WO2014012844A1 - Setting and hardening accelerators in powder form for sprayed concrete - Google Patents

Setting and hardening accelerators in powder form for sprayed concrete Download PDF

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Publication number
WO2014012844A1
WO2014012844A1 PCT/EP2013/064701 EP2013064701W WO2014012844A1 WO 2014012844 A1 WO2014012844 A1 WO 2014012844A1 EP 2013064701 W EP2013064701 W EP 2013064701W WO 2014012844 A1 WO2014012844 A1 WO 2014012844A1
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Prior art keywords
accelerator
formula
anyone
aluminium sulphate
accelerator according
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PCT/EP2013/064701
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French (fr)
Inventor
Cristiano Maltese
Massimo Stefanoni
Carlo Pistolesi
Original Assignee
Mapei S.P.A.
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Application filed by Mapei S.P.A. filed Critical Mapei S.P.A.
Priority to EP13744457.6A priority Critical patent/EP2874971A1/en
Priority to JP2015522044A priority patent/JP2015522516A/en
Publication of WO2014012844A1 publication Critical patent/WO2014012844A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/04—Portland cements
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
    • C04B40/0028—Aspects relating to the mixing step of the mortar preparation
    • C04B40/0039—Premixtures of ingredients
    • C04B40/0042—Powdery mixtures
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
    • C04B2103/10—Accelerators; Activators
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00034—Physico-chemical characteristics of the mixtures
    • C04B2111/00146—Sprayable or pumpable mixtures
    • C04B2111/00155—Sprayable, i.e. concrete-like, materials able to be shaped by spraying instead of by casting, e.g. gunite

