KR102199929B1 - Shotcrete composition using cement composition for increased durability - Google Patents

Abstract

The present invention relates to a cement composition capable of improving overall penetration resistance, compressive strength and durability, and a shotcrete composition using the same. The present invention provides the cement composition for increasing durability which, in ordinary 100 wt% of Portland cement having a fineness of 3,200 to 3,500 cm^2/g and an SO_3 content of 2.2 to 2.8 wt%, substitutes 15 to 25 wt% of Portland cement with blast furnace slag fine powder, and 5 to 10 wt% of Portland cement with fine limestone powder having a fineness of 6,000 to 9,000 cm^2/g.

Description

Shotcrete composition using cement composition for increased durability

The present invention relates to a cement composition capable of improving overall penetration resistance, compressive strength and durability, and a shotcrete composition using the same.

Shotcrete (sprayed concrete) is concrete made by spraying the concrete conveyed into the hose to the nozzle position by using a compressor or pump on the construction surface with compressed air.

The performance of shotcrete can be set through a mix proportion at the outlet of a nozzle, and the required spraying performance to suit the purpose and use of the structure to be applied, such as tunnel and underground space, slope protection, repair and reinforcement, etc. Rebound), and the initial and long-term strength and durability of shotcrete must be set.

Conventional shotcrete is based on ordinary Portland cement suitable for KS L 5201, and admixtures such as accelerators, air entrainers, and water reducing agents are applied to meet the required performance, and the ingredients and amounts of the quick-setting agents are adjusted. There have been techniques such as controlling the physical properties of shotcrete or increasing the powderiness of cement to improve the rapid setting, increasing the content of SO ₃ , and mixing steel fibers to reduce the amount of rebound.

However, a comprehensive study on the distribution of hydrates and pores according to the cement composition and the performance change of shotcrete accordingly, and attempts to derive a cement that can improve the overall performance of shotcrete through this, were insufficient.

1. Registered Patent 10-1323773 "Shotcrete composition and its manufacturing method" 2. Registered Patent 10-0704869 "High-performance shotcrete composition in which metakaolin and silica fume are mixed and blended" 3. Registered Patent 10-1654568 "Creed steel shotcrete composition" 4. Registered Patent 10-1252962 "Shotcrete composition containing quick-setting high powder cement"

1.KCS 14 20 51: 2018 shotcrete

Its purpose is to provide a cement and shotcrete composition that can improve overall durability through a comprehensive study, experiment, and analysis on the distribution of hydrates and pores according to the components of cement and the resulting change in the performance of shotcrete.

In order to solve the above-described problems, the present invention replaces 15 to 25 wt% with blast furnace slag fine powder in 100 wt% of ordinary Portland cement having a powder degree of 3,200 to 3,500 cm 2 /g and a content of SO ₃ of 2.2 to 2.8 wt%, and 5 to It provides a cement composition for improving durability, characterized in that 10wt% is substituted with fine limestone powder having a powder degree of 6,000~9,000㎠/g.

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In addition, in the present invention, water is mixed with the cement composition to have a water-cement ratio of 38 to 53, and a rapid setting agent containing 28 to 34 wt% of Al ₂ O ₃ and 40 to 48 wt% of CaO is 4 to 7 wt% compared to the cement composition. It provides a shotcrete composition, characterized in that added together.

In addition, in the present invention, the reaction of [Chemical Formula 4] proceeds with the reaction of [Chemical Formula 1] at the beginning of the reaction until 1 day of age, and the unhydrated aluminate phase decreases, so that the reaction from 1 day to 7 days of age It provides a shotcrete composition, characterized in that the reaction of the following [Formula 2] is suppressed in the middle period.

[Formula 1]

C ₃ A or C ₁₂ A ₇ + C$H ₂ + H → C ₆ A$ ₃ H ₃₂

C: CaO, A: Al ₂ O ₃ , H: H ₂ O, $: SO ₃

[Formula 2]

C ₃ A or C ₁₂ A ₇ + C ₆ A$ ₃ H ₃₂ → C ₄ A$H ₁₂ (monosulphate)

[Formula 4]

C ₃ A or C ₁₂ A ₇ + C· C + H → C ₄ ACH ₁₁ (monocarbonate)

C : CO ₂

According to the present invention described above, it is possible to obtain shotcrete having excellent penetration resistance, compressive strength for each age, and durability overall according to the improvement of cement.

