KR20030092712A - concrete composite mixed with limestone powder - Google Patents

Abstract

PURPOSE: A mass concrete composition incorporated with a limestone fine particle is provided to decrease the hydration heat of the concrete and the time needed for the solidification of the concrete. CONSTITUTION: The concrete composition is characterized by comprising a Class 4 low heat cement incorporated with 20-50 parts by weight of a limestone fine particle based on the total weight of particles, an aggregate and water. The concrete composition optionally further comprises 0.5-2.0 wt% of a high performance water-reducing agent based on polycarbonate.

Description

Concrete composition mixed with fine limestone powder {concrete composite mixed with limestone powder}

The present invention relates to a concrete composition incorporating limestone fine powder suitable for mass concrete structures. More specifically, the present invention relates to a concrete composition suitable for controlling the temperature and temperature cracking of mass concrete structures. In particular, unlike conventional low-exposure concrete, the temperature cracking due to heat of hydration, such as a large-scale mass concrete wall structure having a large one-time concrete height, When the side pressure of concrete with control is a problem, the temperature rise due to the heat of hydration is reduced, and the condensation time of the concrete can be shortened to prevent the occurrence of excessive side pressure, and as a result, a large scale that can save the form design and installation cost. It is suitable for wall-type mass concrete structures, and it is possible to use powder material with cement that does not greatly increase the maximum temperature caused by the hydration reaction of Portland cement. Cement-only concrete boat In order to be used at the time of the integrated design, fine powder of limestone is used as the powder material, and low-grade cement of the fourth kind is used as the portant cement. Since the initial hydration reaction of the cement is accelerated by the concrete composition in which the limestone fine powder is mixed, the condensation time of the concrete is shortened, so that excessive side pressure does not occur even when the temperature of the outside air is low, thereby enabling economic mass concrete construction. In addition, because the initial hydration reaction is accelerated, the condensation time is shortened, but the low temperature cement is used, and because the limestone fine powder which does not significantly affect the maximum insulation temperature rise temperature is used, the maximum temperature of the mass concrete wall is greatly reduced and the temperature is cracked. Can be controlled.

In general, the most important problem in the construction of mass concrete is the control of temperature cracking by the heat of hydration. The method of temperature cracking control by heat of hydration is slightly different depending on the restraint condition. It is effective to reduce the temperature difference between the center part of the member and the surface part temperature in the concrete structure with strong internal binding, and the maximum rise inside the member in the concrete structure with strong external binding. It is effective to reduce the temperature. As such, in order to control the temperature cracking by the heat of hydration of the mass concrete structure, a temperature cracking control plan suitable to each constraint condition should be used. This temperature crack control method is effective to be composed of various combinations at the design stage, the compound design stage and the construction stage. In particular, in the concrete design stage, the use of low heat cement and low unit cement amount are considered in the compound design stage. However, the problems that appear in the concrete mix design for mass concrete has the following.

First, the amount of unit cement or unit bond can not be lowered by more than a certain amount. In other words, concrete is composed of cement, water, fine aggregate, coarse aggregate, admixture (materials exhibiting pozzolanic reaction: fly ash, blast furnace slag fine powder, etc.) and admixture (general water reducing agent, high performance water reducing agent, etc.), cement or binder (cement + admixture) If you design a very low amount, the overall mixing ratio is poor workability. Therefore, since a certain amount of cement or binder is included in the concrete, the mass concrete structure always causes a problem of a certain temperature or more. That is, for a given unit quantity, it means that more quantity is required than unit cement amount or binder amount necessary to obtain the target compressive strength.

Second, the use of low calorific cement or low cement volume delays the setting time of concrete. In general, the delay of the setting time does not have a significant effect on the slab mass concrete structure. However, in the wall-type mass concrete structure, when the condensation time is delayed, large side pressure is generated in the formwork, and large form design and construction cost are required. This tendency is large in large-walled mass concrete structures with a large thickness and a large one-time placing height, and there is a risk of safety accidents due to the collapse of formwork.

