Effect of prehydration of Portland cement on the superplasticizer consumption and the impact on the rheological properties and chemical reaction

Efeito da pré-hidratação do cimento Portland no consumo de superplastificante e o impacto nas propriedades reológicas e na reação química

Abstract

The use of pre-hydrated cement in formulation of mortar and concrete is common because there is not always effective control on the cement production, grinding, transportation and subsequent storage. This paper presents a case study on the optimization of admixture for use with prehydrated cement by assessing changes in the rheological properties of Portland cement artificially pre-hydrated. The cement was artificially pre-hydrated by exposure to relative humidity (RHs) of 90%, in an environment of NH₄Cl saturated solution. Additionally, the cement pastes were evaluated with and without superplasticizer. Stepped flow test using a parallel-plate geometry was the method choose to evaluate the rheological behavior, apparent viscosity, yield stress and hysteresis area of each paste at the early age. Oscillatory rheometry was conducted to evaluate the storage modulus (G’), comparing the consolidation with the hydration kinetics obtained by calorimetric evaluation of the same suspensions. Initial rheometer results indicate that the pre-hydrated sample presents lower level of shear stress than the reference sample, because of the higher reactivity of the non-pre-hydrated sample.

Keywords:
Portland cement; prehydration; chemical reaction; rheology; superplasticizer