Specification and use of Geopolymer Concrete. By Fred Andrews-Phaedonos

Transcription

1 Specification and use of Geopolymer Concrete By Fred Andrews-Phaedonos

2 Conventional and Geopolymer Concretes Geopolymer concrete consists of > 80% Fly Ash, GGBF Slag, Silica Fume or metakaolin up to 20% alkaline components (alkaline activator) sand, stone (up to 75% to 80% of total mass) to water and admixtures Conventional concrete characterised by the formation of Calcium Silicate Hydrates (CHS) - (Calcium based system) Geopolymer concrete characterised by an amorphous (non-crystalline) microstructure of an -Aluminium silicon based system Geopolymerisation Process Alkaline solution dissolves out aluminium and silicon molecules from the fly ash and/or slag and enhances reaction Dissolved components rearrange into an aluminosilicate gel (Si-O-Al-O) which then cross-links and hardens to form the geopolymer binder Fly ash Fly ash particles Solid Sodium Silicate Start of Geopolymer phase development 2

3 Typical Geopolymer Mix Design Materials Mass (kg/m 3 ) Cementitious Binder Coarse Aggregates (60%) Precast/Cast-in-situ/Pipes VR330/32-VR470/55 - Equiv 20 mm Similar to Conventional 14 mm Similar to Conventional Fine Sand (40%) Fly Ash GGBF Slag (%) Large % Mineral Additives (GP Cement) (x %) Sodium Silicate solution(sio 2 /Na 2 O=2) Sodium Hydroxide Solution - Solid Sodium Silicate (y %) Superplasticiser Air Entrainer Water Water/Binder Ratio Slump Similar to Conventional % Could be low to large Nil (in some systems small amount) - Some Nil Some Much higher than conventional Relatively High mm Where s the geopolymer recipe?? What did you do with the geopolymer recipe???? 3

4 Supplementary Cementitious Materials (SCMs) - Sustainable Green VicRoads Concrete for more than 20 Years - Reduction of CO 2 by ~ ~15% - 30% per Cubic Metre - Both structural & general purpose concrete construction SCMs Activity in Concrete Fly Ash Improved Qualities of Concrete Replacement Levels Single Combination GGBF Slag Treble Blends Special Applications Silica Fume 4

5 Since 1990, Standard Specification Section 610 allowed use of industry by-products such as fly ash, ground granulated blast furnace slag and silica fume - has resulted in a lower carbon footprint than Portland cement concrete! - & more durable concrete bridges 5

6 Provision of Geopolymer Concrete in VicRoads Specifications, Section 703 General concrete paving Introduced as equivalent product to Portland cement concrete - in Definitions to facilitate compliant use: Alkaline Component: Combinations of alkali and alkali earth containing salts, minerals and glasses Geopolymer Binder: Binder containing greater than 80% fly ash, Slag, silica fume or metakaolin and up to 20% alkaline components Geopolymer Concrete: Concrete which comprises geopolymer binder, aggregates, water and admixtures. Strength grade same as normal concrete of 20 MPa, 25 MPa and 32 MPa. Construction requirements of placing, compaction, finishing, curing and sampling & testing of geopolymer concrete same as conventional concrete. Due to greater susceptibility to unsatisfactory practices, manufacture and delivery practices for geopolymer concrete more in line with Section 610. This must be the first standard specification in the world to define geopolymer concrete! 6

7 Section 701 Underground stormwater drains Cross-reference to geopolymer concrete requirements of Sec703 early 2013 Concrete pipes defined as follows: Precast Reinforced Concrete Pipes: pipes manufactured from Portland cement-based concrete or geopolymer binder-based concrete as specified in Section 703. For manufacture of RC pipes, Portland cement concrete and geopolymer binder concrete - equivalent products Geopolymer binder-based precast RC pipes required to comply with requirements of AS/NZS 4058 and Section 701 Compressive strengths appropriate to the nominated load class performance requirements as stated in AS/NZS

8 Section 705 Drainage pits Geopolymer concrete as defined in Sec 703 introduced in Sec 705 in 2013 Can be used for drainage pits provided supply and construction of geopolymer concrete comply with Section as per conventional concrete; and Satisfy the concrete grade requirements of Section 705, namely, Steel reinforced drainage pits - minimum concrete grade VR330/32 Fibre reinforced precast drainage pits - minimum concrete grade VR450/50 Concrete mix designs to comply with Sec 610 for structural concrete Re-registered on an annual basis, unless mix components change prior to the expiry of registration 8

9 Section 711 Wire Rope Safety Barrier (WRSB) Geopolymer binder-based concrete To comply with requirements of Section 703 Manufactured to comply with the minimum 28 day compressive strength requirements for each strength grade ranging from 20 MPa to 32 MPa Strength grades of geopolymer concrete used for anchor blocks, post footings, maintenance strips and other associated concrete works are specifically identified. 9

10 Geopolymer Concrete Footway Panels Salmon Street Bridge Over West Gate Fwy 180 precast footway units, concrete grade VR470/55 to Section 610 manufactured and installed in 2009 The full scale production and installation completed within the same timeframe as achieved by conventional type concrete Satisfactory in-service performance based on visual monitoring for past 5 years Satisfactory structural performance without evidence of distress. 10

