New ASR in concrete Control Strategies

New ASR Control Strategies – Metakaolin and Other Alternatives

Adjusting ASR Control Strategies In light of changes with Fly Ash and Lithium

ACI Carolina ChapterSeptember 28, 2016by Claudio Manissero President – ChemCognition LLC

Agenda

Introduction to Alkali Silica Reactivity (ASR) ASR Control Options Lithium Nitrate new Developments Status of Fly Ash

– Availability– Control of new chemistries involved

New Alternatives – Metakaolin, VCas Economic Considerations

Introduction to ASR

Alkali Silica Reaction (ASR) occurs between the reactive silica in aggregates used to make concrete, and the hydroxide and alkalis (sodium or potassium) present in the concrete pore solution.

The products of these reactions are alkali silica gels, which may cause expansion and cracking of concrete in service.

ASR an issue only if deleterious (e.g. causes damage) Development of ASR takes a long time to develop depending on conditions

and reactivity of aggregates ASR issues identified in most of the ACI region ASR can significantly impact lifecycle as it prevents concrete from meeting

design life.

Identification - Recognize Signs of Potential ASR

Identification - Signs of ASR

Identification of ASR - References

Field Inspection - See AC 150/5380-8 – Handbook for Identification of ASR in Airfield Pavements – 2/2/04 http://www.faa.gov/airports_airtraffic/airports/resources/advisory_circulars/media/150-5380-8/150_5380_8.pdf

SHRP C-315 – AASHTO Guidehttp://leadstates.transportation.org/asr/library/C315/

Obtain cores - Petrographic analysis Laboratory investigations (EM, etc.) Review construction records Aggregate history Mix design Testing records Review maintenance records Obtain deicer usage records (if applicable)

http://www.faa.gov/airports_airtraffic/airports/resources/advisory_circulars/media/150-5380-8/150_5380_8.pdf

http://www.faa.gov/airports_airtraffic/airports/resources/advisory_circulars/media/150-5380-8/150_5380_8.pdf

What causes ASR induced cracking?

Solubility of Si+ as Function of pH

ASR Control Options - SHRP Findings

Use low alkali cement - 0.6% as Na2O equivalent(Na2O + 0.658 K2O)

Use nonreactive aggregates• Petrographic analysis (ASTM C-295)• Mortar bar test (ASTM C-1260)• Field history

Use pozzolans or GGBFS to reduce mobility of alkali. Fly ash most commonly used, but in many cases only F allowed (really based on CaO content)

Use Lithium compounds Issue is how to predict efficacy of option

Composition of Tested Fly Ashes

Composition of Tested Fly Ashes

Also note that with the ashes shown here, the calcium contents are very different

ASTM C227 Mortar Bars

ASR Testing Controversy

ASTM C 1260

Designed for aggregates only Mortar Bar Test (MBT) – soak bar in solution of 1 N NaOH

for 14 days. If it passes at ≤ 0.10% expansion @ 14 days, OK

If not, then test with the Concrete Prism Test (CPT) for 1 year

Don’t use 28 days unless you already know that this is appropriate for the aggregate

ASTM C 1567

Modification of C1260 to test mixes/maeterials – including fly ash.

Don’t use unless you have compared the C 1260 result with the CPT

If it falls into the correct range, then proceed

If not, then do the 2-yr CPT

FHWA Guidance

All stresses combine to cause cracking

Basis of Recommendations

Real Life

Table of Results from the CANMET Program

Comparing the 14 day and the 2 yr CPT

False Positives % of Total1 3.6

False Negatives % of Total4 14.3

14 day AMBT vs. 2 yr CPT

Comparing the 28 day and the 2 yr CPT



28 day AMBT vs. 2 yr CPT

Comparing the 14 day and the slab



14 day AMBT vs. Slab

Comparing the 2 yr CPT and the slab



2 yr CPT vs. Slab

Comparing the 28 day and the slab



28 day AMBT vs. Slab

Precision of Tests

The CPT, like all tests, gives at best an approximate value – for two main reasons

– The precision of the test – The wide range of situations it is supposed to apply to, although it only

uses a single ‘mix design’ and a single alkali loading From ASTM C 1293 ---- The multi-laboratory coefficient of variation of a

single test result (mean of measurements of three prisms) for average expansion greater than 0.014 % has been found to be 23 % (CSA A23.2-14A-00). Therefore, results of two properly conducted tests in different laboratories on the same aggregate should not differ from each other by more than 65 % of their average, nineteen times out of twenty.