Definitions

  • the present invention relates to powder accelerators for sprayed concrete or mortars which promote very high mechanical strengths, in particular at the beginning of curing time. Furthermore, they are able to reduce the setting time of the cementitious system, also when used at low dosage.
  • the cement mixture is directly sprayed on the rocky surface, by means of high pressure nozzles, without the necessity of moulds.
  • the cement materials should meet the following requirements: 1) to adhere permanently on the rock walls; 2) to have a low rebound (a phenomenon arising mainly by the high spraying pressure) which causes a large concrete loss; 3) to harden very quickly; 4) to develop high early strengths.
  • Concrete can be sprayed through dry or wet mix method.
  • the former technique requires that cement, sand and powder accelerator should be conveyed by compressed air through a hose; the water needed for hydration is introduced at the spraying nozzle.
  • cement, sand and powder accelerator should be conveyed by compressed air through a hose; the water needed for hydration is introduced at the spraying nozzle.
  • cement, sand and powder accelerator should be conveyed by compressed air through a hose; the water needed for hydration is introduced at the spraying nozzle.
  • For the wet mix process concrete is previously prepared and pumped into a nozzle, where liquid accelerator is added and pneumatically projected onto the substrate.
  • Liquid or powder based accelerating admixtures are usually utilised in order to guarantee an excellent adhesion of the sprayed material to the rock wall and a rapid compressive strength development.
  • the first condition can be evaluated by measuring the capability of the accelerator to reduce the setting time of a cement paste.
  • the second requirement is determined by measuring the mechanical strength development during the first hours of hydration of a cementitious mortar or concrete.
  • alkaline accelerators such as: soda, potash, silicate or alkali metal aluminates. Nevertheless, such accelerators are known to negatively affect the long term mechanical strengths. Moreover, due to their alkaline nature, they are irritating to the skin and particular protective devices are requested for the workers' s safety. Furthermore, alkali metal substances reacting with aggregates, could favour alkali silica reaction (AS ) which impairing the concrete properties. Finally, they release alkaline substances that, by increasing the pH of ground waters, could be dangerous polluting agents. These problems favoured the development "low in alkali” or "alkali-free" accelerators.
  • AS alkali silica reaction
  • New "alkali-free" admixtures consisting of fluoro aluminates and aluminium sulfate are also known in the art (EP 1 167317 Bl). These accelerators can be in the form of powder or water solutions which cause a quick concrete setting, thereby allowing good adhesion to the rock walls. Nevertheless, they inhibit, in particular during the first hours of hydration, an effective mechanical strength development of the sprayed cementitious material.
  • WO 2005040059 describes liquid or powder based accelerators containing fluoro-carboxylates of aluminum, sodium aluminate and manganese sulphate allowing an effective setting time reduction and a proper mechanical strength development of the sprayed material.
  • FR 2031950 discloses the use of aluminium sulphate as setting or hardening accelerator. Nevertheless, it has to be used at high dosages.
  • WO 201 1026825 discloses a process for the preparation of a sprayable hydraulic binder composition containing water, aggregates, hydraulic binder, set accelerator, characterised in that calcium silicate hydrated is added before and/or at the spray nozzle.
  • the main disadvantages of this approach are the following: 1) It is necessary the use of two different admixtures (a hardening accelerator containing calcium silicate hydrated and a flash setting accelerator); high dosages of both admixtures are necessary to get proper mechanical strength developments.
  • the invention concerns accelerating admixtures for hydraulic binders capable to develop high mechanical strength while maintaining an efficient setting time reduction.
  • accelerators for concrete and mortar containing aluminium sulphate have better performances compared to the commercial ones. Accelerator performances are further improved by adding calcium hydrosilicate, amines and/or alkanolamines, in particular diethanolamine, and/or aluminium hydroxide and/or carboxylic acids and/or soluble fluorides.
  • Accelerator performances are further improved by adding calcium hydrosilicate, amines and/or alkanolamines and/or aluminium hydroxide and/or carboxylic acids and/or water soluble fluorides.
  • Aluminium sulphate used according to the invention is a commercial product characterised by an Al 2 O 3 content between 14 and 17%, containing at least 15% by mass of aluminium sulphate (expressed as Al 2 (SO 4 ) 3 ) characterised in that at least 50% of the total mass of aluminium sulphate has particle size lower than 1 mm.
  • the accelerator according to the invention contains at least 15% by mass of aluminium sulphate (expressed as Al 2 (SO 4 ) 3 ) which is characterized by an Al 2 O 3 content between 14 and 17%, and at least 50% of its mass has a particle size lower than 1 mm.
  • Calcium hydrosilicate could arise from precipitation process of soluble salts of calcium in combination with soluble salts of silicate.
  • Another source of calcium hydrosilicate are minerals selected from Wollastonite (wollastonite; xonotlite; nekoite); Tobermorite (clinotobermorite); Jennite (metajennite); Gyrolite.
  • the concentration of calcium hydrosilicate may range from 1 to 85% by mass of the admixture.
  • the accelerator of the invention is a powder and can be easily prepared mixing the components at ambient temperature in order to get a homogeneous mixture.
  • Example 1 All the components of the examples are expressed as per cent by weight.
  • the mortars were prepared according to EN 934/5.
  • the accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds.
  • the mechanical strength was measured by a digital force gauge (O faux Fischer Betonà, Sprayed Concrete Guideline, Wien, March 1999) and it was expressed in N.
  • the mechanical strength was measured according to the EN 196/1 and the values were expressed in MPa. The results are shown in Table 4. Table 4. Mechanical strength development
  • the mortars were prepared according to EN 934/5.
  • the accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds.
  • the mechanical strength was measured by a digital force gauge (O faux Fischer Betonà, Sprayed Concrete Guideline, Wien, March 1999) and it was expressed in N.
  • the mechanical strength was measured according to the EN 196/1 and the values were expressed in MPa. The results are shown in Table 8.
  • the mortars were prepared according to EN 934/5.
  • the accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds.
  • Table 9 are compared the values of setting times of mortars containing a common aluminium sulphate with a concentration of particles lower than 1 mm of 46% respect to Formula 5 according to the invention. Table 9.
  • the mortars were prepared according to EN 934/5.
  • the accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds.
  • Table 10 are compared the values of setting times of mortars containing an accelerator containing sodium aluminate respect to Formula 3 according to the invention. Table 10. Compositions and setting times
  • the mortars were prepared according to EN 934/5.
  • the accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds.
  • Table 1 1 are compared the values of setting times of mortars containing Aluminium Sulphate 0-2 mm respect to Formula 4 according to the invention.
  • Table 11. Compositions and setting times
  • Table 1 1 clearly indicate that the mortar containing the accelerator according to the invention (Formula 4) is characterised by a lower setting time compared to the one added with common aluminium sulphate (Formula 1).
  • the mortars were prepared according to EN 934/5.
  • the accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds.
  • the mechanical strength was measured by a digital force gauge (O faux Fischer Betonà, Sprayed Concrete Guideline, Wien, March 1999) and it was expressed in N.
  • the mechanical strength was measured according to the EN 196/1 and the values were expressed in MPa. The results are shown in Table 12.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Curing Cements, Concrete, And Artificial Stone (AREA)

