10/12/2012
Although physical testing of concrete is vital
(mechanical, NDT, etc), this presentation
will focus on chemical testing only at the
g of concreting
g
different stages
It also focuses on the need and significance
of every requested test.
It does not provide solutions for repair.
Concrete Chemical
Testing Requirements and
TestingRequirements
Implications
Prepared by: Mohammad Dokmak-TQP
Presented at the UNESCO Palace-Beirut
Oct 16, 2012
Concreting Stages
Concrete shall be chemically monitored and controlled
at each stage from production to post hardening.
Stage 1: Raw materials
Stage 2: Fresh concrete
Stage 3: Hardened concrete
Stage 4: Old concrete or Concrete under specific
circumstances
Every stage necessitates certain chemical tests to
be conducted. Some other tests are only required
upon doubt.
Concreting Stages
Project
specifications are almost crowded
with chemical tests that to be conducted.
As an engineer, you might not necessarily
be knowledgeable of how to conduct a
test; however, you should be aware of the
reason behind requesting such test, able
to analyze the obtained result, and almost
able to recommend the proper solution.
What to test and Why?
Raw Materials
In the subsequent slides, We will be focusing
on what
h t and
d why
h to
t test
t t att each
h stage
t
off
concrete.
Concrete raw materials comprise the following:
Cementetious materials (cement, fly ash,
silica fume, etc)
Water
Aggregate (CA, MA, CS, and NS)
and Admixtures (retarding, accelerating, air
entraining, etc)
To ensure the quality of your concrete you should select the
best concrete constituents, free of deicing chemicals , with
minimum organic matters, non reactive with alkali, etc.
10/12/2012
Raw Materials- Cementetious
Test
Chemical analysis
Chromium VI content
Shrinkage tests (in water, in
sulfate, etc)
Method
ASTM C114, or BS
EN 196-2
EN 196-10
196 10
ASTM C452,C1012,
C596, or C1038
Raw Materials- Cementetious
Need for cement Chemical Analysis
Cement is almost reliable (consistent); however it has to be checked upon
doubt of its properties, when bizarre strength results occurs under
controlled conditions, to confirm type, etc.
Indicators of alteration in cement composition are such that:
Early strength results at 7 days due to increase in Tricalcium Silicate
(C3S)%.
S)%
Dicalcium Silicate (C2S) hardens slowly and contributes largely to strength
increases at ages beyond 7 days.
Tricalcium Aluminate (C3A) liberates a large amount of heat during the first
few days of hardening and, together with C3S and C2S may somewhat
increase the early strength of the hardening cement (this effect being due to
the considerable heat of hydration that this compound evolves). It does affect
setting times.
Tetracalcium Aluminoferrite (C4AF) contributes very slightly to strength gain.
However. Contributes to the color effects that makes cement gray.
Raw Materials- Cementetious
Raw Materials- Cementetious
Need for cement Chemical Analysis
Chromium VI
Magnesium Oxide (MgO) causes delayed expansion when present in
large amounts. ASTM limits all cements to 6.0%.
Sulfuric anhydride (SO3) is an indirect measure of the amount of
gypsum or calcium sulfate (CaSO4) in the cement. Gypsum is added to
cement for the purpose of regulating setting time. Too much gypsum
and, therefore, SO3 is g
generally
can cause expansion
p
y limited ((C150))
Insoluble Residue is an indication of the efficiency of the burning
process. (I.E. Determines the amount of unburnt raw materials (clay) ;
ASTM limit is 0.75%
Alkalies: Large amounts can cause certain difficulties in regulating set
times of cement.. Also, increase the risk of ASR reaction. ASTM has
an optional limit in total alkalies of 0.60%, calculated by the equation
Na2O + 0.658 K2O.
The above is just to mention the severe effect of cement composition
on its behavior
Do not use cement which contains, when hydrated, more
than 0.0002 % (2 ppm) chromium (VI) by dry weight of
cement.
Raw Materials- Cementetious
Shrinkage/Expansion tests
C596 is used to develop data on the effect of a hydraulic
cement on the drying shrinkage of concrete made with
that cement
C1038 is used to determine the amount of expansion of a
mortar bar when it is stored in water. Expansion may
become excessive when the cement contains too much
sulfate.
lf t
C452 is also used to establish that a sulfate-resisting
Portland cement that meets the performance requirements
of Specification C 150 by adding different % of gypsum
to the cement and testing.
C1012 provides a means of assessing the sulfate
resistance of mortars made using Portland cement. The
standard exposure solution used in this test method
contains 50g of Na2SO4 /L.
