The influence of cement paste volume in mortar on the rheological effects of the addition of superplasticizer Jacek Gołaszewski Silesian University of Technology

Introduction The effects of SP on rheology of cement mixtures depend on cement and SP properties, SP content, time of SP addition, and on w/c. The relations of influence of SP on rheological properties of cement mixtures not always are unequivocal. Ambiguous effects of SP may be caused by different cement paste content in cement mixtures

Introduction The main objective of investigation was to explore the influence of SP content on the rheological parameters of different in cement paste volume fresh mortars.

Testing program Factor  m/ p SP content 1, 1.5, 2, , 1, 1,5, 2, , 1, 1,5, 2 2, 2.5, 3, 3.5  m/p - factor of uncompacted sand filling by cement paste. w/c 0.35

Testing program Factor  m/ p 2.22 – – – – 4.78 w/c 0.47, 0.50, 0.53, 0.56  m/p - factor of uncompacted sand filling by cement paste. 0.50, 0.53, , 0.47, 0.50, 0.53

Fresh cement mixtures exhibit the Bingham viscoplastic behaviour  - shear stress  - shear rate  o - yield value  pl - plastic viscosity Testing method. 1

Viskomat PC rheometer T = g + N h g – parameter corresponding to yield value h – parameter corresponding to plastic viscosity M – shear resistance N – rotation rate Start of measurement - speed 120 rev/min held for 3 min. Measurement of T at N = /min. Testing method

Influence of  m/p and SP content on yield value g

Influence of  m/p and SP content on plastic viscosity h

Mathematical relations of influence of SP content on g & h g = A g  SP Bg where: SP - superplasticizer content; A g, B g, A h, B h, C h - material constants depending mainly of cement paste volume in mortar and sand graining (factor  m/p ), of properties of cement and SP, and of time. h = A h  SP 2 + B h  SP + C h

Influence of  m/p and w/c on g & h

Effect of SP contentEffect of w/c Influence of  m/p, w/c and SP on g & h – comparison of results

Conclusions Effects of superplasticizer addition on rheology of fresh mortar and concrete should be considered in respect to cement paste volume. It is difficult to unequivocally predict effects of superplasticizer on rheology of mortar or fresh concrete and its changes with time basing on tests made on cement paste.

Conclusions The influence of increasing superplasticizer content and increasing w/c on yield value of mortars is similar. In the same time such influence on plastic viscosity may be distinctly different. It is difficult to set out such composition of mortars without and with superplasticizer that for similar yield value will be characterised by the same plastic viscosity.