100 parts cement. In all cases the rate of hardening is 5 more rapid than that of the plain concrete at 10T, and the 28 day compressive strength is as good as that of the plain concrete.

0 Table III

Compressive Strength (kg/cm 2 / % tr a Trial Admixture Dose Slump % A i.r 4--- Water 1 day 3 days 7 days 28 days (cm) W TY Reduction ±)%-0 (G to _r_ 0 Micro-air 0.04 18.4 6.8 Frozen 170 kg/m 3 3.8 24.7 73.5 191.2 100 100 100 Ca C12 2.0 1 19 5.9 Frozen 4.9 % 7 47 124.3 315.9 Micro-air 0.04 185 190 169 165 Example 4 1.96 2 19 6.8 5.5 4.9 % 9.4 45.3 123.3 299.5 Micro-air 0.05 248 183 168 157 Example 4 3.92 3 17.8 6.0 5.13 5.2 % 11.5 59.6 190.3 348.5 Micro-air 0.45 304 241 259 182 G) W N to W1 W m m 00 Table 1 V

Compressive Strength 2 (kglcm 1 % % Trial Admixture Dose Slump % Air 0 c: - Water 1 day 3 days 7 days 28 days of Example (cm) W I- Reduction (D -0:1 41 1- 0 m m = CC 27.9 117.3 207.3 368.1 0 12.7 1.9 7.82 176 kg/m 3 100 100 100 27.2 86.4 224 444.3 1 1 4.55 12.7 3.0 3.25 10.1 % 97 74 108 121 27.3 76.4 224.6 445.8 2 4 3.92 13.3 2.7 3.62 9.8 % 98 65 108 121 21.2 47.25 197 364 3 4 3.27 12.7 2.3 3.62 7.1 % 76 40 95 99 28.6 58.4 223.3 394.9 4 4 2.61 12.7 2.2 3.50 9.5 103 50 108 107 27.5 56 163.7 369.9 4 1.96 12.7 1.8 4.75 7.1 98 48 96 100 1 1 c) M m C.0 M W 00 00 1, 9 GB2195328A 9 Example 29

Two plain concrete samples are prepared, one of which (trial 0) is made, poured and cured at 1WC, while the other (trial 1) is made at 1WC, then poured and cured for 3 days at -WC, then further cured at WC. Trial 2 is as trial 1, but contains 3.48 parts/100 parts cement of the admixture formulation of Example 10. The results are shown in Table V.

Example 30

A plain concrete sample is made, poured and cured at 10'C while concrete samples of trials 1 to 17 are made at 10'C, poured and cured for 1 day at -5C; then the 28 day samples are cured at 10C.

Results shown in Table VI demonstrate that, compared to the plain concrete reference, the time to reach the initial-setting (rate of hardening) of trials 1 to 17 is largely reduced, and that the compressive strength performances after 28 days are superior. The trial samples did not freeze at the -5'C temperature.

Example 31

The plain concrete and concrete of trials 1 to 3 (containing the admixture of Example 4) are all made, poured and cured at 21'C.

Results are shown in Table V11. The admixtures of the invention are shown to be effective at this higher temperature.

Example 32

Two plain concretes are prepared. One (trial 0) is made and cured at 1WC. The other one (trial 1), like the concrete samples of trials 2 to 9, is made at 3-WC, cured for 3 days at a temperature which varies from - 15 to O'C, and then cured at a temperature which varies from 25 - 15 to 50C.

Results are shown in Table V111.