It has Short term effect. Skin ulcers or allergy,
gy,
Irritation of the nasal mucosa, and holes in the nasal
septum, Nosebleeds, Nausea, Itching.
It also has long term effects like: Carcinogenic in
humans site, Lung and sinonasal cavity, runny nose,
sneezing, and holes in the nasal septum, Kidney and
liver damage, irritation of the gastrointestinal tract,
stomach ulcers, and convulsions, Damage of the
DNA, Death.
Raw Materials- Water
Test
Method
Chemical analysis of water
for use in concrete
AASHTO-T26
pH TDS
pH,
TDS, Sulfate,
Sulfate Chloride,
Chloride ASTM D516,
D516 D512,
D512
Total alkalies.
C114, AASHTO T 26,
Potable water is suitable for use in concrete.
10/12/2012
Raw Materials- Water
Raw Materials- Water
Others
Chloride
The most important chemical in water for
concrete use is the Chloride. It is limited to
pH below 7 causes little deterioration
(etching) of concrete.
Sulfate shall not exceed 3000ppm. (rarely
occurs)
Alkalies as (Na2O + 0.658 K2O) shall be
<600 ppm; else, ASR reaction is more likely
to occur (to be detailed soon).
Total dissolved salts is limited to 50,000ppm
(5%). (rarely occurs)
500 ppm for prestressed concrete or in bridge
decks and to 1000 ppm for other reinforced
concrete in moist environments.
Water for concrete curing is of equal
importance to mixing water, especially that
salt crystals remains at the surface after
water evaporates and would later dissolve
and penetrate at any occasion.
Raw Materials- Aggregates
Raw Materials- Aggregates
Test
Method
Potential alkali reactivity,
ASR & ACR
Chloride Content
S lf Content
Sulfate
C
ASTM C289 &
BS 1744 P1
BS 1744 P1
Soundness by Sodium or
Magnesium Sulfate
ASTM C88
Methylene blue absorption
Organic impurities of fine
aggregates
Some aggregates react with the alkali hydroxides in
concrete, causing expansion and cracking over a period
of many years. This alkali-aggregate reaction has two
formsalkali-silica reaction (ASR) and alkali-carbonate
reaction (ACR).
(
)
Will be detailed in Concrete section
ASTM C837
ASTM C40
Raw Materials- Aggregates
Raw Materials- Aggregates
Chloride and Sulfate
Soundness
Effects and limits will be discussed under
concrete.
Acid or water soluble? The water soluble is
the reactive part and is less than or max
equal to the acid soluble part.
In other word acid soluble chloride or sulfate
represents the total ppm but usually
requested for safety.
Alkali Reactivity ASR/ACR
This test measures aggregate soundness
when subject to weathering action in
concrete or other applications.
Both Sodium and magnesium can be used
alternatively but with different concentration.
The allowable limits for soundness shall be
12 % if sodium sulfate is used and 18 % if
Magnesium sulfate is used (5 cycles).
10/12/2012
Raw Materials- Aggregates
Raw Materials- Fine Aggregates
Methylene Blue Absorption MBA
Organic impurities
MBT is a direct measure of Clay %.
MBT is a also a smart test that identify whether
the decrease in the sand equivalent value is
really
y due to clay
yp
presence or because of silt
size materials.
Aggregates are considered excellent for MBT
values <0.4g/100g and poor for values
>1.0g/100g (Rock Manual)
If Methylene blue test passes you can safely
use your sand with moderate decrease in sand
equivalent values
Raw Materials- Admixtures
Raw Materials- Admixtures
Test
pH, specific gravity and
solids
lid content off admixture
d i
Sulfate content of admixture
Chloride content of
admixture
Method
ASTM C494
Gravimetric
BS EN 480-10,
Potentiometric
Although chloride if harmful to concrete, only
relatively high concentrations in admixture are
significant.
2000ppm of chloride in admixture can be
reported as 0.0%
0 0% (BS 5075: part 1 appendix E)
The contribution of admixture is relatively small.
But what if admix has 30% of its solid content
chloride?
Effects and limits of chloride and sulfate will be
discussed under concrete.
pH should be > 7. lower values could be an
indication of admixture rancidity (expiration).
Solid content and specific gravity are used for
cost control.
S lf t content
t t in
i admix
d i iis nott a major
j
Sulfate
deicing chemical to concrete because of the
relatively small contribution of admix. 10% of
sulfate in admixture could be considered
marginal compared to sulfate coming from the
cement (See combined sulfate example in
concrete)
What to test and Why?
Fresh Concrete
Raw Materials- Admixtures
Fine aggregate shall be free of injurious
amounts of organic impurities.
