76 Questions
What is the main influencing factor for Alkali-Carbonate Reaction (ACR)?
Clay content between 5% to 25%
Which ASTM standard is used for Petrographic Examination to test Alkali-Carbonate Reaction (ACR)?
ASTM C 295
What is the recommended method for controlling Alkali-Carbonate Reaction (ACR)?
Spraying lithium nitrate solution
Which material can be used for sweetening limestone to reduce the risk of Alkali-Silica Reaction (ASR) in concrete?
Crushed limestone
What is the key factor influencing the expansion of mortar bars due to Alkali-Silica Reaction (ASR)?
Limiting the alkali loading in the mix
What causes D-cracking in concrete pavements?
Freeze-thaw deterioration of the aggregate
Which of the following is a potential harm caused by aggregates with reactive substances?
Significant volume changes in the concrete
What is a popout in concrete terminology?
Breaking away of a small fragment of concrete surface
Iron oxide stains in aggregates are caused by:
Impurities in the coarse aggregate
What does AAR stand for in the context of concrete?
Alkali-Aggregate Reactivity
Why does aggregate represent 60% - 75% of concrete volume?
To reduce the cost of concrete production
What is the primary purpose of using aggregate in civil applications?
To improve the durability and strength of structures
How do iron particles in aggregates impact concrete?
They can lead to staining and rusting in concrete structures
What is a common issue associated with Alkali-Aggregate Reactivity (AAR) in concrete?
Deterioration due to expansion and cracking
In what way can harmful reactive substances impact the performance of concrete?
Lead to long-term degradation and weakening of concrete
Why is Alkali-Silica Reaction (ASR) more concerning than Alkali-Carbonate Reaction (ACR)?
ASR occurs more frequently in aggregates with reactive silica minerals.
Which visual symptom is associated with Alkali-Silica Reaction (ASR)?
Relative displacements and a network of cracks
What is the mechanism behind Alkali-Silica Reaction (ASR)?
Alkali hydroxide + Reactive silica + Moisture --> Alkali Silica Gel + Alkali Silica gel filling microcracks
Which testing method is not used for detecting Alkali-Silica Reaction (ASR)?
Petrographic Examination (ASTM C 295)
How can ASR be controlled?
By observing the alkali-silica reaction rim around the reactive aggregate
Which type of concrete is produced using natural gravel and sand as aggregates?
Normal-weight concrete
What is the typical density range for structural lightweight concrete?
1450 to 1850 kg/m3
Which substance is commonly used in producing high-density concrete for radiation shielding?
Steel punchings or shot
What type of rocks are commonly used as aggregates in concrete production?
Sedimentary rocks
Which material is NOT mentioned in the text as a source of concrete aggregate?
Expanded polystyrene
What is the purpose of grading an aggregate?
To analyze the particle-size distribution of the aggregate
Which ASTM standard is referenced for the majority of tests and characteristics related to aggregates?
ASTM C 33
What type of aggregate is light and classified as a fine aggregate?
Normal weight aggregate
In ASTM sieve sizes, what is the range for fine aggregate openings?
From 150 μm to 9.5 mm
Based on particle size distribution curve, how can we determine if aggregate grading is good or poor?
By evaluating the particle-size distribution curve against ASTM standards
What does the ASTM C33 grading limit specify for the percentage passing through the 4.75 mm sieve?
95-100%
In concrete aggregate analysis, what does the nominal maximum size refer to?
The standard sieve opening immediately smaller than the smallest sieve through which all of the aggregate must pass
What does the maximum size of aggregate represent in concrete construction?
The size that all aggregate must pass through
What is the purpose of determining the nominal maximum size of concrete aggregate for construction projects?
To avoid excessive segregation in concrete mixtures
How does the sieve analysis result influence the suitability of an aggregate for a construction project?
By assessing the aggregate's potential to cause D-Cracking
In concrete construction, why is it important to adhere to ASTM C33 grading limits for aggregates?
To prevent harmful reactive substances from affecting the concrete
What causes D-cracking in concrete pavements?
Excessive moisture content in concrete mixtures
How can harmful reactive substances impact the performance of concrete?
By causing internal expansion and cracking over time
What is a popout in concrete terminology?
A surface protrusion caused by a piece of aggregate falling out
How do iron particles in aggregates impact concrete?
They cause discoloration on the concrete surface
What is a common issue associated with Alkali-Aggregate Reactivity (AAR) in concrete?
Increased potential for internal swelling and cracking
What is the primary cause of D-cracking in concrete pavements?
Presence of Iron particles in aggregates
How can harmful reactive substances impact the performance of concrete?
By reducing compressive strength
What do popouts refer to in concrete terminology?
Fragments breaking out of the surface
How do iron particles in aggregates impact concrete?
Cause discoloration in the concrete
Which type of issue is commonly associated with Alkali-Aggregate Reactivity (AAR) in concrete?
Cracking and expansion
What is the primary cause of D-cracking in concrete pavements?
Failure of carbonate fine aggregate
Which of the following does NOT classify an aggregate as potentially harmful due to reactive substances?
Production of harmless by-products
What is a popout in concrete terminology typically caused by?
Internal pressure within the concrete
How do iron particles in coarse aggregate contribute to concrete issues?
Cause popouts in concrete surfaces
What is the main reaction involved in Alkali-Aggregate Reactivity (AAR)?