For ASTM C1567 – 43%

ASTM C1293 Precision

Owner Protection from ASR

Achieving Balance

Does the C1547 Work in Real Life?

Lithium Effect

USACE CRD-C 662

Based on ASTM C1567 The soak solution storage time is increased to 28 days Add the lithium admixture to the mortar in the mixture at the

dosage level to be evaluated– Details of calculation given in the procedure

Add the lithium admix to the soak solution at half the molar ratio evaluated in the mortar– Details of calculation given in the procedure

Dosage passes if the expansion at 28 days is < 0.08%

Design / New Construction

The potential for ASR should always be considered when using silica containing aggregates.

History of ASR is a red flag for new construction. Lack of ASR, e.g. mix and aggregate history is not a reliable

indicator. Traditional test methods not always reliable. Stricter testing

requirements being adopted. Potential for ASR derives from both the coarse aggregate and the

fine (e.g. sand). Both should be tested. Raw material changes Provide industry with alternatives to prevent ASR. Economics will

dictate the best option for the specific case.

ASR Control Options - Considerations

Low alkali cementsMost states require 0.6% - At times too high - ASR occurs even with low alkali cement. Not effective if using deicing salts.Sources of low alkali cements diminishingIssues with total alkali vs. soluble alkaliNew plants very expensive, environmental barriersNot available in many key regions.Cement companies reacting to ASR issues by developing IP cements Effect of higher levels of limestone (increases Ca content) Does not compensate for external alkalies, concentration of alkaliesNew trend is to look at total alkali content


Nonreactive AggregatesNot available in many regionsTransportation costs make it unlikely that nonreactive aggregates will be shipped very farMany states require ASR TestingTests being adopted are severe (C1260), not good predictors of performance in-filed or take a long timeVarious categories of reactivityUnreliable and incomplete field histories.Sources of nonreactive aggregate diminishing.Expensive option! (more later)


Lithium admixturesLithium admixtures have proven in the field to be the most reliable effective solution for prevention of ASRTheir use is being specified in a number of new projectsRecent issue is that lithium market is short due to increasing demand in batteries – raw material cost has increased 2-3 X over last six months.Result is that pricing of lithium admixtures has more than doubled.Material is available at higher price but not worthwhile if lower price.Only way to make it more economically viable is to decrease amount used by combining with low alkali cement and with pozzolans.Still best option for critical uses (e.g. nuclear, critical infrastructure)

ASR Control Options - Lithium

ASR Control Options – Pozzolans Considerations

Choice of alternative pozzolans dependent on desired properties, availability and cost – options:Fly ash GGBFS (slag)Silica FumeMetakaolinLow alkali finely ground glass (VCas)Natural pozzolansNew approach that is yielding promising results is ternary mixtures or combination of multiple options

Fly Ash - Considerations

WHEN available, fly ash is the preferred option due to cost and historical experience

Issues that are affecting fly ash– Availability post Duke spills– War on coal issues– Economics of coal vs. natural gas– Changing chemistries driven by new restrictive environmental controls at power

plants– F ash is useful at correct dosages, but not C. Issue is lime content.– Dosage may need to be increased if subject to deicers, due to changes in cement

(higher lime content), longer design life, adoption of new more stringent testing requirements.

Introduction to ASR

Fly Ash - Availability

Availability in our area has definitely decreased driven by a number of factors. Overall availability on East coast is sufficient to meet demand but often not

available at the time it is needed and or right location. Industry is implementing a number of strategies to improve it:

– Building significant storage capacity to store during low demand– Previously unutilized locations being brought on stream– Reclamation for fly ash ponds (material has to be moved in any case)– Improvements in infrastructure and logistics for shipping material further

There are some imports popping up but logistics make it impractical. Beware of quality and consistency!

