RU2132314C1 - Method of manufacturing cellular concrete, raw mixture for manufacturing cellular concrete, and method of manufacturing structures - Google Patents

Abstract

FIELD: manufacture of building materials. SUBSTANCE: invention, in particular, relates to open-air hardening cellular concretes and manufacturing in-place structures. Method is distinguished by introducing integrated technics in continuous manufacture of cellular body containing required components and in manufacture of cellular concrete structures ensuring formation of homogeneous material with high heat-protection properties, strength characteristics, and minimum shrinkage stress. To that end, composition additionally contains anti-shrinkage and stiffening components. Cellular body is prepared by separately adding foam, cement, and inert silica filler, while continuously controlling dispensing, agitating, and laying cellular body into monolithic structures. EFFECT: accelerated construction of heat-insulated residential buildings. 3 cl, 2 tbl

Description

 The invention relates to methods for the manufacture of building materials, namely foam concrete, monolithic structures of buildings and structures.

 Known methods for the preparation of foam concrete, including the preparation of foam when dry components are introduced into the foam and mixing, with 55 - 75% of the dry components being preliminarily introduced into the foam, are mixed at a speed of 300 - 400 rpm (1).

 However, the foam concrete prepared in this way has a high average density due to a decrease in the multiplicity with stirring and low intensity of the introduction of dry components.

 Known for the closest combination of features is a method of preparing foam concrete, including preliminary introduction of 55-75% of dry components into the foam and mixing at a speed of 450-600 rpm and exposure of the foam mass with compressed air supplied under a pressure of 1.15 -1.25 atm at the intensity of the introduction of dry components 4-8 kg / min per 1 liter of water in the foam, additional mixing at a speed of 30-40 rpm and stirring when adding the remaining amount of dry components to the foam mass at a speed of 300-400 rpm and the impact on the foam mass compressed in zduhom supplied under pressure of 1.3 - 1.4 bar at an intensity introducing dry components 9-14 kg / min to 1 l of water in the foam (2).

 However, the simultaneous introduction of dry components into the foam creates an unstable structure of the mixture, in which a larger fraction of a siliceous filler destroys the walls of the pore structure of the foam and promotes delamination (sedimentation) of the mixture, i.e. settling of a heavier filler at the bottom of the mixer.

 The complete elimination of this drawback is impossible even by sparging with air, i.e., due to the instability of the structure, the introduced air phase is also quickly removed. In part, this drawback is exacerbated by high mixer speeds. Another reason for separation is the insufficient viscosity of the foam.

 Another serious drawback of the known method is the cyclical dosage of the components for a certain volume of the kneading mixture, when the simultaneous supply of components is stopped after a certain time interval, and the prepared mixture is delivered to the place of laying. This creates the need for frequent repetition of the mixing process, which is inevitable with this technology, causes the accumulation of error due to the frequent bringing the installation to a stable operation mode.

 As a result, significant deviations of up to 25-30% in volumetric mass of foam concrete are observed, which unacceptably worsens the quality of the material being prepared.

 Also known is a mixture for the preparation of foam concrete, including cement, sand, water and an additive - foaming agent (3).

 However, the foam concrete obtained from such a mixture has a high density, delaminates, which leads to an inhomogeneous structure and, accordingly, to a decrease in strength, an unjustified increase in shrink stresses in the initial period of hardening.

 Also known is a mixture for the preparation of foam concrete, including cement 45-46%, ground quartz sand 45-46%, foaming agent - Konifol adhesive 0.2%, foam stabilizer SDB (sulfite-yeast mash) 0.002 - 0.006% and the rest water (4) .

 However, the foam concrete obtained from such a mixture is characterized by a large-pore heterogeneous structure, low strength, late formation and strength development, high density and thermal conductivity, high shrinkage and creep under load, low frost resistance.

 There is also a method of erecting structures from cellular cementless autoclave concrete, including the preparation of a raw mix, the preparation of molds or formwork, the supply of a mixture in them, laying and curing, at least, to a set of stripping strength (5).

 However, such a method, including the manufacture of structures of porous concrete, randomly laid in formwork and form, causes shrinkage stresses in the finished products and, consequently, crack formation. Porization through gas formation during the preparation of the mixture creates the conditions for an uncontrolled reaction and the production of material with unpredictable properties. Such material is not transportable, which narrows the scope of its application.

