Ultrathin staircase: a challenging UHPC application - part 2

The previous blog described the challenging ultra high performance concrete staircase project. The ultimate goal of the UHPC staircase is to realise a unique concrete staircase. This blog will keep you informed of the progress on the ultrathin staircase.

The first trial in which concrete was poured into the formwork for the ultrathin concrete staircase did not go too smoothly. See previous blog. To resolve the problems, these were analysed in further detail. From this analysis it appeared that the reinforcement and the steel fibres were blocking the flow of the mortar. Also, UHPC is very sticky, which causes air in a closed form to become trapped. Ventilation is a lot easier with normal concrete and air will flow through the mortar to the pouring side. In short, the analysis demonstrated that the above occurs less or not at all with UHPC.

Through further analysis of the problem and understanding the mechanism, several techniques were devised. The supplier was consulted on how best to implement the adjustments. The results are as follows:

• A special ventilation technique was applied to remove the accumulation of air during pouring of the concrete.
• The design of the reinforcement was adjusted to create some form of flow paths. The flow paths enable the concrete to flow everywhere in the mould and the air is simply expelled.
• Special compaction techniques were used.
• It was also considered whether the concrete mixture could still be adapted.

We put it to the test again. The result has considerably improved: 

Following this, the supplier further enhanced the pouring procedure and the compaction technique has improved. This result is almost perfect: