WO2008130107A1

WO2008130107A1 - Rapid set cement foam and the method for preparing the same

Info

Publication number: WO2008130107A1
Application number: PCT/KR2008/001800
Authority: WO
Inventors: Min-Hwa Park
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-04-20
Filing date: 2008-03-31
Publication date: 2008-10-30
Anticipated expiration: 2009-10-20
Also published as: KR100760039B1

Abstract

The present invention provides a rapid set cement foam as replacement for a foaming resin, which is a petrochemical product in the art, and the method for preparing the same. The rapid set cement foam is prepared by mixing: an aqueous solution composed of water and a foaming agent; cement mixed with the aqueous foam solution to be foamed; silica; ceramic powder; and an accelerating agent mixed with the foam cement. The method for preparing a rapid cement foam includes; a step for foaming an aqueous foam solution obtained by dissolving a foaming agent in water; a step for forming a cement slurry by mixing a foam and cement; a step for adding an accelerating agent to the cement slurry; and a step for forming a rapid set cement foam by casting the cement slurry mixed with additives into a mold or over walls of a building.

Description

[DESCRIPTION]

[Invention Title]

RAPID SET CEMENT FOAM AND THE METHOD FOR PREPARING THE SAME

[Technical Field]

The present invention relates to a rapid set lightweight cement foam excellent in insulation and soundproof effects and the method for preparing the same. Particularly, the present invention relates to a lightweight cement foam that is prepared by diluting a foaming agent in water to obtain an foam solution, foming the foam solution, adding cement and additives thereto to make a microporous cement slurry, and rapidly setting the cement slurry such that it is hardened at room temperature while maintained in the foamed state.

[Background Art]

In general, building construction includes insulation works to install insulation along outer walls of a building in order to prevent energy waste as heat from inside and outside the building is transmitted through the outer walls. Typically, the insulation also has a soundproofing function to lessen living discomfort due to noise.

As air cells created during foaming are known to be highly effective for insulation and sound absorption, it has been customary to use a microporous ceramic or a foaming polymer material singly to maximize insulation effects, or a mixture of a porous ceramic with an air space and a sound absorption material to increase the soundproofing effect. Conventionally used insulation and soundproof materials are foamed polystyrene, glass wool, foamed polyethylene, polyurethane foam, vermicullite, pearlite, ureafoam, cellulose thermal insulation materials, soft fiberboard, phenol foam, aerogel, and lightweight cement. In case of foamed polystyrene, although its high insulation effect and lightweight is helpful for easy delivery and good workability, it has the safety temperature limit as low as 7O⁰C, is weak at ultraviolet rays, and can be fatal to human life because it is much likely to cause an ignition and generate toxic gases during a fire breakout. Glass wool, on the other hand, has a sealed air space as an insulation layer between glass fibers, so it shows superiority not only in insulation but also in fire resistance, sound absorption, workability, and mobility, and is not likely to suffer a decrease in effective thickness caused by compression or subsidence, or degraded insulation due to its water containing nature. The absence of water vapor resistance in glass wool, however, requires an additional damp proof layer to be installed. Foamed polyethylene is widely used for thermal insulation in sheet and tubular form showing the self-extinguishing behavior, in which the sheet or tubular is manufactured by laminating and thermally fusing sheet-type foaming agents (or foam sheets) prepared by mixing a foaming agent and a fire retardant with polyethylene resin for extrusion foaming, and cooling the foam extrusion mixture. Although it is excellent in insulation effects by presenting the thermal conductivity of 0.039 kcal/mh°C or lower at average temperature, its safety temperature limit is just 8O⁰C, producing toxic gases in the event of fire breakout and becoming fatal to human life. Polyurethane is an insulation and soundproof material of an organic foam (separated vapor structure) obtained by expansion molding a polyurethane foam which contains polyurethane, polyol, polyisocyanate, and flame retardant additive(s) as main ingredients. Despite somewhat low heat resistance (e.g., safety temperature limit: 100⁰C), its insulation performance is good enough to be used as a cold insulation material for freezing equipment. When processed, however, it contracts and has lower thermal conductivity, and similar to other foamed polymer materials it produces toxic gases when a fire breaks out. Meanwhile, vermiculite is a porous inorganic material obtained by firing mica-based ore at a temperature of 1000⁰C or higher, and has advantages in insulation, thermal insulation, noncombustible and soundproofing properties, and prevention of dew condensation. Peariite is obtained by firing pearl stone (volcanic stone) at a temperature between 900 and 1200⁰C, followed by crushing and plastic expanding to obtain spherical lightweight grains having micro air gaps inside, and used primarily as lightweight aggregates and insulation materials. Even if vermiculite and pearlite are effective for insulation, thermal insulation, and sound absorption, their main defect is that it takes so much energy like 1000⁰C or above to foam such mineral. In case of aerogel, microstructures having 1/10000th thickness of a human hair are entangled with each other like spun sugar, and air holes therein occupy 95 parts by weight of the total volume. This makes aerogel very effective for insulation and soundproofing, but its high price results in limited use in some industries.

Another example of the foaming agent that was developed and is being currently used as insulation and soundproof material is a kind of petrochemical products. Unfortunately though, such foaming agent is not only the fatal risk to human body by producing toxic gases during a fire, but also causes environmental pollution.

On the other hand, foam cement or lightweight cement uses low-priced cement as a binder to provide an economically efficient foam. However, lightweight cement needs to be cured in a high-temperature, high-pressure reactor (autoclave), so the economic burden on installation expenses increases. In addition, a great amount of thermal energy is consumed to harden the foamed cement, and the cement is cured over a long period of time. Particularly, in case of the lightweight cement, if foamed cement slurries, not in cured form as used in the conventional technique, should be applied directly to the walls of a building structure such as an apartment building, the cement is usually set over several days or more than ten days. The resultant cement is then defoamed, making it impossible to provide lightweight foamed cement for insulation and soundproofing, and bonds between cement particles are broken because the cement is set and defoamed at the same time, so that compressive strength after the cement is completely hardened is substantially degraded.

