JP2017171513A - Concrete for pavement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concrete for pavement reduced in initial cracks and also capable of early traffic opening.SOLUTION: Provided is a concrete for pavement in which a water/cement ratio is 25 to below 36 mass%, unit water quantity is 140 to 180 kg/m, and a fine aggregate ratio is 20 to 50%, including modified fly ash in which ignition loss is 1 mass% or lower by 20 to 80 kg per mof the concrete.SELECTED DRAWING: Figure 1

Description

The present invention relates to a concrete for paving that has few initial cracks and enables early traffic opening.

If the concrete surface is dried in a plastic state where the concrete has not been sufficiently hardened after the concrete is placed, irregular cracks may occur on the surface. This initial crack is mainly caused by drying shrinkage of concrete due to rapid evaporation of the kneaded water. Therefore, initial cracks are likely to occur in concrete with little bleeding, and particularly in concrete pavement, it may occur immediately after construction.

In general, methods for preventing water from evaporating from concrete include film curing, sheet curing, flooding curing, watering curing, and compress curing. Among these, for concrete pavement having a large surface area, film curing is general because the work is relatively easy and the curing effect is high. However, in the film curing, in order to prevent dilution and flow of the film curing agent by bleeding water, it is necessary to perform spraying and coating after the disappearance of bleeding water, and the work is delayed accordingly.

Therefore, as concrete for paving that can reduce initial cracks without performing film curing, Patent Document 1 proposes concrete for paving having a relatively high water-cement ratio and high bending strength. On the other hand, in recent years, there is an increasing demand for paving concrete capable of opening traffic early in paving concrete, but the modified fly ash-containing paving concrete disclosed in Patent Document 1 requires about 5 days after construction to open traffic. It was difficult to achieve early traffic opening.

JP, 2015-151318, A

In the present invention, there is provided a concrete for paving that has few initial cracks and enables early traffic opening.

The inventors of the present invention have completed the present invention as a result of intensive studies in order to achieve the above object. That is, the present invention provides the following [1] to [4].

[1] Pavement concrete having a water / cement ratio of 25% by mass or more and less than 36% by mass, a unit water amount of 140 to 180 kg / m ³ , and a fine aggregate ratio of 20 to 50%,
There is provided a concrete for paving characterized by containing 20 to 80 kg of modified fly ash having an ignition loss of 1% by mass or less per 1 m ³ of concrete.
[2] The pavement concrete according to [1], comprising 0.5 to 2.5% by mass of a high-performance water reducing agent or a high-performance AE water reducing agent with respect to cement.
[3] The concrete for paving according to [1] or [2], wherein the unit coarse aggregate amount is 800 to 1200 kg / m ³ .
[4] The pavement concrete according to any one of [1] to [3], wherein the modified fly ash is a heat-treated product obtained by heat-treating fly ash at 600 to 1000 ° C.

The concrete for paving of the present invention has few initial cracks. Moreover, since the concrete for paving of this invention can express the bending strength of 3.5 N / mm < ² > or more in 1 day of material age, early traffic opening is possible.

It is a figure which shows the example of the steel constrained formwork used for the crack test of concrete.

Hereinafter, the present invention will be described in detail.
The concrete for paving of the present invention has a water / cement ratio of 25% by mass or more and less than 36% by mass, a unit water amount of 140 to 180 kg / m ³ , a fine aggregate ratio of 20 to 50%, and an ignition loss of 1 20 to 80 kg of modified fly ash having a mass% or less per 1 m ³ of concrete is contained.

(1) Modified fly ash First, the modified fly ash used in the present invention will be described. The modified fly ash is an electrostatic classification, flotation, sieving classification, wet classification, crushing classification self-reduction method, vibration classification, jet mill classification, heat treatment, etc. Is a fly ash obtained by classification and removal treatment of unburned carbon. Among these, electrostatic classification is a method in which powder containing two or more kinds of particles is charged, and different particles are selected to remove unburned carbon. The flotation is a method in which water and a surfactant are added to fly ash to form a slurry, which is stirred while air is blown into the slurry to remove unburned carbon adhering to bubbles and floating.