 The objective of the proposed invention is to create a highly efficient continuous process for the preparation of foam concrete, with new anti-shrink additives, pumping it to the place of manufacture of monolithic structures, laying in molds or formwork and obtaining durable monolithic structures of foam concrete without shrinkage deformation, with uniform properties across all sections of the structure .

 The technical result is to improve the quality of the material by increasing the heat transfer resistance while maintaining strength characteristics, reducing shrink stresses in structures made of foam concrete, increasing the strength characteristics of foam concrete by stabilizing the structure of stable fine-grained foam with uniform closed pores, plasticizing the mixture, accelerating the setting of cement, reduce shrinkage and delamination of the mixture, layered in layers into the formwork structure.

 This is achieved by the fact that in the method of preparing foam concrete, which includes the phased introduction of dry components into the foam and mixing, distinctive features of the prototype are that the dry components are introduced separately into the foam, and the siliceous component with the remaining cement fraction is introduced with an intensity of 8-10 kg / min per 1 liter of water in the foam after the introduction of 40-50% Portland cement, injected at a speed of 16-20 kg / min per 1 liter of water in the foam, and the foam is mixed at a speed of 120 - 180 rpm with the creation of a complex turbulent flow ka, after which the mixture is activated by stirring at a speed of 12-20 rpm.

The technical result is also achieved by the fact that the mixture for the preparation of foam concrete, including Portland cement, siliceous filler, foaming agent, water and a foam stabilizer, additionally contains a setting accelerator, lime, anti-shrink additive, and a composition based on Morpen triethanolamine in the following ratio, wt%:
Portland cement - 48-60, siliceous component 12 - 34, Morpen frother - 0.08 - 0.12), foam stabilizer 0.06 - 0.08, setting accelerator - 0.04 - 0.06, lime - 0 , 08 - 0.12, anti-shrink additive - 0.12 - 0.16 and the rest of the water.

 The technical result is also achieved by the fact that in the method of manufacturing at least monolithic structures from cellular cementless autoclave concrete, which includes preparing the mixture, preparing the molds or formwork, supplying the mixture to them, laying, holding until the formwork strength is set, the distinguishing features are that the necessary mixture is fed to the installation site by pumping with a pressure pulsation of not more than 2-2.5 atm, and the foam concrete mixture is laid in molds or formwork in layers in horizontal layers, at volume ratio of the height and width of the cross section of each horizontal layer does not exceed 2.5-2.8.

 The preliminary introduction of Portland cement in the method of preparing foam concrete at a speed of 16-20 kg / min per 1 liter of water in the foam allows to obtain a homogeneous foam mass with a high viscosity index, which creates a stable structure of the foam cells due to the "reservation" of air bubbles by cement particles with the acquisition of the necessary structural strength, the subsequent introduction of sand at a speed of 8-10 kg / min per 1 liter of water 1 in the foam does not cause separation of the mixture, and mixing at a speed of 120 - 180 rpm with the creation of a turbulent flow does not destroy the bubble ki in the foam and allows a uniform penomassu with optimum filling - siliceous fraction that reduces the shrinkage characteristics of the foam.

 The introduction into the mixture for the preparation of foam concrete as a Morpen foam former, as a setting accelerator of Pozolit, as a stabilizer of sodium silicate foam, lime and TIAMAK anti-shrink additive, also allow to reduce the shrinkage characteristics of foam concrete due to the quick setting of Portland cement in the foam mass and stabilization of the structure of the foam.

 The supply of foam concrete to the place of molding the raw mix by pumping with a pressure pulsation of not more than 2-2.5 atm and laying the foam concrete mixture in horizontal layers with a ratio of the height and width of the cross section of each layer of not more than 2.5 - 2.8 also ensures the production of monolithic foam concrete structures high strength without shrinkage stresses arising after curing.

 The combination of the proposed features allows you to get a new result: a single set of works on the preparation of the mixture, its composition and method of manufacturing structures from monolithic foam concrete of high strength, homogeneous structure without shrinkage stresses that arise after the foam concrete strength is set.

 This creates the conditions for obtaining durable structures made of heat-resistant light, relatively cheap material.

 To implement the method, the following materials were used: Portland cement GOST 10178-76, fine-grained sand of the Malyshevsky quarry with a grain size of Mk-1.0 is used as a siliceous filler; a foaming agent - based on the morpen triethanolamine - TU 38.507-63-0118-90; or "TEAS" -TU 38.107-27-87. As a setting accelerator, Pozolit, manufactured according to ASTM-C945, was used. As a foam stabilizer, sodium silicate (water glass) - GOST 13078-4, GOST 9179-77 lime and TIAMAK anti-shrink additive - ASTM-494, tap water in Voronezh.

