Abstract
3D printing concrete technology is advancing rapidly and is considered part of the 4th industrial
revolution, which focuses on using technology to automate processes with more interconnected
systems. 3DP concrete provides the construction industry with certain advantages, such as
increased speed, greater design flexibility for more complex shapes and a smaller labour force is
required. To reduce greenhouse gas emissions, particularly within the construction industry, ecofriendly
and renewable cement replacement materials are being explored. The primary contributor
to carbon emissions in this sector is Portland cement manufacturing. Additionally, cement
extenders aim to reduce costs, ensuring a viable construction industry for future demands with
limited resources. Some studies have suggested using agricultural waste, such as sugarcane
bagasse ash (SCBA) and corn cob ash (CCA), as cement extenders in mortar mixtures. SCBA is a
byproduct of sugar refineries, where sugarcane bagasse is burned for heat generation during
refining. Similarly, CCA is derived from the combustion of corn cobs, typically used for heat
generation. This study explored the influence of SCBA and CCA, produced in South Africa, on
the properties of mortar mixtures. Mortars were prepared with varying proportions of SCBA and
CCA, ranging from 0% to 40%, as cement extenders while maintaining a constant water-to-binder
ratio (w/b) of 0.45. Fresh mixtures were assessed for workability and setting time, and 50 mm
cubes were cast for compressive strength testing at 7 and 28 days. A microstructural analysis of
hardened mortars was also performed using scanning electron microscopy (SEM). The results
indicated that the inclusion of CCA caused a notable reduction in the workability of fresh mixtures,
whereas the impact of SCBA on workability was minimal. Similarly, CCA significantly reduced
the compressive strength of mortars, while the strength loss associated with SCBA was
considerably lower. Regarding setting time, SCBA and CCA demonstrated contrasting effects:
increasing SCBA content led to prolonged setting times, whereas CCA reduced the setting time of
the mixtures. At an optimal SCBA replacement level of 20%, the mortars achieved a 28-day
compressive strength of 66 MPa, a workability value of 179 mm, and initial/final setting times of
213 minutes and 330 minutes, respectively. By examining the values obtained based on a
preselected 3DP mortar mix design, a more optimised 3DP orientated mortar mix design could be
obtained with 20% SCBA and 8% accelerator resulted in a 1-day compressive strength value of
13.7 MPa and a 28-day compressive strength value of 49.9 MPa. The drying shrinkage results of...