# Cost-Effective Temperature Sensor for Monitoring the Setting Time of Concrete
## 4 Discussion  
Within the scope of this study, one of the primary objectives is to validate the capability of the employed sensors to withstand the curing conditions of concrete over an extended duration, ensuring successful monitoring of concrete specimens. During the temperature monitoring of the concrete specimens, it has been observed that the sensors used have correctly recorded the temperature up to the breaking age of 180 days. This shows that the sensors used are sufficiently resistant to water and concrete components for proper operation. Furthermore, the aim is to verify the proper measurement of curing temperature, analyze the obtained results, and compare them across the various materials under investigation. Type II cement samples without zeolite additions have obtained higher maximum temperature values during hydration than the rest of the samples. A high temperature in the early stages of hydration is associated with higher early resistance values, while concretes with lower hydration temperatures reach higher strengths at older ages [20]. This fact is consistent with research on cements with additions of pozzolanic materials, in which it is observed that maximum strengths are reached at later ages compared to reference cements [37; 38]. If we compare the results obtained in the compressive strength test, we can see that the short-term strength of concrete specimens with additions is indeed lower than the strength of the reference cement. Pozzolanic materials give concrete remarkable performance in hot climates where the negative effect of temperature is partly reduced by the pozzolanic reaction, its weak heat of hydration, and its high activation energies [39]. As the temperature conditions in which the specimens were made were low, the contribution of zeolites may not be as significant as in hot climates, since pozzolanic materials help to improve the performance of mortars and the resistance of concrete when exposed to higher-than-normal temperatures, particularly in the range of 35-50 \({}^{\circ}\)C [40]. Therefore, climatic conditions should be considered a relevant parameter when selecting the most suitable materials to plan their use. It is important to note that the temperatures obtained by the specimens do not exceed 50 \({}^{\circ}\)C in any of the cases, a value at which hydration problems begin to occur due to the formation of heterogeneously distributed hydrates, leading to the formation of larger pores [17], a denser C-S-H, and a more equidistant morphology of the ettrinigite [41]. Figure 15: Compressive strength results at 28 and 180 days. In the comparison of the results obtained in the monitoring of the four specimens at 180 days, it can be observed that, except for the initial periods, the values coincide in both tests for the coexistence period. This provides us with two conclusions; on the one hand, that it is indeed in the initial curing periods that most exothermic hydration reactions occur, and on the other hand, that the variations at later ages correspond to external factors (curing water temperature and ambient temperature) and not to intrinsic processes of cement curing. If we compare the compressive strength test results and the temperatures obtained, it can be observed that the concrete sample without zeolite additions is the one that obtains the highest value of early compressive strength and, in addition, it is the one that demonstrates the greatest increase in long-term strength. This sample corresponds to the one with the highest temperature in the first hours of curing. This temperature can be related to a greater number of hydration reactions and therefore greater resistance. Sample 2, which is the second sample with the highest hydration temperature, is the one with the lowest resistance, so it could be said that in the case of samples containing zeolite, no correlation has been found between the temperature in the first hours of curing and the resistances obtained.