CIE 525 Group 1 Final Report

7/25/2019 CIE 525 Group 1 Final Report

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ALKALI- SILICAREACTIONINCONCRETEANDITSEFFECTONSAFETY RELATED NUCLEAR

STRUCTURES

CIE 525 CONCRETE

STRUCTURES

HOMEWORK#1

9/20/2013

Nashwan AlShuwaili

Ma !a"$

Ch$is%&h$ !u'"

E$i' Cul($


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Table of Contents1.0) Alkal Sl!a Rea!ton..............................................................1

1.1) "o# Does ASR Fo$%&..........................................................'

1.') E(e!ts of ASR on Con!$ete..................................................'

'.) Seab$ook N!lea$ *o#e$ *lant.................................................+

'.1) ASR at Seab$ook *o#e$ *lant...............................................+

'.') ASR E(e!t on St$!t$al Inte,$t of Seab$ook *o#e$ *lant. +

'.) Dan,e$ of ASR to N!lea$ *o#e$ *lants.............................../

.) ASR *$eenton L%tn, Alkal Content n Con!$ete................/

.1) I%2le%entn, S22le%enta$ Ce%entn, 3ate$als............4

+.) Con!lson...............................................................................4

Refe$en!es....................................................................................5

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1.0) Alkal Sl!a Rea!ton

Alkali-Silica Reaction (ASR) is a reaction in concrete that occurs over time due to the

interaction between the alkaline found in cement and silica found in aggregates. This reaction

forms a gel that expands when exposed to water that can cause cracking within the concrete.These cracks degrade the ualit! of the concrete reducing some of its ph!sical properties such as

compression and tensile strength. ASR is an issue in the maintenance of concrete structures. As

the cracks expand" the concrete degrades" and so does the structures capacit! to withstand

demands and can cause some serious structural problems over time.

1.1) "o# Does ASR Fo$%&

The alkali-silica reaction (ASR) commonl! found in concrete is a subset of reactions

called Alkali-aggregate reactions (AAR) which consist of both ASR and Alkali-carbonate

reactions. The alkali-silica reaction is a chemical bond that forms between Alkali metals" which

are found on the leftmost column of the periodic table of elements" and Silicon. This reaction

naturall! takes place in concrete because its ingredients naturall! contain these elements. Alkali

metals" most notabl! sodium (#a) and potassium ($) are found in %ortland cement. &ement is

commonl! made with a compound of

Sodium or %otassium and 'x!gen (#a'e

or $'e). Silica is usuall! contained in

numerous aggregates including uart"

which is commonl! used in making

concrete. *uart is comprised of a silicatetrahedral '-Si-'. +hen cement"

aggregate" and water is combined in the

process of creating concrete the reaction is

initiated. A basic solution caused b! the

interaction of the alkali metals and water

attacks amorphous silica within the

aggregate and creates a h!groscopic alkali-

silica gel. This gel attracts water and swells

inducing fractures within the concrete (,ernandes" /).

1.') E(e!ts of ASR on Con!$ete

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Figure 1: Cracking Caused by ASR


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The biggest challenge an engineer faces when dealing with ASR is having to determine

the effect ASR has had on the structural capacit! of a structure. 0eing able to come up with new

concrete properties can be difficult because ASR has different effects depending on the ph!sical

and chemical characteristics of the aggregate" the environment of the structure" and how long

ASR has been present in the concrete.

1n 233" R.#. Swam! and 4.4. Al-Asali published a technical paper giving their results

of an experiment on engineering properties affected b! ASR. Their test consisted of measuring

the degradation of concrete properties using specimens with different 5reactive6 aggregates.

The! used opal and fused silica as their reactive aggregates along with a control specimen that

had a non-reactive aggregate. Swam! and Al-Asali allowed the specimens to cure a set amount

of da!s and then performed a compression" split c!linder" modulus of rupture" d!namic modulus

of elasticit!" and pulse velocit! test. All tests were in accordance to their respective 0ritish

standards.

Table 1: Efects o ASR Expansion on Concrete Properties

The results of the tests showed degradation of the concrete as time elapsed. Table

above shows the results of their experiment. Swam! and Al-Asali were able to conclude that both

tensile strength and compressive strength are directl! affected b! the percent of crack expansion

due to the ASR. The tensile strength of the concrete is more sensitive to the ASR than the

compressive strength. ,or example" after 7 da!s of curing" the modulus of rupture of the fused

silica samples had decreased b! 839 whereas the compressive strength had onl! decreased 9.

This is to be expected because as a specimen is put under compression those cracks formed b!

ASR close" where as in the modulus of rupture test those cracks caused b! ASR continue to

expand.

