WO1999002465A1

WO1999002465A1 - Set-accelerating mixture for concrete

Info

Publication number: WO1999002465A1
Application number: PCT/NO1998/000191
Authority: WO
Inventors: Harald Justnes
Original assignee: Nyfotek As
Priority date: 1997-07-10
Filing date: 1998-07-07
Publication date: 1999-01-21
Also published as: NO973207D0; AU8820298A; NO973207L

Abstract

Combined set- and hardening accelerator composition for use in cement and a method for the manufacture of the same. The composition comprises calcium, anions and an amine compound and is manufactured by providing a reaction mixture comprising (i) an aqueous solution of calcium ions, anions and an ammonium source chosen from the group consisting of ammonium ions and ammonia, and (ii) an epoxy compound, whereby the reaction admixture is maintained at a pH and at a pressure and a temperature sufficient to convert at least partially the epoxy compound and the ammonia to amine containing reaction products. Epichlorohydrin is used as the epoxy compound, thus obtaining the reaction product mono-, di- and/or tri-(3-chloro-propane-2-ol)-amine in a mixture with calcium ions and various anions.

Description

Set-accelerating mixture for concrete

The invention concerns a setting and hardening composition for cement as disclosed by the introductory part of claim 1, and a method for the manufacture of such a composition as disclosed by the introductory part of claim 4 as well as a utilisation thereof.

Background

A number of set-accelerators for cement are known. A lot of attention has recently been directed towards the manufacture of chloride free hardening accelerating compositions to replace the previous commonly used calcium chloride accelerators.

Calcium nitrate (Ca(NO₃)₂) has been suggested as a basis component in a hardening accelerating composition in combination with triethanol amine, see e.g. US Patent No. 4,337,094. According to this publication an additive composition comprising an aqueous solution of calcium mtrate and polyalkanol amine is utilised in an attempt to avoid utilisation of the unfavourable chloride component. The polyalkanol component primarily consisting of diethanol amine and triethanol amine, is also known to exhibit certain hardening accelerating effects on cement, and is according to this prior publication added directly to an aqueous calcium nitrate solution. The main objective for this prior patent seems to be the achievement of the combination of the hardening accelerating effect with the utilisation of a cheap raw material consisting of an alkanol distillate composition.

Rettvin and Masdal ("The use of Calcium Nitrate Solution as Set- Accelerating Admixture in Slipforming of High Strength Concrete", Proc. ERMCO'95, [1995] Istanbul, Tyrkia) showed that addition of a 50% calcium nitrate solution (ammonium free) to concrete yielded a set acceleration that was proportional with the amount added up till 0,50% of the cement weight. These authors have also described the utilisation of calcium nitrate to ensure a sufficient slipforming rate for the building of the shafts in the Troll-platform in the North Sea (with a height of 369 m). In 1992 a thorough study was initiated i.e. to investigate the possibility of utilising the cheap and available raw material calcium nitrate, which is primarily used for fertilizers. The study was directed towards utilisation of technical calcium nitrate, which is a complex nitrate salt based on calcium and ammonium and some crystal water, as additives to concrete. A typical formulation of technical calcium nitrate is described by the formula

xNH₄NO₃*yCa(NO₃)₂*zH₂O

where x=0,092, y=0,500 and z=0,826.

