Influência da relação água/cimento na precisão de modelos preditivos de absorção capilar em materiais cimentícios

Abstract

The durability of concrete structures is strongly related to the behavior of water inside cementitious materials, with capillary absorption being one of the main mechanisms for fluid transport in their porous matrix. The movement of water in the cementitious matrix is a determining factor in degradation processes, as it influences the penetration of aggressive agents and affects the physical and mechanical properties of the material, contributing significantly to the reduction of durability over time. In this context, the present study aimed to investigate the influence of the water/cement ratio (w/c) on the accuracy of predictive models of capillary absorption in hardened cementitious materials, evaluating the adequacy of different mathematical formulations in relation to experimental data obtained in accordance with standards NBR 9779 (ABNT, 2012) and ASTM C1585 (ASTM, 2013). Test specimens with five different w/c ratios (0.45, 0.48, 0.52, 0.56, and 0.60) were molded and subjected to capillary water absorption testing. Five predictive models available in the literature were adjusted to the experimental results: Single Tangent (M1), Square Root of Time (M2), Fourth Root of Time (M3), Adaptation of the Fourth Root of Time (M4), and Feng & Janssen (M5). The fit of the models was evaluated using the Akaike information criterion (AIC) and root mean square error (RMSE) statistical criteria, allowing for a comparison of the accuracy and representativeness of each model. It was observed that models M1, M2, and M5 presented the best fits to the experimental data in almost all a/c ratios, satisfactorily reproducing the absorption behavior over time and accurately capturing both the initial and stabilization phases. On the other hand, model M3 showed significant limitations, overestimating the experimental values in all w/c ratios, while M4 showed intermediate performance. It is concluded that the a/c ratio has a significant influence on the adjustment of the absorption models, especially due to the variation in porosity and pore connectivity, which alter the absorption rate and regime over time.