Imagine you are building your dream home, and it rains during ongoing important concreting work like slab casting. You will panic, as this process plays a decisive role in the durability and life of your home. In this situation, you will wonder if you should carry out the concrete pouring activity during the rain or call it off. You would want a reliable answer to the question: Can you pour concrete in the rain? And what happens if it rains on fresh concrete?
In this article, Gharpedia provides precautions for concrete pouring during the rain to save you from huge losses. It also explains the impact of rain on freshly mixed concrete and how rain affects your concrete pouring process.
So, let us start this journey by understanding what happens if it rains on fresh concrete or wet concrete and your structure’s strength and durability.
What Happens if it Rains on Fresh Concrete and its impact on Construction Durability
To understand the rain’s impact on fresh concrete and construction durability, you need to have a clear idea of what concrete is and how it works in terms of quality, strength, and durability.
For those who are unaware of how concrete is made or the ingredients of concrete, it is a mixture of construction materials such as cement, aggregate, water, admixture, etc. Mixing all the materials in proper proportion makes superior quality concrete (as per the design given by your consultants) with high strength and durability. Water plays a crucial role in concrete quality, as the water-cement ratio is directly related to concrete’s workability. This is the property of concrete, which determines its homogeneity in terms of quality.
Before proceeding further, it’s imperative to know the difference between concrete and cement. It will help you understand the whole concept. So, click on the link below to know their difference:
If you are pouring concrete in the rain, the rainwater will increase the proportion of water in the concrete mix during the concreting process, such as mixing, transporting, placing, compacting, and finishing. Apart from the concreting process, other materials such as sand and aggregate also get wet, raising the water content in the concrete. Altogether, these factors increase the water-cement ratio of the concrete mix and ultimately reduce its strength to a significant extent.
In any case, you must avoid excess water to achieve the desired strength of your structure. However, this does not mean you cannot pour concrete in the rainy season.
So, can concrete be poured in the rain? Let’s understand.
Can You Pour Concrete in the Rain?
When you pour concrete in the rain, the following risks are possible, depending on the setting time of the concrete. In simple words, the impact of rain on concrete varies with time, which means the impact of rain on concrete after 4 hours, 8 hours or 24 hours is different. Hence, it is important to first understand the concept of setting time of cement or concrete. So, click the link below to learn about setting time.
01. If it Rains during Concreting or within the initial setting time of Concrete, i.e. before 30 minutes
The rain certainly affects the concrete before 30 minutes of pouring or during pouring. 30 minutes is the initial setting time for concrete. This means the concrete is still wet before 30 minutes have passed.
If you pour concrete in the rain, the rain increases the water-cement ratio of the freshly mixed concrete, which results in the bleeding of the concrete. During the bleeding of concrete, free water in a mix moves towards the concrete’s surface because of the settlement of solid particles by gravity. Water bleeding also carries the cement particle with it and forms a laitance. If this happens at the slab’s top layer, it creates a porous and weak surface, resulting in poor strength of concrete. At times, the surface of concrete may develop plastic shrinkage cracks.
02. If it Rains between the initial setting time and the final setting time of Concrete, i.e. after 30 minutes and before 600 minutes (10 Hours)
Concrete’s initial setting time is 30 minutes, and the final setting time is 600 minutes (10 hours). The rain affects the concrete pouring after the initial setting time and before the final setting time. In simple words, if it rains on concrete after 2 hour, 4 hours or 8 hours, it affects the concrete. In this period, the concrete is initially set, which means it is not fresh or solid. Simply put, the concrete is in gel condition (your finger leaves only an impression but does not dip into the concrete when you touch it).
In this case, low-intensity rain does not impact the mix very much, but the rain droplets leave an impression on the surface of the concrete. It looks unappealing as rain impacts the surface finish but not the concrete’s strength. However, if the intensity of rainfall or the internal voids are high in concrete, rain may affect the top layer of concrete.
03. If it Rains after the final setting time, i.e. after 600 minutes (10 Hours)
Rainwater does not affect concrete when it occurs after the final concrete setting time (> 600 min). It means the concrete is in stiff condition (your finger does not leave an impression on the surface when you touch it). On the contrary, light rain helps to cure the concrete and ultimately achieve good strength.
Precaution while Pouring Concrete in the Rain
By following these precautionary tips, you are sure to avoid rain interruptions during the concrete pouring process.
01. Most Important and General Instruction
Do not use rainwater in a concrete mix, as it may be contaminated. If you plan to pour concrete after rainfall, removing surface water from the slab’s edge or surface is important. Avoid pouring concrete over wet surfaces or in water-filled cavities.
02. Provide Plastic Tarpaulin Sheets
You can use plastic tarpaulin sheets to cover the pouring area during the rainy season. You need to provide an adequate and high quality plastic sheet during concrete pouring.
03. See the Weather Forecast
Always check weather forecasts and the probability of rain on websites like skymetweather.com to avoid any disturbance from rainfall.
04. Proper Placement of Plastic Sheets on Concrete’s Surface
Remember that the plastic sheet should not touch the surface when you cover the concrete surface during rain. If you lay it directly on the surface, it may increase the setting time of the concrete and disturb the finishing. Thus, you must cover the plastic sheet, so the concrete gets air and workers can easily complete the concreting process.
05. Adjust the Water-Cement Ratio
Reduce the water-cement ratio, as rainwater is already present on the aggregate surface, or increase the quantity of cement, which is worth it. Ask your consultant what quantity of water is to be reduced depending upon the intensity of the rain. Also, take all precautions. After getting the consultant’s permission, you can reduce the water-cement ratio by mixing the appropriate admixture.
Understanding the significance of the water-cement ratio is crucial when working with concrete. To gain insight into this important aspect, click the link below:
06. Provide Staging
It is imperative to cover the pouring area with a plastic sheet to provide staging.
07. Cover Construction Materials during Rain
Covering construction materials such as sand, aggregate, reinforcement, etc. is imperative. This is because if they are wet, they can increase the water-cement ratio and cause corrosion in steel reinforcement. This will directly affect the structure’s strength.
You can cover construction materials other than cement, as the moisture effect on cement bags is very different from them. So, you need to be extra careful with cement storage during the rainy season.
08. Conduct Quick Visual Inspection
If it rains on wet concrete, it leads to damages like uneven surfaces and lumps and bumps on the concrete. Hence, a visual inspection of the concrete pouring surface after rainfall is a must. You can use a screwdriver to scratch the concrete surface and check its hardness.
Conclusion
On a final note, the answer to the question, “can you pour concrete in the rain?” is here. You can pour concrete in the rain with the precautions mentioned above. Nevertheless, it is highly advisable to suspend the concrete pouring in heavy rains, as it will wash away the cement slurry in the freshly laid concrete. If there is rain while you are working, check the concrete surface for any damage due to the rain.
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