2. Suliman AYEADH Al-Otaibi Howaidi Mutlaq Al-Shaibani

Challenges of the Kingdom: Pumping Concrete in high-rise structures. Producing concrete in volumes. Hot weather conditions.

Pumping Concrete in High Rise Structures Al-Zoebi Towers Al-Khobar   Al-Zoebi Towers in Khobar, 136 meters high, 32 story office tower, is the tallest building in Eastern Province.

What is Ready Mixed Concrete: It is the concrete which is prepared in a computerized concrete batching plant.

Advantages of Ready Mixed Concrete: Better quality concrete is produced Selected materials can be used in the production of RMC and stored properly in the batching plant Ingredient materials for concrete production are weighed and mixed by automated devices Elimination of storage space for basic materials at site Wastage of basic materials is avoided Labour associated with production of concrete is eliminated Time required is greatly reduced Noise and dust pollution at site is reduced.

Quality Control of RMC It is defined as: “Producing, improving, planning and servicing with the most economical and practical way” Classification of Quality Control of RMC: (a) Forward Control (b) Immediate Control (c) Retrospective Control

 Forward Control: Material storage Material storage Monitoring of qualities of materials Monitoring of qualities of materials Modification of concrete mix design Modification of concrete mix design Batching plant maintenance Batching plant maintenance Transfer and weighing equipment Transfer and weighing equipment Plant mixers and truck mixers Plant mixers and truck mixers It covers the following:

 Immediate Control: Weighing Weighing Observation of concrete during production, Observation of concrete during production, Workability of the fresh concrete Workability of the fresh concrete Making adjustments at the plant automatically or manually to batched quantities Making adjustments at the plant automatically or manually to batched quantities Inspection at delivery by driver and customer for uniformity and adjustments to workability within company policy. Inspection at delivery by driver and customer for uniformity and adjustments to workability within company policy. It covers the following:

 Retrospective Control: Sampling of concrete Sampling of concrete Testing and monitoring of test results Testing and monitoring of test results Stock control of materials Stock control of materials Diagnosis and correction of faults identified from complaints Diagnosis and correction of faults identified from complaints It covers the following:

Concrete Construction Practices Batching and mixing Batching and mixing In ready mixed concrete, the material quantities (cement, coarse aggregate, fine aggregate, water and admixtures) are measured with a high degree of accuracy using the computer. Fig-1

Handling of Aggregates: Handling of Aggregates: The aggregates are stocked in piles under the sheds to protect them from weather and adequate drainage is provided to eliminate gross variations in aggregate moisture contents. [Fig-4] [Fig-4] [Fig-2] [Fig-2] To maintain concrete temperature in the specified range, ice or the chilled water should be used. Use of Ice or Chilled Water: Use of Ice or Chilled Water: [Fig-3] [Fig-3]

Batching Equipment: Batching Equipment: - Manual - Semi Automatic - Automatic [Fig-5] [Fig-5] Through mixing is essential for the complete blending of the materials that are required for the production of homogeneous, uniform concrete. Long mixing times do not improve the quality of concrete and may cause some breakdown of the aggregate and decreases the air content. Mixing of concrete ingredients: Mixing of concrete ingredients:

Mixing Times: Mixing Times: The optimum mixing time depends on: [Fig-5] (a) Type of mixer (b) Condition of mixer (c) Speed of rotation (d) Size of charge (e) Nature of constituent materials F A good thumb rule for minimum mixing time is 1 min of mixing time for 1 m 3 of concrete plus ¼ min for each additional 1 m3

Types of Mixers: Types of Mixers: (a) Drum mixers (b) Pan mixers (c) Continuous mixers

Mixing of Concrete: Mixing of Concrete: (a) Transit Mixed (or "truck-mixed") Concrete: In this method, all the raw ingredients are charged directly in the truck mixer. Most or all water is usually batched at the plant. The mixer drum is turned at charging (fast) speed during the loading of the materials. There are three options for truck mixed concrete: Concrete mixed at the job site. Concrete mixed in the yard. Concrete mixed in transit. Concrete that is partially mixed in a plant mixer and then discharged into the drum of the truck mixer for completion of the mixing is called shrink mixed concrete. (b) Shrink Mixed Concrete:

(c) Central Mixed Concrete: Central mixing concrete batch plants include a stationary, plant-mounted mixer that mixes the concrete before it is discharged into a truck mixer. Central-mix plants are sometimes referred to as wet batch or pre-mix plants. The truck mixer is used primarily as an agitating haul unit at a central mix operation. Dump trucks or other non-agitating units are sometimes be used for low slump and mass concrete pours supplied by central mix plants. Principal advantages include: Faster production capability than a transit-mix plant Faster production capability than a transit-mix plant Improved concrete quality control and consistency and Improved concrete quality control and consistency and reduced wear on the truck mixer drums. There are several types of plant mixers, including: There are several types of plant mixers, including: - Tilt drum mixer - Horizontal shaft paddle mixer - Dual shaft paddle mixer - Pan mixer - Slurry mixer [FIG-6] [FIG-6]

 Transportation of Ready Mixed Concrete: Freshly mixed concrete may be transported in a open dump truck if the jobsite is near the plant. Freshly mixed concrete may be transported in a open dump truck if the jobsite is near the plant. It is remixed once it arrives at the jobsite to ensure that the proper slump is obtained. It is remixed once it arrives at the jobsite to ensure that the proper slump is obtained. The concrete that is remixed at jobsite tends to set more rapidly than concrete mixed only once. The concrete that is remixed at jobsite tends to set more rapidly than concrete mixed only once. Materials, such as water and some varieties of admixtures, are often added to the concrete at the jobsite after it has been batched to ensure that the specified properties are attained before placement. Materials, such as water and some varieties of admixtures, are often added to the concrete at the jobsite after it has been batched to ensure that the specified properties are attained before placement. Slight agitation of the concrete during transit prevents segregation of the materials and reduces the amount of slump loss. Slight agitation of the concrete during transit prevents segregation of the materials and reduces the amount of slump loss.

SAMPLING OF CONCRETE Sampling is done by: The Company - To maintain the required standard, the company performs cube and cylinder tests and the test results are analyzed. The Municipality - The mobile teams of Riyadh Municipality takes random samples of mixed concrete and test the physical properties of concrete and prepare report for the renewal of the licensee for the next year.

Sampling concrete from a ready mixed concrete truck: Molding and Curing Concrete Cylinders A representative sample of concrete is obtained from the truck mixer. Concrete should be sampled from the middle of the load.

Ice Plants, Aggregate washing plants to ensure high quality of concrete Almost any natural water that is drinkable and has no pronounced taste or odor may be used as mixing water for concrete. However, some waters that are not fit for drinking may be suitable for concrete. Excessive impurities in mixing water not only may affect time and concrete strength, but also may cause efflorescence, staining, corrosion of reinforcement, volume instability and reduced durability. Specifications usually set limits on chlorides, sulfates, alkalis, and solids in mixing water unless tests indicate that the water will not negatively impact concrete properties.

Well equipped Quality Control lab in accordance with BS and ASTM. The aggregates should be clean and free from any matter that might affect the quality of the concrete.