CT-37-60

Subsidence refers to the settlement of concrete after removing the slump cone, due to its jelly-like state.

Subsidence refers to the settlement of concrete after removing the slump cone, due to its jelly-like state.

1. True slump: Concrete settles vertically with a slight drop. 2. Shear slump: The top portion shears off and slides to one side. 3. Collapse: The concrete completely collapses and flattens.

Bending causes vertical cracks in the middle of the beam, while shear causes inclined cracks near the supports.

The compaction factor test measures the workability of stiff concrete. Formula: CF = (w2 - w1)/(w3 - w1), where w1 = weight of empty cylinder, w2 = weight with partially compacted concrete, w3 = weight with fully compacted concrete.

A lower compaction factor indicates lower workability of concrete.

A rich mix has more cement than specified proportions (all design mixes), while a lean mix has less cement than specified proportions.

Pervious concrete has high permeability, uses only coarse aggregate, and is used for drainage in pavements and footpaths, not for structural applications.

VDF (Vacuum Dewatered Floor) concrete is used in industrial floors to remove excess water from green concrete.

SCC is concrete that compacts under its own weight without vibration, used in heavily reinforced structures where vibration is difficult.

Unit weight of RCC is 25 kN/m³ and PCC is 24 kN/m³.

1. Ultrasonic sound wave test: Detects voids in hardened concrete. 2. Profometer: Determines steel bar details (number, spacing, cover, diameter). 3. Half-cell potential survey: Detects corrosion in steel bars of old structures.

It tests the consistency/workability of stiff concrete in the laboratory by measuring the time for concrete to change from a slump cone to a cylinder (Vee Bee Degree).

More Vee Bee time means less workability; less Vee Bee time means more workability.

1. Compressive strength (CTM) 2. Split tensile strength (CTM) 3. Flexural strength (UTM) 4. Modulus of Elasticity (UTM)

Tensile strength of concrete is 1/8th to 1/12th of its compressive strength.

Water/cement ratio, time/age of concrete, and curing period.

At 3 days: 1/3 strength; at 7 days: 2/3 strength; at 28 days: 100% strength.

Type of cement, aggregate, admixtures, degree of compaction, mix proportions, curing temperature, and water/cement ratio.

Cube: 100mm or 150mm; Cylinder: 150mm diameter x 300mm height.

140 kg/cm²/min or 14 N/mm²/minute.

1, 3, 7, 14, 28, 56, and 91 days.

Individual specimen strength should not be less than -15% or more than +15% of the average strength of all specimens.

Cylindrical specimens better resemble field conditions because the direction of casting and loading is the same as in actual structures.

A 150mm diameter x 300mm cylinder is loaded radially, causing it to split due to tension. Formula: Splitting tensile strength = 2P/πld.

Tensile strength is 10% to 20% of compressive strength.

A beam specimen (100x100x500 mm or 150x150x700 mm) is loaded in bending using a UTM to determine its flexural strength (Modulus of Rupture).

σ = M/I ymax or σ = Pe/bd², where σ is the flexural strength, P is load, b is width, d is depth. p.10-11

σ = 3Pa/bd², where a is the distance from the cracked section to the nearest support.

If failure is near the support (a << l/3), it is due to shear, not bending.

Approximately 370 kg of cement is required for 1m³ of M30 grade concrete.

High strength concrete fails in aggregate particles; normal concrete fails in the mortar joint between aggregates.

Nominal mix uses fixed proportions without considering properties; design mix is based on specified performance and optimized proportions.

Maximum cement content is 450 kg/m³.

f'ck = fck + 1.65 S, where f'ck is target mean strength, fck is characteristic strength, S is standard deviation. p.12-13

M10-M15: 3.5 N/mm²; M20-M25: 4.0 N/mm²; M30-M55: 5.0 N/mm².

Decreasing aggregate size increases water content due to more surface area; increasing size decreases water content.

They reduce mixing water by 5-15% at constant workability, increasing strength, or increase workability at constant w/c ratio.

Thin walls, deep beams, tremie concreting, pumping, hot weather concreting, ready mix concrete.

For every 25mm increase in slump, add 3% to the given water content.

To determine the proportions of ingredients for specified workability, strength, durability, and economy.

Grade designation, type of cement, maximum nominal size of aggregate, minimum cement content, maximum water-cement ratio.

SSD stands for Saturated Surface Dry, a condition where aggregates are neither absorbing nor releasing water.

Coarse aggregate: ~2800 kg/m³; Cement: ~1400 kg/m³ or 14 kN/m³.

Shrinkage is the reduction in volume of concrete, mainly due to loss of water.

Water-cement ratio, environmental conditions, time, and type of aggregate.

Aggregates with high moisture movement and low elastic modulus cause more shrinkage; sandstone causes more shrinkage than limestone.

Accelerating admixtures increase shrinkage; lime replacement reduces it.

Creep is the deformation of concrete under sustained load, occurring in the direction of the applied force.

Creep strain is 1-3 times the instantaneous elastic strain and is proportional to cement-paste content.

Durability is the ability of concrete to perform satisfactorily in its environment, resisting deterioration and retaining its form, quality, and serviceability.

Loss of strength, corrosion of rebars, and reduced service life.

The concrete system (materials and process) and the service environment (physical and chemical actions).

Cement from reputed manufacturers, river sand with silt <5%, cubical and innocuous aggregates.

Unsound materials cause unacceptable volume change, cracks, and affect durability; examples include aggregates with shale, clay, coal, or iron pyrites.

It increases permeability, leading to volume change, cracks, disintegration, and failure.

1% voids decrease the strength of concrete by 5%.

They allow very low water-cement ratios (as low as 0.29) while maintaining high workability (slump >250 mm).

Ductile materials are tested for Young's Modulus, while brittle materials (like concrete) are tested for Modulus of Elasticity.

MOR measures the flexural strength or bending tensile strength of concrete. p.4, 11

Proper compaction ensures strength and durability; over-compaction causes segregation, under-compaction increases voids. p.6, 24

DoC is when the specimen is cast; DoT is when it is tested for strength.

Admixtures modify properties such as workability, strength, and durability, and can reduce water content or increase workability.

Shrinkage increases with drying and decreases with higher humidity.

Shrinkage occurs rapidly at first, with most shrinkage happening in the first year.

More finer particles and higher cement content increase shrinkage.

PPC (Portland Pozzolana Cement) causes more shrinkage than OPC due to finer particles.

Durability depends on the concrete system (materials, process) and the aggressiveness of the environment (physical and chemical actions).

The pH value should be between 6 and 8.

It can cause cracking and reduce durability due to chemical reactions between alkalis in cement and certain aggregates.

Low permeability helps resist deterioration by limiting ingress of water, chemicals, and gases.

It determines the number, spacing, cover, and diameter of steel bars in concrete structures.

It is used to detect corrosion in steel reinforcement of old concrete structures.

Over-compaction leads to segregation; under-compaction increases voids and reduces strength.

The aspect ratio is 2 (height/diameter = 300mm/150mm).

Strength, which is the ability to resist load in compression, flexure, or shear.