Application and Advantages of Steel Fiber Reinforced Concrete in Highway Pavement Repair: Pavement Damage and the Superiority of Steel Fiber Reinforced Concrete

With the development of transportation, the issue of road surface damage has intensified, particularly the cracks and fractures in cement concrete pavements, which have increased the cost of renovation and extended the construction period. The vehicle load and density on urban roads and national trunk highways continue to increase, and the driving speed is also gradually increasing, leading to the increasingly prominent problem of road surface damage. Especially for the damage of cement concrete pavements, not only is the cost of renovation high, but the construction period is also long, posing a serious threat to traffic flow and driving safety. Although ordinary cement concrete pavement repair materials have high strength, excellent plate properties, and a certain degree of wear resistance and durability, their defects such as high brittleness, susceptibility to cracking, and poor temperature resistance cannot be ignored. The problem of pavement panels breaking due to bending occurs from time to time, which requires that the pavement panels must have sufficient bending and tensile strength and thickness.

The advent of steel fiber reinforced concrete (SFRC) provides an effective solution to this problem. By uniformly dispersing steel fibers within the matrix concrete, their dispersive effect can significantly reduce the stress concentration at the ends of fine cracks caused by loads, thereby controlling the expansion of concrete cracks and enhancing the crack resistance of the entire composite material. Furthermore, the strong interfacial bond between concrete and steel fibers enables external forces to be transferred to the fibers with high tensile strength and good elongation, allowing SFRC to resist external forces as a whole. This significantly enhances the tensile and flexural strength, as well as the fracture elongation of concrete, especially improving its toughness and impact resistance. By enhancing crack resistance, flexural strength, and toughness, SFRC effectively improves concrete performance and reduces the need for road repairs. Practice has proven that SFRC, as a high-strength composite material, has achieved remarkable results in road repairs. It not only enhances the crack resistance, flexural resistance, impact resistance, and fatigue resistance of roads but also improves the performance of road surfaces, prolongs their service life, and reduces the excavation of old roads, thereby bringing significant economic and social benefits. It has become a key approach to enhancing road reinforcement and reconstruction.

Application of 02 steel fiber concrete in pavement repair

► Basic Requirements for Steel Fiber Reinforced Concrete When applying steel fiber reinforced concrete for pavement repair, a series of basic requirements must be met. Firstly, the amount of steel fibers incorporated must be moderate, ensuring sufficient reinforcement effect while avoiding instability in material properties caused by excessive amounts. Secondly, process control during construction is crucial, including uniform mixing, compact vibration, and other aspects, to ensure that steel fibers are evenly dispersed in the concrete. In addition, the design thickness and strength grade of the pavement also need to be reasonably determined based on actual conditions to ensure the bearing capacity and durability of the pavement. Finally, attention should be paid to environmental protection and safety measures during construction to ensure the smooth progress of the construction process.

► Material Characteristics of Steel Fiber Reinforced Concrete (SFRC)

Steel fiber reinforced concrete (SFRC), a novel high-strength composite material, is created by ingeniously incorporating a certain amount of short and fine steel fibers into ordinary concrete. These steel fibers effectively hinder the formation of cracks in the matrix concrete, allowing the material to retain not only the excellent properties of ordinary concrete but also to excel in flexural strength, impact resistance, and fatigue resistance. By combining the characteristics of steel fibers and cement, SFRC possesses high flexural, impact, and wear resistance capabilities. Additionally, its low shrinkage rate, good toughness, and strong wear resistance enable the pavement thickness to be reduced by more than 50%, and the spacing between contraction joints to be increased to 15m to 30m, thereby eliminating the need for expansion and longitudinal joints.

► Mix proportion design of steel fiber reinforced concrete The mix proportion design of steel fiber reinforced concrete mixture aims to ensure that the pavement thickness can be reduced while meeting the requirements of high flexural strength, in order to meet the structural design's expectations for strength grade and ensure workability during construction. The mix proportion design determines the optimal water-cement ratio, steel fiber volume fraction, and mixture dosage through an eight-step process. The specific design steps are as follows:

Based on the design strength value and the construction preparation strength enhancement factor, determine the trial preparation compressive strength and flexural strength.

