Physical Properties of Cement

Course Overview

• The course covers the background of concrete, its ingredients, different types of cement, and their chemical properties
• Properties and handling of aggregates will be discussed
• Study of the chemical admixtures, cement replacement materials, and new advanced materials
• Investigation of fresh concrete properties like workability, segregation and bleeding; with strength of hardened concrete (compressive, tensile, flexural shear, bond) will be performed
• The course will also cover effective presentation skills, background usage, audience engagement, and capturing attention

Physical Properties of Cement

• Different cement blends used in construction are characterized by their physical properties
• Parameters include:
  • Fineness
  • Soundness
  • Consistency
  • Strength
  • Setting time
  • Heat of hydration
  • Loss of ignition
  • Bulk density
  • Specific gravity (relative density)

Fineness of Cement

• The fineness is the size of the cement particles
• The required fineness of good cement is achieved through grinding the clinker
• Fineness controls hydration rate

Soundness of Cement

• Soundness defines the ability of cement to resist shrinking upon hardening
• Good quality cement retains volume after setting without delayed expansion caused by excessive free lime and magnesia

Consistency of Cement

• Consistency refers to the ability of cement paste to flow
• It is measured by Vicat Test

Reasons for Unsoundness:

• Excessive use of gypsum in cement
• Excess of lime
• Insufficient burning
• Excessive magnesia content
• Several tests ensure cement soundness, including the Le Chatelier Test and the Autoclave Test

Consistency in Cement

• Uniformity in material nature leads to higher consistency; hence cement should have high consistency
• A synonym for the flowing ability of cement paste, measured through the Vicat Test

Specific Gravity of Cement

• Defined as the ratio of the mass of cement to mass of water for the same volume
• Can also be defined as the ratio of the density of cement to the density of water for the same volume
• In both definitions, the volume of cement and water must be the same for accurate values
• It is a comparison of the mass or density of any substance to a standard substance, usually water
• Specific gravity determination is best achieved using a liquid that does not react with cement, such as water-free kerosene

Le Chatelier Specific Gravity Flask

• Used to determine the specific gravity of cement and other fine materials, like dust and sand
• This specific gravity value is essential for figuring out the amount of material needed in concrete

Portland Cement

• Has a specific gravity of about 3.15, measured with ASTM C188
• When calculating cement for mix design the specific gravity of cement is regarded as 3.14
• Affects mix design
• Frequent testing specific gravity before mixing is essential
• Old cement is rejected due to increased specific gravity, which occurs due to its liability to accumulate external moisture

Required Equipment for Specific Gravity Tests on Cement:

• Le Chatelier's flask
• Weighing balance
• Kerosene (free from water)

Specific Gravity of Cement Procedure

• Clean the Lechatlier flask and is weight before use (W1)
• Add around 50 gm of cement and weight to find W2
• Fit the stopper and add kerosene to the flask up to the bottle neck
• Mix well making sure to remove any bubbles, then re-weight to find W3
• Empty the flask and clean it thoroughly
• Add kerosene up to the bottle neck without the cement and find W4

Calculation

• Can be calculated using this equation: (W2 – W1) / ((W2 – W1) – (W3 – W4) X 0.79)
  • W1 = Weight of Empty Flask
  • W2 = Weight of Flask + Cement
  • W3 = Weight of Flask + Cement + Kerosene
  • W4 = Weight of Flask + Kerosene
• Kerosene has a specific gravity of 0.79g/cc
• The typical specific gravity is 3.15 of tested cement

Density Test of Hydraulic Cement (ASTM-C-188)

• The density of cement is vital in determining the design of concrete, concrete mix proposition is based on the weigh batching
• For the density test the follows materials are need:
  • Ordinary Portland Cement
  • Constant Temperature Water Bath
  • Heavy Rubber Pad
  • Glass Funnel
  • A Shallow Tray
  • Weighing Balance
  • Kerosene with a specific gravity not less than 0.731
• The laboratory should be maintained at 25°C to 29°C
• Determination of the density of hydraulic cement is connection with the design of Portland cement concrete mixtures
• The following is needed:
  • Standard Le-Chatelier Flask
  • Heavy rubber pad (12 in. x 12 in. square)
  • Lead ring weight for the flask stem
  • Funnel
  • Thermometer
  • Portland cement
  • Kerosene
• Calculation: The volume of liquid(kerosene oil or naphtha) displaced by the mass of cement in a test

Formula for Density Test of Hydraulic Cement:

• Density of Hydraulic Cement = Mass of Cement (in g) / Displaced Volume (in cm³)
• The density value for hydraulic cement is 2.8 g/cm³
• The relative density(specific gravity) of hydraulic cement is 3150 kg/m³, which is equal to 3.15 grams/ml or 3.15 g/cm³ or 3.15 kg/liter
• The bulk density of cement is nearly 1.14
  • A standard density of one cement bag is equal to 1.14 grams/m, 1.14 g/cm³, or 1440 kg/m³

