(209m) Evaluating the Effect of Chemical Admixtures on the Rheological Properties of Fresh Cement Paste

Kayello, H., The University of Akron
Visco, D. P. Jr., University of Akron
Biernacki, J., Tennessee Technological University

In the construction industry, the ease with which cement-based systems (concrete) are mixed, placed and consolidated in forms is essential. This is normally referred to as workability, a property that is considered to improve the ease of placement and finishing of cement-based systems. A simple industry standard flow (slump) test has often been an acceptable measure of flow properties since it is a general indicator of flow behavior. Cement paste is defined as a Bingham plastic fluid. In particular, there exists a direct correlation between workability, yield stress, and viscosity of cement mixes. Organic compounds such as lignosulfonates and hydroxylated carboxylic acids (sugar acids) are often used to attain a desired level of workability in cementitious material suspensions. This work aims to measure the effect of eighteen low molecular weight organic chemicals that belong to classes of compounds such as sugars, sugar alcohols, sugar acids, and alcohols on the rheology of cement paste suspensions, the binder in concrete, directly through obtaining yield stress and viscosity data for freshly mixed cement paste by employing a parallel plate rheometer.  A minislump cone test was also performed in compliance with industry standards. Chemical structures are examined and analyzed for their effect on yield stress, plastic viscosity, and workability.  Sugar acids, with one carboxylic functional group, proved to be the most effective at reducing yield stress, viscosity, and at increasing workability. For sugar alcohols, more hydroxyl groups and a longer carbon backbone tend to decrease the plastic viscosity of the paste.