GB2039271A

GB2039271A - Cement compositions

Info

Publication number: GB2039271A
Application number: GB7940961A
Authority: GB
Original assignee: Denki Kagaku Kogyo KK
Current assignee: Denka Co Ltd
Priority date: 1978-11-29
Filing date: 1979-11-27
Publication date: 1980-08-06
Also published as: FR2442804B1; DE2948129C2; GB2039271B; IT7912850A0; DE2948129A1; FR2442804A1; IT1124365B

Abstract

A cement composition comprises a cement, and from 0.1% to 2.5% by weight, based on the weight of said cement, of a dextrin having a cold- water solubility of from 10% to 80% by weight. The inclusion of the dextrin in the cement composition suppresses heat of hydration, so that mortars or concretes incorporating the cement composition have reduced liability to thermal cracking.

Description

SPECIFICATION Cement compositions The invention relates to cement compositions.

Large quantities of concrete and mortar are used nowadays in constructional work. The generation and accumulation of heat, arising from the hydration of the cement included in the concrete or mortar mix, increases as increasingly large quantities of concrete and mortar are mixed. Hence the temperature of the mortar or concrete rises abruptly, particularly at the initial stage of ageing, and this can cause internal stresses after cooling creating a thermal cracking problem in the finished mortar or concrete. The problem of thermal cracking which occurs when a normal cement is used is increased when an expansive cement is used, for example for compensating dry shrinkage or for realizing a special effect in the chemical pre-stressing process, since the hydration reaction of the expansive cement is accelerated as compared to that of the normal cement.

Grout mortars containing expansive agents mainly composed of calcium sulphoaluminate or lime or iron powders, such mortars being mixed with various chemicals, are known. These grout mortars have advantageous characteristics in that lesser bleeding and settlement are caused and higher adhering and shearing strengths are obtainable when compared to normal cement mortars. They are conveniently used for fixing anchor bolts of bridges and for installing machine bases, but have even more frequent thermal cracking problems than normal cement mortars since grout mortars generate larger quantities of heat on hydration than normal cement mortars.

The problem of thermal cracking may be reduced or overcome by, for example, using a lesser amount of cement per unit volume of concrete or mortar being prepared, selecting a cement having a lower heat of hydration, cooling the cement prior to hydration or during hydration, preparing the concrete or mortar in smaller batches, providing shrinkage joints or strictly controlling the ageing process, but commercial or practical difficulties limit the application of these measures in constructional works. A conventional practice is to add a small amount of an additive, for example one mainly composed of a lignin sulphonate, an oxycarboxylate or a sugar. These additives retard the commencement of the hydration reaction, which nevertheless takes place later generating substantially the same temperature rise in the moulded body of concrete and leading to the same thermal cracking problem.

A cement composition according to the invention comprises a cement and from 0.1% to 2.5% by weight, based on the weight of said cement, of a dextrin having a cold-water solubility of from 10% to 80% by weight.

The inclusion of the dextrin suppresses the heat of hydration and improves the development of strength.

These effects are achieved not only with "normal" Portland and mixed cements but also with "special effect" cements such as expansive cements and rapid hardening cements, without loss of the "special effect".

Cement compositions according to the invention are also useful in grouts, suppressing the heat of hydration without deteriorating the properties of the grout. The grout fluidity is also improved, resulting in easy handling as for example in injection into small spaces or gaps.

The term "cold-water solubility" is used throughout the specification and claims to mean the amount of the components of the dextrin which dissolve in distilled water at 21"C. The cold-water solubility is determined by putting 10 g of dextrin in a 200 ml messflask, adding 150 ml of distiiled water at 21"C, filtering after allowing to stand for an hour at from 20"C to 23"C, evaporating the filtrate to dryness and measuring the weight of the residue, from which weight the cold-water solubility is calculated.