Determination of Normal Consistency of Cement

• Find the normal consistency of cement, used to prepare a cement paste and set up the experiment to follow the procedural steps
• Next fill up the observation table and report as per instruction
• Normal consistency of cement can the percentage of water by weigh, produces a cement paste of standard consistency
  • 10 mm diameter to penetrate up to a depth of 5 mm to 7 mm above the bottom of Vicat's Mould.
• The water % varies from cement and from batch to batch
  • Normal consistency has 26 to 33 percent of dry cement by weight
• Higher values are observed when old or fine cement with (very high specific surface area)is present

Equipment Required

• Vicat-apparatus with the plunger (10 mm diameter, 50 mm long)
• Vicat's mold with mild steel base plate
• A Balance with weights (capacity 1 kg, the sensitivity up to 0.1 gram)
• Trowel (small, weighing about 210 gm)
• Marble stone slab (non-porous plate), Enamel tray
• Measuring glass (100 cc - 2 numbers), Thermometer range (50 degree Celsius)
• Stopwatch and Standard spatula
• Specimen supplied Portland cement = 400 gram (for each trial)
• A dry cement (400 grams) is measured accurately and place in an enamel tray
• 25% of clean water is added mix with a spatula
  • The mixing time is between 3 to 5 minutes

Experimental Setup of Vicat Plunger

• Polished brass, 10 mm diameter, 50 mm long with a threaded projection at the upper end
• For fixing into the movable rod lower age flat, shall be fixed
• The plunger should indicate a reading of zero in its scale resting on a non-porous plate

Procedure

• Vicat mould is filled with the cement paste resting on a marble slab
• Make the surface of the cement paste leveled with the top of the mould/trowel (210 grams), shake to dispel air bubbles.
• The mould is put together with a non-porous plate and bottom of the plunger gradually to the surface of the cement paste.
• A reading from 5 to 7 mm is desired for the normal consistency
• Trial pastes can be prepared and retested until the plunger shows the desired penetration

Precautions for the Test

• The temperature of cement, water, and the test room must be between 25 to 29 degrees Celsius
• Gauging appliances have to be neat and clean
• The gauging time is between 3 to 5 minutes
• In filling the mould, the operator's hand and the blade of the trowel along be used
• Plunger and mould must be cleaned

Report

• Calculations added water and results/ consistency
• Diagrams is added with a conclusion/ discussion

Heat of Hydration

• Generated when water reacts in contact with cement powder
• The amount released depends on the cement composition, curing temperature, water to cement ratio, and cement fineness

Factors Affecting Heat of Hydration

• Certain Materials can be selected to minimize or maximize heat of hydration based on preference Cements with higher contents of:
  • Tricalcium silicate
  • Tricalcium aluminate
  • High fineness e.g. Type III cements
• Have higher rates of heat generation
• Tricalcium silicate and tricalcium aluminate chemically generate more compared to dicalcium silicate or other cement compounds
• Higher fineness = higher surface area for water to wet, increasing the reaction speed between cement and water

Tests for Heat of Hydration

• Two common methods:
  • ASTM C 186, Standard Test Method for Heat of Hydration of Hydraulic Cement
    • Uses a heat of solution procedure, sample is dissolved in an acid & temperature rise is recorded
  • Sample can be hydrated for any amount of time

Nonstandard procedure

• Conductive container is used to place sample and kept at a specific temperature (using a thermoelectric device)
• Water is added, energy is recorded to maintain & the heat rate measured is usually limited to 3 days.

Loss on Ignition

• Measures organic matter content in samples such as:
  • Soil
  • Cement
  • Sludge
  • Waste
• Volatile materials lost in analysis = combined water (hydrates, example) & CO2 carbonates
• Can be used to volatile organic matter quality

LOI Calculation

• LOI is reported as an elemental or oxide analysis of a mineral
  • Calculated by comparing weight of sample before and after high temp.
• LOI calculation represents amount of organic matter in the sample
• Can be tested with thermogravimetry for the determination of the Loss on Ignition on Petrochemical Catalysts

Strength of Cement

• Measured via compressive, tensile and flexural tests
• Varies on certain factors such as:
  • Water-cement ratio
  • Cement-fine aggregate ratio
  • Curing conditions
  • Size and shape of specimen
• Cement mortar strength and concrete strength have no relationship
• Cement strength is a quality control measure
• Strength tests are performed on cement mortar mix NOT PURE cement paste
• Cement gains strength over time

Common Strength Testing:

• Compressive strength
• Most common test
• Subject to compressive load until failure.
• Must follow the loading sequence (between 20-80 seconds)

Standard Tests

• AASHTO T 106 and ASTM C 109: Compressive Strength of Hydraulic Cement
  • Mortars (Using 50-mm or 2-in. Cube Specimens)
  • ASTM C 349: Compressive Strength of Hydraulic Cement Mortars (Using Portions of Prisms Broken in Flexure)

Tensile strength Test

• Previously used but not useful properties for the properties of cement
• Flexural strength
• Tensile strength by bending. Test performed in 40×40 x 160 mm cement mortar beam
• Loaded at its center until failure.

