KR100808113B1 - The Manufacturing Method Of The Powdered Superplasticizer Developed To Improve Slump Loss Rate - Google Patents

Abstract

The present invention relates to a powdered admixture that can improve the field applicability of recycled aggregate concrete by improving the slump loss of concrete and recycled aggregate concrete using the same. The powdered admixture according to the present invention is obtained by mixing the blast furnace slag with a high performance water reducing agent, calcining, grinding, sieving, and then secondarily milling and filtering a 250 μm sieve. Incorporation at -7.5% yields recycled aggregate concrete with improved slump loss. Concrete according to the present invention can not only maintain more than 85% of the initial slump even after 1 hour of blending while using industrial blast furnace slag in an optimum amount, and also improves the compressive strength, splitting tensile strength, flexural strength and elastic modulus of concrete. This also reduces the dry shrinkage strain.

Powder admixture, recycled aggregate, high performance water reducing agent, concrete, slump loss

Description

The manufacturing method of the powdered superplasticizer developed to improve slump loss rate

1 is a flow chart for preparing a powdered superplasticizer according to the present invention,

Figure 2 is a view showing the powdered admixture of the present invention, the final treatment, (a) after the secondary milling process, (b) is a photograph after filtering to a 250㎛ sieve,

3 is a graph showing the particle size distribution of the powdered admixture according to the present invention,

Figure 4 is a graph showing the relationship between the mixing conditions of the aggregate type and grade and the initial slump ( SLo ),

5 is a graph showing the change of slump over time, (a) shows the recycled coarse aggregate grade 1 + recycled fine aggregate, (b) shows the recycled coarse aggregate grade 3 + recycled fine aggregate concrete,

6 is a graph showing the change in the slump flow loss slope κ, (a) after 60 minutes, (b) after 90 minutes, (c) after 120 minutes,

7 is a graph showing the slope of the slump loss compared to the mixing conditions, (a) shows the slump, (b) shows the slump flow,

8 is a graph showing the effect of the powder admixture according to the present invention on the relationship between aggregate mixing conditions and age 28 days compressive strength,

9 is a graph showing the change in intensity expression with age, (a) shows Series I, (b) shows Series II, (c) shows Series III,

10 is a graph showing the change of each role characteristics of the root of the compressive strength of concrete at 28 days of age according to the recycled aggregate compounding conditions in the concrete mixed with the powder admixture (a) is the split tensile strength, (b) Is the flexural strength, (c) is the elastic modulus,

11 is a graph showing the change in dry shrinkage strain according to the mixing of the powder admixture (a) is a natural coarse aggregate and natural fine aggregate, (b) is a recycled coarse aggregate 1 grade and regenerated fine aggregate, (c) is Shows concrete with recycled coarse aggregate grade 3 and recycled fine aggregate.

The present invention relates to recycled aggregate concrete with improved slump loss and powdered admixtures used therein. More specifically, the slump loss is improved to maintain 85% or more of the initial slump even after 1 hour after mixing. It relates to a admixture and recycled aggregate concrete applying the same.

The change in the normal recycled aggregate concrete over time is about 1.5 times larger than that of ordinary concrete due to the high absorption rate of the recycled aggregate.

The most important things to improve these changes over time is when the sensitizer is introduced and when the sensitizer starts to appear. The effect of the water reducing agent will ensure some fluidity from 15 to 30 minutes after injection. However, in the ready-mixed concrete plant, in order to ensure the quality of the concrete, a reducing agent is generally added simultaneously with the mixing. In order to increase the effect on the field application of the sensitizers added in the early stage of the formulation, the fluidity improvement effect of the sensitizers should be gradually reacted and maintained for a long time after the addition.

However, considering that the time from the mixing of the concrete to the casting time is 30 minutes to 60 minutes, the field workability of the recycled aggregate concrete may be significantly lower than that of ordinary concrete using natural aggregate. In addition, injecting the water reducing agent directly into the ready-mixed concrete in the field can not control the optimum amount of water reducing agent may cause quality degradation due to the material separation of the concrete.

Methods to improve the slump loss of concrete over time include the initial high fluidity, the use of a retardant, the use of admixtures such as slag and the control of the timing of reducing agent input. Therefore, as the researches on these methods continue to accumulate, the data for improvement over time have been accumulated. However, considering the high absorption rate of recycled aggregates, it is necessary to supplement them from the mix design to apply these methods to recycled aggregate concrete.

