Before construction, a site survey is required. A tailored plan should be developed for each bridge based on its span, traffic flow, and terrain characteristics, and implementation should be phased according to the level of safety urgency.
Bridge Railing Casting: Mix Proportion: To ensure a smooth and aesthetically pleasing concrete surface, the choice of cement and mix proportion are crucial. After several trials, the following mix proportion was adopted: water: cement: sand: 0.5-1cm small stones: 1-2cm large stones (0.5:1:1.74:1.52:1.85). 525# ordinary Portland cement is used, with a cement dosage of 370kg and a sand ratio of 34%. Excessive concrete slump can lead to bleeding, a rough surface, and noticeable watermarks. Insufficient slump makes compaction difficult, resulting in more honeycomb and air bubbles. Strict requirements are placed on the raw materials used in the concrete; sand and small stones must be sieved, and the quantities must be accurately measured according to the mix proportion.
Concrete Mixing: The mixer operator must strictly control the water usage, and the mixing time should not be less than 3 minutes to ensure the concrete is uniformly mixed, meets the slump requirements, and has good workability. Concrete Pouring: Concrete is poured in three layers. The first layer is poured to the bottom edge of the guardrail (the transition point), the second layer to the upper corner of the transition point, and the third layer to the top. The placement time and volume of each layer are controlled by the vibration operator. The concrete distribution must be uniform, and the vibration time must be strictly controlled, with each layer vibrating for no less than 1 minute and no more than 1.5 minutes.
Finishing: After the guardrail concrete is poured, the top surface is finished three times. The first time, it is smoothed with a wooden trowel; the second time, it is smoothed and initially compacted with a steel trowel; the third time, after the concrete has initially set, it is firmly compacted with a roller.
Formwork Removal: Formwork removal is based on the air temperature and concrete strength. For non-load-bearing components, formwork can be removed after 10-20 hours. After demolding, the concrete should be air-dried for half a day (mainly to ensure color consistency). Air bubbles should be sealed with cement slurry mixed with white cement, and the concrete should be covered with straw mats (or other coverings) to prevent contamination. Watering is recommended for curing; do not spray with film-forming agents.
During construction, road occupancy permits must be obtained in advance. Traffic warning signs and guidance facilities must be properly installed. Dedicated traffic assistants must be assigned to manage traffic flow, and safety measures must be implemented to ensure construction and traffic safety.
Construction quality supervision includes conducting design compliance reviews, hiring external supervisors, and implementing a three-inspection system. Key materials must undergo self-inspection and third-party testing. Supervisors will be stationed on-site to guide key processes.
Maintenance work includes addressing guardrail defects, following maintenance standards for painting processes, controlling coating thickness and adhesion, and systematically renovating the guardrails to improve safety, durability, and appearance.