Correct Placing of Fresh Concrete

Concrete Pouring

• Firstly, it’s important to check if all concrete characteristics on site are according to the relevant standards and additional requirements. Workability of the concrete should be sufficient in order to ensure easy and safe placing as well as subsequent vibrating and finishing.
• If possible, the concrete should not be poured diagonally against vertical formwork to prevent localized abrasion of the release film. The pour should be kept away from the form as much as possible by using tremie pipes.
• Avoid great falling heights especially with fair-faced and self-compacting concrete to prevent segregation and achieve uniform concrete surface appearance.
• If pouring a second layer, the joint between the two concrete parts has to have sufficient roughness to ensure bonding between the hardened and the fresh concrete. This can be achieved by surface retardation of the first pour leading to an exposed aggregates surface in the joint, which can be achieved with Sika® Rugasol®.
• If a subsequent concrete pour is going to be installed after hardening of the previous pour, the joint between the two concrete parts has to have sufficient roughness in order ensure bonding between the hardened and the fresh concrete. This can be achieved by surface retardation of the first pour leading to an exposed aggregates surface in the joint. When concreting the subsequently fresh concrete against such rough joint required bond is ensured. Surface retardation can be achieved with Sika® Rugasol®.

Vibration

• Correct compaction of the concrete is a vital step, because only with correct execution it is possible to obtain the target air void content and therefore the required hardened concrete properties.
• Internal vibration should be carried out with a vibration poker which needs to be immersed quickly to the bottom of the concrete layer and then reversed in one go slowly back over the entire concrete layer. Excessive vibration can have a negative impact on the homogeneity of the fresh concrete.
• Make sure that the poker vibrators do not come too close to the formwork skin or touch it. If they do, they exert high mechanical stress on the form surface, which can result in abrasion of the release agent and later to localized adhesion of the concrete.

Finishing

• Finishing characteristics of the fresh concrete can be influenced by superplasticizer technology in particular – especially application of suitable superplasticizers based on polycarboxylate-ether (PCE) which can significantly influence the finishing characteristics of fresh concrete. In addition, finishing aids like SikaFilm® can be especially useful.
• Timing plays a critical factor regarding finishing and it’s important to evaluate the correct timing, especially when finishing industrial floors with power floats, for example