The above-mentioned crushing and classification auto-reduction method uses fly ash with a loss on ignition of several percent to classify it into primary treated ash and unburned carbon agglomerated ash with low ignition loss using an improved airflow crusher, In this method, unburned carbon in the aggregated ash is burned and removed at a temperature at which the ash is burned, and further mixed with primary treated ash to obtain low unburned carbon ash. The jet mill classification is a method of classifying after pulverizing fly ash particles by colliding with a jet mill (fine pulverizer). Among these, the heat treatment method that removes unburned carbon by heating fly ash with a heating device such as a rotary kiln or a fluidized bed furnace, and further classifying the particle size if necessary, removes unburned carbon. It is preferable because of high efficiency and low cost of the apparatus and operation cost.

(I) the content of SiO ₂ in SiO ₂ content the modified fly in ash is preferably at least 45 wt%. Above this value, the modified fly ash has a high pozzolanic activity, and the bending strength of the concrete for paving becomes higher. The content of SiO ₂ is more preferably 60% by mass or more.

(Ii) Blaine specific surface area The Blane specific surface area of the modified fly ash is preferably 3000 to 5000 cm ² / g. If the value is less than 3000 cm ² / g, the bending strength may be lowered, and if it exceeds 5000 cm ² / g, the consistency of the concrete may be lowered. The Blaine specific surface area is more preferably 3500 to 4800 cm ² / g.
(Iii) Sieve residue The 45 µm (nominal size) sieve residue of the modified fly ash is preferably 30% by mass or less. If it is below this value, the consistency of concrete will improve. The residue is more preferably 25% by mass or less.

(Iv) Heating temperature The modified fly ash is preferably obtained by heat-treating fly ash at 600 to 1000 ° C. In addition, since the ignition loss of fly ash, which will be described later, is affected by the charging amount and heating time of the fly ash heating device, charging is performed according to the heating time so that it falls within the ignition loss range. Adjust the amount and heating time.

The modified fly ash used in the present invention has a loss on ignition of 1% by mass or less. When the ignition loss exceeds 1% by mass, chemical admixtures such as high-performance AE water reducing agents are adsorbed on unburned carbon, so the amount of unit water necessary to ensure the required workability increases and initial cracking occurs. The effect of reducing becomes smaller. In addition, it becomes difficult to adjust the amount of air. Furthermore, early traffic opening of paving concrete becomes difficult. Since it is difficult to make the ignition loss extremely small, the ignition loss is preferably 0.1 to 0.9% by mass, more preferably 0.2 to 0.8% by mass, particularly preferably. 0.3 to 0.7% by mass.

The amount of the modified fly ash is 20 to 80 kg / m ³ . If the blending amount is less than 20 kg, the effect of reducing initial cracks is small, and if it exceeds 80 kg, workability is deteriorated, and early traffic opening of the paving concrete may be difficult. In addition, the said compounding quantity becomes like this. Preferably it is 35-75 kg / m < ³ >, More preferably, it is 30-70 kg / m < ³ >. If the ignition loss and the blending amount of the modified fly ash are within the above ranges, the effect of reducing the initial cracks of the paving concrete is high, and early traffic opening becomes possible.

The materials and blending other than the modified fly ash will be described.
(2) Cement The cement used in the present invention is not particularly limited, and is usually Portland cement, early strength Portland cement, super early strength Portland cement, moderately hot Portland cement, low heat Portland cement, sulfate resistant Portland cement, blast furnace cement, silica One or more types selected from cement, white cement, eco-cement and the like can be mentioned. The unit cement amount of paving concrete of the invention is preferably not more than 700 kg / ^{m 3} exceed 400 kg / ^{m 3,} more preferably a 440~600kg / ^{m 3.}

(3) Water The water used in the present invention can be used as long as it does not adversely affect the setting and strength of the concrete for paving, and is selected from, for example, tap water, sewage treated water, and supernatant water of fresh concrete. 1 type or more to be mentioned. Moreover, the unit water amount of the concrete for paving of this invention is 140-180 kg / m < ³ >, Preferably it is 150-175 kg / m < ³ >, More preferably, it is 155-170 kg / m < ³ >. When the unit water amount is less than 140 kg / m ³ , the workability of concrete is deteriorated, and when it exceeds 180 kg / m ³ , the effect of reducing initial cracks is reduced. Moreover, the water / cement ratio of the concrete for paving of the present invention is 25% by mass or more and less than 36% by mass, preferably 27 to 35.5% by mass, and more preferably 30 to 35% by mass. When the water / cement ratio is less than 25% by mass, the workability of the concrete is deteriorated, and when it is 36% by mass or more, it is difficult to quickly open the paving concrete.