11 Curing Curing Regime Polyethylene sheet curing >> 7 days (more preferred) Dark green colour retained, indication of integrity of curing Design Strength of 55 MPa - lifting strength 10 MPa readily achieved Microstructure of geopolymer concrete depends on the activating solution used the dosage rates of the chemical activator, and the effectiveness of curing conditions 11

12 Retaining Walls - Bridge over Yarra River Monitoring Junction Boxes, Reference Electrodes & Electro potentials since 2009 Downstream retaining wall Upstream retaining wall MnMnO 2 Reference Electrode The half-cell potentials of upstream & downstream wall cells appear to have stabilised between -350mV and -250 mv CSE Half-cell potentials of retaining walls 12

13 Voltag e (V) Initial Current (ma) Retaining Walls - Bridge over Yarra River Downstream Wall Other Testing ASTM C1202 test results (Chloride Resistance) Total Charge after 6 hours (C) Penetrability Very low This may have resulted from the high slag content of the concrete, which would reduce the amount of ionic charges in the pore solution of the concrete, rather than from low porosity of concrete ASTM C1202 test (Chloride Resistance) NT Build 443 test results (Chloride Diffusion) Duration of immersion (days) Initial Chloride Content (%) Chloride content at the boundary, Cs (%) Diffusion Coefficient (m 2 /s) The low results are aided by the blocking effect of weak solution of sodium metasilicates within the nano- or meso- porosity which in-situ can still percolate as efflorescence via the interconnected void space 13

14 Location Testing Highlights Bridge over Yarra River Volume of Permeable Voids (VPV) Cores - In-Situ Concrete VPV (after 7 months) Ave VPV (%) (cores) Downstream Wall 18 > 16 Upstream Wall 19 > 16 Conventional slag concrete (cores) Average VPV (%) VR400/ < 16 Cores - In-Situ Concrete Compressive Strength (after 7 months) Location Ave Strength (MPa) ( cores) Downstream Wall 50.9 Upstream Wall 44.3 Downstream Wall better quality geopolymer concrete Also supported by petrographic examination Higher VPV not due to larger interconnected void space Due to additional water loss from gel-like materials included in geopolymer mix Excess amount of sodium silicate in mix (releases water as part of chemical reaction) Not fully assimilated into the geopolymer binder and caused the high VPV Large amounts of water soluble sodium silicate also confirmed by SEM/EDX results Further refinement of geopolymer concrete mix design required Use of compatible chemical admixtures to reduce amount of water in mix To optimise the amount of sodium silicate in the mix 14 To significantly reduce VPV of geopolymer concrete

15 Bicycle Paths, Footpaths, No-Fines Geopolymer Concrete Significant lengths of footpath and bicycle path using 25 MPa geopolymer concrete per Section 703 since 2009 Ongoing visual monitoring since construction, performing well with no detected cracking or other defects No-fines geopolymer concrete used on M80 WRR as a granular back fill filter material to act as B4 filter for subsurface drainage per Section

16 Geopolymer Concrete Wall, M80 Western Ring Road Near vertical 450 metre long chevron or zig-zag landscape retaining wall designed to double up as raised planter beds First major in-situ construction on a major infrastructure project in Australia in mid 2012 Geopolymer concrete with equivalence to concrete grade VR400/40 Complied with all requirements of Section 610 Except for VPV found to slightly exceed the specified requirements, for the same reasons as identified with the Swan Street Bridge retaining walls 16

17 Precast Footway Deck Planks, Longford Bridge Trial synthetic fibre reinforced geopolymer concrete (FRGC) precast footway deck planks early No m x 2.8 m x 150 mm thick Also steel reinforced, grade VR400/40 equivalent Manufactured and installed on pedestrian bridge as part of long term monitoring of in-situ performance Dry delivered 250 km from Melbourne - water, fibres, activator added on site Steel reinforced geopolymer concrete samples with variable concrete cover were also made for future monitoring. 17

18 Geopolymer Concrete Pipes 18 Provision for geopolymer concrete pipes in VicRoads Section 701 has facilitated manufacture of such pipes by a Victorian pipe manufacturer early 2013 Proof and ultimate load testing demonstrates that geopolymer concrete pipes are as good as conventional cement based pipes and are in compliance with the requirements of AS/NZS Proof and Ultimate Load Pipe Type First crack kn/m Proof Load kn/m Ultimate Load kn/m Geopolymer Pipes Conventional Pipes AS/NZS 4058 Min. Proof Requirement kn/m AS/NZS 4058 Minimum Ultimate Requirement kn/m 45-80

19 Geopolymer Concrete Pipes Water absorption results demonstrate compliance to AS/NZS 4058 VPV results demonstrate that both geopolymer and conventional concretes comply with the requirements of section 610 for VPV for concrete cores Satisfactory VPV results achieved through use of refined geopolymer concrete suitable for an accelerated pipe manufacturing environment. Average Absorption (AS/NZS4058) and VPV Values (Section 610/AS ) Pipe Type Average AS/NZS4058 VPV Maximum VPV Absorption Max Allowable % Values at 28 % % days, (%) for core, Section 610 Geopolymer rounded down Conventional rounded down 15 Water absorption samples VPV testing 19