Standard test

• ASTM C 348: Flexural Strength of Hydraulic Cement Mortars

Setting Time of Cement

• Setting and hardening occurs when water is added
• Time varies, based on fineness of cement, cement-water ratio, chemical content, and admixtures

Two Measures Setting Time

• Initial set - When the paste begins to stiff noticeable (occurs within 30-45min) Final set - When the cement hardens (below 10 hrs)

Standard Tests

• AASHTO T 131 and ASTM C 191: Time of Setting of Hydraulic Cement by Vicat Needle
• AASHTO T 154: Time of Setting of Hydraulic Cement by Gillmore Needles
• ASTM C 266: Time of Setting of Hydraulic-Cement Paste by Gillmore Needles
• Again, setting time can also indicate hydration rate

Fineness of Cement

• Particle size = fineness
• Fineness is achieved by grinding clinker.
• Fineness controls hydration rate
• Two Ways to tested fineness
  • Sieving
  • Determining specific surface area (total surface area of all particles in 1g of cement) by air-permeability apparatus
    • Can be expressed as cm2/gm or m2/kg
    • Generally uses Blaine Air permeability apparatus

Soundness of Cement

• Ability of cement to resist shrinking upon hardening
• High quality cement retains its volume without delayed expansion caused by free lime & magnesia

Le Chatelier Test

• Tests cement expansion due to lime
• Cement paste (normal consistency) is between glass slides & submerged in water for 24 hours at 20+1°C
• Measure the distance between indicators, then put back the device & allow to boil again for 25-30 mins
• Cool the device then measure again.

Autoclave Test

• Cement paste (normal consistency) is placed in an autoclave.
• Brought to 2.03 MPa & remain for 3 hrs.
• Specimen length changes is measured after autoclave & expressed as a percentage
• High quality cement should be 0.80% autoclave expansion

Heat of Hydration

• When water is added to cement, the process is called hydration
• Generates heat, can affect the quality of cement and maintain curing temperature
• Too much heat in large structure may cause stress
• C3S, C3A, ratios, and fineness affect heat of hydration
• Determined via difference between hydrated cement and dry specimen (tested by days 7 and 28)

Loss of Ignition

• Heating in 900 - 1000°C causes weight loss
• Improper storage, transport, pre-hydration, and carbonation may increase ignition
• AASHTO T 105 & ASTM C 114 tested for chemical analysis hydraulic cement

Bulk Density

• Volume gets filled with water and replaces air
• Bulk density of cement is not very important
• Has a varying of range and density depending on cement composition
• Density is anywhere from 62 to 78 pounds/ cubic foot

Specific Gravity

• Used in mixture proportioning calculations.
• Portland cement (3.15 specific gravity) and special cement blend (around 2.9 specific gravity)

Chemical Properties of Cement

• Raw materials of cement production
  • Limestone (calcium)
  • Sand/clay (silicon)
  • Bauxite (aluminum)
  • Iron ore

Tricalcium Aluminate (C3A)

• Makes cement resistant to sulfate; gypsum reduces hydration
• Cement type I has to 3.5% SO3
• (in cement having more than 8% C3A) Cement type II has to 3% SO3 (in cement having less than 8% C3A)
• Tricalcium silicate (C3S) Responsible for the cement's early strength and an initial set.
• Dicalcium silicate helps strength increase after one week

Ferrite

• Decreases the melting temperature (3,000°F to 2,600°F)
• Does not contribute much to the cement’s strength

Magnesia (MgO)

• Used during production of Portland Cement
• Too much can make cement unsound, but can increase slightly if a minuscule amount
• Less CO2 emission
  • Limited to 6% content

Sulfur & Iron

• Sulfur makes the cement unsound
• Aside from strength, Iron is responsible for its color
• Amounts of K20 affects alkali content in the cement
• High amounts create regulating issues during setting Free lime can cause expansion of the cement mixture

10-Silica fumes

• Added to cement mixtures improve compressive strength
• Also increases abrasion resistance and bond Strength

11-Alumina

• Contains high alumina, making it resistant to withstand frigid temperature since alumina is chemical-resistant
• Can quickens the setting of the cement although weakening it.