Fresh State Stability of Multi-Mix Elements
Functionally graded concrete is a promising technology for minimising cement use. However, one challenge when fabricating graded concrete is the control of the fresh state deformations of multiple mixes cast into the same mould. This applies not only to horizontally cast elements, where different concrete mixes are placed in layers, and also to vertically cast elements, where different concrete mixes are placed side-by-side. Our research seeks to identify acceptable differentials between mixes to ensure that the placement of material is as intended. To date, the rheology, maufacturing process and density have been found to be significant.
Early Age Concrete Properties and Manufacturing Implications
When functionally graded concrete members are fabricated multiple mixes are cast into a mould and interlayer zones with different properties are introduced. These areas are susceptible to the formation of a potential weak zone and/or excessive intermixing if the adjacent materials are not compatible. An appropriate combination of concretes and casting processes for multi-layered members can minimise or avoid these risks. A deep understanding of the early age properties of concretes (setting behaviour and strength development) is therefore crucial for the successful production of multi-layer members.
The setting of concrete describes the limit of handling and beginning of strength development and is typically evaluated using standardised tests on cement pastes or mortars. However, a method to directly measure the setting on concrete is lacking. Ultrasonic pulse velocity (UPV) techniques are being investigated as a means of monitoring the setting processes and strength development. UPV techniques are powerful since they can be applied not only to cement pastes and mortars but also to concretes. Therefore, UPV measurements may be a valuable tool to deeply investigate the early age behaviour directly on single or multi-layer concrete mixtures. As such, UPV measurement techniques are being applied to single and layered concrete compositions with the aim of establishing tools to assess the compatibility of concrete mixtures and to avoid weak interlayer zones.
Publications
| Brault A, Lees JM. (2020) Wet casting of multiple mix horizontally layered concrete elements. Construction and Building Materials, 247, 118514. https://doi.org/10.1016/j.conbuildmat.2020.118514 |
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Torelli G, Giménez Fernández M, Lees JM. (2020) Functionally graded concrete: Design objectives, production techniques and analysis methods for layered and continuously graded elements. Construction and Building Materials, 242, 118040. https://doi.org/10.1016/j.conbuildmat.2020.118040 |
| Torelli G, Lees JM. (2019) Fresh state stability of vertical layers of concrete. Cement and Concrete Research, 120, 227-243. https://doi.org/10.1016/j.cemconres.2019.03.006 |
