Tests on cement

• Tests conducted for Cement

a)Field test

• when hand is inserted into the cement bag after opening it, it gives a cool feeling.
• moreover it gives a smooth feel , when a pinch of cement taken & felt between fingers.
• Take handful of cement  & throw into bucket full of water, the cement particles starts floating & after sometime it starts to sink down .

B) Labortary tests

1) Fineness test

• Weigh 100g of cement & take onto the standard IS Sieve No.9 (90 microns).
• Break down the lumps present ,if any, with fingers.
• Sieve the sample  for about 12-15 minutes (mechanical sieving can also be done)
• Weigh the weight of the residue left on sieve.
• Weight of residue should be less than 10%

    Illustration Of Sieve Test: 

Weight of cement (before sieving)  in gram	Weight of sample (after sieving ) in gram	%difference in weight	Remarks
100	7.8	7.8 %	Less than 10%

2) Standard Consistency test (Normal Consistency test)

• This test is used to determine the initial setting time , final setting time & soundness of cement
•  This test is done by using “ Vicat Apparatus”

Procedure:

• Take 500 g cement & make paste by mixing it with water with different w/c ratios.Fill the sample in vicat mould within 3 -5 minutes i.e “gauging time. Attach a Standard plunger & allow it to dropdown by its self weight & penetrate into the cement paste.
• Repeat the  process with different percentage of water in the ccement paste
• The percentage of water by weight of cement at which the plunger penetrated for a depth of 33-35mm  from top is considered as the percentage of water required to make paste of standard consistency .it is denoted with “ P”
• Calculation of P

            P= w/c *100       

  (where, w= quantity of water used & c= quantity of cement used)

  (NOTE: Least count of balance =  1g & measuring cylinder =1 ml)

General value of P for OPC lies between 24 to 31%

3) Setting time test

     

a) Initial setting time

It is the time interval throughout which the cement remains in plastic condition required for mixing,placing & compacting.

Procedure:

• Take500g of cement  & gauge it with water (0.85P)
•  Fill the paste  in mould & place it under the needle of the vicat apparatus.
• The time elapsed from the adding of water to the point where the needle penetrates the   test block to a depth of 33-35 mm is noted.
• The time is the initial setting time. 
• The minimum initial setting time should be minimum 30 mins

b) Final setting time

• It is the time at which the concrete looses its plasticity & start gaining strength.
• When the vicat needle is unable to pierce through the test block more than 0.5 mm.it is considered, it has attained its final setting time
• The maximum final setting time should not be more than 10 hours 

4) Soundness test

• As presence of excess  lime , magnesia & sulphates causes unsoundness of cement as they lead to undesirable expansion of set & hardened mass.Thus soundness test is the remedial measure to prevent the cause.
• Autoclave Test is performed  for measuring soundness of cement, it indicates the presence of excess of both lime & magnesia ,unlike Le- Chatelier’s Test which indicates only presence of lime

Procedure:

• A cement specimen (25 x 25 mm) is placed in the standard autoclave & the steam pressure is raised to 21 kg/cm²  (gauge pressure) within 1 hour of turning on the heat.
• This pressure is maintained for next 3 hours.
• The autoclave is allowed to cooled & then the length of the specimen is measured again
• The % expansion of the specimen is found to be less than 0.8 %

Conclusion

Higher  the expansion of the specimen indicates the higher content of excess lime & magnesia

Physical Characteristics of Cement are mentioned in the Table:

Classification & Types of Cement

This Topic covers the classification of cement and its types as per:
1. ASTM Classification
2. IS Specifications

1. American Society for Testing Materials (ASTM)

As per ASTM , Cement is designated as
a) Type I   b)Type II   c)Type III   d)Type IV  e)Type V 

Type I (Ordinary Portland Cement)

•  Used for general construction work when the special properties of the other types are not required.
•  Normally used for reinforced concrete buildings, bridges, pavements and sidewalks when the soil conditions are normal, for concrete masonry units, and for all uses where the concrete is not subjected to special sulfate hazard, heat of hydration is not objectionable, where freezing thawing is not expected. 

Type I A (OPC with Air Entraining Agent)

• It is used where air entrainment is necessary. 
• Air-entrainment:Air intentionally incorporated by means of a suitable agent.
• Magnitude of these air bubbles are in the order of 0.05 mm in size.
• Entrained air produces separate cavities in the cement paste so that no channels for the passage of water are formed and the permeability of the concrete is not increased. 
• The voids never become filled with the products of hydration of cement as gel can form only in water.

