KR102260810B1 - Mid to longterm strength-enhancing accelerator composition for shotcrete - Google Patents

Abstract

The present invention relates to a strength-enhancing accelerator composition to be mixed with shotcrete, wherein the strength-enhancing accelerator composition is formed by mixing a rapid hardening agent in which calcium aluminate, metakaolin, and aluminum sulfate are mixed, a calcium sulfoaluminate expanding agent, a cellulose-based thickener, blast furnace slag, and a silica fume composite enhancer. According to the present invention, a strength-enhancing characteristic which is an essential characteristic basically required for shotcrete is not degraded, and degradation of medium and long term strength, which is a continuous side effect of an existing strength-enhancing accelerator for shotcrete, can be drastically reduced.

Description

A quick-setting composition for medium to long-term strength-increasing shotcrete {MID TO LONGTERM STRENGTH-ENHANCING ACCELERATOR COMPOSITION FOR SHOTCRETE}

The present invention relates to a quick-setting composition to be mixed with shotcrete, and a quick-setting agent in which calcium aluminate, metakaolin and aluminum sulfate are mixed, a calcium sulfoaluminate expanding agent, a cellulose-based thickener, a blast furnace slag and silica fume complex It is composed of a mixture of enhancers.

Shotcrete is concrete that is poured by spraying fluidized concrete at high pressure on the construction surface, such as inside a tunnel or on a steep slope, and is used as a support hole for the tunnel excavation surface or a protection hole for a steep slope. Patent No. 1431575 may be mentioned.

As for shotcrete, fluidized concrete is prepared by mixing cement, aggregate, and water just like conventional concrete. However, the fluidized concrete is pumped through a spraying device and a rapid setting agent is added immediately before spraying on the construction surface to achieve rapid hardening and strength development. constructed in a guided manner.

In such shotcrete, various functional agents are added to the above-mentioned rapid setting agent in order to satisfy the specific construction conditions and required performance. An expanding agent and initial strength to suppress the shrinkage and crack formation of the hardened shotcrete caused by the rapid setting action of the rapid setting agent Various admixtures may be added for the purpose of securing.

In particular, shotcrete not only needs to be smoothly transported through the pressure-feeding pipe in the injection device, but also needs to quickly and densely penetrate into irregular construction surfaces such as tunnel excavation surfaces and complex pouring spaces pre-arranged. In addition, considerable fluidity is also required, so a large amount of air entraining agent is added at the time of minimum mixing before adding quick setting.

As such, shotcrete needs to satisfy complex requirements that require rapid hardening, initial strength development, and sufficient fluidity. Various additives are applied. As a result, the basic performance of shotcrete, such as rapid hardening and workability, is improved, but after pouring, The medium-to-long-term strength that is continuously increased or maintained after curing is in progress or curing is completed is a situation in which the strength is markedly deficient compared to other concrete.

Nevertheless, interest in the mid- to long-term strength of shotcrete was negligible due to the urgency of constructing support and protection works for both temporary and permanent structures, such as tunnels and steep slopes, As it is a major consumer of , attempts to develop technology to improve the mid- to long-term strength of shotcrete are also insignificant.

However, in the construction of tunnels or steep slopes, the required construction precision is improved, and as the simplification of support or protection work is continuously required while maintaining structural performance, the medium- and long-term strength improvement of the shotcrete structure and its use as a permanent structure are demanded. is continuously increasing.

The present invention was devised in view of the above problems, and as a quick-setting composition for shotcrete, a quick-setting agent in which calcium aluminate, metakaolin and aluminum sulfate are mixed, an expanding agent having a weight of 10% of the weight of the quick-setting agent, and a quick-setting agent A thickener by weight of 5% of the weight and an enhancer by weight of 5% by weight of the fast economy are mixed to form a quick setting agent, wherein the expanding agent is calcium sulfoaluminate, the thickener is a cellulose-based thickener, and the enhancer is a blast furnace In the mid- to long-term strength-increasing type shotcrete quick-setting composition comprising a mixture of slag and silica fume, calcium stearate of 0.2% of the weight of the quick-setting agent is added as an antifoaming agent to the rapid setting agent for medium- and long-term strength increasing type shotcrete It is a quick-setting composition.

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Through the present invention, it is possible to remarkably reduce the mid-to-long-term strength decrease, which is a chronic side effect of the conventional quick-setting for shotcrete, without causing a decrease in quick-setting property, which is an essential characteristic required for shotcrete.

By maintaining the quick-setting properties of the shotcrete, the performance of the shotcrete as a short-term immediate support is stably secured, and at the same time, the workability of the construction target structures such as tunnels and the Not only can workability be secured, but the shotcrete hardened body can be used as a permanent structure or a reinforcing structure, thereby enabling efficient process management for the construction of the structure and improving the structural stability and durability of the finished structure. .