The dextrin contained in cement compositions according to the invention preferably has a cold-water of from 10% to 65% by weight. If the cold-water solubility is lower than 10% by weight, the advantageous effect of suppressing the temperature rise due to the heat of hydration is not realized, the strengths at the early and later stages are not increased and the water reducing property of the resultant product is inferior. On the contrary, if the cold-water solubility exceeds 80% by weight, the dextrin will act only as a retarder, that is to say it only retards the generation of the heat of hydration at the early stage so that the temperature of the cement rises abruptly after the lapse of about 30 hours and the cement is thus deprived of its resistivity against thermal cracking.

The dextrins contained in the cement compositions according to the invention are preferably contained in an amount of from 0.2% to 2.0% by weight based on the cement. If the amount of dextrin is less than 0.1% by weight, the suppression of the temperature rise due to the heat of hydration is not realized and the strength is not increased so much. On the contrary, if the amount of dextrin exceeds 2.5% by weight, the creation of strength is retarded too much and the strength thus created does not reach a higher level although the suppression of the temperature rise does occur.

The dextrin used in the invention may be prepared by any suitable method, for example, by adding a dilute acid to a dextrin to thermally decompose the latter, by decomposing a dextrin with an enzyme or by condensating glucose.

The cements useful in the invention include various Portland cements such as normal Portland cement, high early strength Portland cement, super high early strength Portland cement, moderate heat Portland cement, white Portland cement or the like; mixed cements such as silica cement, fly ash cement, blast furnace cement or the like; expansive cements containing, as the main expansive agent, a combination of calcium sulphoaluminate, lime and calcium sulphate, a combination of calcium aluminate and calcium sulphate. a high sulphate slag, lime, magnesia or the like; and rapid hardening cements containing calcium aluminate such as 12CaO-7AI203 and/or calcium haloaluminate such as 11CaO-7AI203-CaX7 (wherein X represents a halogen atom) together with calcium sulphate or the like.

A s,,:,,- tive agent is preferably added to the cement compositions according to the invention The surface active agent may be a water reducing agent, an air entraining water reducing agent or an air entraining agent. The inclusion of such surface active agents has the effect of further suppressing the temperature rise and may improve other physical properties of the cement, such as its workability. Suitable water reducing agents include those mainly composed of any polysaccharides, oxycarboxyiates, polyalkylaryl sulphonates, and polycondensation products of triazine modified with an alkali metal sulphite.Suitable air entraining water reducing agents include those mainly composed of lignin sulphonate, creosote oil-formaldehyde condensate modified with a salt of sulphurous acid, metal salt of naphthalene sulphurous acid-formaldehyde condensate and polyoxyethylene alkylaryl ether. The air entraining agents include those mainly composed of sodium abietate or a triethanolammonium hydrocarbon sulphonate, and specific examples of commercially available air entraining agents are those sold under the Trade Names of "Vinsol" (produced by Yamaso Chemicals Co. Ltd.) and "Darex" (produced by W.R. Grace Co. Ltd.).Particularly preferred surface active agents are those mainly composed of polyalkylaryl sulphonates including li-napthalene sulphonic acid formalin condensate and those mainly composed of lignin sulphonate or sodium abietate, since their temperature suppressing effect in combination with dextrin is high. The nature and the amount of the surface active agent added depends upon the properties that it is desired to impart to the cement composition, but the amount will usualiy be 1% by weight based on the weight of the cement.

A retarder may also be added to cement compositions according to the invention. Suitable retarders include carbohydrates such as glucose, fructose, galactose, sucrose, lactose, cellulose and derivatives thereof; high molecular weight organic acids such as lignin, derivatives of lignin and salts thereof and tannic acid; carboxylic acids and salts thereof such as lactic acid, acetic acid, maleic acid, maleic acid and salts thereof; lower and higher alcohols; and inorganic acids and salts thereof such as phosphoric acid, boric acid, and carbonic acid and salts thereof such as phosphates and silicofluorides. By adding a retarder to cement compositions according to the invention, the temperature rise of the moulded body after the hydration retarding period may be suppressed and the thermal cracking may be prevented.The amount of the retarder added is suitably less than 3% by weight based on the weight of the cement.