[Fig. 1] is a scatter plot matrix graph showing the correlation between the amount of OPC, SP, and LSF mixed, penetration resistance, and compressive strength.
[Fig. 2] is a graph showing the result of optimizing the mixing material addition rate using the mixture design method of the Minitab program.
[Fig. 3] is a scatter plot matrix graph showing the correlation between OPC powderiness and SO ₃ content, penetration resistance, and compressive strength.
[Fig. 4] is a graph showing the results of optimization of OPC powder and SO ₃ content using the response surface design method of the Minitab program.
[Fig. 5] shows the XRD pattern change for each age according to the mixing material replacement rate.
[Figure 6] is a graph showing the change in the amount of crystalline hydrates (AFt, AFm, CH) by age according to the mixing material substitution rate.
[Fig. 7] shows the XRD pattern change according to age according to the difference in OPC powder.
[Fig. 8] shows the change in the XRD pattern of each age according to the OPC SO ₃ content.
[Fig. 9] is a graph showing the change in the amount of crystalline hydrates (AFt, AFm, CH) according to age according to OPC powder and SO ₃ content.
[Fig. 10] is a graph showing the results of analyzing the pore distribution of the paste at 28 days of age according to the mixing material substitution rate.
[Fig. 11] is a graph showing the results of analysis of pore distribution of a paste at 28 days of age according to OPC powder and SO ₃ content.
[Fig. 12] is a scatter plot matrix graph showing the correlation between the initial hydrate amount, penetration resistance, and daily compressive strength.
[Fig. 13] is a scatter plot matrix graph showing the correlation between the amount of luggage at the age of 7 and 28 and the compressive strength at the age of 28.
[Fig. 14] is a photograph taken by comparing the test results of chloride penetration resistance by test body.
[Fig. 15] is a graph showing the chlorine ion diffusion coefficient for each test body.
[Fig. 16] is a photograph taken for comparison of the carbonation penetration resistance test results for each test body.
[Fig. 17] is a graph showing the carbonation depth for each test body (week 8).
[Fig. 18] is a picture taken for comparison of freeze-thaw test results for each test body.
[Fig. 19] is a graph showing the relative dynamic modulus of elasticity for each test body.
[Fig. 20] is a photograph taken by comparing the result of whitening phenomenon by test body.
[Fig. 21] shows the manufacturing process of the rapid setting agent applied to the present invention.

In the present invention, in 100wt% of ordinary Portland cement with a powdery degree of 3,200~3,500㎠/g and a content of SO ₃ of 2.2~2.8wt%, 15~25wt% is substituted with blast furnace slag fine powder, and 5~10wt% is powdery 6,000 It provides a cement composition for improving durability, characterized in that it is replaced with a fine limestone powder of ~9,000㎠/g.

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In the cement composition of the present invention as described above, air pollutants (CO ₂ , NOx, SOx, etc.) generated in the cement sintering process are reduced to within 20% compared to ordinary Portland cement.

In addition, in the present invention, water is mixed with the cement composition to have a water-cement ratio of 38 to 53, and a rapid setting agent containing 28 to 34 wt% of Al ₂ O ₃ and 40 to 48 wt% of CaO is 4 to 7 wt% compared to the cement composition. It is provided with a shotcrete composition, characterized in that added.

In addition, in the present invention, the reaction of [Chemical Formula 4] proceeds with the reaction of [Chemical Formula 1] at the beginning of the reaction until 1 day of age, and the unhydrated aluminate phase decreases, so that the reaction from 1 day to 7 days of age It provides a shotcrete composition, characterized in that the reaction of the following [Formula 2] is suppressed in the middle period.

[Formula 1]

C ₃ A or C ₁₂ A ₇ + C$H ₂ + H → C ₆ A$ ₃ H ₃₂

C: CaO, A: Al ₂ O ₃ , H: H ₂ O, $: SO ₃

[Formula 2]

C ₃ A or C ₁₂ A ₇ + C ₆ A$ ₃ H ₃₂ → C ₄ A$H ₁₂ (monosulphate)

[Formula 4]

C ₃ A or C ₁₂ A ₇ + C· C + H → C ₄ ACH ₁₁ (monocarbonate)

C : CO ₂

The present invention as described above is derived based on the mortar performance comparison by component of cement for application as a binder of shotcrete, paste hydration reaction analysis results, and durability test results. Hereinafter, the derivation process and contents of the present invention will be described in detail through an experiment and analysis process.

Ⅰ. Test of condensation and compressive strength of shotcrete

1. Test materials and methods

(1) Test material

For the performance test as a binder, in order to evaluate the effect of the addition of the mixed material, ordinary Portland cement (ordinary Portland cement, hereinafter referred to as'OPC') and blast furnace slag powder (hereinafter referred to as'SP') to which the mixed material was not added. ) And limestone powder (hereinafter referred to as'LSP') were mixed in a certain ratio. In addition, in order to evaluate the effect of OPC's fineness and SO ₃ content, OPC was applied to 3 levels (3,200cm ² /g, 3,500cm ² /g, 3,900cm ² /g) and SO ₃ content according to the fineness. As a result, samples of 3 levels (1.6 wt%, 2.2 wt%, 2.8 wt%) were prepared. [Table 1] below summarizes the contents and names of samples used in the test.