1 is a view showing the compressive strength of shotcrete applied to the present invention by age;
Figure 2 shows the compressive strength of the antifoaming agent applied shotcrete according to the antifoaming agent content of the present invention;

The detailed configuration of the present invention and the operation of each configuration will be described as follows.

The quick-setting composition of the present invention includes a quick-setting agent that imparts quick-setting properties to shotcrete, an expanding agent that suppresses shrinkage that may be caused by the quick-setting action of the quick-setting agent, and a thickener that prevents material separation by securing the viscosity of the shotcrete mixture and an enhancer that enhances the medium and long-term strength of the shotcrete hardened body.

In addition, an air entraining agent added to increase the fluidity of the shotcrete or an antifoaming agent for removing bubbles that may be caused by the thickener may be added.

The quick-setting agent is a factor that accounts for most of the components of the quick-setting agent of the present invention, and gives quick-setting properties, which is a basic function of the quick-setting agent for shotcrete. In the present invention, the quick-setting agent is basically a fine powder containing an aluminum compound, aluminum trioxide It is composed of a mixture of the base powder formulation and aluminum sulfate.

First, among the quick-setting components of the present invention, the aluminum trioxide-based powder formulation is composed of calcium aluminate and metakaolin. Calcium aluminate is a mineral composed of calcium oxide and aluminum trioxide, and is It has the property of rapidly setting while forming a hydrated hardening body when mixed. Metakaolin is also a finely powdered clay mineral containing aluminum trioxide. It is composed of amorphous silica and aluminum trioxide. to accelerate the curing of

In particular, when mixed with shotcrete, amorphous silica, the main component of metakaolin, is dissolved, and the reaction of cement in shotcrete is accelerated. At the same time, as silica reacts with calcium hydroxide in cement, calcium silicate hydrate in fine fibers is formed. By filling the pores in the shotcrete, the initial strength of the shotcrete is improved, and the medium and long-term strength is also increased by densifying the structure of the hardened shotcrete.

That is, calcium aluminate and metakaolin, which are aluminum trioxide-based powder formulations constituting the rapid setting agent of the present invention, each individually perform the function of accelerating the hardening of cement, and at the same time have excellent fast setting properties, but lower long-term strength Metakaolin works in a way that complements the properties of calcium aluminate that can cause

In general, in the case of a single agent or single agent-driven rapid economy, it is a common belief that a formulation with an early expression of strength lacks long-term strength, and a formulation with excellent long-term strength has a relatively insufficient initial strength. In the present invention, as a fast economy, a variety of formulations are mixed, and the conventional wisdom as described above cannot be applied without modification.

Therefore, as described above, even if the basic mechanism by which calcium aluminate and metakaolin share the initial strength and long-term strength enhancement, respectively, was established, the content of each component performs the originally planned function quantitatively and linearly. It cannot be determined that

In addition, aluminum sulfate, which is a component of the quick-setting agent of the present invention, also has the property of accelerating the hardening of cement by accelerating the formation of ettringite. In particular, it has a function as an alkali stimulant for slag, which will be described later. do.

However, due to the addition of aluminum sulfate, the composition of a sulfate environment may be caused in the process of curing and using the shotcrete as a structure, although slightly, this may adversely affect the durability of the shotcrete structure. For the purpose of securing durability in a sulfate environment As in the case of calcium aluminate cement that has been developed, calcium aluminate, which can be said to be the main component of rapid economics among the rapid setting agents of the present invention, can sufficiently secure the chemical resistance to sulfate of the shotcrete structure to which the present invention is applied. can

After all, calcium aluminate, metakaolin, and aluminum sulfate, which constitute the quick-setting agent of the present invention, not only promote individual curing, but also perform complementary functions in long-term strength expression and durability assurance. Exhibits excellent fast setting, but metakaolin compensates for the lack of long-term strength of calcium aluminate at the same time as tissue densification, and aluminum sulfate induces long-term strength expression of slag, which will be described later, but calcium aluminate may be caused by aluminum sulfate. In a way to prevent deterioration of chemical resistance, the action of each component is organically combined to perform an optimal function in terms of quick-setting and initial strength expression as well as securing long-term strength and durability.

On the other hand, if excessive shrinkage occurs in the rapid process of shotcrete, drop-off of the sprayed shotcrete or cracks in the hardened shotcrete result. In order to suppress the shrinkage action that may be caused by the quick-setting action of the rapid economy as described above, It is necessary to incorporate a swelling agent, and in the present invention, calcium sulfoaluminate is applied as a swelling agent.