The results of this experiment can help guide an engineer in the process of tr!ing to

determine the degradation of the concrete but these results might not alwa!s represent the actualperformance of a concrete structure. Swam! and Al-Asali:s experiment showed that compression

strength can be affected b! the presence of ASR" but these test were done on c!linders or cubes

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in a lab which doesn:t represent the actual in-situ stresses concrete structures ma! face. Things

like confining reinforcement and other loadings ma! affect the concrete properties and should be

considered. The actual data results was dependent on the t!pes of aggregates used and differentmix designs ma! !ield different results. The experiment did conclude that ASR negativel!

impacts the strength of concrete and can harm the structural integrit! of a structure" especiall!

over a long period of time.

'.) Seab$ook N!lea$ *o#e$ *lant

;uring the renewal process of the Seabrook #uclear %ower %lant in 2" aninvestigation observed that there was excessive intrusion of moisture into the walls of man!

5&ategor! 6 or safet! related structures or structures designed to withstand maximum potential

seismic loads. RA>nerg!" the presence of ASR is unexpected due to the use of tested igneous rock aggregates andlow alkali %ortland &ement (#ext >ra >nerg!" /).According to %rofessor %aul 0rown from

%enn State =niversit!" ASR at Seabrook %ower %lant could have developed due to sources of

moisture present at local areas where there was sufficient alkali present" or there was a sufficientamount of salt water intrusion that can help the development of ASR (0rown" ).

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Figure : Seabrook Po!er Plant


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'.') ASR E(e!t on St$!t$al Inte,$t of Seab$ook *o#e$ *lant

After the discover! of ASR at Seabrook %ower %lant" a series of investigations were

conducted to determine the amount of ASR present and how much the ASR had degraded theconcrete. The first thing engineers did was extract concrete core samples from six different

locations" as seen in ,igure /below. According to the =S#&R 1nspection Report" these corewere then mechanicall! tested to discover the degree of degradation and determine the ke!concrete properties needed to determine the strength of existing structures. These tests showed

that the compressive strength of the degraded concrete was relativel! unaffected due to ASR but

the modulus of elasticit! had been reduced b! 9. ;espite these results" engineers concludedthat the data was not a good representation of the structural performance of the concrete. 0!

removing the cores from the structure" these cores are no longer sub?ected to stresses and strains

that are present b! the confinement of the ASR expansion due reinforcing and loadings (=S#&R"

). >ven though the data from these tests were not a good indication of the strength of theconcrete" the core samples were still used as a method of finding the presence of ASR.

Figure ": Concrete Core Sa#ple $ocations

The engineer:s alternative method of determining the degree of degradation was a 5walkdown6 review of the structures and a six-month crack indexing measurement to determine the

progression of the ASR and the rate of expansion (=S#&R" ). The 5walk down6 reviewconsisted of visual inspections of structures which found ASR crack patterns" actual ASR gel"and discoloration of concrete due the ASR gel. >ngineers are also in the process of a large scale

experimentation at the =niversit! at Texas to test specimens that better represent the conditions

at Seabrook.After the completion of the 5walk down6 review and the crack indexing stud!" engineers

needed to determine if the power plant was structurall! adeuate to continue operations. The first

thing engineers looked at was the flexural capacit! of the affected structures and their d!namic

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response to seismic loads. To accomplish this" engineers made finite element modules and

conservativel! assumed the current state of concrete degradation using research on ASR along

with some concrete properties from the mechanical tests which the! saw consistent with theirresearch findings (=S#&R" ) . These finite modules showed no concern for immediate

structural issues. >ngineers also checked if the shear capacit! of certain structures were still

adeuate b! again using a finite element module with conservative assumptions of the concretedegradation. These modules also did not show an! immediate concern.

>ven though engineers are continuing to research and investigate the long term structural

integrit! of the Seabrook %ower %lant" the! concluded that the power plant is still structurall!adeuate to continue operations. +ith the help of continued visual investigations along with the

current research being done at =niversit! of Texas" engineers are hopeful the! will be able to

determine if the power plant is safe for long term usage or if ma?or repairs are needed.

'.) Dan,e$ of ASR to N!lea$ *o#e$ *lants

>ven though ASR has not caused an! serious structural issues at Seabrook %ower %lant!et" if left unchecked there can be some serious safet! issues. The cracks caused b! the ASR gel

can continue to expand and degrade the concrete. These cracks also lead to man! issues with

reinforcing steel and anchorages. >ven though the engineer:s investigations showed that there

hadn:t been an! corrosion to rebar at this point in time" water will be allowed to penetrate the

concrete deeper and lead to the corrosion as the cracks continue to grow. There is also a concern

of micro cracks forming around embedded anchorages that would lower the overall structural

capacit! of these anchorages that support safet! components. 'verall" ASR reduces the strength

of the concrete and can lead to problems with corrosion" anchorage" and concrete spalling. This

reduces the structural capacit! of the power plant:s structural s!stems. 'ver time the structural

capacit! will continue to diminish while the ph!sical demands will remain the same. >ventuall!the power plant:s structures ma! become inadeuate and potentiall! lead to severe safet! issues

for those working at the plant and surrounding areas.

