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Low pH concrete resistance Low pH concrete resistance against - - PowerPoint PPT Presentation

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MECHANISMS AND MODELLING OF WASTE/CEMENT INTERACTIONS 2 nd International Workshop Low pH concrete resistance Low pH concrete resistance against underground water against underground water aggression aggression Jos Luis Garca Calvo 1 , Ana

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SLIDE 1

José Luis García Calvo1, Ana Hidalgo1, Mª Cruz Alonso1, Luis Fernández Luco2

1- Eduardo Torroja Institute for Construction Sciences, CSIC, Madrid, Spain 2- IECA- Spanish Institute for the Cement and its Applications, Madrid, Spain

MECHANISMS AND MODELLING OF WASTE/CEMENT INTERACTIONS 2nd International Workshop

Low pH concrete resistance Low pH concrete resistance against underground water against underground water aggression aggression

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SLIDE 2

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

SCOPE

  • Design of low

Design of low-

  • pH cements for underground

pH cements for underground repositories of HLRW repositories of HLRW

  • Microstructure evolution of low

Microstructure evolution of low-

  • pH cement

pH cement pastes pastes

  • OPC based

OPC based

  • CAC based

CAC based

  • Resistance of low

Resistance of low-

  • pH

pH cementitious cementitious materials materials to underground waters aggression to underground waters aggression

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SLIDE 3

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Access tunnel Concrete plug Bentonite plug Canisters Liner 2.40 m 2 m

Design of low Design of low-

  • pH cements for underground repositories of HLRW

pH cements for underground repositories of HLRW Role of Cementitious Materials in Deep HLRW Structural cast concrete Structural cast concrete: road paving, floors or operational structures. Shotcrete Shotcrete: : either for tunnels linings, rock support or for plug tunnels Rock bolts Rock bolts Grouting Grouting: : to inject fractures, for sealing

Concrete Plug (ESDRED)

Surface instalations Deep Instalations

10000 Concrete Tons Granitic Reposit.

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SLIDE 4

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

pH

7 8 9 10 11 12 13 Desired Acceptable Bad Uncertain

pH

7 8 9 10 11 12 13 Desired Acceptable Bad Uncertain

Need of Low-pH Cements for HLRW Repositories

Interaction of concrete with ground waters liberates “Hyper-alkaline plume” pH>12.6 perturbs the integrity of Bentonite barrier

2 m 2 m

The risk corrosion alteration of bentonite barrier is higher if pH >>11 Bentonite Concrete

Ground Waters Interface

USE LOW pH CONCRETE ⇒ LOW-pH CEMENT

REQUIREMENT: Pore water pH ≤11

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SLIDE 5

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

2 0 4 0 6 0 8 0 1 0 0 1 2 0 6 7 8 9 1 0 1 1 1 2 1 3 1 4

pH V H N O 3 ( m l)

pH = 1 0 p H =7 C a (O H ) 2 C S H N a +, K +, O H - A l a n d F e p h a s e s p H= 1 2 .5

2 0 4 0 6 0 8 0 1 0 0 1 2 0 6 7 8 9 1 0 1 1 1 2 1 3 1 4

pH V H N O 3 ( m l)

pH = 1 0 p H =7 C a (O H ) 2 C S H N a +, K +, O H - A l a n d F e p h a s e s p H= 1 2 .5

Cement components responsible for high alkaline pH of pore water: Na+, K+ and Portlandite (Ca(OH)2)

Criteria for designing low-pH cements from OPC

Elimination of OH- sources Portlandite Crystals

Pozzolanic Pozzolanic Reaction Reaction Ca(OH)2 + Mineral Admix.

