KR100615674B1 - High strength concrete - Google Patents

Abstract

The present invention relates to an environmentally friendly concrete composition using dolomite produced as a by-product in limestone mines as a concrete aggregate of fine aggregates and coarse aggregates as concrete aggregates. In the present invention, in the manufacture of concrete blocks, the unit weight (kg / ㎥) is 1650 ~ 1720, the specific gravity is 2.90 ~ 3.20, the absorption rate (absorption rate,%) is 0.5 ~ 1.0 as an aggregate component Dolomite coarse aggregate (FM) of 5.0 to 7.0 is used in an amount of 5 to 20 wt% based on the total aggregate content, the unit weight (kg / ㎥) is 1750 to 1900, and specific gravity is 2.60 to 2.88. Regarding the concrete block composition using 95-80 wt% of dolomite residue aggregate (DFA) having an absorption rate (%) of 1.2 to 1.5 and an assembly rate (FM) of 2.0 to 4.5, based on the total aggregate content, When using the composition is to provide an environmentally friendly concrete block composition that provides an excellent concrete block having a low absorption rate of 320 ~ 450kgf / cm ² .

Concrete, aggregate, dolomite

Description

Composition for high strength concrete block

1 is a view showing the compressive strength and the water absorption of Examples 1 to 3.

The present invention is to provide an environment-friendly composition for the production of concrete blocks by using dolomite having a specific physical property produced as a by-product in limestone mines as aggregate for concrete blocks.

It is important to determine the characteristics of concrete, which means that the cement is surrounded by cement paste, which is made of grass by opening the cement with water, using a hydration reaction where the cement reacts with water to harden. One of the factors is aggregate. The properties of aggregates in concrete must be characterized first by their porosity, particle size distribution, absorption rate, shape and surface texture, strength of the aggregate itself, modulus of elasticity and types of harmful components.

Aggregates for concrete should be solid and chemically stable, with the most common aggregates being gravel and sand. Depending on the diameter of the grain is more than 5mm thick aggregate, less than 5mm is called fine aggregate. In addition, it is divided into natural aggregate and artificial aggregate according to the output state. Natural aggregates are gravel, sand, etc. collected from Gangagal, mountain, and sea.

Mountain gravel and mountain sand have a harmful effect on concrete due to the mixing of organic impurities and clay, and sea gravel and sea sand corrode rebar in concrete due to salts. So sometimes it is neutralized by mixing chromate or nitrite with water that beats the concrete.

Natural lightweight aggregates include volcanic forces, pumice stones and volcanic sand, which are used for lightweight blocks. Crushed stone is an aggregate made by smashing natural rock into a suitable size. Artificial aggregates include industrial by-products and artificial light aggregates, and industrial by-products are coal residues, expanded slag, etc., and are improved or used as they are.

Artificial lightweight aggregates are made by firing expanded clay, fly ash, expanded shale, etc. In recent years, lighter and stronger structural artificial light weight aggregates have also been manufactured, but the field of use has become wider.

In general, the mineral composition present in natural rock that can be used as aggregate is, in principle, a very hard mineral composed of silica or SiO ₂ crystals and is present in acidic igneous rocks (over 65% of SiO ₂ ) such as granite or rhyolite. Silicate minerals or those belonging to this category are, next, feldspar, iron magnesium, mica and clay minerals. They are almost similar to quartz in hardness but differ in chemical composition and crystallographic properties. There are several kinds of feldspar. Orthoclase and micro plagioclase feldspar contains potassium _{(K 2 O · Al 2 O} 3 · 6SiO 2) is called, plagioclase feldspar or soda to sodium aluminum silicate, calcium aluminum silicate or both a potassium aluminum silica. Also, potassium and sodium are generally igneous rocks with high silica content such as granite and rhyolite. Iron magnesium minerals from igneous and metamorphic rocks are made of iron, magnesium or silica containing both simultaneously.

