3 Ways Moisture Affects Concrete Strength

Water is an essential component when making concrete. The moisture that water provides also gives concrete its strength during the curing process. While water is one of the most important ingredients in concrete, it can also be the most destructive in excessive amounts. As one of the most common building materials used in construction, appropriate concrete drying solutions are necessary to ensure concrete strength and safety.

Sources of Excess Moisture in Concrete

• Free water, or too much water in concrete mix
• Moisture rising from beneath a slab
• Failing to install a vapor barrier
• Poor ventilation
• Leaks
• Groundwater and poor drainage
• Inadequate landscaping grade
• Dew point condensation
• High relative humidity levels
• Lack of protection from the elements
• Not allowing concrete to dry and cure properly
• Lack of climate control

How Moisture Affects Concrete Strength

1. Increased space between cement grains

Higher water-to-cement ratios result in greater spacing between the aggregates in cement, which affects compaction. Similarly, increased moisture levels reduce the concrete’s compressive strength and durability. As concrete’s surface area increases, particularly with the addition of fine aggregates, so does the demand for water. The increased water leads to a higher water-to-cement ratio.

When excess water creates greater spaces between aggregate materials, the voids fill with air after the moisture evaporates. The resulting inadequate compaction reduces the concrete’s strength. Concrete with trapped air levels as little as 10 percent experiences reductions in strength of up to 40 percent.

2. pH levels could compromise adhensive bond and strength

Relative humidity levels and pH in concrete are directly related. As humidity levels increase, so does the concrete’s pH and temperature. As pH levels in concrete increase, the more likely floor covering adhesive bonds will fail. While higher temperatures allow concrete to dry faster, it results in a less structured, more porous product.

Water containing bicarbonate ions and carbon dioxide causes a reaction known as carbonation in concrete. This often happens in the presence of salts and acid rain. As the acidic substances lower the concrete’s pH, the calcium carbonate within the aggregates dissolves and reduces the concrete’s strength. Eventually, the concrete will crumble into sand and rock. As the concrete becomes more acidic and damage progresses, the acids will eventually affect the protective layer of iron oxide on steel reinforcements, leading to corrosion. Steel expands as it corrodes. This expansion within already weakened concrete will cause it to further break and crack.

3. Microbial growth

High relative humidity levels, increased temperatures and porous concrete create the perfect breeding ground for mold, bacteria and other organisms. While concrete doesn’t contain sufficient organic materials for mold to feed on, it traps dust, pollen, microorganism and salts, which are food sources. When mold feeds on the particles trapped within concrete, it excretes acids that degrade the building material’s strength and integrity. To prevent mold growth, dry concrete should not remain wet for more than 24 hours.

Construction Drying Solutions

Excessive moisture is most problematic in concrete when there is a lack of climate control and air circulation. To better guarantee the material’s strength and meet project deadlines, it is best to follow the manufacturer’s installation and drying guidelines for your respective region, and pair this knowledge with temporary climate control solutions. Humidity and temperature control solutions provide the ideal environment for concrete to dry and cure, regardless of the weather. When you create a good foundation for floor coverings, surface coatings and other structural components, you ensure their strength and long-term success. Talk to a Polygon specialist today to learn more about how construction-drying technologies including moisture content monitoring will benefit your job site. 

[Photo from Carsten aus Bonn via CC License 2.0]