20 Geopolymer concrete pipes stored on site and during installation Princess Highway Duplication at Winchelsea in south western Victoria Drainage works in Harley Street, City of Greater Bendigo and Bendigo Airport in Victoria Following VicRoads acceptance of geopolymer concrete pipes in early

21 Geopolymer Structural Concrete Walls at Dudley Street Railway Bridge 21 Reinforced soil & post and panel walls based on equivalence to concrete grade VR400/40, part of Regional Rail Link works Two metre wide precast panels with height of between 2-4 metres Two thirds with rough textured finish and rest with flat surface finish Review/acceptance of mix based on VicRoads Section 610 Confidence to proceed based on successful use by VicRoads and provision of geopolymer concrete into VicRoads specifications Practices and procedures no different to conventional concrete

22 Geopolymer concrete used in other applications Sec 703 facilitated the steady increase in paving & commercial applications Significant amounts of footpath, K & C, footings and associated paving At least one local council to allow use in general concrete paving works Commercial construction of a library building which utilised precast panels Panels 9m x 3m, 40 MPa - sand blasted to expose the quartz pebble On site work for this site included footings and general paving Upcoming potential projects include multi-storey residential buildings for green construction & potentially Quarantine facility, Donnybrook Road, Mickleham, Victoria (2200 m 3??)?? VicTrack Access, a State owned enterprise allows use of 32 MPa geopolymer concrete for the construction of protection post and marker post footings to take advantage of its sustainability credentials including low embodied carbon 22

23 Properties of Geopolymer Concrete (1) For specific geopolymer concrete systems properties similar to cement system Geopolymer concrete able to comply with requirements of Sections 703 & 610 Strength satisfactory Drying shrinkage to 730 microstrain < 750 microstrain at 56 days VPV only property struggling. Pipes o.k - refined mix to suit manufacture Tensile 4.5 MPa for 32 MPa and 6.0 MPa for 40 MPa mixes (@Aldred and Day) Flexural strength 6.2 MPa for 32 MPa and 6.6 MPa for 40 MPa mixes Elastic modulus GPa for MPa mixes (similar to cement system) Poisson s ratio of 0.20 to 0.24 slightly higher than cement based systems Specific Creep 15 to 29x10-6 /MPa after 1 year for strength of MPa (@Wallah) about half of conventional concrete. Creep Coefficient 0.4/0.5 for 67MPa, 0.5/0.6 for 40MPa to 57MPa 23

24 Properties of Geopolymer Concrete (2) Higher VPV not due to larger interconnected void space (exceed Sec 610) Due to excess amount of sodium silicate in mix which is not fully assimilated into the geopolymer binder Not picked up by RCPT or Diffusion Test Excess water soluble sodium silicate also confirmed by SEM/EDX results!! Low chloride diffusion coefficient Large amount of water in geopolymer concrete mix Weak sodium metasilicate gel deposited in capillary pores Preventing transport of chloride ions during the test However, in-situ it can be carried through to the surface as efflorescence VPV Test (AS ) 24

25 Excess water additions can have highly pronounced effects on properties of Geopolymer Concrete Geopolymer concrete is less forgiving & it is more susceptible to excess water additions compared to conventional concrete 25

26 Summary The use of geopolymer concrete is underpinned by a desire to take advantage of its sustainability credentials including low embodied carbon Use by VicRoads over the past five years has served as an impetus for significant progress in the commercialisation of geopolymer concrete both in Victoria and other parts of Australia general concrete paving works reinforced concrete pipes precast reinforced soil panels precast building panels footings and slabs, etc The definition and provision of geopolymer concrete in VicRoads standard specifications serves to overcome the barriers created by the unfamiliarity of this new material and the entrenched use of conventional concrete over the decades It further provides the confidence and pathway required by designers, contractors and asset owners and managers to specify and use low carbon geopolymer concrete 26

27 Impediments to the wider use of Geopolymer Concrete Resistance to releasing or sharing Intellectual Property of geopolymer mix design Major Issue, need to overcome! Commercialisation still in infancy with only small number of plants operating Joint ventures are difficult to set up due to IP issue Need to increase geographic capacity in order to help boost demand Existing concrete supplier companies not shown a keen interest in technology More experience required to optimize geopolymer mix on a commercial basis Require to significantly improve mix designs to facilitate workability, flowability, compactability and finishability by utilising suitable water reducing and superplasticising admixtures to significantly minimise the amount of water used geopolymer concrete - water much higher than conventional compared to structural conventional concretes of L/m 3 to significantly reduce W/B Ratio & penetrability (reduce VPV) Lack of an Australian Standard Takes years & some may not be supportive supporters! Didn t I tell you, don t be an impediment to progress! Geopolymer concrete is good stuff! Specifications YES!! When?????????????!!! 27