Abstract

The present invention relates to powder accelerators for sprayed concrete or mortars which promote very high mechanical strengths, in particular at the beginning of curing time

Description

SETTING AND HARDENING ACCELERATORS IN POWDER FORM FOR SPRAYED CONCRETE
The present invention relates to powder accelerators for sprayed concrete or mortars which promote very high mechanical strengths, in particular at the beginning of curing time. Furthermore, they are able to reduce the setting time of the cementitious system, also when used at low dosage.
BACKGROUND OF THE INVENTION
The excavation of tunnels requires large amount of cementitious materials (mortars and concrete) which are used to prepare temporary or definitive protective shells.
For these purposes, the cement mixture is directly sprayed on the rocky surface, by means of high pressure nozzles, without the necessity of moulds. In order to speed up the tunnelling work and for safety reasons, the cement materials should meet the following requirements: 1) to adhere permanently on the rock walls; 2) to have a low rebound (a phenomenon arising mainly by the high spraying pressure) which causes a large concrete loss; 3) to harden very quickly; 4) to develop high early strengths.
Only if the aforementioned conditions are satisfied, a structural consolidation of the tunnel can be obtained allowing fast excavation rates and safe working conditions.
Concrete can be sprayed through dry or wet mix method. The former technique requires that cement, sand and powder accelerator should be conveyed by compressed air through a hose; the water needed for hydration is introduced at the spraying nozzle. For the wet mix process, concrete is previously prepared and pumped into a nozzle, where liquid accelerator is added and pneumatically projected onto the substrate.
Liquid or powder based accelerating admixtures are usually utilised in order to guarantee an excellent adhesion of the sprayed material to the rock wall and a rapid compressive strength development. The first condition can be evaluated by measuring the capability of the accelerator to reduce the setting time of a cement paste. The second requirement is determined by measuring the mechanical strength development during the first hours of hydration of a cementitious mortar or concrete.
In the past, several alkaline accelerators were used, such as: soda, potash, silicate or alkali metal aluminates. Nevertheless, such accelerators are known to negatively affect the long term mechanical strengths. Moreover, due to their alkaline nature, they are irritating to the skin and particular protective devices are requested for the workers' s safety. Furthermore, alkali metal substances reacting with aggregates, could favour alkali silica reaction (AS ) which impairing the concrete properties. Finally, they release alkaline substances that, by increasing the pH of ground waters, could be dangerous polluting agents. These problems favoured the development "low in alkali" or "alkali-free" accelerators. According to European rules (Osterreichischer Betonverein, Sprayed Concrete Guideline, Wien, March 1999 and pr EN 934-5 "Admixtures for Sprayed Concrete- Definitions, Requirements, Conformity, Marking and Labelling"), an accelerating admixture is classified as "alkali-free" when the concentration of sodium and potassium, expressed as equivalents of Na2O, is lower than 1%. Lithium is also an alkali metal, however the scientific literature shows that it does not negatively affect the concrete and therefore it is not considered in the calculation of equivalents of Na2O.
New "alkali-free" admixtures consisting of fluoro aluminates and aluminium sulfate are also known in the art (EP 1 167317 Bl). These accelerators can be in the form of powder or water solutions which cause a quick concrete setting, thereby allowing good adhesion to the rock walls. Nevertheless, they inhibit, in particular during the first hours of hydration, an effective mechanical strength development of the sprayed cementitious material. WO 2005040059 describes liquid or powder based accelerators containing fluoro-carboxylates of aluminum, sodium aluminate and manganese sulphate allowing an effective setting time reduction and a proper mechanical strength development of the sprayed material.
FR 2031950 discloses the use of aluminium sulphate as setting or hardening accelerator. Nevertheless, it has to be used at high dosages.
DE 2122710 discloses calcined aluminium sulphate as setting accelerator. Nevertheless, calcination process requires an exposition to temperatures of 450- 490°C for 24 hours thus increasing the final cost of the material.
A powder or liquid accelerator based on amorphous aluminium hydroxy- sulphate is described in US 5660625. Nevertheless, the synthesis of such a substance is extremely complex and its performances are quite poor.
WO 201 1026825 discloses a process for the preparation of a sprayable hydraulic binder composition containing water, aggregates, hydraulic binder, set accelerator, characterised in that calcium silicate hydrated is added before and/or at the spray nozzle. The main disadvantages of this approach are the following: 1) It is necessary the use of two different admixtures (a hardening accelerator containing calcium silicate hydrated and a flash setting accelerator); high dosages of both admixtures are necessary to get proper mechanical strength developments.
The development of new accelerators characterised by low production costs, promoting high mechanical strength development and reduced setting times, possibly at low dosages, is required by the market.
DESCRIPTION OF THE INVENTION
The invention concerns accelerating admixtures for hydraulic binders capable to develop high mechanical strength while maintaining an efficient setting time reduction. In fact, it has been found that accelerators for concrete and mortar containing aluminium sulphate have better performances compared to the commercial ones. Accelerator performances are further improved by adding calcium hydrosilicate, amines and/or alkanolamines, in particular diethanolamine, and/or aluminium hydroxide and/or carboxylic acids and/or soluble fluorides.
