## 1 Introduction  
The construction industry is a major contributor to the global economy, but it has been mainly relying on traditional technologies, although the trend is changing after the digitalization in industry after the 1970s. Based on this, additive manufacturing (AM) has achieved significant progress in the construction industry, bringing innovative approaches to the design and production of building elements. AM is a process to fabricate physical objects directly from computer-aided design models in a layer-by-layer manner [1, 2, 3, 4]. Among the different additive manufacturing techniques that can be used in construction, as shown in Figure 1, selective cement activation is a process of interest in the field of selective particles bed binding. The \"selective particles bed binding\" technique can be divided into two methods [5]. In the so-called \"selective paste intrusion\", a component is fabricated by spreading thin layers of aggregate, followed by the local application of cement paste to achieve hardening [6]. The second method, \"selective cement activation (SCA)\", relates to local hardening obtained by spraying water on a layer of mixed cement and aggregate [7, 8, 9, 10]. This process is composed of two main steps. In the first one, the dry powder is uniformly distributed as a thin layer with the aid of a roller or doctor blade of the required layer thickness. The second step involves the activation of the powder by the liquid phase sprayed through a travelling nozzle. The technique when used for the activation of limestone is called selective limestone activation (SLA). [PERSON] et al. [11] examined the use of water in selective cement activation in two configurations: (a) spraying very small droplets (in the picoliter range) onto the particle bed or (b) jetting water at variable pressure. The strength achieved without post-treatment reaches 15.5 MPa, which classifies the material as lightweight concrete with a bulk density of 1.6 g/cm\({}^{3}\). The authors did observe that higher water-to-cement ratios decrease porosity and increase strength, but reduce shape accuracy. Similarly, larger aggregate particle sizes produced superior strengths with loss of shape accuracy, while higher water jet pressure had insignificant effects on strengths and shape accuracy, but increased porosity and reduced homogeneity. [PERSON] et al. [12] extended the original model based on the Washburn equation for the time-dependent prediction of fluid intrusion into particle beds. Their study indicated that the initial fluid penetration (capillary intrusion) is very rapid and almost spontaneous with no significant influence from the particle size, followed by further capillary action, which is responsible for inter-layer bonding and geometric precision. [PERSON] et al. [13] focused on the behavior of a blended binary cement mixture, consisting of ordinary Portland cement (OPC) and quick-setting cement in binder jetting 3D printing. It was observed that OPC content in the dry mixtures affected the flow properties, with a lower OPC concentration showing better flowability. A higher OPC content enhanced the density of the 3D-printed specimens, together with the mechanical properties. [PERSON] et al. [14] used magnesium oxychloride cement-based material and investigated the interaction of the powder and binder to point out how the binder droplets interact with the powder bed to affect the quality of the printed blocks. The mechanical strength was generally correlated with the volume of cementitious bonds; finer particles provided a larger surface area for bonding, thereby improving the resistance. In another work, [PERSON] et al. [15] focused on the 3D printing of geopolymer-based concrete: metakaolin was selectively activated using an alkaline activated solution and the maximum modulus of rupture obtained was 4.4 MPa. Despite the growing interest in materials obtained by alkali activation, very little research has been focused on the alkali activation of calcium-carbonate-containing compounds like, for example, limestone.