KR20090036952A - Concrete composition for tunnel lining - Google Patents

Abstract

A concrete composition for tunnel lining is provided to prevent crack caused by dry shrinkage and heat of hydration and deterioration of structural functions, thereby effectively constructing concrete for tunnel lining. A concrete composition for tunnel lining comprises 250-500 kg/m^3 of binding material containing cement; 150-180 kg/m^3 of water, 600-1000 kg/m^3 of fine aggregate, 800-1200 kg/m^3 of coarse aggregate and 0.1-2.0 kg/m^3 of fiber reinforcing material on a basis of unit volume of concrete. The fiber reinforcing material is selected from the group consisting of polyethylene fiber, polyamide fiber, polyacryl fiber, polyester fiber, polypropylene fiber, polyvinylalcohol fiber and cellulosic fiber. The fiber reinforcing material is 1-100mm in length and 10-70mum in thickness or diameter.

Description

Concrete composition for tunnel lining {CONCRETE COMPOSITION FOR TUNNEL LINING}

The present invention relates to a concrete composition for tunnel lining comprising cement, water, aggregate, and fiber reinforcement.

The tunnel structure plays a role as a means of transportation such as balanced transportation between regions through rapid transportation of bulk logistics and efficient use of the whole country. Therefore, in Korea, where about 70% of the country is mountainous region, the rapid growth of national economy and life The construction of tunnel facilities is expected to be accelerated with the expansion of social indirect capital due to the improvement of the level.

Currently, the design of NATM tunnel construction in Korea is mostly considered as the primary structure as a permanent structure. Therefore, the tunnel is stabilized by the primary support material in some form and the internal lining concrete is intended to maintain the secondary function rather than the structural function of the tunnel. Therefore, drainage tunnels are designed to withstand only their own weight.

However, as the problem of cracks in tunnel lining concrete has recently been raised, it is considered as a structural material which is the final supporting means to maintain the stability of tunnels. The cracks generated in tunnel lining concrete are concrete construction method, concrete quality and curing process. Occurs in Therefore, there is a need for research on preventing cracking in tunnel lining concrete and developing better physical properties.

The present invention is to improve the fluidity of the tunnel lining concrete, to reduce the heat of hydration and durability, and to provide a concrete composition for tunnel lining to prevent quality improvement, crack reduction and deformation.

The present invention relates to a) concrete unit volume, the binder containing cement 250 to 500 kg / m ³ , b) concrete unit volume, water 150 to 180 kg / m ³ , c) concrete unit volume, fine aggregate 600 to 1000 kg / m ³ , d) for coarse linings, coarse aggregate 800 to 1200 kg / m ³ , and e) for concrete unit volume, for fiber linings comprising fiber reinforcements 0.1 to 2.0 kg / m ³ To provide a concrete composition.

Hereinafter, the present invention will be described in more detail.

Concrete is one of the most used construction materials, and cement and aggregate are mixed with water to harden through a hydration reaction. At this time, concrete causes temperature cracking due to dry shrinkage cracks and heat of hydration. As such, the minute cracks in the concrete have a great effect on the concrete, which reduces the watertightness of the concrete and accelerates the deterioration caused by the penetration of harmful substances.

As a result, the service life of concrete structures, as well as structural deterioration is accelerated.

In particular, as a method widely used in tunnel construction method recently, in the tunnel construction method, the excavation work and the joint ball and the lining concrete structure are performed in parallel, causing cracking or strength in the lining concrete where the blasting vibration generated during blasting is poured. It can be lowered, so it is very important to prevent it.

Accordingly, the present invention includes a fiber reinforcing material such as polyamide fiber to improve the problem of cracking or strength reduction in lining concrete generated during the construction of the tunnel lining using the existing general concrete composition and to efficiently cast the tunnel lining concrete It is to provide a concrete composition for tunnel lining.

The concrete composition for tunnel lining of the present invention includes a binder containing cement with respect to the concrete unit volume of 250 to 500 kg / m ³ , preferably 280 to 470 kg / m ³ . The binder is preferably included in the concrete design reference strength in terms of 250 kg / m ³ or more, it is preferable to include less than 500 kg / m ³ in terms of reducing the heat of hydration, economical.

In the concrete composition for tunnel lining of the present invention, the cement is preferably used portland cement, but can be used in addition to all the various types of cement available on the market.

In addition, the binder of the present invention may further include at least one mineral admixture such as blast furnace slag powder and fly ash together with the cement.

In the present invention, the blast furnace slag fine powder may be one obtained by pulverizing slag discharged from the blast furnace and granulating it. The blast furnace slag fine powder has a density of 2.8 g / cm ³ or more and a specific surface area of 4,000 to 10,000 cm ² / g, preferably 4,000 to 8,000 cm ² / g, according to KS F 2563 standard.

