Aggregates in Construction

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Questions and Answers

What is the specific gravity of Portland cement calculated without voids between particles?

3.15 (correct)

2.85

3.50

4.00

What are the two basic raw ingredients required to make Portland Cement?

Limestone and water

Clay and asphalt

Silica and alumina

Calcareous material and argillaceous material (correct)

Which chemical compounds in Portland Cement provide the desired characteristics of concrete when hydrated?

Blast furnace slag and cellulose

Alumina and iron

C3S and C2S (correct)

C3A and C4AF

How does fineness of Portland cement affect its performance?

Fineness is measured by the percentage passing through a 0.045mm sieve. Signup and view all the answers

What is the purpose of including alumina and iron (C3A and C4AF) in the raw materials for Portland Cement?

To reduce the temperature needed for producing C3S Signup and view all the answers

What is an important factor affecting the density of bulk cement?

Handling and storage conditions Signup and view all the answers

What effect do voids have on hydrated cement?

They decrease the overall strength of concrete. Signup and view all the answers

What testing standard is used to determine the specific gravity of Portland cement?

ASTM C188 Signup and view all the answers

What defines coarse aggregate?

Particles retained on a 4.75mm sieve Signup and view all the answers

What is the maximum aggregate size?

One sieve size larger than the nominal maximum aggregate size Signup and view all the answers

Which of the following is considered a natural source of aggregate?

Gravel pits Signup and view all the answers

Fine aggregates are characterized by particles that:

Pass through a 4.75mm sieve Signup and view all the answers

What is one of the primary purposes of aggregates in construction?

As underlying material for foundations and pavements Signup and view all the answers

Which characteristic is important for evaluating aggregates?

Soundness and durability Signup and view all the answers

Heavyweight aggregates can include which of the following materials?

Steel slag and bearings Signup and view all the answers

What is the importance of aggregate characteristics in construction?

They depend on how aggregates will be used in the structure Signup and view all the answers

What is the fineness modulus range for fine aggregates?

2.3 to 3.1 Signup and view all the answers

Which sieve size is not used for fine aggregates?

9.5 mm Signup and view all the answers

What does a high Sand Equivalent value indicate about aggregates?

Good quality Signup and view all the answers

What is the most common reaction in alkali-aggregate reactivity?

Between silica and alkalis in cement Signup and view all the answers

What is a consequence of alkali-silica reaction in concrete?

Excessive expansion Signup and view all the answers

Which of the following properties is NOT categorized under mechanical properties of aggregates?

Chemical composition Signup and view all the answers

What is the purpose of the AASHTO T176 test?

To limit clay content in fine aggregates Signup and view all the answers

Which of these describes the mechanical property that aggregates must possess under loads?

Resistance to crushing and disintegration Signup and view all the answers

What should be prevented during concrete transportation to maintain strength?

Adding more water than specified Signup and view all the answers

Which method of curing involves direct contact with water to maintain moisture?

Ponding or Immersion Signup and view all the answers

How long should the minimum curing period be for most concrete structures at temperatures above 5°C?

7 days Signup and view all the answers

Which factor is NOT mentioned as influencing the minimum curing period?

Environmental humidity Signup and view all the answers

What is a potential consequence of adding water to concrete beyond the specified limit?

Decreased compressive strength Signup and view all the answers

Which curing method utilizes special compounds to form a barrier against moisture loss?

Membrane-Forming Compounds Signup and view all the answers

What is the purpose of curing concrete?

To ensure complete hydration for strength gain Signup and view all the answers

Which of the following is NOT a type of curing mentioned?

Electrical Curing Signup and view all the answers

What is the primary purpose of the autoclave expansion test (ASTM C151)?

To assess the soundness of the cement paste Signup and view all the answers

Which property of hydrated cement refers to its ability to retain volume after setting?

Soundness Signup and view all the answers

What is a common application for Type III high early strength cement?

Fast-track construction Signup and view all the answers

What is the water-cement ratio used to improve in concrete?

Strength Signup and view all the answers

What kind of cement is more environmentally friendly and offers improved workability?

Blended Cement Signup and view all the answers

What is one of the consequences if the cement is unsound after setting?

Expansion after setting Signup and view all the answers

Which standard specifies acceptance criteria for questionable water in concrete mixes?

