Influence of mixing intensity on the hardening of cement suspensions in two-stage mixing processes

Transcription

1 Institut für Angewandte Bauforschung Weimar gemeinnützige GmbH Influence of mixing intensity on the hardening of cement suspensions in two-stage mixing processes Dipl.-Ing. Mirko Landmann Dr.-Ing. Ulrich Palzer Kolloquium Rheologische Messungen an mineralischen Baustoffen in Regensburg

2 Motivation 2

3 Project Presentation of R&D project: Werkstofforientierte und simulationsbasierte Untersuchungen zum Dispergieren feindisperser, hydraulisch erhärtender Partikelgemenge unter Variation der maschinenund werkzeugspezifischen Einflussgrößen verschiedener Mischertechnologien als Basis für zukünftige Maschinenentwicklungen und Werkstoffoptimierungen Project management: EURONORM, market-oriented research for external industrial research institutions Reg.-No.: MF Short title: Inno-MiTec Project time: April 2014 to September

4 R&D Project Activities: Experimental works Variation of material composition Variation of operational factors Mixing and order of addition Rotational speed, mixing time and filling level Simulation-based investigations Investigations on hydration kinetics (two-step mixing) Object of this presentation 4

5 (depends on mixing process and mixer type) Input kinetic energy Mixing intensity and primary influencing factors Mixing intensity Mixing time [Sec.] mm Paste 24.0 C 5.0 Vol.-% 330 mm Paste 22.5 C 0.1 Vol.-% (365 mm) Paste 24.5 C 0 Vol.-% 320 mm Paste 72.0 C 0.2 Vol.-% 5

6 (depends on mixing process and mixer type) Input kinetic energy Mixing intensity and primary influencing factors Mixing intensity Mixing time [Sec.]

7 Influencing factors macroscopic Effects during mixing microscopic Homogenization Dispersion Attrition macroscopic and microscopic distributive factor dispersive factor Isotropic qualities Mixing quality disaggregation, wetting and stabilization, liquefaction Influence on setting/hardening + rheology Particle breakage Shear and impact Abrasion Surface comminution through attrition + Mixing temperature 7

8 Temperature [ C] Dynamic elastic modulus [GPa] Two-stage mixing of cement paste increasing mixing intensity (mixing time) Time [h] Development of dynamic E-Modulus on mortar samples (with PCE) Time [h] Mean sample temperature at 20 C in climate chamber (with PCE) 0 Sec. 60 Sec. 120 Sec. 300 Sec. 900 Sec. Suspension mixing time 8

9 Temperature [ C] Dynamic elastic modulus [GPa] Two-stage mixing of cement paste increasing mixing intensity (mixing time) shorter induction period accelerated CSH growth Time [h] Time [h] Development of dynamic E-Modulus on mortar samples (with PCE) Mean sample temperature at 20 C in climate chamber (with PCE) 0 Sec. 60 Sec. 120 Sec. 300 Sec. 900 Sec. Suspension mixing time 9

10 Temperature [ C] Final setting time [h] Dynamic elastic modulus [GPa] Final setting times increasing mixing intensity (mixing time) shorter induction period accelerated CSH growth Time [h] Time [h] Suspensionsmischzeit Suspension mixing time [Sec] Reduction of final setting time after short intensive mixing time Other samples show similar trend 10

11 Electron microscopy Shock freezed samples in NanoSEM (Bauhaus University Weimar, FIB) Suspension mixing time 0 Sec. Suspension mixing time 120 Sec. Suspension mixing time 900 Sec x 1000 x 1000 x 8000 x 8000 x 8000 x 11

12 Potential energy Electron microscopy Shock freezed samples in NanoSEM (Bauhaus University Weimar, FIB) Suspension mixing time 900 Sec x Quelle: Barrett E. Rabinow: Nanosuspensions in drug delivery Nature Reviews Drug Discovery 3, (September 2004) 8000 x 12

13 Electron microscopy Sublimated samples Suspension mixing time 0 Sec. Suspension mixing time 900 Sec x 1000 x Microattrition Abrasion of first products Ettringite (30 32 H 2 O-Molecules) [Ca 8000 x 6 Al 2 (OH) 12 24H 2 O] 6+ [3(SO 4 ) 2H 2 O] x 13

14 Nano-SEM (Cryo) coarser particles smaller (colloidal) particles Segregation zones ( too much SP and/or water) 14

15 More aspects 15

16 (depends on mixinf process and mixer type) Input kinetic energy Secondary influencing factors Mixing intensity Mixing time [Sec.] Other influences of mixing intensity in dependence on the mixing time: Kinetic energy input (intensity of forced particle movement) Other influencing factors X: Temperature increase resulting from intensive mixing process (radiation heat and particle collisions) Dispersive factor (adsorption SP, disaggregation) (Micro)attrition (abrasion und particle breakage) Structure-changing processes (in particular of organic admixtures) due to different stresses.x. 16

17 Temperature of paste after 900 Sec. [ C] Temperature of paste [ C] Temperature increase through particle-particle interactions and radiation heat Temperature increase in dependence on mixing time t M Max. temperature increase from radiation heat (continuous operation) Mixing time t M in suspension mixer [Sec.] ϕ = [l/l] Temperature increase after 900 Sec. in dependence on solid concentration c [Vol.] Setting window 20 FM1 PCE1 FM2 PCE2 KSM Limestone powder Solid concentration c [l/l] 17

18 Temperature [ C] Temperature [ C] Temperatur independence Suspension mixing time 900 Sec. Mean sample temperature at 20 C in climate chamber (with PCE1) Suspension mixing time 0 Sec US_M1_1.1 US_M1_1.2 US_M1_1.3 US_M1_2.1 US_M1_3.1 US_M1_3.2 US_M1_4.1 US_M1_ Sek Time [h] Mean sample temperature at 20 C in climate chamber (with PCE2) US_M1_1.1 US_M1_1.2 US_M1_1.3 US_M1_2.1 US_M1_3.1 US_M1_3.2 US_M1_4.1 US_M1_ Sek Time [h] 18

19 Summary and outlook Complex conditions during two-step mixing, but also in terms of other technological processes (e.g. shaping and compaction): Understanding of processes and learning Improved fluidity through intensive mixing of binder matrix at low mixing times (better particle dispersion) Faster setting and hardening Possibilities for concrete technological optimizations through a two-step mixing process regarding: Reduction of W/C- or W/B value as well as SP dosage Cement reduction through better dispersion and faster setting/hardening (often significantly excessive cement contents in industrial production) Reduction of CO 2 emissions 19

20 Institut für Angewandte Bauforschung Weimar gemeinnützige GmbH Thank you for your attention. Dipl.-Ing. Mirko Landmann Tel.: IAB Weimar ggmbh Forschungsbereich Baustoffe Über der Nonnenwiese Weimar Germany Kolloquium Rheologische Messungen an mineralischen Baustoffen in Regensburg