% of CH at 90 days of curing

2 4 6 8 10 12 14 No addition 10%SF- 10%FA 40% SF 35%SF- 30%FA 50% SF 50%SF- 30%FA % CH

18% * %SiO2 in binder 29% 47% 51% 55% 65%

% of CH at 90 days of curing

2 4 6 8 10 12 14 No addition 10%SF- 10%FA 40% SF 35%SF- 30%FA 50% SF 50%SF- 30%FA % CH

18% * %SiO2 in binder 29% 47% 51% 55% 65%

Alkaline plume origin

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SLIDE 6

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Criteria for designing low-pH cements from OPC

% of CH at 90 days of curing 2 4 6 8 10 12 14 No addition 10%SF- 10%FA 40% SF 35%SF- 30%FA 50% SF 50%SF- 30%FA % CH

18% * %SiO2 in binder 29% 47% 51% 55% 65%

% of CH at 90 days of curing 2 4 6 8 10 12 14 No addition 10%SF- 10%FA 40% SF 35%SF- 30%FA 50% SF 50%SF- 30%FA % CH

18% * %SiO2 in binder 29% 47% 51% 55% 65%

SF is very efficient ↓ pH SF>>>FA ↑%MA ↓pH

9,5 10 10,5 11 11,5 12 12,5 13 13,5 2 4 6 8 10 12 14 CH (%) pH

⇑%CH ⇑⇑pH

Pastes based on OPC

9,5 10 10,5 11 11,5 12 12,5 13 13,5 20 40 60 80 100

Curing time (days)

pH

OPC OPC-SF OPC-FA OPC-SF-FA

50SF 35SF+30FA 50HS+30FA Ref 10SF+10FA 20SF 50FA 40 SF

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SLIDE 7

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Microstructure evolution of low-pH cement pastes – OPC based

  • Dissaprearance of CH
  • C2S and C3S
  • ettringite

200 400 600 800 1000 1200 5 10 15 20 25 30 35 40 45 50 55 60

2θ

I (counts)

2 days 7 days 30 days 90 days pH=12.8 pH=12.7 pH=12.3 pH=11.2

OPC+SF

  • No micro cracks.
  • Good texture.
  • Anhydrous grains of SF
  • C/S ratios of the CSH gel

between 1-0.7

  • Anhydrous cement

200 400 600 800

76 80 84 88 92 96 100

f h g

TG(%) DTA Temperature (ºC) TG (%)

  • 20
  • 16
  • 12
  • 8
  • 4

DTA (μV)

200 400 600 800 84 88 92 96 100

TG (%)

f g

Temperature (ºC) TG(%)

  • 300
  • 250
  • 200
  • 150
  • 100
  • 50

50 100

DTA DTA(μV)

OPC+SF OPC 90 d

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SLIDE 8

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

2nd.- Conversion Process: 3 CAH10 C3AH6 + 2 AH3 + 18 H 3 C2AH8 2 C3AH6 + AH3 + 9 H ↑ Porosity→ ↓ compressive strength

Criteria for designing low-pH cements from CAC

Pastes based on CAC

9.5 10 10.5 11 11.5 12 12.5 13 13.5 20 40 60 80 100

Curing Time (days)

pH

Ref 20%SF 30%SF 50%SF 30%FA 50%FA 20%SF-10%FA

90 days: pHs < 12. MA do not significantly ↓pH (50% MA ↓pH in 0.5 points)

1st.- CAC achieves an acceptable pore fluid pH

Pastes based on OPC

9,5 10 10,5 11 11,5 12 12,5 13 13,5 20 40 60 80 100

Curing time (days)

pH

OPC OPC-SF OPC-FA OPC-SF-FA

50SF 35SF+30FA 50HS+30FA Ref 10SF+10FA 20SF 50FA 40 SF

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SLIDE 9

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Microstructure evolution of low-pH cement pastes – CAC based Short Ages (< 7d) CAC and CAC+SF CAH10 C2AH8 AH3 CAC AH3 C3AH6 CAC + SF alumina gel AH3 C2ASH8 C3AS3-XH2X Long Ages (>30d)

30 40 100 200 300 400 500 600 700

C 3AH 6 C 3AH 6 C 3AH 6

I (counts) 2 Theta

REF CAC+MA

BSEM confirms the existence of hexagonal platelets of gehlenite

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SLIDE 10

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Resistance of Low-pH concretes to water aggression: Percolation test

