KR0147002B1 - Process for preparing concrete - Google Patents

Abstract

[purpose]

We provide manufacturing method of high durability concrete

[Configuration]

The unit cement content is 550kg / cm ^2, and the slag mixing rate is 0%, 12.5%, 25%, and the fly ash is 0%, 15%, 30%, silica fume 10% and blast furnace slag 12.5% , 10% silica fume, 25% blast furnace slag, 15% fly ash and 12.5% blast furnace slag are used as cement variables to make highly durable concrete by adding and adding 0.04% air emulsifier and high fluidizing agent.

Description

Manufacturing method of high durability concrete

1 is an explanatory diagram of a chlorine ion permeation test device,

2 is a specimen shape of reinforcing bar corrosion test,

3 is an explanatory diagram of the rebar corrosion test apparatus,

4 is a block diagram of the ultrasonic velocity measuring device.

The present invention relates to a manufacturing method of high durability concrete, and more particularly to a manufacturing method of high durability concrete for high-quality construction.

Civil engineering facilities using concrete have important status in the national economy as a national infrastructure. These concrete civil engineering facilities are exposed to various special physical and chemical environmental conditions from the moment of construction, and these physical and chemical environmental conditions have a direct and indirect effect on the installation.

For concrete structures, the ultimate desire is that the facility will exist for the desired period of time as the facility is performing well, but from the time the facility is installed, it will be affected by various invasive factors, depending on the characteristics of the facility and the location of the installation. Intrusive physical and chemical environments acting on the structure will cause damage to the structure, that is, deterioration of the structure. Due to the deterioration of the structure, the structure has a certain lifetime, that is, the lifetime, which must be secured so that the facilities can maintain usability for the target lifetime.

In particular, it is a general view that concrete used in many civil facilities is a material superior in durability compared to other construction materials, but recently, even a concrete structure has not been sufficiently secured. This is due to the development of analysis and design technology, but the design standards are precise, but the difficulty of securing materials such as aggregates, the effects of new extreme environmental conditions, the lack of organic relations due to the division of labor, and the misconception that they will have a semi-permanent lifespan The importance of research for securing high quality durability is increasing further.

Therefore, in relation to the endurance of civil engineering facilities, the performance degradation phenomenon occurring in concrete structures is first examined by the cause and type, and the causes of performance degradation can be analyzed to derive the method of improving the durability of concrete structures. It is an object of the present invention to propose a suitable formulation.

First, the causes of performance degradation of concrete structures will be examined. The durability of a structure is its ability to maintain a satisfactory level of reliability and serviceability throughout the life of the structure. Here, usability refers to the ability to fully perform the desired function during the design and construction of the structure, and durability of the structure refers to performance degradation phenomenon that occurs in the structure due to weathering, chemical reaction, abrasion or other deterioration process of the structure. Can be defined as the ability to resist.

Therefore, external factors include physical, chemical, and mechanical factors, which are considered as the causes of performance deterioration of structures. These include external air influences, extreme temperature changes, friction, electrochemical action, natural or industrial liquids, The influence by gas can be mentioned.

In addition, internal factors such as alkali-aggregate reaction, volume change due to the difference in thermal properties of hardened cement and aggregate, and damage due to the permeation of concrete are included. In particular, the permeability of concrete is the main determinant of concrete's vulnerability to external action. Therefore, concrete must be watertight in order to become a durable concrete resistant to degradation. In other words, the performance degradation of water present in the concrete and cement hard body can be summarized as follows.

1) In materials containing voids, moisture causes physical manifestations of poor performance and is a means of transporting many harmful ions.

2) The physico-chemical phenomena associated with the movement of moisture in the material, including voids, are affected by the material's permeability.

3) The degradation rate is affected by the type and concentration of ions in the water and the chemistry of the material.

Civil engineering facilities are often exposed to moisture, at least in contact with water by rain or the like. Therefore, how to control and control the range of moisture exposed to concrete structures, and how to improve and maintain the water tightness of concrete, is an important factor in its durability.

① Concrete structures may have a temperature change in which the temperature inside the concrete falls below the freezing point of the pore water and above and below the freezing point due to natural or artificial temperature rise or drop. It is then subjected to freezing and thawing, which causes structural degradation.