Classification by mixing material addition rate Classification by OPC property Sample name Sample content Sample name Sample content OPC
SP20
SP10
LSP10
LSP5
SP20LSP5


OPC 100wt%
OPC:SP = 80:20
OPC:SP = 80:10
OPC:LSP = 90:10
OPC:SP = 95:5
OPC:SP:LSP = 75:20:5


B3200S1.6
B3200S2.2
B3200S2.8
B3500S1.6
B3500S2.2
B3500S2.8
B3900S1.6
B3900S2.2
B3900S2.8 Blaine 3,200, SO ₃ 1.6wt%
Blaine 3,200, SO ₃ 2.2wt%
Blaine 3,200, SO ₃ 2.8wt%
Blaine 3,500, SO ₃ 1.6wt%
Blaine 3,500, SO ₃ 2.2wt%
Blaine 3,500, SO ₃ 2.8wt%
Blaine 3,900, SO ₃ 1.6wt%
Blaine 3,900, SO ₃ 2.2wt%
Blaine 3,900, SO ₃ 2.8wt%

[Table 2] below is an analysis of the chemical composition of the binder used in the test.

Sample name Chemical composition (%) Fineness
(cm ² /g) LOI SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO SO ₃ K ₂ O OPC OPC 0.21 21.91 5.19 3.60 63.19 2.01 2.24 1.01 3,480 B3200S1.6 0.21 21.89 5.24 3.63 63.21 2.03 1.60 0.99 3,210 B3200S2.2 0.29 21.97 5.23 3.67 63.19 1.99 2.26 0.94 3,510 B3200S2.8 0.38 21.71 5.20 3.59 63.15 2.00 2.80 0.97 3,930 B3500S1.6 0.25 21.94 5.36 3.72 63.06 2.14 1.61 0.99 3,210 B3500S2.2 0.29 21.97 5.23 3.67 63.19 2.06 2.26 1.00 3,510 B3500S2.8 0.35 21.71 5.20 3.59 63.15 2.00 2.82 0.97 3,930 B3900S1.6 0.24 22.07 5.39 3.63 63.00 2.05 1.58 1.01 3,210 B3900S2.2 0.33 21.97 5.23 3.67 63.19 2.04 2.23 0.95 3,510 B3900S2.8 0.36 21.71 5.20 3.59 63.15 2.02 2.90 0.97 3,930 SP 1.61 34.07 14.93 1.42 37.44 6.81 3.15 0.57 4,140 LSP 36.85 10.88 3.69 1.79 43.67 1.33 0.70 1.04 7,452

(2) Test method

[Table 3] below summarizes the test items and methods. As described in [Table 3], the blended binder is prepared as a W/B 50% paste (the proper W/B range of the shotcrete composition is 38-53%), and then a quick-setting agent (hereinafter'SC') is 5% compared to the binder. By addition, the pores of the hydration reactants and cement paste by age were analyzed.

Test goal Test items and methods I. Mixed material (SP, LSP) by replacement rate
Performance evaluation (1) Condensation (penetration resistance, KS F 2782 rapid setting agent for shotcrete)
(2) Mortar compressive strength (KS F 2782 quick setting agent for shotcrete)
(3) cement hydrate analysis
-After preparing the blended binder into a 50% W/B paste, 5% of the rapid setting agent was added to start the hydration reaction. Air curing for 1h, 8h, 1d, 7d, 28d from the time of addition of the rapid setting agent. After a certain age, each sample is pulverized, immersed in acetone, maintained for 24 hours, dried and re-ground to stop the hydration reaction, and qualitative/quantitative analysis of the hydration reaction product using XRD and TG-DTA.
-XRD measurement conditions: 40kV, 250mA, 5∼65°, 2.4°/min
-TG-DTA measurement conditions: Air gas, 20℃/min, 40～1,100℃
(4) Cement paste pore distribution analysis
-After preparing the blended binder into a 50% W/B paste, 5% of the rapid setting agent was added to start the hydration reaction. Analysis of pore size distribution using MIP (Mercury intrusion porosimetry) after air curing for 28d from the point of addition of the rapid setting agent II. By OPC properties (powder, SO ₃ content)
Performance evaluation

As shown in [Fig. 21], the rapid setting agent (SC) is water-cooled, pulverized, and mixed with additives to produce amorphous calcium aluminate (12CaO.7Al ₂ O ₃ ) generated in an electric furnace for melting quicklime and bauxite. To manufacture.
As a result, the rapid setting agent contains 28 to 34 wt% of Al ₂ O ₃ and 40 to 48 wt% of CaO, and 4 to 7 wt% of the cement composition provided by the present invention is added to express the characteristics of the hydration reaction. If Al ₂ O ₃ is less than 28wt% in the rapid setting agent, the setting characteristics of the cement composition of the present invention are deteriorated, and if it is more than 35wt%, the setting is rapid, but the increase in compressive strength is hindered. When CaO is 40wt% or less in the quick-setting agent, the compressive strength enhancement rate of the cement composition of the present invention is lowered, and when it is 48wt% or more, the setting properties are deteriorated. Details on the characteristics of the hydration reaction will be described later.