Calcium sulfoaluminate not only forms a hydration hardening body by itself, but also exerts an expansion effect in the reaction process to compensate for the shrinkage accompanying hardening, thereby suppressing the drop-off phenomenon and cracking caused by excessive shrinkage of the shotcrete.

In addition, in the present invention, as described above, in addition to securing mid-to-long-term strength through the organic complex and mutually complementary action of quick-economy components, the medium-to-long-term strength enhancing effect is achieved through improvement of the physical structure of the shotcrete structure.

That is, by adding a thickener, an enhancer, and an antifoaming agent to the rapid setting agent of the present invention having the above-described rapid economy and expanding agent as main components, the structural properties of the cured shotcrete structure are improved, and at the same time, strength enhancement in the medium to long term is induced.

First of all, the thickener added to the quick setting agent gives viscosity to the shotcrete mixture within the range that does not impair fluidity, handling convenience, and diffusivity on the spraying surface during the pressure feeding process in the injection device of shotcrete, thereby reducing the concentration of aggregates and materials. To prevent separation, in the present invention, a fine powdered cellulose-based preparation is applied.

As the cellulosic thickener of the present invention, hydroxypropylmethylcellulose (HPMC, Hydroxy Propyl Methyl Cellulose), methylethylhydroxyethylcellulose (MEHEC, Methyl Ethyl Hydroxy Ethyl Cellulose), or a mixture thereof is applied.

These hydroxypropylmethylcellulose and methylethylhydroxyethylcellulose are powder formulations with excellent preservation and stability, and can be uniformly dispersed in the water contained in shotcrete, and exhibit a stable thickening effect without causing side reactions.

However, when these cellulose-based thickeners are applied, bubbles may be generated to form fine cavities in the shotcrete hardened body tissue, but this can be effectively suppressed by adding an antifoaming agent, which will be described later.

In addition, in the present invention, in order to supplement the medium and long-term strength of the hardened shotcrete, a powdery enhancer is added as a configuration that maintains a long-term hardening reaction at the same time as the densification of the physical tissue structure. As the enhancer, fine blast furnace slag powder and silica fume are applied.

Blast furnace slag is a by-product generated in the process of separating pig iron from iron ore in a blast furnace, which is a blast furnace. Its main components are silicon dioxide, aluminum trioxide, calcium oxide, and magnesium oxide. It is a glassy calcium aluminosilicate with a base.

Blast furnace slag also performs the same hardening action as cement. Unlike cement clinker mineral, which undergoes a hydration reaction immediately upon contact with water, blast furnace slag does not show immediate hydraulic property even when in contact with water. It has latent hydraulic properties indicating hydraulic properties.

In particular, such latent hydraulic blast furnace slag not only exhibits hydraulic properties without continuous supply of an alkali stimulant after the alkali atmosphere is created by the alkali stimulant, but also has a characteristic of sustaining a hydration reaction for a long time, thereby increasing the strength of the hardened body over a long period of time.

Therefore, by applying the blast furnace slag to the quick setting agent of the present invention, the medium and long-term strength of the shotcrete hardened body can be continuously increased, and through this chemical reinforcing property, as well as the unique dispersibility of the blast furnace slag fine powder, Since uniform diffusion is possible, the tissue compactness of the hardened shotcrete body can also be improved, so that chemical reinforcement and physical reinforcement effects can be obtained at once.

On the other hand, in the present invention, as the alkali stimulator of the blast furnace slag, aluminum sulfate, which is a component of the rapid economy, can be applied. Therefore, there is no need to add a separate alkali stimulant, and therefore, in the rapid setting agent of the present invention, aluminum sulfate is At the same time, it behaves as a latent hydraulic stimulant of blast furnace slag.

Silica fume, which is applied as an enhancer of the present invention together with blast furnace slag, is a by-product that is generated in the form of gas in an electric furnace during the production of ferrosilicon, etc. and then collected as a kind of high-purity fine powder amorphous. Silica, which forms a hardened body through the pozzolan reaction accompanying the cement hydration reaction, and has fine particle properties superior to that of cement particles, fills the pores formed by free water in concrete including shotcrete form a structure

In particular, silica fume provides high watertightness, leaching resistance and water inseparability to shotcrete before and after curing by closing fine pores through the unique permeability and diffusivity derived from the fine powder phase. The leaching resistance and inseparability in water not only enhance the medium and long-term strength of the shotcrete hardened body, but also reduce environmental pollution including groundwater contamination and soil contamination during construction and curing processes.