Cement compositions according to the invention may be used in the preparation of grout compositions.

The grout compositions comprise cement compositions according to the invention in admixture with one or more of water glass, asphalt emulsions, cement expansive agent, cement rapid hardening agents, bentonite and mixtures of iron powders and oxidizing agents, the particular admixture materials being selected depending on the intended use of the grout composition.For instance, a grout composed of a cement composition according to the invention admixed with water glass or a cement rapid hardening agent may be used as a soil consolidation or water stopping grout; a grout composed of a cement composition according to the invention admixed with an asphalt emulsion may be used as a slub grout; a grout composed of a cement composition according to the invention admixed with fly ash or bentonite may be used as a tunnei construction grout; and a grout composed of a cement composition according to the invention admixed with a cement expansive agent or a mixture of iron powders and an oxidizing agent may be used for fixing anchor bolts of a bridge or for installing a machine base.The cement compositions according to the invention are particularly preferred for use as the grout for fixing anchor bolts of a bridge or for the installation of machine base, wherein a severe dimensional stability is required. To these grout compositions there may be added a desired quantity of a thickener such as polyvinyl alcohol or carboxymethyl cellulose; a foaming agent such as aluminium; a variety of cement dispersing agents such as those mainly composed of oxycarboxyiates, those mainly composed of polyalkylaryl sulphonates and those mainly composed of lignin sulphonates.

Such grout compositions may be used in the form of cement paste, cement mortar or cement concrete.

The invention is illustrated by the following Examples, and by the drawings which are graphs of temperature against time in the preparation of various concrete and mortar moulds as described in the Examples.

Example 1 Mortars were prepared from 100 parts by weight of a normal Portland cement, 200 parts by weight of a river sand (from the beach of Sagami River) having a particle size of less than 5 mm and each of the parts by weight set forth in Table 1 of dextrins having the cold-water solubilities also set forth in Table 1. The mortars each had a water-cement ratio of 42% and was adjusted to a temperature of 20"C after kneading. Each was put into a cylindrical container made of a foamed polystyrene and having a height of 30 cm, an inner diameter of 13 cm and a thickness of 10 cm and aged in a constant temperature chamber maintained at 20 C, and the temperature at the substantial centre portion of the mortar was measured continuously and automatically by a thermo-couple. The results are shown in Table 1 and Figure 1.

The same mortars were moulded in a mould of 4 cm / 4 cm / 16 cm dimensions to form test specimens which were cured in water at 20 C and then subjected to compressive strength tests. The results are shown in Table 2.

Further experiments were conducted similarly as in the preceding experiment except in that a variety of dextrins having cold-water solubilities as set forth in Table 3 were added. Similarly, the temperature at the substantial centre portion of each mortar was measured. The maximum temperatures thus determined and the ages at which each mortar reached said maximum temperature are shown in Table 3 together with the test results of the preceding experiments.

In Table 3, there are also shown the results of the compressive strength test conducted similarly as in the preceding experiments using the mortar test specimens of 4cm x 4cm x 16 cm after cured in water at 20 C, and the data of table flow values determined generally in accordance with the JIS-R5201 method (JIS means Japanese Industrial Standard).