0 Table V Example 29 Compressive Strength (kg/cm 2 / % Trial Admixture Dose Slump % Air 0 Water 1 day 3 days 7 days 28 days (pm) Reductfon -&--% L_ 0 m 19.9 109.55 215 382.2 0 Micro-air 0.05 12.1 5 10.50 172.1.100 100 100 100 kg/m 3 9.8 34.1 108.5 257.25 Micro-air 0.05 12.7 5.8 15.5 1 49 31 50 67 Example 10 3.48 20.8 78.75 306.9 462.3 13.3 6 4.63 9 2 Micro-air 0.05 105 72 143 121 0 '1', G) W N CO M W N) CO 0 1 Table V1 Example 30 Compressive Strenqth (kglcm 2 1 % C7 Trial Admixture Dose Slump % Air C, c ta Water 1 day 28 days L_ (cm) W Reduction OU w:3 -bj %_ 0 0 12.4 1.6 8.75 170 kg/m3 24.7 347.1 100 1 2 4.32 12.7 2.8 3.88 9.4 23 441.8 93 128 2 3 4.25 13.3 3.3 4.0 8.7 16 452.3 130 3 4 3.92 13.3 3.1 ' 4.13 12.1 18.8 449.75 76 130 4 5 3.84 13.3 3.0 4.0 6.7 16 466.1 134 6 4.12 13.3 2.4 3.75 5 20.6 413 83 119 G) C0 NJ to (n W N 00 P--) Table VI (cont'.) Compressive Strength (kg/cm 2 / %) cr Trial Admixture Dose Slump % Air 0 r- Water 1 day 28 days &- (cm) (1) Reduction a) -0 =3 4J &- 0 to M = 6 7 4.04 12.7 2.7 3.75 9.4 15.75 498.75 64 144 7 8 3.72 12.7 2.5 3.88 8.7 19.3 460.5 78 133 8 9 3.64 12.7 2.8 3.38 6.4 18.6 435.2 126 9 10 3.48 13.2 2.8 3.88 9.1 20.4 446.5 83 129 11 3.32 13.3 3.1 4.38 14.1 22.3 476.8 137 11 12 3.24 13.3 3.5 3.88 11.7 20.1 497.8 81 143 i G) M rli CO M W rli CO r,j I 1, e, Table VI (contl.) Compressive Strength (kg/cm 2 / %) er Trial Admixture Dose Slump % Air' 0 Water 1 day 28 days (cm) Reduction 4-1 0 m 90 = CC =- 12.13 2.92 14 2.9 4.50 11.7 18.8 432.9 76 125 13 14 2.84 13.3 2.9 4.38 13.4 16.2 436.4 66 126 14 is 3.04 12.7 2.4 4.13 6.7 18.6 435.3 125 16 2.72 12.7 2.5 4.0 7.4 17.9 434.8 73 125 16 17 2.64 13.3 2.7 4.25 8.1 14.6 425.7 59 123 17 18 2.58 13.3 2.9 4.25 9.4 14.6 405.1 59 117 W a) m hi G M W N) CO W P.

Table VII Example 31 Compressive Strength 2 (kg/cm % CP % r Trial Admixture Dose Slump % Air Water 1 day 3 days 7 days 28 days (cm) W L_ Reduction W -0 =3 1- 0 0 7.6 5.7 5.375 158 3 81.8 202.1.299.7 388.5 kg/M MB-VR 0.06 100 100 100 100 Example 4 1.31.

1 5.1 5.2 25 6.7 133.6 283.9 398.8 506.4 3.

MB-VR 0.1 163 140 133 130 Example 4 2.62 2 5.7 6 2.75 8.2 142.9 298.8 3 97.9 484.3 MB-VR 0.1 175 160 133 125 Example 4 3.92 3 5.7 6.4 2.50 10.5 175.4 366 425.5 530.9 MB-VR 0.09 214 181 142 137 C 1, G) CD hi W M W N 00 -Pb 11, '11 1 Table VIII

Example 32

Comprdssive Strength (kg/cm 2 1 %) C Trial Admixture Dose Slump % Air Water (cm) Reduction 3 days 7 days 28 days to m= Q: = - 169 kg/M3 0 16.2 5.3 5.23 78.75 154.9 277.4 166 kg/M3 17.15 5.1 Frozen 64.05 154.4 294.5 Micro-air 0.05 100 100 100 2 Example 19 3.92 16.2 7.4 4.625 1.2.3 178.4 314 405.1 278 203 137 3 Example 20 3.92 15.2 7.8 3.625 15.8 188.5 314 412.9 294 203 140 Example 21 3.92.

4 16.5 5.5 5.125 9.5 53.9 260.5 378.1 1 Mi cro-air 0.035 240 169 130 0 G) W N) (0 (n W N CO (n (3) Table VIII (cont'.) Compressive Strength (kg/cm 2 / % Trial Admixture Dose Slump % Air 4- % 3 days.7 days 28 days Water (cm) -0 =3 Reduction 4-1 S_ 0 tu Od Example 22 3.92 16 5.8 5.875 10.5 166.1 306.1 395.2 Micro-air 0.04 260 198 134 Example 23 5.6 15.9 5.9 6.5 12.6 162 353.6 49. 8.3 6 Micro-air 0.02 253 289 169 7 Example 24 5.6 15.9 6.9 6.0 12.3 190.8 360.2 467.5 298 233 159 8 Example 25 5.6 16.4 5.8 5.625 10.5 175.8 327.5 433.7 275 212 147 Example 26 5.6 16.5 5.3 6.75 8.1 171.4 319.1 414.75 9 Micro-air 0.025 268 207 141 1, G) W (0 M W 00 a) 111 Q' GB2195328A 17