In addition, the pozzolan reaction of silica fume is independently performed without the intervention of an irritant, unlike the latent hydraulic-based hydration reaction of blast furnace slag, and is performed simultaneously with the pouring of shotcrete. In the initial stage of pouring, it actively reacts with free water in the inter-particle voids to form a tightly closed solid body, which can dramatically improve the leaching resistance and inseparability of shotcrete in water, thereby leaching groundwater. Stable and rapid construction is possible even in underwater or semi-underwater construction conditions such as flooded areas or flooded areas.

On the other hand, as described above, the thickener among the quick-setting components of the present invention can form bubbles when mixed with shotcrete. In the present invention, a trace amount of an antifoaming agent is added to suppress bubbles and secure the compactness of the shotcrete hardened body. As such an antifoaming agent, calcium stearate, which is easy to store and handle, is stable in chemical aspects such as side reactions, and is easily miscible with the components of shotcrete including cement, is applied as a calcium salt.

The antifoaming agent of the present invention can express a sufficient effect even when a relatively small amount is mixed compared to other components, and it not only suppresses the bubble generation by the above-described thickener, but also is required at the initial stage of pressurization, spraying and pouring of shotcrete. In order to express a high degree of fluidity, it is also possible to effectively control the mid- to long-term strength reduction caused by the air entraining agent that is generally mixed during the initial mixing of shotcrete.

That is, air entrainment in order to provide high fluidity due to the nature of the work of shotcrete, which must penetrate in various directions regardless of the direction of gravity between irregular construction surfaces or pre-reinforced reinforcement after being sprayed at high pressure via the pressure feeding pipe of the injection device. Since it is common to apply an agent, the bubbles formed thereby remain even after curing of the shotcrete and have no choice but to erode the tissue compactness and mid-to-long-term strength of the hardened shotcrete. In the present invention, calcium stearate is added as an antifoaming agent, which is Not only the possible side effects, but also the side effects caused by the air entrainment agent can be eliminated at once.

In particular, the defoaming action by calcium stearate does not proceed rapidly, but progresses gradually and continuously throughout the curing process, so it does not cause an immediate and serious decrease in the fluidity required at the initial stage of press-feeding, spraying and pouring of shotcrete. Since calcium stearate exhibits a significant lubricating effect, it is possible to compensate for the decrease in the fluidity of shotcrete due to the defoaming action, so that it is possible to stably maintain workability and permeability required for shotcrete.

As such, the quick setting agent of the present invention is a fast-setting agent in which various kinds of quick-setting minerals are combined, an expanding agent that compensates for the contraction caused by the quick-setting agent, a thickener that suppresses material separation, and an enhancer that performs a long-lasting coagulation reaction and tissue densification and an antifoaming agent that removes air bubbles in the tissue. In the present invention, these components are not simply mixed, but are organically combined to complement each other.

That is, as described above, metakaolin compensates for the shortcomings of calcium aluminate, which may cause a decrease in long-term strength, although excellent in quick-setting among the quick-setting components, and aluminum sulfate is a stimulant of slag in the enhancer at the same time as its rapid-setting itself. Calcium aluminate compensates for the weakness of aluminum sulfate, which is the decrease in durability, and each component faithfully performs its unique individual action while at the same time complementing the deficiencies of other components. It is possible to solve the mid-to-long-term lack of strength, which is a chronic problem of conventional shotcrete, while sufficiently maintaining the formation and workability.

The rapid setting composition for shotcrete of the present invention can perform an appropriate function and exhibit a desired effect through appropriate mixing of each of the above-mentioned components, and the present invention consisting of a fast-acting agent, a swelling agent, a thickener, an enhancer and an antifoaming agent, etc. The rapid setting agent is a fine powder formulation, and each of the above components is also applied in the form of a fine powder formulation, thereby securing convenience in storage and handling, as well as convenience in mixing with shotcrete.

In the present invention, as for the amount of the quick setter for shotcrete in which water, cement, fine aggregate and coarse aggregate are blended, it is preferable to use a quick setter with a weight of about 7% of the weight of the cement, similar to the amount used for general quick setter for shotcrete.

In addition, in the present invention, the composition ratio of the quick-setting agent, the expanding agent, the thickener, and the enhancer constituting the quick-setting agent is set according to the function of each element, as in a quick-setting hardening body such as general shotcrete or grout, the setting action of the quick-setting agent It is preferable to apply 5% to 15% of the weight of the expansion agent to compensate for the shrinkage accompanying the rapid economy.

In the composition ratio of the quick-setting agent and the expansion agent in the rapid setting agent of the present invention, when an expanding agent having a weight of less than 5% of the weight of the quick-setting agent is mixed, drop-off and shrinkage cracks may occur due to excessive shrinkage of the cured shotcrete, and 15 of the weight of the quick-setting agent When an expanding agent having a weight exceeding % is mixed, expandable deformation and insufficient strength may occur due to excessive expansion of the cured shotcrete body.