Type II (Modified Portland Cement):

•  It has better resistance to the action of sulfates than normal (ordinary) Portland cement and used where sulfate concentrations in groundwater are higher than normal but not very severe. 
• Generates heat at a slower rate than OPC and is used in certain concrete mass work like retaining walls.
•  Reduced temperature rise is beneficial for hot weather concrete, too. 

Type II-A (Air-Entrained Type II Cement) 

Type III: (High Early Strength Cement)

• Used where high early strengths are required at early periods, usually a week or less.
•  It is particularly usefull where it is required to remove forms as soon as possible or when the structure must be brought into service quickly. 
• High-early strength makes it possible to reduce the period of Total protection for concrete during cold weather. 

Type III-A (Air Entrained Type III)

Type IV (Low Heat Portland Cement):

• It is used where the amount and rate of heat generation must be minimized. 
• Strength is also developed at a slower rate.
• It is intended for use in massive concrete structures such as dams.

Type V (Sulfate Resistant Portland Cement):

• It is used in structures subject to sulfate attack, chemical plants, etc.
• It is also resistant to the action of sea water.

2) IS Specifications

1. OPC- Ordinary Portland Cement

There are three different types of ordinary Portland cement, classified on the basis of strength achieved in 28 days.

i) 33 Grade

ii) 43 Grade

iii) 53 Grade

Other Types of cements used in India are as follows:

Cement & its Constituents

1.Introduction

• Cement is the most vital material in building and other construction practices.
• Cement is manufactured from limestone and clay either by 'old wet process' or 'new dry process'
• Modern method of manufacturing is patented by Joshep Aspdin in 1824.
• Cement is available in grey powder form,which when mixed with water ,sets to hard durable mass

2. What actually does cement do?

Ans: Cement act as a binding material in mortar or concrete .

3. Why called Portland Cement?

Ans: As the resulting material is found to be similar in look to the stone found in Portland (United Kingdom) , Thats why it is called Portland Cement

4. What are Bogue's Compounds? 

Ans: Bogue's Compounds are constituents of cement that give cementing Properties 

a) Tri-calcium Silicate (C3S)  ⇒ (21- 45 %)

b) Di-calcium Silicate (C2S)   ⇒ (25- 31%)

c) Tri-calcium Aluminate (C3A) ⇒ (6 -12%)

d) Tetra-calcium Aluminoferrite (C4AF)⇒ (8 - 14 %)

Tricalcium silicate:
Hardens rapidly. Responsible for initial set and early strength.

Dicalcium silicate:
Hardens slowly and its effect on strength increases occurs at ages beyond one week.

Tricalcium aluminate:
Contributes to strength development in the first few days. It is the first compound to hydrate. The least desirable component because of its high heat generation and its reactiveness with soils and water containing moderate to high sulfate concentrations.

Tetracalcium aluminoferrite:
Lowers clinkering temperature. C4AF contributes very little to strength of concrete even though it hydrates very rapidly.

Note: If C3A & C4AF are kept low, then resistance to chemical increases.

•  C2S & C3S  are responsible for strength
•  Average content : C3S- 45% , C2S- 25%
• Total percentage of C2S & C3S is around 70%
• C3S- Responsible for "early strength"of concrete
• C2S- Responsible for "later strength" of concrete
• For producing low heat cement , C2S is increased and C3S & C3A decreased

5,  Heat of Hydration

• when water is added in cement, an exothermic reaction takes place between cement. and water and heat is liberated, The liberation of heat is called "Heat of Hydration".
• Heat is evolved due to the reaction of aluminates and sulphates.
• The early heat of hydration is mainly contributed from hydration of C3S.
• Hydrated aluminates doesn't contribute towards strength.

6. Chemical or OxideComposition  of cement

1. CaO-  (60-67%)
2. SiO2- (17-25%)
3. Al2O3- (3-8%)
4. Fe2O3 - (0.5- 6%)
5. MgO- (0.1- 4%)
6. Alkalies( K2o, Na2O) - (0.4 - 1%)
7. SO3- (1.3-3%)

7. Setting Of Cement

• The beginning of noticeable stiffening in the cement paste is known as the initial set. 
• The final hardening process which is responsible for its strength known as the final set. 
• The time from the addition of the water to the initial and final set are known as the setting times.
• Setting time is affected by: cement composition, cement fineness, rate of hydration, and the ambient temperature

a) Initial  Setting Time

• Initial Setting time - Generally 30 minutes
• It is the time interval throughout which the cement remains in plastic condition required for mixing,placing & compacting. 

b) Final Setting Time

• Final Setting Time- Generally 10 hours (600 Minutes)
•         It is the time at which the concrete looses its plasticity & start gaining strength.

Vicat Apparatus is Used to measure initial & final setting time