Concrete + ground waters leaching of pore solution alteration of the solid phases

loss of concrete properties

Although the degradation rate is very slow its evaluation is important for structures near field RWR, where extremely long-term stability is needed. In laboratory accelerated tests are used to qualify the different concretes for deep repositories Cement degradation depends on: composition, porosity, density, leachant characteristics, flow rate, Tª and water chemical composition

2 m 2 m

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SLIDE 11

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

Basic concretes samples

70%CAC+30%SF 60%OPC+40%SF

Constituents Kg/m3 Water (kg/m3) 128 Binder (kg/m3) 320 Water/binder 0.4 Fine Gravel (4-8 cm) (kg/m3) 855 Sand (0-4 cm) (kg/m3) 1033 Superplasticizer (kg/m3) 3.2 Constituents Kg/m3 Water (kg/m3) 160 Binder (kg/m3) 320 Water/binder 0.5 Fine Gravel (4-8 cm) (kg/m3) 855 Sand (0-4 cm) (kg/m3) 1033 Superplasticizer (kg/m3) 3.2

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SLIDE 12

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

Cores from shotcreted concrete (Äspö) 60%OPC+40%SF

150 x 300 mm cylinder cast at Santa Barbara Fresh concrete discharge from the truck mixer to te pump 150 x 300 mm cylinder cast at Santa Barbara Fresh concrete discharge from the truck mixer to te pump

Low pH cement formulations Compatibility with chemical admixtures Low pH basic concrete design

Shotcreted plug

Shotcreting

Constituents Kg/m3 Water (kg/m3) 277.2 Binder (kg/m3) 307.2 Water/binder 0.9 Coarse Aggregate (8-12 mm) (kg/m3) 615.6 Superplasticizer (kg/m3) 5.5 Medium Aggregate (4-8 mm) (kg/m3) 199.7 Sand (0-4 mm) (kg/m3) 818.1 Accelerator (kg/m3) 18.5

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SLIDE 13

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

Cores from shotcreted concrete (Äspö) 60%OPC+40%SF Core Extraction of cores for testing

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SLIDE 14

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

Percolation Test (accelerated)

Ground water composition from Äspö

Cl- SO4

2-

NO2

  • or

NO3

  • Na+

K+ Ca2+ Mg2+ Si4+ pH [ppm] 2681 225

  • 1129

9.36 355 5.75 7.50 8.20

Concrete or shotcrete plug samples Leached solution Air inlet for achieving the defined pressure value (0.5 bars)

Ground water inlet Leachate

  • utlet

Methacrylate cylinders Concrete sample O-rings Block sealed with epoxi- resin

Column leaching test (open system). Unidirectional flow. Control of the inflow and outflow solutions. Samples are saturated for 24 hours.

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SLIDE 15

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

Parameter Tested

Upper part Lower part

leachate

solid phases

Test time: low-pH concretes: 14 months; low-pH shotcrete : 2 years

Water flow

Middle part

  • Leachate flow rate

Hydraulic conductivity Variations Requirement (≈1x10-10 m/s)

  • Leachate pH
  • Chemical composition

Measure continuously during test 5cm Techniques used in each sample part

  • Back Scattering with EDAX analyses
  • Optical microscopy (Carbonation test)
  • Mercury Intrusion Porosimetry
  • DRX
  • ATD/TG
  • RMN
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SLIDE 16

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

Leachate results

Hydraulic conductivity evolution pH evolution

1,00E-12 1,00E-11 1,00E-10 1,00E-09 1,00E-08 1,00E-07 100 200 300 400 500 600 700 800 Time (days)

K(m/s)

70CAC+30SF 60OPC+40SF 60OPC+40SF Shotcrete 5 6 7 8 9 10 11 12 13 100 200 300 400 500 600 700 800

