KR101613901B1

KR101613901B1 - Ultra high strength PHC pile using ultra rapid harding cement

Info

Publication number: KR101613901B1
Application number: KR1020160018569A
Authority: KR
Inventors: 염홍섭
Original assignee: 주식회사 성암
Priority date: 2016-02-17
Filing date: 2016-02-17
Publication date: 2016-04-20

Abstract

The present invention relates to a concrete composition for a PHC pile and an ultra-high strength PHC pile manufactured by using the same. More specifically, the present invention relates to a concrete composition for showing greater than or equal to 120 MPa of ultra-high strength with the application of ultrarapid hardening cement, and to a manufacturing method of an ultra-high strength PHC pile by using the same. In addition, the present invention relates to a technique for increasing the production efficiency of a PHC pile product, lowering a defect rate, and shortening a load waiting period without the investment of large-scale plant equipment. The ultra-high strength PHC pile of the present invention comprises water, a binding material, fine aggregate, and coarse aggregate.

Description

Ultra high strength PHC pile using ultra rapid cement (Ultra high strength PHC pile using ultra rapid hardening cement)

The present invention relates to a concrete composition for a PHC pile having an ultra-high strength of 120 MPa or more at a compressive strength of at least 120 MPa and an ultra-high strength PHC pile made using the same. More particularly, the present invention relates to a cement composition (3 days) without extra large-scale plant facility investment, and a method for manufacturing an ultra-high strength PHC pile fabricated using the same.

The PHC file (Pretensioned spun high strength concrete pile) is generally cured after centrifugal molding and compressive strength of about 80 ~ 90 MPa is exhibited at 7 days of age. However, the demand for ultra high-strength PHC pile products with compressive strength of 100 MPa or more has been increasing due to the increase in the recognition of the safety of the structure due to the increase in the demand for the high-rise apartment buildings, coastal area development, special structures, etc. Recently, Or more of the compressive strength is exhibited.

JP-A-10-1247400 (hereinafter referred to as "technology 1") discloses an ultra high strength PHC pile composition in which a compressive strength of 120 MPa or more is expressed within one day after molding. However, the above-mentioned compressive strength is not exhibited within 1 day after the molding is based on the characteristics of the curing process in which the high-temperature high-pressure curing is carried out secondarily after the atmospheric-pressure vapor curing is performed first, [0038] to [0048] section). The high-temperature and high-pressure curing described in Technique 1 means the autoclave curing, and the large-scale facility investment cost (more than 1 billion won in the first stage) due to the installation of the autoclave Yang, There is a disadvantage in view of the recent tendency that the diameter of the PHC pile is large and the mass production thereof is small because the curing capacity is small.

In the patent No. 10-1172635 (hereinafter referred to as "technology 2"), an ultra-high strength PHC file in which a compressive strength of 120 MPa or more is expressed is introduced. After the centrifugal molding of the pile and the atmospheric pressure steam curing, And the productivity is improved (see the patent registration publication identification number [0016] part of the technique 1).

Considering that a 14 day curing period was normally required for the production of PHC files through atmospheric steam curing prior to Technique 2 above, it is remarkable that Technique 2 shortened the shipment period to 7 days. However, even though it is due to autoclave curing, the period of seven days is not short as long as technology 1, which shortened the shipment period to one day, appears.

Since the volume of the PHC file is large, it is difficult to secure a large yard in the factory in order to cure it in the factory for 7 days. It is considered that the biggest problem is to shorten it as much as possible. It is also.

In other words, conventionally, a large-scale plant facility for early shipment of PHC files or a yard where more than seven days can be stored has to be secured. Both of these methods have been problematic in cost and efficiency.

There is another important problem commonly occurring in the concrete composition for centrifugal molding ultra high strength PHC pile including the above technologies 1 and 2.

Since the unit water content of the composition is lowered for the ultrahigh strength development, the mixing time for the even dispersion of the binder, aggregate, and compounding water becomes longer. Delay in composition mixing time leads to lowering of productivity. Therefore, a technique for shortening the mixing time even in the case of a low unit water amount, that is, a technique for improving dispersibility is required.

Also, the PHC file must be condensed immediately after centrifugal molding to maintain the shape of the pile, thereby reducing the defective rate. In this process, a technique of accelerating condensation is required.

However, the dispersing performance and the condensation promoting performance of the concrete composition can be regarded as opposite to each other, and thus there arises a contradictory situation in which one of the above two properties must be exhibited in one composition.