In addition, there are clay minerals, but in terms of hardness, they are so small that they cannot be compared with the above, making them difficult to use as aggregate. Therefore, it can not be directly used as aggregate for concrete and often becomes a harmful substance.

The depletion of natural aggregates, which are scarce in Korea as well as in resources, is already reaching a serious level. To solve this problem, industrial wastes and by-products have been introduced. As a matter of fact, aggregates made of industrial wastes currently used are blast furnace slag, fly ash and concrete waste.

Blast furnace slag cooled slowly in ladles, pits or iron molds is densified and of high strength when crushed to make it suitable for use as aggregate. The aggregate properties change with slag composition and cooling rate. Generally, in acidic slag, it becomes a denser aggregate, and basic slag tends to make a so-called honeycomb structure with many bubbles having a small apparent specific gravity (2 to 2.8). Generally, the unit volume mass of slowly cooled slag varies mainly from 1.120 to 1.360 kg / m ^3, which is roughly in the middle of normal natural and structural lightweight aggregates. This aggregate is widely used in concrete secondary products such as masonry blocks, waterways and fan posts.

Fly ash is essentially an alumina silicate glass made up of spherical particles that are produced when the powdered coal is burned in a thermal power plant. Bulk ash has been attempted to be recycled as lightweight aggregate without being used in many industrial parts of the world. However, the change of fineness and carbonic acid content is a big problem when managing the quality of sintered fly ash aggregate.

Aggregate materials are made from concrete fragments, gravel, and other obsolete materials that are being rebuilt, which may contain cement hydrates, used aggregates and small amounts of gypsum, as well as other materials. Most of the dimensions that correspond to fine aggregates contain cement hydrate and gypsum, making them inadequate for the production of non-solid concrete mixtures. However, the large equivalent to coarse aggregate is likely covered by cement hydrate. It is known that the compressive strength and modulus of elasticity of concrete using recycled aggregate shows at least 2/3 of the concrete compared with concrete made of natural aggregate, and it is reported that it shows satisfactory workability and durability. All that is required is the cost of crushing, particle size analysis, dust management and removing unwanted parts.

Recycled aggregates contain crushed glass, tend to make concrete with poor workability and affect long-term durability and strength due to alkalinity. Metals such as aluminum react with alkalis and cause excessive expansion. Paper and organic waste may cause problems with cement concrete condensation or hardening regardless of incineration. Thus, aggregate from municipal waste is generally not suitable for structural concrete.

In addition to these waste resources, as a way to recycle resources and protect the environment by using waste pottery discharged from pottery producers, the use of it as aggregate is being studied, but it has not been put into practical use.

The depletion of natural aggregate, which is lacking in most countries as well as in resources, has reached a serious level and raises many environmental issues. To solve this problem, we are actively researching ways to recycle industrial wastes and by-products. Accordingly, an object of the present invention is to propose a method of recycling dolomite, a by-product of limestone mines, to be used as aggregate, and to propose an environment-friendly suitable concrete composition including the same.

Dolomite, which is considered as aggregate for concrete in the present invention, is a double salt composed of CaCO ₃ and MgCO ₃ in solid solution. Dolomite deposits usually contain some free CaO because limestone is necessarily involved, but its effect is known to be very small. In other words, although CaO is generally higher than 21.9% by weight of MgO, 30.4% by weight of CaO, and 47.7% by weight of CO ₂ , MgO is more than the theoretical value because it is magnesia dolomite.

In general, when dolomite is heated, MgCO ₃ is decomposed at around 800 ° C, CaCO ₃ is decomposed at around 950 ° C, and CO ₂ is released to form a mixture of MgO and CaO. Currently, the most widely used place for the manufacture of basic refractories for steelmaking. Dolomite, even if calcined at a high temperature, occurs a lot of (slaking), so in order to slow down the digestion, the silica is calcined at a high temperature to stabilize the clinker.