The thickener in the quick setting of the present invention increases the mid- to long-term strength by improving the tissue compactness by suppressing the separation or bias of each material including the aggregate of the shotcrete, and the thickener in the quick setting of the present invention fills unnecessary voids in the shotcrete and lasts for a long time. As to increase the mid-to-long-term strength by inducing a coagulation action, as a result, it is to compensate for the mid-to-long-term strength decrease accompanying the quick-setting reaction of the quick-setting reaction.

That is, the mixing amount of the thickener and enhancer in the rapid setting agent of the present invention follows the content of the rapid setting agent in the rapid setting, but unexpected side reactions may occur when excessive mixing, so both the thickener and the enhancer weight 2% to 8% of the weight of the rapid setting agent It is preferable to mix with

On the other hand, as described above, as the thickener in the present invention, hydroxypropylmethylcellulose or methylethylhydroxyethylcellulose may be applied as a fine powdered cellulose-based preparation, and these two types of cellulose-based preparations may be applied separately Of course, they may be mixed, and in the Examples to be described later, fine powdered hydroxypropylmethylcellulose and methylethylhydroxyethylcellulose were mixed in the same weight ratio to constitute a thickener.

In addition, in the enhancer, the mixing ratio of fine blast furnace slag powder, which induces a long-lasting hydration reaction, and silica fume, which expresses initial and mid-long-term strength, can be adjusted according to site conditions and required performance. Silica fume was mixed in an equal weight ratio to constitute an enhancer.

As described above, Sokkyung, which occupies the largest proportion of the quick-setting composition of the present invention, is composed of two types of aluminum trioxide powder and aluminum sulfate powder composed of calcium aluminate and metakaolin, and each of these powder formulations is individually prepared. Since it has rapid hardening, it is possible to secure the quick setting of the minute unit time, which is the basic performance factor of shotcrete. Therefore, it is possible to set the compounding ratio with a wide range of fluctuations for the above three types of powder formulations, but Calcium aluminate 40% by weight, metakaolin 40% by weight and aluminum sulfate to ensure the leading function of calcium aluminate for expression and a mechanism to compensate for the mid-to-long-term strength decrease due to calcium aluminate through metakaolin 20% by weight was set as the basic composition ratio, and the composition ratio of these three components was slightly changed in the experiment to be described later, and the presence or absence of an adverse reaction according to the composition ratio change was confirmed.

The formulation of the shotcrete to which the rapid setting agent of the present invention is applied is shown in Table 1 below, and in each experiment conducted while varying the composition of the rapid setting agent, the rapid setting agent was applied to the shotcrete of the same mixing ratio.

Shotcrete mixing ratio Water-cement ratio (%)
W/C Fine bone ratio (%)
S/(S+G) Consumption (kg/㎥) quick payment W (water) C (cement) S (fine aggregate) G (coarse aggregate) 47.5 59.7 190 400 1027 694 C×0.07

In the shotcrete formulation, ordinary Portland cement was used as cement (C), and washing sand and crushed stone with a particle diameter of 13 mm or less were applied as fine aggregate and coarse aggregate, respectively. 7% was added, so the unit usage, which is the amount of quick settling per 1m3 of shotcrete, is 28 kg.

First, in order to check whether the quick setting properties, which is the basic performance of the quick setting agent for shotcrete, are suitable, the quick setters having different composition ratios of calcium aluminate, metakaolin and aluminum sulfate constituting the quick setting in the quick setting were used as shown in Table 1 above. The setting time was measured by putting it into the shotcrete, and the setting time measurement was started immediately after the rapid setting of 7% of the weight of the cement (C) in the shotcrete was added and mixed.

The control group consisted of a rapid setting agent by mixing 10% by weight of the weight of Sokkyung and Sokkyung, but did not add any additional agents such as thickeners or enhancers, and Sokkyung was made of calcium aluminate, metakaolin or aluminum sulfate. It was applied alone.

The experimental group consisted of a quick-setting agent by mixing a fast-setting agent at 10% by weight of the weight of Sokkyung, a thickening agent of 5% by weight of the weight of Sokkyung, and an enhancer of 5% by weight of the weight of Sokkyung, calcium aluminate, The composition was composed by mixing metakaolin and aluminum sulfate, but by varying the composition ratios of these calcium aluminate, metakaolin and aluminum sulfate, an experimental group of a total of four composition ratios was established.

Calcium sulfoaluminate was applied as a swelling agent in both the control group and the experimental group, and the thickener of the experimental group was prepared by mixing the above-mentioned fine powdered hydroxypropylmethylcellulose and methylethylhydroxyethylcellulose in the same weight ratio. The enhancer of the experimental group was prepared by mixing fine blast furnace slag powder and silica fume in fine powder form in the same weight ratio.