When the temperature of the hardened concrete in the wet state decreases, the pore number in the capillary gap of the cement mortar freezes, increasing the volume by about 9.1%. The pore water pressure is generated as a resistance against loss of water in the freezing portion due to the different freezing point of the pore number according to the gap, and the gap in the freezing portion is gradually expanded by capillary action. In addition, when freezing and melting of continuous pore water occur, volume change intensifies and repeated freezing and thawing action has a cumulative effect.

② Concrete exhibits strength as a binder due to the hydration of cement. Calcium hydroxide, which produces about one third of the amount of cement in the hydration of cement, exhibits strong alkalinity of about pH 12-13. The pH of the entire hydrate is determined. Calcium hydroxide is converted into calcium carbonate (CaCO ₃ ) and water by the following reaction in contact with weakly acidic carbon dioxide (CO ₂ ) contained in the atmosphere.

In the above reaction, the pH of the portion changed to calcium carbonate is lowered to about 8.5 to 10, so it is called Neutralization Carbonization. Neutralization proceeds inward from the surface of the concrete, which becomes heavier and denser as the weight reacted with carbon dioxide. And as the neutralization proceeds, some very fine cracks occur, but this is not a problem.

Therefore, the physical deterioration caused by neutralization is the deterioration of corrosion of reinforcing bar. Neutralized concrete may cause the alkali passivation film surrounding the internal reinforcing bars to become unstable and cause corrosion, resulting in performance degradation of the structure.

The neutralizing CO ₂ also reacts to small amounts in the air, where CO ₂ in the air is 0.03% in rural areas, 0.1% in unventilated laboratories, 0.3% in large cities, and in 1% in special cases. The difference is large. As in the above formula, Ca (OH) ₂ is carbonized with CaCO ₃ and other cement components are decomposed into silica hydrate (Hyrated silca), aluminine (Alumine), and also produce ferric oxide (Ferric oxide). Decomposition of calcium compounds occurs at normal low CO ₂ pressures but very slowly across the surface of the concrete.

③ The alkali-aggregate reaction is an alkali in the aggregate of pore solution (alkali metal ions (alkali metal ions Na ⁺ , K ⁺ _, hydroxide OH ⁺ ) eluted) that contains alkali hydroxide in concrete. It includes the phenomenon of cracking in concrete due to volume expansion accompanied with the production and absorption of reaction product (alkali silica gel Alkari-silicate) .Alkali-aggregate reaction is classified into three types according to the reaction mechanism. do.

(1) Alkari-silica reaction (ARS)

(2) Alkari-carbonate rock reaction

(3) an alkali-silicate reaction

Since most reactions are alkali-silica reactions, usually alkaline-aggregate reactions refer to alkali-silica reactions. Alkaline-silica reaction is a reaction in which silica (SiO ₂ ) of aggregate reacts with alkali metal ions (Na ⁺ , K ⁺ ) in concrete solution to form alkali silicate gel (Alkari-silicate gel) to absorb and expand water.

Alkaline-aggregate reactions result in the formation of alkali-silica gels and changes in aggregate boundaries, which are in the ultimatelywelling type, which tends to absorb moisture and increase volume. This alkali-silica gel is surrounded by the surrounding cement hardening, causing internal pressure and eventually causing expansion, cracking, and pop-outs of the hardening of the cement.

The expansion is due to the hydrostatic pressure expressed through the osmotic potential and is caused by the expansion pressure of the solids produced in the alkali-silicone reaction. Therefore, this volume expansion can cause fatal damage to the concrete structure. Some of the relatively soft gels are dissolved in water pore water and settle in the cracks caused by the expansion of the aggregates.

④ When concrete structure is in contact with soil, the most common and widespread deterioration of concrete structure is caused by sulfate attack. In groundwater or soil, naturally occurring sulfates such as sodium, potassium, calcium and magnesium are present. In particular, clay soils contain large amounts of sulfates. In addition, civil engineering facilities perform functions such as sewage treatment, and thus are exposed to wastewater and sewage, so they are placed in an environment containing a lot of sulfates. Therefore, the performance degradation mechanism caused by sulfates in civil engineering facilities is one of the more questions to be identified.

