Dimensional stability of calcium aluminate and ...stisrv13.epfl.ch/masters/img/23.pdf ·...
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Laboratory of Construction Materials Master Project - Spring semester 2010 Dimensional stability of calcium aluminate and sulfoaluminate systems Julien Bizzozero Supervisors: Dr. Christophe Gosselin and Prof. Karen Scrivener Introduction Objectives Understand the main mechanisms of expansion. This is done by: • Scanning different compositions to find the expansion profile in function of gypsum addition • Analyzing the hydration kinetics of the different systems • Studying the microstructure and the phase evolution Main reactions CAC + Gypsum: 3CA + 3C$H 2 + 32H C 3 A.3C$.H 32 + 2AH 3 CSA + Gypsum: C 4 A 3 $ + 2C$H 2 + 34H C 3 A.3C$.H 32 + 2AH 3 The main hydrates are ettringite and amorphous aluminium hydroxide. Cement shorthand notation: C: CaO A: Al 2 O 3 $: SO 3 H: H 2 O Expansion Cement is the most widely used material in the world, its annual production is of about 2 billion tons. This increasing need in concrete is responsible of 5 to 8% of global manmade CO 2 emissions [1] [2]. The different ways to reduce these emissions are: • To optimize the cement manufacturing process • To modify the binder used in concrete: • add SCMs in order to reduce clinker content • use alternative raw materials (less CaCO 3 ) • use low-energy clinkers (easier to grind) Calcium Aluminate Cements (CAC) and Calcium Sulfoaluminate Cements (CSA) can respond to these needs (less limestone, bauxite). Microstructure CSA systems CAC and CSA have different kinetics CSA 2 peaks CAC + Gypsum 2 peaks Induction period not affected by gypsum addition Peak intensity and width affected CAC systems CAC systems CSA systems CSA: crack threshold CAC: crack threshold High expansion Low expansion Cracks Cracks Cracks High expansion Low expansion 4 days: sample broken CSA: crack threshold CAC: crack threshold Expansion 50%eqCA – 50%G_4d 50%CA – 50%G_30d CSA system at 4 days CAC system at 30 days Hydration kinetics Gypsum content increase 1 st peak widens and 2 nd peak delayed CAC and CSA systems have different hydration kinetics but comparable cumulative heat XRD on samples cured in water SEM – BSE images Ettringite stable and AH 3 and ettringite intermixed in CSA systems. 60%CA – 40%G 14d 55%CA – 45%G 14d 52%eqCA – 48%G 14d 50%eqCA –50%G 14d CAC systems at 14 days CSA systems at 14 days Low expansion High expansion CAC and Gypsum CSA Different distribution of the hydrates between CAC and CSA systems Microstructure Low expansion High expansion Isothermal calorimetry Expansion tests Water content effect Water content increase 1 st peak widens and covers the 2 nd peak Comparable behaviour to gypsum addition Increase water content increase porosity and potential space for hydrates precipitation Hypothesis :more space for the precipitation by adding gypsum or water expansion stable after 3 days. Ettringite precipitation continues on over 1 or 2 weeks but expansion still increases afterwards. Crystallization pressure theory Damage caused by the precipitation of crystals from the pore solution. The crystal growing in pores will encounter the pore wall and exert pressure on it [3]. where Q/K is the supersaturation, r is the pore radius. Conclusions References [1] Gartner, E., Industrially interesting approaches to "low-CO2" cements. Cement and Concrete Research, 2004. 34(9): p. 1489-1498. [2] Darntoft, J.S., et al., Sustainable development and climate change initiatives. Cement and Concrete Research, 2008. 38(2): p. 115-127. [3] Scherer, G.W., Stress from crystallization of salt. Cement and Concrete Research, 2004. 34(9): p. 1613-1624. Hydration Microstructure Expansion Hypothesis: the precipitation of ettringite and AH 3 during the first peak is levelled off by a lack of free space and may restart into residual porosity. Hypothesis: CSA systems have a finer porosity (smaller r) and there is a higher supersaturation (Q/K) in high expansion systems (to be confirmed). Different distribution of hydrates between CAC and CSA systems leads to a different expansion behaviour (critical for CSA). Threshold between low expansion and high expansion systems is at 45-50%mol of gypsum content (comparable stoichiometric conditions ).
Transcript of Dimensional stability of calcium aluminate and ...stisrv13.epfl.ch/masters/img/23.pdf ·...
