lecture#8 - water

8/11/2019 Lecture#8 - Water

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WATER

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Dr. Adeel Zafar , CE-803 , Fall 2013


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Necessity of Water in Concrete

Minimum quantity of mixing water

required for hydration of cement

Water in excessrequired to act

lubricant between aggregates toproduce workable and economical

concrete

Lesserwater makes it difficult to

work with concrete and non-uniformmixing makes it weaker in strength

Water is also used for curingand

aggregate washing



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Water Quality

A safe drinking water is safe for concrete


Fit for drinking.

No taste.

No odour.

Some water with

some impurities can

be acceptable


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Water Basic Requirements

ASTM C-191 (AASHTO T-131) tests should be madeto ensure that impurities in the mixing water do notadversely shorten or extend the setting time of thecement

Water of questionable suitability can be used formaking concrete if mortar cubes (ASTM C-109 orAASHTO T-106) made with it have 7-day strengthsequal to at least 90%of companion specimens made

with drinkable or distilled waterAcceptable criteria for water to be used in concreteare given in ASTM C-94 (AASHTO M-157) andAASHTO T-26



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Limits for Wash water as Mixing water


* parts per million

Water containing less than 2000 parts per million (ppm) of total dissolved solids can

generally be used satisfactorily for making concrete. Water containing more than 2000

ppm of dissolved solids should be tested for its effect on strength and time of set.


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Analysis of some City water vs Seawater



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10/25Dr. Adeel Zafar , CE-803 , Fall 2013

Alkali Carbonate and Bicarbonate

Carbonates and bicarbonates of sodium and

potassium have different effects on the setting

times of different cements

Sodium carbonate can cause very rapid setting,bicarbonates can either accelerate or retard the

set

In large concentrations, these salts can materially

reduce concrete strength


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Chlorides in Water

Concern over a high chloride content in mixing water is

chiefly due to the possible adverse effect of chloride ions

on the corrosion of reinforcing steel

Chloride ions attack the protective oxide film formed on

the steel

Placing an acceptable limit on chloride content for any

one ingredient, such as mixing water, is difficult

considering the several possible sources of chloride ions

in concrete.

An acceptable limit in the concrete depends primarily

upon the type of structure and the environment to which it

is exposed during its service life.



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Chloride content limits by ACI


The ACI 318 building code limits water soluble

chloride ion content in reinforced concrete to the

following percentages by mass of cement:

Prestressed concrete 0.06% Reinforced concrete exposed to chloride in service

0.15%

Reinforced concrete that will be dry or protected from

moisture in service 1.00% Other reinforced concrete construction 0.30%


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Sulfates


Concern over a high sulfate content in mix water

is due to possible expansive reactions and

deterioration by sulfate attack, especially in areas

where the concrete will be exposed to highsulfate soils or water


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Sea Water


About 78% of the salt is sodium chloride, and15% is chloride and sulfate

Although concrete made with seawater may have

higher early strength than normal concrete,strengths at later ages (after 28 days) may belower

This strength reduction can be compensated for

by reducing the water-cement ratio in plaincement concrete (PCC)

If aggregates are known to have alkali-reactivity,sea water should not be used in even PCC


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Sea Water


Seawater is not suitable for use in making steel

reinforced concrete and it should not be used in

prestressed concrete due to the risk of corrosion

of the reinforcement, particularly in warm andhumid environments

For PCC, Types-II or MS, should be used along

with a low water-cement ratio

Seawater used for mix water also tends to cause

efflorescence and dampness on concrete

surfaces exposed to air and water


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Acid Waters


Acceptance of acid mixing water should be based onthe concentration (ppm) of acids in the water

Occasionally, acceptance is based on the pH, whichis a measure of the hydrogen-ion concentration on alog scale

The pH value is an intensity index and is not the bestmeasure of potential acid or base reactivity

The pH of neutral water is 7.0; values below 7.0indicate acidity and those above 7.0 alkalinity (abase)

Organic acids, such as tannic acid, can have asignificant effect on strength at higher concentrations


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Acid Waters



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Alkaline Waters


Waters with sodium hydroxide concentrations

dictates alkalinity of water

Higher concentrations of hydroxides may reduce

concrete strength


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Organic Impurities / Algae impurities


Presence of organic substances effects the setting

timeof OPC and the ultimate strength of concrete

Highly colored waters, waters with a noticeable odor,

or those in which green or brown algae are allindications of high organic impurities

Water containing algae is unsuited for making

concrete because the algae can cause an excessive

reduction in strength.Algae in water leads to lower strengths either by

influencing cement hydration or by causing a large

amount of air to be entrained in the concrete


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Sugar / Sucrose


Small amounts of sucrose, as little as 0.03% to

0.15% by mass of cement, usually retard the

setting of cement

The upper limit of this range varies with differentcements

The 7-day strength may be reduced while the 28-

day strength may be improved Sugar in quantities of 0.25% or more by mass of

cement may cause rapid setting and a substantial

reduction in 28-day strength


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Oils


Mineral oil (petroleum) has less effect on strength

development if in less quantities / concentration

Mineral oil in concentrations greater than 2.5% by

mass of cement may reduce strength by morethan 20%


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Tolerable limits

for Impurities



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lecture#8 - water

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