Effects of Mixing Variables on Early-Age Characteristics of Portland Cement Systems

The performance and economy of infrastructure system is dependent on the specifications used to construct it. Good specifications contain requirements that correlate with improved performance and/or economy. There are several standards and specifications for mixing field concrete. These documents provide requirements for the mixing process. However, limited research has been performed on how mixing time and number of drum revolutions affect concrete characteristics. With advanced technologies that can delay the set and improve the workability, the current documents may not be applicable. This paper presents an assessment of pastes and mortars mixed for different times and varying number of mixer revolutions. Early-age characteristics include the assessment of time-variant ion concentration in solution, flowability, setting time, and chemical shrinkage. Results indicate that these early-age characteristics of pastes and mortars mixed in the laboratory are influenced by the mixing time and number of mixer revolutions. The rate of dissolution (R-d) of ions in solution and temperature are the material parameters directly affected by the mixing processes and these parameters can alter the rates of hydration reactions, resulting in changes of the early-age characteristics of cement systems. (C) 2016 American Society of Civil Engineers.