Cement Properties and Testing

Cement Properties and Testing

• Cement is a bonding material that reacts with water to bond construction materials together, undergoing a process called hydration to produce new compounds that give strength to the concrete mix.

Types of Portland Cement

• There are six types of Portland cement:
  • Ordinary Portland cement (O.P.C)
  • Portland blast furnace cement
  • Rapid-Hardening Portland cement
  • Low-heat Portland cement
  • Sulphate resisting Portland cement
  • White Portland cement

Composition of Cement

• Cement consists of the following compounds:
  • C3S (3CaO.SiO2)
  • C2S (2CaO.SiO2)
  • C3A (3CaO.AL2O3)
  • C4AF (4CaO.AL2O3.Fe2O3)

Laboratory Tests for Cement

• There are five important laboratory tests for cement:
  • Standard consistency
  • Setting time
  • Compressive strength
  • Fineness
  • Soundness

Standard Consistency Test

• The aim of the test is to determine the required amount of water to have a cement paste with standard consistency.
• Tools used: Vicat apparatus, graduated cylinder, balance, stop watch, and spatula.
• Work method:
  1. Take a suitable amount of water/cement (w/c) and 400 gm of cement.
  2. Calculate the required water from the w/c ratio.
  3. Mix the cement with the calculated water for about 240±5 seconds.
  4. Put the cement paste in a Vicat mould and drop the Vicat plunger.
  5. If the penetration is 5±1 mm from the base, the w/c ratio is recommended.

Setting Time Test

• The aim of the test is to measure the setting time of the cement paste and compare it with IQS No. 5-2019.
• Tools used: Vicat apparatus, graduated cylinder, balance, stop watch, and spatula.
• Work method:
  1. Take 400 gm of cement and mix it with the amount of water obtained from the standard consistency test.
  2. Take the time from the moment of adding water to cement.
  3. Put the paste in a Vicat mould and lower the needle to be in contact with the cement paste surface at a distance not less than 10 mm from the edge of the Vicat mould.
  4. Repeat the penetration process in different positions until the needle reaches 5 mm from the base of the Vicat apparatus.

Compressive Strength Test

• The aim of the test is to determine the compressive strength of the cement paste.
• Tools used: Mould, jolting apparatus, set of sieves, graduated cylinder, balance, and spatula.
• Work method:
  1. Prepare a mix of one part of cement to three parts of standard sand and one half part of water (w/c = 0.5).
  2. Place the water and cement into a bowl, and immediately start the mixer at low speed while starting the timer.
  3. Add the sand steadily during the next 30 seconds, and then switch the mixer to high speed and continue mixing for an additional 30 seconds.
  4. Stop the mixer for 90 seconds, and then remove the mortar adhering to the wall and bottom part of the bowl.
  5. Mould the specimens immediately after the preparation of the mortar.
  6. Compact the mortar using a jolting apparatus, and then level the surface with a small spreader.
  7. Remove the excess mortar, and label or mark the moulds for identification purposes.

Fineness of Cement Test

• The aim of the test is to determine the specific surface area of the cement by measuring the time required for a specific volume of air to pass through a porous media of cement with a known surface area.
• Tools used: Blain apparatus.
• Test method:
  1. Put a specific amount of sample (w) with a known surface area γ in a permeability cell.
  2. Compress the sample by a metal piston to record the standard volume.
  3. Blow air from point A to let the liquid rise to point B, then close the valve.
  4. Record the time required for the liquid to flow from point C to point D.

Soundness of Cement Test

• The aim of the test is to determine whether the cement paste once it sets, does not undergo a large change in volume, and there is no appreciable expansion which could result in a disruption of the hardened cement paste.
• There are two tests to obtain the soundness of cement:
  • Le Chatelier test
  • Autoclave test

Aggregate Tests

Definition of Aggregate

• Aggregate: a granular and gradual material that is inert, does not react with concrete and cement components
• Types of aggregates:
  • Gravel (Coarse aggregate): retained on 4.75 mm opening sieve
  • Sand (Fine aggregate): passing 4.75 mm opening sieve
  • All-in aggregate: a mixture of coarse and fine aggregate