TABLE 1 (Unit: C) Experiment Age (hr.) 0 5 10 15 20 25 30 35 40 45 50 No. Added Quantity (part) 1 Not Added 21.0 25.0 49.0 59.8 57.1 52.6 43.6 38.3 33.5 30.1 29.2 Dextrin 0.4 2 (Cold-water Solubility:18.3wt%) 21.5 24.5 38.2 47.5 48.4 46.0 40.9 37.2 34.5 31.8 30.4 Dextrin 0.4 3 (Cold-water Solubility:85wt%) 21.0 21.5 22.2 28.1 42.9 56.3 58.0 53.1 45.2 39.3 36.1 Dextrin 0.4 4 (Cold-water Solubility:8wt%) 20.0 24.5 46.3 59.8 57.4 52.4 44.2 38.6 33.7 30.0 29.0 TABLE 2 Experiment No. 1 2 3 4 Compressive Strength 7 Days 461 487 415 468 (Kg/cm2) 28 Days 572 598 576 562 TABLE 3 Experiment No. 1* 4* 5 2* 6 7 8 3* Cold-water Solubility Not of Dextrin (wt%) Added 8 10 18.3 60 65 80 85 Maximum Temp.Temp.( C) 59.9 59.8 52.3 48.4 48.0 48.0 51.6 58.0 and Age Age (hr.) 15 15 18 20 23 23 27 30 Compressive Age Strenght (Kg/cm2) 7 Days 461 468 478 487 470 469 468 415 28 Days 572 562 583 598 582 582 576 576 Table Flow (mm) 211 213 223 231 236 237 240 240 Note: (1) Numbers attached with * indicate the Experiment Nos. shown in Table. 1.

(2) The added quantities of dextrin in Experiment Nos. 5,6,7 and 8 are, respectively, 0.4 parts by weight similarly as in the preceding Experiments.

The highest temperature recorded in any of Experiments Nos 2,5,6,7 and 8 (those according to the invention) was 52.3"C, lower than in any of the Comparative Experiments. The lowest compressive strengths recorded in any of Experiments 2,5,6,7 and 8 were 468 kg/cm2 at 7 days and 576 kg/cm2 at 28 days, these being equal to or higher than in any of the comparative Experiments. The table flow values were also good.

In Experiments Nos 1 and 4, wherein no dextrin was added or the cold-water solubility of the dextrin was less than 10% by weight, the temperature reached 59.8"C, showing poor temperature suppressing effect and the compressive strength was not increased, either. In Experiment No.3, in which the cold-water solubility of the dextrin exceeded 80% by weight, the dextrin acted only to retard the hydration, and did not suppress its vigour as seen from the recorded temperature of 58"C at 30 hours.

Example 2 A concrete was prepared by mixing 100 parts by weight of a normal Portland cement, 352 parts by weight of a coarse aggregate consisting of a river gravel from the beach of Sagami River and 255 parts by weight of a fine aggregate consisting of a river sand from the beach of Sagami River having a particle size of less than 5 mm with water to bring the water-cement ratio of 56% and dextrin was added according to the invention.

The concrete was kneaded and then adjusted to a temperature of 20"C after kneading. The concrete was then cast into an iron mould frame having dimensions of 50 cm x 50 cm x 50 cm which was enclosed with a 10 cm thick foamed polystyrene on its four faces while the main two faces were left open, and the temperature at the substantial centre portion of the concrete during the curing at 20"C in a constant temperature chamber was measured automatically by a thermo-couple.

For comparison purposes, tests were conducted on similar concretes in which the dextrin was omitted, one having gluconic acid as an additive and the other having no additive. The results are shown in Table 4 and Figure 2.

TABLE 4 (Unit: C) Experiment No. Age(hr.) Material 0 5 10 15 20 25 30 35 40 45 50 Added (part) 9 Not Added 21.5 25.2 29.8 40.0 43.3 42.0 39.6 37.0 34.7 32.6 30.9 10 Dextrin 0.4 (Cold-water Solubility: 21.0 22.3 27.8 34.0 35.9 35.7 34.3 33.0 32.5 32.0 31.5 18.3wt%) 11 Gluconic Acid 0.15 20.7 20.9 21.3 23.5 33.2 42.7 42.2 38.4 35.9 33.6 33.0 Example 3 A mortar composed of 90 parts by weight of a normal Portland cement, 10 parts by weight of each of the commercially available cement expansive agents set forth in Table 5, 200 parts by weight of a natural sand, 42 parts by weight of water and 0.6 parts by weight of dextrin was prepared. The water-cement ratio thereof was adjusted to 42% and the temperature after kneading to 20"C.About 3.5t of this mortar was cast into a cylindrical container made of a foamed polystyrene and having a height of 30 cm, an internal diameter of 13 cm and a thickness of 10 cm, and cured at 20"C in a constant temperature chamber. The temperature at the substantial centre of the mortar during the curing period was automatically measured using a thermo-couple. The specific kinds of the cement expansive agents and dextrins used and the test results are shown in Table 5 and Figure 3.