Normally, a foamed ceramic is manufactured by either a high-temperature process or long hours of process carried out in large scale facilities, so energy loss is great and productivity is lowered. Also, costly facilities are required for compressively molding the ceramic in a designated frame, and expensive materials like aerogel is utilized. These together lower price competitive power of the foamed ceramic, and limit its application range to building insulation and soundproofing fields.

To address the above deficiencies and to provide a porous lightweight structure as an insulation and soundproof material, Korean Patent Application Publication No. 2006-0099979 proposes a method of preparing a ceramic foam molding with voids inside by utilizing imperfect sodium silicate gel, which is prepared by adding an acid, amphoteric oxide, or amphoteric hydroxide to liquid sodium silicate, as a binder. Even though this method could make the foam molding lighter and increase sound absorption, sound isolation, and thermal insulation effects, it has not necessarily brought much technical advance because the imperfect sodium silicate gel in colloid phase was used simply as a binder in the manufacture of a conventional ceramic foamed molding. Korean Patent Application Publication No. 2006-0092782 proposes a method of preparing a ceramic foam molding with increased durability, by mixing foam cement particles used singly or in mixture of pulverized foamed vermiculite, pearlite, obsidian, pitchstone, more than one kind of inorganic adhesives including plaster, cement, paper clay, sodium silicate, incomplete sodium silicate gel, sodium silicate cement, etc., and other strengthening materials such as steel fiber, clastic fiber, pulverized paper (including powder form), and glass wool; and/or applying a wire net or synthetic resin net to inside. Although the foam cement preparation method described above can provide an air space with the insulation property, it has some downsides in that a vast amount of heat energy and installation expenses are consumed to pulverize natural rock materials, e.g., vermiculite, pearlite, obsidian, and pitchstone, to a desired size, and to heat the pulverized particles at high temperature of 800-1400⁰C. Besides, this ceramic foam molding cannot be casted or placed in the construction field because it is only a mixture of foam cement particles and an inorganic adhesive selected from plaster, cement, paper clay, sodium silicate, incomplete sodium silicate gel, sodium silicate cement, etc. Korean Patent Application Publication No. 2003-0086955 discloses a non-flammable lightweight foamed concrete sandwich panel as a finish material of building outerwalls in consideration of insulation. In detail, natural vermiculite is heated at high temperature to obtain expanded vermiculite having voids, and the resulting expanded vermiculite is added with a surfactant, e.g., a lauryl alkylbenzene sulfonate-based material, to adjust the air density to about 40-50 kg/cm², and air cells being produced, a cement slurry, and the expanded vermiculite are mixed together to obtain the non-flammable panel that does not emit toxic gases during a fire. Overall, the surfactant provides excellent foaming properties and the cement used as an inorganic binder improves economic value. However, since the hardened lightweight cement is cured over 1-2 days, it is not hardened immediately when casted directly over the walls of a building. In brief, this type of panel cannot be used for direct casting in the construction field. Korean Patent Application Publication No. 2000-0060707 discloses a soundproofing panel using a lightweight foamed concrete as a sound absorbing material that is obtained by adding a foaming agent to a mixture of cement, lime, and silicious fine powder, and carrying out a steam curing or high-temperature and high-pressure steam curing process. Although the porous lightweight concrete is excellent in sound absorption effect, a problem still remains because those steam curing processes require costly equipment, while increasing facility expenses and production cost. Moreover, since the curing processes take a great amount of time, the overall manufacturing cost increases accordingly. Further, this type of lightweight foamed concrete is not hardened immediately after it is casted over the walls, so it cannot be casted directly over the walls of a building, either.

[Disclosure] [Technical Problem] The present invention is conceived to solve the aforementioned problems in the prior art. An object of the present invention is to provide a rapid set cement foam preferably used as replacement for a foaming resin, which is a petrochemical product in the art, and the method for preparing the same. Another object of the present invention is to provide a rapid set cement foam that can be obtained without carrying out a high-temperature, high-pressure steam curing process or a heating process, and the method for preparing the same.

A further object of the present invention is to provide a rapid set cement foam that can be casted directly over the walls of a building, and the method for preparing the same.

[Technical Solution]

According to an aspect of the present invention, there is provided a rapid set cement foam prepared by mixing: an aqueous solution including water and a foaming agent; cement mixed with the aqueous foam solution to be foamed into a slurry state by a foam system; and an accelerating agent mixed with the cement slurry.

According to another aspect of the invention, the rapid set cement foam further comprises silica and/or ceramic powder added to the aqueous foam solution together with the cement. According to another aspect of the invention, the rapid set cement foam further comprises a sound absorbent functioning as a strength reinforcing agent.

According to another aspect of the invention, the sound absorbent is selected from : natural fibers including cellulose based fiber, staple or filament type protein based fiber, and mineral based fiber; and man-made fibers including regenerated fiber, semi-synthetic fiber, synthetic fiber, metal fiber, glass fiber, rock fiber, slag fiber, and carbon fiber.

According to another aspect of the invention, the sound absorbent is a fiber having a thickness of 3-50 μm. According to another aspect of the invention, the sound absorbent is a fiber having a length of 1-50 mm.

According to another aspect of the invention, the sound absorbent is added at an amount of 1-20 parts by weight with respect to 100 parts by weight of silica and ceramic powder. According to another aspect of the invention, the rapid set cement foam further comprises a water-resistance reinforcing agent containing a water dispersible polymer resin for improvement of water resistance.

According to another aspect of the invention, the water-resistance reinforcing agent contains a water dispersible polymer resin selected from the group consisting of: acryl, vinyl acetate, alkyd, melamine resin, solution styrene butadiene rubber, epoxy resin, and polyurethane.

According to another aspect of the invention, the aqueous solution is a mixture of a foaming agent added by 0.1-10 parts by weight with respect to 100 parts by weight of water. According to another aspect of the invention, the cement is used singly or in mixture selected from : portland cement such as ordinary portland cement, moderate heat portland cement, high-early-strength portland cement, sulphate resistant portland cement, white portland cement, oil well cement, and colloid cement; mixed cement such as blast-furnace cement, fly ash cement, silica cement, super-low-heat cement, geothermal well cement, RCCP cement; alumina cement; ultra-rapid setting cement, and GRC low alkali cement. According to another aspect of the invention, the cement is added at an amount of 25-80 parts by weight with respect to 100 parts by weight of water. According to another aspect of the invention, the ceramic powder is selected from the group consisting of: elvan, loess stone, olivine, kaolin, silica minerals, magnesite, bauxite, bentonite, pumice, borate, serpentine, acid clay, iron oxide, garnet, carbonate minerals, attapulgite, sepiolite, nephrite, apatite, illote-mica, feldspar, peaiiite, vermiculite, zeolite, barite, talc, diatomaceous earth, graphite, hectorite, clay minerals, zirconium minerals, titanium minerals, tourmaline, fume silica, aerogel, sly ash, and blast-furnace slag powder, which are used singly or in mixture.