1. Patent No. 10-1247400 "A concrete composition for PE-file for securing a high early strength and a method for producing the same" 2. Patent Application No. 10-1172635 entitled "Ultra High Strength Concrete Composition for Centrifugal Forming PEI Seal Pile"

It is an object of the present invention to provide a concrete composition for ultra high strength PHC pile satisfying the following conditions.

- Ultra high strength of compressive strength of 120 MPa or more should be exhibited.

- Shipment period (aging for compressive strength of 120 MPa or more) should be shortened to 3 days while performing atmospheric steam curing (without autoclave curing)

- shortening composition mixing time before centrifugal molding (to improve dispersibility of concrete composition)

- Quick condensation should proceed after centrifugal molding (reduce the defect rate of the product)

In the present invention, " 100 to 150 kg / m < Binders 550 to 800 kg / m3; Fine aggregate 450 ~ 800㎏ / ㎥; And coarse aggregate 950 to 1,450 kg / m3; And the binder is composed of 65 to 85 wt% of cement and 15 to 35 wt% of high-strength mixed material, and the cement is composed of 45 to 99 wt% of one kind of ordinary cement and 1 to 55 wt% of ultra fast cement, The mixed material is composed of 35 to 50 wt% of calcium oxide (CaO, quicklime), 15 to 30 wt% of sulfur trioxide (SO ₃ ), 1 to 5 wt% of alumina (Al ₂ O ₃ ), and alpha-CaSO ₄ · 1 / 2H ₂ O ) Based on the total weight of the binder, and a polycarboxylate-based high-performance water reducing agent containing an amine-based surfactant and a methyl-cellulose thickener is added in an amount of 1.5 to 2.5 wt% And a compressive strength of 120 MPa or more at 3 days of age after being steam-cured for 10 to 14 hours at a normal pressure and a steam temperature of 55 to 65 ° C.

The fine aggregate may be composed of 1 to 65 wt% of steel sand and 35 to 99 wt% of crushed sand, and the coarse aggregate has a maximum dimension (a dimension of the smallest sieve among the sieve having a coarse aggregate passing ratio of 90 wt% ) Is in the range of 13 mm to 25 mm.

The concrete composition for ultra high strength PHC pile is prepared by first mixing the fine aggregate, cement and high strength mixed material, adding the water and the polycarboxylate high performance water reducing agent to secondary mix, and adding the coarse aggregate to tertiary mix The mixing time of the material can be shortened.

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The present invention has the following effects.

1. It is possible to produce a PHC file that exhibits ultra-high strength of 120 MPa or more in compressive strength while shortening production time and shipment time and improving the reliability of products (reduction of defect rate).

2. Mixing order of materials is changed from conventional (1) aggregate (coarse aggregate and fine aggregate) → (2) binder → (3) water and admixture (1) fine aggregate and binder → (2) water, admixture → (3) coarse By changing the order of the aggregates, the material mixing time is shortened.

3. Use of a polycarboxylate-based high-performance water reducing agent containing an amine-based surfactant and a methyl-cellulose thickener improves the dispersibility of the concrete composition and increases the viscosity to prevent material separation.

4. After the centrifugal molding of the concrete composition is accelerated by the alpha-hemihydrate gypsum and alumina contained in the cement and the high strength mixture, the defective rate of the product can be lowered by maintaining the molding condition of the product well.

5. Self-heating effect by fast speed cement and alumina reduces the curing time while lowering the steam temperature (without autoclave curing) while performing the atmospheric steam curing after the centrifugal molding of the PHC pile .

6. Because of the effect of accelerating the condensation of cement with fast speed, alumina and alpha hemihydrate gypsum, ultrahigh strength of more than 120 MPa is exhibited on the 3rd day of the year.

[Figure 1] compares the cured state of the PHC pile after centrifugal molding according to the mixing state of the concrete composition.

In the present invention, " 100 to 150 kg / m < Binders 550 to 800 kg / m3; Fine aggregate 450 ~ 800㎏ / ㎥; And coarse aggregate 950 to 1,450 kg / m3; And the binder is composed of 65 to 85 wt% of cement and 15 to 35 wt% of high-strength mixed material, and the cement is composed of 45 to 99 wt% of one kind of ordinary cement and 1 to 55 wt% of ultra fast cement, The mixed material is composed of 35 to 50 wt% of calcium oxide (CaO, quicklime), 15 to 30 wt% of sulfur trioxide (SO ₃ ), 1 to 5 wt% of alumina (Al ₂ O ₃ ), and alpha-CaSO ₄ · 1 / 2H ₂ O ) Based on the total weight of the binder, and a polycarboxylate-based high-performance water reducing agent containing an amine-based surfactant and a methyl-cellulose thickener is added in an amount of 1.5 to 2.5 wt% &Quot;

In the present invention, water is blended in the range of 100 to 150 kg / m3. When the unit water content is lower than 100 kg / m 3, the productivity of the product tends to be poor due to the fluidity problem of the product, and when it exceeds 150 kg / m 3, it is difficult to exhibit the ultrahigh strength with a compressive strength of 120 MPa or more. The water binding ratio is formed in the range of 12.5 to 27.3 wt%.

