KR102283150B1 - Pores and surface tretment of recycled aggregates for cement concrete using aqueous polymer emulsions - Google Patents

Abstract

The present invention relates to a pores and surface treatment method of a recycled aggregate for improving physical properties and durability of cement concrete, which: immerses a recycled aggregate in an aqueous polymer emulsion made by mixing one or more selected from liquid polymers of styrene butadiene rubber latex (SBR), polyacrylic acid ester (PAE), ethylene vinyl acetate (EVA), styrene-acrylic acid ester (SAE), acrylic emulsion (PA), and epoxy emulsion (EP), which are an aqueous polymer emulsion or powdered polymers of ethylene vinyl acetate (EVA), styrene-butyl acrylic acid (St/BA), methyl acrylate-butyl methacrylate (MMA/BA), and vinyl acetate-vinyl ester of versatic acid (VA/VeoVa); fills pores of the recycled aggregate with polymer particles; and coats a surface of the recycled aggregate through a drying process, thereby improving the physical properties and durability of cement concrete.

Description

Pores and surface tretment of recycled aggregates for cement concrete using aqueous polymer emulsions {Pores and surface tretment of recycled aggregates for cement concrete using aqueous polymer emulsions}

The present invention relates to a void and a surface treatment method of a recycled aggregate for cement concrete using an aqueous polymer emulsion in order to reduce the absorption rate of the recycled aggregate for cement concrete.

Recycled aggregate refers to aggregate that meets the quality standards through physical or chemical treatment of construction waste in accordance with Article 2, No. 7 of the Act on Promotion of Recycling of Construction Waste. Among these construction wastes, recycled aggregate produced by crushing waste concrete and asphalt concrete is used for road base layer, road auxiliary layer, concrete, concrete product manufacturing, sand replacement fine aggregate for sewage pipe installation, asphalt concrete, frost protection layer and barrier layer by use. It is classified into 13 categories including , roadbed, furnace body, backfilling and backfilling, filling, covering, and covering of landfill facilities.

Among them, the recycled aggregate used in the present invention is for cement concrete, and is divided into recycled coarse aggregate and recycled fine aggregate. The quality standards of recycled aggregate for concrete are more stringent than those of recycled aggregate for other uses, so there are limited construction waste intermediate processing companies that can produce them.

In December 2003, necessary ground rules such as obligatory use of recycled aggregate for the ordering party were implemented in case the contract-related law to which the state is a party is applied as it is required to prepare an active and systematic recycling system using construction waste, which is increasing every year. The "Construction Waste Recycling Promotion Act" was enacted, the "Recycled Aggregate Quality Standard" was finalized in August 2005, the recycled aggregate quality certification was implemented in January 2007, and the recycled aggregate quality certification workplace was reviewed from October 2016. Standards have been strengthened. In addition, in December 2017, the 'Recycled Aggregate Quality Standard' was revised to expand the volume of recycled aggregate mixed into cement concrete, and at the same time, some quality standards for the quality of recycled fine aggregate were raised so that it could be used in reinforced concrete structures. did.

Coarse recycled aggregate products for cement concrete currently produced satisfy the quality standards for recycled coarse aggregates and can be used for cement concrete with a design standard compressive strength of 27 MPa or less, but among various physical property standards, density 2.50 g/cm3 or higher and absorption rate 3% or lower Products that are barely satisfactory are being produced. There is a question as to whether quality control to satisfy these physical regulations can be sustained in a small construction waste intermediate treatment company.

Therefore, many researchers have now concluded that recycled aggregate can be mixed with cement concrete and used. However, the volume of recycled aggregate with respect to the total aggregate volume mixed into cement concrete is not to exceed 30%, and the maximum The design standard compressive strength is also limited to 27 MPa or less.

