Admixtures and C Ash - A Challenge to Modelblogs.cae.tntech.edu/hydration-kinetics/files/2009/07/roberts... · International Summit on Cement Hydration Kinetics, Quebec, PQ Admixtures

July 27-29, 2009

International Summit on Cement Hydration Kinetics, Quebec, PQ

Admixtures and C Ash - A Challenge to Model

Lawrence Roberts, Roberts Consulting Group LLC

July 27-29, 2009 International Summit on Cement Hydration Kinetics, Quebec, PQ 2

Acknowledgment

The author would like to thank W. R. Grace which has sponsored his participation in this conference, and for his

many colleagues who developed the data seen here.


Bibliography

§ ASTM C 618-05, “Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete,” ASTM International, West Conshohocken, PA, 2005, 3 pp.

§ Bauset, R., “Abnormally Delayed Setting of a Low-heat Portland Cement with Calcium Lignosulfonate Admixture”, Proceedings, Fifth International Symposium on the Chemistry of Cement, Tokyo, 1968, Vol. 9, 53067, Cement Association of Japan

§ Cost, V. T.,” Incompatibility of Common Concrete Materials – Influential Factors, Effect and Prevention”, Concrete Bridge Conference, 2006

§ Cost, V. T., and Gardiner, A., “ Practical Concrete Mixture Evaluation via Semi-Adiabatic Calorimetry”, 4th Annual Concrete Technology Forum, Focus on Performance Prediction, NRMCA, Cincinnati, 2009

§ Khalil, S. M., and Ward, M. A., "Influence of SO3 and C3A on the Early Reaction Rates of Portland Cement in the Presence of Calcium Lignosulfonate", Ceramic Bulletin, Vol. 57, No. 12, 1978, pp. 1116-1122


Bibliography

§ Lerch, W., "The influence of gypsum on the hydration and properties of portland cement pastes", Proceedings, 1946, Vol. 46, American Society for Testing Materials

§ Meyer, L. M. and Perenchio, W. F., "Theory of Concrete Slump Loss Related to Use of Chemical Admixtures", Research and Development Bulletin RD069.01t, Portland Cement Association, 1980

§ Roberts, L.R., “Recent Advances in Understanding of Cement Admixture Interactions,”33rd Annual Technical Symposium, Institute of Concrete Technology, April. 2005.

§ Roberts, L. R., “ How Chemical Admixtures Work”, Presentation at Univ. Toronto, CIV 1299S, May 2008.

§ Roberts, L. R. , and Taylor, Peter C., "Understanding Cement-SCM-Admixture Interactions", Concrete International, January 2007, pp. 33-41.

§ Sandberg, P., and Roberts, L.R., “Studies of Cement-Admixture Interactions Related to Aluminate Hydration Control by Isothermal Calorimetry,” Seventh CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, SP-217,V.M. Malhotra, ed., 2003, pp. 529-542.


Bibliography

§ Sandberg, P.J., and Roberts, L.R., “Cement-Admixture Interactions Related To Aluminate Control,” Journal of ASTM International, V. 2, No. 6, June 2005, pp. 219-232.

§ Tenoutasse, N., “The Hydration Mechanism of C3A and C3S in the Presence of Calcium Chloride and Calcium Sulphate, Supplementary Paper II-118, Fifth International Symposium on the Chemistry of Cement, Tokyo, 1968, 372-378, Cement Association of Japan

§ Tuthill, L. H., Adams, R. F, Bailey, S. N, Smith, R. W., "A Case of Abnormally Slow Hardening Concrete for Tunnel Lining", Journal ACI, March 1961, pp 1091 – 1109

§ Wang, H., Farzam, H., Lansing, G., and Leigh, E., Cement Performance – Significance of the Absence and Presence of Mineral and Chemical Admixtures, ICCC 2007, Montreal


Hydration Modeling State of the Art

§ That’s what we’re here for

§ As practitioner, my interest is how models may:

• Give field decision makers tools to prevent problems

• Permit combinations of materials which meet new challenges, such as climate change

§ As scientist, my interest is also to imagine how odd behaviors seen over the years may enable better model development.

• Want to impart some of this experience

• Some behaviors imply a sensitive “switch” controlling hydration

§ Interactions of C Ash – Admixture systems provides a good example

• Widely applied – enough problems have arisen to see a number of effects

• Easy to reproduce for model investigation

• Societal need to use as much as possible conflicts with need to avoid problems


Hydration Modeling State of the Art

§ Does seem to me to have strong focus on silicate hydration

§ C Ash system silicate hydration behavior reacts dramatically to changes in sulfate levels,

• This infers strong impact of aluminate hydration on silicate behavior

• For models to be fully useful, replication of this behavior is desirable

§ So goal here is to bring before the modeling community some examples, primarily from the literature so that more detailed data are available, with a challenge:

Model this and your models will be stronger for it

§ And unlike some difficult-to-reproduce cement problems, this can be reproduced any time you want it


A simple case - Effect of C Ash on Hydration – Well Sulfated Cement

§ 30.5% CaO C Ash

§ 0.48 SO3/C3A Mass ratio

§ Note significant ~ 2.5 hrs time between main peak max and start of third exotherm for cement curve

§ Moderate retardation as expected

§ Similar slope

§ With ash, sulfate depletion ~3 hrs before main peak max

§ Area under curve roughly proportional to cement substitution From Wang et al 2007


Effect of C Ash on Hydration – Less Well Sulfated Cement

§ Same C Ash

§ 0.42 SO3/C3A mass ratio

§ Note short ~ 1hr time between initial peak maximum and second exotherm

§ Both delay and slope change seen

§ With ash, sulfate depletion point not obvious

§ Significantly lower area under exotherm

From Wang et al 2007


Mild Effect C Ash

§ Alternative view same data – total heat basis

§ Lower total heat with lower SO3 ratio cement clearly seen

From Wang et al 2007

0.42 SO3/C3A

0.48 SO3/C3A


Is this new?