The blast furnace slag powder is not hydrophobic in itself, but stimulates alkalinity in cement to hydrate slowly, and improves workability and long-term strength of concrete, and improves water tightness and chemical resistance by dense structure.

As fly ash, pulverized coal ash collected by cooling and solidifying the non-combustible portion floating in the molten state when burning coal dust in a thermal power plant or the like can be used. The fly ash may have a density of 1.95 g / cm ³ or more and a specific surface area of 3,000 cm ² / g or more according to KS L 5405 standard. In addition, fly ash is a spherical particle with a smooth surface, which acts as a ball bearing to improve the workability of concrete, that is, its fluidity. Strength and water tightness can be increased.

Here, the content ratio of the blast furnace slag powder and fly ash may be used in a weight ratio of 1: 1 to 5: 1, preferably 1: 1 to 3: 1.

In particular, the binder of the present invention may comprise 25 to 100% by weight of cement, 0 to 50% by weight of blast furnace slag, and 0 to 25% by weight of fly ash, preferably 50 to 90% by weight of cement, blast furnace slag fine powder 5 to 30% by weight, and 5 to 15% by weight of fly ash.

The concrete composition for tunnel lining of the present invention comprises 150 to 180 kg / m ³ , preferably 160 to 170 kg / m ³ of water relative to the concrete unit volume, the content of water in the optimum range in terms of strength and fluidity of the concrete Can be adjusted with

Aggregate in the present invention may be generally used for concrete, may be composed of fine aggregate and coarse aggregate. As the fine aggregate, particles having a particle size of 0.15 to 2.5 mm, an absolute dry density of 2.5 g / cm ³ or more, an absorption rate of 3% or less, and a stability of 10% or less may be used as the fine aggregate. In addition, as a coarse aggregate, those having a particle size of 2.5 to 40 mm, an absolute dry density of 2.5 g / cm ³ or more, an absorption rate of 3% or less, a stability of 10% or less, and a wear rate of 40% or less according to KS F 2526 standard can be used.

Tunnel lining concrete composition of the present invention with respect to the concrete unit volume, the fine aggregate comprises 600 to 1000 kg / m ³ , preferably 700 to 900 kg / m ³ , the fine aggregate is in terms of fluidity and material separation reduction Preference is given to using in the content range.

In addition, in the present invention, the coarse aggregate is preferably included from 800 to 1,200 kg / m ³ , preferably 850 to 1,100 kg / m ³ with respect to the concrete unit volume in terms of fluidity and material separation reduction.

The present invention also incorporates the blast furnace slag powder and fly ash to improve fluidity and durability, reduce heat of hydration, and evenly disperse fiber reinforcing materials such as short-fiber reinforcing polyamide fibers in a cement matrix to provide tensile strength, Flexural strength and flexural toughness can be greatly improved.

In the present invention, the fiber reinforcing material may be at least one selected from the group consisting of polyethylene fiber, polyamide fiber, polyacrylic fiber, polyester fiber, polypropylene fiber, polyvinyl alcohol fiber, cellulose fiber, and the like. Polyamide fiber can be used. For example, as the polyamide fiber, standard and crimp types may be used as short fibers.

In particular, the most mass produced polyamide fibers include nylon 66 and nylon 6. Nylon 66 is called nylon 66 because it is made between abicinic acid and hexamethylenejimic acid and the carbon number of these two elements is hexavalent. Nylon 6 is made by heating by heating caprolactam having 6 carbon atoms alone. Compared to nylon 6, nylon 66 is excellent in heat resistance and strength. Polyamides are relatively excellent inert compounds and are known to be resistant to a variety of organic and inorganic materials, including strong bases.

In addition, since polyamide fibers have a partial (-) charge on N or O in the molecule, they act as an electrostatic interaction with H of a water molecule having a partial (+) charge. Coating a coating solution containing a surfactant has a number of advantages, such as strengthening the bonding strength with the cement paste, excellent dispersibility and finish.

Since the fiber reinforcement has no thermal conductivity, it has its own fire resistance, and when the temperature rises above the melting point of the fiber reinforcement due to a fire, the fiber may be melted to form voids in the concrete, preferably 120 to 400 ° C., more Preferably a fiber reinforcement having a melting point of 220 to 300 ℃ can be used. Heat and gas are moved through the air gap as described above to prevent the explosion of concrete material due to fire.

The length of the fiber reinforcement of the present invention is 1 to 100 mm, preferably 6 to 40 mm, and the diameter or thickness of the cross section of the fiber reinforcement is 10 to 70 m, preferably 20 to 40 m. The length and diameter or thickness of the fiber reinforcement can be adjusted to the optimum range according to the quality of the desired concrete, durable performance and tensile strength, flexural strength and flexural toughness.