Corrosion of steel reinforcement in concrete is one of the major causes of deterioration of concrete structures. Reinforced concrete compensates for the weakness of concrete by embedding reinforcing steel with the same thermal expansion coefficient and excellent adhesion to concrete, while surrounding concrete is a composite material with excellent durability that protects corrosion, which is a weak point of reinforcing steel. However, if the concrete structure is exposed to the corrosive environment periodically or long term, the passivation film around the reinforcing bar is destroyed and the corrosion of the reinforcing bar causes the performance of the reinforcing bar itself and the fall of the concrete film. In particular, since large-scale civil engineering structures, such as reclamation facilities, are installed directly in contact with the sea, corrosion problems of rebar due to salt damage are serious.

When a certain amount of chloride ions or acidic anions are present in the concrete due to the external environment of the concrete structure or due to the concrete structure itself, the passivation film around the reinforcing bar is destroyed by the action thereof and the reinforcing bars are easily corroded. Corrosion of reinforcing steel in concrete causes the cross section of the steel to be lost, reducing the overall strength of the structure as well as expanding the steel to about 2.5 times its original volume and causing cracking at the expansion pressure. When a crack occurs, the supply of oxygen or water is facilitated, which promotes corrosion of the reinforcing steel, and eventually the coated concrete falls off, resulting in a significant performance degradation of the structure.

⑥ Degradation due to other causes

Ⓐ Dry shrinkage of concrete structures by wet and dry is a phenomenon in which the concrete contracts when it is dried and expands when the concrete gets wet again. The volume change due to the change of moisture is inherent in hydraulic cement concrete. As a result of the damage caused by wet and dry, the change of moisture content in the hardened cement constricts or expands the concrete, while internal restraint is provided by internal restraint due to the difference of contraction expansion, restraint of aggregate and reinforcement, and restraint according to the external structure type and stress This happens. It can be seen that cracks occur in the concrete structure due to such stress.

Ⓑ In the performance degradation caused by the precipitation of soluble salts, one of the performance degradations that can occur in concrete that is in contact with the ground containing the groundwater, etc., is one of the characteristics of concrete due to the precipitation of soluble salts contained in hardened concrete cement. It is a performance degradation phenomenon of the structure. When alkali salts are dissolved and precipitated out of concrete, the pH inside the concrete decreases, and the reinforcing steel present in the concrete is placed in an environment where corrosion easily occurs. In addition, the dissolution of salts creates a gap inside the concrete. Due to this mechanism, it can be seen that degradation of concrete structures such as corrosion of reinforcing bars occurs.

Ⓒ As a civil engineering structure due to the performance deterioration due to impact and wear fragments, structures such as coastal breakwater structures, bridges and drainage locks are designed to resist waves, wind and vehicles. These facilities are degraded by shock waves generated by impact loads. In addition, the shock wave caused by the earthquake also causes performance degradation.

In the case of the civil structures, the parts directly in contact with the flow of water to the structural structure, due to the energy release by the bubbles of water droplets, the performance decreases due to wear caused by small voids and fractures on the concrete surface. In the case of structures such as breakwater structures and drainage locks adjacent to the seawater, sand and rock components contained in the seawater while the structure is in contact with the seawater. In the case of structures, the sand, rock component, etc., contained in the seawater as the structure is in contact with the seawater. The surface of the structure is destroyed as these seawater components are rubbed on the surface of the structure, resulting in the performance degradation of the structure.

As a result of damage caused by impact and abrasion, the concrete surface is broken or many small cavities are generated by the impact and abrasion. Broken concrete surfaces damage the concrete's function. In addition, when the concrete surface is damaged by abrasion, the cover of the reinforcing bar becomes thin and the material causing rebar corrosion easily penetrates, thereby promoting the corrosion of the reinforcing bar, and it is thought that the intrusion of harmful substances into the concrete is facilitated.

In order to achieve the object of the present invention for maximizing the durability of concrete to suppress or prevent the cause of performance degradation of concrete structures as described above, various performance tests are performed on various experimental variables, and as a result, strength and durability characteristics are The analysis yielded the most rational solution.