§ No! Even with plain cement

§ Red line indicates silicate exotherm max when well sulfated

§ Suppression of silicate hydration clearly seen at low SO3

Note retarded silicate at low SO3

From Lerch, 1946

1.25%

1.5%

1.9%

2.4%

3.0%


Is this new?

§ No again

§ Particularly useful as pure compounds used

§ Must be through solution

§ Indicates this is a fundamental behavior of materials, not due to minor element changes

From Tenoutasse, 1968

0.9%

1.4%1.9%

Percents as % SO3

2.3%

2.8%


Effect of Lignin Admixture on Rate of Hydration of Type 10 & Type 50 Cements at Various Sulfate Levels

% Hours to C3S Peak Max

CEMENT SO3 BLANK LIGNIN

C3A: 9.22% 10 1.65 12 20

10 2.15 10 16

10 2.65 10 15

10 3.15 10 15

C3A: 3.24% 50 0.80 15 80

50 1.30 11 32

50 1.80 11 18

50 2.30 11 18

§ High iron cement much more strongly affected by undersulfated condition

Data from Khalil & Ward, 1978


Early Experience with C Ash - 1989 Problem

§ Type I Cement @ 2.3% SO3, ASTM C-494 Type A, Class C (unknown CaO%) fly ash

§ Any two ok, all three together gave two problems:

• Rapid slump loss

• Green concrete at 1 day

§ Vicat set 30 minutes --- Why????

§ 60/40 anhydrite in Cement + C3A from Fly Ash

• X-ray diffraction showed increase in C3A at time of problem

§ Type A slowed SO3 availability, speeded C3A

§ Fix? --- 0.5% more SO3 = only 0.2% as plaster

• Problem went completely away


2001 – Paving Problem – Marginally Undersulfated Cement + C Ash

§ Note sulfate depletion point ~ 2.5 hours before initial peak maximum

§ Addition of ash alone shows marked delay, slope reduction and area reduction

§ With lignin based water reducer at 325 mL/100 kg, presumably aluminate-based exotherms in 1.5 –4 hrs time frame

§ No subsequent silicate reaction Data as presented in Roberts and Taylor, 2007

Cement

68:32 Cement:C Ash

68:32 Cement;C Ash + WRA

Table 1. Sulfate forms in portland cement

% by Weight Equiv. % SO3Gypsum 0.3 0.14Plaster 1.7 0.94

Anhydrite 0.8 0.47Total 1.6

C3A = 6% Bogue


Effect of Adding More Sulfate

§ Added sulfate restores reaction

§ No significant improvement beyond 1.2% added SO3

§ Data not shown indicated 20% ash hydrated far faster

Data as Presented in Roberts and Taylor, 2007

Cement only

68:32 Cement:C Ash

68:32 (Cement+2.1% SO3):C Ash + WRA

68:32 Cement:C Ash + WRA


Extreme example showing inverse temperature effect

§ Semi-adiabatic field calorimetry

§ 25% Class C ash, normal corn syrup – amine water reducer

§ 22, 32, 38 °C

§ 2.8, 3.3, 3.7, 4.1% SO3

§ Higher temperature shows more early [aluminate] reactions, diminishes silicate peaks

§ Higher SO3 restores normal silicate peak

From Cost, 2006


Data of Cost 2006, as presented in Roberts & Taylor, 2007

Net Effect of Mix Temperature on Strength with C Ash, Water Reducer


High Sensitivity to Small Changes in Cement SO3 – Why?

From Cost and Gardiner, 2008

SO3 -Normal variation in one plant in one week


Other useful tidbits

§ Tuthill et al, 1961, showed similar diminished silicate reactionrestored by higher sulfate with Type II cement, normal lignin retarder, no ash.

§ Bauset, 1968, showed similar results with a simple lignin and low C3A cement, no ash

§ Roberts, 2008, showed that a case of extended hydration with calcium nitrite and Type V cement was dependent both on dispersion in the system and on nitrite level, and was overcome by added sulfate or by change in order of addition of admixtures

§ Roberts & Taylor 2007 mention one cement which failed to set in overdose situation – only difference detectable was `0.1% soluble alkali as Na2O


Conclusions

§ Inadequately controlled aluminate reactions can and do shut downsilicate reaction for extended times

§ Class C fly ashes are frequently involved with these problems, but other systems can show the same effect.

§ Criticality of early sulfate availability

§ Admixtures play a key role

• Chemistry, Dispersion, Dosage, Timing

§ Combinations with Class C ash allow us to easily recreate undersulfated “misbehaving” systems, providing opportunity for quick checking of model predictions

§ Role of iron needs investigation

§ To effectively predict real-world behavior, models must reproduce the sulfate, temperature, and admixture dose sensitivities found.

§ Closer study with modeling may both more rapidly advance capability of hydration models and beneficially impact real world challenges


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Admixtures and C Ash - A Challenge to Modelblogs.cae.tntech.edu/hydration-kinetics/files/2009/07/roberts... · International Summit on Cement Hydration Kinetics, Quebec, PQ Admixtures