The fiber reinforcing material may include 0.1 to 2.0 kg / m ³ , preferably 0.5 to 1.0 kg / m ³ with respect to the concrete unit volume. If the content of the fiber reinforcing material is less than 0.1 kg / m ³ with respect to the concrete unit volume, it is difficult to obtain an excellent difference in effect in terms of reducing the cracks. And, if the content of the fiber reinforcement exceeds 2.0 kg / m ³ with respect to the concrete unit volume, the fiber reinforcement is not uniformly dispersed to increase the voids inside the concrete, which is crack cracking performance and strength performance and fire resistance performance It may result in decreasing results.

In the concrete composition for tunnel lining of the present invention, at least one admixture consisting of an AE agent, a water reducing agent, an AE water reducing agent, and a high performance water reducing agent, which are known as chemical admixtures for concrete according to the KS F 2560 standard, may be further mixed with water.

AEs (or surfactants) generally refer to substances that adsorb on two or more phases or interfaces of substances to significantly change the properties of the interface.The basic molecular structure is two identical structures, ie, insoluble in water. It is composed of hydrophobic group and hydrophilic group which is soluble in water, and is classified into anionic, cationic and nonionic according to the electrical properties of hydrophilic group ions in aqueous solution. Anionic AE agents comprise most of the commercially available AE agents, and the main chemical components are resinates, sulfate esters, and sulfonates. Cationic AEs have a cation in the hydrophilic group and are not used as AE agents. In addition, nonionic AE agents do not dissociate into ions in water, and ethers and esters are used as the molecules themselves have an interfacial action.

The reducing agent and the AE reducing agent are admixtures that can reduce the unit amount by dispersing cement particles in concrete, or improve workability while entraining fine bubbles in the concrete, while reducing the unit amount by the dispersing effect. Reducing agents and AE reducing agents are classified into standard type, delay type and accelerated type according to the condensation and initial curing rate of concrete, respectively.Lignin sulfonate, alkylaryl sunphonic acid and polyoxyethylene alkylaryl ether type , An oxycarboxylic acid system, a melamine sulfonic acid system, a pulley main company type, etc. can be used.

High-performance susceptors are admixtures that can greatly reduce the unit quantity by using a high addition rate without adversely affecting coagulation delay, excessive air entrainment, and strength deterioration by effectively dispersing cement particles by further improving the function of general susceptors. The high performance reducer was first used in concrete in Japan and Germany in the early 1960s and began to spread to Europe and the United States, and mainly naphthalene, melanin and polycarboxylic acid may be used.

In the present invention, the slump is from 8 to 23 cm, preferably from 12 to 21 cm. The compressive strength of the concrete provides tunnel lining concrete with a maximum of 40 Mpa, preferably 21-30 MPa.

The present invention improves the fluidity of the tunnel lining concrete, reducing the heat of hydration and durability performance, reducing the cracks and structural performance degradation due to drying shrinkage and hydration heat, it is possible to construct the tunnel lining concrete of excellent performance more efficiently.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

[ Example ]

Each component used in the tunnel lining concrete composition according to an example of the present invention is as follows:

(1) cement, blast furnace slag powder, fly ash

The chemical composition and physical properties of "Ordinary Portland Cement" (OPC), "Ground Granulated Blast Furnace Slag (GGBFS)" and "Fly Ash (FA)" used in the present invention As shown in Table 1 below.

ingredient OPC GGBFS FA SiO ₂ (%) 20.2 31.7 57.6 Al ₂ O ₃ (%) 5.8 14.5 25.5 Fe ₂ O ₃ (%) 3.0 0.7 6.1 CaO (%) 63.3 41.7 3.4 MgO (%) 3.4 5.4 0.9 SO ₃ (%) 2.1 2.1 - Ignition loss (%) 1.2 2.6 4.3 importance 3.15 2.90 2.20 Powder level (cm ² / g) 3,120 4,450 3,590

(2) aggregate

The coarse aggregates were used with crushed gravel having a maximum dimension of 25mm, and the fine aggregates were used for washing sea sand. The physical properties of the aggregates are as shown in Table 2 below.

In the above, the fine aggregate may have a particle diameter of 0.15 to 2.5 mm, and a density of 2.5 g / cm ³ or more, and a coarse aggregate has a particle diameter of 2.5 to 40 mm and a density of 2.5 g / cm. Those according to KS F 2526 "Concrete Aggregates" consisting of cm ³ or more may be used.

Kinds Specific gravity Absorption (%) Percentage of solids (%) F.M. Unit weight (kg / m ³ ) Fine aggregate 2.60 0.94 56.8 2.80 1,475 Coarse aggregate 2.68 0.78 65.4 6.97 1,552

 (3) fiber reinforcement

As a fiber reinforcing material, a polyamide fiber having a fiber length of 20 mm as shown in Table 3 was used, and a standard usage amount was 0.6 kg / m ³ .

Item Diameter Length importance Tensile force Modulus of elasticity Phosphorus Melting point color Properties 23 μm 20 mm 1.16 896 MPa 5.17GPa 103 MPa 225 ℃ White

Example  1 to 4 and Comparative example  1 to 2

Tunnel lining concrete composition was formulated in the composition as shown in Table 4.

