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
• • 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
  • C04B2111/00112—Mixtures characterised by specific pH values
• • 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

Definitions

• the present invention concerns the preparation and use of calcium carbonate based accelerators which promote very high performances of the sprayed concrete layer and characterised by a very high storage stability.
• 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.
• 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 of "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 B l).
• 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.
• US 6302954 and EP 1 1 14004 disclose alkali-free accelerators based on aluminium carboxylate and aluminium sulphate. These accelerators, although they allow high mechanical strength development compared to the ones described in EP 1 167317, they are not enough during the initial phase of cement hardening. Such retarded setting negatively affect the initial structural stability of the sprayed concrete.
• 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.
• EP2080741A1 describes a complex spraying method which comprises mixing water and a powder quick setting admixture comprising an alkaline earth metal carbonate, water soluble acidic substance, calcium aluminate and an alkali metal sulphate to form a slurry quick setting admixture; mixing this slurry with concrete which is immediately projected on the substrate.
• Concrete material can solidify in the pump when it comes in contact with the slurry
• High raw material cost of the powder quick setting admixture being composed of at least 4 different components.
• the object of the present invention is to provide a liquid accelerating admixtures for concrete or mortars containing calcium carbonate capable to develop high mechanical strength while maintaining an efficient setting time reduction, also at low dosages.
• liquid accelerators with a pH higher than 6.5 which allow to obtain sprayed concrete characterised by very high performances.
• the admixture of the invention is a water suspension consisting of:
• Alkali earth metal carbonate is preferably calcium carbonate.
• Compound (b) is preferably aluminium hydroxide.
• Compound (b) can also be a mixture of aluminium hydroxide and sodium aluminate.
• compound (b) is sodium silicate.
• Alkali earth metal carbonate dosage is typically between 10 and 80% by mass and compound (b) content is between 0.25 and 50% by mass.
• amines preferably diethanolamine, diols or polyols, preferably glycerine, and/ or hydrated calcium silicates.
• Calcium hydrosilicate could arise from precipitation process of soluble salts of calcium in combination with soluble salts of silicate.
• Another source of calcium hydrosilicate could be minerals chosen among: Wollastonite (wollastonite; xonotlite; nekoite); Tobermorite (clinotobermorite); Jennite (metajennite); Gyrolite, Xonotlite and Wollastonite are preferred hydrated calcium silicates.
• the admixture of the present invention can be easily prepared by mixing the components at room temperature in order to get a homogeneous suspension with a pH higher than 6.5.
• inorganic or organic viscosity increasing agents such as bentonites and bentones, sepiolite, clays, pyrogenic silica, cellulose, biopolymers, amides can be used.
• the performance of the admixture are further improved if the size of 50% of its particles is lower than 100 ⁇ , preferably lower than 20 ⁇ .
• the admixture of the invention is added at the nozzle where it is mixed with concrete and the resulting mixture is sprayed on the substrate, it could also be used according to the following procedure:
• the admixture according to the invention can be dosed between 3 and 40% by cement mass. It favours compressive strength development of sprayed concrete or can allow cement and alkali-free accelerator dosage reduction.
• aluminium fluoride was prepared (called “Intermediate Fluoride”): 300 g of water and 1 10 g of aluminium hydroxide were added to 2 1 volumetric flask at room temperature; the resulting suspension was mixed for 5 minutes; then, 214 g di hydrofluoric acid (40% water solution) were added leaving the suspension under constant agitation for at least 20 minutes in a termostatic bath at 85°C; The temperature of the solution increases to a maximum of about 95°C; 376 g of water were therefore added, and the resulting transparent solution was collected.