Example
The preparation of natural hardened foam concrete according to the claimed method was carried out on an experimental type installation having characteristics corresponding to the production purpose installed on the experimental site of the Chernozemstroyinvest construction department. Productivity of foam concrete preparation is 3.5 - 4.0 cubic meters / hour. The installation consists of containers for cement and siliceous filler, a tank for water, an injection foam generator of a radial-jet type, a concrete mixer, a storage tank and a mortar pump.

 The method of preparing the mixture is as follows.

 Foam is fed into the concrete mixer, after which, simultaneously with the rotation of the mixer at a speed of 120-180 rpm, cement supply starts in the amount of 40-50% of its total mass with an intensity of 16-20 kg / min per 1 liter of water in the foam. The range of 120 - 180 rpm is justified by the fact that when the mixer shaft rotational speed is less than 120 rpm, the mixing intensity decreases, which leads to the need to increase the drive power and, therefore, not rationally, but increase the speed to 200 - 250 rpm, entails intensive destruction of the foam structure and rapid loss of the air phase. The cement feed rate of less than 16 kg / min lengthens the preparation time, the mixing cycle, and therefore creates excessive deaeration of the mixture. A decrease in the quality of the mixture depends on the mechanism of its deaeration, when a high frequency of rotation of the mixer blades, mixing time or low viscosity of the mixture lead to the merging of small air bubbles into larger ones, which are easier to float and carry away a significant part of the air introduced into the mixture, violate the uniformity of pore distribution over the cross section the volume of foam laid in the structure.

 An increase in the feed rate of cement in excess of 20 kg / min leads to subsidence of the cement and the separation of the solution, loss of its hardening quality, and a sharp increase in resistance to mixing. The interval of intensity of cement supply 16 - 20 kg / min corresponds to the optimal mixing speed of 120-180 rpm and its most uniform distribution over the volume of foam, which creates the most favorable conditions for the "reservation" of the foam structure, i.e. uniform distribution of cement particles in inter-pore volumes of the foam structure. After the introduction of 40 - 50% of cement, the entire amount of the siliceous component is supplied together with the remaining cement, with an intensity of 8-10 kg / min per 1 liter of water in the foam, which corresponds to the optimal ratio of cement and sand in the volume of the finished mixture, subject to continuous supply all components during the steady-state process of preparing foam concrete.

 With a decrease in the sand feed rate of less than 8 kg / min, the mixture creates conditions for an intensive shrinkage process when drying and hardening the material. An increase in sand supply of more than 10 kg / min leads to an increase in the bulk density of foam concrete and the loss of its resistance to heat transfer (an increase in the coefficient of thermal conductivity).

 Mixing of the mixture is carried out in a turbulent mode of flow of the mixture, which occurs under conditions characterized by a Reynolds number (Re), in the range of 2500 - 3200. This state of the flow of the mixture creates a vortex mode of movement of particles with complex trajectories, when the particle velocity is uniform over the flow cross section, but pulsates by time. Particles in such a stream are separated and evenly distributed throughout the entire volume of the foam mass, which positively affects not only the viscosity, structure, and immiscibility of the mixture, but also increases the speed and degree of hydration of the cement particles, i.e. increase the strength characteristics of foam concrete.

 The speed of rotation of the blades of the concrete mixer, the diameters of the blades, their gaps between the walls of the mixer (which determine the thickness of the wall foam flow) are selected from the conditions for creating the most effective mode for mixing. Next, the mixture coming from the mixer into the storage tank is activated by stirring at a speed of 12-20 rpm, which best affects the preservation and air saturation of the composition, ready to be pumped to the place of laying.

 During this period of low-intensity mixing, cement hydration processes are activated in the mixture. This contributes to the formation of future strength properties of foam concrete, and also this time is necessary to include all types of additives, and, most importantly, an accelerator of hardening of foam concrete and additives - a compensator for shrinkage of the material.

 The advantage of this method of preparing foam concrete is the separate introduction of cement and a siliceous filler, which advances the supply of cement, “armors” the foam, increases the viscosity of the mixture, preparing it for introducing a siliceous filler, thereby preventing sand particles from delaminating and deaerating the structure. The possibility of using low revolutions of the mixer also contributes to maintaining the properties of the mixture.