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2. Test result

(1) Penetration resistance and compressive strength

1) Compressive strength by mixing material addition rate

[Table 5] below summarizes the test results of penetration resistance and compressive strength by mixing ratio (weight ratio) of OPC, SP and LSP, and [Fig. 1] shows this as a scatter plot matrix. In [Table 5] below, when the SP replacement rate is 10~20wt% and the LSP replacement rate is 3~7wt%, penetration resistance (1min, 3min, 7min) and compressive strength by age (1 day, 7 min) compared to when using OPC Days, 28th) were all always.

Formulation (wt%) Penetration resistance (kgf/cm ² ) Compressive strength (MPa) OPC SP LSP 1 minute 3 minutes 5 minutes 1 day 7 days 28 days 100 0 0 13 61 88 14.5 22.0 39.8 80 0 20 23 67 97 11.4 28.7 38.1 75 25 0 27 73 96 11.3 30.7 42.7 55 25 20 36 98 134 9.1 28.9 38.7 77 20 3 45 118 154 14.6 32.8 42.3 75 20 5 50 125 159 15.8 32.6 45.8 73 20 7 54 128 162 16.5 33.1 41.3 80 20 0 30 81 113 12.0 30.2 40.2 77 20 3 42 120 152 14.2 31.3 40.3 72 25 3 46 117 147 14.0 32.1 43.8 67 30 3 4 112 145 13.4 31.8 45.1 95 5 0 25 70 109 14.3 22.3 40.9 95 5 5 25 70 109 14.3 22.3 40.9 90 10 0 28 79 124 13.5 24.6 41.0 85 10 5 45 121 150 15.1 22.4 39.8 85 15 0 38 96 125 12.9 24.9 40.9 80 15 5 46 121 149 15.2 33.9 43.0

2) OPC fineness and SO ₃ Compressive strength by content

[Fig. 2] is based on the above test results, using the mixture design method of the Minitab ^® program to calculate the formulation that maximizes penetration resistance for 1,5 minutes and compressive strength for 1,28 days, and 15~25wt% of SP among binders When mixed within the range of 5 to 10 wt% LSP, it was analyzed that the penetration resistance and compressive strength performance were significantly improved compared to the case of using 100 wt% of OPC.

[Table 6] below shows the test results of penetration resistance and compressive strength by OPC powder and SO ₃ content, and [Fig. 3] shows this as a scatter plot matrix. When the SO ₃ content is the same, the penetration resistance and compressive strength are the best at the level of around 3,500㎡/g of the powder, and at the level of 3,900㎡/g, it has been analyzed that there is no improvement effect or decreases slightly. As the SO ₃ content of OPC increases Penetration resistance and compressive strength were improved.

Formulation (wt%) Penetration resistance (kgf/cm ² ) Compressive strength (MPa) Fineness
(㎡/g) SO ₃ 1 minute 3 minutes 5 minutes 1 day 7 days 28 days 3200 1.6 22 58 70 10.1 16.1 26.2 3200 2.2 30 68 90 17.4 32.0 37.3 3200 2.8 46 106 147 19.0 29.4 37.8 3500 1.6 24 60 78 13.3 26.8 32.9 3500 2.2 36 96 124 16.3 31.5 37.5 3500 2.8 42 104 146 20.8 32.5 38.6 3900 1.6 21 48 56 13.6 27.9 34.5 3900 2.2 34 84 102 15.4 27.4 32.9 3900 2.8 42 108 158 17.6 28.5 35.9

According to the concrete standard specification (KCS 14 20 51 shotcrete), the standard value of the initial strength (age 1 day) of shotcrete is 5.0 to 10.0 MPa, and the long-term design standard compressive strength (age 28 days) is 21 MPa or more (however, with the concept of permanent support material). In case shotcrete is poured, it is 35MPa or more). OPC can meet the design standard strength of shotcrete for permanent support under the conditions of 3200~3500㎡/g of powder and 2.2~2.8wt% of SO ₃ content.

