Wet casting of multiple mix horizontally layered concrete elements

Abstract

Functionally graded concrete, where multiple mixes are layered in structural elements, is a promising technology for minimising cement use. However, a challenge when fabricating weton-wet graded concrete is the control of the fresh state deformations of multiple mixes cast into the same mould. Horizontally cast elements with two different concrete mix layers were investigated to ascertain the influence of mix density, workability and layer sequence on the intended material placement. Horizontal layers were achievable unless the workability of the top layer was much stiffer than that of the bottom, or the top layer was denser and both mixes were fluid. The findings underpin opportunities for the exploitation of lower carbon materials and cement efficiency.

A preliminary study on the development of the normal concrete-UHPC composite beam via wet casting

“…Since the SCM mixture had a much lower viscosity and fresh unit weight compared to the UHPC, it could not resist the weight of UHPC as a separate layer in case a UHPC mixture with a stiff plastic consistency was poured on it. A similar issue was also reported in a previous study [21].…”

Efficient Use of Graphene Oxide in Layered Cement Mortar

“…Studies [ 40 , 41 , 42 ] showed that horizontally layered FGC elements with a short delay time (20–60 min) between the deposition of each concrete mix layer could be fabricated. A slight delay (at least 20 min) enables the base layer to have some degree of a thixotropic structure before receiving the concrete layer on top, ensuring that the ideal hardened layer geometry is achieved [ 29 ]. Andre et al [ 29 ] observed that concerning the expected deviation from a horizontal interface between mixes, the combination of the lower layer mixture (the highest density and the lowest fluidity) and the upper layer mixture (the lowest density and the highest fluidity) is likely the best-case scenario.…”

“…A slight delay (at least 20 min) enables the base layer to have some degree of a thixotropic structure before receiving the concrete layer on top, ensuring that the ideal hardened layer geometry is achieved [ 29 ]. Andre et al [ 29 ] observed that concerning the expected deviation from a horizontal interface between mixes, the combination of the lower layer mixture (the highest density and the lowest fluidity) and the upper layer mixture (the lowest density and the highest fluidity) is likely the best-case scenario. For sample L12T50 in this study, the fluidity of the top layer was significantly higher than that of the bottom layer, which hydrated for 50 min, although the densities of the two layers were almost equal.…”

“…Torelli et al [ 28 ] applied a wet-on-wet process to produce layered cement elements and showed that the relationship between the delay time and layer-to-layer bonding strength is nonlinear. Brault and Lees [ 29 ] found that suitable concrete mix combinations must be achieved to satisfy the intended layer-to-layer geometry of horizontally layered multiple mix elements. It was reported [ 30 ] that an extended delay time negatively impacted the mechanical shear strength of layered self-compacting concrete fabricated by the horizontally sequential casting of two layers.…”

An analysis of the potential for improving cement efficiency through functionally graded concrete elements with durability-driven concrete specification

“…The target slump is 10-30 mm (slump class S1 in EN 206 [7]). This slump value was chosen since the layer stability in fresh-on-fresh cast FGC was found to be favourable for mixes of higher stiffness [25]. Furthermore, it is assumed that workability requirements for all mixes are constant for the study to be comparative (i.e.…”