Currently, the input of a high performance water reducing agent to secure the field workability in concrete has been proposed 30 minutes after the formulation. However, precisely controlling and introducing the amount of sensitizer at about 30 minutes after the formulation is practically difficult. It is not only difficult to control the slump according to the amount of reducing agent, but also to adjust the reducing agent input by a non-specialist.

In addition, Japanese Patent Laid-Open No. 63-11,553 describes the use of a high-purity blast furnace slag of 6,000 to 14,000 cm ² / g to improve the initial strength reduction and separation resistance. If the blast furnace slag is poorly pulverized to 6,000 ~ 14,000cm ² / g level, there is a disadvantage that it is not economical due to the increase in manufacturing cost.

On the other hand, the powdered water reducing agent imported from abroad is coagulated with liquid type water reducing agent and processed into a powder form, so that the water reducing effect is not large and is rarely used in the field.

Therefore, if the reducing agent added at the beginning of mixing in the recycled aggregate concrete can show its ability with time, it will be helpful to improve the quality and change over time.

Accordingly, an object of the present invention is to provide a powder-type admixture to improve the change over time with the quality of the water-reducing agent that is initially added in the recycled aggregate concrete to exhibit its ability over time.

It is also an object of the present invention to provide recycled aggregate concrete with improved slump loss since it is not higher in price than the presently used concrete and can exert its ability over time.

According to the present invention to achieve the above technical problem,

To 100 parts by weight of granular type blast furnace slag, 20 to 34 parts by weight of a high performance water reducing agent is mixed, calcined and dried to grind to an average particle diameter of 8 µm and a powder degree of 5,900 to 6,300 cm ² / g to form recycled aggregate concrete. Provided is a method of preparing a powdered admixture for use.

According to another aspect of the present invention,

The recycled aggregate concrete is prepared by mixing 5.0 to 7.5% by weight of the powder-type admixture prepared by the above-mentioned gross unit cement weight.

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

Recycled aggregate concrete using the powdered admixture of the present invention is composed of aggregate, cement, and powder admixture.

In the present invention, the aggregates are natural aggregates, fine aggregates, recycled aggregates, etc., natural fine aggregates and coarse aggregates were used for natural sea sand and crushed stone of Muan, Jeonnam, which are used in the mixing of ready-mixed concrete, and recycled aggregates were made by impact crusher at C company. Those that were crushed and free of impurities and fine powder adhering to the aggregate surface by air classifiers and wet classifiers were used. The quality of aggregates in C's recycled aggregate production system was determined by wet classification. The coarse aggregate was used with a maximum diameter of 25 mm, and the fine aggregate was adjusted to particle size through a sieve of 5 mm in diameter and 2.5 mm in diameter. For reference, the physical properties of the aggregates used in Table 2 in the examples are summarized.

As cement in the present invention, various portland cements such as crude steel, steam for heating, and sulfates may be used.

In the present invention, in order to improve the initial loss of the slump, powdered admixtures obtained from the blast furnace slag and the high strength water reducing agent are partially used in cement.

The blast furnace slag can be used not only blast furnace slag fine powder but also blast furnace slag cement. The blast furnace slag powder is produced at Gwangyang Works, and in case of blast furnace slag cement, domestic S company's blast furnace slag mixed cement is used. (A blast furnace slag may be used with a specific surface area of 4000 cm ² / g to 8000 cm ² / g.)

In addition, the high-performance water reducing agent used in the present invention, as is commonly known, can secure the fluidity of the cement particles, so that the amount of water can be reduced by 20 to 30% when mixing concrete, the same water-cement ratio (W / C) conditions Under the present invention, the workability is excellent and the fluidity lasts for a considerable time without the material separation phenomenon than the concrete without the high-performance water reducing agent, so that it has a component that facilitates the pouring work.

Examples thereof include lignin sulfonate, oxycarboxylic acid, polyol, naphthalin sulfonate, melamine sulfonate, and highly condensed triacin compounds.

Among them, polycarboxylic acid-based water reducing agent is composed of 60% water and 40% solids, and it is 40% solids that actually exhibits water reduction effect. . The naphthalene-based water reducing agent is also composed of 60% water and 40% solids, and is less effective than polycarboxylic acid, but has superior performance and low price compared to other types. Since the water components are all evaporated in the process of plasticizing them with the slag, it is possible to prevent an increase in the amount of units due to the addition of a reducing agent.

Although other types of water reducing agents can be used, the mixing with the slag is not smooth and its performance is also very low. Therefore, in the present invention, it is recommended to use a polycarboxylic acid-based and naphthalene-based water reducing agent in consideration of excellent performance and economical efficiency.

The powder admixture takes the form of blast furnace slag and a high performance water reducing agent, followed by calcination and high powdering.

