Slip-Formed Concrete
Ras Al-Khair Port Silos
The new port under construction at Ras Al Khair will accommodate vessels of up to 70,000 dead weight tons. The port, initially planned as part of Ma’aden’s Ras Al-Khair scheme, will also cater to Ma’aden’s Fertiliser and Aluminium Complexes in addition to other industries, which will be developed in the Ras Al-Khair area.
The project requires the construction of three huge reinforced concrete silos 59.59 m in height, 32 m diameter, and 40 cm in thickness. The concrete for each silo has to be poured continuously around the clock for an average period about three weeks. The slip-formed concrete placement methodology was another major challenge, taking into consideration the heights of the silo and the high wind speeds that the area normally witnesses.
Project Requirements:
- High strength concrete C50 (Cylinder)
- Mineral additives for strength, durability and pumpability
- Slip-formed concrete
- Initial setting time 7-10 hrs
- Slump 150-200 mm
Challenges:
- Produce slip-formed concrete that would comply with the project concrete specifications and achieve a compressive strength of 50 MPa
- Develop the right concrete mix with the best additives that would allow a smooth process of pouring and placing the concrete
- Control the initial setting time and the fresh concrete slump
- Ensure continuous concrete pouring and take all necessary precautions to avoid any unplanned stoppage
- Deliver slip-formed concrete to three huge silos simultaneously
Solutions:
- Pure plastering and pure retarding admixtures were used to control the slump retention and the setting time, respectively.
- Many trial mixes were conducted using different combinations of fly-ash, cement, aggregates, and admixtures to reach the optimum mix that would meet requirements
- To control slump, avoid excessive slump loss and ensure placing within the time limit, truck mixers were initially loaded with 3 to 4 cubic meters per delivery. The loads were gradually increased as the rate of pouring of concrete accelerated.
- The batch plants were operated continuously for 24 hours, 7 days a week. The number of operating manpower was increased to run two shifts and highly experienced concrete technicians were present 24 hours, all to ensure a smooth trouble-free delivery and pouring process. Concrete pumps were cleaned more frequently to avoid any sudden blockages.