JP7851266B2 - hydraulic composition - Google Patents

Description

This invention relates to a hydraulic composition. More specifically, it relates to a hydraulic composition that possesses fluidity while also having resistance to material separation and is less prone to material separation due to compaction.

In recent years, construction projects using concrete have seen an increase in cases where filling concrete formwork is difficult due to the increasing complexity of component shapes and the increased amount of reinforcing steel. Furthermore, the decline in the number of workers and engineers inevitably leads to a decrease in work efficiency.

To address these problems, high-flow concrete that does not require compaction has been developed and used. However, this high-flow concrete requires large amounts of powders such as cement and admixtures such as high-performance AE water-reducing agents during manufacturing, inevitably leading to increased costs. Furthermore, its properties make quality control complicated.

To address the problems in the above-mentioned construction work and the issues with high-flow concrete, the application of "high-flow concrete requiring compaction (hereinafter referred to as medium-flow concrete)," which has higher fluidity than ordinary concrete but requires compaction during construction, is gradually progressing. For example, several cases of its application to tunnel lining concrete have been reported (see, for example, Non-Patent Document 1).

Kazuhiko Suwazono, et al., "Construction of Tunnel Lining Using Thickening Agent-Based Medium-Flow Concrete - Tsunagi Tunnel (Provisional Name) on the South Kyushu West Bypass Expressway," Concrete Engineering, April 2012, Vol. 50, No. 4, pp. 366-371 (368).

Medium-flow concrete has the advantage of high fluidity, allowing for filling with minimal compaction. However, due to the need to minimize cement usage, it tends to have a high water-to-powder ratio and a high unit water content, making it prone to material segregation if compaction time is prolonged.

The inventors of this invention conducted research to solve the above problems. They discovered that by replacing the cement used in medium-flow concrete with blast furnace slag fine powder through internal substitution, using a high-performance AE water-reducing agent containing a thickening component, and adjusting the fine aggregate ratio to a predetermined value, it is possible to improve the resistance to material segregation while maintaining fluidity without lowering the water-to-powder ratio of the concrete. This led to the completion of the present invention.

In other words, the present invention relates to a hydraulic composition comprising a binder (total binder amounting to 100 parts by mass) consisting of 47 to 89 parts by mass of Portland cement clinker, 10 to 50 parts by mass of blast furnace slag fine powder, and 1 to 3 parts by mass of gypsum, a high-performance AE water-reducing agent containing a thickening component, coarse aggregate, fine aggregate, and water, wherein the fine aggregate ratio is 55 to 60%. In the hydraulic composition of the present invention, it is preferable that the slump flow value is 40 to 50 cm and the air content is 3.0 to 6.0%.

The hydraulic composition of the present invention provides a medium-flow concrete that, compared to a medium-flow concrete made using only ordinary Portland cement, maintains equivalent fluidity while improving resistance to material segregation without lowering the water-to-powder ratio. It also offers a medium-flow concrete that does not exhibit material segregation even at a compaction time of 10 seconds, a time at which segregation can occur in conventional medium-flow concrete.

The binder used in the hydraulic composition of the present invention consists of Portland cement clinker, blast furnace slag powder, and gypsum.

Portland cement clinker is not particularly limited as long as it is the clinker used in the manufacture of ordinary Portland cement according to JIS standards. Generally, the mineral composition shown in the Bogue formula is approximately 50-67% _C3S , 12-20% _C2S , 7-15% _C3A , and 7-15% _C4AF .

The fineness of the Portland cement clinker should be within a range suitable for general use, preferably adjusted to 3000-4500 ^cm² /g. The fineness may also be adjusted by adding gypsum.

The method for producing Portland cement clinker is not particularly limited. It can be easily obtained by preparing and mixing known cement (clinker) raw materials in predetermined proportions to achieve desired mineral ratios and coefficients, and then firing them using a known method (e.g., an SP kiln or NSP kiln).

The method for preparing and mixing the cement raw materials can also be any known method as appropriate. For example, the composition of waste, by-products, and other raw materials (CaO sources such as limestone, quicklime, and slaked lime; _SiO2 sources such as silica; _{Al2O3 sources} such as clay; _{Fe2O3 sources} such as iron, etc.) can be measured in advance, and the mixing ratio of each raw material can be calculated from the proportion of each component in these raw materials so that it falls within the above range, and the raw materials can then be mixed in that ratio.