Claims

1. A chloride-free admixture for use as a cold weather concrete set accelerator which com prises (A) 100 parts by weight of at least one soluble inorganic salt having freezing point depres- 5 sant properties, up to 50% wt. of which may be replced by urea (B) from 13.3 to 30 parts by weight of at least one superplasticizer (C) from 3 to 30 parts by weight of at least one inorganic early set and strength accelerator, and (D) from 0 to 10 parts by weight of at least one organic set accelerator.

2. An admixture according to Claim 1 comprising 100 parts by weight (A), from above 15 to parts by weight (B), 5 to 10 parts by weight (C) and 1.3 to 6 parts by weight (D).

3. An admixture according to Claim 1 or Claim 2 in which component A is selected from ammonium, alkali and alkaline earth nitrates and nitfltes.

4. An admixture according to Claim 3 in which component A is calcium nitrate.

5. An admixture according to any one of the preceding claims in which component B is an alkali or alkaline earth salt of a naphthalene sulphonate/formaidehyde condensate or a sulpho nated melamine/formaldehyde condensate, or an acrylic copolymer.

6. An admixture according to Claim 5 in which component B is naphthalene sulphonate/for maidehyde condensate in sodium salt form.

7. An admixture according to any one of the preceding claims in which component C is selected from ammonium, alkali or alkaline earth thiocyanates and thiosulphates.

8. An admixture according to Claim-7 in which component C is sodium thiocyanate.

9. An admixture according to any one of the preceding claims in which component C is selected from methyloiglycolurils, dimethylolurea, monoand di-(N- methylol) hydrantoin, mono- 25 and di-(N-methylol) dimethylhydrantoin, N-methylolacrylamide, tri-(N- methylol) melamine, Whydrox yethylpiperidine, N, N-b is(2-hyd roxyethyl) pipe razine, glutaraldehyde, pyruvaldehyde, furfural and water soluble urea-formaldehyde resins.

10. An admixture according to Claim 9 in which component D is tetra (Nmethyiol)g lycolu ril.

11. An admixture according to any one of the preceding claims comprising (A) 100 parts by weight calcium nitrate (B) 20 parts by weight naphthalene sulphonate/formaidehyde condensate sodium salt.

(C) 6.7 parts by weight sodium thiocyanate and (D) 4 parts by weight tetra (N-methylol)glycoluril.

12. An admixture according to any one of the previous claims in the form of an aqueous 35 solution:

13. An admixture as described in any one of Examples 1-26.

14. A method for agcelerating the set of a concrete or cement mortar mix, suitable for use in cold weather conditions, comprising adding to ' the mix from 0.13 to 5.6 parts (dry weight) of an admixture according to any one of the preceding claims per 100 parts dry weight of cementi- 40 tious material in the mix.

15. A method for accelerating the set of a concrete or cement mortar mix, suitable for use in cold weather conditions, comprising adding to the concrete or cement mortar (1) 0.5 to 4% by weight of cement of at least one component (A), (2) 0.1 to 0.8% by weight of cement of at least one compoent (B), (3) 0.033 to 0.6% by weight of cement of at least one component (C) and (4) 0 to 0.16% of cement of at least one component D, in which components A, B, C and D are as defined in Claim 1.

16. A concrete or cement mortar mix containing (1) 0.5 to 4% by weight of cement of at least one component (A), (2) 0.1 to 0.8% by weight of cement of at least one component (B), (3) 0.033 to 0,6% by weight of cement of at least one component (C) and (4) 0 to 0. 16% of cement of at least one cmponent D, in which components A, B, C, and D are as defined in Claim 1.

17. A concrete or cement mortar mix according to Claim 16 containing 0.02 to 0.16% wt. 55 of component D.

18. A concrete or cement mortar mix according to Claim 17 containing 2.03.0% wt. of component A, 0.4-0.6% wt. of component B, 0.1-0.6% wt. of component C and 0.04-0.12% wt. of component D.

60. 19. A concrete mix comprising an admixture according to Claim 1, as described in any one 60 of Examples 27-32.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.