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November 2018

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Concreting Operations

Operations followed in the making of concrete in compliance with the safety and quality requirements are known as concreting operations. Concreting operations include:

  • Storage of materials;
  • Batching and Mixing of various ingredients;
  • Concrete mix transportation;
  • Concrete placing;
  • Compaction of concrete;
  • Surface finishing; and
  • Curing of concrete.

PURPOSE

Concreting operations are vulnerable to safety and health hazards. This method statement describes the safety requirements and safe work procedure for concreting operations to:

  1. Prevent improper carrying out of concreting works;
  2. Carry works in a manner that’s safe at all times;
  3. Know the hazards involved in performing the activity;
  4. Ensure controls are in place to steer clear of hazard exposure.

Use any other resources and methods not referred to in this method statement to suit the project requirement. Execute the work safely complying with the required standard.

The sequence of activities is a repetitive process and many hazards are common to distinct sites. Include with detail, any crucial information specific to the project. Follow the approved checklists prior to the start of the activity.

PROCEDUREs in concreting operations

Storage of concrete materials

Storage of cement:

  • Store cement in a weatherproof shed to keep it dry,
  • Make proper arrangements to prevent rain penetration,
  • Store cement on a platform raised above ground level.

Storage of Aggregates

  • Keep aggregates in a clean condition. Take necessary measures to prevent contamination with undesirable substances,
  • Make floor of the storage bins with plain cement concrete,
  • Separate storage bins with partitions to prevent mixing of different aggregate sizes.

Batching and Mixing of materials

  • Inspect and check the batching equipment including equipment calibration before the operation begins.
  • Weigh the cementitious materials and aggregates independently in separate compartments.
  • Ensure that the weigh hopper charging and discharging gates close tightly when producing concrete.
  • Make sure that the equipment allows to control the material flow rate and stop the flow within the specified weighing tolerance.
  • Make sure that the measuring accuracy of batch materials weighing scales, and the water measuring equipment meets accuracy requirements before the work begins.  

Concrete mix transportation

The operation of moving concrete mix from the concrete batching plant to the concrete pour location is known as concrete mix transportation.

Ensure that the water-cement ratio and slump are maintained as per concrete design mix before placing of concrete. During transportation, the concrete mix shall maintain its cohesiveness and workability.  

Placing of concrete

Concrete placing
Concrete placing (image credit By Rasbak)
  • Check the formwork and reinforcement before placing the concrete to ensure that they are clean and free of any debris.
  • Deposit the concrete as close as possible to its final position. Make sure that reinforcement dislodging or overfilling of formwork doesn’t occur during concrete discharge.  
  • When filling columns and walls, take care that the concrete does not strike the formwork face, which might impact the surface finish.
  • For deep sections place the concrete in layers that are uniform, generally not exceeding 500 mm thick, each layer being fully compacted.

Compaction of concrete

After the concrete is placed, it contains entrapped air voids. Compaction is the process to expel entrapped air from concrete. Consequently, compaction increases the density of concrete.

Three types of vibrators are available to achieve the desired compaction:

  1. Immersion vibrators or needle vibrators: appropriate for all sorts of sections. As per IS: 3558 [Code of practice for use of immersion vibrators for consolidating concrete],  “the vibrating needle should preferably be inserted vertically. The insertion at an angle, in thick layers, may leave concrete unconsolidated without any indication at the surface.” 
  2. Surface vibrators:  They are appropriate for compacting slabs, industrial floors, road pavements, and similar flat surfaces. Furthermore, they also aid in surface leveling and finishing.
  3. Table vibrators: Vibrating tables are used for the consolidation of concrete in moulds for the manufacture of plain and reinforced concrete or prestressed concrete elements. IS 7246 [Recommendations for use of table vibrators for consolidating concrete.]
  4. Form vibrators: For complex members or members with higher reinforcement congestion, form vibrators are appropriate. They are fixed to the exterior of the formwork. Therefore,  these are also called external vibrators. The formwork needs to be designed to resist the forces imposed on it by form vibrators.

Concrete surface finishing

Concrete surface finish
Concrete surface finish

Finishing is the operation of attaining a concrete surface of desired texture and pattern. Functional and decorative requirements determine the finish of a concrete surface.

As per IS 2571 [Code of practice for laying of in-situ cement concrete flooring]:

The floor finishes shall be laid depending upon the expected load and wear on the floor and the fact whether the topping is to be laid monolithic with the base or separately on a set and hardened base. In either case, special precautions are necessary to ensure a good bond between the topping and the base.”

Finishing makes concrete more functional and aesthetic. Concrete that will be visible, such as driveways, highways, or patios, often needs finishing. Concrete’s end use usually determines the final surface texture and patterns.

Finishing of concrete surface requires one, or many of the following operations:

  1. Level the surface
  2. Edge the concrete
  3. Joint the concrete
  4. Float the concrete
  5. Trowel the concrete
  6. Texture the concrete surface
  7. Cure the concrete

Never add cement or sprinkle water on concrete while finishing it.

Curing of concrete

As per ACI 308R [Guide to Curing Concrete], curing is the process by which hydraulic-cement concrete matures and develops hardened properties over time as a result of the continued hydration of the cement in the presence of sufficient water and heat.

Curing is to maintain desired water content within the concrete for the required time. Start curing of concrete as quickly as possible after finishing of concrete.

HEALTH, Safety, AND ENVIRONMENT for concreting operations

Safety is essential and imperative part of the construction process. Provide personal protective equipment (PPE) to all personnel involved in the Diaphragm wall activity and provide the required safety equipment.

Below are the suggested PPE for concreting operations:

PPE for concreting operations
Safety PPE for concreting operations

Safety Measures for concreting operations:

  • Formwork shall support, without failure, the anticipated vertical and lateral loads. Make sure appropriate design, fabrication, erection, and supports for the formwork,
  • Before erection, inspect shoring equipment to determine that the equipment meets the specified requirements,
  • Inspect erected shoring equipment before, during, and immediately after concrete placement,
  • Make sure all base plates, shore heads, extension devices, and adjustment screws are firmly in contact, and adequately secured, with the foundation and the formwork,
  • Prohibit eccentric loads unless designed for such loading,
  • Provide adequate supports to reinforcing steel installed for vertical structures like columns, walls etc. The supports are needed to prevent overturning and collapse,
  • Vibrator crews should not work under concrete buckets suspended from cranes or cableways,
  • Wash off, as soon as possible,  any concrete splatters on the skin,
  • Provide scaffolds or work platforms for all vertical slip forms where employees need to work or pass,
  • Below are the most critical practices that are unsafe and need to be avoided:
  1. premature removal of formwork;
  2. failure to brace masonry walls;
  3. failure to adequately support precast panels;
  4. inappropriate operation of equipment;
  5. failure to guard the end of reinforcing steel; and
  6. inadequate shoring, which may lead to formwork collapse.
  • Don’t load the concrete with any construction loads till the structure is capable of taking such loads as per the structural design,
  • Guard all protruding reinforcing steel, onto which an individual could fall,
  • Don’t let any person work under concrete buckets while the buckets are in motion,
  • Don’t expose any person to the hazards associated with falling concrete buckets.

Safety questions

Keywords: Concreting operations; Safe Work Method; Construction work procedures.