ASTM C94 Signup and view all the answers

How is compressive strength of mortar typically determined according to ASTM standards?

By preparing 50mm cubes Signup and view all the answers

What is a characteristic feature of air-entrained cements?

Greater workability than non-air entrained types Signup and view all the answers

Which admixture type is used to slow down the setting time of concrete?

Retarders Signup and view all the answers

What should be the average compressive strength of mortar cubes made with questionable water after 7 days compared to those made with potable water?

At least 90% of the normal strength Signup and view all the answers

Which type of cement is suitable for structures that require controlled hydration heat management?

Type IV Low Heat Cement Signup and view all the answers

What ratio indicates optimal hydration in cement?

$0.22 - 0.25$ kg of water per kg of cement Signup and view all the answers

Study Notes

Aggregates

Aggregates are a mass of crushed stone, gravel, sand, etc., predominantly composed of individual particles, but in some cases including clays and silts.
Coarse aggregate: particles retained on a 4.75 mm sieve
Fine aggregate: particles that pass a 4.75 mm sieve
Maximum aggregate size: one sieve size larger than the nominal maximum coarse aggregate size
Nominal maximum aggregate size: one sieve size larger than the first sieve to retain more than 10% of the aggregates

Aggregate Sources

Natural sources: gravel pits, river run deposits, rock quarries
Manufactured aggregates: Slag waste from iron and steel mills, expanded shale and clays to produce lightweight aggregates

Aggregate Uses

Underlying material for foundations and pavements: Aggregate underlying materials, or base courses, can add stability to a structure, providing a drainage later, and frost protection damage.
To limit the clay content: of fine aggregates used in asphalt concrete, AASHTO T176 or Sand Equivalency Test is required.
Sand Equivalent Value:
- 100ℎ𝑠𝑎𝑛𝑑 / ℎ𝑐𝑙𝑎𝑦

Aggregate Properties

Cleanness and Deleterious Materials: aggregates are a natural product so there is a potential for contamination.
Mechanical Properties:
- Toughness, Hardness & Abrasion Resistance: ability of aggregates to resist the damaging effect of loads.

Chemical Properties

Alkali-Aggregate Reactivity:
- Most common reaction is between the active silica constituents of an aggregate and the alkalis in cement (sodium oxide and potassium oxide).
- Alkali-Silica Reaction: results in excessive expansion, cracking, or popouts in concrete.
- Alkali-Carbonate Reactivity: less harmful reaction
- Best way to evaluate potential for alkali-aggregate reactivity: Tests on samples of cement will produce different results

Portland Cement

Production:
- Two basic raw ingredients:
  - Calcareous material: Calcium oxide (limestone, chalk, or oyster shells)
  - Argillaceous material: combination of silica and alumina (clay, shale, blast furnace slag)
Chemical Composition:
- C3S and C2S: provide the desired characteristics of concrete when hydrated.
- Alumina and iron (C3A and C4AF): included with the other raw materials to reduce the temperature required to produce C3S from 2000ºC to 1350ºC.
Fineness: properties of hydrated cement are evaluated either in cement paste (water and cement) or mortar (paste and sand)
- Three properties of hydrated cement: setting, soundness, and compressive strength of mortar
- Initial set: stiffening of the cement paste
- Final set: change from a plastic state to a solid state
- Hardening: strength gain in a set cement paste
Specific Gravity: needed for mixture-proportioning calculations
- Specific gravity of Portland cement (without voids between particles): 3.15.
- Density of bulk cement (including voids between particles): varies depending on handling and storage.
- Cement quantities are specified and measured by weight rather than volume.
Voids in Hydrated Cement: Concrete strength, durability, and volume stability are greatly influenced by voids.
- False set: might occur in which the cement stiffens within a few minutes of being mixed without the evolution of much heat. This can be remedied by remixing.
- Quick set: cannot be remedied
- Flash set: cannot be remedied

Cement Soundness

Soundness: ability to retain its volume after setting.
Expansion after setting: could result if the cement is unsound.
Autoclave Expansion Test (ASTM C151): used to check the soundness of the cement paste.
ASTM C150 limits autoclave expansion to 0.8%

Cement Compressive Strength

Compressive Strength Mortar: measured by preparing 50 mm cubes and subjected to compression according to ASTM C109.
Compressive Strength of Mortar Cubes: is proportional to the compressive strength of concrete cylinders.

