The abrasion resistance of concrete is primarily determined by its compressive strength. Higher strength corresponds to better resistance against abrasion. However, other factors also play a significant role. These include using a water-to-cement ratio (w/cm) of less than 0.45, incorporating dry shakes and toppings, employing appropriate finishing techniques, and ensuring adequate curing. It is important to emphasize the importance of proper inspection and the use of power trowel finish during construction, as these measures can enhance surface resistance. Abrasion resistance refers to the ability of the concrete surface to withstand wear caused by rolling steel wheels, pallet and stillage legs scratching, forklift truck tines, and even impact from falling objects.
7 Factors Affecting Abrasion Resistance of Concrete Surface
1. Factors Impacting Concrete Strength
The factors that impact concrete strength also have a direct influence on concrete abrasion resistance. These factors include a low water-to-cement ratio, low slump value, well-graded aggregate, and air content.
1.1 W/C Ratio
A low to moderately low water-to-cement (w/c) ratio helps in reducing the amount of excess water in concrete. This leads to improved compactness and decreased permeability, resulting in enhanced concrete strength and abrasion resistance.
To decrease the w/c ratio, various approaches can be employed. One method is the utilization of water-reducing admixtures, which allow for a reduction in the water content while maintaining workability. Another approach involves adjusting the mixture proportions to minimize bleeding, the separation of water from the freshly placed concrete.
Careful timing of finishing operations is crucial to avoid the addition of excess water during troweling. By ensuring that water is not introduced during this process, the w/c ratio can be effectively lowered. Additionally, vacuum dewatering can be employed to remove excess water from the concrete, further reducing the w/c ratio.
In summary, reducing the w/c ratio through techniques such as water-reducing admixtures, proper mixture proportions, avoiding water addition during troweling, and utilizing vacuum dewatering helps to decrease free water in concrete. This, in turn, enhances concrete compactness, reduces permeability, improves concrete strength, and ultimately enhances its resistance to abrasion.
1.2 Well-Graded Aggregate
The use of well-graded fine and coarse aggregate in concrete can enhance workability and reduce the amount of water needed. This, in turn, significantly improves the strength of the concrete.
1.3 Air Content
Air content in concrete not only reduces its strength but also contributes to surface delamination and blistering, particularly when finishing works are not timed correctly. Therefore, when abrasion resistance is a requirement, air content should be disregarded unless specific considerations are taken into account. For example, concrete with a total air content exceeding 3 percent should not undergo hard troweling of the surface.
2. Proper Curing Procedure
Proper curing is crucial for constructing floor surfaces with satisfactory abrasion resistance. It enhances concrete strength and toughness, which are key factors in resisting surface abrasion. According to the American Concrete Institute, maintaining continuous moisture on concrete is the recommended curing method for most concrete floors.
3. Use of Supplementary Cementitious Materials
Properly cured polymer concrete, polymer-impregnated concrete, epoxy concrete, calcium aluminate cement, and calcium sulfoaluminate cement exhibit outstanding abrasion resistance when appropriately treated.
4. Two-course Floors
Two-course floors utilizing high strength topping exceeding 40MPa offer outstanding abrasion resistance, but they come at a higher cost compared to conventional floors. It is important to note that two-course floors are specifically employed in situations requiring both abrasion and impact resistance.
5. Special Concrete Aggregates
The type of aggregate used in concrete affects its abrasion resistance. To increase the lifespan of floors, such as warehouse floors that endure severe abrasion from steel or hard rubber-wheeled traffic, it is recommended to utilize hard and tough aggregates. These abrasion-resistant aggregates are typically applied as dry shakes or incorporated into high-strength, bonded toppings. Dry shakes consist of a mixture of aggregates and cement, which are applied dry to the concrete surface during finishing operations.
When prioritizing abrasion resistance, it is advisable to use high-quality quartz, traprock, or emery aggregates. These types of aggregates enhance the strength of the concrete surface. The abrasion resistance can be further improved by incorporating metallic aggregates with cement.
On the other hand, lightweight aggregates are not recommended for achieving high abrasion resistance. Additionally, the abrasion resistance of a concrete surface containing recycled aggregate depends on the compressive strength and type of the aggregate used.
6. Proper Finishing Procedures
Proper finishing time and procedure significantly impact the abrasion resistance of concrete. Floating and troweling activities should commence once the concrete surface loses its sheen. Therefore, it is important to wait until the concrete surface reaches this stage before starting the finishing works. The duration of the delay depends on factors such as temperature, humidity, air movement, and the presence of supplementary cementitious materials. It is crucial to avoid working standing water into concrete surfaces as it diminishes the compressive strength of the surface paste.
7. Vacuum Dewatering
Vacuum dewatering is a process that decreases the water-to-cement ratio (w/cm) in concrete, resulting in enhanced strength and resistance to abrasion. However, it is important to note that the final surface quality is significantly influenced by the timing of the finishing stage.
