Anchoring Material Types for Track Spikes and Strategies for Improving Sleeper Bond Strength
Why is the bond strength of resin anchoring agent 30%-50% higher than that of sulfur cement mortar?
Resin anchoring agent is a high-molecular polymer, which forms a dense bonding layer after curing, with strong bonding force with the spike and sleeper concrete. Its bonding mechanism is the dual action of chemical bonding and mechanical occlusion. Chemical bonding is achieved through the chemical bond combination between resin molecules and concrete components, while mechanical occlusion relies on the anchoring agent penetrating into the sleeper pores to form occlusion. Sulfur cement mortar is an inorganic material, with high porosity of the bonding layer after curing, only relying on mechanical occlusion, so the bond strength is low. In addition, the curing shrinkage rate of resin anchoring agent is only 0.5%, while that of sulfur cement mortar is 3%, and the shrinkage difference will cause gaps between sulfur cement mortar and the sleeper, further reducing the bond strength.
Why do wooden sleepers of ordinary-speed lines prefer sulfur cement mortar as the spike anchoring material?
Wooden sleepers of ordinary-speed lines are made of wood with high porosity. Sulfur cement mortar can penetrate into the wood fiber gaps to form good mechanical occlusion. Its cost is only 1/5 of that of resin anchoring agent, suitable for large-scale laying. Wooden sleepers are sensitive to temperature changes. The thermal expansion coefficient of sulfur cement mortar is closer to that of wood, and the bonding layer is not easy to crack under temperature cycles. The thermal expansion coefficient of resin anchoring agent is quite different from that of wood, which is easy to cause the bonding layer to fall off. Therefore, wooden sleepers prefer sulfur cement mortar, balancing cost and adaptability.
Why is it necessary to choose fast-curing resin anchoring agent for concrete sleepers of heavy-haul lines?
The spikes of heavy-haul lines bear large pulling force, requiring the anchoring material to cure quickly to form a high-strength bonding layer. The curing time of fast-curing resin anchoring agent is only 1/3 of that of ordinary type, which can quickly complete spike anchoring and reduce line downtime. At the same time, the cross-linking density of fast-curing resin is higher, and the bond strength is 20% higher than that of ordinary type, which can effectively resist the high-frequency pulling force of heavy-haul lines. In addition, the shrinkage rate of fast-curing products is lower, avoiding bonding gaps caused by shrinkage and ensuring long-term bonding stability between the spike and the sleeper.
What are the application scope and performance shortcomings of cement slurry as a spike anchoring material?
Cement slurry is suitable for concrete sleepers of low-load ordinary-speed lines, with low cost and convenient construction. However, its bond strength is only 1/3 of that of resin anchoring agent, and the pulling force cannot meet the demand of heavy-haul lines. The cement slurry has a high shrinkage rate after curing, and it is easy to form gaps with the sleeper, leading to spike loosening. In addition, cement slurry has poor durability, and is easy to weather in humid environments, and the bond strength will drop by more than 30% over time. Therefore, cement slurry is only suitable for low-grade lines, and high-grade lines need to choose resin anchoring agent or sulfur cement mortar.
How to improve the bond strength between spike anchoring material and sleeper on site to avoid anchoring failure?
During on-site construction, first clean the impurities and dust in the sleeper anchoring hole to ensure the hole wall is clean and improve the bonding force between the material and the sleeper. For resin anchoring agent, strictly control the ratio and curing temperature. Deviation in ratio will reduce the bond strength by more than 25%. For sulfur cement mortar, heat it to 130-140℃ to ensure uniform melting and penetration into the sleeper pores. At the same time, a coupling agent can be added to the anchoring material to enhance chemical bonding force, increasing the bond strength by 15%-20%. After construction, a pull-out test should be carried out to detect the anchoring force to ensure it meets the standard.