Currently, dolomite powder is frequently used as a raw material for glass and ceramics, and is also used as a fertilizer. Dolomite calcined at a relatively low temperature is used as a dolomite plaster (dolomite plaster) as a building material, but the development of a method to effectively utilize a large amount of dolomite generated as a by-product from limestone mine is urgently needed.

Therefore, the present invention is to provide a concrete production composition for producing high strength concrete using a large amount of dolomite.

As a result of many studies to achieve the above object, dolomite is made of coarse aggregate and fine aggregate having a certain size as aggregate among cement and aggregate constituting concrete, and when it is used as concrete aggregate component, it has very excellent physical properties. Concrete can be produced.

That is, the present invention is characterized in that, in the concrete consisting of cement, water, coarse aggregate and fine aggregate, the coarse aggregate and fine aggregate are made of a particular size of dolomite which is a by-product of limestone mine.

Dolomite coarse aggregate (DCA) used as coarse aggregate in the present invention has a unit weight (kg / ㎥) of 1650 ~ 1720, specific gravity of 2.90 ~ 3.20, absorption rate (absorption rate,%) of 0.5 ~ 1.0 And the granulation rate (FM) is 5.0 ~ 7.0 with 5 ~ 20wt% of the total aggregate content, and the fine aggregate is dolomite fine aggregate (DFA) pulverized dolomite with jog crusher and the unit weight (kg / ㎥) is 1750 ~ 1900, specific gravity of 2.60 to 2.88, absorption rate (%) of 1.2 to 1.5, and assembly rate (FM) of 2.0 to 4.5, when 95 to 80 wt% of the total aggregate content is used. It is possible to produce the concrete of the present invention. In the case of using the aggregate outside the above range it is not possible to obtain a concrete having the desired strength in the present invention even if dolomite is used.

In another embodiment of the present invention, instead of the dolomite fine aggregate as the fine aggregate, the unit weight (kg / m 3), which is crushed aggregate as crushed fine aggregate, is 1750 to 1900, specific gravity is 2.40 to 2.70, and an absorption rate (%) CFA can be used together with or in place of dolomite fine aggregate used as fine aggregate. In particular, in the case of using together, it is possible to achieve a remarkable effect of strength is better, and the mixing ratio of dolomite fine aggregate and crushed aggregate is preferably 2 to 8: 8 to 2 weight ratio.

The present invention is also characterized by the addition of calcium sulfoaluminates as necessary to promote curing and to provide higher strength concrete. Calcium sulfoaluminate is preferably added in an amount of 1 to 3 parts by weight based on 100 parts by weight of cement to enhance strength and promote hardening speed.

In another aspect, the present invention is characterized by providing a concrete block having a compressive strength of 320 ~ 450kgf / cm ² on the basis of 28 days of age using dolomite as aggregate.

Concrete composition of the present invention is basically composed of the above aggregate components, water and cement, cement in the overall composition is not largely limited if the same ratio of the conventional concrete composition, usually 3 to 10% by weight of water, 10-20% by weight of cement. Aggregate should be used in the range of 70 to 87% by weight.

The properties of the aggregates used in this study were measured for specific gravity and water absorption (KS F 2504 for fine aggregates, KS F 2503 for coarse aggregates), particle size test (KS F 2502), and unit volume mass test (KS F 2504). , And assembly rate (KS F 2502) were measured.

In addition, the present invention can be used by adding a conventional cement additive in addition to the above aggregate and cement. Such additives may include various additives such as a water repellent and a dispersant.

In addition, the concrete block prepared by the concrete composition according to the present invention is a sidewalk block, driveway block, sidewalk interlocking block, driveway interlocking block, braille block for the disabled, boundary block, revetment block, retaining wall block, reinforced earth retaining wall block It can be used as such.

Hereinafter, the present invention will be described in more detail with reference to Examples, and the scope of the present invention is not defined by the Examples.