Quality Requirements

• Aggregate for concrete shall consist of any type of coarse aggregate and/or any type of fine aggregate or of all-in aggregate
• Aggregate supplied as a mixture of different sizes or types shall be proportioned and mixed to ensure a reasonable consistency

Harmful Materials

• Organic materials
• Sulfate and chloride contents
• Maximum SO3% in fine and coarse aggregate (Iraqi standard specification I.Q.S. No. 45/1984)

Sieve Analysis

Iraqi Standard Specification (I.Q.S. No. 30/1981)

• Test method:
  • Take sample of aggregate (500 gm sand, 5000 gm gravel)
  • Put the sample on each its own set of sieves
  • Vibrate the sieves for 2-3 minutes
  • Calculate the retained weight on each sieve
• Calculations:
  • Retained percentage = (retained weight on sieve / sample weight) * 100
  • Accumulated percentage = (sum of retained weight on each sieve / sample weight) * 100
  • Passing percentage = 100 - accumulated percentage

Grading of Aggregate

• Single-size aggregate: coarse aggregate with a nominal size
• Graded aggregate: coarse aggregate with a range of sizes
• Specification limits for coarse aggregate (Iraqi standard specification I.Q.S. No. 45/1984)
• Specification limits for fine aggregate (Iraqi standard specification I.Q.S. No. 45/1984)

Density of Aggregate

Iraqi Standard Specification (I.Q.S. No. 31/1981)

• Definition of density:
  • Density: mass of material divided by its volume at a specific temperature
  • Apparent density: mass of material divided by its volume including the volume of impermeable voids
  • Bulk density: mass of material divided by its volume including the volume of permeable and impermeable voids
• Methods to find the bulk density:
  • Compaction method
  • Free fall method
  • Shaking method (only for coarse aggregate)
• Calculations:
  • Bulk density = (weight of filled cylinder - weight of empty cylinder) / volume of cylinder

Specific Gravity of Coarse Aggregate

Iraqi Standard Specification (I.Q.S. No. 31/1981)

• Definition of specific gravity:
  • Specific gravity: weight of a specific volume of aggregate in air divided by the weight of the same volume of water
  • Bulk specific gravity: weight of a specific volume of aggregate in air divided by the weight of the same volume of water without gases
  • Apparent specific gravity: weight of a specific volume of aggregate in air divided by the weight of the same volume of water without gases including the volume of impermeable voids
• Method:
  • Dry the coarse aggregate in an oven at 100-110°C
  • Immerse it in water for 24 hours
  • Raise the aggregate from the water and dry it by towel to obtain saturated surface dry (S.S.D.)
  • Calculate the specific gravity
• Calculations:
  • Bulk specific gravity = (A / (B - C))
  • Apparent specific gravity = (A / (B - C))
  • Absorption ratio = ((B - A) / A) * 100

Specific Gravity of Fine Aggregate

Iraqi Standard Specification (I.Q.S. No. 31/1981)

• Method:
  • Dry the fine aggregate in an oven at 100-110°C
  • Immerse it in water for 24 hours
  • Make the S.S.D. test
  • Calculate the specific gravity
• Calculations:
  • Bulk specific gravity = (A / (B - C))
  • Apparent specific gravity = (A / (B - C))
  • Absorption ratio = ((B - A) / A) * 100

Detecting the SO3 Percentage

Iraqi Standard Specification (I.Q.S. No. 45/1984)

• Method:
  • Dilute the HCL
  • Add the sample to the dilute HCL and boil for 5 minutes
  • Filter it on percolated paper No. 1
  • Prepare BaCl2 base
  • Add the base to the percolated sample and heat for 5 minutes
  • Percolate the resulted sample on percolate No. 42
  • Put the resulted sample in an oven at 1000°C for 20 minutes
  • Balance the resulted sample (salt) and calculate the SO3 percentage
• Calculation:
  • SO3 percentage = ((weight of sample and bowl - weight of empty bowl) / weight of sample) * 34.3
• Limit:
  • SO3 percentage in sand shall not exceed 0.5%
  • SO3 percentage in gravel shall not exceed 0.1%