(4) Coarse aggregate The coarse aggregate used in the concrete for paving of the present invention is not particularly limited, and at least one selected from river gravel, mountain gravel, crushed stone, slag coarse aggregate, lightweight coarse aggregate, and the like. Can be mentioned. The coarse aggregate may be natural aggregate, artificial aggregate, or recycled aggregate. In addition, the unit coarse aggregate amount of the concrete for paving of the present invention is preferably 800 to 1200 kg / m ³ , more preferably 900 to 1100 kg / m ³ .
(5) Fine aggregate The fine aggregate used in the concrete for paving of the present invention is not particularly limited, and river sand, mountain sand, land sand, sea sand, crushed sand, dredged sand, slag fine aggregate, lightweight fine aggregate, etc. 1 type or more chosen from is mentioned. In addition to the natural aggregate, regenerated aggregate can be used as the fine aggregate.

The fine aggregate ratio of the concrete for paving of the present invention is 25 to 50%, preferably 30 to 49%, more preferably 35 to 48%, particularly preferably more than 40% and 47% or less. When the fine aggregate ratio is less than 25%, the workability of the concrete is deteriorated, and when it exceeds 50%, it is difficult to quickly open the paving concrete.

(6) High-performance water-reducing agent or high-performance AE water-reducing agent As the high-performance water-reducing agent or high-performance AE water-reducing agent used in the concrete for paving of the present invention, naphthalenesulfonic acid-based or polycarboxylic acid-based high-performance water-reducing agent or high A performance AE water reducing agent is mentioned. The blending amount of the high-performance water reducing agent or high-performance AE water reducing agent of the concrete for paving of the present invention is preferably 0.5 to 2.5% by mass, more preferably 0.7 to 2.2% by mass with respect to the cement. Especially preferably, it is 0.9-2.0 mass%. If the amount of high-performance water-reducing agent or high-performance AE water-reducing agent is less than 0.5% by mass with respect to cement, the workability of the concrete will deteriorate, and if it exceeds 2.5% by mass, it will be difficult to quickly open paving concrete. become.

(7) Other materials In addition to the above materials, the concrete for paving of the present invention is an admixture such as AE agent, shrinkage reducing agent and thickener, blast furnace slag powder, limestone, as long as the object of the present invention is not impaired. Admixtures such as powder, quartzite powder, silica fume and expansion material may be included.

The properties of the paving concrete of the present invention will be described.
The concrete for paving of the present invention can exhibit a bending strength of 3.5 N / mm ² or more at a material age of 1 day. If the bending strength per day of the material age is 3.5 N / mm ² or more, early traffic opening (traffic opening in about one day after construction) is possible. In addition, in this invention, in order to implement | achieve early traffic opening, as for the bending strength of material age 1 day, 4.0 N / mm < ² > or more is more preferable, especially in order to implement | achieve traffic opening within one day after construction. Furthermore, the bending strength of one day of age is more preferably 4.5 N / mm ² or more.

From the viewpoint of workability and the like, the concrete for paving of the present invention preferably has a slump of 12 to 25 cm, more preferably 15 to 24 cm, and particularly preferably 20 to 23 cm. When the slump is 21 to 25 cm, the slump flow is preferably 30 to 55 cm, more preferably 35 to 45 cm from the viewpoint of preventing material separation. Moreover, the pavement concrete of the present invention preferably has an air content of 3 to 6%, more preferably 4 to 5%, from the viewpoint of improving freeze-thaw resistance.