In the present invention, the binder is blended in the range of 550 to 800 kg / m < 3 >. The binder is composed of 65 to 85 wt% of cement and 15 to 35 wt% of high strength mixture.

The cement is a mixture of one kind of ordinary cement and ultra fast cement and is blended in the range of 65 to 85 wt% when the total amount of the binder is 100 wt%. When the total amount of the cement is 100 wt%, the first kind of ordinary cement is 45 to 99 wt%, and the first speed cement is 1 to 55 wt%. The cement is suitable as a binder of a concrete composition for a PHC pile which is required to be solidified immediately after centrifugal molding because the curing speed and the strength increasing rate of the cement are high due to the exothermic property of the ordinary cement.

When using the above-mentioned quick-speed cement alone, it exhibits a compressive strength corresponding to the strength of 28 days of one kind of ordinary cement within 3 to 4 hours of mixing with water. There is no change in volume due to drying shrinkage, It is applied to expressways, bridges, panic runways, etc., which require emergency work in order to facilitate hydration reaction. However, when the cement composition is used as a single quick-setting cement, there are various problems in production of the factory product due to the rapid condensation speed. In the present invention, by combining the quick-setting cement with 1 to 55 wt% of the total amount of cement (one kind of ordinary cement is 45 to 99 wt% of the total amount of cement), the installation cost is excessive due to interaction with the above- The early condensation effect of the concrete composition for a PHC pile can be obtained without a plant facility having a large energy consumption.

When the total amount of the binder is 100 wt%, the high strength mixture is blended in the range of 15 to 35 wt%. The high strength honhapjae is calcium oxide (CaO, quicklime) 35 ~ 50wt%, sulfur trioxide _{(SO 3) 15 ~ 30wt%} , alumina _{(Al 2 O 3) 1 ~} 5wt% , and alpha half gypsum _{(α-CaSO 4 · 1 /} 2H ₂ O) 10 to 15 wt%.

When the high-strength honhapjae that the composition only the materials listed above, calcium oxide (CaO, quicklime) 50wt%, sulfur trioxide (SO ₃₎ 30wt%, alumina (Al ₂ O ₃₎ 5wt%, and alpha half gypsum (α-CaSO ₄ · 1 / 2H ₂ O). When the blend of blast furnace slag, anhydrous gypsum and the like is mixed with the high strength mixture, the composition ratio of the above listed materials can be adjusted within the above-mentioned range.

The calcium oxide (CaO, quicklime) reacts with the calcium hydroxide generated by hydration of the cement to form a silicate, and the silicate continuously hydrates the water, thereby increasing the initial strength of the concrete composition.

The sulfur trioxide (SO ₃ ) reacts with the calcium oxide to form sulfuric acid ions, and the sulfuric acid ion reacts with C ₃ A of the cement component to swell, thereby contributing to the enhancement of the long-term strength of the concrete composition.

The alumina (Al ₂ O ₃ ) is a hydration reaction material and is involved in the early strength development of the concrete composition.

The alpha hemihydrate (α-CaSO ₄ · 1 / 2H ₂ O) is produced by press hydrothermal synthesis using flue gas desulfurization and phosphate dihydrate, which are produced as natural dihydrate or industrial by-products. Alpha hemihydrate gypsum reacts with water to cure, and is very stable to rapid expansion and shrinkage after rapid settling and curing, and contributes to the development of high compressive strength at the early age of concrete composition.

These alpha hemihydrate gypsum is widely used for medical (dental, plastic surgery), mold (ceramics), etc. and it is used as a high-grade additive because domestic raw materials (flue gas desulfurization) are stable and can be mass-produced. When the alpha-hemihydrate gypsum is mixed with cement, it stabilizes the internal pore in addition to the initial strength development, thereby contributing to the improvement of the durability of the cement.

In the present invention, the alpha-hemihydrate gypsum constituting one component of the high-strength mixed material is used to densify the interior porosity at the initial stage of curing after the centrifugalization of the PHC pile, and thereby the ultrahigh strength of the PHC pile is achieved.

The specific surface area of the alpha-hemihydrate gypsum is 700 to 2000 cm 2 / g, the density is 2.67, and the chemical composition analysis results are as shown in the following Table 1.