The three control quick setters and the four experimental groups set in this way were put into shotcrete formulated as shown in Table 1 above, mixed, and the setting time was measured, and the results are shown in Table 2 below.

Shotcrete setting time division Quick setting (inject 7% of the weight of shotcrete cement) Condensation time (minutes:seconds) Content (wt%) in Sokkyungjae Mixed amount (wt%) compared to Sokkyungjae
sequel
closing calcium aluminium
Nate meta
kaoline sulfuric acid
aluminum
swelling agent
thickener
enhancer control group 1 100 - - 10 - - 3:50 12:43 control group 2 - 100 - 10 - - 4:03 13:27 control group 3 - - 100 10 - - 4:09 13:19 Experimental group 1 40 40 20 10 5 5 4:15 13:53 Experimental group 2 50 30 20 10 5 5 4:11 13:34 Experimental group 3 30 50 20 10 5 5 4:08 13:42 Experimental group 4 45 45 10 10 5 5 4:21 13:51

As shown in Table 2, in both the control and experimental groups, the initial setting time was measured within 5 minutes and the termination time was measured within 15 minutes, and it was confirmed that the basic performance of the quick setting as a shotcrete quick-setting agent was satisfactory.

As such, the rapid setting agent of the present invention in which calcium aluminate, metakaolin, and aluminum sulfate are mixed, calcium sulfoaluminate expanding agent, cellulose-based thickener, blast furnace slag and silica fume mixing enhancer is combined. It can be confirmed that the performance is expressed, and it can be seen that the quick setting property is comparable to that of a conventional quick-setting agent in which a single formulation quick-setting agent and an expanding agent are mixed.

In order to confirm the initial strength and mid- to long-term strength of the quick-setting agent of the present invention, a number of specimens were prepared for each control group and experimental group in Table 2, and then a uniaxial compressive strength test according to the lapse of curing time was performed.

The uniaxial compressive strength test was conducted on a φ100×200mm cylindrical specimen, and for the curing of the cylindrical specimen, 20℃ underwater curing was applied until 7 days of age, and dry curing was applied after 7 days of age.

For the uniaxial compressive strength test, for each of the three control groups and the four experimental groups in Table 2, after sufficiently producing a large number of columnar specimens, the age of 3 hours, 1 day, 3 days, 7 days, 28 days and 90 days was carried out, and the uniaxial compressive strength was measured by selecting two specimens for each of the control group and the experimental group at the age of the test target, and the results are shown in Table 3 and FIG. 1 below.

uniaxial compressive strength of shotcrete division Uniaxial compressive strength (kgf/㎠): average ± average deviation of 2 specimens 3 hours 1 day 3 days 7 days 28 days 90 days control group 1 107.62±3.92 180.75±2.98 214.52±4.02 258.34±1.84 338.12±4.77 364.71±3.92 control group 2 104.29±4.31 161.60±5.04 204.58±3.71 248.29±5.08 350.94±2.33 372.43±2.11 control group 3 103.27±5.37 177.33±4.31 219.08±3.44 245.78±2.27 343.68±3.49 356.03±3.67 Experimental group 1 104.94±4.33 156.27±4.32 197.06±4.32 292.90±4.47 381.59±4.45 411.82±1.56 Experimental group 2 101.38±4.51 133.04±4.65 200.67±5.46 281.79±3.45 402.69±2.67 453.71±3.77 Experimental group 3 108.72±3.66 151.53±1.34 210.27±3.78 287.56±4.76 391.00±3.21 406.96±4.32 Experimental group 4 116.61±5.21 145.33±2.56 204.38±4.21 265.56±1.89 378.25±4.34 433.39±2.34

As shown in Table 3 and attached Figure 1, both the control group and the experimental group did not show any particular difference in the strength of 3 days or less, which can be called the initial strength, but in the strength of 7 days or more, which can be evaluated as mid- to long-term strength, the experimental group This showed good results.

In particular, in the change in strength after 28 days of age, the conventional control group showed a stagnant increase in strength after 28 days, whereas the experimental group showed a continuous increase in strength.

As can be seen from Table 3 and the attached FIG. 1, in all experimental groups 1 to 4, the strength after 28 days of age was confirmed to be superior to that of the control group, calcium aluminate 50% by weight, metakaolin 30% by weight % and 20% by weight of aluminum sulfate were mixed to form a fast economy, and experimental group 2 showed superior mid- and long-term strength compared to the control group as well as other experimental groups.

In addition, as shown in the accompanying Figure 1, the experimental group 2 and the experimental group 4 was confirmed to exhibit a continuous strength increase pattern without slowing the strength increase even after the age of 28 days as well as excellent 90-day strength.