[Fig. 4] shows the results of the test using the Minitab ^® program's response surface design method to calculate OPC quality that maximizes penetration resistance for 1,5 minutes and compressive strength for 1,28 days, and the powderiness is 3,500 m2/g. Both compressive strength and penetration resistance tended to improve until it was increased to ㎡/g. At 3,900㎡/g, the 5-minute penetration resistance was equivalent, but it was analyzed that the compressive strength on 1,28 days decreased significantly. . In addition, it was analyzed that the increase in SO ₃ content improves both penetration resistance and compressive strength.

(2) Carb analysis

1) Hydrate analysis by mixing material addition

[Fig. 5] is a comparison of the XRD patterns for each age according to the mixing material substitution rate using XRD. As a crystalline hydrate, ethringite (6CaO.Al ₂ O ₃ .3SO ₄ .32H ₂ O, hereinafter'AFt'), monocarbonate (4CaO.Al ₂ O ₃ .CO ₂ .11H ₂ O, hereinafter referred to as'AFt') Hereinafter'AFm') and portlandite (Ca(OH) ₂ , hereinafter'CH') were relatively clearly identified in all samples and all ages. In addition, hemicarbonate (4CaO.Al ₂ O) The peak of ₃ .0.5CO ₂ .10H ₂ O) was weakly confirmed, but the peak of monosulfate (4CaO.Al ₂ O ₃ .SO ₃ .12H ₂ O) commonly observed in general OPC hydrates was not observed. Mineral peaks such as gibbsite (AH ₃ ) and stratlingite (stratlingite, 2CaO.Al ₂ O ₃ .SiO ₂ .8H ₂ O), which are known to be generated due to the hydration of CA-based cement, were not observed. .

[Table 7] below summarizes the results of quantitative analysis of the amount of hydrates (AFt, AFm, CH) produced by age according to the mixture replacement rate using TG/DTA. The amount of hydrate produced in [Table 6] below is all expressed as a weight ratio (wt%), where H means time and D means work.

Luggage sample 1H 8H 1D 7D 28D AFt
(Ettringite) OPC 2.04 2.68 5.82 2.52 5.77 SP10 2.09 2.68 4.37 2.39 5.31 SP20 1.80 2.41 4.59 2.33 4.72 LSP5 1.80 2.76 6.94 3.08 5.63 LSP10 1.55 2.17 8.86 3.94 4.93 SP20LSP5 1.86 2.90 7.52 3.54 4.64 AFm
(mono-
carbonate,
hemi-
carbonate,
mono-
sulphate) OPC 1.40 1.24 3.34 5.12 2.56 SP10 1.49 1.39 3.08 4.43 2.07 SP20 1.47 1.21 2.88 3.68 2.42 LSP5 1.64 1.41 2.16 2.71 3.08 LSP10 2.01 1.15 3.01 3.40 3.85 SP20LSP5 1.86 1.73 1.96 3.86 4.11 CH
(portlandite) OPC 0.89 1.23 3.33 3.08 2.52 SP10 0.37 0.86 2.30 2.85 1.89 SP20 0.41 1.07 2.30 2.47 1.56 LSP5 0.41 1.03 1.97 2.59 2.22 LSP10 0.27 0.78 2.10 2.76 2.10 SP20LSP5 0.37 1.64 2.34 2.43 1.77

[Fig. 6] is a summary of the changes in the amount of AFt, AFm, and CH by age according to the mixing material addition rate. When SP is mixed, the CH generation amount was less at 1 hour of age compared to OPC, and ages 1 day and 7 On days and 28, it was analyzed that the amount of AFt and AFm produced was lower than that of OPC. In addition, the amount of CH production was lower than that of OPC at all ages. This phenomenon is believed to occur because C-S-H is produced by consuming CH according to the OPC dilution effect by the addition of SP and the latent hydraulic reaction of SP.

On the other hand, when LSP was mixed, the less CH generation at 1 hour of age was the same as that of SP, but the amount of AFm produced was rather increased, and unlike the case of SP, more AFt than OPC was generated at 1 and 7 days of age. Was analyzed. On the other hand, unlike SP with latent hydraulic properties, LSP is known to have no effect on the amount of CH generation except for the reduction of CH due to the OPC dilution effect, and it is expected that there will be a difference in the amount of CH generation depending on the type of mixed material. No significant difference was observed in the amount of production.

The difference in the amount of AFt produced by the addition of LSP was estimated that the more stable monocarbonate-type AFm was produced by the addition of LSP, and accordingly, the monosulfate-type AFm was reduced, thereby affecting the amount of AFt produced. As shown in the following equation, LSP reacts with the aluminate phase contained in OPC and SC, which is a rapid setting agent, to produce carboaluminate (monocarbonate, hemicarbonate) to stabilize ethrinzite. It is understood that the sulfate is exhausted.