However, in the past, condensation time delay in low heat concrete applied to mass concrete has been taken for granted and generally considered to be an inevitable characteristic of concrete. Therefore, the mixing design of concrete applied to the mass concrete structure has been focused on reducing the temperature rise due to hydration heat, workability and strength, and it has been recognized that the increase in form cost due to the delay of the setting time is inevitable. As a result, costly and uneconomical elements have been generated in the formwork of large-scale wall concrete structures.

The present invention can control the temperature cracking due to the heat of hydration in the construction of the mass concrete structure as described above, and when the setting time is a problem, the setting time can be shortened without significantly affecting the temperature rise due to the heat of hydration. It is an object of the present invention to provide a concrete composition capable of reducing the heat of hydration by reducing the amount of unnecessary cement or binder.

Figure 1a is a specific example of the graph showing the setting time according to the fly ash substitution rate in the fourth kind of low heat cement and fly ash mixed powder.

Figure 1b is a specific example of the graph showing the lead according to the fly ash substitution rate in the fourth kind of low heat cement and fly ash mixed powder.

Figure 2a is a specific example of the graph showing the setting time according to the blast furnace slag fine powder replacement powder in the fourth kind of low heat cement and blast furnace slag fine powder.

Figure 2b is a specific example of the graph showing the leading according to the blast furnace slag fine powder replacement powder in the fourth kind of low heat cement and blast furnace slag fine powder.

Figure 3a is a specific example of the graph showing the setting time according to the limestone fine powder replacement rate in the fourth kind of low heat cement and fine limestone powder mixture.

Figure 3b is a specific example of the graph showing the lead according to the limestone fine powder replacement rate in the fourth kind of low heat cement and limestone fine powder mixture.

4 is a specific example of a schematic diagram showing the relationship between the hydration heating rate and the time of cement.

Figure 5a is a specific example of the graph showing the hydration exothermic rate according to the fly ash substitution rate in the fourth type low heat cement and fly ash mixed powder.

Figure 5b is a specific example of the graph showing the amount of heat of hydration according to the fly ash substitution rate in the fourth type low heat cement and fly ash mixed powder.

Figure 6a is a specific example of the graph showing the hydration exotherm rate according to the blast furnace slag fine powder replacement powder in the fourth kind of low heat cement and blast furnace slag fine powder.

Figure 6b is a specific example of the graph showing the amount of hydration calories according to the blast furnace slag replacement rate in the fourth kind of low heat cement and blast furnace slag fine powder.

Figure 7a is a specific example of the graph showing the hydration exothermic rate according to the limestone fine powder replacement rate in the fourth kind of low heat cement and limestone fine powder mixture.

Figure 7b is a specific example of the graph showing the amount of hydration calories according to the limestone fine powder replacement rate in the fourth kind of low heat cement and limestone fine powder powder.

8 is a specific example of the target structure to which the embodiment is applied.

9 is a specific example of a graph comparing the adiabatic temperature rise curve according to the type of powder.

10 is a specific example of a graph showing the setting time of concrete according to the type of powder.

11 is a specific example of a graph showing the side pressure of concrete according to the type of powder.

Concrete composition incorporating limestone fine powder (LSP) of the present invention for achieving the above object uses a low-grade cement and limestone fine powder of the fourth type as a powder material, the amount of fine limestone powder is the amount of powder (fourth low-heat cement + limestone) Fine powder) 20 to 50% by weight, and 0.5 to 2% by weight of the high performance water reducing agent with respect to the total weight of the powder and water, fine aggregates and coarse aggregates.

The fourth kind of low heat cement increases the hydration heat by increasing the content of C2S (belite), which has low initial strength and low heat of hydration, in the major composition minerals of cement by more than twice that of the first kind of ordinary portland cement. Cement reduced to ~ 70% level, also known as bellite cement. Since the low heat of hydration is lower than that of the second kind of heavy heat cement, the fourth kind of low heat cement is able to control the temperature cracking at the time of mass-concrete casting, and because of its long-term strength, it is widely used in the manufacture of high strength concrete and high flow concrete. .

The limestone fine powder (LSP) is initially known to promote the hydration reaction of the cement to increase the initial strength to some extent, but is not known to contribute to long-term strength because it is not a material showing pozzolanic reactivity. In addition, it is reported that the maximum rise temperature does not increase to the same extent as fly ash or slag in the adiabatic temperature rise curve of concrete of the same substitution rate, but it increases the initial reaction rate considerably.