These experimental groups 2 and 4 have a higher content of calcium aluminate compared to other experimental groups, so it can be estimated that calcium aluminate leads the performance improvement of the shotcrete to which the present invention is applied, but as shown in FIG. 1, the age of 7 days In terms of strength, Experimental Group 1 and Experimental Group 3 are shown to be excellent, and since these Experimental Groups 1 and 3 have a relatively high metakaolin content, each component constituting the quick-setting agent of the present invention is one element. It can be seen that the overall components play complementary roles, rather than completely driving the performance.

In particular, the long-term strength of calcium aluminate, which showed a rapid increase in initial strength, was higher than that of metakaolin in long-term strength, as in Control 1 to which calcium aluminate was applied alone as a fast-acting agent and Control 2 to which metakaolin was applied alone as a fast-acting agent. Although it shows a low aspect, as can be seen through Experimental Group 2 and Experimental Group 4, in the complex rapid economy of the present invention in which multiple preparations are combined, the early expression of strength by calcium aluminate is absolute or dominant in the initial strength. Not only does it not perform a phosphorus action, but also the content of metakaolin does not have an absolute effect on long-term strength, and even if the content of metakaolin is relatively low, when metakaolin above a certain level is applied, the long-term strength of calcium aluminate is stagnant. It was found that the phenomenon could be corrected.

On the other hand, as can be seen from the test results of Controls 1 to 3 to which calcium aluminate, metakaolin, or aluminum sulfate forming a single component, the rapid economy of which is applied, the shotcrete applied with a single component has an initial strength compared to that of the composite component. Although it does not show a significant advantage in strength, it shows a remarkably disadvantageous characteristic in terms of medium and long-term strength as well as long-term strength increase trend.

Therefore, in the composition of the rapid economy of the present invention, it is not preferable that any one element of calcium aluminate, metakaolin and aluminum sulfate extremely overwhelms the other components to constitute a substantial single-component rapid economy, but only the rapid economy It is advantageous to reduce the amount of aluminum sulfate, which has a function as a furnace and as an alkali stimulant for blast furnace slag, but has a risk of causing chemical resistance side effects, compared to other components. % to 80% by weight, 8% to 60% by weight of metakaolin, and 2% to 30% by weight of aluminum sulfate.

As can be seen through the change in strength by age of the experimental groups 1 to 4 described above, the expression characteristics of the initial to short-term strength and the mid-to-long-term strength increase trend can be changed according to the composition ratio of each component constituting the fast economy. Bar, it is possible to satisfy the time series strength specification of shotcrete required according to the field conditions by increasing or decreasing the individual components within the range of the composition ratio of the components in the rapid economy.

On the other hand, in the present invention, an antifoaming agent may be added to suppress the formation of bubbles due to the cellulose-based thickener contained in the quick setting agent. By doing so, the structure of the shotcrete hardened body can be densified and the mid-to-long term strength can be increased.

As described above, in the present invention, as such an antifoaming agent, calcium stearate, which is easy to store and handle, is stable in chemical aspects such as side reactions, and is easily miscible with the constituents of shotcrete including cement, is applied as a calcium salt.

Although gallium stearate can exhibit a sufficient effect even when a relatively small amount is mixed compared to other components constituting the quick setting agent of the present invention, it may cause a delay in setting time due to its unique surface activity when added in excess.

Therefore, calcium stearate was added as a quick-setting component to the shotcrete injected in the above-described experimental group 1, in which calcium aluminate and metakaolin, which are aluminum trioxide-based powder formulations, as main ingredients in the rapid-setting agent, were mixed in equal amounts, but calcium stearate was added as a quick-setting component. The setting time was measured while increasing, and a uniaxial compressive strength test was performed for each Example having a different calcium stearate content in the quick setting.

The setting time measurement and uniaxial compressive strength test for Examples by content of these antifoaming agents were performed by adding a quick setting agent having a different antifoaming agent content to the shotcrete as shown in Table 1 above at 7% of the weight of the cement (C) in the shotcrete to reduce the setting time. Measure, and manufacture a φ100×200mm cylindrical specimen with shotcrete for each example. For the curing of the cylindrical specimen, 20℃ underwater curing was applied until 7 days of age, and dry curing was applied after 7 days of age, and when the age of 90 days was reached The uniaxial compressive strength of the specimen for each Example was measured.

First, the setting time for each content of the calcium stearate antifoam in the quick setting is shown in Table 4 below.