That is, 20-34 weight part of blast furnace slags and a high performance water reducing agent are mixed with respect to 100 weight part of blast furnace slag. At this time, less than 20 parts by weight of the dough is not made, if it exceeds 34 parts by weight of the sub-mixing is too preferable to take too much baking time.

It is then calcined and then pulverized. At this time, the heating temperature and duration in the firing step are very important. If the heating temperature is low or the duration is short, it is not possible to impart activation energy to the material, nor to induce the complete coupling of the high performance water reducing agent with the blast furnace slag. In particular, when moisture remains in the material after firing, the grinding may not be performed smoothly due to the water effect of the materials on the inner surface of the ball mill when grinding the ball mill. On the other hand, if the heating temperature is too high or the duration is long, the chemicals that induce the effect of the high-performance sensitizer will not be able to exert its performance due to the complete combustion and the energy consumption will be too high.

In view of this point, the preferred firing method, temperature and duration to be applied in the present invention are as follows.

The first firing is heated in a furnace at 250-350 ° C. for 22-26 hours, and then the mixed materials are taken out and crushed into granules having an average diameter of 50-75 mm. The reason for the crushing is to shorten the firing time by widening the surface area and to achieve uniform firing. Also, in 24 hours, the water of the high-performance sensitizer mixed with the slag is not completely evaporated, so it is desirable to crush it.

The finely crushed ones are calcined for 1 to 2 hours in a furnace at 250 to 350 ° C to completely remove moisture remaining in the material and maintain a uniform firing state.

After these firing processes, the mixture was cooled in the air for 30 minutes to 1 hour 30 minutes and then pulverized with a ball mill for 30 minutes to 1 hour 30 minutes. These primary polished fine powders pass 740 micrometers body. The average particle diameter of the fine powder passing through these sieves is 50-70 micrometers.

These fine powders are passed through a 250 µm sieve again after the second ball mill pulverization. The average particle diameter of these passed particles is about 8 mu m, which is similar to that of 10 mu m cement.

The particle size of the fine powder is very closely related to the concrete fluidity duration. The larger the particles, the smaller the cement particles are, because the mixing and water-reducing effects are very low in concrete. However, the pulverization technology of fine powders that can pass through 250 µm or less is very difficult and requires considerable grinding time. In consideration of this point, it is judged that the size of the particle size that can pass the 250 μm sieve is the most economical and efficient.

At this time, the residual calcined fine powder is recovered through the 250 μm sieve, and milled again, and may be recycled using the 250 μm sieve. In this way, the average particle diameter of the admixture obtained in 8㎛, the surface area satisfies the level of 5,900 to 6,300 cm ² / g.

When using the powdered admixture prepared in this way, unlike the conventional fine powder slag (specific surface area 3,000 ~ 4,000cm ² / g) can be expected the following action.

In other words, calcium hydroxide and ettringite, which are relatively poor in chemical resistance in concrete composition, are reduced, and physical strength is increased through high powder level of mineral admixture to protect concrete from external deterioration factors.

As described above, by applying a small amount of powder-type admixture obtained from the combination of blast furnace slag and high performance water reducing agent per unit weight of cement, the high performance water reducing agent is applied in a smaller amount than the conventionally used amount, and as a result, secondary convenience such as ease of in-site casting and coagulation delay. Phosphorus problems can be minimized. In addition, the use of mineral admixtures, which are industrial by-products, has the advantage of helping to solve environmental problems, which are important issues at home and abroad.

On the other hand, the powdered admixture has the advantage of improving the resistance and the separation resistance of the initial strength degradation by using the fine surface pulverization of the specific surface area level of 5,900 to 6,300cm ² / g.

In addition, in the present invention, the glass blast furnace slag itself or in the prior art used in the cement after activation, the specific surface area of the slag is pulverized by 6,000 m ² / g or more, and only the reaction surface area is increased to increase the slag activity. It is a simple process of blending high-performance water reducing agent into granular slag, firing, drying and pulverizing, so that it is possible to manufacture high-molecular powder admixtures that are economical and excellent in hydration activity. This will not happen.

In addition, by using the powdered admixture prepared according to the present invention can be used a relatively small amount of a high performance water-reducing agent, because the fineness of the powder to be 5,900 ~ 6,300cm ² / g to use in cement, these are the pores of cement particles By acting as a filler to fill in the concrete, the workability of concrete at the same amount of work is improved.

Such powder admixture has a good range of 5.0-7.5% compared to 100 weight of unit cement, and if it is used at more than 7.5%, the effect of strength expression at the initial stage is less. Not.