The high-performance sensitizer is a polycarboxylic acid-based high performance sensitizer, the polycarboxylic acid-based sensitizer disperses the powder to exhibit an excellent water-reducing effect. In addition, compared to the naphthalene-based high-performance water reducing agent that is used a lot, the amount of use is less in securing the workability of concrete and the condensation time is faster than the naphthalene-based high performance water reducing agent.

Hereinafter, specific embodiments of the present invention will be described in detail.

In a specific embodiment of the present invention, first of all, the coagulation property and the hydration calorific property were tested for powder materials of the fourth type cement, fly ash, blast furnace slag fine powder, and limestone fine powder. The powder and specific gravity of the materials used at this time are shown in Table 1.

division importance Powder level (㎠ / g) Class 4 low heat cement 3.24 3,633 Fly ash 2.35 4,249 Blast furnace slag powder 2.91 4,815 Limestone Fine Powder 2.72 6,283

Based on the materials used in Table 1, three powder materials were composed, and the fourth type of low thermal cement + fly ash, the fourth type of low thermal cement + blast furnace slag powder, and the fourth type of low thermal cement + limestone fine powder. About the said three types of powders, the setting time was measured by the method prescribed | regulated by KSL5102 and KSL5108. At this time, the solidification time was measured according to the substitution rate of each material to determine how much the solidification time was affected by the substitution rate of the fly ash, blast furnace slag fine powder and fine limestone powder mixed with the fourth kind of low heat cement. Substitution rates by material are shown in Table 2. In general, fly ash is used to replace within 25% with respect to the amount of binding material or powder, and in the case of fine blast furnace slag is used to replace within 70%, but is substituted a lot in the range of 40 ~ 60%. In the case of fine limestone powder, there was no specific requirement, so the test was performed in the range of 0 to 70% substitution rate. Test results for each substitution rate for the powders are as shown in FIGS. 1, 2 and 3.

division % Substitution Fly ash 0, 10, 20, 30 Blast furnace slag powder 0, 20, 30, 40, 50, 60 Limestone Fine Powder 0, 10, 20, 30, 40, 50, 60, 70

As shown in FIG. 1, in the case where the fourth type of low heat cement and fly ash are mixed, as the fly ash substitution rate increases, the initial time increases. Factors affecting the concrete lateral pressure are based on the start time rather than the end time. The longer the connection time, the greater the lateral pressure in the wall-like mass concrete structure.

As shown in FIG. 2, even in the case where the fourth type of low thermal cement and the blast furnace slag fine powder were mixed, as in the case of fly ash, the initial time increased as the substitution rate was increased. In general, fly ash and blast furnace slag are materials that exhibit a pozzolanic reaction, and when an appropriate amount is substituted, heat of hydration is reduced. However, the use of these materials can increase the settling time (especially the settling time) as shown in the above results, which can result in large lateral pressure in large wall mass concrete structures.

As shown in FIG. 3, when the fourth type of low heat cement and the limestone fine powder were mixed, the above-described fly ash or blast furnace slag fine powder were completely different. In the case where the limestone fine powder is used, when the substitution rate is substituted in the range of 20 to 50%, it is shown that the time of connection is drawn rather than when the substitution rate is 0%. This means that by replacing the limestone fine powder 20 to 50% with respect to the powder weight, the side pressure can be reduced in the large wall mass concrete structure.

4 is a schematic diagram showing the relationship between the hydration heating rate of cement and time. In FIG. 4, in general, the range in which concrete can be poured is up to stage II, and when the stage II is finished, the cement undergoes a hydration reaction, thereby expressing compressive strength. Therefore, the time until stage II reflects the condensation characteristics of the powder.