Furthermore, the raw materials used in the manufacture of Portland cement clinker are the same as those conventionally used in the manufacture of Portland cement clinker, without any particular restrictions. The use of waste materials, by-products, etc., is also, of course, possible.

In the production of Portland cement clinker, using one or more types of waste and by-products is desirable from the perspective of promoting the effective utilization of waste and by-products. More specifically, examples of usable waste and by-products include blast furnace slag, steelmaking slag, non-ferrous metal tailings, coal ash, sewage sludge, water treatment sludge, papermaking sludge, construction waste soil, foundry sand, fly ash, incinerator fly ash, molten fly ash, chlorine bypass dust, wood chips, waste clay, spoil, waste tires, seashells, municipal solid waste and its incinerator fly ash, etc. (Note that some of these can be used as both cement raw materials and thermal energy sources).

The binder used in the hydraulic composition of the present invention includes, in addition to the Portland cement clinker mentioned above, blast furnace slag powder and gypsum as essential components.

As the blast furnace slag fine powder, any blast furnace slag fine powder known as a cement admixture can be used. Specifically, any blast furnace slag fine powder conforming to JIS A 6206 "Blast Furnace Slag Fine Powder for Concrete" can be used without restriction. The fineness of the blast furnace slag fine powder should be within the range of general use, and it is preferable that it be adjusted to 4000 to 5000 ^cm² /g.

Regarding gypsum, any gypsum known as a raw material for cement production, such as dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum, can be used without particular restriction. Specifically, examples include by-product dihydrate gypsum such as flue gas desulfurization gypsum and phosphate gypsum, as well as natural dihydrate gypsum, hemihydrate gypsum, and type II anhydrous gypsum.

The binder used in the hydraulic composition of the present invention consists of 47 to 89 parts by mass of Portland cement clinker, 10 to 50 parts by mass of blast furnace slag powder, and 1 to 3 parts by mass of gypsum (with the total binder amount being 100 parts by mass). If the amounts deviate from this range, fluidity will decrease or abnormal setting will occur. Preferably, the amounts are 52 to 84 parts by mass of Portland cement clinker, 15 to 45 parts by mass of blast furnace slag powder, and 1 to 3 parts by mass of gypsum.

Regarding the grinding method for adjusting the fineness of the Portland cement clinker, blast furnace slag powder, and gypsum that constitute the binder used in the hydraulic composition of the present invention, known techniques can be used without particular limitation. Each component may be ground individually and then mixed, or ground after mixing. Ball mills, vertical mills, etc., can be used as grinders. Alternatively, the mixture can be produced by mixing the Portland cement and blast furnace slag powder prepared separately.

Here, the binder materials used in this invention may be used individually, or they may be a combination of Portland cement (a mixture of Portland cement clinker and gypsum) and blast furnace slag powder, or they may be blast furnace cement (a mixture of Portland cement and blast furnace slag) alone.

The hydraulic composition of the present invention, in addition to the binder mentioned above, contains a high-performance AE water-reducing agent containing a thickening component, coarse aggregate, fine aggregate, and water.

High-performance AE water-reducing agents containing thickening components can be used if they primarily consist of polycarboxylic acid compounds containing thickening components and conform to JIS A 6204 "Chemical Admixtures for Concrete". The addition rate of the high-performance AE water-reducing agent containing thickening components is acceptable as long as it is within the manufacturer's recommended range, but 1.0 to 1.5% relative to the powder mass is preferable. Examples of high-performance AE water-reducing agents containing thickening components include Frolic SF500F manufactured by Frolic Co., Ltd.

Coarse aggregate and fine aggregate can be any known material used in general concrete production without particular restrictions. Specifically, these include crushed stone, crushed sand, river gravel, hill sand, sea sand, limestone aggregate, etc. For coarse aggregate, it is preferable to use aggregate with a size of 10 to 25 mm. The amount of coarse aggregate used is preferably 700 to 1000 kg/ ^m³ . For fine aggregate, it is preferable to use aggregate with a particle size ratio of about 2.4 to 2.8, or a mixture of several types of fine aggregate to achieve a predetermined particle size ratio. The amount of fine aggregate used is preferably 900 to 1200 kg/ ^m³ . Furthermore, the volume ratio of fine aggregate to the total aggregate (hereinafter referred to as the fine aggregate ratio) is 55 to 60%. If it falls outside this range, the resistance to material segregation decreases, and the fluidity decreases. The preferred range for the fine aggregate ratio is 56.5 to 58.5%.

