Study on the behavior of the phenolphthalein indicator as a chemical sensor in the cement mortar drying process

Abstract Cement and sand mortar is the main material used for coatings in Brazil. This is due to its low cost, availability of raw materials, and easy application. Determining the drying time is crucial for initiating subsequent stages, such as painting, which can only begin once the material is fully dried. Otherwise, various defects may appear in the substrate-paint interface. In this study, the efficiency of using phenolphthalein to determine the moment when the mortar reaches a dry state was evaluated. Thus, the materials used were characterized through X-ray diffraction and scanning electron microscopy. Furthermore, the workability and compressive strength parameters were determined for the coating without additives (ARG0) and for the material containing phenolphthalein (ARG3). It was found that using the additive at a 3% proportion yielded promising results, indicating the presence of moisture in the material by changing the surface tone of the sample until it dried. Regarding the compressive strength of the material, values of 12.03±1.65 MPa were obtained, making its application viable. Finally, comparing the ARG0 composite with ARG3, there was a reduction of 35 and 28 minutes in the initial and final setting times, respectively. Moreover, the microstructure and crystalline structure showed no changes when comparing both materials.