Effect of Nano-Additives and Polymeric Viscosity-Modifying-Admixtures (VMA) on the Fresh and Hardened Properties of 3D Printable Concrete Mixtures (2021-09)¶

In spite of recent advances in construction digitization and concrete 3D printing, engineering a printable concrete mixture for extrudability and buildability still presents technical challenges. Nano-additives such as nano-silica and nano attapulgite clay are gaining increasing interest for their attributes as rheological modifiers. Recent studies showed some of the potential rheological benefits of these materials, although there is a lack of comprehensive studies in this domain. Polymeric additives, e.g. a cellulose derivative (Viscosity Modifying Admixture) and polycarboxylate ether (superplasticizer), can be combined with the nanomaterials to enhance fresh properties. A comprehensive study is presented which depicted the effect of rheological modifiers on flowability and uniaxial compressive load resisting ability of fresh 3D printable concrete mixtures. A time-based flow table protocol was developed to document the change of flow diameter with time pertaining to the mixtures’ thixotropic behavior. Furthermore, the effect of uniaxial compressive loading on fresh concrete (“apparent green strength”) at different resting intervals from the time ofmixing (i.e. at 30, 60, 90, and 120 min)was investigated. Fresh concrete specimens were subjected to compression and loaded until 40% vertical strain or complete failure, whichever occurred earlier. Based on the apparent stress-strain curves, the effect of resting time on the apparent stress, post-peak behavior and failure mode was analyzed.