Many factors impact a construction project but by far, the most common is the weather. By its very nature, construction is dependent on, and vulnerable to, the weather. While working with concrete may come as second nature to many contractors, it is one of the trickiest substances to work with due to how quickly it can change when exposed to different weather conditions.

The impact of hot weather

High temperatures can reduce the workability of the concrete more rapidly. Adding water to the concrete on site can assist with the workability; however it can also reduce the strength of the concrete, increase the permeability and negatively affect the durability of the concrete increasing the chance of drying shrinkage and cracks. Without the additional water though, there is reduced setting time for the concrete, negative effects to the workability and the potential of inadequate compaction which could cause formation of cold joints and poor finishes as well as creating colour differences due to the rates of hydration and cooling effects. Concrete is also more likely to suffer cracks due to the rapid evaporation of moisture and this can be further exacerbated in locations where the heat of the day rapidly cools during the night.

A similar situation arises when concrete is poured during extremely windy weather where the rapid velocity of air will contribute to moisture evaporating from the slab of concrete.

Curing plays an important role in the strength development and durability of concrete. Curing compounds can be used to seal the surface of fresh concrete and prevent rapid loss of moisture. They are an efficient, cost-effective means of curing concrete and can eliminate the need for messy water curing methods and the use of plastic sheeting. Curing compounds should be added immediately to the surface after finishing.

Taking care is cold, ice and frost

Colder temperatures can be detrimental to newly poured concrete as it quickly loses heat and moisture. Lower temperatures either completely stop or slow down the process of cement hydration due to lack of heat, which reduces the masonry’s bond strength. Additionally, plastic shrinkage cracking can occur when the surface of concrete dries before it has fully cured.

Colder winds produce what’s called a “wind chill,” which also strips any excess heat from concrete.

The following suggestions may help in achieving optimal conditions to mitigate cold weather impacts

• Use hot water to mix concrete
• Use extra or a higher strength class of cement to make the reaction hotter and cause concrete to hydrate more rapidly
• Consider alteration of mortar constituents and proportions within the concrete range to reduce the impact of cold weather and increasing the sand content can provide a stiffer mortar mixture. Using lime content will allow also mortar to loose water more easily.

Concrete must maintain a temperature above 10°C for approximately 48 hours for the correct chemical reactions to take place. Two popular options used during cold weather concrete curing are heated enclosures and insulated blankets. Ensure there is proper ventilation for the space heater.

How rainfall affects construction

It would be naive to expect no rain during a construction project and while limited rain is manageable and can actually help in curing the concrete structure post hardening of concrete, heavy rainfall on the other hand, can wash out some of the cement that has been accurately measured and mixed, creating a softer consistency, decreasing the integrity and strength of the final product as it exposes the aggregate and defining construction joints becomes difficult, if concrete activity stops abruptly due to heavy rain. Large amounts of rainwater also present the risk of contaminants entering the mix, which also jeopardizes the concrete.

Concrete exposed to an abundance of additional moisture is at a greater risk of cracking due to the uneven surface created and as additional water enters the cracks, the foundation will weaken over time. Another effect of rainfall on freshly placed concrete is surface scaling which is peeling off of near-surface concrete.

During rainy season, concrete, once poured, should be covered immediately so that it is not exposed to direct rain. Don’t work the rainwater into the concrete surface, this is the biggest mistake you can make and don’t broadcast dry cement onto the concrete to soak up surface water. This will impair the finish and further weaken the top layer. Instead, once the rain passes, use a float to push the water off the edge of the slab before you start finishing.

In conclusion, construction projects are not immune to unpredictable weather conditions so it’s important to have a plan in the instance your construction project is hit with harsh weather conditions. Always choose the correct Sephaku cement type to suit the application. For expert advice, contact the Sephaku call centre on 0861 32 42 52 or speak to your technical representative for more information.