That is, in the present invention, the parameters of the present invention are usually Portland cement (one type) and the unit cement amount is 550kg / m ³ , and fly ash 0%, 15%, 30% and silica fume (Silica fume) in order to examine the effects of admixtures ) 0%, 10%, 20% and blast furnace slag vary from 0%, 12.5%, 25% to fluidity, age-dependent strength and permeability, corrosion resistance, sulphate resistance and freeze thaw resistance. Various endurance tests were carried out, and the application of admixtures was carried out by adopting variables in which 10% silica fume and 12.5% blast furnace slag, 10% silica fume and logo slag 25%, and 15% fly ash and 12.5% logo ash slag were substituted for cement The strength and durability of the case where the increase in cost was reduced by the use of slag was examined. In addition, some variables needed to take into account the effects of air volume are carried out with two variables, one with and without air, and the other admixture is used to determine the interactivity when two or more are mixed and used. At the same time, the experiment was also used. As described above, in order to grasp the strength, flowability, and durability characteristics of the high-quality concrete in the present invention, the experiments were performed with the main variables such as cement type, per unit cement, admixture type, and addition amount.

The unit cement content and water-cement ratio are the variables that have the greatest influence on the properties of hard concrete and hard concrete. In general, when the unit cement amount is high and the water-cement ratio is low, the fluidity of the hardened concrete is reduced, but the mechanical and durable properties of the hardened concrete are improved.

Therefore, in the embodiment of the present invention, H was set as a variable between the unit cement amount and the water-cement ratio. The H mix showed a unit cement content of 550 Kg / m ³ , a water-cement ratio of 0.28, and a fine aggregate ratio of 0.35.

In order to secure the fluidity of the high-quality concrete in the embodiment of the present invention, by selecting an appropriate high fluidizing agent so that the slump is 18 cm or more immediately after concrete mixing, and the slump is 8 cm or more after 1 hour after mixing. In order to ensure sufficient workability, even if the time for transporting is delayed at the site. In addition, the experimental variable was selected as the case where the air amount of about 4% was carried out by administering 0.04% of the air softener to the same specimen. The cement used in the embodiment of the present invention is the first type ordinary portland cement of domestic S company, and the basic physical properties are shown in Table 1 below, which satisfies the KS regulations.

Concrete aggregate is clean, hard, durable, and chemically stable with a suitable particle size, it does not contain harmful substances such as thin slabs, slender slabs, clay, organic impurities, salts, etc. For example, fine aggregates collected from streams near Seoul were used. The specific aggregates used were 2.60 and the absorption rate was 1.5%. Coarse aggregates used in high-strength concrete have better physical properties than steel gravel, but it is better to select coarse aggregates with appropriate maximum dimensions and particle size distribution. However, due to the difficulty in obtaining a suitable grain size, it is difficult to use a crushed stone. Therefore, a maximum aggregate size of 19 mm was used, and the coarse aggregate had a specific gravity of 2.75 and an absorption rate of 1.0%.

Blast furnace slag was used as the main variable, and the blast furnace slag was produced at Gwangyang Works, and the specific surface area was measured by Blain transmission method / g, silica fume was used in Norway E company, fly ash is Boryeong Chungcheongnam. In addition, high fluidizing agent is a domestic Mighty copolymer suitable for ASTM C494 Type DG, specific gravity of 1.20 ± 0.01, solid content 41 ± 1%, color: dark brown, pH 8-10, chloride 0.00%.

The high fluidizing agent used in the embodiment of the present invention was able to reduce the amount of water in the concrete mix by about 20-30% by effective hydration of the cement particles, and separate the material than the concrete without the admixture under the same water-cement ratio condition. The workability is excellent without any phenomenon and the fluidity lasts for a considerable time to facilitate the pouring work.

Air entrainers were used to properly entrain fine air bubbles in concrete. Air entrainment significantly improves the durability of concrete when the concrete is exposed to moisture and freeze-thawed, and entrained air can be sufficiently resistant to peeling of the concrete surface caused by chemical deicers. To make sure. It also improves the workability of stiff concrete and reduces or eliminates material separation and bleeding. Airborne concrete contains fine air bubbles evenly distributed through the cement paste.

The air entrainer used in the examples of the present invention is a water-soluble solution that satisfies the above requirements under the trade name EZAIR of K company in Korea, and does not contain chloride.

Example 1-5

The formulation of the parameters for Example 1-5 is as follows, the test results compressive strength 600Kg / cm , Slump 18 ± 3cm, proper air flow and fluidity were maintained, and the durability was proved to be excellent through the test as described below.