Aggregates producing a color darker than the
standard shall be rejected.
U off a fine
Use
fi aggregate
t failing
f ili iin th
the ttestt is
i nott
prohibited, provided that, when tested for the
effect of organic impurities on the strength of
the mortar, the relative strength at 7 days,
calculated in accordance with ASTM C 87, is
not less than 95 %.
Test
Water content of fresh concrete
Method
ASTM C1079
Chemical testing of fresh or hardened concrete is
similar.
i il
The most useful chemical test that can be conducted on
fresh concrete is the water content. water content of
fresh concrete can be conducted within an hour with
high precision.
Salt of known conc. is added to a measured amount of
fresh concrete; the decrease in the salt conc. in the mix
reflect the water content.
10/12/2012
What to test and Why?
Hardened Concrete
Test
Method
Hardened Concrete
pH and carbonation
pH of concrete
Cement content
using phenol phthaleine
indicator
ASTM C1084
C1084, BS 1881
1881p124
Chloride content
BS 1881-p124
Sulfate content
Alkali-Silica or carbonate reactivity
(ASR/ACR)
Evaluation of thaumasite sulfate
attack
BS 1881-p124
Depth of carbonation
Many...listed below
In a normal good quality reinforced concrete, the steel reinforcement is
chemically protected from corrosion by the alkaline nature of the
concrete. This alkalinity causes the formation of a passive oxide layer
around the steel reinforcement. Concrete will react with
atmospheric carbon dioxide (or sulfur dioxide) to cause gradual
neutralization of the alkalinity from the surface inwards, a process
known as carbonation.
carbonation
The rate at which this occurs is a function of concrete quality, in
particular the cement content, the water/cement ratio and the
compaction.
It is generally accepted that the rate of the carbonation reaction is
inversely proportional to the square root of the age of the structure.
Concrete cover, mm = (Age yrs)
On this basis, even with a cover of only 10mm, steel reinforcement
should be safe for up to 100 years.
Hardened Concrete
Hardened Concrete
pH and carbonation
Cement Content
Ph Ph is an indicator of carbonation; alternatively pH can be
measured
When carbonation take place the pH value will start falling. The
normal pH-value of concrete is above 13 and the pH-value of fully
carbonated concrete is below 9. Once the carbonation process
reaches the reinforcement
reinforcement, and the pH-value
pH value drops beneath 13 the
passive film on the re-bars will deteriorate and corrosion will
initiate.
Carbonation is a very simple test but an essential indicator of
concrete deterioration.
Carbonation is easy to conduct but very tricky and various possible
mistakes might end with misleading results. Examples, extracting
the concrete in the presence of water may move hydroxides to
carbonated areas giving high pH values or pink color instead of
colorless.
Hardened Concrete
Hardened Concrete
Chloride- Full story
Chloride in concrete can originate from two main
sources:
a) "Internal" Chloride, i.e. chloride added to the
concrete at the time of mixing; for example,
contamination of aggregates or admixtures and the use
of sea water or other saline contaminated water.
b) "External" chloride, i.e. chloride ingressing into the
concrete post-hardening. For example, de-icing salt
applied to many highway structures; and marine salt,
either directly from sea water in structures such as
piers, or in the form of air-borne salt spray in structures
adjacent to the coast; and salts from contact with
contaminated soil.
The cement content of concrete is important from the
aspect of durability, impermeability and strength.
Too low a cement content may permit rapid carbonation
and subsequent loss of the protective alkaline
steel
environment for the steel.
Too high a cement content may cause excessive
shrinkage, thermal cracking from the heat of hydration
in large pourings, or the risk of alkali silica reaction if a
susceptible aggregate has been used and the cement is
not a low alkali type.
How precise is the test? To the nearest 40Kg/m3
Chloride
Chloride does not react with steel but act as
catalyst in the corrosion process.
Chloride present in plain concrete that does not
contain steel is generally not a durability concern.
Chloride has nothing to do with durable concrete
(high strength, low permeability, etc)
However, over decades, the concrete would
deteriorate and the chloride is still hiding and
waiting.
What if concrete is already weak, permeable, or
carbonated?
