3D Printing of cementitious materials with superabsorbent polymers

Nowadays, 3D printing of cementitious materials is a hot research topic. In addition to the many advantages of this newly developed technique, the cementitious material should fulfill conflicting requirements in fresh state (i.e. good flowability, high viscosity, controlled setting to benefit the bonding surface and to obtain enough strength,,.) but without compromising on the mechanical performance in hardened state. Apart from these additional requirements, the cementitious material also faces problems inherent to its mix design, indifferent to the procedure and shrinkage is one of the major issues in this case. This phenomenon can induce crack formation and can affect the durability in a negative way. One way to tackle these conflicting requirements is to include superabsorbent polymers (SAPs) in the cementitious material. The addition of these polymers will not only engineer the workability of the mixture but these polymers will also have the ability to absorb part of the mixing water and release it during hardening, inducing interna! curing. Within this research, two different sized SAPs are added to a mixture to investigate the effect on shrinkage and correlate the results with their mechanical performance. First observations showed that the addition of smaller sized SAPs generate the highest reduction in shrinkage, both in X- and Y-direction. Focusing on the mechanical properties, a comparable compressive strength can be observed, indicating that the creation of pores due to the addition of SAPs is compensated by the internal curing effect of the polymers and the generation of a stronger cement matrix. The effect on the interlayer bonding strength is more pronounced. The smaller sized SAPs reduce shrinkage, and consequently also the tensile stresses that occur at the interface resulting in a higher inter-layer bonding strength.