KR-102960932-B1 - Method for Optimal Mix Design of Recycled Aggregates

Abstract

The present invention relates to a method for designing an optimal concrete mix using recycled coarse aggregate and steel slag coarse aggregate. It provides a method for deriving a mix ratio that satisfies quality standards while using at least 50% by weight of recycled aggregate (recycled coarse aggregate + steel slag coarse aggregate) among the total coarse aggregate for the manufacture of reinforced concrete drainage pipes with a design strength of 35.0 MPa. The amount of binder is determined through a preliminary mix test, and the compressive strength, flexural strength, and freeze-thaw resistance are evaluated by varying the substitution rate of steel slag coarse aggregate from 0% to 50% in 10% increments relative to the total weight of the coarse aggregate. The optimal mix is determined by measuring the compressive strength under conditions of steam curing at 85°C for 6 hours followed by curing until 28 days of age, and under conditions of standard underwater curing at 20°C for 28 days of age. Experimental results confirmed that the quality standards are satisfied when steel slag coarse aggregate is replaced at a rate of 20% or more relative to the total weight of coarse aggregate under conditions where 460 kg of binder and 140 kg of water are added per 1 m³ of concrete, the water-to-binder ratio (weight of water / weight of binder × 100) is 30.4% by weight, and the weight ratio of fine aggregate to total aggregate is 42% by weight.

Inventors

• 길현만

Assignees

• (주) 주안기업

Dates

Publication Date

20260507

Application Date

20251023

Claims (1)

1. In the optimal mix design method for concrete using recycled aggregates, Use blast furnace slag fine powder Type 2 cement as a binder, By adding 420 kg of binder, 140 kg of water, and 683 kg of fine aggregate per 1 m³ of concrete Set the water-to-binder ratio (water weight / binder weight × 100) to 33.3%, and Set the weight ratio of fine aggregate to the total weight of all aggregates (fine aggregate + coarse aggregate) to 40%, but Recycled coarse aggregate and steel slag coarse aggregate are used as coarse aggregate, and A first step of conducting a preliminary mix test by replacing the steelmaking slag coarse aggregate with 0%, 10%, 20%, 30%, and 40% of the total weight of the recycled coarse aggregate and the steelmaking slag coarse aggregate; For each mix according to replacement rate, the compressive strength of specimens cured underwater at 20℃ for 28 days and the compressive strength of specimens cured by steam curing at 85℃ for 6 hours followed by 28 days were measured, respectively, and A second step of identifying the lowest replacement rate among the replacement rates exhibiting a compressive strength of 35.0 MPa or higher in both of the two curing conditions above; Based on the results of the above second step, the amount of binder per 1 m³ of concrete is increased to 460 kg, and 140 kg of water is added to adjust the water-to-binder ratio to 30.4%, and Adjust the weight ratio of fine aggregate to the total weight of aggregate to 42%, but A third step of mixing by varying the substitution rate of the steel slag coarse aggregate to 0%, 10%, 20%, 30%, 40%, and 50% relative to the total weight of the recycled coarse aggregate and the steel slag coarse aggregate; For each substitution rate (1) Compressive strength of a specimen cured underwater at 20℃ for 28 days, (2) Compressive strength of specimens cured until age 28 after steam curing at 85℃ for 6 hours, (3) Compressive strength of specimens subjected to 100 freeze-thaw cycles according to KS F 2456 B method after 28 days of curing, (4) A fourth step of measuring the flexural strength of each test specimen cured underwater at 20℃ for 28 days; and A method for designing an optimal mix of recycled aggregates, characterized by including: a fifth step of comprehensively analyzing compressive strength, flexural strength, and freeze-thaw resistance data measured in the fourth step above to determine a mix ratio having a compressive strength of 35.0 MPa or higher under all curing conditions as the optimal mix ratio.

Description

Method for Optimal Mix Design of Recycled Aggregates The present invention relates to a method for designing a concrete mix using recycled aggregates, and more specifically, to a method for deriving an optimal mix ratio that satisfies the quality standards of reinforced concrete drainage pipes by evaluating mechanical properties according to the replacement rate of recycled coarse aggregate and steel slag coarse aggregate (weight ratio of steel slag coarse aggregate to the total weight of all coarse aggregates). Globally, efforts are underway to reduce resource and energy waste and establish a circular economy to preserve the global environment. Due to a shortage of natural river sand, the use of sea sand at domestic construction sites has increased, leading to severe environmental destruction. Steelmaking slag has high potential as a substitute for aggregates. The Korean steel industry generates a large amount of steel slag as a byproduct during production processes such as ironmaking, steelmaking, and rolling. As of 2004, the amount of steel slag generated was approximately 14.07 million tons, of which blast furnace slag accounted for about 8 million tons and steelmaking slag for about 6.07 million tons. Cement, primarily used in the construction industry, is a material that generates 0.87 tons of CO2 per ton produced, making it necessary to reduce carbon emissions. Precast concrete can achieve quality uniformity and cost advantages by being manufactured in a factory, but it has high energy consumption because it is heated and cured at 80 to 90°C for about 6 hours. The pre-curing time, maximum temperature, and temperature rise and fall gradients of steam-cured concrete have an important influence on strength development. Previous studies have investigated the general characteristics of concrete using recycled aggregates, but no systematic optimal mix design method has been presented that takes into account steam curing conditions and freeze-thaw resistance while utilizing recycled coarse aggregates and steel slag coarse aggregates in combination. Figure 1 is a flowchart showing the overall flow of the optimal mix design method for concrete using recycled aggregate according to the present invention. FIG. 2 is a block diagram showing the detailed process of a preliminary formulation test according to the present invention. FIG. 3 is a block diagram showing the detailed process of a test for determining the optimal formulation according to the present invention. Figure 4 is a block diagram showing a concrete mixing process according to the present invention. FIG. 5 is a block diagram showing the process of fabricating and curing a test specimen according to the present invention. FIG. 6 is a block diagram showing a mechanical property evaluation process according to the present invention. FIG. 7 is a block diagram showing the composition of the aggregate replacement rate according to the present invention. FIG. 8 is a block diagram showing an artificial intelligence-based optimal mixture prediction system according to the present invention. Figure 9 is a graph showing the change in compressive strength according to the steelmaking slag aggregate replacement rate according to the present invention. Figure 10 is a graph showing the change in compressive strength according to the steel slag aggregate replacement rate after 100 freeze-thaw cycles according to the present invention. Figure 11 is a graph showing the change in flexural strength according to the steelmaking slag aggregate replacement rate according to the present invention. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. In describing the present invention, detailed descriptions of related known technologies are omitted if it is determined that such detailed descriptions may unnecessarily obscure the essence of the present invention. Furthermore, while preferred embodiments of the present invention will be described below, it is understood that the technical concept of the present invention is not limited or restricted thereto and can be modified and implemented in various ways by those skilled in the art. The terms used in this specification have been selected to be as widely used as possible, considering their functions in the present invention; however, these may vary depending on the intent or convention of those skilled in the art, the emergence of new technologies, etc. Additionally, in specific cases, terms may be arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, terms used in the present invention should be defined not merely by their names, but based on the meanings they possess and the overall content of the present invention. In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, s