On the other hand, fly ash or silica fume etc. which are usually used together with blast furnace slag may be added to the cement.

Hereinafter, the present invention will be described in detail with reference to Examples.

<Example>

Example 1-Powder Admixture

<Manufacture of powder type admixture>

The manufacturing flow chart and photograph of the powder admixture according to the present invention are briefly shown in FIG. 1. Powdered admixture was prepared by mixing blast furnace slag and high performance water reducing agent in a certain ratio to make fine powder after firing process. At this time, as a blending ratio, a high performance water reducing agent was added in an amount of 19, 25, and 35 parts by weight, respectively, per 100 parts by weight of the blast furnace slag. At this time, it was confirmed that the dough is not made at all in 19 parts by weight.

In the process of making the fine powder through the firing process using the 25, 35 parts by weight of the blend, as the first firing, the mixture is heated for 24 hours in a furnace at 300 ° C., and then the mixed material is taken out to have a grain shape having an average diameter of 50 to 75 mm. Chopped into At this time, 25 parts by weight of the formulation was appropriate by going through the above process, but 35 parts by weight of the formulation was not preferred because the baking time should be increased to 50 hours or more.

The finely crushed forms were then calcined again for 1 to 2 hours in 300 furnaces, and this was also undesirable since the 35 parts by weight formulation also had to be calcined for at least 5 hours.

After these firing processes, the mixture was cooled in the air for about 1 hour and then ground in a ball mill for 1 hour. These primary polished fine powders were passed through a 740 micrometer sieve, and the average particle diameter of the fine powder measured at this time was 50-70 micrometers.

These fine powders were again milled through a second ball mill and passed through a 250 μm sieve, where the average particle diameter of the passed particles was about 8 μm.

The photograph of the powdered admixture obtained in this way is shown in FIG.

<Physical Properties of Powder Admixtures>

Figure 3 shows the particle size distribution results of the powdered admixture prepared. The average particle diameter was 8 µm, which is similar to that of cement, which was 10 µm. Specific gravity is 2.93, similar to blast furnace slag, and specific surface area is 5,900 ~ 6,300cm ² / g. The surface color of the material was white when mixed with polycarboxylic acid and light brown when mixed with naphthalene.

Example 2-Blend Design

<Compound Test Body>

The main variables are the grade of recycled coarse aggregate and the mixing rate of SSP. The grade of recycled aggregate was evaluated according to KS F 2573. Recycled coarse aggregates were used for structural grades 1 and 3, and recycled fine aggregates were graded for grade 2. The replacement rate of coarse aggregate and fine aggregate was fixed at 100% in consideration of the most severe change over time when 100% was substituted. Powder-type admixtures were mixed as the main parameters of the mixing conditions of the coarse aggregate and fine aggregate.

Powdered admixtures were classified into two types: PSP-P made from polycarboxylic acid-based high performance sensitizer and PSP-N made from naphthalene-based high performance sensitizer. Each mixing rate was PSP-P (5%), PSP-P (7.5%) and PSP-N (5%). Generally, the admixture means 5.0% or less relative to the amount of cement. In the present invention, the admixture is added up to 7.5% in order to evaluate an optimum mixing ratio of the powder admixture.

Furthermore, 5.0 to 7.5% of the unit cement weight, which is the mixing ratio of the powdered admixture, is determined in order to minimize the effect on the total amount of the high performance water reducing agent added in the preparation of the powdered admixture and the total amount during the formulation. In consideration of the fact that the mixing amount of the high performance water reducing agent is very small, the mixing ratio of 5% of the powdered admixture is less than 0.5% in terms of the high performance water reducing agent alone. In addition, it can be seen that the enemy has economic and economic advantages.

The main parameters of the compound test specimens of this experiment are shown in Table 1 below, and 24 compounds were tested according to these variables. The compressive strength of 28 days was aimed at 30MPa when using natural coarse fine aggregate. The water-cement ratio ( W / C ), fine aggregate fraction ( S / a ), and unit quantity ( W ) in all formulations were constant at 50%, 42% and 175 kgf / m ³ , respectively.

In addition, in the powder-free admixture-free concrete, a polycarboxylic acid-based high performance water reducing agent was directly added to the target slump 200 mm. In the calculation of the compounding weight of each material, the mixing amount of the powder admixture was applied together.