Response of active minerals in aggregates to alkali hydroxides
What is a potential harm associated with iron particles in aggregates in concrete?
Formation of popouts
Which of the following is NOT a potential harm caused by aggregates with harmful reactive substances?
Increase in volume stability
How do iron particles impact concrete in terms of popouts?
Promoting popout formation
Which issue is associated with Alkali-Aggregate Reactivity (AAR) in concrete?
Expansion and cracking
In concrete terms, what does 'D-cracking' refer to?
Surface cracking caused by freezing and thawing cycles
What is a potential harmful effect of D-cracking in concrete pavements?
Increased risk of freeze-thaw damage
How do harmful reactive substances impact the performance of concrete?
Reduced strength and durability
In the context of concrete, what are 'popouts' related to?
Surface defects
How do iron particles in aggregates typically affect concrete properties?
Reduce compressive strength
What is a common issue associated with Alkali-Aggregate Reactivity (AAR) in concrete?
Volume changes leading to cracking
What is a potential issue associated with popouts in concrete terminology?
Formation of cracks at the surface of concrete
How do harmful reactive substances impact the performance of concrete?
Lead to expansion and cracking over time
What is the main issue associated with iron particles in aggregates when used in concrete?
Formation of iron oxide stains on concrete surfaces
What is a potential harm caused by aggregates with reactive substances?
Increased risk of cracking and deterioration
Why is Alkali-Aggregate Reactivity (AAR) a concern in concrete construction?
It can lead to cracking and expansion in hardened concrete
Which phenomenon in concrete is characterized by the development of cracks perpendicular to the slab surface at close intervals?
D-Cracking
What is a common visual indicator of Alkali-Aggregate Reactivity (AAR) in concrete?
Map pattern cracking
In concrete terminology, what are popouts typically caused by?
Iron particles in aggregates
How do harmful reactive substances impact the performance of concrete?
Reduce freeze-thaw resistance
Which characteristic of iron particles in aggregates can lead to staining issues in concrete?
Oxidation potential
What is a key concern associated with Alkali-Aggregate Reactivity (AAR) in concrete construction?
Crack formation due to expansion
Why are ASTM C33 grading limits important for aggregates in concrete construction?
To control aggregate size distribution
Which issue in concrete pavements is primarily associated with D-Cracking?
Cracks perpendicular to slab surface
What does AAR stand for in the context of harmful reactions in concrete aggregates?
Alkali-Aggregate Reactivity
Which reactive substance interaction can cause an increase in expansion and cracking in concrete aggregates?
Alkalis with certain aggregates
Study Notes
Aggregate Characteristics
- Aggregate represents 60% – 75% of concrete volume (i.e., 70% to 85% of its mass)
- Importance of aggregate:
- Significant economic benefits for the final cost
- Volume stability
Types of Aggregate
- Fine aggregate: < 5 mm
- Coarse aggregate: ≥ 5 mm
- Natural gravel and sand
- Rocks and minerals
- Recycled or crushed waste concrete
- Light: Crushed blast-furnace slag
- Heavy: Magnetite, Steel punchings or shot, Iron, Steel punchings or shot
Grading of Aggregate
- Particle-size distribution of an aggregate as determined by a sieve analysis using wire mesh sieves with square openings (ASTM C 33)
- Fine aggregate: 7 standard sieves with openings from 150 μm to 9.5 mm (No. 100 to 3/8 in.)
- Coarse aggregate: 13 sieves with openings from 37.50 mm to 100 mm (0.046 in. to 4 in.)
Aggregate Classification
- Size: Fine (< 5 mm), Coarse (≥ 5 mm)
- Source:
- Natural gravel and sand
- Rocks and minerals
- Recycled or crushed waste concrete
- Weight:
- Light: Crushed blast-furnace slag
- Heavy: Magnetite, Steel punchings or shot, Iron, Steel punchings or shot
Alkali-Silica Reaction (ASR)
- Reaction between active mineral constituents of some aggregates and the sodium and potassium alkali hydroxides and calcium hydroxide in the concrete
- Conditions necessary for ASR to occur:
- Presence of alkali hydroxide
- Presence of reactive silica minerals
- Moisture (H2O)
- Visual symptoms:
- Network of cracks
- Closed or spalled joints
- Relative displacements
- Fragments breaking out of the surface (popouts)
- Mechanism:
- Alkali hydroxide
- Expansion
- Moisture (H2O)
- Alkali Silica Gel
- Filling microcracks
- Filling air pores
Alkali-Carbonate Reaction (ACR)
- Reaction between the active mineral constituents of some aggregates and the sodium and potassium alkali hydroxides and calcium hydroxide in the concrete
- Influencing factors:
- Clay content, or insoluble residue content, in the range of 5% to 25%
- Calcite-to-dolomite ratio of approximately 1:1
- Small size of the discrete dolomite crystals (rhombs) suspended in a clay matrix
- Testing methods:
- Petrographic Examination (ASTM C 295)
- Concrete Prism Test (ASTM C 1105)
- Rock cylinder method (ASTM C 586)
Control of ASR and ACR
- Avoid using reactive aggregates
- Use supplementary cementing materials (fly ash, slag, and silica fume)
- Limit alkali loading
- Control moisture content
Test your knowledge on the classification of recycled waste concrete aggregates based on size, source, and weight. Learn about different types of aggregates such as fine aggregates (< 5 mm) and coarse aggregates (≥ 5 mm) in the context of recycled materials.
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