pouring concrete in rain

Pouring Concrete in Rain | How to Protect Concrete From Rain

Pouring concrete in rain season is one of the big challenges for engineers and workers on construction sites. Rain is unpredictable sometimes, also its intensity different every time. Before pouring concrete in rain we must have to take essential precautionary measures to avoid any damage due to rain.

How Can Rain Damaged Concrete?

One of the biggest problems occurred when poring fresh concrete in the rain that rainwater can potentially become mixed in the concrete, resulting in bleeding of concrete, laitance of concrete, and weaker overall finish of the concrete surface.

Water is an essential ingredient in the concrete mixing process and is carefully proportioned to guarantee the best result but adding more water than necessary will compromise the strength of the concrete mix, and means that your concrete is more at risk of cracking and its also effects on the ultimate strength of hardened concrete.

Ensuring that you’re ready to mix concrete is properly covered during the pouring process and afterward is therefore essential if you want to prevent permanent damage due to rainwater.

Pouring Concrete in Rain | How to Protect Concrete From Rain
Laying Concrete in Rainy Weather

Rain can also affect the internal strength of the concrete. If there is constantly heavy rain for a couple of days, the excess water on the concrete can slow down the curing process. This can affect the internal bonds between the concrete particles and make the mixture weaker than intended.

Read More: Concrete To Water Ratio – Calculate Proper Amount Of Water For Concrete

How to Protect Concrete From Rain

It is important that you check the weather forecast before the placement of fresh concrete so that you aren’t caught short without the necessary equipment and are prepared to take precautions. If another concrete is undertaking the installation of the ready mix concrete on your behalf, you can ask them how they plan to prepare for the eventuality of rain.

  1. If the weather is forecast for the day of the pour, you should cover your pour site effectively with plastic sheets and tarpaulin to ensure that the ground doesn’t become sodden.
  2. Never pour concrete into water-filled cavities or onto very wet surfaces, as the concrete will absorb the moisture and become compromised.
  3. If you are pouring concrete following heavy rain, push any surface water off the edge of the slab.
  4. If you are caught short, make sure you have plastic sheets and timber available to construct a temporary shelter to erect over the fresh concrete.

Effect of Rainwater on Concrete:

We know very well that water is an important ingredient in concrete; however, it affects concrete strength if its quantity used in more than that required, so the rainy season can be particularly hard because it brings water and wind.

Below mentioned are some bad effects of rain if concrete poured during the rainy season:

1. Surface scaling:

Surface Scaling

Due to rainfall, surface scaling on the concrete surfaces can also happen. Surface scaling is a phenomenon where the surface of the concrete will become flaky.

Despite not being visible easily, it may break or crumble when you start putting significant weight by walking on it or storing your appliances and other goods. T

his is something that must be restricted in order to keep the strength of the concrete last longer.

2. Segregation of Concrete Ingredients:

Pouring concrete in rain
Segregation in Concrete

Heavy rainfall can cause problems to freshly poured concrete as it can wash out some of the cement from the mix. This can weaken the surface of the concrete, making it a sifter consistency and decreasing the strength of the concrete.

Read More: Honeycombing Of Concrete – Causes & Repair Methods

3. Higher Water/Cement Ratio:

If the mix of the ingredients is unprotected, heavy rainfall will change the water-cement ratio in the mix. This change in the ratio can cause the concrete to be easily poured but will damage the strength and durability of the concrete.

A mix like this will cause trouble in the future. It will be prone to cracks and can destroy all the effort put by you in making mix and built up a strong building.

4. Lowering the Strength of Concrete:

Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish of the concrete. Even worse, if too much extra rainwater percolates into the concrete mix, this can result in weak concrete overall.

5. Affects on Curing of Concrete:

Rainwater will affect concrete depends on the stage in the curing process that was reached before the rain set in. if the concrete is still fresh (around 2-4 hrs after pouring), it’s important to cover the surface to protect it.

However, once the concrete has been finished (between 4-8 hrs after pouring), and has set enough for walking on, the effects of rain should be minimal. 