There are also shown the results of compressive strength tests conducted on test specimens having dimensions of 4 cm x 4 cm x 16 cm, which specimens were cured at 20"C in water.

Similar tests were conducted on the mortar used in Experiment No. 14 while changing the amount of the dextrins. The results thus obtained are shown in Table 6.

TABLE 5 Exp.

Material Added Temperature at the Substantial Center of the Mortar at Respective ages (hour ( C) Compressive No. Strength (kg/cm) 0 5 10 15 20 25 30 35 40 45 50 7 days 38 days Expansiva Agent Mainly Composed of Calcium Sulfoaluminate (Sold under the Trade Name 20.1 33.2 57.8 59.5 54.2 49.0 44.6 40.2 37.0 33.1 30.1 440 581 12 of "DENKA CSA" from Denki Kagaku Kogyo KK) Dextrin Not Adde Expansive Agent Mainly Composed of Lime 13 (sold inder the Trade Name of "EXPAN" 20.0 38.1 63.2 62.0 56.3 50.2 45.0 39.8 35.3 32.1 29.8 432 573 from Onode Cement Co., Ltd.) Dextrin Not Added Expansive Agent Used in Experiment No. 12 14 Dextrin Having Cold-water Solubility of 20.2 27.2 48.0 65.2 62.2 47.8 44.0 41.0 37.5 34.5 32.2 451 608 18.3 wt% Expansive Agent Used in Experiment No.l3 15 Dextrin Same as that Used in Experiment 20.0 33.2 55.8 59.0 54.5 50.0 46.3 40.7 36.1 32.0 28.5 448 596 No. 14 Expansive Agent Used in Experiment No. 12 16 Dextrin Having Cold Water Solubility of 20.3 22.2 43.8 57.8 59.0 52.5 47.2 42.7 39.2 35.8 33.0 400 583 95 wt% 17 Expansive Agent Used in Experiment No. 12 Dextrin Having Cold-water Solubility of 0% 20.0 33.3 57.8 59.5 54.1 48.8 44.5 40.1 36.9 33.0 30.0 438 571 TABLE 6 Experiment No. 18 19 20 14* 21 22 23 24 Added Quantity (wt%) 0.05 0.1 0.2 0.6 1.5 2 2.5 3 Maximum Temp. Temp. ("C) 59.4 57.4 56.0 55.2 54.1 52.8 52.3 52.2 and Age Age (hr.) 15 15 15 15 20 25 30 45 Compressive 7 Days 441 448 450 451 450 446 432 389 Strength (kg/cm2) 28 Days 581 592 603 608 605 593 587 578 Note: (1) Number attached with * indicates the composition of Experiment No. 14 set forth in Table 5.

(2) The cold-water solubilities of the dextrins used in Experiment Nos. 18 to 24 are 18.3% by weight similarly as in the preceding Experiment.

As will be apparent from the results set forth above, the maximum temperatures in Experiment Nos. 14 and 19 to 23 according to the present invention were about 52"C to about 57"C and the maximum compressive strength reached 608 kg/cm2. However, if the added amount of dextrin is in short of 0.1% by weight as is the case of Experiment No. 18, the maximum temperature raised to 59.4"C, the temperature suppressing effect being not exhibited and the compressive strength being not increased. On the other hand, if the added amount exceeds 2.5% by weight as is the case of Experiment No. 24, the strength development was too late as 578 kg/cm2 at the age of 28 days although the temperature suppressing effect is exhibited.