• Intermediate Fluoride 300 g of water and 1 10 g of aluminium hydroxide were added to 2 1 volumetric flask at room temperature; the resulting suspension was mixed for 5 minutes; then, 214 g di hydrofluoric acid (40% water solution) were added leaving the suspension under constant agitation for at least 20 minutes in a termostatic bath at 85°C; The temperature of the solution increases to a maximum of about 95°C; 376 g of water were therefore added, and
• the admixture according to the invention was prepared as follows: 233 g of water and 167 g of calcium carbonate were added to a 2 1 beaker; the resulting mixture was stirred for 10 minutes at room temperature with a vertical stirrer (500 rpm); then 300 g of aluminium hydroxide and 300 of "Intermediate Fluoride" were added and mixed for 30 minutes; the resulting white suspension was collected. The tests were carried out on mortar samples with composition reported in Table 7.
• 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 ( Machine type Controls model 50).
• a commercial alkali-free aluminium sulphate based flash setting accelerator Mapequick AFK 777 T, produced by Mapei SPA was added (10% by cement mass).
• the second cement paste sample was prepared by adding as accelerator Formula 3 according to the present invention (Tab. 9) and with a particle size distribution reported in Table 10. Setting time of these cement pastes was determined by a manual Vicat method (EN 196/3).
• the admixture according to the invention was prepared as follows: 325 g of water and 235 g of calcium carbonate were added to a 2 1 beaker; the resulting mixture was stirred for 10 minutes at room temperature with a vertical stirrer (500 rpm); then 100 g of aluminium hydroxide, 40 g of sodium aluminate in water solution (18% Al 2 O 3 ) and 300 g of "Intermediate Fluoride" were added and mixed for 30 minutes; the resulting white suspension was collected.
• the admixture according to the invention was obtained as follows: 293 g of water and 167 g of calcium carbonate were added to a 2 1 beaker; the resulting mixture was stirred for 10 minutes at room temperature with a vertical stirrer (500 rpm); then 200 g of aluminium hydroxide and 300 g of "Intermediate Fluoride" and 40 g of sodium aluminate water solution (18% Al 2 O 3 ) were added and mixed for 30 minutes; the resulting white suspension was collected.
• 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 (Machine type Controls model 50).
• Mapequick AF 1000 commercial alkali-free aluminium sulphate based flash setting accelerator, produced by Mapei SPA.
• composition of cement paste samples is reported in Tab. 18. Setting time of these cement pastes was determined by a manual Vicat method (EN 196/3).
• the admixture according to the invention was prepared as follows: 320 g of water and 670 g of calcium carbonate were added to a 2 1 beaker; the resulting mixture was stirred for 10 minutes at room temperature with a vertical stirrer (500 rpm); then 10 g of aluminium hydroxide and mixed for 30 minutes; the resulting white suspension was collected.
• Mapequick AF 1000 (commercial alkali-free aluminium sulphate based flash setting accelerator, produced by Mapei SPA)
• the admixture according to the invention was prepared as follows: 350 g of water and 610 g of calcium carbonate were added to a 2 1 beaker; the resulting mixture was stirred for 10 minutes at room temperature with a vertical stirrer (500 rpm); then 10 g of aluminium hydroxide and 30 of glycerine were added and mixed for 30 minutes; the resulting white suspension was collected.
• the admixture according to the invention was prepared as follows: 265 g of water and 235 g of calcium carbonate were added to a 2 1 beaker; the resulting mixture was stirred for 10 minutes at room temperature with a vertical stirrer (500 rpm); then 150 g of aluminium hydroxide, 40 g of sodium aluminate in water solution (18% Al 2 O 3 ), 300 g of "Intermediate Fluoride" and 10 g of diethanolamine were added and mixed for 30 minutes; the resulting white suspension was collected.

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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)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Medicinal Preparation (AREA)

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Citations (7)

• 2012
  • 2012-09-14 IT IT001528A patent/ITMI20121528A1/it unknown
• 2013
  • 2013-09-05 WO PCT/EP2013/068380 patent/WO2014040908A1/fr not_active Ceased

Patent Citations (8)

Non-Patent Citations (2)

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