According to another aspect of the invention, the rapid set cement foam further comprises a viscosity control to make the viscosity fall within 5,000-200,000 cps. According to another aspect of the invention, the accelerating agent is selected from the group consisting of: aluminum salts including aluminum sulfate, aluminum chloride, aluminum nitrate, and aluminum acetate; carbonates including sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, sodium carbonate, potassium carbonate, ammonium carbonate, and potassium carbonate; silicates including one to four kinds of sodium silicate solutions, sodium silicate powder, sodium silicate, potassium silicate, lithium silicate, and sodium aluminum silicate; silica sol; glyoxal; and ethyl glycol diacetate, which are used singly or in mixture.

According to another aspect of the invention, the accelerating agent is added at an amount of 5-70 parts by weight with respect to 100 parts by weight of cement.

Further the present invention provides a method for prepareing a rapid set cement foam, comprising: a step for foaming an aqueous foam solution obtained by dissolving a foaming agent in water; a step for forming a cement slurry by mixing a foam and cement; a step for adding an accelerating agent to the cement slurry; and a step for forming a rapid set cement foam by casting the cement slurry mixed with additives into a mold or over walls of a building. According to another aspect of the invention, the step for forming cement slurry further comprises: a process for mixing silica and/or ceramic powder with cement.

According to another aspect of the invention, the step for forming cement slurry further comprises: a process for adding a sound absorbent functioning as a strength reinforcing agent or a water resistance reinforcing agent as additives. According to another aspect of the invention, the step for foaming is carried out in a foam system operating by a foamation method that uses rotary wings of a mixer, a dissolver, or a Homomixer, or by using a foamation device that is equipped with a compressor.

According to another aspect of the invention, the step for forming cement slurry is achieved by blending cement singly or a mixture of cement, ceramic powder, and silica with a foam. According to another aspect of the invention, the method further comprises: a step for drying the rapid set cement foam after the step for forming a rapid set cement foam.

According to another aspect of the invention, the step for drying the rapid set cement foam is carried out at room temperature, using hot wind, or using UHF. According to another aspect of the invention, the step for the drying the rapid set cement foam is carried at a temperature of 80-250⁰C by using hot wind or UHF.

[Advantageous Effects]

The rapid set cement foam prepared according to the present invention can be used for direct casting of diverse shapes and diverse thicknesses in the construction field, or can be injected to a mold of a variety of forms. The rapid set cement foam prepared according to the present invention does not require a high temperature heat source for setting, but can be hardened at room temperature without defoaming a large amount of micro cells or closed-cell foams. Accordingly, fine air space (air cells) is created inside the rapid set cement foam to improve insulation and soundproofing effects. The rapid set cement foam prepared according to the present invention can be obtained at reduced facility expenses and lower manufacturing cost because neither high-temperature heat sources nor high-pressure compression molding devices are used.

The rapid set cement foam prepared according to the present invention does not emit toxic gases during a fire breakout, so loss of life during the fire can be minimized. [Description of Drawings]

FIG. 1 is a flow chart describing a method for preparing a rapid set cement foam according to one embodiment of the present invention. FIG. 2 shows photographs of a rapid set cement foam according to one embodiment of the present invention, in which the cement foam is deposited in water over a period of 30 days for a water resistance test.

[Mode for Invention] Hereinafter, preferred examples of the present invention will now be described in detail with reference to the accompanying drawings. As for a foaming agent suitable for the preparation step of a foam, an amino acid based foaming agent called an animal foaming agent, and a foaming agent called a vegetable foaming agent containing an alkyl benzene sulfonate based material or sodium lauryl sulfate and its ester as active ingredients are diluted in water singly or in mixture. Here, any kind of water including tap water, groundwater, industrial water, etc., can be used without particular limitations thereto, with an exception of water containing a large amount of alkaline earth metals to relatively weaken bond strength in result of the reaction with silicate in the subsequent step.

An animal foaming agent is preferred in some cases in order to maintain a foamed state over a long period of time, without defoaming the foam cells. Meanwhile, a vegetable foaming agent is preferred in some cases in order to avoid odor produced from the foaming agent itself during the cell forming process. With respect to 100 parts by weight of water, the foaming agent is added preferably by 0.1-10 parts by weight, more preferably 0.25-8.5 parts by weight, and most preferably 0.5-7.5 parts by weight. If the content of the foaming agent is 0.1 parts by weight or less, foaming capability is so low that micro-porous cells are rarely formed. On the other hand, if the content of the foaming agent is above 10 parts by weight, although a large number of micro cells can be formed, the foaming agent, being composed of an organic material, exhibits degraded bond strength with ceramic powder and is likely to produce a lot of toxic gases during a fire in result of pyrolysis of the foaming agent. The diluted aqueous foaming agent solution can be foamed by any method suitable for producing a large number of micro cells. In general, cells are formed by using a foam system, and the foam system is operated either by rotary wings such as an impeller, or by compressed air from a compressor. The foam system using rotary wings, i.e. an impeller, is more advantageous if a small number of cells are needed, while the foam system equipped with a compressor is more advantageous if a large number of cells are needed. In case of using the foam system to foam by rotary wings, the wings are rotated at a rate of 500-12,000 rpm, and examples of such a foam system include a mixer, a dissolver, and a Homomixer. The foam system equipped with a compressor is useful for forming uniform, micro cells at a large amount where the degree of foamation can be controlled by regulating the density of cells produced at the application of air pressure from the compressor. Next, cement slurries can be formed by any type of method as long as cells produced from the foaming step are not defoamed but remain to be mixed with cement and additive(s). To form cement slurries, foam and cement can be mixed singly, or a mixture of foam, cement, silica, and ceramic powder may be mixed together. To be brief, a foam system can form cement slurries by mixing cement singly with foam, or adding foam to a mixture of cement, silica, and ceramic powder, while keeping cells formed from the reaction. The cement used in the present invention include, but are not limited to, one or more of the following: portland cement systems such as ordinary portland cement, moderate heat portland cement, high-early-strength portland cement, sulphate resistant portland cement, white portland cement, oil well cement, and colloid cement; mixed cement such as blast-furnace cement, fly ash cement, silica cement, super-low-heat cement, geothermal well cement, RCCP cement; alumina cement; ultra-rapid setting cement, and GRC low alkali cement, which is selected according to the usage of a rapid set cement foam. Surface area of the cement is determined depending on the required strength of the rapid set cement foam. Normally, portland cement having the surface area of 3,000-3,500 cm²/g is preferably used to obtain a rapid set cement foam for use in heat insulation materials of a building. To increase the early strength of a rapid set cement foam, high-early-strength cement having the surface area of 4,000-4,600 cm²/g, and ultra high-early-strength cement having the surface area of about 6,000 cm²/g are preferably used. Meanwhile, it is proper to use moderate heat portland cement to obtain hard, lightweight structure cement with long-term strength over one year, sulphate resistant portland cement to increase resistance against sulfate attack, blast-fumace cement to retain long-term strength, increase sea water resistance and chemical resistance and minimize reactivity with an alkali, and fly ash cement to reduce drying shrinkage and heat of hydrate yet increase long-term strength.