Figure 5a shows the relationship between the hydration heating rate and the time of the fourth kind of low heat cement + fly ash powder according to the fly ash substitution rate, Figure 6a is a fourth kind of low heat cement + blast furnace slag fine powder and Figure 7a is a fourth kind of low heat The case of cement + limestone fine powder is shown. In the case of the fly ash, it can be seen that the time until step II increases as the substitution rate is increased. In the case of the blast furnace slag derivative, no significant difference occurs. However, in the case of limestone fine powder, the time until stage II is shortened as the substitution rate increases up to 50%. Therefore, as shown in the measurement of the setting time, it can be seen that incorporating an appropriate amount of fine limestone powder into the fourth low heat cement can greatly increase the setting time of concrete.

5B, 6B and 7B show the calorific value of the powder material used as a function of time. In all cases, the calorific value decreased as the substitution rate of the admixture added to the fourth low heat cement increased. That is, when the limestone fine powder is replaced, unlike other materials, the heat of hydration is reduced and the condensation time can be shortened.

Based on the results of the condensation and hydration calorific properties of the powders, the hydration and condensation characteristics of concrete were investigated. The reference formulation used is that which applies to the underground storage tank sidewalls as shown in FIG. The standard formulation used is the optimum formulation ratio corresponding to the design strength of 300kgf / cm2 determined by considering the heat of hydration, workability and strength, and the powder material is composed of 4 kinds of low heat cement (belite cement) and fine limestone powder (LSP). . On the other hand, the coagulation characteristics of the concrete were determined by the comparative example in which fly ash and the fine slag powder were substituted so as to have the same powder weight (W / P is constant) based on the reference compounding ratio. Table 3 is as follows.

division Powder type W / P (%) S / a (%) C (kg / ㎥) Type IV Admixture (kg / ㎥) High Performance Reducer (%) Example Type IV + LSP 41.6 41.0 261 112 1.15 Comparative Example 1 Type IV + FA 41.6 41.0 261 112 1.40 Comparative Example 2 Type IV + Slag 41.6 41.0 261 112 1.00

As shown in Table 3, even in the case of different powder materials, the amount of polycarboxylic acid-based high performance sensitizer was changed to secure the same workability, so that the air amount (4 to 6%) and the slump criterion (19 to 21 cm) were met.

A comparison of the adiabatic temperature rise curve of concrete is shown in FIG. 9 based on the basic formulations shown in Table 3 and previously published data. As can be seen in Figure 9, the amount of low-grade cement (belite cement) of the fourth kind of concrete and similar low-weight cement (360 kg / ㎥) and the amount of low-grade cement of the fourth kind is 261kg / ㎥ and the limestone fine powder 112kg / ㎥ Comparing the adiabatic temperature rise curve of concrete, the initial slope is similar, but the final rise temperature is significantly decreased when limestone fine powder is added. As a result, it can be seen that the addition of fine limestone powder is an effective method that can greatly reduce the temperature rise in the mass concrete member.

In FIG. 9, when the limestone fine powder and the blast furnace slag fine powder are compared, the initial slope is small while the fine blast furnace slag powder is substituted, whereas the maximum rise temperature is rather large. In the case of blast furnace slag powder, the initial slope is small because, as mentioned above, the hydration heat is delayed early, which is related to the condensation characteristics of concrete.

As can be seen from the examples in Table 2, the amount of the fourth kind of low heat cement required to express the target compressive strength is 261 kg / m 3. If the concrete mixing design using only such a cement amount, the amount of powder is so small that the target slump is high, most of the material separation occurs and the properties of the concrete construction can not appear. To improve this, the amount of cement unit should be increased or blast furnace slag powder or fly ash should be added. However, the addition of blast furnace slag and fly ash not only increases the heat of hydration but also increases the setting time. Even in slab-type mass concrete structures where the setting time is not a problem, additional temperature rise due to hydration heat is unavoidable. Therefore, the addition of fine limestone powder, which does not significantly affect the temperature increase due to the heat of hydration, can improve the deterioration of the properties of the hard concrete due to the low cement content.

The powder level of the limestone fine powder used in the embodiment of the present invention corresponds to about 6,000 cm 2 / g. When the concrete having such a powder degree is mixed in more than 20% of concrete, the viscosity of the concrete increases greatly. Too low a slump thus leads to problems with pump pumpability, so it is advantageous for the slump to be as high as possible. Therefore, the slump is preferably 15 cm or more, and should not exceed 24 cm.

