Developing Mix Proportions for Class C Fly Ash-Based Alkali-Activated 3D-Printed Concrete Mixtures

Abstract

This study investigated the use of class C fly ash (FA) as a precursor for alkali-activated mortar (AAM) for 3D-printed concrete (3DPC). AAMs with different water-to-FA (W/FA), alkaline activator-to-FA (Alk/FA), and sodium silicate-to-sodium hydroxide (SS/SH) ratios were examined to develop mixtures that can be tailored for different structural applications of 3DPC. The fresh properties, including extrudability and buildability, were evaluated through the open time (OT) and immediate deformation tests, respectively. Different cycle times (CTs) were applied to achieve a strain limit state necessary to maintain the printed shape. The strength of AAMs in different directions at different CTs was examined. Scanning electron microscopy (SEM) was carried out on AAM specimens having different CTs for a better understanding of the bond area. OTs ranging from 2.5 min to 31 min and axial strains ranging from 0.17% to 11.2% were achieved depending on the proportions of the AAMs and CT, which offers flexibility in optimizing the speed of printing and strength of concrete for different projects. The 3DPC specimens displayed anisotropic behavior compared with full-height specimens, where the compressive strength of full-height specimens was higher by 0.2% to 18% and 0.9% to 28% than 3DPC specimens when tested parallel and normal to the printing directions, respectively. SEM images and line scan indicated an approximately even intensity of the element concentration at the interfacial zones of AAMs having short CTs, which explained the relatively high compressive strength of those specimens. For AAMs having long CTs, there was a significant change in the intensity of the element concentration at the interfacial bond zone, and voids were observed resulting in low compressive strength of those specimens.

3D Printing of Fiber-Reinforced Calcined Clay-Limestone-Based Cementitious Materials: From Mixture Design to Printability Evaluation

“…The immediate axial deformation test was used to evaluate the shape stability proposed by [26]. The test measured the axial strain of a 700 g fiber-reinforced mortar filled within a 15 mm thick ring plate subjected to incremental loads representing the applied weight of the added layers at different time intervals during 3DP.…”

On the possibility of using waste disposable gloves as recycled fibers in sustainable 3D concrete printing using different additives

“…To determine the mixture's workability, the spread diameter was measured by the flow table test based on ASTM C1437 44 . Also, a shape stability test was performed to check the mixture buildability, which was recommended by the literature 42 , 45 – 47 . This test evaluates the instant axial deformation of the fresh mixture under progressively increasing axial loading loads (by applying weights).…”

Effects of Rest Time and Curing Regime on Short- and Long-Term Strength of Class C Fly Ash-Based Alkali-Activated Mortars

“…The literature lacks consensus on the optimal rest time for AAC (alkali-activated concrete) and whether longer rest times enhance its strength. Previous studies have used varying rest periods ranging from zero to 24 h [6,[10][11][12][13][14][15][16] with no consistent pattern. Moreover, there is a scarcity of studies exploring the optimization of the rest time specifically for alkali-activated class C FA (AACFA).…”