Summary
- Concrete pouring is the job of placing fresh concrete in its final position, compacting it, and smoothing the surface before it sets.
- Prepare the base, formwork, and reinforcement before receiving concrete.
- IS 456 suggests that, in general, the maximum free fall while placing is 1.5 m.
Concrete pouring is a critical phase in slab and structural work. Poor placement or compaction can leave voids and expose reinforcement to moisture.
Put simply, concrete pouring means transporting fresh concrete to its final destination, vibrating out air bubbles, and smoothing the surface before it hardens.
IS 456:2000 refers to placing, compaction, and curing as site operations. These controls are important for reinforced cement concrete as well.
How Do You Prepare for a Concrete Pour?
Make sure the ground, sub-base, damp-proof layer, formwork, reinforcement, and embedded services are ready before the first batch arrives.
Step 1: Prepare the Ground
Cut to the desired depth and clear topsoil, roots, loose fill, and soft areas. Firm the base so it will not settle after pouring. Check the final level and slope.
Step 2: Add the Sub-Base and Damp-Proof Layer
Compact the sub-base as shown in the drawing. Install a plain cement concrete (PCC) levelling course and a damp-proof membrane underneath the slab before reinforcement, where necessary.
Step 3: Set Up the Formwork
Set up the formwork properly for line and level. Protect joints and side supports so the formwork can hold wet concrete when it is being poured.
Fix reinforcement, cover blocks, sleeves, conduits, and embedded items before pouring. On larger sites, record this on a concrete pouring card before the pour.
What Is the Concrete Pouring and Finishing Process?
Concrete pouring and finishing means placing fresh concrete, compacting it, levelling it, finishing the surface, and curing it before it dries out too quickly.
- Mixing: Use a concrete mixer and do not guess the water content. Maintain specified mix proportions for consistency and strength.
- Placement: Place concrete near its final position. IS 456 recommends 1.5 m general maximum free fall to avoid segregation.
- Compaction: Compact each layer with suitable equipment to remove trapped air and fill around reinforcement and formwork.
- Early finishing: Screed to level and use a bull float where needed. Avoid final finishing over bleed water.
- Trowelling: Once bleed water has gone, complete the surface with a steel trowel. Use a groover for joints and an edger for exposed slab edges.
- Curing: Begin curing when the final surface is not damaged by water. Keep concrete moist for the required curing period.
Safety matters throughout the pour. Wet cement is alkaline and may burn skin. According to the Building and Other Construction Workers (BOCW) Central Rules, 1998, workers should wear protective clothing, gloves, head and eye protection, suitable footwear, and waterproof boots.
Which Concrete Pouring Methods and Techniques Improve Quality?
The primary techniques are chute pouring, concrete pumping, crane and bucket pouring, tremie pouring, drop pipe pouring, self-compacting concrete, controlled vibration, and hot weather concrete planning.
- Chute pouring: Useful where the transit mixer can approach the pour area. Do not drag concrete from its placement area.
- Concrete pumping: Used for restricted access, especially slabs, upper floors, and congested sites. Determine the pump line before the mixer arrives.
- Crane and bucket pouring: Used when concrete must be lifted and placed under control, and pour volume makes crane access worthwhile.
- Tremie or drop pipe placement: Used when concrete must be delivered through depth, or free fall needs control.
- Self-compacting concrete: Used for dense reinforcement or where vibration is hard to achieve. Follow manufacturer guidelines and site specifications.
- Controlled compaction: Remove air voids and fill around reinforcement and formwork with suitable vibration. Avoid using a vibrator to push concrete sideways.
- Hot weather concrete planning: Plan pour timing, labour, curing water, and materials. Minimize delay between placement, compaction, and finishing.
Mistakes to Avoid While Pouring Concrete
Avoid these five common errors:
- Adding water at site to facilitate flow: It increases the water-cement ratio, which can reduce strength and durability.
- Pushing concrete sideways with a vibrator: Place concrete close to the final position at the time of compaction.
- Drying bleed water with dry cement: This can cause loss of surface strength.
- Stopping the pour at an unplanned construction joint: Use the approved joint location and treatment.
- Drying the surface during curing: Continue the curing method for the specified amount of time.
What Comes Next After Concrete Pouring?
After pouring, curing starts first. Remove formwork after the specified period and clean it immediately.
IS 456 specifies at least 7 days of moist curing for Ordinary Portland Cement (OPC), and 10 days for concrete made with blended cement or mineral admixtures.
OPC or Portland Pozzolana Cement (PPC) may affect the curing plan.
Before setting, wipe down the chute, mixer drum, and tools.
IS 456 specifies the minimum formwork striking times for appropriate curing and ambient temperature above 15°C.
| Formwork element | Minimum period before striking |
|---|---|
| Vertical formwork to columns, walls and beams | 16 to 24 hours |
| Soffit formwork to slabs, props refixed | 3 days |
| Soffit formwork to beams, props refixed | 7 days |
| Props to slabs spanning up to 4.5 m | 7 days |
| Props to slabs spanning over 4.5 m | 14 days |
| Props to beams and arches up to 6 m | 14 days |
| Props to beams and arches over 6 m | 21 days |
Get structural engineer confirmation for striking times based on the actual mix, member, and site conditions.
Get the Pour Right Before It Sets
After concrete sets, little can be done to correct an error. Check formwork, rebar, supply plan, compaction equipment, and curing before the first batch.
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Frequently Asked Questions
What Is Pouring of Concrete?
The pouring of concrete involves placing fresh concrete in its final location before compaction, finishing, and curing. These steps are done before the concrete sets and ensure that the concrete is properly placed within the formwork.
Why Does Concrete Crack Right After Pouring?
Plastic shrinkage cracks are commonly the first type of crack when there is too much surface moisture lost. This moisture loss can be accelerated by hot, dry, or windy conditions, so attention should be given to the surface and curing conditions immediately after the pour.
How Long After Pouring Concrete Can You Walk on It?
IS 456 does not have a set walk-on time. Observe the engineer or site supervisor for safe timing, as the type of concrete, temperature, curing conditions, and anticipated loads may influence when the surface is ready.
What Is the Maximum Concrete Pouring Height as per IS Code?
In IS 456, some general guidelines are provided for concrete pouring height , with the maximum free fall during pouring kept around 1.5 m. The larger the drop, the more likely segregation will occur, and concrete should be placed near its final position.
What Is the Right Temperature for Concrete Pouring?
No universal temperature for concrete pouring is suggested for every project. Site conditions and weather should be taken into account before placing the concrete because of the requirements of hot- or cold-weather concreting as outlined in BIS IS 7861, Part 1 and 2.
How Do You Spread Concrete Evenly?
Pour concrete close to where it is to be placed and lay it in thin layers. The concrete should be compacted at each layer, and then the top of the layer or reference points should be screeded to the planned height before final finishing work is carried out.