With respect to 100 parts by weight of water used for the preparation of a foam, the cement is added preferably by 25-80 parts by weight, more preferably 35-75 parts by weight, and most preferably 45-65 parts by weight. If the cement is blended by 25 parts by weight or less its adhesion force with a rapid set cement foam is degraded, but if the cement is blended by 80 parts by weight or more its economic efficiency is lower. Silica blended with cement is used to make strong bonding between the cement and ceramic powder. Ceramic powder blended with cement serves to increase adhesion force of the cement according to a cement setting mechanism. Any kind of ceramic powder can be used as long as it does not impair physical properties of a rapid set cement foam. Examples of the ceramic powder to be blended with cement include, but are not limited to, one or more of the following: elvan, loess stone, olivine, kaolin, silica minerals, magnesite, bauxite, bentonite, pumice, borate, serpentine, acid clay, iron oxide, garnet, carbonate minerals, attapulgite, sepiolite, nephrite, apatite, illote-mica, feldspar, pearlite, vermiculite, zeolite, barite, talc, diatomaceous earth, graphite, hectorite, clay minerals, zirconium minerals, titanium minerals, tourmaline, fume silica, aerogel, sly ash, and blast-furnace slag powder. Particle size of silica and ceramic powder being blended with the cement is selected from a relatively broad range of 5nm-1.5mm. If silica and ceramic powder grains are bigger than 1.5mm, surface area of each is so small that adhesion force is reduced at the time of cement setting and the probability of forming micro cells between particles is lowered. This is why it is desired to use silica and ceramic powder with particle size of 1.5mm or less. On the other hand, it does not matter to use silica and ceramic powder with particle size of 1.5nm or less, but such powder having several nm particle size is usually very expensive. From an economic aspect, therefore, it is sufficient to use silica and ceramic powder with a particle size not impairing the adhesion force during cement setting.

With respect to IOOparts by weight of cement, the content of the mixture of silica and ceramic powder are added preferably by 50-750 parts by weight, more preferably 75-600 parts by weight, and most preferably 300-500 parts by weight. If the content of silica and ceramic powder is added by 50 parts by weight of or less, the cement resultantly has a very small amount of inorganic oxides (i.e. silica and ceramic powder), giving rise to problems like a lower economic value and reduced strength. On the contrary, if silica and ceramic minerals are added more than 750 parts by weight, adhesion force is reduced. An admixture may also be added to improve the workability and strength of foamed cement slurries. Such an admixture includes one or more of poly carbonic acid system, melamine system, and naphthalene system. The amount of an admixture is added preferably by 0.5-2.0 parts by weight with respect to 100 parts by weight of cement. In general, if the admixture powder is added to cement at the mixture ratio outside the range, differences in specific weight or particle size between the admixture powder and the cement cause separation during the blending process, and a homogeneous mixture is hard to obtain.

Additives are also used to increase strength or water resistance of a cement foam. For example, a sound absorbent also functioning as a strength reinforcing agent, and a water-resistance reinforcing agent correspond to such additives. A typically used sound absorbent with a strength reinforcing function is fiber. When the fiber type sound absorbent is filled between ceramic particles, not only adhesion force but also soundproofing effects are improved. Because a cement foam is produced at room temperature, any kind of fiber type strength reinforcing agents, such as natural fiber, man-made fiber, etc., capable of increasing strength of the cement foam is acceptable. Examples of natural fibers include, but are not limited to, cellulose based fibers (seed-fiber, bast fiber, leaf fiber, and fruit fiber), staple or filament type protein based fibers, and mineral based fibers. Examples of man-made fibers include, but are not limited to, organic fibers (regenerated fiber, semi-synthetic fiber, synthetic fiber, etc.), and inorganic fibers (metal fiber, glass fiber, rock fiber, slag fiber, carbon fiber, etc.). The sound absorbent also functioning as a strength reinforcing agent has a fiber thickness of 3-50 μm, more preferably 5-25 μm, and most preferably

5-1 Oμm. Thinner fibers, by nature, tend to have a smoother appearance and softer texture, so they demonstrate excellent physical properties and high utility values. However, since all fibers produced from natural fibers, except for glass fiber, and from man-made fibers are mostly 3 μm thick or more, fiber thickness options are limited. On the other hand, fibers of 50 μm or thicker do not have smooth texture by appearance, and show reduced strength. In addition, the sound absorbent also functioning as a strength reinforcing agent has a fiber length of 1-50 mm, more preferably 5-35 mm, and most preferably 10-25 mm. If fibers are 1 mm or shorter, the length of fibers being connected between micro porous cement particles of a 3D silica network is so short that adhesion force during gelling is not large. Meanwhile, if fibers are 50 mm or longer, fibers in the cement slurry formation process are not blended uniformly with cement, but entangled with each other to impair physical properties of the foam cement.