 Continuous dosing of all components of the mixture in the steady-state mode of preparation of foam concrete creates favorable conditions for obtaining the mixture most homogeneous in terms of volumetric change in mass, in contrast to the prototype, where the mixture is prepared cyclically and interrupted in time.

 Foam mixtures were prepared with a composition by weight, presented in table 1.

 Foam concrete samples were tested in the form of 10x10x10 cm cubes and 4x4x416 prisms, taking into account the required bulk density. The test results are shown in table 2.

The most rational for structural and heat-insulating material of the walls is the bulk density of foam concrete 700 kg / m ³ . This is confirmed by the physicomechanical characteristics of the samples.

Composition N 1 has good thermal conductivity, but insufficient in terms of bearing capacity and shrinkage. Composition No. 5, with high strength characteristics, has a sharply increased thermal conductivity, which, given the increased consumption of cement, does not make it possible to consider this composition rational. Composition NN 2, 3, and 4 satisfy all the conditions of the operational characteristics of this material, with a bulk material mass of 600 to 800 kg / m ³ . Composition N 3 is the most optimal in terms of strength, minimal shrinkage, high resistance to heat transfer. This is because this composition provides the best foam composition, and therefore the best pore formation structure in foam concrete. Most effectively, this affects the thermal conductivity of the material. At the same time, the bearing capacity of the material is preserved, which makes it successfully applicable in monolithic construction as an effective material for walling. Introduction to the composition of the raw material mixture of a complex of additives consisting of a cement setting accelerator "Pozolit", a foam stabilizer - sodium silicate, lime, an anti-shrink additive like "TIAMAK", allows to obtain a highly stable foam with the most optimal bubble structure. The quality of the foam is determined by the mechanism of action of all additives. The foam obtained from the introduction of a foaming agent based on triethanolamine type "Morpen" is structured and obtains stability over time by the introduction of sodium silicate. The multiplicity of the foam, i.e. foaming ability, increases from the introduction of the lime component. The introduction of the setting accelerator provides early structuring of foam concrete, preventing delamination of the mixture, as well as rapid hydration of the cement introduced into the foam and accelerated curing of the material (at an air temperature of +10 ^o C to +25 ^o C, the critical strength required for stripping the material is 20-24 hours). The use of the anti-shrink additive TIAMAK allows one to reduce the occurring shrink stresses in the process of cement hydration, hardening and further drying of the material. Its action is aimed at bonding and retaining excess moisture in foam concrete, which favorably reduces shrinkage and increase strength.

 Composition N 3, optimized for the main properties, has a thermal conductivity of 3 times less than similar materials and the prototype according to table. 2. This is due to the formation of the best pore structure in foam concrete. The composition of additives (see table. 1) allows you to get a very stable foam with the most favorable pore size (from 0.3 to 0.8 mm), evenly (uniformly) placed over the material cross section, having a closed structure, spherical shape. The technology of preparation of the material allows you to maximize save and profitable use of the resulting foam structure. In a certain mode of filling it with cement, and then siliceous-cement material, it allows you to get the most durable, non-shrink, less heat-conducting structure. This structure does not deteriorate when the sand fraction is introduced, with stirring, and when pumping over long distances.

 Separate introduction of cement and sand is of key importance in foam concrete technology. The modes of administration and test results of the samples are presented in table 3.

 The data clearly demonstrate the effect of the dosage of pre-introduced cement, which creates a “reservation” of the structure, i.e. providing the foam viscosity required for the technology, on the strength and shrink properties of the material.

 Laying the prepared mixture of foam concrete in the design of formwork forms is carried out by pumping foam mass using a concrete pump with a pressure pulsation of no more than 2 - 2.5 atm.

 This pressure ensures that the mixture moves through the pipeline to a distance of 100 m and is supplied to a height of up to 15 m with a diameter of 50-100 mm of concrete. Exceeding pressure pulsations of more than 2.5 atm causes an irreversible process of air removal from the mixture with the destruction of the pore structure and an increase in the bulk density of foam concrete of more than 10%. This corresponds to a change in the brand of foam concrete in terms of bulk density, which is unacceptable according to the requirements of SNiP standards. Foam mass is laid in formwork in horizontal layers, which reduces the integral indicators of shrinkage stress during the setting, hardening and dehumidification from an array of foam concrete structures during their operation. The indicator of the layer height to its width of more than 3 creates the conditions for increasing the vertical components of shrink stress to critical values, which increases the likelihood of shrinkage deformation of the material.