Accelerator performances are further improved by adding calcium hydrosilicate, amines and/or alkanolamines and/or aluminium hydroxide and/or carboxylic acids and/or water soluble fluorides.
Aluminium sulphate used according to the invention is a commercial product characterised by an Al2O3 content between 14 and 17%, containing at least 15% by mass of aluminium sulphate (expressed as Al2(SO4)3) characterised in that at least 50% of the total mass of aluminium sulphate has particle size lower than 1 mm.
The accelerator according to the invention contains at least 15% by mass of aluminium sulphate (expressed as Al2(SO4)3) which is characterized by an Al2O3 content between 14 and 17%, and at least 50% of its mass has a particle size lower than 1 mm.
Calcium hydrosilicate could arise from precipitation process of soluble salts of calcium in combination with soluble salts of silicate. Another source of calcium hydrosilicate are minerals selected from Wollastonite (wollastonite; xonotlite; nekoite); Tobermorite (clinotobermorite); Jennite (metajennite); Gyrolite.
The concentration of calcium hydrosilicate may range from 1 to 85% by mass of the admixture.
The accelerator of the invention is a powder and can be easily prepared mixing the components at ambient temperature in order to get a homogeneous mixture.
The characteristics and the advantages related to the use of the accelerator of the invention are described in more details in the following examples.
All the components of the examples are expressed as per cent by weight. Example 1
In this example the setting times of cementitious mortars containing commercially available aluminium sulphate characterised by a particle size distribution between 0 and 2 mm (Formula 1 ; Tab. 1 and 3) and the same substance with a particle size distribution according to the invention (Formula 2; Tab. 2 and 3) were compared. The amount of particles with size lower than 1 mm for aluminium sulphate 0-2 mm can be easily calculated from Table 1 according to the following calculation: 26 % (Kept at 0.5 mm) + 19 % (Kept at 0.1 mm) + 1% (Bottom)= 46%.
From Table 2 it is possible to repeat the calculation for the finer aluminium sulphate (Formula 2): 0.1 % (Kept at 0.5 mm) + 79 % (Kept at 0.1 mm) + 20.9% (Bottom)= 100%
The setting times were measured on mortar samples with the following composition:
450 g Cement II/A-S 42.5 ;
1350 g standard sand;
225 g Water;
22,5 g Accelerator.
The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. In Table 3 the values of setting times of mortars containing a common aluminium sulphate with a concentration of particles lower than 1 mm of 46% are compared with an aluminium sulphate according to the invention with a concentration of particles lower than 1 mm of 100%. Table 1. Particle size distribution of common aluminium sulphate (Formula 1)
Figure imgf000007_0001
Table 2. Particle size distribution of aluminium sulphate according to the invention (Formula 2)
Figure imgf000007_0002
Components Formula 1 (%) Formula 2 (%)
Aluminium Sulphate 0-2 mm 100 /
Aluminium Sulphate 0-0,5 mm / 100
Accelerator Dosage (%) Setting time
Formula 1 5 14 min 0 sec
Formula 2 5 8 min and 30 sec The results in Tab. 3 clearly indicate that the mortar containing the accelerator according to the invention (Formula 2) is characterised by a lower setting time compared to the one added with common aluminium sulphate (Formula 1).
Example 2
In this example the mechanical strength of cementitious mortars containing commercially available aluminium sulphate characterised by a particle size distribution between 0 and 2 mm (Formula 1 ; Tab. 1) and the same substance with a particle size distribution according to the invention (Formula 2; Tab. 2) were compared.
The mechanical strength were measured on mortar samples with the following composition:
450 g Cement II/A-S 42.5 ;
1350 g Standard sand;
225 g Water;
22,5 g di Accelerator.
The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. At early curing ages the mechanical strength was measured by a digital force gauge (Osterreichischer Betonverein, Sprayed Concrete Guideline, Wien, March 1999) and it was expressed in N. At later curing ages, when the specimens (40x40x 160mm) become harder, the mechanical strength was measured according to the EN 196/1 and the values were expressed in MPa. The results are shown in Table 4. Table 4. Mechanical strength development
Figure imgf000009_0001
The results clearly indicate that the mortar added with the accelerator of the invention (Formula 2) has a compressive strength development significantly higher than ordinary commercial accelerator (Formula 1).
Example 3
In this example the setting times of cementitious mortars containing commercially available aluminium sulphate characterised by a particle size distribution between 0 and 2 mm (Formula 1 ; Tab. 5) and Formula 3 containing aluminium sulphate with a particle size distribution and concentration according to the invention (Formula 3; Tab. 5 and 6) were compared. From Table 6, it is possible to calculate the amount of particles of aluminium sulphate 0-0,1 mm lower than 1 mm contained in Formula 3 :
17 % (Kept at 0.1 mm) + 23 % (Kept at 0.04 mm) + 50 % (Kept at 0.01 mm) + 10 % (Bottom)= 100%
The setting times were measured on mortar samples with the following composition:
450 g Cement II/A-S 42.5 ;
1350 g Standard sand;
225 g Water;
22,5 g Accelerator. The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. In Table 5 the values of setting times of mortars containing a common aluminium sulphate with a concentration of particles lower than 1 mm of 46% are compared with Formula 3 of the invention containing an aluminium sulphate according to the invention with a concentration of particles lower than 1 mm of 100%.
Table 5. Composition and setting time
Figure imgf000010_0001