Main factor Recycled coarse aggregate: Grade 1, 3 Recycled Fine Aggregate: Grade 2 Powder admixture: Series I: None Series II: PSP-P (5%) Series III: PSP-P (7.5%) Series IV: PSP-N (5%) Basic condition W / C = 50%, S / a = 42%, W = 175 kgf / m ³

Physical Properties of Aggregate

Natural fine aggregate and coarse aggregate were used as natural maritime sand and crushed stone of Muan, Jeonnam, which are used in ready mixed concrete. The recycled aggregates were used by the company C, which were crushed by the impact crusher and the impurities and fine powder attached to the aggregate surface were removed by the air classifier and the wet classifier. The quality of aggregates in C's recycled aggregate production system was determined by wet classification.

The coarse aggregate was used the maximum diameter of 25mm, the fine aggregate was adjusted to the particle size through a sieve of 5mm diameter and 2.5mm.

The physical properties of the aggregates used in Table 2 are shown.

shape Maximum size (mm) Density (g / cm ² ) Water absorption (%) F.M Unit weight (kg / m ³ ) Coarse aggregate natural 25 2.48 1.93 6.52 1,642 play One 2.53 1.60 6.62 1,704 3 2.40 6.24 6.89 1,645 Fine aggregate natural 5 2.53 1.62 2.79 1,455 play 2 2.36 5.37 3.25 1,366

Example 3- Blending and Measuring Methods

combination

The formulation used a 300 l forced mixer with automatic time adjustment. In the mixing method, coarse aggregates and fine aggregates were added to empty for 1 minute, and then cement was added for 1 minute. After mixing for 90 seconds by adding water, the mixture was added and mixed for 180 seconds to improve the change over time.

How to measure

1) Fluidity test of unconsolidated concrete ( SL , SL -F ):

Evaluation was made by slump and slump flow tests according to KS F 2402. To evaluate the slump loss rate over time, the slump and slump flow were measured at 30 minutes, 60 minutes, 90 minutes, and 120 minutes, respectively, immediately after blending.

2) compressive and tensile strength of concrete (f _ck , f _t ):

In order to evaluate the effect of powder admixtures on the properties of hardened concrete, the strength and dry shrinkage characteristics were evaluated, and at 3 days, 7 days, 28 days, 56 days and 91 days using a mold of Φ100 × 200mm Was evaluated. The compressive and tensile strengths of the PSP-N series specimens were measured only at 28 days of age.

3) Flexural strength ( f _r ): Using a specimen of size 150 × 50 × 530 mm, it was evaluated according to KS F 2408 at 28 days of age.

4) Stress-strain relationship and modulus of elasticity (E _c ): measured at 28 days using high-strength compressor and WSG.

5) Dry Strain Strain: W.S.G (WFLM 60-11) was embedded in a Φ150 × 300mm mold and measured.

6) Dry Shrinkage Test: After curing in an average 20 tanks for 14 days, they were automatically measured and stored using TDS 303 at 20 minute intervals for up to 2 days in the constant temperature and humidity room and every 1 hour thereafter. The constant temperature and humidity room was constant with a temperature of 20 and a relative humidity of 60%.

Example 4 Experimental Results and Analysis

Table 3 shows the experimental results of each formulation.

The first letter and the second number in the specimen names of each series indicate the type and grade of coarse aggregate, respectively, and the third letter indicates the type of fine aggregate. G denotes natural coarse aggregate, R denotes regenerated coarse aggregate, s denotes natural fine aggregate, and r denotes regenerated fine aggregate, respectively. For example, R1-r is a combination of 100% recycled coarse aggregate 1 class and 100% recycled fine aggregate 2 class.

The modulus of elasticity (E _c ) is calculated from the slope of the straight line connecting the origin and 45% of the maximum strength in the stress-strain curve.