can, however, also occur in the form of other salts. The effect of addition of technical calcium nitrate on the hardening characteristics of the cement, the compressive strength of the concrete, chloride induced corrosion of steel and freezing- and thawing resistance are available in the reports: H. Justnes and 0. Vennesland, "CN as Concrete Admixture", Report STF70 F92096, (1992), SINTEF; H. Justnes, "CN as set Accelerator for French Cements", Report STF 70 F93013, (1993), SINTEF; and H. Justnes, "The influence of Technical Calcium Nitrate (CN) on the Setting Time, Heat Evolution, Strength Development and Durability of Cement, Mortar and Concretes", Report STF70 F93138 (1993), SINTEF; H. Justnes and E.C. Nygaard: "Technical Nitrate as Set Accelerator for Cement", Nordic Concrete Research, No. 13, p. 70-87 (1993); H. Justnes and E.C. Nygaard: "The Influence of Technical Calcium Nitrate Additions on the Chloride Binding Capacity of Cement and the Rate of Chloride Induced Corrosion of Steel Embedded in Mortars", Proceedings of the Int. Conf. on Corr. and Corr. Protection of Steel in Concrete, vol. 1, p.491-502 (July 25-28, 1994) Sheffield, UK; H. Justnes and E.C. Nygaard: "Technical Nitrate as Set Accelerator for Cement at Low Temperatures", 4th CANMET/ACI Int. Conf. on Super- plasticizers and Other Chemical Admixtures in Montreal, Canada, supplementary papers p.71-80 (October 11-13, 1994); H. Justnes and E.C. Nygaard: "Technical Calcium Nitrate as Set Accelerator for Cement at Low Temperatures", Cement and Concrete Research, vol. 25, No. 8, p. 1766-1774 (1995); H. Justnes and E.C. Nygaard: "Calcium Nitrate - A Multifunctional Concrete Admixture", Proceedings of the International Conference on High-Performance Concrete, and Performance and Quality of Concrete Structures", (June 05-07, 1996), Flroanopolis, Brasil, p. 514-525; H. Justnes and E.C. Nygaard: "Technical Calcium Nitrate as Set Accelerator for Cement Pastes at Low Temperatures", Advances in Cement Research, vol. 8, No. 31 (1996), p. 101-109; H. Justnes and E.C. Nygaard: "The Mechanism of Calcium Nitrate as Set Accelerator for Cement", Proceedings of 10th International Congress on the Chemistry of Cement, Gothenburg, Sweden (June 2-6, 1997), Paper 3iii012, 8 pages; H. Justnes and E.C. Nygaard: "Performance of Concrete with Calcium Nitrate Admixtures", proceedings of the 4th CANMET/ACI International Conference on Durability of Concrete, August 17- 22, 1997, Sydney, Australia, Supplementary Papers, pp. 111-126; H. Justnes and E.C. Nygaard: "The Setting Accelerator Calcium Nitrate - Fundamentals, Performance and Applications", proceedings of the 3rd CANMET/ACI International Symposium on Advances in Concrete Technology, August 24-27, 1997, Auckland, New Zealand, ACI SP-171, pp. 325-338; and finally H. Justnes and E.C. Nygaard: "Changes in Microstructure of Cement Pastes and Concretes due to Calcium Nitrate Additions", proceedings of the 5th CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, October 8-10, 1997, Rome, Italy, ACI SP- 173,, pp. 657-672.

Technical calcium nitrate has accordingly proved to be a valuable setting accelerator for cement with the main objective being to avoid chloride induced corrosion of concrete. A substantial disadvantage with technical calcium nitrate, however, is that the ammonia component in the nitrate, which in solution is present in the form of ammonium ions (NH₄ ⁺), is liberated to gaseous ammonia when untreated technical calcium nitrate is used directly as the accelerator. This disadvantage limits the use of technical ammonium nitrate to low concentrations and to open areas, like bridge constructions, due to the health danger and the lingering smell of the gaseous ammonia.

Norwegian Patent application No. 952096 shows a method for the manufacture of an accelerating composition that overcomes the disadvantages of the liberation of ammonia from technical calcium nitrate during hardening, by adding an epoxy compound to the accelerator composition comprising technical calcium nitrate and allowing the epoxy compound to react with the ammonia under alkalic conditions and to convert at least partially the ammonia to an amine. Amine compounds that are formed are generally denoted mono-, di- and tri-alkanolamines. According to one embodiment ethylene oxide is used as the epoxy compound whereby a composition of mono-ethanol amine (MEA), di-ethanol amine (DEA) and tri-ethanol amine (TEA) are formed. The two latter, DEA and TEA are especially known to promote the setting acceleration of cement. The first reaction product , MEA, which does not exhibit any significant set- accelerating effect, is on the other hand known to be an effective corrosion inhibitor for steel, this property being generally associated with alkanol amines.

The main objective with the invention is to obtain a combined setting and hardening accelerator composition that enhances the hardening development further compared to known hardening accelerators.

The invention

This objective is obtained with a composition according to the characterising part of claim 1 and a method for the manufacture of the same is disclosed by the characterising part of claim 4. Further beneficial features are disclosed by the dependent claims.

A first aspect of the invention concerns a combined set- and hardening accelerator composition to be used for the hardening of cement, which accelerator composition comprises a set accelerator chosen from the group consisting of calcium nitrate, technical calcium nitrate, calcium nitrite, calcium formiate, calcium acetate and a hardening accelerator comprising an amine.