Chemical composition Mg Al Si S K Ca Fe Sr wt% 0.60 0.96 1.86 46.08 0.67 49.51 0.38 0.03

In the present invention, the fine aggregate is blended in the range of 400 to 750 kg / m3. The fine aggregate may be composed of 1 to 65 wt% of river sand and 35 to 99 wt% of crushed sand.

Meanwhile, the coarse aggregate is blended in the range of 950 to 1,450 kg / m 3, and the maximum dimension (the size of the smallest sieve among the sieve having the coarse aggregate passing ratio of 90 wt% or more in the sieve-sieve test) is in the range of 13 mm to 25 mm have.

In the present invention, the fine aggregate ratio (the volume ratio of fine aggregate to the volume of fine aggregate and coarse aggregate - the value determining the workability and filling property of concrete) is 25.0 to 40.0 vol%. If the fine aggregate ratio is inadequate, it may cause defective forming and lowered compressive strength.

The admixture to be used in the present invention is a polycarboxylate type high-performance water reducing agent containing an amine surfactant and a methyl-cellulose thickener, and is added in an amount of 1.5 to 2.5 wt% based on 100 wt% of the binder. The amphoteric surfactant and the methyl-cellulose thickener may be present in an amount of 5 to 20 wt% and 1 to 5 wt%, respectively, in the various components of the polycarboxylate-based high-performance water reducing agent.

The polycarboxylate-based high-performance water reducing agent has an effect of improving the reactivity of cement hydrate to shorten the setting time of concrete and has an excellent effect in maintaining the gel state of cement hydrate, thereby increasing the viscosity of the concrete composition before curing, Thereby preventing the material separation phenomenon that may occur in a homogeneous concrete composition. As a result, it is possible to perform the centrifugal molding operation for producing the PHC pile with the components of the concrete composition dispersed evenly.

[Figure 1] shows a state in which the concrete composition is normally mixed (uniformly dispersed state) and then cured after centrifugal molding (Figure 1 (a)), a state in which the concrete composition is not normally mixed (FIG. 1 (b)) after the centrifugal molding and centrifugal molding and the cured state after the material separation of the concrete composition (FIG. 1 (c) The importance of the dispersion state of the concrete composition can be grasped through [1].

The present invention lowers the water-binding ratio of the PHC pile and increases the viscosity of the PHC pile using a binder having a high degree of powder, so that the mixing time of the material is prolonged. Accordingly, the present invention improves the productivity by shortening the mixing time by changing the mixing order of the constituents of the concrete composition.

Conventional concrete mixing has proceeded to (1) mixing of fine aggregate and coarse aggregate, (2) mixing with binder, and (3) mixing with water and admixture. Here, the mixing of water and the admixture was carried out twice in half.

However, in the present invention, the mixing is performed by (1) mixing fine aggregate, cement and high-strength admixture first, (2) mixing water and admixture (polycarboxylate-based high performance water reducing agent) The aggregate is added and mixed.

[Table 2] below is a formulation chart of one embodiment (hereinafter, referred to as " Example ") of the concrete composition for an ultrahigh strength PHC pile provided by the present invention.

W / B
(wt%) S / a
(vol%) Unit material amount (kg / m3) W B C
(Speed + 1 species) High strength
Mixed material Fine aggregate Coarse aggregate 14.7 32.0 110 750 563 187 523 1128

Table 3 below shows the mixing time of the above embodiments according to the material mixing step described in the [Background of the Invention] section described in Patent No. 10-1247400. It can be seen that the time required for material mixing is 180 to 480 (3 to 8 minutes).

division material Mix time (seconds) Stage 1 Coarse aggregate, fine aggregate 30 to 60 Step 2 Cement, High Strength Mixture 30 to 60 Step 3 Water / Admixture 1/2 60 to 180 Step 4 Water / Admixture Remainder 1/2 60 to 180

Table 4 below summarizes the mixing time of the above embodiments in accordance with the material mixing order of the present invention. It can be confirmed that the time required for material mixing is 120 to 150 seconds (2 to 2.5 minutes).

division material Mix time (seconds) Stage 1 Cement, High Strength Mixture 30 to 40 Step 2 Water, admixture 50 to 60 Step 3 Fine aggregate, coarse aggregate 40 to 50

As the material mixing time is reduced to 1/2 to 1/4 as compared with the conventional method, the productivity in the mixing process is improved by 2 to 4 times. This effect is considered to be partially influenced by the amine surfactant component in the admixture (polycarboxylate-based high-performance water reducing agent) that improves the dispersibility of the concrete composition. When two mixing shafts in the mixer are used, Time can be further shortened.

