Engineers Shift Large Concrete Pours to Night Hours

A version of this article appeared on LinkedIn.

For civil engineering projects across Kenya, the sight of floodlit sites at midnight is becoming as common as daytime labor. Final-year civil engineering technician Mutisya Gideon notes that the shift toward night casting is a strategic move to improve both work efficiency and the long-term durability of structures.

Temperature control remains the primary driver behind this scheduling. When concrete is poured during the heat of the day, particularly in arid or semi-arid regions, the water required for the chemical hydration process evaporates too rapidly.

This loss of moisture often leads to plastic shrinkage cracks. By casting at night, when ambient temperatures are significantly lower, the concrete retains its moisture content longer. This environment promotes proper curing and ensures the material gains strength uniformly across the entire slab or column.

Workability also benefits from the cooler evening air. At lower temperatures, concrete remains in a plastic state for an extended duration. This gives site workers more time to place, compact, and finish the surface without the material prematurely stiffening.

In Kenya’s bustling urban centers like Nairobi and Mombasa, the logistical advantages of night work are undeniable. Major road projects and high-rise developments often face severe delivery delays during the day due to gridlock.

Night casting allows transit mixers and pump trucks to move through city streets with minimal interruption. This ensures a continuous supply of material, which is critical for preventing the formation of cold joints.

A cold joint occurs when a new batch of concrete is poured against a layer that has already started to set. In large-scale pours for bridges or building foundations, maintaining a seamless bond is vital for structural integrity.

The efficiency extends to the machinery itself. Concrete pumps and transport equipment are prone to overheating when operating under direct sunlight. Intense daytime heat can cause the mixture to set inside the pumps, leading to expensive mechanical failures and site delays.

However, the transition to night operations is not without its specific requirements. Gideon emphasizes that contractors must prioritize proper lighting systems to ensure the quality of the finish and the safety of the crew.

Supervision remains a critical factor. Senior site engineers must be present to monitor the slump of the concrete and ensure that safety protocols are strictly followed in low-light conditions.

Safety measures for workers are heightened during these hours, requiring reflective gear and clearly marked hazard zones. Furthermore, the transition back to daytime requires a plan for adequate curing after casting.

Once the sun rises, the fresh concrete must be protected from the sudden spike in temperature. This often involves ponding, wet burlap, or curing compounds to maintain the moisture levels established during the night pour.

As Kenya continues to push for faster delivery on major infrastructure, the move to a 24-hour construction cycle appears to be the new standard for high-volume concrete works.