Polyamide fiber reinforced concrete is applied in Examples 1 to 4 in order to reduce cracks, improve durability and structural performance by applying polyamide fiber reinforced concrete to increase watertightness and maintenance cost caused by various cracks of tunnel lining concrete. An amount of 0.6 kg / m ^{3 was} mixed to prepare a concrete composition.

At this time, the design reference strength (f _ck ) of concrete was selected from two types of 24 MPa, 27 MPa, which is the strength mainly used in the tunnel lining concrete currently being constructed.

In addition, in order to improve the flowability, quality and durability of concrete, Examples 2 and 4 used a three-component binder (Binder) mixed with cement 78%, blast furnace slag fine powder 15% and fly ash 7%.

In Table 4, the air amount and the slump are the target values for the blend design. In Examples 1 to 4 and Comparative Examples 1 and 2, the target slump flow was set to 50 ± 5.0 cm and a target air amount of 4.5 ± 1.5%, and the amount of high-performance sensitizer and AE agent was adjusted to achieve this.

division f _ck (MPa) W / B (%) S / a (%) AD1 (B ×%) AD2 (B ×%) Unit Weight (kg / m ³ ) W Binder S G NF C BFS FA Example 1 24 49.1 46.5 0.005 1.0 162 330 0 0 832 1000 0.6 Example 2 24 41.4 46.5 0.005 1.0 162 305 27 59 820 947 0.6 Example 3 27 45.3 45.5 0.007 0.9 163 360 0 0 819 985 0.6 Example 4 27 38.5 45.5 0.007 0.9 163 330 30 63 789 949 0.6 Comparative Example 1 24 49.1 46.5 0.007 0.9 162 330 0 0 832 1000 0 Comparative Example 2 27 45.3 45.5 0.007 0.9 163 360 0 0 819 985 0

W / B: water-binding ratio S / a: fine aggregate fraction

W: water C: cement BFS: blast furnace slag fine powder FA: fly ash

S: fine aggregate, G: coarse aggregate

NF: Polyamide fiber, AD1: Made by AE AD2: High performance reducer

[ Experimental Example ]

Experiment method

(1) Characteristics of Unconsolidated Concrete

As shown in Fig. 1, the air content of the concrete was conducted in accordance with KS F 2421 "Air content test method by the pressure method of concrete which is not solid", and the slump flow was determined in accordance with KS F 2402 "Test method of concrete slump". The slump cone was vertically lifted by the method specified in the slump test method, and the average diameter of the concrete spreading was measured up to 0.5 cm in the largest direction and at right angles thereof, and the average value was defined as the slump flow value.

(2) compressive strength test

For the test of compressive strength of concrete, a cylindrical specimen of Φ10 × 20cm was used. After the specimen was manufactured, curing was performed at 20 ℃ and 60% constant temperature and humidity chamber, and the compressive strength of early strength 15h, 18h, 24h was measured. Standard curing was carried out in water at 20 ± 2 ℃, and was carried out in accordance with KS F 2505 "Testing method for compressive strength of concrete" at 3, 7 and 28 days of age.

(3) tensile strength test

Tensile strength test of concrete was carried out in accordance with KS F 2423, `` Test method for tensile strength of concrete '' at 28 days of age after the test specimen was prepared with a cylindrical specimen of Φ10 × 20cm and subjected to standard curing in water of 20 ± 2 ℃.

 (4) flexural strength test

In the test of bending strength of concrete, the specimens of 150 × 150 × 550 mm were prepared and subjected to standard curing in water at 20 ± 2 ℃, and the simple beams were divided into three points according to KS F 2408, `` Testing method for bending strength of concrete '' at 28 days It was carried out according to the loading method.

 (5) dry shrinkage test

Drying shrinkage of concrete was measured by the comparator method in accordance with KS F 2424 "Testing method for changing the length of mortar and concrete". The specimen for measuring the length change by dry shrinkage is attached to the frosted glass for marking by using a mold of 100 × 100 × 400 mm so that the distance from both ends on the centerline of the side surface of the specimen to the frosted glass marking is 25 mm or more. Then, the water was cured up to 7 days of age, and then, as shown in FIG. 6A, the length change was measured at a predetermined age by exposing to a dry state (temperature 20 ± 2 ° C., humidity 65 ± 10%).

(6) accelerated neutralization experiment

In the neutralization experiment, a columnar specimen of φ10 × 20 cm was prepared, and the specimens were cut in half after undergoing underwater curing for 28 days, and a neutralized specimen was prepared from the specimen of φ10 × 10 cm. In order to prevent errors due to bleeding and material separation, a polyurethane paint was applied to the circumferential surface so that neutralization could occur from the cut surface. Accelerated neutral experiments were carried out under the conditions of 5% CO ₂ concentration, 60% relative humidity, 20 ℃ temperature, the experiment was terminated at the age of 56 days. The neutralization depth was measured by neutralizing the specimens after the accelerated neutralization was completed.