Series Psalter SL , mm SL -F , mm fck , MPa fr , MPa ft , MPa Ec , MPa Min. Min. Days 0 30 60 90 120 0 30 60 90 120 3 7 28 56 91 28 d 28 d 28 d Series Ⅰ  G-s 230 205 195 180 145 583 508 430 360 315 17.08 30.66 47.76 49.80 59.32 4.46 3.16 37581  G-r 210 185 150 135 110 438 388 283 293 169 14.56 24.36 38.60 41.80 43.20 3.88 2.45 30104 R1 -s 185 155 140 130 115 415 363 260 280 240 15.26 28.43 42.30 42.30 49.60 3.71 2.53 31855 R1 -r 190 165 145 110 95 400 374 360 249 219 11.89 21.66 31.88 31.84 37.16 3.22 2.46 22834 R3 -s 220 190 165 140 125 483 417 341 288 272 14.12 26.90 37.50 37.90 43.60 3.98 2.68 26445 R3 -r 225 160 135 105 75 418 350 275 235 208 11.36 21.20 32.80 33.10 40.72 2.96 2.23 22006 Series Ⅱ  G-s 150 145 140 140 135 233 238 242 283 270 18.26 30.47 48.50 51.48 62.50 4.60 3.25 38928  G-r 170 200 195 160 120 415 400 380 325 320 13.57 23.04 35.08 39.40 45.60 3.76 2.56 30034 R1 -s 180 170 145 150 135 390 370 338 290 275 14.53 27.55 41.80 43.50 52.60 3.93 2.66 31763 R1 -r 200 195 190 180 170 440 485 418 388 355 12.30 22.30 30.74 31.5 37.35 3.724 2.34 25812 R3 -s 145 180 175 150 120 335 333 273 230 233 13.88 27.41 36.88 39.24 45.10 3.98 2.56 29401 R3 -r 225 205 190 150 130 415 330 315 303 284 11.25 20.60 32.05 31.61 40.91 3.14 2.25 22930 Series Ⅲ  G-s 190 185 180 165 165 380 383 355 356 348 16.72 30.57 50.44 49.85 63.30 4.69 3.33 34592  G-r 160 155 155 130 115 365 345 305 260 245 12.40 24.53 36.40 37.10 46.20 4.29 2.92 28244 R1 -s 150 140 130 125 110 225 231 254 244 231 15.48 29.56 45.80 46.92 58.15 4.14 3.00 35307 R1 -r 210 210 185 155 145 398 378 350 337 258 11.68 24.06 34.86 35.11 41.72 3.81 2.82 26268 R3 -s 200 185 180 170 160 385 358 336 320 273 13.50 28.55 37.07 38.70 47.04 3.99 2.59 26218 R3 -r 250 225 210 180 165 585 547 455 360 295 10.84 22.51 30.06 30.37 37.44 3.14 2.30 20867 Series Ⅳ  G-s 235 215 210 205 195 555 488 465 464 399 - - 51.70 - - - 3.12 36241  G-r 215 195 180 165 150 420 380 376 309 263 - - 33.92 - - - 2.42 26529 R1 -s 190 182 170 155 150 330 313 305 268 286 - - 57.06 - - - 2.89 36932 R1 -r 195 210 170 150 135 393 380 355 266 254 - - 39.41 - - - 2.55 24630 R3 -s 170 160 150 135 130 283 271 243 254 275 - - 42.30 - - - 2.67 27549 R3 -r 245 235 210 185 165 610 555 482 396 356 - - 35.14 - - - 2.01 20272

1) Initial Liquidity

4 shows the relationship between the mixing conditions of the aggregate type and grade and the initial slump ( SL ₀ ).

In the series without powder admixture, the high performance water reducing agent was adjusted for the target slump, and the water reducing agent was in the range of 0.8 ~ 1.4%. In concrete using recycled fine aggregate, the initial fluidity was low due to the inclusion of dust.

The initial slump of concrete substituted with powder admixtures was up to 20% lower than that of the liquid polycarboxylic acid system (Series), but the slump of 150 mm or more was maintained.

Although the effect of the amount of the powder admixture on the initial slump was not large, the PSP-N agent was advantageous to the initial fluidity improvement rather than the PSP-P agent. This is because the mixing ratio of the naphthalene-based water reducing agent is higher than the polycarboxylic acid type as the difference in the input ratio of the high-performance water reducing agent in the powder type admixture preparation.

2) Slump change with time

Figure 5 shows the change in slump over time, Figure 5 (a) is the recycled coarse aggregate grade 1 and recycled fine aggregate grade 2, and 5 (b) is the recycled coarse aggregate grade 3 and recycled fine aggregate grade 2 used Is concrete. The vertical axis to the initial slump (SL ₀₎ a slump (SL) with the passage of time as the relative slump was won dimensionless.

The slump of concrete with high performance water reducing agent drastically decreased with time, and after 120 minutes it fell below 50% of the initial slump. However, the slump of concrete incorporating powder admixtures remained almost unchanged until 30 minutes after mixing and maintained more than 85% of the initial slump after 1 hour.

In particular, as shown in Table 3 above, in the formulation using recycled coarse aggregate and natural fine aggregate, there was more than the initial slump until 1 hour after the combination.

Slump flow also showed the same trend as slump. These effects are also shown in the slump state change with the passage of time of the R3-r specimen of series 3 shown in FIG. This shows that the effect of the high performance water reducing agent, which was emphasized in the development phase of the powder admixture, is being exhibited over time.

