Innovative Concrete to Achieve Special Finish | Roadstone
Dublin City University
Services (Technical Disciplines):
Design of architectural concrete mix.
Project Objectives/ Outcomes:
Opened in late 2018 the open auditorium of DCU’s “U” Building forms the center piece of this state-of-the-art student facility. The design of the auditorium required that all primary structural elements be exposed with a ‘special finish’ to EN 13670:2009 Execution of concrete structures specified for the concrete elements. This special finish placed numerous requirements on the concrete beyond what would be typically expected including:
- A light colour
- Consistency of colour
- Minimal blemishes
- “DCU SU” embossed lettering
To aid in achieving uniformity of colour and finish Roadstone tested the consistency of each load of concrete prior to dispatch to site and maintained close communication with site engineers for the duration of the project.
Completed in separate pours over a six-month period, over 20 loads of architectural concrete were supplied to DCU Hub. As well as meeting the demands of an architectural finish the concrete also met structural and durability requirements.
An architectural concrete was required to achieve the special finish and the specific design team requirements for the concrete used in the central auditorium.
The design of the architectural concrete mix required a slightly different approach to that of conventional concrete mixes, with particular attention placed on the mix proportions of the cements and aggregates. A relatively high cement content was required with the proportion of sand in the mix not being twice that of the cement content.
In addition, a single sized 20mm coarse aggregate was used. Designing the mix in this manner resulted in a gap graded mix and allowed for the finer materials in the mix to migrate to the formwork surface following placement and compaction, producing a high-quality finish with minimal blemishes.
Sample panels were poured to assess the performance of the architectural concrete mix and the workmanship required to achieve a high-quality finish prior to pours commencing. This allowed for an assessment of a variety of criteria and their impact on the quality of the concrete finish.
This aided the concrete contractor, site engineers and Roadstone concrete technologists in understanding the impact of workmanship and the concrete mix on the concrete finish. The criteria included:
- Type of formwork
- Grout-tight formwork joints
- The release agent and its application
- The method and rate of placement of the concrete
- The suitability and consistency of the concrete mix
- The compaction plan
- The most suitable time at which to strike the formwork
Geoscience Ireland Contact:
Diarmuid McCarty (firstname.lastname@example.org)