That is, the reaction proceeds as shown in [Chemical Formula 1] at the beginning of the reaction (until the first day of age), but on days 1 to 7 when C ₃ A becomes excessive compared to SO ₃ , through the reaction of [Chemical Formula 2], At the end of the reaction, the reaction of [Chemical Formula 3] occurs again by creating an excessive SO ₃ environment. When LSP is added here, it reacts as shown in [Chemical Formula 4] along with ethrinzite formation reaction at the beginning of the reaction (C: CaO, A: Al ₂ O ₃ , H: H ₂ O, $: SO ₃ , C : CO ₂ ) _.

[Formula 1]

C ₃ A or C ₁₂ A ₇ + C$H ₂ + H → C ₆ A$ ₃ H ₃₂ (ettringite, AFt)

[Formula 2]

C ₃ A or C ₁₂ A ₇ + C ₆ A$ ₃ H ₃₂ → C ₄ A$H ₁₂ (monosulphate, AFm)

[Formula 3]

C ₄ A$H ₁₂ + C$H ₂ → C ₆ A$ ₃ H ₃₂ (ettringite)

[Formula 4]

C ₃ A or C ₁₂ A ₇ + C· C + H → C ₄ ACH ₁₁ (monocarbonate, AFm)

According to [Formula 4], the unhydrated aluminate phase such as C ₃ A and C ₁₂ A ₇ decreases. Accordingly, it is estimated that the reaction of [Chemical Formula 2] in which AFt is re-decomposed into AFm in the middle of the reaction, 1-7 days, is suppressed. In addition, in general OPC hydration, although monosulfate was commonly observed in the middle of the reaction during the reaction of [Formula 2], the formation of monosulfate could not be clearly confirmed in this test. This is calcium aluminate of SC used as a rapid setting agent. As the component reacts with C$H ₂ of OPC as in [Chemical Formula 1], the tendency to generate AFt increases, and at the same time, the reaction of [Formula 4], which reacts with C· C supplied from the binder, occurs. Is estimated to be.

2) OPC fineness and SO ₃ Hydrate analysis by content

[Fig. 7] and [Fig. 8] compare XRD patterns according to age according to OPC powderiness and SO ₃ content using XRD. As with the result of hydrate analysis for each mixed material, it can be confirmed that AFt, AFm, and CH were generated as major hydrates. [Table 8] is a quantitative analysis of the amount of AFt, AFm, and CH produced using TG/DTA. The amount of hydrate produced in [Table 8] below is all expressed as a weight ratio (wt%), where H means time and D means work.

Luggage sample 1H 8H 1D 7D 28D AFt
(Ettringite) B3500S1.6 0.94 1.47 2.79 1.25 2.34 B3500S2.2 0.99 1.10 2.76 2.81 3.25 B3500S2.8 1.53 1.53 5.66 3.75 5.08 B3200S2.8 1.02 1.58 4.10 2.53 3.31 B3900S2.8 1.45 1.77 5.15 4.08 5.08 AFm
(mono-
carbonate,
hemi-
carbonate,
mono-
sulphate) B3500S1.6 3.02 2.02 4.29 4.26 3.16 B3500S2.2 2.25 1.55 3.45 3.66 2.39 B3500S2.8 1.30 1.32 3.89 3.66 2.35 B3200S2.8 1.41 1.21 3.60 4.12 3.22 B3900S2.8 1.27 1.32 2.36 3.20 2.94 CH
(portlandite) B3500S1.6 0.04 1.07 2.55 3.45 3.15 B3500S2.2 0.16 1.15 2.77 3.44 3.36 B3500S2.8 0.29 0.90 2.59 3.38 3.25 B3200S2.8 0.37 0.99 2.14 3.09 3.54 B3900S2.8 0.63 1.40 3.19 3.39 3.54

[Fig. 9] is a summary of changes in the amount of AFt, AFm, and CH by age according to the difference in OPC powder and SO ₃ content. First, looking at the hydrate change according to the fineness, it can be seen that the higher the fineness, the greater the amount of CH generated in 1, 8 hours and 1 day, and the greater the amount of AFt generated in 1H. As age elapsed, the CH amount did not show a difference according to the powderiness, but AFt and AFm amounts showed more AFt amount and less AFm amount of the powdery one after 1 day. This phenomenon is because the size of the C ₃ A crystal in OPC decreases as the powderiness increases, and accordingly, the reaction to the monosulfate as shown in [Chemical Formula 2] is suppressed as more AFt is produced smaller and stably at the beginning of the reaction. It is judged to appear because of.

In addition, the change in SO ₃ content did not affect the amount of CH production, but it was observed that as the SO ₃ content increased, the amount of AFt produced increased and the amount of AFm produced decreased. This phenomenon is considered to be because the AFt generation reaction according to [Chemical Formula 1] may occur more actively as more SO ₃ is supplied. In particular, the production of monosulfate could not be confirmed even in the B3500S1.6 sample having an extremely low SO ₃ content as in other samples. From these results, it is estimated that when SC is added to OPC, AFt is produced preferentially due to the calcium aluminate component of SC, and the calcium aluminate component that does not react with C$H ₂ is estimated to produce monocarbonate rather than monosulfate. .