The results in Tab. 5 clearly indicate that the mortar containing the accelerator according to the invention (Formula 3) is characterised by a lower setting time compared to the one added with common aluminium sulphate (Formula 1).
Table 6. Particle size distribution of aluminium sulphate 0-0,1 according to the invention (Formula 3)
Particle size (mm) Kept (%)
1.0 0
0.1 17
0.04 23
0.01 50
<0.01 10 Example 4
In this example the mechanical strength of cementitious mortars containing commercially available aluminium sulphate characterised by a particle size distribution between 0 and 2 mm (Formula 1) and Formula 4 containing aluminium sulphate with a particle size distribution according to the invention (Tab. 7). The mechanical strengths were measured on mortar samples with the following composition:
450 g Cement II/A-S 42.5 ;
1350 g Standard sand;
225 g Water;
22,5 g Accelerator.
The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. At early curing ages the mechanical strength was measured by a digital force gauge (Osterreichischer Betonverein, Sprayed Concrete Guideline, Wien, March 1999) and it was expressed in N. At later curing ages, when the specimens (40x40x 160mm) become harder, the mechanical strength was measured according to the EN 196/1 and the values were expressed in MPa. The results are shown in Table 8.
Table 7. Composition
Components Formula 4 (%)
Aluminium Sulphate 0-0,1 mm 80
XONOTLITE 20 Table 8. Mechanical strength development
Figure imgf000012_0001
The results clearly indicate that the mortar added with the accelerator of the invention (Formula 4) shows a compressive strength development significantly higher than ordinary commercial accelerator (Formula 1).
Example 5
In this example the setting times of cementitious mortars containing commercially available aluminium sulphate characterised by a particle size distribution between 0 and 2 mm (Formula 1 ; Tab. 9) and Formula 5 containing aluminium sulphate with a particle size distribution according to the invention (Tab. 6) were compared. The setting times were measured on mortar samples with the following composition:
450 g Cement I 42.5 ;
1350 g Standard sand;
225 g Water;
22,5 g Accelerator.
The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. In Table 9 are compared the values of setting times of mortars containing a common aluminium sulphate with a concentration of particles lower than 1 mm of 46% respect to Formula 5 according to the invention. Table 9. Compositions and setting times
Figure imgf000013_0001
The results in Table 9 clearly indicate that the mortar containing the accelerator according to the invention (Formula 5) is characterised by a lower setting time compared to the one added with common aluminium sulphate (Formula 1).
Example 6
In this example the setting times of cementitious mortars containing a commercially available powder accelerator based on sodium aluminate (Formula 6, Tab. 10) and Formula 3 containing aluminium sulphate with a particle size distribution according to the invention (Tab. 10) were compared. The setting times were measured on mortar samples with the following composition:
450 g Cement I 42.5 ;
1350 g Standard sand;
225 g Water;
22,5 g Accelerator.
The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. In Table 10 are compared the values of setting times of mortars containing an accelerator containing sodium aluminate respect to Formula 3 according to the invention. Table 10. Compositions and setting times
Figure imgf000014_0001
The results in Table 10 clearly indicate that the mortar containing the accelerator according to the invention (Formula 3) is characterised by a lower setting time compared to the one added with common aluminium sulphate (Formula 6).
Example 7
In this example the setting times of cementitious mortars containing a commercially available aluminium sulphate characterised by a particle size distribution between 0 and 2 mm (Formula 1 ; Tab. 1 and 1 1) and Formula 4 containing aluminium sulphate with a particle size distribution according to the invention (Tab. 11) were compared. The setting times were measured on mortar samples with the following composition:
450 g Cement IV/A 42.5 ;
1350 g Standard sand;
225 g Water;
22,5 g Accelerator.
The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. In Table 1 1 are compared the values of setting times of mortars containing Aluminium Sulphate 0-2 mm respect to Formula 4 according to the invention. Table 11. Compositions and setting times
Figure imgf000015_0001
The results in Table 1 1 clearly indicate that the mortar containing the accelerator according to the invention (Formula 4) is characterised by a lower setting time compared to the one added with common aluminium sulphate (Formula 1).
Example 8
In this example the mechanical strength of cementitious mortars containing commercially available aluminium sulphate characterised by a particle size distribution between 0 and 2 mm (Formula 1) and Formula 4 containing aluminium sulphate with a particle size distribution according to the invention (Tab. 7). The mechanical strengths were measured on mortar samples with the following composition:
450 g Cement II/A-LL 32.5 ;
1350 g Standard sand;
225 g Water;
22.5 g Accelerator.
The mortars were prepared according to EN 934/5. The accelerating admixture was added at the end of the mixing cycle and further mixed for 10 seconds. At early curing ages the mechanical strength was measured by a digital force gauge (Osterreichischer Betonverein, Sprayed Concrete Guideline, Wien, March 1999) and it was expressed in N. At later curing ages, when the specimens (40x40x 160mm) become harder, the mechanical strength was measured according to the EN 196/1 and the values were expressed in MPa. The results are shown in Table 12.
Table 12. Mechanical strength development
Figure imgf000016_0001
The results clearly indicate that the mortar added with the accelerator of the invention (Formula 4) shows a compressive strength development significantly higher than ordinary commercial accelerator (Formula 1).