6. Deterioration on Concrete:

Rainwater composed of different chemicals from dissolved particulate materials in the atmosphere. Thus the composition of rain varies from place to place.

Human activities, industrial fission, local climate condition, and biome functions affect the type of particulates in the atmosphere, which in return, affect the chemical composition of water.

When such rainwater gets in contact with concrete, it triggers a certain process (e.g., carbonation, acid, and sulfate reaction) that makes concrete vulnerable to deterioration.

By knowing this process and understanding the vulnerabilities of concrete will help you in detecting rain damage and minimizing maintenance costs and repairs.

Read More: How To Make Concrete – Batching, Mixing, Transporting & Placing

Precautionary Measures to be taken While Concreting in Rainy Season:

Contractors need to keep an eye on their concrete structures during the rainy season. Rain might affect the surface appearance of the concrete as well as the internal strength of it.

When the concrete is between its initial setting time and final setting time, the rain can leave patch marks and pores in the wet concrete. This may be disturbing the uppermost layer of the concrete before it can cure properly.

Here are some points to be considered when pouring concrete in the rainy season.

1. Use Less Water in the Concrete Mixture During the Rainy Season:

     If you store your aggregates outside, the rain will make the sand and crushed stone wet. This will add extra water to the concrete mix, so remember to use less water when making a batch of concrete.

You will also need to keep an eye on your cement and ensure that no moisture gets into the bags while they are being stored. The cement needs to be stored in a dry environment at all times.

2. Use of Waterproofing Admixtures in Your Concrete:

During the rainy season, consider using hydrophilic crystalline admixtures in your concrete batch. These admixtures react with water and cement to form calcium silicates crystals. The crystals block pores and micro-cracks in the concrete and prevent water seeping into the structure. Essentially, they seal the concrete and protect it from excess water damage. 

3. Avoid Pouring of Concrete During Rainy Season:

     Make sure that the weather conditions are not too wet or windy before you decide to pour concrete. Keep an eye on the weather forecasts and try to find a gap of at least 12 hours where there is no rain. Fresh concrete needs about 12 hours to start the curing process and any rain could affect this.

The wind can also have a negative impact on the curing process. Strong winds can cause bleeding in the concrete and affect the evaporation rate of its internal moisture.

4. Weather Forecast Before Concreting:

It is a well-known fact that rain can affect traffic on the road. This can create undesirable delays for the transportation and delivery of fresh concrete batches. Suppliers need to keep an eye on the weather and avoid making deliveries during the rain.

If this is not possible, then drivers should plan to use alternatives routes with less traffic. Any delays in the placement of concrete reduce the workability which ultimately causes a reduction in the initial strength of the concrete. Delays in delivery will be costly to the project and will allow water to affect the construction site.

5. Use of Waterproof Covers to Protect Concrete from Rainwater:

Plastic sheets and waterproofing canvas should be kept on-site during the rainy season. Once a concrete batch is poured, cover it with the sheeting to shield the concrete from the rain. This will keep moisture in the concrete and keep excess water out.

Waterproof covers can also be used to protect aggregated and keep them dry. Using covers and traps will protect small slabs. A self-leveling compound can be applied later if necessary to smoothen the surface. Tarps and covers can also be used for larger areas to good effect.

5. Good Drainage:

This ensures no rainwater pools in trenches dug for footings, foundations, and slabs. This is important, as rainwater can bring with it contaminants. As long as it drains away there won’t be a problem with pouring concrete in the rain

6. Perform Inspections After the Rain:

Once the rain has subsided, asses the concrete and see if there is any damage or pools of water on the surface. A simple scratch test can be done to see if the surface of the concrete has been affected by the rain.

If there is any surface damage or dimples left by the rain on the concrete surface, contractors can use a float to remove excess pools of water and smooth the surface of the concrete at the same time.

The key to ensuring the success of a building during the rainy season is preparation. Be ready for heavy rains and have the right types of equipment and materials on-hand to deal with the wind and water.

Pouring concrete in the rain is not advisable, rather stop and wait for the rain to pass and clear the atmosphere then remove the surface water in the foundations or on the already-poured concrete before completing the pouring of concrete. 

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