Example 4 A concrete was prepared by mixing 90 parts by weight of a normal Portland cement, 10 parts by weight of a commercially available expansive agent mainly composed of calcium sulphoaluminate (sold under the Trade Name of "DENKA CSA"), 352 parts by weight of a coarse aggregate consisting of a river gravel having a grain size of less than 25 mm and 255 parts by weight of a fine aggregate consisting of a river sand having a particle size of less than 5 mm. The concrete was kneaded at the water-cement ratio of 56%, and a dextrin having a cold-water solubility of 18.3% by weight was added. The concrete was adjusted to a temperature of 20"C after kneading.The concrete was cast into an iron mould frame having dimensions of 50 cm x 50 cm x 50 cm and being enclosed with a 10 mm thick foamed polystyrene on four faces, the remaining two faces being left open, and the temperature at the substantial centre portion of the concrete during the curing at 20"C in a constant temperature chamber was measured automatically by a thermo-couple.

For comparison purposes, tests were conducted on similar concretes in which the dextrin was omitted, one having gluconic acid as an additive and the other having no additive. The results are shown in Table 7 and Figure 4.

TABLE 7 Experiment Material Added Temperature at the Substantial Center of the Concrete No. at Respective Ages (hour) ("C) 0 5 10 15 20 25 30 35 40 45 50 25 Not Added 20.3 23.6 32.5 45.6 46.2 44.0 40.8 37.7 34.9 32.3 30.2 Dextrin 26 0.8 parts by weight 20.4 22.0 28.8 37.8 40.2 40.0 38.3 36.5 34.5 32.8 31.5 Gluconic Acid 27 0.15 parts by weight 20.0 20.5 20.8 24.0 34.0 43.6 45.4 43.2 40.3 37.2 34.2 Example 5 Mortar composed of 100 parts by weight of a normal Portland cement, 200 parts by weight of a river sand having a particle size of less than 5 mm, 0.4 parts by weight of a dextrin having a cold-water solubility of 18.3% by weight and each of the parts by weight of commercially available surface active agents as set forth in Table 8 was prepared.The water-cement ratio of the mortar was adjusted to 42% and the temperature after kneading to 20"C. After 3.5 litres of each of these mortars was cast into cylindrical containers made of a foamed polystyrene and having a height of 30 cm, an internal diameter of 13 cm and a thickness of 10 cm, and cured at 20 C in a constant temperature chamber. The temperature at the substantial centre portion of the mortar during curing was measured automatically by a thermo-couple. The results are shown in Table 8 and Figure 5.

There are also shown in Table 8 the results of compressive strength tests conducted on test specimens having dimensions of 4 cm x 4 cm x 16 cm, which specimens were cured at 20"C in water.

Experiments Nos. 29 to 32 are the samples of the present invention.