Although there are restrictions on the amount of recycled aggregate used and the design standard compressive strength, there is currently no record of using recycled aggregate as a reinforced concrete structure in construction sites. This is because the social awareness of recycled aggregate is not high, and although it is a product that has obtained recycled aggregate quality certification, it is believed that it is because the quality of the products obtained by small and medium-sized enterprises is distrust, and the additional economic effect when replacing existing materials is not so great. can

However, in Korea's construction culture, where the proportion of concrete structures is very large compared to other countries, recycling of construction waste is becoming a necessity, not an option. This is because it has reached the limit of dumping at sea, landfilling, and incineration.

Therefore, it is most important to improve the quality of recycled aggregate for 100% recycling of construction waste, especially waste concrete. Existing studies also revealed that the use of recycled aggregate lowered neutralization resistance, chloride penetration resistance, freeze-thaw resistance, and drying shrinkage resistance compared to the case of using recycled aggregate. In order to secure long-term durability, physical properties that exceed the current recycled aggregate quality standards The properties need to be improved, and the basic property is to improve the absorption rate.

The present invention is to solve the problems in the background art, and the voids in the cement mortar and cement paste parts attached to the surface of the recycled aggregate by immersing the recycled coarse aggregate and the recycled fine aggregate that are partially mixed into cement concrete in various polymer emulsions. The polymer particles penetrate into the interior to fill the voids, and at the same time, a polymer film is formed on the surface of the recycled aggregate to reduce the absorption rate and improve adhesion in the cement concrete. The ultimate goal is to improve the long-term durability of cement concrete. .

In order to achieve the above object, first, recycled coarse aggregate with a particle size of 5 mm to 25 mm and fine recycled aggregate with a particle size of 0.15 mm to 5 mm, made by crushing waste concrete, are mixed with an aqueous polymer emulsion of styrene budaziene rubber latex (SBR), Liquid polymers such as polyacrylic acid ester (PAE), ethylene vinyl acetate (EVA), styrene-acrylic acid ester (SAE), acrylic emulsion (PA), and epoxy emulsion (EP) and ethylene vinyl acetate (EVA), styrene-acrylic acid butyl (St) /BA), methyl methacrylate-butyl acrylate (MMA/BA), and vinyl acetate-vinyl valsdate (VA/VeoVa), 1-50% of polymer solid content made by adding water and at least one selected from powdered polymers After immersing in the aqueous polymer emulsion solution for 1 hour to 48 hours, dry in the air for 1 hour to 24 hours at 20°C or by treating the surface for 1 hour to 12 hours using a hot air machine to make recycled coarse aggregates and fine recycled aggregates. .

In addition, the mixing ratio of the surface-treated recycled aggregate and general aggregate is 1-60 of the total volume of coarse aggregate, that is, the ratio of the volume of mixed coarse aggregate to the sum of the volumes of recycled coarse aggregate and crushed coarse aggregate. % and the ratio of the volume of recycled fine aggregate to the sum of the volumes of recycled fine aggregate and natural fine aggregate is mixed into cement concrete in the range of 1 to 30%.

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

The recycled aggregate used in the present invention is made by crushing waste concrete, and satisfies the quality and particle size of recycled aggregate for concrete prescribed in the recycled aggregate quality standards presented by the Enforcement Decree of the Ministry of Land, Infrastructure and Transport. It is 25 mm, and the particle size of the recycled fine aggregate is 0.15 mm to 5 mm.

As a polymer emulsion for filling the pores of the mortar or paste on the surface of the aggregate by immersing the recycled aggregate for concrete, styrene budaziene rubber latex (SBR), polyacrylic acid ester (PAE), ethylene vinyl acetate (EVA), Styrene-acrylic acid ester (SAE), acrylic emulsion (PA), and epoxy emulsion (EP) are used.

The polymer emulsion is composed of polymer particles and water at the time of production, and each polymer particle solid content is contained in an amount of 45 wt% to 55 wt% with respect to 100 wt% of water. That is, 1,000 g of polymer emulsion contains 450 g to 550 g of water and 550 g to 450 g of polymer particle solid content.