(7) Freeze thawing experiment

The freeze-thawing experiments were carried out using a method of freezing underwater melting which was proposed in Method A of ASTM C 666 after producing 100 × 100 × 400 mm square specimens and curing them under water for 14 days. The measurement cycle was carried out up to 300 cycles in which the center temperature of the specimen was frozen and thawed from -18 ° C to 4 ° C as one cycle. The specimens were taken out every 30 cycles and the vibration frequency and weight change of the concrete were measured. In addition, the relative dynamic modulus of elasticity was calculated according to the following equation 1 proposed in ASTM C 666:

 [Calculation 1]

In the formula,

P _c is the relative dynamic modulus of elasticity (%) after the cycle,

n _c is the vibration frequency after the cycle,

n is the oscillation frequency before freeze thaw experiment.

Experiment result

(1) Properties of Unconsolidated Concrete

Examples 1 to 4 and Comparative Examples 1 to 2 to measure the "characteristic of the concrete is not firm" for the concrete is shown in Table 5 below. As shown in Table 5, because the fluidity of the solid concrete was all determined by the mixing design, it was found that the target slump flow 50 ± 5.0 cm and the air content 4.5 ± 1.5%.

The slump flow of the unconsolidated concrete was greater in concrete incorporating blast furnace slag powder and fly ash in Examples 2 and 4 than when only the ordinary Portland cements of Comparative Examples 1 and 2 were used.

division Slump flow (cm) Air (%) Example 1 49 4.2 Example 2 50 4.4 Example 3 48 4.3 Example 4 53 4.4 Comparative Example 1 46 4.5 Comparative Example 2 46 4.5

(2) compressive strength

The compressive strength of the concrete prepared according to Examples 1 to 4 and Comparative Examples 1 to 2 was measured and shown in Table 6 below. Design basis strength is 24 MPa and 27 MPa, respectively, Comparative Examples 1 and 2 In the ordinary Portland cement (OPC), Example 0.6 kg / m ³ incorporated in the first and third usually added to the polyamide fiber in the cement (ONF) and In Examples 2 and 4, the compressive strengths of the three types of concretes containing 0.6 kg / m ^{3 of} mixed polyamide fibers (OSFNF) in the three-component cement containing blast furnace slag powder and fly ash in the ordinary Portland cement were measured. , The measurement results are shown in Figures 2a and 2b below.

FIG. 2A shows the design reference strength (f _ck ) of 24 MPa, respectively, and shows the compressive strengths of OPC of Comparative Example 1, ONF of Example 1, and OSFNF type 3 concrete of Example 2, and FIG. 2B shows design reference strength (f _ck). 27 MPa, and the compressive strengths of the OPC of Comparative Example 2, the ONF of Example 3 and the OSFNF 3 type concrete of Example 4 were respectively shown.

According to the measurement results of FIGS. 2A and 2B, regardless of the design reference strength, the 28-day compressive strength was found to be large in the order of "OPC <ONF <OSFNF", and the compressive strength of the OSFNF concrete of Example 2 was shown in Comparative Example 1 The compressive strength of the OSFNF concrete of Example 4 was about 18% larger than that of OPC concrete, and the compressive strength of the OSFNF concrete of Example 4 was 18% larger than that of OPC concrete.

The OSFNF concretes of Examples 2 and 4 exhibited greater compressive strength than concrete using only ordinary Portland cement because the hydrophobic fine blast furnace slag powder, the pozzolanic reaction of fly ash, and polyamide fibers were reinforced.

 (3) tensile strength

As shown in Figure 3a, the tensile strength of the concrete prepared according to Examples 1 to 4 and Comparative Examples 1 and 2 was measured, and the results are shown in Figures 3b and 3c.

Figure 3b is the design reference strength (f _ck ) 24 MPa, showing the tensile strength at 28 days of age of OPC of Comparative Example 1, ONF of Example 1 and OSFNF type 3 concrete of Example 2, respectively. As shown in Figure 3b, by reinforcing the polyamide fibers in the three-component cement in Example 2, the tensile strength of the concrete obtained about 19% larger than the concrete using only ordinary Portland cement of Comparative Example 1.

In addition, Fig. 3c is the design reference strength (f _ck ) 27 MPa, and shows the tensile strength at 28 days of age of OPC of Comparative Example 1, ONF of Example 1 and OSFNF type 3 concrete of Example 2, respectively. As shown in Figure 3c, by reinforcing the polyamide fibers in the three-component cement in Example 4, the tensile strength of the concrete obtained about 20% greater than the concrete using only ordinary portland cement of Comparative Example 2.