The water used can be any type commonly used in concrete manufacturing, without any particular restrictions. Specifically, tap water, groundwater, etc., can be used as long as they conform to JIS A 5308 "Ready-Mixed Concrete".

The slump flow value and air content are preferably within the range conforming to JIS A 5308 "Ready-Mixed Concrete," specifically, a slump flow value of 40 to 50 cm and an air content of 3.0 to 6.0% are preferred. By maintaining this range, it is possible to improve the resistance to material segregation while preserving the fluidity of the concrete, and furthermore, because it conforms to JIS A 5308 "Ready-Mixed Concrete," it is possible to create a highly versatile hydraulic composition.

The slump flow value and air content are measured according to JIS A 1150 "Test Method for Slump Flow of Concrete" and JIS A 1128 "Test Method for Air Content of Fresh Concrete by Pressure."

The hydraulic composition of the present invention, within the JIS A 5308 "Ready-Mixed Concrete" category, is a normal-strength concrete controlled by slump flow, and generally corresponds to medium-flow concrete when the slump flow value is 40 to 50 cm.

In this invention, the method for producing a hydraulic composition by kneading (mixing) Portland cement, blast furnace slag fine powder, a high-performance AE water-reducing agent containing a thickening component, coarse aggregate, fine aggregate, and water can be any conventional production method used in ready-mix concrete plants or precast concrete product plants without particular limitations.

In this invention, any mixer used for mixing the hydraulic composition can be any mixer that is generally used for mixing mortar or concrete. Specifically, examples include pan-type mixers, forced twin-shaft mixers, tilt mixers, mortar mixers, and hand mixers.

The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

Medium-flow concrete was mixed using ordinary Portland cement (NC), blast furnace slag powder (BS), a high-performance AE water-reducing agent containing thickening components (admixture), coarse aggregate, fine aggregate, and water. Various tests were conducted to evaluate its fresh properties and resistance to material segregation.

(Materials used)
NC: Tokuyama Corporation ordinary Portland cement (containing 98 parts by mass of Portland cement clinker and 2 parts by mass of gypsum; density 3.16 g/ ^cm³ , fineness 3210 ^cm² /g),
BS: Esment 40P manufactured by Nippon Steel Blast Furnace Cement Co., Ltd. (density 2.91 g/ ^cm³ , fineness 3980 ^cm² /g),
Admixture: Floric SF500F manufactured by Floric Co., Ltd.
Coarse aggregate: Crushed hard sandstone 2010 (surface dry density 2.69 g/ ^cm³ ) and 1505 (surface dry density 2.69 g/ ^cm³ ) from Miyano, Yamaguchi City, Yamaguchi Prefecture.
Fine aggregate: Crushed sand from Kumehijiri, Shunan City, Yamaguchi Prefecture (surface dry density 2.66 g/ ^cm³ , coarseness 2.79) and hill sand from Onga, Fukuoka Prefecture (surface dry density 2.58 g/ ^cm³ , coarseness 1.21)
I used it.

The fine aggregate was prepared by mixing crushed sand and hill sand in a ratio of 81.8% to 18.2% so that the coarseness ratio of the synthesized sand was 2.55. The water-to-binder ratio (W/B) was set at 55%.

A 100L pan-type forced-mix mixer (TM-100) manufactured by Taiheiyo Kiko Co., Ltd. was used for mixing. The mixing procedure involved first adding the powder, coarse aggregate, and fine aggregate to the mixer and stirring for 30 seconds, then adding the admixture and water and mixing for 90 seconds. The target fresh properties for the medium-flow concrete were a slump flow value of 45±5cm and an air content of 4.5±1.5%. Table 1 shows the mixing ratio of the binders used in each example, Table 2 shows the levels of the medium-flow concrete, and Table 3 shows the results of various tests.

