Operational trials assessing the performance of the different mixes with different weather conditions such as cold and warm weather and wet and dry weather proved essential in understanding the performance of the mixes and planning accordingly for such conditions prior to each individual concrete pour.
A C35/45 air entrained mix to a 50 year design life was required to meet durability requirements with XD3 being the most onerous exposure class. Compressive strengths of greater than C32/40 are uncommon for air entrained mix types. This high strength classification resulted in the cement content being higher than is typically required for barrier mixes.
Control of the workability of the mix proved crucial. Trials were conducted to assess the mix performance. That trials demonstrated that if the mix arrived onsite too wet the placed concrete was prone too slumping resulting in levels being off.
If the mix was too dry the concrete was prone to setting too quickly, with separating and cracking due the high cement content and the use of a straight CEM II mix. The trials resulted in the slipform contractor requiring a mix that slumped onsite at 25mm ±5mm. Such tolerances are extremely tight. As a result of there was a particular focus placed on quality and service.
Every load was checked or tested at the supply plant with additional checks on raw materials also conducted. There was also close communication between the slipform contractor and the batching plant to ensure that each load arrived onsite at just the right time.