# Short-Term Deformability of Three-Dimensional Printable EVA-Modified Cementitious Mortars
## 4 Results and Discussion
### Drying Shrinkage  
Drying shrinkage is one of the major causes of cracking in concrete. Once exposed to air, concrete starts to dry out and the dried surface contracts. The internal moisture, however, suppresses shrinkage  
Figure 10: Relationship between the compressive strength and modulus of elasticity.  
in the outer part. Accordingly, the surface regions undergo tensile stresses, and when the stress-induced drying shrinkage exceeds the direct tensile strength of the concrete, cracking occurs.  
One advantage of 3 DCP is that formwork is not necessary. This removes a barrier between the curing concrete and ambient environment. Printed layers often have a greater exposed surface area than cast concrete. However, lower water/cement ratios than those seen in casting concrete are typical in 3 DCP mortars. Hence, the likelihood of cracking resulting from autogenous shrinkage is increased. Therefore, mix designs must minimize dimensional changes due to dry and autogenous shrinkage and greater care should be taken when curing [25].  
In typical cementitious mortar and concrete, the degree of drying shrinkage ranges from \(200\times 10^{-6}\) to \(1200\times 10^{-6}\), depending on the aggregate/cement ratio [26]. Figure 11 presents the drying shrinkage test results for up to 28 days in relation to the EVA/cement ratio. Figure 11a shows the results for up to 24 h, while Figure 11b indicates the results for up to 28 days. Here, the results are presented in two separate figures to make the initial-stage strain caused by drying shrinkage more distinct.  
One hour after placement, autogenous shrinkage was initiated; substantial shrinkage occurred from 4 to 11 h. After demolding, drying shrinkage continued to increase until 28 days. At 28 days, the drying shrinkage was \(331\times 10^{-6}\), \(349\times 10^{-6}\), \(379\times 10^{-6}\), \(418\times 10^{-6}\), and \(461\times 10^{-6}\) when the EVA/cement ratios were 0, 0.05, 0.10, 0.15, and 0.20, respectively, indicating that the shrinkage increased as the EVA/cement ratio increased (see Figure 12). Based on these results, an increased rate was calculated when the EVA/cement ratio of zero was set as a reference. The rates were 5%, 14%, 26%, and 39% when the EVA/cement ratios were 0.05, 0.10, 0.15, and 0.20, respectively. This drying shrinkage development trend was related to an increase in the water/cement ratio from 0.45 to 0.55 with an increase in the EVA/cement ratio, as shown in Table 8. This is considered a disadvantage of the redispersible EVA powder.  
In a previous study by [PERSON] et al. [27], at 28 days and a water/cement ratio of 0.5, the drying shrinkages were 0.0128%, 0.0217%, 0.0222%, and 0.0224% when the EVA/cement ratios were 0, 0.03, 0.05, and 0.08, respectively. When the water/cement ratio was 0.6, the drying shrinkages were 0.0380%, 0.0527%, 0.0538%, and 0.0546% and the EVA/cement ratios were 0, 0.03, 0.05, and 0.08, respectively. This indicates that the drying shrinkage increased as both the EVA/cement ratio and water/cement ratio increased.  
Figure 11: Drying shrinkages for different EVA/cement ratios at (**a**) 24 h and (**b**) 28 days.  
In contrast, in SBR latex-modified cementitious mixtures, drying shrinkage was reported to decrease with an increase in polymer content [19; 24; 28]. Likewise, when modified with latex, cementitious mortar exhibited less drying shrinkage; this is ascribed to the effects of the surfactants and antifoamers contained in the latex [29]. The significant drying shrinkage seen in EVA-modified cementitious mixtures can be significantly reduced by using shrinkage reducing agents such as polyethylene glycol [30] and ethylene [18], but attention must be paid when following this course because adverse effects, such as strength degradation, may occur.