When the recycled aggregate is immersed in such a polymer emulsion as it is, it is difficult for the polymer particles to penetrate into the pores of the mortar and paste on the surface of the recycled aggregate due to the viscosity of the polymer emulsion. It is not suitable for cement concrete because the aggregate is agglomerated. Therefore, it is necessary to lower the viscosity of the polymer emulsion, by adding water to lower the polymer solid content in the range of 1% to 50% and immersing the recycled aggregate therein.

In addition, the re-emulsifying powder polymer for filling the pores of the mortar or paste on the surface of the aggregate by immersing the recycled aggregate for concrete is ethylene vinyl acetate (EVA), styrene-acrylic acid butyl (St/BA), methyl methacrylic acid-acrylic acid butyric acid (MMA/BA) and vinyl acetate-vinyl valsdate (VA/VeoVa) is a mixture of any one or two or more types, and since this polymer is a powder, water must be mixed to form a polymer emulsion.

In order to make a polymer emulsion using the re-emulsifying powder resin, 1 to 50% of each polymer powder is mixed with 1 to 50% by weight of each polymer powder with respect to 100% by weight of water based on the polymer solid content.

Into the water-based polymer emulsion and the polymer emulsion made of the re-emulsifiable powder polymer, the recirculating coarse aggregate and the recirculating fine aggregate corresponding to the mixing ratio required for manufacturing cement concrete are sufficiently immersed.

After the immersed recycled aggregate is left in the liquid polymer emulsion for 1 hour to 48 hours, the recycled aggregate is taken out and the polymer emulsion deposited on the surface of the aggregate is filtered through a 0.15 mm sieve, followed by drying in the air at 20°C for 1 hour to 24 hours For quick drying and drying, dry the polymer particles in the pores of the recycled aggregate for 1 to 12 hours at 30~100℃ with a hot air blower so that the polymer particles are dried and strengthened.

In such a dry environment, the polymer particles filled in the voids of the recycled aggregate are formed into a polymer film, which greatly improves the absorption rate, thereby improving the durability of cement concrete using the same.

Here, the durability of cement concrete means neutralization resistance, chloride ion permeation resistance, freeze-thaw resistance, and drying shrinkage resistance. Adhesion to cement hydrate is also improved by the polymer film on the surface of the aggregate, so flexural strength, which is a physical property of cement concrete , improvement of tensile strength and adhesive strength can be expected.

The aggregate for manufacturing cement concrete is subjected to primary drying by mixing both crushed aggregate and natural fine aggregate, which are general aggregates, according to the composition ratio of recycled aggregate surface-treated with polymer emulsion and cement concrete.

The mixing ratio of the recycled aggregate surface-treated with the polymer emulsion and the general aggregate is based on the mixing for cement concrete production, the total volume of coarse aggregate, that is, the sum of the volumes of the recycled coarse aggregate and the crushed aggregate. The volume of recycled fine aggregate is mixed in the range of 1 to 30% with respect to the volume of 1 to 60% and the sum of the volumes of recycled fine aggregate and natural fine aggregate.

As a binder for the manufacture of cement concrete, ordinary Portland cement alone or one or two types of admixtures is used as an admixture based on Portland cement as an admixture, using fine blast furnace slag powder and fly ash.

According to the present invention, the high absorption rate of recycled aggregate used in cement concrete is immersed in a polymer emulsion to fill the pores of the recycled aggregate with polymer particles, and then, during the drying process, the polymer particles filled in the pores form a polymer film and become solid. To improve the long-term durability of cement concrete by reducing the absorption rate, a method for treating recycled aggregate pores and surfaces was provided.

[Figure 1] is a conceptual diagram of the voids and surface treatment method of the recycled aggregate for cement concrete using the aqueous polymer emulsion of the present invention.