Pricing of fly ash is inevitably increasing at time substantially (expect $ 40-60/ton increases)

Fly Ash – Control of Changing Chemistries

Important parameters to be considered in fly ash for concrete use – LOI – affects air – Presence of activated carbon (PAC use for Hg removal)– Alkali – e.g. Na2O equivalent, soluble vs. total – Use of trona for scrubbing– Ratio of oxides – particularly relative amounts of silica oxides vs. alumina oxides– MgO content (hardburned) – Increased use of MgO for scrubbing– Free sulfate content– Other components (e.g. amines, ammonia, bromide, mercury etc.)

Traditional Classification no longer important or valid (F vs. C) Industry implementing fly ash treatment processes at power plants to

remove/neutralize activated carbon and other undesirable components No good solution yet to prevent delayed expansion if MgO content is

increased by adoption of this scrubbing method.

Fly Ash – Addressing PAC issues with AEA

Work conducted by Headwaters

Fly Ash – Addressing PAC issues with AEA

Work conducted by Headwaters. Implementation of RestoreAIR technologies.

ASR Control Options - Metakaolin

Limited work has been done with metakaolin to establish control levels for ASR using new tests

Data according to standard tests indicate that levels of metakaolin needed are 8-12% cement replacement

Limited work has been done on tests similar to C1567 in Brazil and material has performed well in a number od dam projects there.

Properties vary depending on source of metakaolin – some material can have high water absorption and requires high levels of HRWR

Material readily available from various sources and interest in its use for ASR is increasing.

Testing program being devised and seeking sponsors.

ASR Control Options - Metakaolin

ASR Control Options - VCas

VCas is a recycled ground glass that is produced from e-glass, low alkali type glass. Two grades available VCas1 and VCas2

Other type glass not good for ASR due to high alkali levels Material is a pozzolan as it will react with lime to make CSH Testing of both conducted on highly reactive rhyolite from NM using a

modified ASTM C1567 (AMBT) and USACE CRD-C 662 Comparisons with F fly ash and lithium nitrate admixture were evaluated Combinations with lithium nitrate were also evaluatedCONCLUSIONS VCAS1 and VCAS2 materials were more effective in ASR control with the

highly reactive rhyolite than equivalent amounts of Class F fly ash VCAS1 and VCAS2 materials were very effective in combination with lithium

nitrate admixture

ASR Control Options - VCas

How Does ASR Impact The Industry?

The design engineer needs to be aware of ASR potential with currently available local materials

Warranty and liability issues are likely to increase New technologies are now available to produce ASR-resistant concrete The engineer has a fiduciary duty towards the owner to utilize the latest

knowledge and new technologies when applicable. Owner concerns are durability and design life – ASR affects both Owners have to understand that in the new reality ASR control

strategies will result in higher costs Does lowest initial cost provide a prudent approach to durability?

Recommendations to address ASR

Require testing of both coarse and fine aggregates– Modified ASTM C1260 with expansion less than 0.1 % at 28 days– If field history shows ASR, then require ASR abatement

Require low alkali cement (below 0.6% Na2O eq.) – but provide allowance based on test performance

Allow the following mitigation options– Use of unreactive aggregates– Use of appropriate pozzolans – No definition of Class but implement restrictions on

chemistry.– Broaden allowed pozzolans to include metakaolin, low alkali glass (Vcas), natural

pozzolans– Use of lithium admixtures for critical infrastructure – follow manufacturer

recommendations– Allow combinations of low alkali cements, multiple pozzolans pozzolans and lithium

Require testing of mix– Modified ASTM C1567 with expansion less than 0.1 % at 28 days

Economics

Cost of the various options is reasonable and are in general comparable. Best option varies dependent on specific locations.

Mitigation options are usually less costly than obtaining nonreactive aggregates if those must be shipped >100 miles or more depending on mix design and local economics.

Cost of options is minimized by using it in combination with suitable pozzolans. There may be problems with availability of traditional/good Fly Ash in area, but

overall availability is being addressed. Costs to beneficiate Fly Ash as well as supply/demand will affect price of fly ash. For critical infrastructure lithium is a prudent choice and is available. Overall expect the following:

– Fly ash will continue to be available but cost will probably increase – Need to revise mixes to look at alternative options (lithium, mixed pozzolans etc.)– Lithium increasing costs will limit its economic viability but effectiveness is proven– Expect that overall cost of durable concrete will increase.

Example Economics

New ASR in concrete Control Strategies

Engineering

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