Experimental results for fluidity test, compressive strength test, splitting tensile strength test, flexural tensile strength test, permeability test, sulfate resistance test, freeze thaw resistance test, corrosion resistance test, etc. As follows.

The fluidity test described above was performed according to KS F 2402 and ASTM C143, and the slump loss was observed up to 1 hour by measuring from the slump of the base concrete before the addition of the high fluidizing agent and immediately after the mixing.

In this experiment, in order to secure the fluidity of high-quality concrete, the slump should be more than 18cm immediately after the concrete mixing and at least 8cm after 1 hour after the mixing. The experiment was adjusted to secure.

In addition, the air volume of concrete was measured according to the provisions of KS F 2421 and ASTM C231,457, and the entrained air volume was added to about 4% by adding 0.4% of the AE agent with the air entrainer added.

In the compressive strength test, the test was carried out according to the test of the compressive strength test of EKS F2405 concrete. The test specimen was a 10 × 20cm circular specimen, and the prepared specimen was cured in a constant temperature water bath at 20 ± 2 ℃ until the test, and the compressive strength of 3 days, 7 days, 28 days, and 56 days with a compression tester with a maximum capacity of 200t. Is a measurement of

The splitting tensile strength test was performed in accordance with the provisions of the splitting tensile strength test of KS F2423 concrete. The specimen is a 10 × 20cm circular specimen, and the prepared specimen was subjected to underwater curing in a constant temperature water bath at 20 ± 2 ℃ until the test, and the splitting tensile strength of 28 days was measured by a strength tester with a maximum capacity of 200t.

In the test of flexural tensile strength, the test was conducted according to the test of flexural tensile strength test of KS F2408 concrete, the test specimen was a 10 × 20cm circular specimen, and the prepared specimen was immersed in a constant temperature water bath at 20 ± 2 ℃ until the test. Afterwards, the flexural tensile strength of 28 days was measured by a strength tester with a maximum capacity of 200t.

In the water permeability test, the permeability of each specimen was measured indirectly by measuring the resistance to the penetration of chlorine ions in the specimen. Of course, the actual permeability of concrete was determined by the natural pressure or air pressure of the concrete specimen. Although this method requires a lot of time to permeate and the actual amount of water permeated is very small, it is intended to avoid a long time test. Therefore, the method of using the chlorine ion permeation due to the potential difference shows the distinctive characteristics between the specimens, which makes it possible to obtain the relative index of permeability for concrete specimens in a short time.

The chlorine ion permeation test was performed according to ASTM C1202-91 Electrical indication of concrete's ability to resist chloride ion pemetration and the method of AASHTO T259. That is, as shown in FIG. 1, a concrete specimen of 10 cm diameter cured in water for 28 days was cut to a length of 5 cm, and the relative humidity was maintained at 95% or higher until the experiment was carried out, and the test specimen was fixed to the Applied Voltage Cell. To configure the circuit.

In this circuit, the power supply provides a stable supply of 60 ± 0.1V direct current of ± 0.1V. The sealant used to prevent the electrolyte solution from leaking during the experiment is a rubber product and weighs 20-40g. The specimens were fixed between them.

The current can be measured by connecting a known resistor to the circuit and measuring the voltage. The resistance used at this time is to use the smallest possible resistance to minimize the voltage applied to the concrete specimen. 0.2ohm was used.

As shown in FIG. 2, the corrosion test of rebar was carried out by immersing a 16cm-high specimen in a 1%, 2cm, and 4cm depth in a 10cm-thick concrete surface to a depth of 13cm in a 5% sodium chloride solution, as shown in FIG. As shown in the figure, a DC circuit was constructed by connecting a positive pole of the 20V DC power supply to rebar and a negative pole of 5% sodium chloride solution. In FIG. 3, the potential difference between the positive electrode and the negative electrode not only promotes penetration of chlorine ions, but also promotes rebar corrosion.

In the corrosion measurement method of the specimen, the crack is formed by the expansion pressure due to the corrosion of the reinforcing bar, and the electrolyte penetrates between the cracks of the concrete, thereby increasing the amount of current. To measure this point, connect a 10ohm resistor to each specimen, measure the voltage across the resistor, and convert it to current. The current voltage was measured every 30 minutes using a data logger. In addition, when a crack is formed by corrosion, a sudden increase in voltage occurs, and the cracked specimen is removed from the circuit and the crack is generated.