The various measurement methods are as follows.
(1) Slump measurement: Measured according to the method in accordance with JIS A 1101.
(2) Measurement of slump flow: Measured in accordance with the method of JIS A 1150.
(3) Measurement of air volume: Measured in accordance with the method of JIS A 1128.
(4) Measurement of coarse aggregate retention rate: The measurement was performed in accordance with the coarse aggregate settlement test considered by the Japan Concrete Institute Concrete Committee 358 Research Subcommittee on Mix Design and Construction Technology for High-Flow Concrete Requiring Compaction.

Specifically, the test involves pouring 20 liters of concrete into a bucket container with a diameter of 30 cm and a height of 35 cm, inserting a rod-shaped vibrator (Exen Corporation D32D, vibration frequency 200-242 Hz) into the center of the container, 1 cm from the bottom, and vibrating it for a predetermined time. After that, 2 liters of the surface layer of the concrete is collected and wet-screened to wash out the coarse aggregate, and the ratio of the amount of coarse aggregate to the design value is measured. Here, wet screening means washing the concrete using a sieve with a mesh size smaller than or equal to the minimum size of the coarse aggregate, separating the coarse aggregate from the other materials. In this test, the greater the degree of material separation, the more the coarse aggregate settles to the bottom, reducing the amount of coarse aggregate washed out and resulting in a smaller test result. Regarding the vibration time, we set it at 10 seconds, which is the median value of the recommended vibration time of "approximately 5 to 15 seconds" for ordinary concrete as described in the Standard Specifications for Concrete and the Standard Specifications and Commentary for Building Construction JASS 5. For medium-flow concrete, since the compaction time is shorter than for ordinary concrete, we set it at 6 seconds.

The reference example uses ordinary concrete with a commonly used slump value of 18 cm. The residual aggregate content after 10 seconds of vibration (a typical compaction time for concrete) was 75.0%.

Comparative Examples 1 and 2 were examples of medium-flow concrete that does not contain blast furnace slag powder and uses only ordinary Portland cement, which is a conventional technology, and were conducted to demonstrate the effect of the binder of the present invention. Comparative Example 1 was an example of medium-flow concrete that satisfied the target slump flow value and target air content. The slump flow value was 44.5 cm and the air content was 5.0%, satisfying the target values. However, the coarse aggregate retention rate was 65.2% at a compaction time of 6 seconds and 57.8% at a compaction time of 10 seconds, which were significantly lower than the values of the reference example. Comparative Example 2 was based on Comparative Example 1, but the amount of water was reduced to 175 kg/ ^m³ to improve the coarse aggregate retention rate. The coarse aggregate retention rate improved to 88.7% at a compaction time of 6 seconds and 74.2% at a compaction time of 10 seconds, showing a better coarse aggregate retention rate than Comparative Example 1. However, the slump flow value decreased to 37.0 cm.

Comparative Example 3 is an example where the fine aggregate ratio falls outside the range specified in the present invention. Using the same ratio of binder as in Example 3, the fine aggregate ratio was set to 60.6%, which is outside the range specified in the present invention. While the coarse aggregate retention rate was 86.9% at a compaction time of 6 seconds and 75.1% at a compaction time of 10 seconds, the slump flow value decreased to 36.3 cm. From the results of the comparative example, it is clear that it is difficult to improve the coarse aggregate retention rate while maintaining the target slump flow unless the requirements of the present invention are satisfied.

Examples 1-3 show the results when the binder was mixed in the proportions shown in Table 1 and the mix design conditions were as shown in Table 2. In all three examples, while satisfying the target slump flow value, a good coarse aggregate retention rate of over 80% was observed at a compaction time of 6 seconds, and over 68% at a compaction time of 10 seconds. This indicates that the present invention can suppress material segregation at the appropriate compaction time of 6 seconds for medium-flow concrete, and that even at a longer compaction time of 10 seconds, the appropriate compaction time for ordinary concrete, the degree of material segregation can be reduced compared to ordinary medium-flow concrete.

Claims (2)

A hydraulic composition comprising 47 to 89 parts by mass of Portland cement clinker, 10 to 50 parts by mass of blast furnace slag fine powder, and 1 to 3 parts by mass of gypsum (total amount of binder being 100 parts by mass), a high-performance AE water-reducing agent containing a thickening component, coarse aggregate, fine aggregate, and water, characterized in that the fine aggregate ratio is 55 to 60%. The hydraulic composition according to claim 1, wherein the slump flow value is 40 to 50 cm and the air content is 3.0 to 6.0%.