It has surprisingly been discovered that when the amine component comprises an amine compound chosen from the group consisting of mono-, di- and tri (3-chloro-propane-2- ol)-amine used in combination with a calcium compound, a hardening acceleration that surpasses the effect from the known alkanol amines is achieved. It should be noted that it was also discovered that the amine compound di-(3-chloro-propane-2-ol)-amine and also di-ethanol amine did not give any hardening acceleration when used alone in a cement composition, but actually retarded the hardening process in a standard cement. While di-(3-chloro-propane-2-ol)-amine is the preferred amine, a technical effect is also obtained with the mono- and tri-amines. It should further be noted that the chlorine group in the amines can be substituted by alkaline hydrolysis to form mono-, di- and tri- (propane-2,3-diol)-amine. It is actually possible that it is this hydroxy-substituted variant that constitutes the active compound in the combination with cement, but the invention is not limited to such a definite explanation.

The technical effect can be verified by time/temperature data for the hardening process as well as measurements of the compressive strength for the concrete as a function of time and accelerator composition. This is accounted for in more detail by the examples.

A second aspect of the invention concerns a method for the manufacture of a combined set- and hardening accelerator composition comprising a calcium salt and an amine compound to be used for the hardening of cement, by providing a reaction mixture comprising

(i) an aqueous solution of calcium ions, anions such as nitrate, nitrite, formiate and acetate, and an ammonium source chosen from the group consisting of ammonium ions and ammonia, and (ii) an epoxy compound, whereby the reaction mixture is maintained at a pH and at a temperature sufficient to convert at least partially the epoxy compound and ammonia to amine containing reaction products.

According to the invention epichlorohydrin is used as the epoxy compound for the formation of one or more reaction products chosen from the group consisting of mono-, di- and tri-(3-chloro-propane-2-ol)-amine plus the corresponding amines where the chlorine group is substituted by hydroxy by subsequent alkaline hydrolysis or by addition to the cement in a mixture with calcium ions and anions. In addition to the hardening effect that results from the use of this mixture comprising calcium and the above mentioned amine compounds, this method also renders it possible to use technical calcium nitrate without ammonia being liberated from the accelerator. Examples of calcium salts include calcium nitrate, technical calcium nitrate, calcium nitrite, calcium formiat and calcium acetate.

Examples of sources of ammonia include ammonia, ammonium nitrate and technical calcium nitrate. The last example can serve both as a calcium salt and an ammonium source.

More precisely the accelerator composition is manufactured by generally mixing (ammonium containing) technical calcium nitrate, increasing pH (e.g. by adding calcium hydroxide) to liberate ammonium to NH₃ (aq) and thenadding epichlorohydrin, in this way forming an aqueous solution of calcium ions, nitrate ions and di-(3-chloro-propane- 2-ol)-amine.

According to another embodiment of the present invention the accelerator composition is manufactured by the mixing of ammonium nitrate with calcium hydroxide or calcium oxide and epichlorohydrin, in this way forming an aqueous solution of calcium ions, nitrate ions and di-(3-chloro-propane-2-ol)-amine.

Another advantage of the use of epichlorohydrin in the present method is that the compound is a liquid at room temperature, as opposed to e.g. ethylene oxide as described in NO-A-952096, which will make it substantially easier to manufacture and handle the accelerator composition. It should also be noted that epichlorohydrin is much cheaper than ethylene oxide.

The reaction occurs easily at atmospheric pressure and room temperature.

The obtained reaction composition can be used as it is, but due to transportation etc. it is preferred to remove the liquid component, e.g. by evaporation to provide a hardening accelerator composition in the form of a solid material. The solid hardening accelerator composition may be given further steps of treatment like granulating, pelletisation or the like if that is desired. The invention is further described by the following examples and with reference to the enclosed drawing, where the symbols "a" and "g" corresponds to α and γ in the examples below.

Example 1 : Ordinary cement (reference)

A cement paste of ordinary Portland cement was manufactured with a water/ cement number of 0.4. This paste is denoted paste A in the following.

Hardening development The hardening of A and the other cement pastes referred to in the examples below was conducted by pouring ca. 200 g freshly mixed cement paste in a styrofoam cup with a lid and measuring the temperature as a function of time during hardening. The temperature development for ordinary cement in comparison with the accelerated cement paste is described by figure 1.

