12. Kolloquium und Workshop über „Rheologische Messungen an mineralischen Baustoffen“ 12. und 13.März 2003 in Regensburg Testing compatibility of cement - superplasticizer system Jacek Gołaszewski, Janusz Szwabowski Silesian University of Technology, Gliwice, Poland

Introduction zThe main trend in concrete technology is to produce concrete of high strength, durability and reliability. zProduction of such a concrete cause technological problems. zThese problems are a result of conflict between requires high workability (high W/C) and requires high strength and durability (low W/C).

Introduction zSuperplasticizers make possible to solve this conflict - its addition allow to obtain required workability of low W/C fresh concrete. zThe key element in efficient workability shaping is to find out cement superplasticizer compatible system and the complex knowledge on rheological effects of superplasticizer addition.

Introduction zIn the paper methodology of testing of superplasticizer performance using workability two point test is presented and some effects of cement composition on rheological properties of superplasticized mortars are discussed.

Workability - traditional approach zWorkability is a physical property of fresh concrete alone and define its ability on applied methods of transport, placing and compacting without segregation

Workability - rheological approach zThe definition of workability in concrete technology should be considered in terms of the state of the system.

Workability - rheological approach zThis state is determined by the relationship between two factors: (1) the rheological properties of given mix and (2) the forces acting on it during processing.

Workability - rheological approach zTherefore, concrete mix workability is determined by the reaction of the mix to the forces acting on it during transport and mechanical processing as the resistance of its structure to these forces.

Workability - rheological approach zRequired workability can be achieved: (1) to the given method and conditions of concrete processing rheological properties of concrete mix are adjusted or (2) to given rheological properties of concrete mix method and conditions of concrete processing are adjusted.

Rheological model of fresh concrete zFresh concrete (and also fresh mortars), behaves as bingham body, whose properties can be expressed by the two fundamental rheological parameters, the yield stress and the plastic viscosity according the formula: where  (Pa) is the shear stress at shear rate (1/s)  o (Pa) is the yield value  (Pas) is the plastic viscosity. zThe physical interpretation of yield value is that of the stress needed to be applied to a material in order to start flowing. When the shear stress is higher then the yield value the mix flows and its flow resistance depends on plastic viscosity.

Factors influencing rheological properties of fresh concrete - key role of superplasticizer

Testing of superplasticizer performance zThe key elements in efficient workability shaping using superplasticizers are: yto find out the compatible cement - superplasticizer system; yto know how addition of superplasticizer influences the rheological properties of fresh concrete in different technological conditions.

Conventional vs. Rheometrical workability tests CONVENTIONAL WORKABILITY TESTS zconventionality – simulate only specific methods of concreting; zphysically ambiguous – there is no correlation between results of measurements and rheological parameters of concrete mix; zlimited measurement range - (slump test, Marsh cone test) - one point measurement; zambiguous measurements - the results of measurement of mixes of different rheological parameters can be the same RHEOMETRICAL WORKABILITY TEST zunequivocal – measurements basing on physical principles; zphysically unequivocal – measurements results expressed in physical units; zfull measurement range - two point measurement; zunequivocal measurements results – makes possible physical and statistical analysis and computer simulation of fresh concrete behaviour during concreting process.

Rheometrical Workability Test zMeasurement of shear resistance of fresh concrete mix in function of time in order to determine rheological parameters of mix and changes of these parameters in respect to technological factors (mix composition, time, temperature).

Rheometrical workability test zRheological parameters of fresh concrete are measured by applying a given shear rate (rotation rate N of paddle or probe) and the measuring the resulting shear stress (torque T). The rheological parameters are determined by regression analysis according to the relation: T = g + N h where g constant corresponding to yield value  o h constant corresponding to plastic viscosity .

Rheometrical workability test - what kind of mix to be used? Cement paste - most popular in testing cement - SP compatibility, easy to manage but due differences between rheology of cement paste and fresh concrete mix and problems with proper interpretation of results gives ambiguous information on influence of superplasticizer on rheological parameters. Fresh concrete - difficult to manage (due cost of apparatus and material and labour consumption), due changeable grading of aggregate proper interpretation of superplasticizer performance is difficult. Fresh mortar - model of concrete, using CEN model sand effect of changeable aggregate grading can be eliminated, easy to manage, makes possible to chose compatible cement - SP system and gives qualitative information of superplasticizer performance useful for workability shaping.

Rheometrical workability test Testing procedure and example of measurement

Effect of cement composition on rheological properties of mortars zIn the research following factors were investigated:  mineral and chemical composition of cement  C 3 A 2%; 7%; 12%;  Na 2 O eq 0,3%; 0,7%; 1,1%;  SO 3 2,5%; 3,0%; 3,5%  cement specific surface 320; 370; 420 m 2 /kg  SP type6 SPSNF, SMF, PC, PE1, PE2, PE3  W/C ratio 0,55; 0,45;  SP dosage1%; 2% i 3% m. C zMortars were prepared and tested according PN EN 196-1:1996 and PN EN 934-2:1999.

Effect of cement specific surface and composition on rheological properties of mortars W/C=0,55

Effect of cement specific surface and composition on rheological properties of mortars W/C=0,55; SP PE1; 1%

Effect of cement specific surface and composition on rheological properties of mortars W/C=0,45; SP PE1; 3%

Effect of cement composition on rate of changes of rheological parameters of mortars in time W/C=0,55; W/C= 0,55; SP PE1; 1%; W/C=0,45; SP PE1; 3%

Effect of cement composition on rheological properties of mortars W/C=0,55; SP PE1 1%; SP SNF 2%; SP SMF 2%

Effect of cement composition on rheological properties of mortars W/C=0,45; SP PE2 2%; SP PE3 2%; SP PC 2% (after 10 min)

Effect of cement composition on rheological properties of mortars W/C=0,45; SP PE2 2%; SP PE3 2%; SP PC 2% (after 60 min)

Summary zThrough the investigation with RWT it is possible to precisely determine the influence of superplasticizers on the rheological properties of mortars. On the ground of this it is possible to choose compatible cement - superplasticizer system and optimise the composition of mortar and concrete from workability point of view. zThe type, chemical and phase composition of the cement are the decisive factors for the performance of superplasticizers. General relationships between cement properties and rheological parameters of no- and superplasticized mortars are discussed in paper. zTesting properties of mortars using RWT it is possible to recognise how other admixtures and additives as: air entraining agents, accelerators, retarders, silica fume, fly ashes, slags affecting rheological properties of fresh concretes in different technological conditions.