2. Calculate the water-cement ratio based on the compressive strength obtained from trial mixing.

3. Under the guidance of trial compressive strength, determine the appropriate volume fraction of steel fibers.

4. Determine the water consumption per unit volume based on the required consistency for construction.

5. Set the sand ratio reasonably.

6. Calculate the amount of mixed materials to determine the trial mix proportion.

7. Conduct mixture performance tests, adjust the water consumption per unit volume and sand ratio based on the test results, and establish the benchmark mix proportion for strength tests.

8. Based on the results of the strength test, further adjust the water-cement ratio and steel fiber volume fraction to ultimately determine the mix proportion for construction.

Mixing, pouring, and vibrating of steel fiber reinforced concrete

When mixing steel fiber reinforced concrete, to prevent fiber agglomeration, the mixing volume should not exceed 80% of the mixer's rated capacity. It is recommended to use a rolling mixer and ensure that the steel fibers are evenly distributed during the mixing process. Adopt a step-by-step feeding and mixing process, that is, first add coarse aggregates, then dry mix for 1 minute before adding steel fibers, followed by adding fine aggregates and cement and continuing to dry mix for another 1 minute. The steel fibers should be added in three times, while mixing, and then mixed with yellow sand and cement. After all the materials are added, mix again for 2 to 3 minutes, and finally wet mix for 1 minute with water added. During the mixing process, it is necessary to prevent fiber agglomeration and ensure even distribution. The total mixing time should be controlled within 6 minutes to prevent wet fiber agglomeration. Following this procedure can ensure that the mixture is uniform and free of agglomeration, thereby improving the quality of the concrete.

Application case analysis

1. Detailed Explanation of Construction Materials and Procedures: Select high-quality raw materials and conduct precise construction based on the laboratory mix ratio to ensure construction quality and efficiency. The cement is 425# ordinary Portland cement, the fine aggregate is medium-coarse sand, and the coarse aggregate is 5mm~20mm crushed stone. The steel fibers are structural steel shear-twist type steel fibers produced by a factory in Zhejiang, with the model number DN-30, which have stable performance and excellent use effect. The construction process includes multiple steps such as base preparation, pavement pouring, concrete mixing process, transportation and pouring, curing and joint cutting, ensuring that each step meets the construction requirements of steel fiber reinforced concrete.

2. Construction quality control and economic benefits emphasize quality control and long-term benefits. During the construction process, strict monitoring is required, focusing on raw materials, mix proportions, and construction procedures, to ensure that each batch of concrete produced meets design requirements and construction standards. By strictly monitoring the construction process, costs are saved and social benefits are enhanced, thereby ensuring the quality of the engineering project and bringing better economic benefits to society.

Economic and social benefits of steel fiber reinforced concrete

The application of steel fiber reinforced concrete in pavement repair brings significant economic benefits. It can significantly reduce the thickness of the surface layer, shorten the construction period, save raw materials and reduce the amount of work, thereby lowering related costs. Furthermore, extending the service life of the pavement and reducing maintenance costs are also important economic benefits it brings. In terms of social benefits, it improves traffic efficiency and engineering quality, having a profound impact on society, promoting the healthy development of the industry, and enhancing the overall level of engineering construction.

Steel fiber reinforced concrete (SFRC) has been widely applied in engineering fields such as highway pavements, bridge decks, and airport runways, achieving significant economic and social benefits. It exhibits outstanding flexural strength, along with excellent impact resistance and crack resistance. Relevant experimental studies have shown that adding 1% to 2% volume fraction of steel fibers can significantly enhance the impact resistance of concrete, reaching 10 to 20 times that of the matrix concrete. The bending toughness is improved by about 20 times, the flexural strength is increased by 1 to 6 times, the tensile strength is doubled, the fatigue strength is improved by 50%, and the crack resistance and compressive strength are also increased by 2 times and 10% to 30%, respectively. These data fully demonstrate the excellent performance of SFRC in terms of crack resistance and impact resistance.