5 With respect to 100 parts by weight of cement powder, the content of fibers used as the sound absorbent and the strength reinforcing agent is preferably 1-20 parts by weight, more preferably 2.5-15 parts by weight, and most preferably 5-10 parts by weight. If the sound absorbent is added by 1 parts by weight of or less almost no reinforcing effects are exerted on the cement foam,o but if the sound absorbent is added by 20 parts by weight or more it is hard to blend the cement powder with the fiber.

As for the water-resistance reinforcing agent, a water dispersible polymer resin or micro powder polymer resin can be added. Any kind of water dispersible polymer resin that can be mixed homogeneously with water is acceptable.5 Examples of such a water dispersible polymer resin include, but are not limited to, water dispersible acryl, vinyl acetate, alkyd, melamine resin, solution styrene butadiene rubber, and so on. With respect to 100 parts by weight of cement powder, the content of water dispersible polymer resin is preferably 1.0-25 parts by weight, more preferably 2.5-25 parts by weight, and most o preferably 5-10 parts by weight. If the amount of the water dispersible polymer resin being added is 1 parts by weight of or less, a sufficient polymer coating cannot be applied among foam cement particles and therefore, the resulting water resistance is not great. However, if the amount of the water dispersible polymer resin being added is 25 parts by weight of or more,5 although water resistance is increased substantially, a large amount of toxic gases is produced by polymer decomposition in the event of a fire breakout, becoming fatal to human life.

Examples of micro powder polymer resin include, but are not limited to, PET, low-density polyethylene, high-density polyethylene, PVC, PMMA₁ PS, PP, EVA, PU, polycarprolacton, and so on. With respect to 100 parts by weight of of cement powder, the content of micro powder polymer resin is preferably 0.5-15 parts by weight, more preferably 2.5-12 parts by weight, and most preferably 5-10 parts by weight. If the amount of the micro powder polymer resin being added is 0.5 parts by weight of or less, a sufficient polymer coating cannot be applied among foam cement particles and therefore, the resulting water resistance is not great. However, if the amount of the micro powder polymer resin being added is 15 parts by weight of or more, although water resistance is increased substantially, a large amount of toxic gases is produced by polymer decomposition in the event of a fire breakout, becoming fatal to human life.

Although smaller particle size is recommended for the micro powder polymer resin, the particle size may preferably be in a range of 0.5μm - 0.1mm, more preferably 0.5μm - 1mm, and most preferably 5-50μm. If the particle size of the powder is smaller than 0.1 μm, its surface area is increased and the powder is very likely to disperse in water, but dust from particles does not make work easier and lowers economic value. Meanwhile, if the particles size of the powder is greater than 0.5 mm, its surface area is decreased, and such a large particle size results in a low probability of homogenous fusion of the powder to the ceramic powder. At this time, viscosity of the cement slurry is maintained preferably at a level of 5,000-200,000 cps, more preferably 15,000-180,000 cps, and most preferably 35,000-160,000 cps. If the viscosity of the cement slurry is 5,000 cps or less, which is very low, the closed-cell foamed cement slurry can easily be defoamed. Meanwhile, if the viscosity of the cement slurry is 200,000 cps or mover, mobility of the cement slurry becomes too small. In result, the cement slurry does not flow well into places like comers of a mold to form a cement foam, so a cement foam of desired shape may not be obtained. Next, the cement slurry is mixed with an accelerating agent (or a rapid setting admixture) in the rapid setting admixture addition step. There is no specific limit to rapid setting admixtures, but they should be able to harden the cement slurry within several seconds to several tens of minutes. Although the start point of setting or setting of the cement slurry may vary depending on the kind of a rapid setting admixture used, once the cement slurry is blended with the rapid setting admixture, it should preferably be casted over the walls or injected to a mold immediately.

The accelerating agent is a kind of admixtures that accelerates coagulation and setting of cement, and includes, but is not limited to, one or more of the following: aluminum salts such as aluminum sulfate, aluminum chloride, aluminum nitrate, and aluminum acetate; carbonates such as sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, sodium carbonate, potassium carbonate, ammonium carbonate, and potassium carbonate; silicates such as one to four kinds of sodium silicate solutions, sodium silicate powder, sodium silicate, potassium silicate, lithium silicate, and sodium aluminum silicate; silica sol; glyoxal; and ethyl glycol diacetate. Preferably, the amount of the accelerating agent is added by 5-70 parts by weight of 100 parts by weight of cement. If a cement foam needs to be hardened within several minutes, more accelerating agent should be added, i.e. up to 5-35 parts by weight. If the accelerating agent is added to a cement foam by 5 parts by weight of or less, the cement foam is hardened so slowly that cells being foamed might be defoamed during the casting step. If the accelerating agent is added to a cement foam by 70 parts by weight of or more, however, the cement foam is hardened too quickly even before the casting step is completed so one cannot cast the cement foam in a desired shape and degree. For convenience, aluminum salts, carbonates, glyoxal, and ethylene glycol diacetate are diluted in water before use. In particular, since sodium bicarbonate among carbonates is easily transformed into sodium carbonate, it should be used as quickly as possible. Meanwhile, any kind of silicates can be used as long as it is either dissolved or dispersed homogeneously in water to cause a quick setting reaction to the cement. Preferably used examples of such silicates include one or more of the following: one to four kinds of sodium silicate solutions, sodium silicate powder, sodium silicate, potassium silicate, lithium silicate, and sodium aluminum silicate. Potassium silicate and lithium silicate can provide a cement foam excellent in adhesion and water resistance during the formation of ceramic foams, but are costly. On the other hand, sodium aluminum silicate is relatively cheap, but its adhesion force is somewhat weak because the silica content in the silicate is comparatively smaller than the aluminum content. Moreover, sodium silicate powder is usually dissolved in water by heating, and the dissolving takes a long period of time. Sodium silicate type I (SiO₂/Na₂θ, mole ratio= 2.1-2.3), one of four kinds of sodium silicate solutions, has the viscosity of 100,000 cps which is very high, so water needs to be added to control a slurry state. Unfortunately, this causes adhesion force or bonding strenght to be degraded, and it is very likely to be solidified like ice when construction takes place in winter season, only lowering workability.