Example 2: Cement with addition of standard accelerator (reference)

A standard accelerator admixture denoted was manufactured from pure calcium nitrate and water, the amount of calcium nitrate being 2 % by weight with reference to the total cement of the resulting paste.

The accelerator composition α was combined with an ordinary cement paste A in which the water was substituted by the α composition. The resulting cement paste is denoted Aα. The hardening development for the resulting paste A is described by the enclosed figure 1 in comparison with other accelerated cement pastes and ordinary cement paste.

Example 3: Cement with addition of standard accelerator and DEA (reference) An accelerator composition was manufactured according to example 2 above, but with the further addition of diethanol amine (DEA) in a concentration of 2 % by weight of DEA with respect to the total amount of cement in the resulting paste. This accelerator composition is denoted αβ.

The accelerator composition αβ was combined with an ordinary cement paste A in which the water was substituted by the αβ composition. The resulting composition is denoted Aαβ. The hardening development (time of setting, t_s, hardening rate ΔT/Δt, and maximum temperature T_max) for this cement paste is described by table 1 below in comparison with the cement paste A and Aα from example 1 and 2 above (ordinary cement and ordinary cement with standard accelerator).

Example 4: Cement with addition of accelerator according to the invention This example illustrates the technical effect of an accelerator according to the invention in comparison with the closest known accelerator described in example 3 above. The other purpose of this example is finding the preferred relative amounts of components in the accelerator composition according to the invention, as well as finding a preferred amount of the composition in a cement paste.

An aqueous solution of di-(3-chloro-propane-2-ol)-amine was manufactured. In more detail 24 ml of 25% ammonia (aq) was diluted with 242 ml water and 50 ml epichlorohydrin was added. The resulting composition was stirred (moderately) for about 24 hours, thus producing a 20% solution of di-(3-chloro-propane-2-ol)-amine in water. This amine solution was used as a basis for the manufacture of an accelerating composition αγ according to the invention and according to example 5 below.

This amine solution was mixed with a standard accelerator solution α according to example 2 in varying concentrations and in varying relative amounts of calcium and amine. The basic solution is denoted αγ Concentration and relative amounts of components for the other variants are disclosed by table 2 and figure 1.

The accelerator composition αγ according to the invention was added to ordinary cement paste A to provide an accelerated cement paste A αγ . The effect on the hardening process as a function of concentration and relative amounts between calcium and di-(3-chloro-propane-2-ol)-amine is disclosed by table 2 and figure 1 below.

Example 5: Cement and amine only (reference)

A cement paste Aβ was manufactured by adding pure diethanol amine (DEA) to a cement paste A (without calcium nitrate or other accelerators) to a DEA concentration of 2 % by weight with respect to the total cement amount present in the paste. A cement paste Aγ was also manufactured by adding pure di-(3-chloro-propane-2-ol)-amine to cement paste A (without calcium nitrate or other accelerators) to a di-(3-chloro-propane- 2-ol)-amine concentration of 2% by weight.

The hardening development for cement paste Aβ and Aγ was compared with the hardening development for a standard cement paste A, cf. table 1 below. The result of this comparison shows that the amine compounds actually retard the hardening development in a standard cement when used alone at the tested concentrations.

Example 6: Compressive strength for the concrete

Measurements of compressive strength were conducted for a standard mortar consisting of a standard cement and sand in the relation 1 :3 and a water/ cement number of 0.5 (mortar A (reference mortar) manufactured according to the EN 196-1 standard. A variant A_^α was also manufactured from the mortar A,,, with the addition of 2% by weight of pure calcium nitrate (with respect to the total amount of cement in the mortar) as well as two variants A^γ with the further addition of 0.5 and 1.0 % by weight of the accelerator composition γ according to the invention (see table 1 and 2).

Measurements of compressive strength were conducted on end parts of 40x40x 160 mm prisms at 7 hours, 17 hours and 28 days after the manufacture. The results of these measurements are disclosed in table 3 below. The masses of the prisms are also stated.