(3) Analysis of pore distribution

1) Analysis of pore distribution by mixing material addition rate

[Fig. 10] is a graph showing the result of analyzing the pore distribution of cement paste at 28 days of age according to the type and addition rate of the mixed material, and [Table 9] is the definition of Mindness based on this (S.Mindness JFYoung, D.Darwin, Concrete , 2002). ), and the amount of pores corresponding to capillary pores and the amount of pores corresponding to gel pores are summarized. As the amount of SP added increases, both capillary pores and gel pores decrease.This is due to the latent hydroponic reaction of SP, resulting in a more dense structure of CSH, reducing the gel pores, and at the same time, the particle size of SP is smaller than OPC. It is believed that the capillary void is also reduced due to the fine filling effect. On the other hand, the sample in which 5wt% of LSP was substituted and mixed was difficult to confirm the change in the pore structure compared to that of OPC. However, in the sample in which 10wt% of LSP was substituted and mixed, the gel pore height and capillary pores decreased by about 10 vol%. The SP20LSP5 sample, which was used together with SP and LSP, significantly reduced capillary voids compared to OPC.

Pore size OPC SP10 SP20 LSP5 LSP10 SP20LPSP5 Capillary pores Large (0.05-10㎛) 2.39 2.34 2.15 2.23 2.36 2.32 Medium(0.01-0.05㎛) 5.70 4.52 4.15 5.66 5.13 3.02 Gel pores(0.002-0.01㎛) 9.79 8.79 7.93 10.6 8.76 8.91 Total pores 17.9 15.6 14.2 18.5 16.3 14.3

2) OPC fineness and SO ₃ Analysis of pore distribution by content

[Fig. 11] is an analysis of the pore distribution of the cement paste at 28 days of age according to OPC powder and SO ₃ content, and [Table 10] summarizes the amount of pores. Compared to the 1.6wt% SO ₃ sample, the capillary voids of the 2.2wt% and 2.8wt% samples significantly decreased, but there was no significant difference in the amount of gel voids, and there was little difference between the 2.2wt% and 2.8wt% samples. In addition, depending on the difference in powder, no significant difference could be observed in the amount of voids.

Pore size B3500S1.6 B3500S2.2 B3500S2.8 B3200S2.8 B3900S2.8 Capillary pores Large (0.05-10㎛) 2.08 1.98 1.70 2.29 1.86 Medium(0.01-0.05㎛) 6.78 4.06 4.10 5.03 5.15 Gel pores 12.5 13.5 12.7 10.3 11.7 Total pores 21.4 19.5 18.5 17.6 18.7

4. Organize test and analysis results

[Fig. 12] shows the correlation between the amount of hydrates, penetration resistance, and compressive strength per day of 1,8 hours and 1 day old age based on the above analysis results (AFt/AFm/CH-1H,8H ,1D: AFt/AFm/CH production at each age (1,8,24 hours), 1 minute, 5 minutes: penetration resistance at each age, 1 day: compression strength of 1 day age). Penetration resistance is expected to be related to the initial hydrate of hydration, and the maximum amount of AFt at 1 hour of age was not too much or too little at 1.5 wt%, and the amount of AFm at 1 hour of age was at a certain level (about 1.9 wt%). It has little effect up to ), but it greatly reduces penetration resistance beyond that. In addition, for AFt and AFm, the compressive strength per day was higher as the amount of AFt produced at the age of 1 day increased and the AFm decreased within 8 hours between the compressive strengths per day.

Taking these analysis results together, it is judged that when SP or LSP is added at an appropriate level, the chemical change in which the amount of AFt generation is controlled to an appropriate level leads to an increase in penetration resistance and daily strength than when only OPC is used. In particular, in the case of LSP, when the amount of addition increases, the amount of AFt generation decreases significantly, and the amount of AFm generation increases significantly, and it is judged that the effect of improving penetration resistance no longer appears. In addition, as the SO ₃ content increases, the amount of AFm generated significantly decreases, which is believed to be the cause of the phenomenon that the penetration resistance and compressive strength per day increase as the SO ₃ content increases.

