Sulphate Attck on Concrete

7/23/2019 Sulphate Attck on Concrete

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SULPHATE and SOFT

WATERATTCK ON CONCRETE



SULPHATE and SOFT WATERATTCK ON CONCRETE



SULPHATE and SOFT WATERATTCK ON CONCRETE



1- Gypsum reacts with C3 A :

C3 A + 3CaSO4 C3 A.3CaSO4.32H2O

Reactions During Cement

Hydration

4- The forme phase is referre to as !Afm" or mo#osu$phate.

%- &ttri#'ite formatio# i#(o$(es co#siera)$e (o$ume i#crease.

2- The forme crysta$ is ca$$e *&ttri#'ite or Aft !A$umi#o-

ferrite-tri"

3- ,f the ceme#t co#tai#s e#ou'h C3 A the reactio# wi$$ co#ti#ue

after co#sumi#' the 'ypsum as fo$$ows:

C3 A.3CaSO4.32H2O + 2C3 A 3!C3 A.CaSO4.12H2O"



Reactions During Cement

Hydration



Sot Water Attac!"

1- Soft water perco$ati#' throu'h co#creteisso$(es hyratio# proucts i# the

fo$$owi#' orer:

a# Ca$cium Hydro%ide &CH'(# )onosu$*+ate

c# Ettringite

d# C#S#H

C#S#H is deca$ciied once CH is una($e to

maintain t+e Ca ion concentration



Diferent Types o Attack

1- Internal Attack2- External Attack



n erna acDelayed Ettringite Formation(DEF):

1-Ettringite is not formed if concrete temperature exceeds 70C.

2- If curing is at elevated temperature, or if self heating in large pours

(or in hot eather! ettringite might not "e formed.

#- $onosulphate is present and most of the sulphates are a"sor"ed "%

C-&-'.

- )hen concrete cools don to am"ient temperature, these phases arenot sta"le and ettringite cr%stals form ith considera"le expansion.

*- In man% cases this dela%ed ettringite formation leads to crac+ing

through the paste and around the aggregate particles.



n erna acDelayed Ettringite Formation(DEF):



Precautions to A,oid DEF"

1- A(oi ouri#' Co#crete i# Hot weather 2- ar'e pours accumu$ate heat at the

rate of 12C/100 ' ceme#t.

3- How much is the rise of temperature fora co#crete mi co#tai#i#' 400 '

ceme#t/m3

4- The use of f$y ash or s$a' to reuce theheat of hyratio# is 'oo.

%- ow C3 A su$phate resisti#' ceme#t

seems to ha(e $ower ris of &5.



E%terna$ Attac!

1- Su$phates are prese#t i# 'rou# water6 a# soi$.

2- Commo# su$phate sa$ts are: soium6 ma'#esium6

potassium6 a# ca$cium.

3- &ter#a$ su$phates react with C3 A a# mo#osu$phates

!Afm" to form ettri#'ite !Aft"

4- Aitio#a$ reactio# taes p$ace with CH to form'ypsum:

Ca!OH"2 + SO42- 7 CaSO4.2H2O +2OH-



E%terna$ Attac!

%- ,f a$$ CH is co#sume6 eca$cificatio# of C-S-H taesp$ace.

8- -n sodium su$*+ate attac!6 crac formatio# is the

mai# ama'e mecha#ism.

9- -n magnesium su$*+ate attac!6a- there is $ess craci#' )ut more rapi $oss of C-S-H $eai#' to

the estructio# of the structure

)-a# i#so$u)$e hyroie is forme !)rucite". ,f it precipitates

i#to co#crete6 it wi$$ acce$erate the reactio# of ma'#esium io#

with CH. ,# the case of sea water6 )rucite forms a protecti(e

$ayer that reuces the su$phate attac.



E%terna$ Attac!

Sulphate solutionSO4

2-

Un reacted zone C3A(CS !12

Sulphate SolutionSO4

2-

Un reacted zoneC3A(CS !12

Ettrin"ite #or$ation C3A(CS3 !32



E%terna$ Attac!


2-



%&psu$ #or$ation C3A(CS3 !32

And reduced Ca(O!2 CS!2


2-




And reduced Ca(O!2 CS!2


And 'ecalci) o* CS! SiO2 a+

CS!2



E%terna$ Attac!T+aumasite Formation

1- Thaumasite has the compositio#:

Ca3Si!OH"8!SO4"!CO3".12H2O

2- ,t is forme throu'h a com)i#atio# of su$phate attac a#car)o#atio#

3- Su$phates is usua$$y from a# eter#a$ source )ut car)o#ate

may )e eri(e from the a''re'ate or ceme#t co#stitue#ts.

4- ,t forms i# wet co#itio#s at temperatures )e$ow 1%C.

%- The attac o# C-S-H $eas to comp$ete estructio# of the

ceme#t paste.



E%terna$ Attac!T+aumasite Formation

,hau$asite Under SE Ettrin"ite Under SE



S*eciying Concrete or

Su$*+ate E%*osure"1- C$assiying e%*osure conditions" !water

a# soi$"




Su$*+ate E%*osure".# Concrete /ua$ity




Su$*+ate E%*osure"0# Aggregate Ty*e"

a" Ge#era$$y6 A''re'ate type oes #ot ha(e 'reat

effect o# the rate of reactio#

)" Howe(er6 i# case of pipes $imesto#e is

recomme#e so it isso$(es as we$$ a# oes#ot form e)ris

c" ,f the aci supp$y is $imite6 $imesto#e wi$$ a$so

assist i# #eutra$i;i#' it.

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Sulphate Attck on Concrete