[Example 1] Primary absorption rate of circulating coarse aggregate before and after polymer emulsion immersion

Primary absorption rate (%): Aggregate preparation-Aggregate drying (100℃ drying furnace, absolute dry weight A)-Water or polymer emulsion immersion (20℃)-Removal of surface moisture (surface dry, internal moisture content weight B): BA/ A×100

The absorption rate of the recycled coarse aggregate made by crushing the waste concrete was measured, and the results are shown in [Table 1].

[1st water absorption] First, 500 g of coarse circulating aggregate having a particle size of 5 mm to 20 mm was prepared three each under the conditions of Preparation Example 1 to Preparation Example 12. The recycled aggregate was dried in a dryer (100°C±2°C) for 24 hours. After taking out from the drying furnace, the coarse recycled aggregate was cooled in the atmosphere at 20°C and weighed to determine the absolute dry weight. Thereafter, as in Preparation Example 1, the concentration of various polymer emulsions was reduced with water, not the polymer emulsion, and as in the other Preparation Examples, a polymer emulsion solution was prepared based on the polymer particle solid content, and the circulating coarse aggregate was immersed for 48 hours. After immersion, the surface of the recycled coarse aggregate was wiped with an experimental paper towel to make aggregate in a surface dry state (surface dry and internal moisture content). The value obtained by dividing the weight in the absolute dry state measured here by the value obtained by subtracting the weight in the dry state from the weight in the dry state was expressed as the primary water absorption rate.

As can be seen in [Table 1], when the absorption rate of the recycled coarse aggregate under the same conditions was measured in water, the primary absorption rate was 2.11%, which satisfies the recycled aggregate standard for concrete of 3% or less, and was immersed in the polymer emulsion. In all the preparation examples, the primary absorption rate was higher than that of immersion in water. This can be attributed to the fact that several micro-sized polymer emulsion particles penetrate into the pores of the circulating coarse aggregate and remain immersed, and this phenomenon can be considered because the density of the polymer particles is slightly larger than that of water. In addition, the higher the solids concentration of each polymer emulsion, the higher the water absorption rate can be seen because there are many polymer particles that can penetrate into the pores of the recycled aggregate. However, in the case of using SBR, the decrease in water absorption at high solids content of 20% or more can be attributed to the fact that when the concentration is increased to a certain level, it is rather difficult to penetrate into the pores of the circulating coarse aggregate due to the viscosity of the polymer particles. [Example 2 ] Secondary absorption rate of circulating coarse aggregate before and after polymer emulsion immersion

Secondary absorption rate: Aggregate preparation-Aggregate drying (100°C drying furnace, absolute dry weight A)-Water or polymer emulsion immersion (20°C)-Removal of surface moisture (surface dry, internal moisture content weight B)- Aggregate drying again (100 ℃ Drying furnace, absolute dry weight C)-Water immersion (20℃)-Removal of surface moisture (Surface dry, internal moisture content weight D): DC/C ×100

[Secondary absorption rate] is to dry the recycled coarse aggregate in the dry condition obtained from the primary absorption rate in a dryer (100℃±2℃) for 24 hours again to make the recycled aggregate in the absolutely dry state, and then immerse it in water for 24 hours to dry it. After wiping, the aggregate in the dry state was prepared and the secondary absorption rate was calculated in the same way as the primary absorption rate. The secondary absorption rate is important here because after the polymer emulsion fills the pores of the circulating coarse aggregate, a polymer film is formed as the polymer particles dries, which can greatly reduce the absorption rate of the aggregate itself. It is judged that the difference in the absorption rate will be large depending on the drying method, especially the drying temperature and time.

In the results of [Table 1], the secondary absorption rate shows an important result in the present invention. The primary absorption rate was 2.11% to 2.93%, which satisfies the recycled aggregate quality standard of 3% or less, but the secondary absorption rate was 1.24% to 1.76%, which was reduced by up to 57.7%.

