## 1 Introduction  
Some geopolymers are materials and products with satisfactory physicochemical, mechanical, and thermal properties for construction in general. Therefore, they have great potential to be a sustainable alternative to Portland cement. Properties such as good adhesion to other materials such as steel, glass, ceramics, fresh concrete and old substrates, high compressive and abrasion resistance, low shrinkage and thermal conductivity, fast and controlled curing, high acid resistance, high pH to protect reinforcement, reduced emission of pollutants, and good fire resistance have shown the good performance of geopolymer materials in construction [1, 2, 3, 4, 5]. In this context, the metakaolin-based geopolymer is one of the alternatives. Metakaolin is a kaolinite clay of high fineness and reactivity. When it is calcined, a process that allows almost complete dehydroxylation of the raw material, it becomes an amorphous and irreversible phase with pozzolanic properties. When this amorphous metakaolin is subjected to the geopolymerization process (alkaline activation), the geopolymer is formed [6]. Geopolymerization consists of an exothermic chemical reaction between an aqueous solution of high alkalinity, called an activator, and materials of geopolymer origin composed of minerals such as silica and alumina, resulting in polymers with polysialate-like bonds. The quality of the geopolymer depends essentially on the type of starting material [7]. Several works on geopolymerization have been developed in the laboratory of DECFUC. Some are related to structural applications [8], others to the development of geopolymerized material [9]. Other work has been related to the evaluation of the resistance of geopolymers [10; 11; 12; 13] and the modulus of elasticity of concrete in different situations [14; 15]. For example, [PERSON] [10] demonstrated that the mechanical properties of metakaolin-based geopolymers remained practically constant from the 14 th day of maturity of the samples. It was also found that the activator was more effective between a ratio of 1:1.75 and 1:2 (hydroxide:silicate), and achieved better resistance, although the maximum value of the elastic modulus was just outside this range. [PERSON] [11] analyzed the effect of curing temperature of geopolymer blends composed of two types of metakaolin: white \"MetaMAX(r) HRM\" and brown \"ARGECO\". He concluded that curing temperatures above 30 \({}^{\circ}\)C led to a loss of the resistant properties. [PERSON] [12], analyzing the influence of the percentage of metakaolin in the mixture and also the change in the composition of aggregates with granulometric variations, to evaluate their effects on tensile and compressive strength, concluded that the amount of binder is not a fundamental parameter to improve the resistance of geopolymers. In turn, changing the composition of the aggregates in the mixes did not provide conclusive results. The authors have already performed some tests on geopolymer-reinforced beams [8] and they found that it would be very important to study the basic mechanical characteristics of the material, such as, the shrinkage in fly ash-based geopolymers. Regarding the modulus of elasticity of metakaolin-based geopolymers, the authors did not find any work that indicates the time evolution of this parameter. Knowledge of this mechanical characteristic of the material is fundamental, not only for structural analysis. Working in the context of the finite element method and also verifying the safety conditions of structures in relation to deformation can be mentioned as examples of this. This article presents some of the findings that would be very useful for the structural design of structural members. The way in which the strength rises over time and the necessary curing time are also 2 important features to analyze. In this regard, the following must be said. In the bibliography it is possible to find several works on the mechanical characteristics of concrete, including the modulus of elasticity.