10/12/2012
Hardened Concrete
Hardened Concrete
Chloride
Chloride
ACI 222.1, chapter 3:
The result would be similar to the below
(<20 years old):
For about 20% cement content 0.10% or 1000ppm by weight
of cement is about 200ppm by weight of concrete
Hardened Concrete
Hardened Concrete
Chloride
Sulfate
Contribution of each constituent-example
Mix Design as
provided by the
batch plant
Weight
(SSD)
Approx Chloride
Total Chloride
content by
Chloride
% by
content by weight
weight of
content, ppm,
weight, A
of cement, ppm =
concrete, ppm,
B
total x 100/A
A x B /100
cement
silica fume
water
370
15
145
15
1
6
130
0
30
20
0
2
superplasticizer
Coarse
Aggregate
Medium
aggregate
Crushed sand
Natural sand
Total
10.8
0.4
2000
687
28
70
20
370
291
540
2429
15
12
22
100
70
70
150
11
8
33
103
Hardened Concrete
686
Sulfate
Sulfate attack can be 'external' or 'internal'.
Internal: due to a soluble source being
incorporated into the concrete at the time of
mixing, gypsum in the aggregate, for
example.
External: due to penetration of sulfates in
solution (soluble), in groundwater for
example, into the concrete from outside.
Cement usually has 3% sulfate (insoluble
form)
Hardened Concrete
Sulfate- Ettringite
Sulfates can attack concrete causing an expansive
disruptive effect resulting in gradual deterioration of the
cement matrix. The reaction occurs between the sulfate
salts and the tricalcium aluminate (C3A) giving needle
like crystals of ettringite (calcium sulphoaluminate) of a
considerably larger volume than the reactants and, if
growing in pores in restricted space, exert a bursting
pressure on the concrete, causing cracking and
disruption.
Microcracks filled with Ettringite
Ettringite formation in a pore of
cement paste
10/12/2012
Hardened Concrete
Hardened Concrete
Sulfate
Sulfate
Contribution of each constituent-example 1
Mix Design as
provided by the
batch plant
Weight
(SSD)
Approx sulfate
Total sulfate
Sulfate
content by
% by
content by weight
content, ppm,
weight of
weight, A
of cement, ppm =
B
concrete, ppm,
total x 100/A
A x B /100
cement
350
15
30,000
4359
silica fume
water
superplasticizer
Coarse
Aggregate
Medium
aggregate
Crushed sand
Natural sand
Total
15
145
10.8
1
6
0.4
0
200
100,000
0
12
448
687
29
250
71
370
291
540
2409
15
12
22
100
250
200
300
38
24
67
5021
33473
Contribution of each constituent-example 2
% by
weight, A
Sulfate
content,
ppm, B
Approx Sulfate
content by
weight of
concrete, ppm,
A x B /100
400
15
145
10.8
15
1
6
0.4
30000
0
200
100,000
4880
0
12
448
687
29
250
71
370
291
540
2409
15
12
22
100
250
200
300
38
24
67
5021
Mix Design as
Weight
provided by the
(SSD)
batch plant
cement
silica fume
water
superplasticizer
Coarse
Aggregate
Medium
aggregate
Crushed sand
Natural sand
Total
Total Sulfate
content by
weight of
cement, ppm =
total x 100/A
33984
One more bag of cement/m3 contributes as much as
100000 ppm of admix.
Hardened Concrete
Hardened Concrete
Sulfate
Alkali Reactivity ASR/ACR
Some aggregates react with the alkali hydroxides in
concrete, causing expansion and cracking over a period
of many years. This alkali-aggregate reaction has two
formsalkali-silica reaction (ASR) and alkali-carbonate
reaction (ACR).
(
)
Alkali-silica reaction (ASR) is more common. In ASR,
aggregates containing certain forms of silica will react
with alkali hydroxide in concrete to form a gel that swells
as it adsorbs water from the surrounding cement paste or
the environment. These gels can swell and induce
enough expansive pressure to damage concrete
Table: Test Methods for Alkali-Silica Reactivity (Source: Farny and Kerkhoff, 2007)
Hardened Concrete
Hardened Concrete
Alkali Reactivity ASR/ACR
Test Methods for Alkali Reactivity
Alkali-carbonate reactions (ACR) are observed with
certain dolomitic rocks. The breaking down of dolomite, is
normally associated with expansion. The deterioration
caused by ACR is similar to that caused by ASR;
gg g
however,, ACR is relativelyy rare because aggregates
susceptible to this phenomenon are less common and are
usually unsuitable for use in concrete for other reasons.
(like abrasion, absorption, etc.)