10 shows the condensation time for each concrete pouring temperature according to the type of powder used. As can be seen in Figure 10 it can be seen that the relationship between the casting temperature of the concrete and the setting time within the measured range is almost linear regardless of the powder type.

And when the limestone fine powder (LSP) according to the embodiment of the present invention was added at the same pouring temperature, the setting time was shortest, and the case of using the fly ash of Comparative Example 1 was found to have the longest setting time. This is believed to be due to the fact that the limestone fine powder (LSP) significantly accelerated the hydration of the cement with the influence of the powder level of the powder used.

In the case of the fly ash, the setting time of the powder material containing the fly ash is not only delayed, but also the powder is small and the setting time is relatively high since the high performance water reducing agent is used more than the other two formulations to secure the same workability. It was judged that it appeared delayed, and the lower the casting temperature of concrete, the larger the difference in the setting time.

In order to examine the side pressure change of the concrete according to the present embodiment and the comparative example, the side pressure was calculated for the side wall of the structure shown in FIG. 8, and the details of the side wall are shown in Table 4.

Lot No. Design strength (kgf / ㎠) Thickness (m) Height (m) Concrete casting date One 270 3.000 5.250 Oct 4, 2000 2 300 5.017 3.800 Jan. 30, 2001 3 270 3.000 3.912 Feb. 26, 2001 4 270 3.000 8.000 March 26, 2001 5 270 3.000 8.000 Apr 19, 2001 6 270 3.000 8.000 May 21, 2001 7 270 3.000 8.000 June 12, 2001 8 270 3.000 8.000 July 2001 9 270 3.000 5.750 Aug. 2001 10 300 1.500-3.000 3.550 2001. 9 · Compressive strength management order: 91 days · Slump: 18 ± 3cm · Air volume: 4 ~ 6% · Minimum temperature crack index: 1.0

The equation used in the lateral pressure calculation was calculated using a dietary standard of DIN 18218.

P max = G × C 2 × KT × （ 0.48 V + 0.74） kN / ㎡

Where C 2 = 0.065 × Tv + 1.0

KT = (145-3 × T ) / 100

G = unit weight (kN / ㎥)

Tv = concrete setting time (hr)

T = concrete pouring temperature (℃)

V = concrete pouring speed (m / hr)

By substituting the condensation time measured earlier in the above equation, the monthly concrete side pressure can be calculated, and the result is shown in FIG. 11. At this time, the pouring speed of concrete was used 0.3m / hr.

As can be seen in FIG. 11, when the temperature of the outside air is low and the casting temperature of the concrete is low, condensation of the concrete is delayed and excessive side pressure occurs. When fly ash is used, it is January to March, November, and December. In case of using fine slag powder, the maximum lateral pressure of concrete in January, February and December was over 50kN / m2. However, when limestone fine powder (LSP) was used, the maximum side pressure of 50kN / m2 was shown to be the most economical regardless of the season.

According to the mass concrete composition incorporating the limestone fine powder of the present invention, in the construction of large-scale mass-concrete wall structures having one-time high casting height, the temperature rise due to the heat of hydration can be reduced and the condensation time of concrete can be shortened, thereby reducing the formwork cost. It is possible to construct mass concrete that can be used and has high durability. In addition, it is very effective to improve the properties of the hardened concrete when the low cement content is designed.

Claims (5)

Aggregate and water are mixed with powder of the fourth kind of low heat cement and limestone fine powder containing 20 to 50% by weight of limestone fine powder, and the heat of hydration and the setting time of concrete are reduced and shortened. Concrete composition mixed with fine powder. The concrete composition of claim 1, further comprising 0.5 to 2.0% by weight of a high performance water reducing agent in the powder. The concrete composition incorporating limestone fine powder, characterized in that the high-performance water reducing agent is a polycarboxylic acid-based. The concrete composition incorporating limestone fine powder according to any one of claims 1 to 3, wherein the fineness of the limestone fine powder is at least 6,000 cm 2 / g or more. The concrete composition according to any one of claims 1 to 3, wherein the unconsolidated concrete has a slump range of 15 to 24 cm.