Time (days)

pH 70CAC+30SF 60OPC+40SF 60OPC+40SF Shotcrete

Hydraulic conductivity (HC) ≅ 1x10-10 m/s Concretes < shotcrete OPC: pH leachate becomes stable soon (pH≤9) CAC: pH decreases slowly, ranges 12→9

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SLIDE 17

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

Optical microscopy- phenolphtaleine test

A small altered front can be seen with both types of cement CAC based OPC based 650μm ± 100μm 700μm ± 130μm 70%CAC+30%SF 60%OPC+40%SF Estimation of the altered front

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SLIDE 18

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

BSEM

60%OPC+40%SF shotcreted concrete

  • Good aggregate-paste interfaces.
  • Presence of anhydrous phases.
  • CSH: CaO/SiO2≈0.65-0.7

x350

Initial low-pH sample

  • Porosity increases
  • ⇓ Anhydrous cement grains
  • ⇓ CaO/SiO
  • Good agg.-paste interfaces
  • No ⇑ microcracks
  • Calcite precipitation in surface
  • Rich Mg solid phases

x1000 x350

  • Porosity increases
  • ⇓ Anhydrous cement grains
  • CaO/SiO2 similar to ref.
  • Good agg-paste interfaces.
  • Densification in lower part
  • No ⇑ microcracks

x350 x35

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SLIDE 19

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

60%OPC+40%SF-shotcreted concrete- EDX Profiles

0,4 0,8 1,2 1,6 2 10 20 30 40 thickness (mm) (%) %Cl 0,4 0,8 1,2 1,6 2 10 20 30 40 50 thickness (mm) (%) %Cl 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 10 20 30 40 50 thickness (mm) C/S 5 10 15 20 25 30 %MgO CaO/SiO2 %MgO 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 10 20 30 40 thickness (mm) C/S 5 10 15 20 25 30 %MgO CaO/SiO2 %MgO

60%OPC+40%SF EDX Profiles

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SLIDE 20

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

BSEM

70%CAC+30%SF

  • Good aggregate-paste interfaces.
  • Presence of anhydrous phases.
  • Paste composed of CASH
  • Platelets of gehlenite.

Initial CAC+SF concrete

  • ⇓ Anhydrous phases
  • Paste composed of CASH
  • ⇑ gehlenite platelets
  • Good agg-paste interfaces
  • No ⇑ microcracks
  • Calcite precipitation
  • ⇓ Anhydrous phases
  • Paste composed of CASH
  • ⇑ gehlenite platelets
  • Good agg-paste interfaces
  • No ⇑ microcracks

x350 x350 x35 x350

Control of Hydrate conversion

x500 x200 x350

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SLIDE 21

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Interaction of low-pH concretes with ground waters

70%CAC+30%SF EDX Profiles

10 20 30 40 50 60 10 20 30 40 50 thickness (mm) (%) Al2O3 SiO2 CaO

%Cl- CAC based > %Cl- OPC based

After 14 months CASH analyses similar to initial state

0,5 1 1,5 2 2,5 3 3,5 4 10 20 30 40 50 thickness (mm) Cl-(%) CAC+SF OPC+SF

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SLIDE 22

Mechanisms and modelling of waste/cement interactions-2nd International Workshop/ October 12-16, 2008, Le Croisic

Preliminary Conclusions

  • 1. The development of low-pH cement formulations implies the use of MA

with high silica content, both for materials based on OPC and on CAC, in the first case for decreasing the pore fluid pH and in the second case for controlling the conversion process.

  • 2. Microstructure of low-pH cement pastes based on OPC shows a dense

paste based on a CSH matrix with C/S ratio = 1-0.7

  • 3. Microstructure of low pH cement pastes based on CAC also presents a

dense aspect and it is mainly based on a CASH matrix.

  • 4. Preliminary results of percolation tests show a good resistance of the

fabricated low-pH concretes against ground water aggression, although an altered front is observed from the surface in all the tested samples. Tested samples show a good HC and pH leachate value during all the test time.

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SLIDE 23

Thank you for your attention