Laboratory of Construction MaterialsMaster Project - Spring semester 2010
Dimensional stability of calcium aluminate and sulfoaluminate systemsJulien Bizzozero
Supervisors: Dr. Christophe Gosselin and Prof. Karen Scrivener
Introduction ObjectivesUnderstand the main mechanisms of expansion.This is done by:
• Scanning different compositions to find the expansion profile infunction of gypsum addition• Analyzing the hydration kinetics of the different systems• Studying the microstructure and the phase evolution
Main reactionsCAC + Gypsum: 3CA + 3C$H2 + 32H � C3A.3C$.H32 + 2AH3
CSA + Gypsum: C4A3$ + 2C$H2 + 34H � C3A.3C$.H32 + 2AH3
The main hydrates are ettringite and amorphous aluminium hydroxide.Cement shorthand notation: C: CaO A: Al2O3 $: SO3 H: H2O
Expansion
Cement is the most widely used material in the world, its annualproduction is of about 2 billion tons. This increasing need in concreteis responsible of 5 to 8% of global manmade CO2 emissions [1] [2].The different ways to reduce these emissions are:
• To optimize the cement manufacturing process• To modify the binder used in concrete:
• add SCMs in order to reduce clinker content• use alternative raw materials (less CaCO3)• use low-energy clinkers (easier to grind)
Calcium Aluminate Cements (CAC) and Calcium SulfoaluminateCements (CSA) can respond to these needs (less limestone, bauxite).
Microstructure
CSA systems � CAC and CSA have different kinetics
� CSA � 2 peaks
� CAC + Gypsum � 2 peaks
� Induction period not affected by
gypsum addition
� Peak intensity and width affected
CAC systems
CAC systems CSA systems
CSA: crack threshold
CAC: crack threshold
High expansion
Low expansion
Cracks
Cracks Cracks
High expansion
Low expansion
4 days: sample broken
CSA: crack threshold
CAC: crack threshold
Expansion
50%eqCA – 50%G_4d 50%CA – 50%G_30d
CSA system at 4 days CAC system at 30 days
Hydration kinetics
Gypsum content increase�1st peak widens and 2nd peak delayed
CAC and CSA systems have different hydration kinetics but comparable cumulative heat
XRD on samples cured in water
SEM – BSE images
Ettringite stable and
AH3 and ettringite intermixed in CSA systems.
60%CA – 40%G 14d
55%CA – 45%G 14d
52%eqCA – 48%G 14d
50%eqCA –50%G 14d
CAC systems at 14 days CSA systems at 14 days
Lowexpansion
High expansion
CAC and Gypsum CSA
Different distribution of the hydrates between CAC and CSA systems
Microstructure
Lowexpansion
High expansion
Isothermal calorimetry Expansion testsWater content effect
Water content increase�1st peak widens and covers the 2nd
peak
Comparable behaviour to gypsum addition
Increase water content �increase porosity and potential space for hydrates precipitation
�Hypothesis :more space for the precipitation by adding gypsum or water
expansion stable after 3 days.
Ettringite precipitation continues on over 1 or 2 weeks but expansion still increases afterwards.
Crystallization pressure theoryDamage caused by the precipitation of crystals from the pore solution. The crystalgrowing in pores will encounter the pore wall and exert pressure on it [3].
where Q/K is the supersaturation, r is the pore radius.
Conclusions
References[1] Gartner, E., Industrially interesting approaches to "low-CO2" cements. Cement and Concrete Research, 2004. 34(9): p. 1489-1498.[2] Darntoft, J.S., et al., Sustainable development and climate change initiatives. Cement and Concrete Research, 2008. 38(2): p. 115-127.[3] Scherer, G.W., Stress from crystallization of salt. Cement and Concrete Research, 2004. 34(9): p. 1613-1624.
HydrationMicrostructure
Expansion
� Hypothesis: the precipitation of ettringite and AH3 during the first peak is levelled off by a lack of free space and may restart into residual porosity.� Hypothesis: CSA systems have a finer porosity (smaller r) and there is a higher supersaturation (Q/K) in high expansion systems (to be confirmed).� Different distribution of hydrates between CAC and CSA systems leads to a different expansion behaviour (critical for CSA).� Threshold between low expansion and high expansion systems is at 45-50%mol of gypsum content (comparable stoichiometric conditions ).
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