[Examples 1-3]

A concrete composition was obtained by mixing one common Portland cement having a specific gravity of 3.15 and a powder degree of 3,200 cm ² / g and the aggregate of Table 1 in the mixing ratio of Table 2 below.

[Table 1] Aggregate Types

[Table 2] Consumption by component in concrete specimen (1m ³ )

The concrete was mixed by mixing the cement and aggregate for 30 seconds using a forced pan mixer, and then mixed with water for 159 seconds. After the bibim finished concrete was filled 1/2 of the mold (φ10x20cm) and the rod was compacted 25 times, it was repeated twice to prepare a specimen. In addition, the specimens were demolded 24 hours after production and subjected to standard level curing (20 ± 3 ° C.) until the age of measurement.

The hardened concrete absorption rate was calculated by measuring the test specimen's surface and dry mass, and the compressive strength was measured by the method of KS F 2405.

Figure 1 shows the compressive strength and water absorption of concrete Example 2 (concrete B), Example 3 (concrete C) in which the concrete A and DFA of Example 1 using only CFA are substituted in proportion. As can be seen in Figure 1 it can be seen that the compressive strength has the highest value when the DFA content is 50% by volume in the amount of the same unit cement, it is lower than that when 50% by volume at 100% by volume. As of 28 days, the compressive strength of concrete A using CFA alone is about 332kgf / cm ² , and the compressive strengths of concrete B and C with proportional substitution of DFA are 365kgf / cm ² and 340kgf / cm ² . It was higher than the intensity.

The reason why the compressive strength is high when the content of DFA is 50% by volume is low because the specific gravity of CFA is high and the specific gravity of DFA is large, and when aggregated with CFA and DFA, the total aggregate contained in the same volume as the DFA content increases. It is considered that the amount of s increased and the compressive strength increased.

The reason why the compressive strength decreases when the content of DFA is 100% by volume is that, as described above, the amount of aggregate contained in the same volume is increased, but the amount of voids in the DFA itself is large, so the concrete is increased as the content of DFA is increased. It is determined that the total porosity is affected when the external stress is given, and the absorption rate is the lowest when the content of DFA is 50% by volume as shown in FIG. 1. This is related to the increase in the compressive strength of concrete as the content of DFA increases, it can be seen that the absorption rate increases at 100% by volume of DFA.

As described above, according to the present invention, it can be seen that the dolomite which is a by-product of limestone mine has sufficient strength and low water absorption to be used as aggregate of concrete, particularly preferably, aggregate of secondary concrete for civil engineering. Therefore, waste dolomite can be utilized as aggregate of concrete secondary products, and has an excellent advantage that can simultaneously solve the problem of depletion of natural resources due to the collection of aggregates and the recycling of waste resources that are disposed of.

Claims (4)

In the concrete composition containing cement, aggregate, and water, dolomite coarse aggregate having a unit weight (kg / m 3) of 1650-1720, specific gravity of 2.90-3.20, absorption of 0.5-1.0, and granulation rate of 5.0-7.0 20 wt%; Dolomite fine aggregate and unit weight (kg / ㎥) of 1750 ~ 1900, specific gravity of 1750 ~ 1900, specific gravity of 2.60 ~ 2.88, absorption of 1.2 ~ 1.5, modulus of 2.0 ~ 4.5 Aggregate consisting of 95 ~ 80wt% of the aggregate aggregate of crushed stone aggregate having a water absorption of 2.40 ~ 2.70, 1.4 ~ 1.8 and modulus of 2.0 ~ 4.5 in a weight ratio of 2 ~ 8: 8 ~ 2; A concrete composition for providing concrete having a compressive strength of 320 to 450 kgf / cm ² containing 1 to 3 parts by weight of calcium sulfoaluminate. delete delete Concrete block selected from the sidewalk block, driveway block, sidewalk interlocking block, driveway interlocking block, handicapped braille block, boundary block, guard block, retaining wall block, reinforced earth retaining wall block made of the composition of claim 1.

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