Can You Pour Concrete on Wet Ground? - Engineering Web (2024)

Concrete requires moisture to develop strength, but is it advisable to pour it on wet ground? What if the situation leaves you with no other options?

Pouring Concrete on Wet Soil

When pouring concrete directly on the soil, the soil must be damp to ensure proper curing. However, when the soil is saturated with water, it is too wet and could adversely affect the concrete curing process.

Concrete hardens through a process called curing. Here, the concrete is allowed enough moisture for a chemical reaction called hydration.

The ratio between water and cement in the concrete mix design determines the resultant concrete strength. Adding more water than is necessary weakens the concrete. However, removing water from the mix design also adversely affects the concrete since the cement may not have sufficient water to react with.

There is a delicate balance between supplying adequate water for hydration and curing and not supplying enough, both of which result in weakened concrete.

Dampen the Soil

When preparing the soil for a concrete pour, the soil must be compacted and dampened to form a firm substrate to support the concrete’s weight. If the soil isn’t adequately compacted, it will shift and settle once the concrete is poured, resulting in crack formation in the hardened concrete. Dampening the soil ensures that the moisture present in the concrete isn’t absorbed into the soil.

What Happens if You Pour Concrete on Wet Ground?

When the soil is too wet, it cannot hold its form and often has muddy puddles on the surface. The soil’s inability to hold its shape means it can’t support the concrete’s weight.

Once the concrete is poured, it will shift and settle, resulting in crack formation. The extra water on the surface will seep into the concrete mix design, altering the water-to-cement ratio and weakening the concrete. This is also the main reason why pouring concrete during heavy rain is not recommended.

Factors to Consider When Pouring Concrete on Wet Ground

Water content has a marked effect on concrete strength, and wet soil can adversely affect concrete quality. Here are some factors to consider when pouring concrete on wet soil.

1. Moisture Level of the Soil

• High Moisture Content: If the moisture content of the soil is too high, do not pour concrete on it. The soil will be saturated here, possibly with water pooling on the surface.
  Saturated soil also typically can’t hold its shape, falling down when placed in a heap. In this case, the soil is unable to carry the concrete’s weight, leading to settling and shifting. When the substrate shifts, the concrete will settle unevenly, leading to cracking in the hardened concrete.
• Dry Soil: Suppose the soil’s moisture content is too low. In that case, it is also not advisable to pour concrete on it since moisture from the concrete will be absorbed into the soil, affecting strength gain.

Ideally, the soil should be well compacted and damp when pouring concrete.

A good rule is that the soil should be moist to the touch but not have water glistening on the surface.

* The exact moisture levels needed will vary depending on climate, environmental conditions, and the concrete mix design.

2. Potential for Soil Erosion or Instability

Wet soil runs off quickly and is prone to erosion and instability. Water pockets trapped in the soil that doesn’t seep into the concrete entirely will create cavities underneath the concrete, creating unstable pockets underneath the hardened concrete.

A shifting, unstable substrate also negatively affects concrete strength and durability.

3. Effect on Concrete Strength and Durability

Pouring concrete on excessively wet soil effectively adds water to the lower layers of the mix design. Additional water increases the water-to-cement ratio, which decreases compressive strength. Here, the bottom layers have lower compressive strength than the top layers, causing irregular resistance to shrinkage and other stresses.

Irregular strength gain leads to cracking and even delamination, negatively affecting concrete durability.

In extreme cases, water trapped on wet soil could wash cement paste from the mix design, leaving only aggregate in its place. This phenomenon is called honeycombing and is detrimental to concrete durability.

Honeycombed concrete has very little compressive strength since nothing effectively holds the aggregates together. This concrete cannot bear the load and withstand stresses without cracking and failing.

Techniques for Pouring Concrete on Wet Ground

At times, pouring concrete on wet soil is inevitable. Here, precautions must be taken to protect the concrete’s integrity, ensuring a successful pour.

1. Use of a Vapor Barrier

Using a vapor barrier prevents water from seeping into the fresh concrete from below. A vapor barrier could be a physical barrier, like plastic sheeting, or a chemical barrier, sprayed onto the substrate before pouring the concrete.

2. Modification of the Mix Design

The mix design can sometimes be modified to accommodate the wet soil. If you’re not doing underwater concreting, this may not be the most effective way to go about it since the excessive water is only present at the bottom of the pour, not necessarily at the sides and top.

This situation could still lead to uneven strength development since the side of the pour exposed to excessive moisture will be weaker than the rest of the structure.

3. Use of Curing Methods

Curing is essential for concrete strength development, regardless of how it’s poured. Once the concrete is in place and consolidated, best curing practices involve keeping it sufficiently wet to prevent drying out, and protecting it from environmental elements, like wind, extreme temperatures, and excessive loads while still soft.