S. Peters, M. Stöckigt, C. Rößler · Bauhaus-University Weimar Results: Set time and slump of cement pastes in dependence of PUS application (w/c 0.37, 0.1 % SP) Slump 122 mm 158

F.A. Finger-Institute for Building Materials Scienc eBauhaus-University Weimar

ibausil17th International Conference on Building Materials

23rd – 26th September 2009, Weimar

Influence of Power-Ultrasound on the Fluidity and Setting of Portland Cement Pastes

S. Peters, M. Stöckigt, C. Rößler


Outline of presentation

• Brief description on effects of Ultrasound on suspensions

• Experimental setup

• Results

• Perspective for Application of Power-Ultrasound in Concrete Production


Vibration of sonotrode (amplitude ca. 2 - 100 µm): compression and rarefaction of liquid

Power-Ultrasound: frequency 20 kHz – 1 GHz

Cavitation:

1. Tensile strength of liquid is exceeded, cavities form

1

Power-Ultrasound (PUS) in aqueous suspensions - phen omenon of acoustic cavitation

PUS effects: degassing and bubble formation, temperature and pressure variations, crystallization processes are accelerated

2

3

4X+,Y-

X+,Y-

2. Vapor ingress in cavities

3. Compression causes cavities to implode, jet streams are formed

4. Liquid and particles are accelerated, particle collisions occur, diffusion is enhanced


Study Objective

- To evaluate if PUS is a suitable method to accelerate hydration of alite in Portland cement pastes

- To measure impact of PUS on fluidity, setting behaviour, strength development and microstructure of cement pastes

- Outline a concept for implementation of PUS in concrete production


Experimental Setup of Ultrasound Device UIP1000hd (H ielscher, Germany)

13

2

4

7

5

6

[www.hielscher.com]

1. Pump

2. Sample storage container

3. Sonification vessel

4. Sonotrode

5. Booster

6. Transducer

7. Generator

8. Wattmeter


Experimental Setup

Mixture

• CEM I 42. 5 R, w/c 0.37,

• Polyacrylate superplasticizer 0.1 % referred to the amount of cement

Methods

• Vicat Needle test, Non-destructive testing (ultrasonic pulse velocity),

slump, temperature, Environmental SEM, compressional strength of

mortar prisms


Results: Time-Temperature curves of cement pastes i n dependence of PUS application

20

25

30

35

40

0 2 4 6 8 10 12 14 16 18 20 22 24

time [h]

tem

pera

ture

[°C

]

reference

Power-Ultrasound (35°C)

temperature pulse 38°C

x first C-S-H phases (ca. 500 nm)

Main hydration period is accelerated by PUS.


Results: Microstructure of cement pastes in depende nce of PUS application

Power-Ultrasound Reference

Larger C-S-H phases in PUS treated cement paste.

5 h Hydration (setting time)


Results: Set time and slump of cement pastes in dep endence of PUS application (w/c 0.37, 0.1 % SP)

158 mm122 mmSlump

4 h 30 min6 h 45 minFinal Set

3 h 45 min5 h 15 minInitial Set

PUSReference

PUS application accelerates initial and final set of cement paste and increases fluidity.


Results: Non-destructive testing of setting process - ultrasonic pulse velocity in dependence of hydration time and PUS ap plication

1500

2000

2500

3000

3500

0 6 12 18 24

reference

P o wer-Ult raso und (38°C )

temperatur pulse 48°C

ultr

asou

nd v

eloc

ity v

P [m

/s] .

hydration period [h]

∆ = 2h

Accelerated rigidification of PUS treated cement pastes, increased ultrasonic velocity after 24 and 72 h of hydration indicates higher strength of pastes.


Results: Compressional strength of mortar prisms in dependence of hydration period and PUS application

0

5

10

15

20

25

30

35

40

45

50

6 8 10 12 14 16 18 20 22 24

Hydration period [h]

Com

pres

sion

al s

treng

th [N

/mm

2 ]

Reference

PUS 43 µm / 75 Ws/ml

PUS 85 µm / 150 Ws/ml

Increased early strength in PUS treated cement pastes.


Summary

• Power-Ultrasound is a useful technique to accelerate formation of C-S-H phases, setting and thus development of early strength of Portland cement pastes.

• It was shown that by an input power of ~ 10 kWh / m3 cement paste (~ 2 - 3 m3 concrete, ≤ 1 Euro / m3 concrete) approx. 2 h acceleration of setting and early strength is achieved.

• Due to the possibility to increase fluidity by application of PUS, superplasticizer dosage can be reduced.

• Efficient input of PUS is only achieved for cement suspensions, thus mixing procedure of concrete has to be varied if PUS application is desired.


Perspective / Vision

• Optimisation of ultrasound parameters (time and duration of PUS application, amplitude, pressure)

• Feasibility study for precast concrete plant

• Reduction of heating power in precast concrete production

• Implementation of Power-Ultrasound and alternative mixing process (for example suspension concrete, www.germansucon.com) in precast concrete plant.

+ = Efficient mixing and hardening of concrete

Suspension concrete PUS

Documents

S. Peters, M. Stöckigt, C. Rößler · Bauhaus-University Weimar Results: Set time and slump of cement pastes in dependence of PUS application (w/c 0.37, 0.1 % SP) Slump 122 mm 158