Sodium silicate type Il (SiCVNa₂O, mole ratio= 2.4-2.6) contains more silica sol than sodium silicate type I, but its viscosity is still as high as 10,000-50,000 cps overall. Therefore, sodium silicate type Il shows similar disadvantages found in sodium silicate type I. Meanwhile, sodium silicate type III (Si(VNa₂O, mole ratio= 3.15-3.30) is not highly viscous so one can easily control a cement slurry state, and a low price is another merit of sodium silicate type III. Lastly, sodium silicate type IV (SiO₂/Na₂O, mole ratio= 3.4-3.6) can form a large number of silica networks, and has a relatively low viscosity to make it easy to control the cement slurry state. However, its shortcoming is a high unit price. For silica sol (colloidal silica) as the accelerating agent, commercial colloidal silica of 10-110 nm in size, or chemically instable silica sol produced from a reaction between silicate and acid may be prepared on the spot. In case of using a commercial silica sol as the accelerating agent, one can control the hardening or setting rate of a rapid set cement foam, taking advantage of the fact that the smaller particle size increases the setting speed. If a cement foam needs to be set completely within several seconds, silica sol of 10-30 nm in size is preferably used. However, if a cement foam can be set slowly, silica sol of 30-100 nm in size is preferably used. In case of preparing a chemically instable silica sol on the spot by reacting silicate with acid, the resulting mixed solution of acid and silicate should preferably have pH between 2 and 9. If pH of the mixed solution of acid and silicate is too low, cement exhibiting a strong basicity as a strong alkali by nature produces water as it is added and neutralized by the acidic solution, and strength of the resulting cement foam may be impaired substantially. The acidic solution used at this time is preferably a diluted acid that includes, but is not limited to, one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, formic acid, acetic acid, citric acid, maleic acid, and oleic acid. Among them, sulfuric acid, acetic acid, and citric acid are desirably used because they are cheap and can minimize environment contamination. With respect to "lOOparts by weight of water, the amount of an acid to be diluted is preferably 10-75 parts by weight, more preferably 25-50 parts by weight, and most preferably 30-45 parts by weight. If an acid being diluted is at an amount below 10 parts by weight, it takes many hours to obtain a chemically instable silica sol from the reaction between silicate and the acid. On the other hand, if an acid being diluted is at an amount above 75 parts by weight, acidity (or pH) becomes extremely high that silica gel is formed instead of a chemically instable silica sol, which cannot function as an accelerating agent. Next is the step of forming a rapid set cement foam by casting cement slurries directly over walls or injecting them to a mold. That is, cement slurries mixed with an accelerating agent is either injected to a mold, or spread over walls, floors, and/or roofs of a building. Lastly, in the drying step the cement slurries are dried (cured) by a heating device or naturally at room temperature. In the former case, the cement slurries are injected to a mold to form a rapid set cement foam. In the latter case, however, the cement slurries may be casted directly over walls, roofs, and/or roofs of a building. Even when the cement slurries are casted directly over walls of a building for example, a housing can be installed at the walls to function as a mold to which the cement slurries are injected to form rapid set cement foams. In this manner, the rapid set cement foams may have a uniform thickness and increased strength.

In the drying step, cement slurries are mixed with an accelerating agent to form the shape of rapid set cement foams, and moisture in the produced foams is evaporated as quickly as possible without causing any physical transformation in the foams. At the same time, the water dispersible resin contained primarily to improve water resistance is fused onto the surface between cement particles, thereby increasing water resistance and strength.

The drying step can be performed at room temperature, or by using hot wind pre-curing from an oven or UHF (microwaves, so to speak). The drying step at room temperature (that is, natural air drying) is preferably used when a rapid set cement foam is thin, or can be casted directly over a building and left aside for a long period of time. On the other hand, hot wind from an oven and UHF are preferably used to evaporate moisture in rapid set cement foams that are formed by injecting cement slurries to a mold. In case of using UHF for the drying step, 2,450 MHz UHF is irradiated to oscillate polar water molecules and temperature is increased by the oscillation heat energy to dry moisture. This method has a merit in that moisture in an object can be removed at a very high speed. However, in order to dry large rapid set cement foams used as a heat insulating material, a large scale UHF facility is required and it costs a lot to install such a facility. Meanwhile, the drying method using hot wind from an oven is advantageous in that moistures are dried within a short period of time, and installation cost is relatively lower than that of the UHF facility.

Whether the drying method is carried out by using UHF or hot wind, cement foams are preferably dried at a drying temperature of 80-250⁰C, more preferably 90-220⁰C, and most preferably 100-200⁰C. When the cement foams are dried at a heating temperature of 8O⁰C or lower, moisture retained until the cement foam forming step is not removed quickly enough, and it is hard to fuse the water dispersible polymer resin or the micro powder polymer resin added for the improvement of water resistance, not being fused over the surface of the cement. On the other hand, if the cement foams are dried at a heating temperature above 25O⁰C, moisture is evaporated at a high speed, and it is easy to thermally fuse the polymer resin onto the surface of the cement within a short period of time especially because 25O⁰C is above the melting point of the micro powder polymer resin. However, there is a drawback to this method in that physical properties of the polymer are changed at high temperature. Preferred examples of the present invention will now be described in detail.

Embodiment 1 An animal foaming agent (manufactured by Hankuk Industry Co., Ltd., Korea) was added at an amount of 2% of water to prepare 1 liter of an aqueous foam solution by using a Homomixer. To the solution is added a mixture of 50Og of ordinary portland cement (manufactured by Hanil Cement Co., Ltd., Korea), 1.5kg of silicate powder (No. 5), 2Og of blast-furnace slag powder, and 1g of a naphthalene based admixture to obtain a cement slurry. Next, 5Og of waterglass type III (manufactured by Youngil Chemical Co., Ltd., Korea) was added as an accelerating agent (or rapid-setting admixture) and homogeneously blended together with the cement slurry. The resulting mixture is injected immediately to a mold, so as to form cement foams that were hardened at room temperature.