The concrete composition mixed for the shortened time as described above has a shape as a PHC file in the conventional PHC file centrifugal molding method and accelerates the condensation through the atmospheric steam curing. However, in a situation where contradictory properties are required together with a requirement for accelerating the condensation in the product molding stage, the dispersibility of the components including the alpha-hemihydrate gypsum of the high-strength mixed material is poor In the molding process of the product without affecting, the condensation is promoted and the problem of the contradiction situation is solved.

Further, according to the present invention, the steam temperature can be lowered and the curing time can be shortened compared with the conventional steam curing. Typical steam curing is carried out at room temperature and steam temperature of 75 ~ 85 ℃ for 10 ± 2 hours.

Table 5 below shows the formulation table of the PHC pile concrete composition of the conventional level of 120 MPa (hereinafter referred to as "Comparative Example"), and Table 6 below shows the curing temperature and time of the PHC pile formed in the above Example . The steam curing for the comparative example was conducted for a total of 12 hours.

W / B
(wt%) S / a
(vol%) Unit material amount (kg / m3) W B C
(3 species + 1 species) High strength
Mixed material Fine aggregate Coarse aggregate 22.0 33.0 110 500 350 150 616 1251

division transposition Heating maintain Slow cooling Sum Conventional Curing temperature (℃) 45 85 85 Room temperature - Curing time (hours) 4 2 4 2 12

However, since the self-heating phenomenon is strongly exhibited by cement and alumina at a very short period of time in the curing step of the present invention, sufficient accelerated curing effect can be obtained even if the steam temperature is lowered. The steam curing of the present invention exhibits an effect equal to or higher than that of the conventional steam curing even when the steam curing is carried out at 55 to 65 ° C under atmospheric pressure and steam temperature for 10 to 14 hours and since the holding temperature is low, Curing time can be shortened.

Table 7 below shows the curing temperature and time of the PHC pile formed in the example of Table 2. [ Steam curing for the examples was conducted for a total of 12 hours.

division transposition Heating maintain Slow cooling Sum Conventional Curing temperature (℃) 40 60 60 none Curing time (hours) 3 2 7 none 12

Table 8 below summarizes the state of change in compressive strength of each of the comparative examples and the examples according to the age after steam curing.

division Compressive strength (MPa) 1 day 3 days 7 days 14 days Comparative Example (Conventional) 96.8 102.5 113.5 124.3 EXAMPLES (invention) 111.6 122.4 126.9 -

In Table 8, it can be seen that the period in which the compressive strength of 120 MPa is manifested is remarkably shortened in spite of the fact that the embodiment cures the steam at a low temperature for a short period of time as compared with the comparative example.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. It is therefore intended that the appended claims cover such modifications and variations as fall within the true scope of the invention.

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Claims

Water 100 to 150 kg / m 3; Binders 550 to 800 kg / m3; Fine aggregate 450 ~ 800㎏ / ㎥; And coarse aggregate 950 to 1,450 kg / m3; And the binder is composed of 65 to 85 wt% of cement and 15 to 35 wt% of high-strength mixed material, and the cement is composed of 45 to 99 wt% of one kind of ordinary cement and 1 to 55 wt% of ultra fast cement, The mixed material is composed of 35 to 50 wt% of calcium oxide (CaO, quicklime), 15 to 30 wt% of sulfur trioxide (SO ₃ ), 1 to 5 wt% of alumina (Al ₂ O ₃ ), and alpha-CaSO ₄ · 1 / 2H ₂ O ) Based on the total weight of the binder, and a polycarboxylate-based high-performance water reducing agent containing an amine-based surfactant and a methyl-cellulose thickener is added in an amount of 1.5 to 2.5 wt% And a compressive strength of 120 MPa or more at 3 days of aging after 10 to 14 hours of steam curing at 55 to 65 ° C under normal pressure and steam temperature.

The method of claim 1,
Wherein the fine aggregate is composed of 1 to 65 wt% of river sand and 35 to 99 wt% of crushed sand.

The method of claim 1,
Wherein the coarse aggregate has a maximum dimension (dimension of the smallest sieve among the sieve having a coarse aggregate permeability of 90 wt% or more in the sieve-forming test) in the range of 13 mm to 25 mm.

4. The method according to any one of claims 1 to 3,
The fine aggregate, the cement and the high strength mixed material are first mixed,
The water and the polycarboxylate-based high-performance water reducing agent are added and mixed by secondary mixing,
And the coarse aggregate is added to the mixture to be mixed in tertiary strength.

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