[Fig. 13] shows the correlation between the amount of hydrate at the age of 7,28 days, the amount of voids at the age of 28, and the compressive strength at the age of 28. The pores that have the highest correlation with compressive strength at 28 days of age are capillary pores (CP-M) with a size of 0.01 to 0.05 μm and gel pores (GP) of less than 0.01 μm, and the smaller the amount (volume) of these pores, the older the The 28-day compressive strength was low, and the degree of influence of CP-M and GP on the 28-day compressive strength was estimated to be similar to each other. In addition, CP-M showed a tendency to increase as the amount of AFt decreased and the amount of CH increased, whereas the GP of GP showed a tendency to increase as the amount of AFt increased and the amount of CH decreased. From these results, it is estimated that when SP is added, the compressive strength on 28 days is improved as capillary pores and gel pores decrease due to the latent hydraulic reaction of SP and the fine powder filling effect.

Ⅱ. Shotcrete durability test

Hereinafter, the cement of the present invention consisting of OPC 100wt%, OPC 80wt% and SP 20wt% (hereinafter'Comparative Example 1') and OPC 75wt%, SP 20wt% and LSP 5wt% (hereinafter'Example 1') The results of the durability test (chloride penetration resistance, carbonation penetration resistance, freezing and thawing, whitening) are described.

1. Chloride penetration resistance

[Fig. 14] is a photograph taken by comparing the results of the chloride penetration resistance test for each test object, and [Fig. 15] is a graph showing the chloride ion diffusion coefficient for each test object. As shown in [Fig. 14], the chloride penetration depth for each test specimen is OPC 14.3 mm, which is 7.9 mm in Comparative Example 1, but is reduced to 4.2 mm in Example 1. In addition, as shown in Fig. 15, the chloride ion diffusion coefficient of Example 1 is about 20% of the OPC, and is less than 50% compared to Comparative Example 1, so that the chloride penetration resistance is greatly improved by the use of LSP.

2. Carbonation penetration resistance

[Fig. 16] is a photograph taken for comparison of the results of the accelerated carbonation test for each specimen, and [Fig. 17] is a graph showing the carbonation depth for each specimen (week 8). The cross section of the test specimen does not appear purple due to the penetration of CO _{2. The} carbonation depth based on the 8th week of the deterioration acceleration neutralization test was 4.8 mm in OPC and 2.3 mm in Comparative Example 1, whereas it was 1.8 mm in Example 1. Accordingly, it can be seen that carbonation penetration resistance is significantly improved by the application of SP substitution and further improved by the application of LSP substitution.

3. Freeze and thaw

[Fig. 18] is a photograph taken for comparison of freeze-thaw test results for each test body, and [Fig. 19] is a graph showing the relative dynamic modulus of each test body. In the case of OPC, the relative dynamic modulus decreased sharply as freezing and thawing was repeated, but in Comparative Examples 1 and 1, the relative dynamic modulus did not change significantly until the freezing and thawing tests were repeated 300 cycles. Comparative Example 1 is rather superior to Example 1 in terms of resistance to freezing and thawing, but it is judged that there is no technically significant difference.

4. Whitening phenomenon

[Fig. 20] is a photograph taken by comparing the result of whitening phenomenon by test body. In Example 1, it is determined that the whitening phenomenon is also reduced as the amount of OPC used is reduced.

The present invention has been described in connection with the test results and preferred embodiments as mentioned above, but various modifications and variations are possible within the scope without departing from the gist of the present invention, and can be used in various fields. Accordingly, the claims of the present invention include modifications and variations that fall within the true scope of the previous invention.

Not applicable

Claims (6)

In 100wt% of ordinary Portland cement with a powder of 3,200~3,500㎠/g and a content of 2.2~2.8wt% of SO ₃ , 15~25wt% is replaced with blast furnace slag fine powder, and 5~10wt% of powder is 6,000~9,000㎠ In a cement composition for improving durability, characterized in that it is substituted with fine limestone powder of /g,
Mix water so that the water-cement ratio is 38~53,
Al ₂ O ₃ 28 to 34 wt% and CaO 40 to 48 wt% of the quick-setting agent containing 4 to 7 wt% of the cement composition was added,
The reaction of [Chemical Formula 4] proceeds with the reaction of [Chemical Formula 1] at the beginning of the reaction until 1 day of age, and the unhydrated aluminate phase decreases, so that the following [Chemical Formula 1] Shotcrete composition, characterized in that the reaction of 2] is suppressed.
[Formula 1]
C ₃ A or C ₁₂ A ₇ + C$H ₂ + H → C ₆ A$ ₃ H ₃₂
C: CaO, A: Al ₂ O ₃ , H: H ₂ O, $: SO ₃
[Formula 2]
C ₃ A or C ₁₂ A ₇ + C ₆ A$ ₃ H ₃₂ → C ₄ A$H ₁₂ (monosulphate, AFm)
[Formula 4]
C ₃ A or C ₁₂ A ₇ + C· C + H → C ₄ ACH ₁₁ (monocarbonate, AFm)
C : CO ₂ delete delete delete delete delete

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