Test Name
Purpose
ASTM C 227,
Potential alkali-reactivity of cement-aggregate
combinations (mortar-bar method)
To test the susceptibility of cement-aggregate
combinations to expansive reactions involving
alkalies
ASTM C 289,
Potential alkali-silica reactivity of aggregates
To determine potential reactivity of siliceous
aggregates
ASTM C 294,
Constituents of natural mineral aggregates
To give descriptive nomenclature for the more
common or important natural mineralsan aid in
determining their performance
ASTM C 295,
Petrographic examination of aggregates for
concrete
To outline petrographic examination procedures
for aggregatesan aid in determining their
performance
ASTM C 342,
Potential volume change of cement-aggregate
combinations
To determine the potential ASR expansion of
cement-aggregate combinations
ASTM C 441,
To determine effectiveness of supplementary
Effectiveness of mineral admixtures or GBFS in
cementing materials in controlling expansion from
preventing excessive expansion of concrete due
ASR
to alkali-silica reaction
10/12/2012
Table: Test Methods for Alkali-Silica Reactivity (Source: Farny and Kerkhoff, 2007)
Hardened Concrete
Hardened Concrete
Thaumasite Sulfate Attack (TSA)
Test Methods for Alkali Reactivity
Test Name
Purpose
To outline petrographic examination
ASTM C 856,
procedures for hardened concreteuseful in
Petrographic examination of hardened concrete
determining condition or performance
ASTM C 856 (AASHTO T 299),
Annex: Uranyl- acetate treatment procedure
To identify products of ASR in hardened
concrete
Los Alamos staining method (Powers 1999)
To identify products of ASR in hardened
concrete.
ASTM C 1260 (AASHTO T303),
To test the potential for deleterious alkali-silica
Potential alkali reactivity of aggregates (mortarreaction of aggregate in mortar bars
bar method)
ASTM C 1293,
To determine the potential ASR expansion of
Determination of length change of concrete due
cement-aggregate combinations.
to alkali-silica reaction (concrete prism test)
ASTM C 1567, Potential alkali-silica reactivity of To test the potential for deleterious alkali-silica
combinations of cementetious materials and
reaction of cementetious materials and
aggregate (accelerated mortar-bar method)
aggregate combinations in mortar bars
The availability of carbonate ions (CO3)2- changes
the reaction products when sulfates enter the
concrete. Below about 15C in the presence of water,
the reactions between the calcium silicate hydrate, the
carbonate and the sulfate ions p
produces thaumasite
(CaSiO3.CaCO3.CaSO4.15H2O). The calcium silicate
hydrates provide the main binding agent in Portland
cement, so this form of attack weakens the concrete as
well as causing some expansion and, in advanced
cases, the cement paste matrix is eventually reduced to
a mushy, incohesive mass (see pic).
Hardened Concrete
Hardened Concrete
Thaumasite Sulfate Attack (TSA)
Thaumasite Sulfate Attack (TSA)
Since TSA does not depend on the level of calcium
aluminate hydrates, Sulfate resisting concretes (SRPC,
low C3A) can be also susceptible to this form of attack.
Concretes containing granulated ground blastfurnace
slag
g ((GGBS)) as p
part of the cement have g
good
resistance to TSA.
Decreasing permeability can be good defense against
TSA.
Thaumasite has formed around coarse limestone aggregate
What to focus on?
Hardened Concrete
Other Circumstances
Concrete subject to fire
Concrete subject to contact with chemicals
(spillage, contaminated soil or water, etc)
Concrete subject to renovation or addition of
structure
Concrete showing some sorts of damage
(Crack, efflorescence, spalling, coloring, etc)
Concrete under Specific circumstances
Situation
Tests in order
Concrete subject to
fire
Visual, strength, carbonation, tensile
of steel, load test,
Concrete in contact
with deicing
chemicals
Chloride, sulfate, permeability, steel
condition (corrosion), Petrographic,
etc
etc.
Visual, strength, carbonation, tensile
of steel, chloride, sulfate, steel
condition (corrosion), Steel scan,
dimensions, etc.
Visual, crack monitoring, strength,
carbonation, tensile of steel, chloride,
sulfate, steel condition (corrosion),
ASR detection, thaumasite detection,
petrographic, etc.
Concrete subject to
renovation or
addition of structure
Concrete showing
some sorts of
damage-Crack
Remark
Conducted
subsequently.
Petrographic might
be needed to
identify possible
defects
Crack causes are
numerous; further
testing might be
conducted
progressively.
10/12/2012
Hardened Concrete
Concrete Efflorescence
When water penetrates into concrete, it
dissolves the non-hydraulic CH (and various
salts, sulfates and carbonates of Na, K, Ca)
Remember C-S-H and CH is produced upon
hydration of C3S and C2S
These salts are taken outside of concrete by
water and leave a salt deposit.
Concrete Best Property
I nominate Impermeability as the best
immunity for best durable concrete
What about you?
Thank you for being durable
p
to such presentation.
