Low-lime Calcium Silicate-based Cement (CSC):...

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Low-lime Calcium Silicate-based Cement (CSC): Microscopic Phase Evolution, Reaction Kinetics, and StrengthWarda B. Ashraf1, Jan Olek2, Vahit Atakan3, Sadananda Sahu4

1 Graduate Research Assistant, Lyles School of Civil Engineering, Purdue University, USA. Email: washraf@purdue.edu2 Professor, School of Civil Engineering, Purdue University, USA. Email: olek@purdue.edu3,4 Solidia Technologies, NJ, USA. Email: vahit@solidiatech.com, ssahu@solidiatech.com

7. Strength

8. ConclusionsThe concluding points of this work are: The final reaction products of CSC system are highly polymerized silicagel (consisting of Q3 and Q4 species) and calcium carbonate.Both, crystalline and amorphous forms of calcium carbonate are presentin the carbonated system. The carbonation activation energy of CSC binder is around 46 to 55KJ/mol at 10% CO2 concentration. Activation energy is expected to belower at higher CO2 concentration. CSC can be used to produce mortars samples with compressivestrength around 3000 psi to 6000 psi and concretes with compressivestrength 7000 psi to 11600 psi. Compressive strengths can be controlledby varying w/c ratio and extent of carbonation.

Calcium silicate-based cement (CSC) [1,2] is a newly developed binder thathardens as a result of carbonation reaction. The primary components of thiscement are non-hydraulic calcium silicates, including rankinite, wollastoniteand pseudo-wollastonite. Because of the utilization of low-lime calciumsilicates, production of CSC requires lower amount of limestone and 250°Clower kiln temperature compared to the ordinary portland cement (OPC).This poster presents the results on the microscopic phase evolution duringhardening process, reaction kinetics, and strength development of this novelbinder material.

1. Introduction 3.Materials 4. Sample PreparationTo monitor the microscopic phase evolution, paste samples wereprepared with 0.4 w/c ratio. Mortar samples were prepared usingthe sand to cement ratio of 2.75 and variable w/c ratios. All of thesamples (i.e., paste, mortar, concrete) were subjected to carbonationimmediately after casting. The extent of carbonation was monitoredusing thermogravimetric analysis (TGA).

5.1 Crystalline phases: X-ray Powder diffraction results

2. ObjectivesThis study addresses the following issues:

Evolution of the microscopic phases during the carbonationreaction.

Effects of w/c ratio, RH, and temperature on carbonation reactionrate.

Strength of the CSC mortar and concrete

5. Microscopic Phase Evolution

7th Advances in Cement-Based MaterialsJuly 10-13, 2016, Northwestern University, Evanston, IL

6. Reaction Kinetics

References:[1] R. E. Riman, T. E. Nye, V. Atakan, C. Vakifahmetoglu, Q. Li, & L. Tang (2015). Synthetic formulations and methods of manufacturing and using thereof. US patent US 9216926 B2, Washington, DC, U.S. [2] Sahu, S., & DeCristofaro, N. (2013). Solidia Cement TM. Solidia Technologies, White Paper. Retrieved from: http://solidiatech.com

Silica gel Calcium carbonate

Unreacted grain

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Silica gelCalcium carbonate

5.2 Evolution of Silicate Species: 29 Si MAS NMR

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5.2 Amorphous phases: 29Si {1H} and 13C {1H} CP-NMR results

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0.0028 0.003 0.0032 0.0034

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Normalized degree of carbonation:

휉(푡) = 휉0 + 퐴. exp(퐵. 푡)

Carbonation rate:

푑휉푑푡 = 퐴.퐵. exp(퐵. 푡)

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Effect of w/c ratio Effect of RH Effect of Temperature

퐶푂2 +퐻20 ⇆ 퐻+ +퐻퐶푂3−

322

32

.3...3

COCaOyHSiOxCaOHCOSiOCaO

Reaction Mechanism Decomposition of CaCO3

Degree of Carbonation,DOC =

퐶푎퐶푂3 푐표푛푡푒푛푡 푎푡 푡푖푚푒 푡푀푎푥푖푚푢푚 퐶푎퐶푂3 푐표푛푡푒푛푡 × 100%

Inte

nsity

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y uni

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Akermanite/ Gehlenite

Pseudowollastonite/ wollastoniteQuartz

Rankinite

LarniteAnorthite

Calcite

DOC = 0%

DOC = 12%

DOC = 70 %

DOC = 100%

10 20 30 40 50 60 70 80Two theta

Degree of Carbonation (%) 0 12 40 70 80 100

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Vaterite

Aragonite

Calcite

Rankinite

Belite

Pseudowollastonite/ WollastoniteNon reactive (Akermanite/ Ghelenite/Quartz)

Wei

ght (

%)Semi-quantitative

phase proportions (without taking into account the amorphous phases)

Chemical Shifts (ppm)

Q3 -98 ppm

Q3 (OH)-103 ppm

Q4-113 ppm

Silica gel (or Ca-modified silica gel)

From SEM/EDS: Ca/Si atomic ratio = 0.4

Chemical Shifts (ppm)

Amorphous calcium carbonate (ACC)

Q1 Q2

Q3 Q4

Q0

Q0

-60 -70 -80 -100 -110 -120-90Chemical Shifts (ppm)

Carbonation duration (hour)

6.2 Apparent activation energy (Ea) of Carbonation at 90% RH and 10% CO2

6.1 Effects of Carbonation Conditions (at 10% CO2 concentration)

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Carbonation at 60⁰C

Carbonation at 30⁰C

90% RH, 10% CO2, w/c = 0.4

Arrhenius plot Calculated Ea for DOC < 80%

w/c ratios:

Compressive Strength (Psi)

Elas

tic M

odul

us (P

si)

Sand/ cement ratio = 2.75Carbonation at 60⁰C, 60%RH99.9% CO2

SiO44- Unit

29Si {1H} NMR

13C {1H} NMR

w/c: 0.3 ~ 0.4, cement: 674 lb/yd3, sand:1161 lb/yd3, coarse aggregate: 1911lb/yd3, 72 hours carbonation at 99.99%CO2, 60⁰C, 60%RH

CSC concrete

ACI 318: 57000√fc