Water-Cement Ratio

Ratio of the weight of water to the weight of cement.
Strength and other desirable properties are improved by reducing the amount of water used.
Hydration: chemical reaction between cement and water.
- Two components in the reaction: chemical and physical
- Chemical bonding: requires approximately 0.22 to 0.25 kg of water per 1 kg of cement.
- Cement cannot fully hydrate without gel-water: 0.19 kg of gel-water per 1 kg of cement.
- PCA recommends a minimum of 0.40.

Mixing Water

Any potable water is suitable for making concrete.
Some non-potable water may also be suitable.
Impurities in mixing water: can affect concrete set time, strength, and long-term durability.
Chloride ions can accelerate corrosion of reinforcing steel.
Acceptance criteria for questionable water: specified in ASTM C94.

Types and Applications of Standard Portland Cement

Type I: Normal; general concrete work; suitable for floors, reinforced concrete structures, pavements
Type II: Moderate Sulfate Resistance; protection against moderate sulphate exposure
Type III: High Early Strength; used for fast-track construction
Type IV: Low Heat of Hydration; used when mass of structure requires careful control of the heat of hydration
Type V: High Sulfate Resistance; protection from severe sulfate exposure

Other Cement Types in the Philippines

Portland Pozzolan Cement (PPC): blended cement made by combining Portland cement with supplementary cementitious materials
Portland Slag Cement (PSC): blended cement made by combining Portland cement with supplementary cementitious materials

Admixtures for Concrete

Ingredients added to concrete to impart a specific quality to either the plastic mix or the hardened concrete (ASTM C494).
Admixture classifications:
- Air Entrainers:
- Water Reducers:
- Retarders:
- Hydration Controller Admixtures:
- Accelerators:
- Specialty Admixtures:
Reasons for Using Admixtures:
- Improve workability of the concrete:
- Increase strength:
- Decrease water content:
- Improve durability:

Disposal and Reuse of Concrete Wash Water

Waste water generated from truck wash systems, washing of central mixing plants, storm water runoff from ready-mix plant yards, and conveyor washdown.
Considered hazardous.
Convention practice: dumping at the job site, dumping at land fill, or dumping into a concrete wash water pit at the ready-mix plant.
Alternatives:
- Settling ponds:
- Storm water detention/retention facilities:
- Water reuse systems:
- Chemical stabilizing admixture systems:

Concrete Curing

Concrete curing involves maintaining a moist environment for a specified time after placing to allow continued hydration and improve concrete strength.
Do not add water to concrete during transportation.
Adding water during transportation reduces concrete quality and strength.
The engineer must ensure the specified amount of water from the mix design is used.
Minimum curing period: At least seven days or until 70% of the specified compressive strength is reached for most concrete structures at temperatures above 5°C (40°F).
Curing period: Depends on factors like cement type, mix proportions, required strength, weather, structure size, shape, future exposure conditions, and curing method.

### Curing Methods

Ponding or Immersion: Submerging the concrete in water.
Spraying or Fogging: Spraying water onto the concrete surface.
Wet Coverings: Applying wet burlap or other permeable materials to the concrete surface.
Impervious Papers or Plastic Sheets: Covering the concrete with plastic or paper sheets.
Membrane-Forming Compounds: Applying a liquid that forms a waterproof membrane.
Forms Left in Place: Leaving the forms in place until the concrete cures sufficiently.
Steam Curing: Exposing the concrete to steam.
Insulating Blankets or Covers: Covering the concrete with insulating materials.
Electrical, Hot Oil, and Infrared Curing: Using various methods to heat the concrete.

### Steel Producers and Service Centers

Producers of structural steel: Responsible for producing hot-rolled structural shapes and hollow sections.
Service centers: Function as warehouses and provide limited preprocessing of structural materials.
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This quiz explores the different types of aggregates used in construction, including their sources and uses. Understand the critical distinctions between coarse and fine aggregates, as well as their roles in foundational stability and pavement structures. Test your knowledge on how aggregates contribute to overall construction quality.