Standards of performance deterioration by sulfates include specimen expansion, strength, reduction, and weight reduction. In this experiment, the weight loss as well as the length change were investigated.

The experiment was carried out by dipping two 28-day aquatic specimens in 10% sodium sulfate solution per experimental variable by US Bureau of Reclamation Test Method 4908B to measure the change in length and weight loss over time. The 10% sodium sulfate solution was prepared by dissolving 100 g of sodium sulfate in 900 ml of water and adding water to make 1000 ml of solution, which was 704 mol / m. This is the solution.

The specimens in this experiment were 5 × 5 × 25 cm square specimens and were immersed in two specimens for each experimental variable. ASTM C341-89 (Standard Test Method for length Change) was used to measure the expansion caused by sulfate. Experiments were carried out at intervals of one week after immersion in accordance with the provisions of Drilled and Sawed Specimens of Cement Mortar and Concrete. The measurements were made using a gnat mole strain gauge, which is 200 mm long and can measure up to 1 / 1,000 mm. And the weight change by sulphate was measured at 1 month interval after immersion.

Next, in measuring the deterioration and durability due to the freezing and thawing action of concrete, KS F 2456 (Test of Resistance to Rapid Freezing Melting) was performed by periodically applying the temperature below the freezing point of the pore water and the temperature above the freezing point. ) And ASTM C666 (Resistance of concrete to rapid freezing and thawing). The damage after freeze-thaw test was determined by measuring the dynamic elastic modulus at regular intervals. The dynamic elastic modulus was calculated by the ultrasonic velocity method as shown in FIG. The test was carried out on 300 cycles, but the test was terminated when the relative dynamic modulus was less than 60%.

Hereinafter, the results of the property test of the concrete produced by the present invention.

1) Liquidity test result

The dosage of the high fluidizing agent was 1.6-1.8% to meet the target slump of 18 cm and over 1 cm of sludge after 1 hour.

Various characteristics of hardened concrete (durable formulation)

2) The strength characteristics test result shows unit cement amount 550Kg / m The compressive strengths for the formulations with a molar cement ratio of 0.28 are as follows.

3) The permeability test results are as follows.

4) In the corrosion resistance test, when the current flowing in the DC circuit of each experimental mixing variable is measured, when the corrosion of the reinforcing steel in the concrete advances, the current rises rapidly due to the crack caused by the volume expansion of the steel. In addition, when the current gradually increases, it is based on the experiment until the amount of current reaches 20 mA.

Corrosion resistance test time for each variable is as follows.

5) The results of freeze-thaw resistance test are as follows.

In this experiment, we used two methods of measuring the relative dynamic modulus by ultrasonic velocity method and the method of measuring the relative modulus of elastic modulus using ERUDITE. The experiment was terminated when the relative dynamic modulus was less than 60%.

6) The results of the sulfate resistance test are as follows.

As described above, according to the present invention, it was possible to obtain highly durable concrete for construction of high quality than before.

Claims (5)

And in preparing the durable concrete, the concrete is usually cement per 1m ³ 550kg, 154kg water, fine aggregate 609kg, blending a superplasticizer in a ratio of 1.8% by weight of the coarse aggregate (gravel), 1,142kg, the cement of the largest dimension 19mm Method for producing highly durable concrete, characterized in that. The method according to claim 1, wherein 82.5 kg of fly ash is usually added to 467.5 kg of cement as an admixture, and 0.04 wt% of the air entrainer and 1.7 wt% of the high softening agent are added to the cement and the fly ash. The manufacturing method of the high durability concrete to make. The method for producing high-strength concrete according to claim 1, wherein the compound is usually added and blended with 495 kg of cement at a ratio of 55 kg of silica fume as a admixture. The method according to claim 1, characterized in that the cement is added in a ratio of 82.5 kg of fly ash and 55 kg of silica fume as a admixture in a ratio of 412.5 kg of cement and in a ratio of 1.6 wt% of a high fluidizing agent based on cement, fly ash, and silica fume. Method of producing high-strength concrete. Manufacture of high strength concrete according to claim 1, wherein the cement is added in a ratio of 137.5 kg of blast furnace slag as a admixture and in a ratio of 2.0% by weight of a high fluidizing agent relative to cement and blast furnace slag. Way.