Fractional factorial design to study admixtures used for 3D concrete printing applications

Mortar mix design for 3D printing applications is growing at a fast pace. The array of available materials proposed for such an application creates a lot of opportunities for mix designs. However, it makes the selection between the available options an onerous task to fulfill. The objective of this study is to reduce the material required to assess the importance of admixtures on fresh properties of cement-based mixes. Among the competing objectives required in a mix design for 3D printing applications, the dynamic yield stress and the flow are investigated. The dynamic yield stress of the cement-paste mixtures is measured by a rotary rheometer and the ASTM C1437 flow test is used to measure the spread of the mortar mixes. The spread is correlated with the pumpability of the mixes, whereas the dynamic yield stress indicates the extrudability and the structure deformation of the mixes. The cement used is blended with silica fume. Fine local sand is selected and the admixtures used are a superplasticizer based on synthetic organic polymers, a biopolymer polysaccharide viscosity modifying agent, a nanoclay made of magnesium silicate, crystalline calcium silicate hydrates, and an accelerator with a water-reducing effect. Design of experiments methods are employed. To evaluate the influence of each admixture, the main effects and interactions are measured and the probability plots are graphically illustrating the results. First, an analysis is made on a two-level full factorial design with four factors. The results of the analysis are then compared with a half-fractional factorial design of a resolution IV. A fractional factorial design accurately discriminates the factors and reduce the number of experiments in mortar mix designs for 3D concrete printing applications.