As described above, the reason why the concrete incorporating the polyamide fiber in addition to the three-component cement as in Example 2 and 4 has a high tensile strength is because the polyamide fiber absorbs moisture due to the hydrophilicity, which is a surface property of the polyamide fiber. This is because the induction of hydrogen bonds leads to an increase in adhesion between concrete and fibers, thereby faithfully crosslinking the fibers.

(4) flexural strength

Flexural strength of concrete prepared according to Examples 1 to 4 and Comparative Examples 1 to 2 was measured, and the results are shown in FIGS. 4A and 4B.

Figure 4a is the design reference strength (f _ck ) 24 MPa, shows the results of measuring the bending strength of the concrete of OPC of Comparative Example 1, ONF of Example 1 and OSFNF of Example 2, Figure 4b is the design reference strength (f _ck ) It is 27 MPa and the result of having measured the bending strength with respect to OPC of the comparative example 2, ONF of Example 3, and OSFNF concrete of Example 4 is shown.

As shown in Figs. 4A and 4B, as in Examples 2 and 4, by adding and reinforcing polyamide fibers to the three-component cement, the flexural strength of the concrete is about 3% higher than the concrete using only ordinary Portland cement of Comparative Examples 1 and 2. To 5% greater.

The reason why the concrete including the polyamide fiber reinforcement is not significantly different from the concrete in the flexural performance is that the polyamide fiber is a fiber reinforced for the purpose of crack control rather than the structural reinforcement, so the mixing rate is not high. On the other hand, when the length of the fiber is increased, the bending length of the fiber is increased when subjected to the bending load, it is determined that it will affect the ductile fracture behavior.

(5) dry shrink

The length change by dry shrinkage of the concrete prepared according to Examples 1 to 4 and Comparative Examples 1 to 2 was measured as shown in FIGS. 5A and 5B, and the results are shown in FIGS. 5C and 5D.

FIG. 5C shows a design reference strength (f _ck ) of 24 MPa, and shows the result of measuring the length change generated during drying of OPC of Comparative Example 1, ONF of Example 1, and OSFNF three types of concrete of Example 2. As shown in Figure 5c, the dry shrinkage of the concrete reinforced with polyamide fiber to the three-component cement of Example 1 is more than the dry shrinkage of concrete using only ordinary portland cement of Comparative Example 1 as the dry age shrinkage width The increase was about 23% at 56 days of age.

Figure 5d is the design reference strength (f _ck ) 27 MPa, and shows the results of measuring the length change generated when drying the OPC of Comparative Example 2, ONF of Example 3 and OSFNF concrete of Example 4. In FIG. 6D, the concrete drying shrinkage of the OSFNF of Example 4 was reduced by about 11% compared to that of the OPC concrete of Comparative Example 2.

As such, the effect of reducing shrinkage of polyamide fiber-reinforced concrete using three-component cements is very large, so that the resistance to cracking caused by plasticity and dry shrinkage may be greatly increased when applied to tunnel lining concrete.

(6) neutralization

The scene of measuring the neutralization depth at 56 days of age of the concrete prepared according to Examples 1 to 4 and Comparative Examples 1 to 2 is shown in FIG. 6A, and the results are shown in FIGS. 6B and 6C.

In general, cement reacts with water to produce a large amount of Ca (OH) ₂ , a hydration product, and CO ₂ penetrated through the pores of hardened concrete reacts with cement hydrate, especially Ca (OH) ₂ , to provide stable insoluble CaCO. Converted to ₃ , which is called carbonation. Carbonation tends to increase some strength due to filling pores in concrete, but this causes concrete problems in concrete, because of the decrease of pH in concrete and the corrosion of reinforcing bars.

The most influential factor for neutralization is the amount of Ca (OH) ₂ in concrete, which is known to have a slight difference in neutralization after curing because the hydration characteristics are different depending on the cement type. Amorphous silica in the usual case of Portland cement, and about 30% of the unit cement content created with Ca (OH) _2, blast furnace slag and fly ash, etc. When using a mineral admixture, the Ca (OH) ₂ and a mineral admixture Due to the latent hydrophobic and pozzolanic reactions, the amount of Ca (OH) ₂ decreases and the amount of CSH increases, densifying microstructures, while increasing the neutralization rate.

6B is a design reference strength (f _ck ) of 24 MPa and shows the result of measuring the accelerated neutralization depths of OPC of Comparative Example 1, ONF of Example 1, and OSFNF three types of concrete of Example 2. As shown in Fig. 6B, the neutralization depths up to 28 days of measurement age showed similar tendencies, but in particular, the neutralization depth of the OSFNF concrete of Example 2 was significantly reduced. This can be seen that in the case of the OSFNF concrete of Example 2, the concrete structure becomes dense as the long-term age, the reaction rate between the cement hardened body and the CO ₂ is lowered and the neutralization rate is reduced.