The method for kneading the concrete for paving of the present invention is not particularly limited. For example, after a solid material (cement, modified fly ash, aggregate, etc.) is put into a mixer and mixed, a liquid material (water, high performance AE) A water reducing agent or the like) may be put into a mixer and kneaded, or mortar may be first kneaded and coarse aggregate may be added to the mortar and kneaded. The mixer used for kneading is not particularly limited, and a pan mixer, a biaxial mixer, or the like can be used. Moreover, the construction method of the concrete for paving of this invention is not specifically limited, It can construct by the same method as normal concrete paving.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
1. Materials used (1) Modified fly ash (CfFA): Loss on ignition of heat treated product of fly ash 0.7 mass%, SiO ₂ content 68 mass%, Blaine specific surface area 3800 cm ² / g, 45 μm sieve residue 20 mass %
(2) Cement (C): Early strong Portland cement (manufactured by Taiheiyo Cement)
(3) Fine aggregate (S1): mountain sand (density 2.57 g / cm ³ )
Fine aggregate (S2): Crushed sand (density 2.66 g / cm ³ )
(4) Coarse aggregate (G): Crushed stone 2005 (density 2.70 g / cm ³ )
(5) High-performance AE water reducing agent (SP): Product name Floric SF500S (polycarboxylic acid type) manufactured by Floric
(6) AE agent: product name Floric AE-4 manufactured by Floric

2. Concrete mix Table 1 shows the concrete mix.

The SP addition rate in Table 1 represents mass% with respect to cement.

3. Concrete mixing method The concrete mixing procedure is as follows. Cement, modified fly ash, fine aggregate, and coarse aggregate are put into a biaxial mixer and kneaded for 15 seconds, and then mixed with a chemical admixture (high performance). Water containing dissolved AE water reducing agent and AE agent) was added and kneaded for 60 seconds, and the concrete adhered to the side wall of the mixer was scraped off and kneaded again for 60 seconds. The amount of AE agent added was adjusted so that the amount of air in the concrete was 4.5 ± 0.5%.

4). Evaluation of Concrete (1) Initial Crack Test Next, the prepared concrete for paving was placed on a steel constraining mold 10 shown in FIG. 1, and surface finishing was performed using concrete compaction and a trowel. Thereafter, the concrete surface was irradiated with light using an incandescent bulb, and the generation of cracks was promoted by blowing air under conditions of an air temperature of 40 ° C., a relative humidity of 30%, and a wind speed of about 4 m / second. And when 24 hours passed after the said placement, the width and length of the crack which generate | occur | produced on the concrete surface were measured using the crack scale, and the total area of the crack was calculated | required.
The dimensions in FIG. 1 are in mm. The steel constraining mold 10 was made by embedding 10 16 bolts 12 on each side of a quadrilateral using a steel material 11 having a thickness of 4 mm so as to protrude 75 mm. Fig.1 (a) is a top view, (b) is a side view, (c) is steel sectional drawing from the arrow direction of an AA 'surface. The bottom surface 13 was formed of a Teflon sheet (Teflon is a registered trademark) and a polyester film. The test was performed twice on the same mix of concrete.
(2) Bending strength test The prepared concrete for paving was prepared in accordance with JIS A 1106 "Concrete bending strength test method" to prepare a prismatic specimen having a length of 10 cm, a width of 10 cm and a length of 40 cm. After demolding, the bending strength was measured. In addition, the specimen after demolding was subjected to standard curing until the material age of 7 days, and the bending strength of the specimen at the material age of 7 days was also measured.

5. Properties of concrete Properties of concrete are shown in Table 2.

* 1 Comparative Example 2 is a slump value.

As shown in the above table, the pavement concrete of the present invention has a smaller maximum crack width and total crack area per unit area than the pavement concrete of Comparative Example 1 that does not contain modified fly ash, and the occurrence of initial cracks. It turns out that it is remarkably few. Moreover, the concrete for paving of the present invention expresses a bending strength of 4.4 N / mm ² or more at the age of 1 day, and it can be seen that early traffic opening is possible.

10 Steel Constrained Form 11 Steel 12 Bolt 13 Bottom

Claims (4)

Concrete for paving having a water / cement ratio of 25% by mass or more and less than 36% by mass, a unit water amount of 140 to 180 kg / m ³ , and a fine aggregate ratio of 20 to 50%,
A concrete for paving comprising 20 to 80 kg of modified fly ash having a loss on ignition of 1% by mass or less per 1 m ^{3 of} concrete. The concrete for pavement of Claim 1 containing 0.5-2.5 mass% high performance water reducing agent or high performance AE water reducing agent with respect to cement. The concrete for pavement of Claim 1 or Claim 2 whose unit coarse aggregate amount is 800-1200 kg / m < ³ >. The concrete for pavement according to any one of claims 1 to 3, wherein the modified fly ash is a heat-treated product obtained by heat-treating fly ash at 600 to 1000 ° C.