## 4 Conclusions  
The main objective of this work was to characterize the time evolution of the modulus of elasticity of 3 metakaolin-based geopolymers. For this purpose, since it is impracticable to follow the indications of standard EN 12390-13 [30], they were adapted to this work. Furthermore, an attempt was made to evaluate the impact of improved aggregate composition on the geopolymer mechanical resistance.  
Having completed this exploratory work, it is possible to draw some important conclusions, summarized below.  
Firstly, it was possible to show that improving the compactness of the mixtures did not significantly increase (less than 10%) the strengths of the geopolymers. It even decreased in the compression and in the modulus of elasticity test.  
With regard to the modulus of elasticity, the conservative use of only 1 specimen is sufficient to lead to realistic results.  
The second conclusion drawn from the work deals with the test load rate. It has been shown that the modulus of elasticity is not dependent on this parameter, at least up to values specified in the test standard for concrete.  
Figure 14: Daily evolution of the modulus of elasticity.  
It was also concluded that the time-based evolution of the modulus of elasticity of metakaolin-based geopolymers, cured at room temperature, ends at around 420 h of curing. This trend is nearing a polynomial line of the 2 nd degree. And the modulus of elasticity oscillates around 18 GPa. This value is consistent with the results obtained by [PERSON] et al. [20] (~16 GPa at 28 days) and [PERSON] et al. [21] (21 GPa at 28 days).  
So, the geopolymer has a lower modulus of elasticity than concrete, leading to ~70% greater strain for the same stress level from a mechanical perspective. However, it is important to add that this is only the instantaneous deformation. As it is well known, the deformation of concrete (in the long term) must include the long-term phenomena of creep and shrinkage [33]. Regarding the metakaolin-based geopolymer, the impacts of long-term phenomena on deformation are unknown. In the case of concrete, the long-term deformation can be several times greater than the instantaneous deformation.  
In the rupture tests of the samples, strains of about 1.7% were recorded at the time of the maximum compressive stresses. In addition, the secant modulus values at 60% and 80% of maximum stress do not differ by more than 12% from the equivalent value at 40% of the maximum stresses.  
Considering the deformation of the material, equivalent to the 28 th day of an OPC-based concrete, one can conclude that the maturity of metakaolin-based geopolymers is reached around day 15 or 16 of curing.  
All authors were involved in all parts of the work, but with different weights, as described next. For conceptualization, methodology, analysis and writing: A.L., S.L. and M.F. Experimental work and computing of data: A.L. and M.F. Final editing: A.L. All authors have read and agreed to the published version of the manuscript.  
This research was sponsored by FEDER funds through the program COMPETE--Programa Operacional Factores de Competitividade--and by national funds through FCT--Fundacao para a Ciencia e a Tecnologia--, under the project UIDB/00285/2020.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. Data evaluated in laboratory tests belong to the authors and to the University of Coimbra and are not publicly available.  
The authors would like to express their gratitude to the students [PERSON], [PERSON], [PERSON] and [PERSON] who have also collaborated in this investigation.  
The authors declare no conflict of interest.