Figure 6c is the design reference strength (f _ck ) 27MPa, measured by the OPC of Comparative Example 2, the ONF of Example 3 and the OSFNF concrete of Example 4 accelerated neutralization test results are shown. In FIG. 6C, the neutralization depth of the OPC of Comparative Example 2 and the OSFNF concrete of Example 4 was about 40% from the initial age of measurement, which indicates that the OPC of Comparative Example 2 and the OSFNF concrete of Example 4 were subjected to accelerated neutralization experiments. The difference in compressive strength was about 18%, and the OSFNF concrete of Example 4 appeared largely due to the difference in the sealing degree of the hardened cement.

(7) freeze thaw resistance

Freeze-thawing experiments were performed using the apparatus shown in FIG. 7A related to freeze-thaw resistance for concrete prepared according to Examples 1 to 4 and Comparative Examples 1 to 2, and the results are shown in FIGS. 7B to 7C. It was.

When concrete is repeatedly subjected to freeze-thawing action, microcracks or surface peeling occur due to freeze-thawing of water in the pores to promote deterioration. Experimental methods for evaluating the resistance by freezing-thawing of concrete include various experimental methods such as rapid freeze-melting resistance test (ASTM C 666), critical expansion test (ASTM C 671), surface peeling resistance test (ASTM C 672), etc. This is prescribed. In this study, as the acceleration test, the dynamic elastic modulus was measured according to the cycles of freezing in water and the concrete melted in water.

FIG. 7B shows the shape of the test piece before freeze-thawing test and after 210 cycles of freeze-thawing of the ONF of Example 1, OSFNF of Example 2, and OPC concrete of Comparative Example 1 having a design reference strength (f _ck ) of 24 MPa. 7e shows the shape of the test specimen before and after 210 cycles of freeze-thawing of concrete of Example 3 (ONF), Example 4 (OSFNF), and Comparative Example 2 (OPC) having a design reference strength (f _ck ) of 27 MPa. will be.

In addition, Figure 7d is the design reference strength (f _ck ) 24 MPa, relative elastic modulus by measuring the dynamic elastic modulus of every 30 cycles of freeze-thawing of OPC of Comparative Example 1, ONF of Example 1, OSFNF of Example 2 concrete It is represented by the coefficient ratio. As shown in FIG. 7D, freeze thaw resistance of Example 1 (ONF) and Example 2 (OSFNF) concretes was superior to that of Comparative Example 1 (OPC) concretes. It can be seen that the polyamide fiber in the concrete increases the resistance to shrinkage and expansion caused during the freezing and melting iteration process, thereby significantly improving the freeze-thawing resistance of the concrete according to the present invention.

FIG. 7E shows the design reference strength (f _ck ) 27 MPa and indicates the relative elastic modulus by measuring the dynamic modulus at every 30 cycles of freezing-thawing of OPC of Comparative Example 2, ONF of Example 3, and OSFNF concrete of Example 4. . As shown in FIG. 7E, resistance to freeze-thawing of Comparative Example 2 (OPC), Example 3 (OSF), and Example 4 (OSFNF) type 3 concrete showed a similar tendency.

Generally, the freeze-thawing resistance of mixed cement-based concrete is greater than that of ordinary concrete. This is because the voids in the concrete decrease due to the influence of mineral admixtures, so that the internal hydraulic pressure due to the East Sea is relatively large.

All the concrete used in this experiment was based on the target air volume of 4.5 ± 1.5%. Also, the use of mineral admixture is expected to increase the ratio of finer bubbles than ordinary concrete, and the limit bubble spacing coefficient will be increased than that of ordinary concrete. I think. As a result, the dynamic resistance of concrete mixed with mineral admixtures was superior to that of ordinary concrete.

Therefore, in order to improve the resistance to freezing and thawing, it can be seen that a method of increasing the resistance by using a suitable air entrainer and simultaneously mixing the mineral admixture to alleviate the large expansion pressure generated when the concrete is freeze-thawing.

The present invention by mixing the fiber reinforcement in the concrete composition for tunnel lining, improve the fluidity of the tunnel lining concrete, reduce the heat of hydration and increase the durability performance, reduce the cracking and structural performance degradation by drying shrinkage and hydration heat, excellent performance more efficiently It is possible to construct tunnel lining of concrete, which can greatly improve the work efficiency.

1 is a photograph of the measurement of "air volume of concrete not stiff" and "slump flow" according to an example of the present invention.

Figure 2a is a graph showing the results of measuring the compressive strength for three types of concrete (f _ck = 24 MPa) of Comparative Example 1 (OPC), Example 1 (ONF) and Example 2 (OSFNF) according to an example of the present invention.

Figure 2b is a graph showing the results of measuring the compressive strength for three types of concrete (f _ck = 27 MPa) of Comparative Example 2 (OPC), Example 3 (ONF) and Example 4 (OSFNF) according to an example of the present invention.

Figure 3a is a photograph of the tensile strength of the concrete according to an example of the present invention.