TABLE 8 Exp. Material Added (part by weight Temperature at the Substanntial Center of the Mortar at Respective Ages (hour) ( C) Compressive No. Strength (kg/cm2) 0 5 10 15 20 25 30 35 40 45 50 7 days 38 days 28 Not Added 21.0 25.0 49.0 59.8 57.1 52.6 43.6 38.3 33.5 30.1 29.2 461 572 Dextrin 0.4 Water Reducing Agent Mainly Composed of Oxycarboxylate (Sold under the Trade 29 Name of "PALIC" from Fujisawe 0.2 20.8 24.3 35.8 43.8 46.2 44.4 41.3 38.8 35.2 32.8 31.5 470 589 Pharmaceutical Company Limited) Dextrin 0.4 Air Entraining Water Reducing Agent Mainly Compossed of lignin sulfonate 30 (sold under the Trade Name of 0.25 20.9 24.3 35.6 42.8 44.9 43.6 40.1 37.5 34.5 31.5 29.3 469 592 "POZZOLITH NO 5L" from Nisso Master Builders Co., Ltd.) Dextrin 0.4 Water Reducing Agent Mainly Composed of 31 Polyalkylary Sulfonate (Sold under 0.25 21.2 23.8 31.8 40.0 44.0 42.7 41.0 38.8 35.8 33.6 32.2 469 598 the Trade Name of "MIGHTY 150" from Kao Soap Co., Ltd.) Dextrin 0.4 Air Entraining Agent Mainly Composed 32 of Abletate (Sold under the Trade 0.02 20.9 23.8 32.8 41.6 43.0 41.7 39.4 37.0 34.6 32.4 31.0 469 585 Name of "VINSOL" from Yamaso Chemicals Co., Ltd.) Example 6 A concrete was prepared by mixing 100 parts by weight of a normal Portland cement, 352 parts by weight of a coarse aggregate consisting of a river gravel having a grain size of less than 25 mm, 255 parts by weight of a fine aggregate consisting of a river sand having a particle size of less than 5 mm and each of the parts by weight of additives as set forth in Table 9.The concrete was kneaded at the water-cement ratio of 56% and the temperature after kneading was adjusted to 20"C. The concrete was cast into an iron mould frame having dimensions of 50 cm x 50 cm x 50 cm which was enclosed with a 10 mm thick foamed polystyrene on four of its faces, the remaining two faces being left open, and the temperature at the substantial centre portion of the concrete during the curing at 20"C in a constant temperature chamber was measured automatically by a thermo-couple. The results are shown in Table 9 and Figure 6. The cold-water solubility of the dextrin used was 18.3% by weight. Experiment No.33 is an example of the invention.

TABLE 9 ( C) Temperature at the Substantial Center of Exp.No. the Concrete at Respective Ages (hour) Material Added (part by weight) 0 5 10 15 20 25 30 35 40 45 50 Dextrin 0.4 33 Water Reducing Agent Mainly Composed or 20.6 21.2 26.0 31.0 34.1 33.8 32.8 32.5 32.1 30.9 30.5 Polyalkylaryl Sulfonate (Sold under the Trade Name of "MIGHTY 150") 0.25 34 Gluconic Acid 0.15 20.7 20.9 21.3 23.5 33.2 42.7 42.2 38.4 35.9 33.6 33.0 Example 7 Cement mortars to be used as a grout was prepared by mixing and kneading a normal Portland cement, a grout additive mainly composed of calcium sulphoaluminate and sold under the Trade Name of "DENKA TASCON" from Denki Kagaku Kogyo KK, each of the dextrins having solubilities as set forth in Table 11, a natural sand (F.M. ::2.7) and water, and adjusting the temperature after kneading to 20"C (the mixing ratios are shown in Table 10). About 4 litres of each of the mortars was cast in a cylindrical container made of a foamed polystyrene and having a height of 30 cm, an internal diameter of 13 cm and a thickness of 10 cm.

The temperature at the substantial centre portion of the mortar during the curing at 20"C in a constant temperature chamber was automatically measured by a thermo-couple. The results are shown in Table 11 and Figure 7. Experiment No. 38 is an example of the invention.

TABLE 10 (part by weight) Exp. Cement Grout Dextrin Water Sand No. Additive 35 3115 385 0 1400 7000 36 3115 385 21 1400 7000 37 3115 385 21 1400 7000 38 3115 385 21 1400 7000 TABLE 11 Exp. Cold-water Temperature at the Substantial Center of the No. Solubility Mortar at Respective Ages (hour) ("C) of Dextrin (wt%) 0 5 10 15 20 25 30 35 40 45 50 35 Not Added 22 36 57 58 57 55 52 49 46 42 38 36 1 22 35 56 57 57 54 51 48 45 41 37 37 99 22 23 23 25 43 58 56 52 49 44 41 38 20 22 28 39 45 47 46 43 40 36 32 29 These cement mortars used for grouts did not show bleeding and settlement at all. Each of these grouts was spontaneously poured into one side of a mould frame of 3 cm thickness, 40 cm width and 170 cm length provided with a barrier wall of 3 cm thickness, cm width and 20 cm length located at the centre thereof.