Table 1 Parameters describing the hardening development of the cement paste A (w/c=0,4) with different accelerators: α, β and γ.

t. ΔT/Δt T max

Example Code Amount (hours.min ( °C/hour) ( °C)

1 A 0 / 0 % 4:05 1.35 28.0

2 Aα 2 / 0 % 3:00 1.13 28.0

3 Aαβ 2 / 2 % 3:10 1.35 28.6

4 Aαγ 2 / 2 % 2:10 2.27 29.1

5 Aβ 0 / 2 % 6:30 1.94 27.5

5 Aγ 0 / 2 % 5:00 1.84 28.4 t_s = setting time (when the temperature increases for the second time in figure 1) ΔT/Δt = hardening rate (the slope of the second temperature rise)

_Tax = maximum temperature (the peak of the second temperature rise)

Table 2 Parameters describing the hardening development for cement paste A (w/c=0,40), with different amounts of di-(3-chloro-propane-2-ol)-amine (γ) in combination with pure calcium nitrate (α).

t *s Δ ^ι-*TΛ./ιΔ*Λtt. T max Example Code Amount (hours:min) ( °C/hour) (°C)

1 A 0 / 0 % 4:05 1.35 28.0

2 Aα 2 / 0 % 3:00 1.13 28.0

4 Aαγ 2 / 0.4 % 2:00 1.55 29.0

4 Aαγ 2 / 0.8 % 2:05 1.61 28.3

4 Aαγ 2 / 1.6 % 2:00 2.07 29.2

4 Aαγ 2 / 2.0 % 2:10 2.27 29.1 Table 3

Mass (m) and compressive strength (σ_c) for standard mortar (A_m) (1:3, w/c=0,50), prisms (40x40x160 mm) with different accelerators: α and γ.

Mixture Mass m 7 hours σ_c 17 hours σ_c 28 days σ_c (g) (MPa) (MPa) (MPa)

A™ 0 / 0 % 588 ± 1 1.52 ± 0.04 12.8 ± 0.3 54.6 ± 0.8

A_mα 2 / 0 % 588 ± 0 2.33 ± 0.02 12.1 ± 0.1 57.6 ± 0.9

A_mαγ 2 / 0.5 % 580 ± 2 4.72 ± 0.07 15.6 ± 0.2 52.4 ± 1.2

A_rnαγ 2 / 1.0 % 577 ± 1 5.25 ± 0.06 15.0 ± 0.2 49.6 ± 1.0

From the prism masses it is evident that the γ introduces some air. This side effect can be removed by using a defoaming agent thereby increasing the early compressive strength further as well as achieving a better strength at 28 days.

As disclosed in table 3 above a mortar with an accelerator according to the invention will exhibit a compressive strength that is at least 125% higher than a standard accelerated mortar after 7 hours.

The invention provides a combined set- and hardening accelerator composition for use in cement as well as a method of the manufacture of the same. This composition provides a significant improvement in relation to previously known techniques.

Claims

1. Combined set- and hardening accelerator composition for use in cement, wherein the accelerator composition comprises a set accelerator chosen from the group consisting of calcium nitrate, technical calcium nitrate, calcium nitrite, calcium formiate and calcium acetate and a hardening accelerator comprising an amine, characterised in that the amine is a compound chosen from the group consisting of mono-, di- tri-(3-chloro-propane-2-ol)-amine, mono-, di- and tri-(propane-2,3-diol)- amine or mixtures thereof.

2. Composition according to claim 1, characterised in that the accelerator composition has the form of a powder.

3. Composition according to claim 1 or 2, characterised in that the amine is di-(3-chloro-propane-2-ol)-amine and/ or di-(propane- 2,3-diol)-amine.

4. Method for the manufacture of a combined set- and hardening accelerator composition comprising calcium, anions and an amine compound for use in cement, by providing a reaction mixture comprising (i) an aqueous solution of calcium ions, anions and an ammonium source chosen from the group consisting of ammonium ions and ammonia, and (ii) an epoxy compound, wherein the reaction admixture is maintained at a pH and at a pressure and a temperature sufficient to convert at least partially the epoxy compound and the ammonia to amine containing reaction products, characterised in that the epoxy compound is epichlorohydrin, thus obtaining a reaction product chosen from the group consisting of mono-, di-, tri-(3-chloro-propane-2-ol)- amine, mono-, di- and tri-(propane-2,3-diol)-amine or mixtures thereof, in combination with calcium ions and various anions.

5. Use of a combined set- and hardening accelerator composition in the form of an aqueous solution comprising a set accelerator chosen from the group consisting of calcium nitrate, technical calcium nitrate, calcium nitrite, calcium formiate and calcium acetate and a hardening accelerator comprising di-(3-chloro-propane-2-ol)-amine in cement.