3B is a graph showing tensile strength measurement results for three types of concrete (f _ck = 24 MPa) of Comparative Example 1 (OPC), Example 1 (ONF), and Example 2 (OSFNF) according to one example of the present invention. 28 days].

3C is a graph showing tensile strength measurement results for three types of concrete (f _ck = 27 MPa) of Comparative Example 2 (OPC), Example 3 (ONF), and Example 4 (OSFNF) according to one example of the present invention. 28 days].

4A is a graph showing the bending strength measurement results for three types of concrete (f _ck = 24 MPa) of Comparative Example 1 (OPC), Example 1 (ONF), and Example 2 (OSFNF) according to one example of the present invention.

4B is a graph showing the bending strength measurement results for three types of concrete (f _ck = 27 MPa) of Comparative Example 2 (OPC), Example 3 (ONF), and Example 4 (OSFNF) according to one example of the present invention.

Figure 5a is a photograph related to the dry shrinkage test body and the experimental apparatus according to an example of the present invention.

5b is a photograph of measuring the change in the length of the concrete related to drying shrinkage in accordance with an example of the present invention [ling 56 days]

5C is a graph showing dry shrinkage measurement results for three types of concrete (f _ck = 24 MPa) of Comparative Example 1 (OPC), Example 1 (ONF), and Example 2 (OSFNF) according to an example of the present invention. 56 days].

5D is a graph showing dry shrinkage measurement results for three types of concrete (f _ck = 27 MPa) of Comparative Example 2 (OPC), Example 3 (ONF), and Example 4 (OSFNF) according to one example of the present invention. 56 days].

6a is a photograph of concrete neutralization depth measurement in accordance with an example of the present invention.

6B is a graph showing the results of neutralization measurements for three types of concrete (f _ck = 24 MPa) of Comparative Example 1 (OPC), Example 1 (ONF), and Example 2 (OSFNF) according to an example of the present invention. Work].

6C is a graph showing the results of neutralization measurements for three types of concrete (f _ck = 27 MPa) of Comparative Example 2 (OPC), Example 3 (ONF), and Example 4 (OSFNF) according to one example of the present invention. Work].

Figure 7a is a photo-elastic coefficient measuring apparatus and freeze thaw tester according to an example of the present invention.

FIG. 7B is a freeze thaw test before and after 210 cycles of freeze thawing for three types of concrete (f _ck = 24 MPa) of Comparative Example 1 (OPC), Example 1 (ONF) and Example 2 (OSFNF) according to one example of the present invention. Shape photograph of the test piece.

FIG. 7C is a freeze thaw test before and after 210 cycles of freeze thawing for three types of concrete (f _ck = 27 MPa) of Comparative Example 2 (OPC), Example 3 (ONF) and Example 4 (OSFNF) according to one example of the present invention. Shape photograph of the test piece.

7D is a graph showing the results of dynamic elastic modulus measurements for three types of concrete (f _ck = 24 MPa) of Comparative Example 1 (OPC), Example 1 (ONF), and Example 2 (OSFNF) according to one example of the present invention.

7E is a graph showing the results of dynamic elastic modulus measurements for three types of concrete (f _ck = 27 MPa) of Comparative Example 2 (OPC), Example 3 (ONF), and Example 4 (OSFNF) according to one example of the present invention.

Claims (8)

a) 250 to 500 kg / m ³ binder comprising cement, per unit volume of concrete; b) 150 to 180 kg / m ^{3 of} water, relative to the concrete unit volume; c) for aggregate concrete volume, fine aggregate 600 to 1000 kg / m ³ ; d) coarse aggregate 800 to 1200 kg / m ^{3 for} concrete unit volume; And e) 0.1 to 2.0 kg / m ^{3 of} fiber reinforcement, relative to the concrete unit volume Tunnel lining concrete composition comprising a. The concrete composition for tunnel lining according to claim 1, wherein the fiber reinforcing material is at least one selected from the group consisting of polyethylene fiber, polyamide fiber, polyacrylic fiber, polyester fiber, polypropylene fiber, polyvinyl alcohol fiber, and cellulose fiber. . The concrete composition for tunnel lining according to claim 1, wherein the fiber reinforcement has a length of 1 to 100 mm. The concrete composition for tunnel lining according to claim 1, wherein the fiber reinforcement cross section has a diameter or thickness of 10 to 70 µm. The concrete composition for tunnel lining according to claim 1, wherein the fiber reinforcement has a melting point of 120 to 400 ° C. The concrete composition for tunnel lining of claim 1, wherein the binder further comprises at least one selected from the group consisting of blast furnace slag fine powder and fly ash. The concrete composition for tunnel lining according to claim 6, wherein the content ratio of the blast furnace slag powder and the fly ash is 1: 1 to 1: 5 by weight. Tunnel lining concrete prepared using the composition according to claim 1, having a slump of 8 to 23 cm and a compressive strength of 40 Mpa or less.

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