This mould frame was completely charged with any of these mortars at the charge ratio of 100% when pouring the mortar from either side of the mould. The compressive strengths at the ages of 7 and 28 days and the adhesive shearing strength at the age of 28 days of any of the test specimens made of these mortars were, respectively, about 432 kg/cm2, 615 kg/cm2 and 25kg/cm2.

Claims

1. A cement composition comprising a cement and from 0.1% to 2.5% by weight, based on the weight of said cement, of a dextrin having a cold-water solubility (as herein defined) of from 10% to 80% by weight.

2. A cement composition according to claim 1 wherein the cement is a Portland cement, mixed cement, expansive cement or rapid hardening cement.

3. A cement composition according to claim 1 or claim 2 wherein the cement is a normal Portland cement, a high early strength Portland cement, a super high early strength Portland cement, a moderate heat Portland cement or a white Portland cement.

4. A cement composition according to claim 1 or claim 2 wherein the cement is a mixed cement being silica cement, fly ash cement or blast furnace cement.

5. A cement composition according to claim 1 or claim 2 wherein the cement is an expansive cement containing an expansive agent mainly composed of a combination of calcium sulphoaluminate, lime and calcium sulphate, a combination of calcium aluminate and calcium sulphate, a high sulphate slag, lime or magnesium.

6. A cement composition according to claim 1 or claim 2 wherein the cement is a rapid hardening cement containing 12CaO-7Ai203 and/or 1 1CaO.7A12O3.CaX2 (X representing a halogen atom), and calcium sulphate.

7. A cement composition according to any preceding claim further comprising a surface active agent.

8. A cement composition according to claim 7 wherein the surface active agent is a water reducing agent, an al enw. ai:-"ng water reducing agent or an air entraining agent.

9. A cernent composition according to claim 7 or claim 8 wherein the surface active agent is 3 water reducing 9 agent mainly composed of a polysacchardie, an oxycarboxylate, a polyalkylaryl sulphonate or a polycondrsation product of triazine modified with an alkali metal sulphite.

10. A cement composition according to claim 7 or claim 8 wherein the surface active agent is an air en@@a@nng water educing agent mainly composed of lignin sulphonate, a creosote oil-formaldeh/de condensate modified with a metal salt of sulphurous acid, a metal salt of naphthalene sulphurous acid-formaldehyde condensate or a polyoxyethylene alkylaryl ether.

11. A cement composition according to claim 7 or claim 8 wherein the surface active agent is an air entraining agent mainly composed of sodium abietate or a triethanol-ammonium hydrocarbon sulphonate.

12. A cement composition according to any preceding claim further comprising a retarder.

13. A cement composition according to claim 12 wherein the retarder is a carbohydrate, a high molecular weight organic acid, a carboxylic acid and/or a salt thereof, a higher or lower alcohol or an inorganic acid or a salt thereof.

14. A grout composition comprising a cement composition according to any preceding claim and at least one of water glass, an asphalt emulsion, a cement expansive agent, a cement rapid hardening agent, fly ash, bentonite or a mixture of iron powders and oxidizing agents.

15. A grout composition according to claim 14 further comprising a thickener and/or a foaming agent anchor a cement dispersing agent.

16. A grout composition according to claim 15 wherein the thickener is polyvinyl alcohol or carboxymethyl cellulose.

17. A grout composition according to claim 15 wherein the foaming agent is aluminium.

18. A grout composition according to claim 15 wherein the cement dispersing agent is mainly composed of an oxycarboxylate or a polyalkylaryl sulphonate.

19. A cement composition substantially as described herein with reference to any of experiments 2,5,6,7,8,10,14,15,19,20,21,22,23, or 26 in the Examples.