In the powdered admixture, slump loss is achieved even after 30 to 60 minutes after blending by the initial reaction with water to ensure the initial fluidity of the water-reducing agent component on the surface of the powdered admixture. Could be prevented.

3) Slump loss slope

Referring to FIG. 5, it can be seen that the slump decreases almost linearly with increasing time. In general, since the fluidity of concrete decreases with time, the decrease in slump in a straight line means that the loss of fluidity of concrete increases. In addition, Figure 7 shows the slump loss slope calculated from the regression analysis of the experimental results shown in Figure 5 according to the concrete aggregate mixing conditions.
This slump loss slope was especially large for recycled aggregate grade 3 concrete without powder admixtures. However, when 5.0% of the powdered admixture was added, the slope of the slump loss was improved more than two times regardless of the recycled aggregate type and grade. However, when the mixing ratio of the powder admixture was 7.5%, the slump loss slope was slightly lower than that of 5.0%. The high performance sensitizer used in the preparation of the powdered admixture was superior to the polycarboxylic acid type than the naphthalene type.

As a result, the powdered admixture according to the present invention is very effective in improving the aging change of concrete, and especially in the recycled aggregate concrete having a large slump loss rate, the flowability after 1 hour after mixing is greatly improved. PSP-P agent was superior to PSP-N agent and the optimal amount was 5%.

4) compressive strength

Figure 8 shows the effect of the powder admixture on the relationship between the aggregate mixing conditions and age 28 days compressive strength.

In general, the compressive strength of concrete using recycled aggregate was 70 ~ 85% lower than that of natural aggregate. In particular, the compressive strengths of the R1-r and R3-r specimens with regenerated fine aggregates rather than regenerated coarse aggregates were significantly lower. The compressive strength of concrete with powder admixture was the same or 10% higher than Seires concrete with liquid polycarboxylic acid system.

In addition, the change in intensity expression rate according to age is shown in FIG. 9. In this case, the strength expression rate indicates the relative compressive strength with respect to the 28-day compressive strength.

The 3-day compressive strength expression rate of concrete mixed with PSP-P was 2.5% lower than that of concrete containing liquid polycarboxylic acid. However, the intensity expression after 7 days was similar, and the intensity expression after 56 days increased by 7% on average. This is because the blast furnace slag, which is the main component of the powder admixture, contributes to the enhancement of long-term strength.

Powdered admixtures had no harm to the development of compressive strength of recycled aggregate concrete, but were beneficial for long-term strength enhancement.

5) Split tensile strength, flexural strength and modulus of elasticity

)의 루트승에 비례하여 나타낸다. 상기표 3에 이들 역학적 특성들에 대한 실험결과를 자세히 나타내었으며 도 10에는 분말형 혼화제가 혼입된 콘크리트에서 재생 골재 배합조건에 따라 재령 28일에서 콘크리트 압축강도의 루트승에 대한 각 역학적 특성의 변화를 나타내었다. The splitting tensile strength ( f _t ), flexural strength ( f _r ) and modulus of elasticity ( E _c ) are the compressive strengths of concrete.

In proportion to the root power of Table 3 shows the experimental results of these mechanical properties in detail, and FIG. 10 shows the change of the mechanical properties of the root strength of the concrete compressive strength at 28 days according to the recycled aggregate mixing conditions in the concrete mixed with the powder admixture. Indicated.

)는 액상형의 폴리카르본산계가 투입된 콘크리트에 비해 평균 15% 높았다. 하지만 재생 굵은골재 3등급 또는 재생 잔골재가 사용된 시험체(R1-r, R3-s, R3-r)들에서 분말형 혼화제가 혼입된 경우의 는 액상형의 폴리카르본산계가 투입된 콘크리트와 비슷한 수준이었다. Splitting Tensile Strength Ratio of Concrete with Powder Admixture

) Was 15% higher on average than that of the liquid type polycarboxylic acid-based concrete. However, when the powder admixture was mixed in the test specimens (R1-r, R3-s, R3-r) using recycled coarse aggregate grade 3 or recycled fine aggregate, the level was similar to that of the liquid polycarboxylic acid-based concrete.

) 및 탄성계수비 (

)에 미치는 영향은 매우 우수하였다. ACI 318-05에서는 휨강도비와 탄성계수비를 각각

와

로 제시하고 있다. 액상형의 폴리카르본산계가 투입된 재생골재 콘크리트에서는 이들 ACI 기준에서 제시하는 값보다 낮았다. Flexural Strength Ratio of Concrete Admixtures

) And modulus of elasticity (

), The effect was very good. In ACI 318-05, the flexural strength ratio and elastic modulus ratio

Wow

Presented by. The recycled aggregate concrete with liquid polycarboxylic acid system was lower than the values suggested by these ACI standards.