Embodiment 2

A vegetable foaming agent (product name: Informer, manufactured by Hanilcon Corporation) was added at an amount of 2% of water to prepare 1 liter of an aqueous foam solution by using a Homomixer. To the solution is added a mixture of 50Og of ordinary portland cement (manufactured by Hanil Cement Co., Ltd., Korea), 1.5kg of silicate powder (No. 5), 2Og of blast-furnace slag powder, and 1g of a naphthalene based admixture to obtain a cement slurry. Next, 100g of sodium bicarbonate was added as an accelerating agent and homogeneously blended together with the cement slurry. The resulting mixture is injected immediately to a mold, so as to form cement foams that were hardened at room temperature.

Embodiment 3 An animal foaming agent (manufactured by Hankuk Industry Co., Ltd., Korea) was added at an amount of 2% of water to prepare an aqueous foam solution by using a cell (bubble) generating device. To the solution is added a mixture of 50Og of ordinary portland cement (manufactured by Hanil Cement Co., Ltd., Korea), 1.5kg of silicate powder (No. 5), 2Og of blast-furnace slag powder, 2Og of epoxy resin (product name: KEM-128-70, manufactured by Kukdo Chemical Co., Ltd.) as a water-resistance reinforcing agent, and 1g of a naphthalene based admixture to obtain a cement slurry. Next, 100g of colloidal silica (product name: YGS-20, manufactured by Youngil Chemical Co., Ltd., Korea) was added as an accelerating agent and homogeneously blended together with the cement slurry. The resulting mixture is injected immediately to a mold, so as to form cement foams that were hardened at room temperature.

Embodiment 4

An animal foaming agent (manufactured by Hankuk Industry Co., Ltd., Korea) was added at an amount of 2% of water to prepare an aqueous foam solution by using a cell (bubble) generating device. To the solution is added a mixture of 50Og of ordinary portland cement (manufactured by Hanil Cement Co., Ltd., Korea), 1.5kg of silicate powder (No. 5), 2Og of blast-furnace slag powder, 2Og of epoxy resin (product name: KEM-128-70, manufactured by Kukdo Chemical Co., Ltd.) as a water-resistance reinforcing agent, and 1g of a naphthalene based admixture to obtain a cement slurry. Next, waterglass type III (manufactured by Youngil Chemical Co., Ltd., Korea) and 50% sulfuric acid were mixed to produce a chemically instable colloidal silica with pH of 3.5, and the colloidal silica was homogeneously blended together with the cement slurry. The resulting mixture is injected immediately to a mold, so as to form cement foams that were heated and hardened for 3 hours in a 100⁰C oven.

Embodiment 5

An animal foaming agent (manufactured by Hankuk Industry Co., Ltd., Korea) was added at an amount of 2% of water to prepare an aqueous foam solution by using a cell (bubble) generating device. To the solution is added a mixture of 50Og of high-early-strength portland cement (manufactured by Hanil Cement Co., Ltd., Korea), 80Og of silicate powder (No. 5), 50Og of fly ash, 20Og of fume silica, 2Og of blast-furnace slag powder, 2Og of fiber (purchased from Dyntex Korea) as a strength reinforcing agent, 2Og of latex, a copolymer of butadiene and styrrene (product name: KTR 101, manufactured by Kumho Petrochemical, Korea), and 1g of a naphthalene based admixture to obtain a cement slurry. Next, waterglass type III (manufactured by Youngil Chemical Co., Ltd., Korea) and 50 parts by weight sulfuric acid were mixed to produce a chemically instable colloidal silica with pH of 3.5, and the colloidal silica was homogeneously blended together with the cement slurry. The resulting mixture is injected immediately to a mold, so as to form cement foams that were dried and hardened for 30 minutes in a microwave oven.

Comparative Example 1

50Og of ordinary portland cement (manufactured by Hanil Cement Co., Ltd., Korea), 1.5kg of silicate powder (No. 5), 2Og of blast-furnace slag powder, and 1g of a naphthalene based admixture were blended together to obtain a cement slurry. The cement slurry was then injected to a mold, and left aside at room temperature to be hardened. (The addition of an accelerating agent is omitted.)

Comparative Example 2

An animal foaming agent (manufactured by Hankuk Industry Co., Ltd., Korea) was added at an amount of 2% of water to prepare 1 liter of an aqueous foam solution by using a Homomixer. To the solution is added a mixture of 50Og of ordinary portland cement (manufactured by Hanil Cement Co., Ltd., Korea), 1.5kg of silicate powder (No. 5), 2Og of blast-furnace slag powder, and 1g of a naphthalene based admixture to obtain a cement slurry. The cement slurry was then injected to a mold, so as to form cement foams that were hardened at room temperature.

Table 1 below shows test results on the effects of cement foams that were prepared by Examples 1-5 and Comparative Examples 1-2, respectively. Particularly, the rapid set cement foams prepared by Examples formed a large number of micro closed cell structures excellent in water resistance despite that they did not go through other processings, but were only hardened at high speed with the help of an accelerating agent. For a water-resistance test, the rapid set cement foams were deposited in water for a 30-day period of time as shown in Fig. 2 to check if they float on the water.

[Table 1]

As apparent from Table 1 , the cement structure without foams prepared according to Comparative Example 1 did not have insulation and soundproofing effects, and was sunk in the water right away, demonstrating no water-resistance. Meanwhile, the cement structure with micro foams prepared according to Comparative Example 1 failed to maintain the foamed state even though it went though the foaming process because silica with a large specific weight and the cement moved in a downward direction due to gravity during the setting process after a lapse of 8 hours of initial setting. Therefore, as shown in Table 1 above, the insulation performance was degraded and the cement structure was sunk immediately when put in the water. On the contrary, the cement foams prepared by Examples of the present invention were hardened completely with the addition of an accelerating agent before cement slurries thereof were defoamed, so a large number of micro closed cell structures were provided even at room temperature, and the cement slurries were kept from running down even during construction, making them suitable for the direct casting method over walls or roofs of a building. In addition, they mostly showed superior compressive strengths to those of the Comparative Examples, and were excellent in insulation performance. From the density comparison, it is learned that there are a lot of air spaces (cells) inside the rapid set cement foams, and such air spaces contributed to the improvement in soundproofing effects and insulation performance, respectively. Moreover, based on the test results on floating on the water over a period of 30 days, it is verified that the cement structure according to the Examples of the present invention have outstanding water resistance. While the present invention has been illustrated and described in connection with the accompanying drawings and the preferred embodiments, the present invention is not limited thereto and is defined by the appended claims. Therefore, it will be understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the invention defined by the appended claims.

