This paper focuses on the characterization of setting and hardening of accelerated cementitious matrices by ultrasound propagation velocity, correlating these processes with chemical parameters and the phase evolution obtained by in situ XRD. Evolution of temperature and determination of setting times complemented this analysis. The technique employed provided a continuous monitoring of the setting and hardening of the hydrating matrix and was susceptible to changes in accelerator reactivity and phase composition. Results showed that ettringite formed by accelerator reaction improves the solid-phase interconnectivity and increases initial ultrasound velocity. P-wave propagation during the acceleration period is directly proportional to alite and C3A degrees of hydration. The influence of AFm phases to increase ultrasound velocity is stronger than ettringite and C-S-H. Based on an extensive statistical analysis, multivariate linear regressions were established between ultrasound velocity and the main chemical properties influencing its evolution, leading to a better comprehension of how these parameters are related.

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