를 ACI 기준값 이상으로 상승시켰으며

도 액상형의 폴리카르본산계가 투입된 재생골재 콘크리트에 비해 현저히 상승하였다.However, the powder admixture contributed to the increase of the flexural strength and modulus of elasticity. When powder admixture is mixed, all test specimens except R3-r

Raised above the ACI threshold,

Compared to the recycled aggregate concrete in which the liquid polycarboxylic acid system was added, the degree was significantly increased.

6) dry shrinkage strain

Figure 11 shows the change in dry shrinkage strain according to the mixing of the powder admixture. Figure 11 (a) is a natural coarse aggregate and natural fine aggregate, 11 (b) is a regeneration coarse aggregate grade 1 and regenerated fine aggregate, 11 (c) is a case where regenerated coarse aggregate 3 grade and regenerated fine aggregate, respectively.

Dry shrinkage of concrete using recycled aggregates increased as compared to the case of using only natural aggregates as in previous studies.

Powder admixtures slightly reduced the dry shrinkage of concrete regardless of aggregate type, but the effect was small. Up to 10 days of early aging, most of the concrete's dry shrinkage strain was in the 200μ range regardless of the presence of powder admixtures. The change of dry shrinkage was different according to the incorporation of the powder admixture with time. The range of 600 ~ 700μ was observed at 90 days of recycled aggregate concrete.

Powder admixtures reduced the dry shrinkage of concrete by about 5-15%.

7) Result Analysis

1) The initial slump of concrete with a water-cement ratio of 50% mixed with powder admixture was up to 20% lower than the concrete injected with liquid polycarboxylic acid for the target slump of 200 mm, but maintained a slump of 150 mm or more.

2) The slump of concrete with liquid type high performance water sensitizer decreases rapidly with time and falls below 50% of the initial slump after 120 minutes. No more than 85% of the initial slump was maintained after 1 hour. This shows that the effect of the high performance water reducing agent, which was emphasized in the development phase of the powder admixture, is being exhibited over time.

3) The concrete with 5% powder admixture improved the slump loss slope more than 2 times regardless of the recycled aggregate type and grade.

4) The compressive strength of concrete mixed with powder admixture was the same or 10% higher than that of concrete with liquid polycarboxylic acid. In particular, the flexural strength and modulus ratio of the compressive strength of the recycled aggregate concrete mixed with powder admixture were improved beyond the ACI 318-05 standard value.

5) Powder type admixture did not affect the early age dry shrinkage of concrete, but at 90 days, the dry shrinkage was reduced by 5 ~ 15% compared to the concrete under the same condition with liquid type water reducing agent.

6) In order to improve the slump loss of recycled aggregate concrete, the powder admixture developed in this study improves not only the fluidity but also the mechanical properties of the concrete. The optimum mixing ratio of the powder admixture was 5.0 to 7.5% based on the unit cement weight. In the future, the slump loss may be actively used to improve the site applicability of concrete, which is particularly severe.

According to the present invention, the slump of the concrete mixed with the powder admixture is almost unchanged until 30 minutes after mixing, and maintains more than 85% of the initial slump even after 1 hour, as well as the powder admixture is the initial fluidity, compressive strength In addition, the tensile strength, flexural strength and modulus of elasticity were improved, and the dry shrinkage strain could be reduced.

Claims (4)

To 100 parts by weight of granular type blast furnace slag, 20 to 34 parts by weight of a high performance water reducing agent is mixed, calcined and dried, and the average aggregate diameter is 8 µm and the powder is pulverized to 5,900 to 6,300 cm ² / g to be recycled aggregate concrete composition. Method for preparing a powdered admixture for improving slump loss used in the process. The method of claim 1, wherein the firing, drying and grinding step A first step of heating at 250 to 350 ° C. for 22 to 26 hours, then removing and crushing to 50 to 75 mm particle diameters; A second step of heating the finely divided kernels for 1 to 2 hours at 250 to 350 ° C; Removing the heated kernel and cooling it for 30 minutes to 1 hour and 30 minutes at room temperature; A fourth step of ball milling the coolant for 30 minutes to 1 hour 30 minutes and then passing the 740 μm sieve to obtain a fine powder; And And a fifth step of obtaining the high fine powder by passing the 250 μm sieve after the ball mill pulverizing the fine powder. The method of claim 2, further comprising a sixth step of recovering the remaining calcined fine powder after the fifth step and repeating the fifth step again. delete

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