Understanding the Effectiveness of Polycarboxylates as Grinding Aids

Abstract

Over recent years, polycarboxylate superplasticizers have found their way into grinding aids used in cement production to reduce the electrical energy consumption. The effectiveness of these large molecules challenges the pre-existing theories concerning the factors that govern the performance of grinding aids. This paper reports on molecular dynamics simulations to examine a physical property believed to control the effective¬ness of grinding aids, namely their adsorption energy. The molecules selected are TIPA (Triisopropanol amine), TEA (Triethanol amine) and glycerine. The surfaces examined are dry and hydroxylated C3S surfaces, which are believed to be more representative of reality, since some humidity is always present during the grinding. Detailed results of this part of the work show that glycerine interacts relatively more with dry as well as hydroxylated surfaces of C3S both at 25°C, ambient temperature and 110°C, grinding temperature with respect to TIPA and TEA. These result help to better understand the specific interaction of these molecules with cement surfaces. In the second part of this work oligomers of some PCE superplasticizers are examined with similar numerical tools on dry and hydroxylated surfaces of C3S. Results for different types of these oligomers, together with the previous results, shed light onto the reasons why polycarboxylate superplasticizers have found to also be effective grinding aids in cement production.