Shotcrete setting time by antifoaming agent content division Quick setting (inject 7% of the weight of shotcrete cement) Condensation time (minutes:seconds) Content (wt%) in Sokkyungjae Mixed amount (wt%) compared to Sokkyungjae
sequel
closing calcium aluminium
Nate meta
kaoline sulfuric acid
aluminum swelling agent thickener enhancer Antifoam - Calcium Stearate Example 1
(Experimental group 1) 40 40 20 10 5 5 - 4:15 13:53 Example 2 〃 〃 〃 〃 〃 〃 0.1 4:13 13:57 Example 3 〃 〃 〃 〃 〃 〃 0.2 4:28 14:28 Example 4 〃 〃 〃 〃 〃 〃 0.5 4:37 14:25 Example 5 〃 〃 〃 〃 〃 〃 1.0 4:51 14:57 Example 6 〃 〃 〃 〃 〃 〃 2.0 4:57 14:43 Example 7 〃 〃 〃 〃 〃 〃 4.0 5:28 14:53

The uniaxial compressive strength test of the short strip cured body by the amount of the antifoaming agent was conducted by selecting two specimens for each example at the age of 90 days for Examples 1 to 7 of Table 4 above, and the results are shown in Tables 5 and 2 below. same as

90-day old shotcrete uniaxial compressive strength by antifoaming agent content division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 quick economy
Calcium stearate antifoam content (wt%) - 0.1 0.2 0.5 1.0 2.0 4.0 Uniaxial compressive strength at 90 days of age (kgf/㎠)
2 specimens mean ± mean deviation 411.82
±1.56 413.37
±2.74 416.43
±3.01 435.39
±2.97 439.21
±3.97 441.04
±8.78 439.61
±7.87

As can be seen through Table 4, Table 5, and the accompanying Figure 2, the initial setting time and the termination time were within 5 minutes and within 15 minutes, respectively, despite the increase in the content of the calcium stearate antifoaming agent in the quick setting to a certain level. It can be confirmed that it is relatively stable, but it can be seen that the initial setting time is delayed as the content of the antifoaming agent is increased.

In particular, as the content of the calcium stearate defoaming agent exceeds 2% by weight compared to the fast economy, the excessive delay of the initial setting time is clearly confirmed. exceeded.

As shown in Table 5 and FIG. 2, the 90-day strength also shows an increase in uniaxial compressive strength when the content of the calcium stearate antifoaming agent increases within a certain level, but the calcium stearate antifoaming agent content exceeds 2% by weight compared to fast economy As a result, it was confirmed that not only the strength increase was significantly slowed down, but also the average deviation of the measured values was rapidly expanded, so that the mid- and long-term strength enhancing effect of the antifoaming agent was insignificant and the possibility of side effects was also confirmed.

As such, in consideration of the setting time and the change in strength, the content of the calcium stearate antifoaming agent in the quick setting is preferably set to 2% by weight or less of the weight of the quick-setting agent.

In addition, even with the addition of a small amount of antifoaming agent, the effect of improving medium and long-term strength appears, so the lower limit of the content of the calcium stearate antifoam in the quick setting does not need to be limited, but as shown in Table 5 and FIG. It appears that the strength of 90 days of age increases relatively rapidly starting from Example 3 in which the antifoaming content is applied. .

In the rapid setting composition of the present invention as described above, various elements are organically combined to form a fast economy, thickeners and enhancers are added to induce tissue densification and a long-lasting hydration reaction, and to promote mutual complementary action of each component. , it is possible to improve the medium and long-term strength of the shotcrete hardened body.

Claims (3)

A quick-setting composition for shotcrete, comprising a quick-setting agent in which calcium aluminate, metakaolin and aluminum sulfate are mixed, an expanding agent having a weight of 10% of the weight of the quick-setting agent, a thickener having a weight of 5% of the weight of the quick-forming agent, and the weight of the quick-setting agent A rapid setting agent is constituted by mixing an enhancer of 5% of the weight, wherein the expanding agent is calcium sulfoaluminate, the thickener is a cellulose-based thickener, and the enhancer is a medium to long-term strength-enhancing type shotcrete composed of a mixture of blast furnace slag and silica fume. In the quick-setting composition for
The sokkyongjae is composed of a mixture of 50% by weight of calcium aluminate, 30% by weight of metakaolin, and 20% by weight of aluminum sulfate, and the cellulose-based thickener is a fine powder of hydroxypropylmethylcellulose and methylethylhydroxyethylcellulose (同量) is mixed in the weight ratio, the enhancer is composed of blast furnace slag fine powder and fine powder silica fume mixed in the same weight ratio, and calcium stearate of 0.2% of the weight of the rapid setting agent is used in the quick setting agent. A quick-setting composition for long-term strength-enhancing shotcrete, characterized in that it is added as an antifoaming agent. delete delete

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