.) ASR *$eenton L%tn, Alkal Content n Con!$eteResearch in the past has shown that an expansive reaction in concrete is unlikel! to occur

if the content of alkali in the cement is below .79. Recent research has indicated that Alkali-

Silica Reaction can occur in the field when low alkali cements are used" however" the .79

value has become the maximum limit in the =nited States to be used with reactive aggregates

(@Selecting 4easure to %revent ;eleterious Alkali-Silica Reaction in &oncrete@) . This value appears inAST4 & Standard Specifications for %ortland cement. ,igure 8 below describes the

relationship between cements of var!ing alkali content and the expansion cracks produced. The

figure shows that the alkali content is controlled b! the ratio of the cement content and the alkalicontent of the concrete" rather than the cement alkali level b! itself (=S;'T" ).

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Figure %: Alkali Content &s' Expansion Cracking


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,rom ,igure 8

above" a &oncreteAlkali &ontent value between /. B 8. kgCm /" the expansion at one !ear is uite different

depending on the content of cement in the concrete. ,igure shown below shows the

relationship between &oncrete Alkali &ontent and the expansion cracks produced dependent ondifferent t!pes of reactive aggregates. TD Sand" siltstone" and limestone are the three reactive

aggregates that were tested.


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.1) I%2le%entn, S22le%enta$ Ce%entn, 3ate$als

Research has shown that there are man! different t!pes of supplementar! cementing

materials that can be used to replace %ortland cement. The principle of using these materials is

to replace some of the cement containing alkali-silica with another cementing material. The t!peand amount of cementing materials is sometimes tough to determine and is based on the

following criteria (=S;'T" )E

The nature of the reactive aggregate.

o T!picall!" the more reactive the aggregate is" the more

supplementar! cementing materials reuired.

>xposure conditions of the concrete

Alkali availabilit! within the concrete

The nature of the cementing materials

Table below gives a list of supplementar! cementing materials and their reuired

replacement level to reduce expansion cracking due to Alkali-Silica Reaction.

+.) Con!lson

ASR s a ,el fo$%n, $ea!ton n !on!$ete !ase9 b t:e !:e%!al $ea!ton oft:e alkalne n t:e !e%ent an9 t:e sl!a n t:e a,,$e,ate. T:s ,el !an abso$b #ate$an9 e;2an9 !asn, t:e !on!$ete to !$a!k. T:ese !$a!ks 9e,$a9e t:e Cate,o$ 1? o$ Safet Relate9 st$!t$es

at Seab$ook. Usn, $esea$!: an9 a$os tests= en,nee$s :ae 9ete$%ne9 t:atSeab$ook s stll safe to o2e$ate bt tests !ontne to @,$e ot f t:e 2lant s safefo$ lon, te$% sa,e o$ f $e2a$s nee9 to be %a9e. ASR !an be !ont$olle9 b2$eenton. testn, a,,$e,ates an9 sn, lo# alkalne !e%ents= ASR !an be2$eente9.

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Table : Supple#entary Ce#ent +aterials


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Refe$en!es

$o#n= *. B'01'). Co##entary on t,e Alkali-Silica Reaction in Concrete Structuresat t,e Seabrook .uclear Plant'Une$st *a$k= *A *enn State Une$st.

Ene$,= N. B'01).ASR Root Cause E&aluation Su##ary'Seab$ook= N".

Fe$nan9es= I.= $oek%ans= 3. B'01). AlkalSl!a Rea!tons An Oe$e#. *a$t I.+icrostruct' Anal' +etallograp,y/ +icrostructure/ and Analysis= '78-'/8.

S#a%= R. B1554). T,e Alkali-silica Reaction in Concrete'CRC *$ess.

S#a%= R.= Al-Asal= 3. B1544). En,nee$n, *$o2e$tes of Con!$ete A(e!te9 bAlkal-Sl!a Rea!ton.AC0 +aterial ournalBSe2te%be$-O!tobe$)= /8-8+.

U. S. B'01'). Seabrook Station -.RC 0nspection Report 2(222%%"321224'Kn, of*$ssa= *A.

Unte9 States De2a$t%ent of T$ans2o$taton BUSDOT). B'01'). Selecting +easure toPre&ent 5eleterious Alkali-Silica reaction in Concrete'

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CIE 525 Group 1 Final Report

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