Claims

1. An accelerator in powder form for sprayed concrete containing at least 15% by mass of aluminium sulphate (expressed as Al2(SO4)3) whose particle size distribution lower than 1 mm is higher than 50% of the total amount of aluminium sulphate.
2. An accelerator according to claim 1 containing also at least one hydrocalcium silicate.
3. An accelerator according to anyone of claims 1 and 2 wherein hydrocalcium silicate belongs to the group of Wollastonite Tobermorite, Jennite and/or Gyrolite.
4. An accelerator according to anyone of claims 1 to 3 containing Xonotlite.
5. An accelerator according to anyone of claims 1 to 3 containing Wollastonite.
6. An accelerator according to anyone of claims 1 to 5 containing hydrocalcium silicate arising from a precipitation process from soluble salts of calcium and silicate.
7. An accelerator according to anyone of claims 1 to 6 containing hydrocalcium silicate arising from a precipitation process from soluble salts of calcium and nitrate.
8. An accelerator according to anyone of claims 1 to 7 containing from 1 to 85% by mass of hydrocalcium silicate.
9. An accelerator according to anyone of claims 1 to 8 containing aluminium hydroxide.
10. An accelerator according to anyone of claims 1 to 9 containing soluble fluorides.
1 1. An accelerator according to anyone of claims 1 to 9 containing amines.
PCT/EP2013/064701 2012-07-18 2013-07-11 Setting and hardening accelerators in powder form for sprayed concrete WO2014012844A1 (en)

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EP13744457.6A EP2874971A1 (en) 2012-07-18 2013-07-11 Setting and hardening accelerators in powder form for sprayed concrete
JP2015522044A JP2015522516A (en) 2012-07-18 2013-07-11 Powder-shaped setting hardening accelerator for shotcrete

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IT001255A ITMI20121255A1 (en) 2012-07-18 2012-07-18 ADDITIONAL ADDITIVES OF GRIPPING AND HARDENING
ITMI2012A001255 2012-07-18

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WO2021024853A1 (en) * 2019-08-02 2021-02-11 デンカ株式会社 Cement admixture and hydraulic composition
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