Claims

[CLAIMS] [Claim 1 ]

A rapid set cement foam, comprising: an aqueous solution including water and a foaming agent; cement mixed with the aqueous foam solution to be foamed into a slurry state by a foam system; and an accelerating agent mixed with the cement slurry.

[Claim 2]

The rapid set cement foam according to claim 1, further comprising: silica and/or ceramic powder added to the aqueous foam solution together with the cement.

[Claim 3]

The rapid set cement foam according to claim 1 or claim 2, further comprising: a sound absorbent functioning as a strength reinforcing agent.

[Claim 4]

The rapid set cement foam according to claim 3, wherein the sound absorbent is selected from natural fibers including cellulose based fiber, staple or filament type protein based fiber, and mineral based fiber; and man-made fibers including regenerated fiber, semi-synthetic fiber, synthetic fiber, metal fiber, glass fiber, rock fiber, slag fiber, and carbon fiber.

[Claim 5]

The rapid set cement foam according to claim 4, wherein the sound absorbent is a fiber having a thickness of 3-50 μm.

[Claim 6] The rapid set cement foam according to claim 4, wherein the sound absorbent is a fiber having a length of 1-50 mm.

[Claim 7]

The rapid set cement foam according to claim 4, wherein the sound absorbent is added at an amount of 1-20 parts by weight with respect to 100 parts by weight of silica and ceramic powder.

[Claim 8]

The rapid set cement foam according to claim 1 or claim 2, further comprising: a water-resistance reinforcing agent containing a water dispersible polymer resin for improvement of water resistance.

[Claim 9]

The rapid set cement foam according to claim 8, wherein the water-resistance reinforcing agent contains a water dispersible polymer resin selected from acryl, vinyl acetate, alkyd, melamine resin, solution styrene butadiene rubber, epoxy resin, and polyurethane.

[Claim 10]

The rapid set cement foam according to claim 1 or claim 2, wherein the aqueous solution is a mixture of a foaming agent added by 0.1-10 parts by weight with respect to 100 parts by weight of water.

[Claim 11] The rapid set cement foam according to claim 1 or claim 2, wherein the cement which is used singly or in mixture selected from: Portland cements including ordinary portland cement, moderate heat portland cement, high-early-strength Portland cement, sulphate resistant portland cement, white portland cement, oil well cement, and colloid cement; mixed cement including blast-furnace cement, fly ash cement, silica cement, super-low-heat cement, geothermal well cement, RCCP cement; alumina cement; ultra-rapid setting cement; and GRC low alkali cement.

[Claim 12]

The rapid set cement foam according to claim 1 or claim 2, wherein the cement is added at an amount of 25-80 parts by weight with respect to 100 parts by weight of water.

[Claim 13]

The rapid set cement foam according to claim 1 or claim 2, wherein the ceramic powder is selected from the group consisting of: elvan, loess stone, olivine, kaolin, silica minerals, magnesite, bauxite, bentonite, pumice, borate, serpentine, acid clay, iron oxide, garnet, carbonate minerals, attapulgite, sepiolite, nephrite, apatite, illote-mica, feldspar, pearlite, vermiculite, zeolite, barite, talc, diatomaceous earth, graphite, hectorite, clay minerals, zirconium minerals, titanium minerals, tourmaline, fume silica, aerogel, sly ash, and blast-furnace slag powder, which are used singly or in mixture.

[Claim 14]

The rapid set cement foam according to claim 1 or claim 2, further comprising: a viscosity control to make the viscosity fall within 5,000-200,000 cps.

[Claim 15] The rapid set cement foam according to claim 1 or claim 2, wherein the accelerating agent is used singly or in mixture selected from: aluminum salts including aluminum sulfate, aluminum chloride, aluminum nitrate, and aluminum acetate; carbonates including sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, sodium carbonate, potassium carbonate, ammonium carbonate, and potassium carbonate; silicates including one to four kinds of sodium silicate solutions, sodium silicate powder, sodium silicate, potassium silicate, lithium silicate, and sodium aluminum silicate; silica sol; glyoxal; and ethyl glycol diacetate.

[Claim 16] The rapid set cement foam according to claim 1 or claim 2, wherein the accelerating agent is added at an amount of 5-70 parts by weight with respect to 100 parts by weight of cement.

[Claim 17]

The rapid set cement foam according to claim 1 or claim 2, further comprising: an admixture mixed with the foam cement.

[Claim 18]

A method for preparing a rapid set cement foam, comprising: a step for foaming an aqueous foam solution obtained by dissolving a foaming agent in water; a step for forming a cement slurry by mixing a foam and cement; a step for adding an accelerating agent to the cement slurry; and a step for forming a rapid set cement foam by casting the cement slurry mixed with additives into a mold or over walls of a building.

[Claim 19] The method according to claim 18, wherein the step for forming cement slurry further comprises: a process for mixing silica and/or ceramic powder with cement.

[Claim 20]

The method according to claim 18, wherein the step for forming cement slurry further comprises: a process for adding a sound absorbent functioning as a strength reinforcing agent or a water resistance reinforcing agent as additives.

[Claim 21]

The method according to claim 18, wherein the step for foaming is carried out in a foam system operating by a foaming method that uses rotary wings of a mixer, a dissolver, or a Homomixer, or by using a foamation device that is equipped with a compressor.

[Claim 22]

The method according to claim 18, wherein the step for forming cement slurry is achieved by blending cement singly or a mixture of cement, ceramic powder, and silica with a foam.

[Claim 23]

The method according to claim 18, further comprising: a step for drying the rapid set cement foam after the step for forming a rapid set cement foam.

[Claim 24]

The method according to claim 23, wherein the step for drying the rapid set cement is carried out at room temperature, using hot wind, or using UHF.

[Claim 25] The method according to claim 23, wherein the step for drying the rapid set cement is carried at a temperature of 80-250⁰C by using hot wind or UHF.