 Domestic and foreign experience in the use of foam concrete notes that these materials, with their high heat-saving ability, have low strength and a large amount of shrinkage when the material dries. Only a complex technological sequence of special techniques aimed at reducing shrink stresses and preserving strength characteristics can solve this problem. This is how the proposed method solves this problem.

 The composition of the material used contains components that improve the quality of the foam, the structure of the pores and reduce shrinkage characteristics. This is ensured by: introducing the optimal amount of sand with a particle size modulus <1.2, accelerating the setting of concrete to prevent delamination, and the shrink-reducing additive TIAMAK. The method of preparing foam concrete provides the most optimal mode of introducing cement and sand, which allows the most complete implementation of the cement hydration reaction, creating an effective viscosity of the foam mass "armored" by cement particles and not allowing sedimentation (separation) of the sand fraction, i.e. creating the most effective pore structure.

 The most effective technique for stabilizing the properties of the foam concrete being prepared is the applied technology of continuous dosing and preparation of foam concrete. This ensures minimal deviations in the bulk density of the material, i.e. uniformity of quality indicators across all sections of concrete structures. This is due to a one-time setup of the equipment, but cannot be provided with cyclic kneading of the preparation of foam concrete.

 The foam concrete mass prepared in a continuous mode is pumped and laid in formwork in a way that eliminates the loss of foam concrete quality and excludes the occurrence of even slight shrinkage deformations.

 The implementation of concreting of foam concrete structures by the proposed method allows at each stage of work (composition, preparation, laying) to have a high guarantee of the quality of the material obtained and those structures that are manufactured with its use.

 This method is the basis of a new technology for high-speed construction of houses, where the material is produced at the construction site and fits into the structures being constructed continuously with its production.

 The chain of declared technological operations will allow to obtain high-quality heat-insulating and structural material with a high guarantee of reliability of the required properties.

 This technology allows you to quickly control the properties of the prepared foam concrete and effectively control the process of erecting building envelopes.

Sources of information
1. USSR author's certificate N 1662988, cl. From 04 to 38/10, 1988

 2. USSR author's certificate N 17634286, cl. S 04 V 38/10, 1990

 3. Instructions for the manufacture of cellular concrete products SN-277-80, 1981

 4. Copyright certificate of the USSR N 1766887, cl. S 04 V 38/10, 1995

 5. RF patent N 2010021, cl. S 04 V 38/10, 1993

Claims (2)

 1. A method of preparing foam concrete, comprising the phased introduction of dry components into the foam and mixing, characterized in that the dry components are introduced separately into the foam, and the siliceous component with the remaining cement fraction is introduced at an intensity of 8-10 kg / min per 1 liter of water in the foam after the introduction of 40 - 50% of Portland cement, introduced at a speed of 16 - 20 kg / min per 1 liter of water in the foam, and the foam is mixed at a speed of 120 - 180 rpm with the creation of a complex turbulent flow with a Reynolds number of 2500-3200, after which produce an asset tion stirring of the mixture at 12 - 20 rev / min. 2. The raw material mixture for the preparation of foam concrete, including Portland cement, a siliceous filler, a foaming agent, water and a foam stabilizer, characterized in that it additionally contains a setting accelerator, anti-shrink additive, lime, and as a foaming agent a composition based on Morpen type triethanolamine in the following ratio, wt. %:
Portland cement - 48 - 60
Siliceous filler - 12 - 24
Frother - 0.08 - 0.12
Foam Stabilizer - 0.06 - 0.08
Setting accelerator - 0.04 - 0.06
Anti-shrink additive - 0.12 - 0.16
Lime - 0.08 - 0.12
Water - Else
3. A method of manufacturing at least monolithic structures from cellular cementless autoclave concrete, comprising preparing a mixture, preparing molds or formwork, feeding the mixture into them, laying, holding to a set of stripping strength, characterized in that the foam concrete mixture is fed to the installation site by pumping with the pressure pulsation is not more than 2 - 2.5 atm, and the foam concrete mixture is laid in molds or formwork in layers in horizontal layers, while the ratio of the height and width of the cross section of each horizontal layer is n e exceeds 2.5 - 2.8.

Images