Prof. Dr. Ing. Habil. Janusz Szwabowski
Rheological properties of fresh cement mortars containing new generation superplasticizers
Superplasticizers were developed especially to enhance the placing characteristics of fresh mortars and concretes by increasing workability level at given W/C ratio. Therefore they allow easier placement of fresh mortars and concretes, especially when low W/C is required for strength of durability reason. Addition of superplasticizers cause significant changes in the rheological behaviour of fresh concrete comparing to fresh concrete without admixture, but not only - also other properties of fresh concrete, as setting times, very important from technological point of view can be changed significantly. Thus the complex knowledge of superplasticizers influence on properties of fresh mortars or concretes is the key element in their efficient usage.
In the paper the methodology and test results of an investigation on the influence of chemically different superplasticizers (new generation of superplasticizers for self compacting concrete) on rheological behaviour of modified standard mortars are presented and discussed. Additionally setting times and compressive strength after 2 and 28 days of mortars were tested The rheological parameters of mortars - yield value and plastic viscosity were determined using VISCOMAT PC rheometer, the setting times were tested according PN EN 480-2, the compressive strengths were tested according PN EN 196.
In the research program the influence of following factors were investigated: superplasticizers chemical origin (traditional - SNF /naphthalene sulfonic acid/, PC-A /copolymer of acrylic acid/, PCE /methacrylic polyethylene graft polymer/),superplasticizer content, W/C ratio, cement type (CEM I, CEM II and CEM III). Additionally the influence of elevated temperatures on performance of superplasticizers were measured.
Obtained results generally show very high effectiveness of new generation superplasticizers. On the other hand for some of tested cements disadvantageous effects of superplasticizers were observed as: elevated plastic viscosity and considerable changes in setting times.
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