[Example 3] Compressive strength and flexural strength of cement concrete mixed with voids and surface-treated recycled aggregate with polymer emulsion

[Table 2] shows the cement concrete formulation table for measuring the compressive strength, flexural strength, and carbonation depth according to the aggregate replacement rate of recycled aggregates treated with voids and surfaces with polymer emulsion. [Table 2] A cylindrical mold with a diameter of 10×20 cm made according to the formulation table was used for compressive strength and carbonation depth experiments, and a 6×6×24 cm cuboid mold was used for manufacturing cement concrete for flexural strength. Recycled aggregates treated with voids and surfaces of recycled aggregates with polymer emulsion were prepared according to the formulation shown in [Table 2], then cured in water at 20°C for 28 days, and then compressive and flexural strengths were measured. As can be seen from the results of [Table 3], the compressive strength decreased slightly as the amount of recycled aggregate increased, and when the surface of the recycled aggregate was treated with a polymer emulsion, there was no significant improvement in strength compared to the case without treatment. However, in the case of flexural strength, compared to the compressive strength, the case of treating the aggregate surface with a polymer emulsion showed an improvement in strength. This can be considered as the result of improving the adhesive strength of the adhesive interface between the aggregate and the cement hydrate by the polymer film by treating the pores and the surface of the recycled aggregate with a polymer emulsion.

[Example 4] Measurement of carbonation depth of cement concrete mixed with voids and surface-treated recycled aggregate with polymer emulsion

A recycled aggregate process the voids and the surface of a polymer emulsion as a mixed cement concrete specimen carbonation promoting device was allowed to stand 14 days at (30 ℃, RH50%, CO 2 concentration: 5%), by cutting the specimen to cut phenolphthalein 1% After spraying the alcohol solution, the area that does not change to red and does not change was used as the carbonation area, and six points were measured using a vernier caliper, and the average was determined as the carbonation depth. As can be seen from the results of [Table 3], unlike the compressive strength and flexural strength, the carbonation depth showed a tendency to decrease significantly when the recycled aggregate was treated compared to the case where the recycled aggregate was not treated with the polymer emulsion. In this carbonation process, carbon dioxide can permeate through the pores of the mortar and paste attached to the aggregate, and when treated with a polymer emulsion, the pores are filled with a polymer film, which can be seen to inhibit the penetration of carbon dioxide.

From the above results, if the recycled aggregate made by the void and surface treatment method of the recycled aggregate for cement concrete using the aqueous polymer emulsion of the present invention is mixed and used in cement concrete, the physical properties and durability can be greatly improved.

Claims (3)

In order to reduce the absorption rate by filling the pores of the mortar or paste attached to the surface of recycled coarse aggregate with a particle size of 5 mm to 25 mm and fine recycled aggregate with a particle size of 0.15 mm to 5 mm,
It is characterized in that the recycled aggregate is immersed in a liquid polymer emulsion made by adding water to lower the viscosity by adding water so that the polymer particle solid content of the water-based polymer emulsion or powder polymer becomes 1 to 50% by weight, and then dried and used for cement concrete. Recycled aggregate voids and surface treatment method. in claim 1
The aqueous polymer emulsion is a liquid polymer of styrene budaziene rubber latex (SBR), polyacrylic acid ester (PAE), ethylene vinyl acetate (EVA), styrene-acrylic acid ester (SAE), acrylic emulsion (PA), and epoxy emulsion (EP). or ethylene vinyl acetate (EVA), styrene-butyl acrylic acid (St/BA), methyl methacrylate-butyl acrylate (MMA/BA), or a powder polymer of vinyl acetate-vinyl valsdate (VA/VeoVa) It is a mixture of one or two or more, and the voids and surface treatment method of recycled aggregate made using this in claim 1
The recycled aggregate immersion and drying method involves immersing the recycled aggregate in an aqueous polymer emulsion for 1 to 48 hours, then taking the recycled aggregate out of the aqueous polymer emulsion and drying it in an air at 20 ° C. Recycled aggregate voids and surface treatment method drying for 1 to 12 hours at ℃

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