CONSMAT MODULE 2 PART 2

Particle Shape and Surface Texture

The shape of the individual aggregate particles, determines how the material will pack into a dense configuration and also determines the mobility of the stones which a mix (bonding and workability)

Angularity, Flakiness

What are the Two consideration in shape of Material

Angularity

angular, subangular or rounded.

Flakiness

flaky, elongated or flaky and elongated.

Workability, Water Content, Shape and Texture of Aggregate

Mixing of Concrete

Water Cement Ratio, Density

Strength of Concrete Mix

Surface Texture

rough & smooth

Surface Texture

The roughness of the aggregate surface plays an important role in the way the aggregate compacts and bonds with the binder material. Rough textured aggregates are more difficult to compact into a dense configuration than smooth aggregates. Rough texture generally improves bonding and increases interparticle friction. In general, natural gravel and sand have a smooth texture, whereas crushed aggregates have rough texture

Sound and Durability

The ability of aggregate to withstand weathering is defined as soundness or durability. Aggregates used in various civil engineering applications must be sound and durable, particularly if the structure is subjected to severe climatic conditions.

Soundness Test

It simulates weathering by soaking the aggregates in either a sodium sulfate or a magnesium sulfate solution.

Absorption

It is the property of aggregate particles to absorb water into their pores.

Absorption

although aggregates are inert, they can capture water and asphalt binder in surface voids. The amount of water the aggregate absorbs is important in the design of Portland cement concrete since moisture captured in the aggregate voids is not available to improve the workability of the plastic concrete and to react with the cement. There is no specific level of aggregate absorption that is desirable for aggregate used in Portland cement concrete, but aggregates absorption must be evaluated to determine the appropriate amount of water to mix into the concrete.

Oven Dry, Air Dry, Saturated Surface Dry, Moist or Wet

What are the Moisture Content of a aggregate

Oven Dry

It means the aggregate contains no moist at all. This requires drying the aggregate in an oven to constant mass

Air Dry

containing less moisture than the aggregate capable of absorbing

Saturated Surface Dry

1. containing only absorbed moisture

Moist or Wet

containing free moisture on the surface in addition to absorbed moisture.

Sand

nearly always in condition 4 when it is batched

Coarse Aggregates

under condition 2 & 4 rarely 1 and never in 3

Specific Gravity

the ratio of the weight of the material to the weight of water. An average ____________ for sand and gravel is 2.65 (means the material is 2.65 times as heavy as water, water weight approximately 1000 kg/m3, thus the average density of aggregate is 2650 kg/m3.

Specific Gravity

the higher the specific gravity, the heavier the concrete. Low specific gravity (below 2.5) indicates a possible porous, soft or highly absorptive aggregate of potentially doubtful quality.

Specific Gravity

Use of aggregate of low specific gravity in concrete sometimes results in low strength, pop-outs, scaling and poor durability.

Bulk Dry Specific Gravity, Bulk Specific Gravity, Apparent Specific Gravity, Effective Specific Gravity

What are the Four Types of Specific Gravity

Bulk Dry Specific Gravity

the ratio of the weight in air of a unit volume of aggregates (including permeable and impermeable voids in the particles but not including the voids between particles) at a stated temperature to the weight in air of an equal volume of gas - free distilled water at a stated temperature

Bulk Specific Gravity

the ratio of the weight in air of a unit volume of aggregate, including the weight of water within the voids filled to the extent achieved by submerging in water for approximately 24hours ( but not including the voids between particles) at a stated temperature, compared to the weight in air of an equal volume of gas - free distilled water at a stated temperature.

Apparent Specific Gravity

the ratio of the weight in air of a unit volume of the impermeable portion of aggregate at a stated temperature to the weight in air of an equal volume of gas free distilled water at a stated temperature

Effective Specific Gravity

Used for asphalt mix designs, takes into account the asphalt absorbed by aggregate

Toughness, Hardness and Abrasion Resistance. Strength and Modulus. Reactivity. Cleanliness. Gradation and Particle Size

What are the Properties of Aggregates?

Toughness, Hardness and Abrasion Resistance

The ability of the aggregate to resist the damaging effect of loads is related to hardness of the aggregate particles and defined as toughness or abrasion resistance. The aggregate must resist crushing, degradation and disintegration when stockpiled, mixed as either Portland cement or asphalt concrete, placed and compacted and exposed to loads.

Los Angeles Abrasion Test

It evaluates the aggregates toughness and abrasion resistance. In this test, aggregates blended to a fixed size distribution are placed in a large steel drum with standard - sized steel balls that act as an abrasive charge. The drum is rotated, typically for 500 revolutions. The material is recovered from the machine and passed through a sieve that retained all the original material. The percentage weight loss is the abrasion number.

Strength and Modulus

The strength of Portland cement and asphalt concrete cannot exceed that of the aggregate. The tensile strength of aggregate ranges from 0.7MPa to 16MPa (100 - 2300psi) while the compressive strength ranges from 35MPa to 350MPa (5000 to 50,000 psi)

Modulus of Elasticity

Resilient Modulus test (AASHTO T292) for pavements

Reactivity

An aggregate that is chemically inert does not react with the cement and is not affected chemically by other influences in or on the concrete. A petrographic analysis or ASTM standard C227, mortar bar expansion test, identifies rock types so as to discover not only potentially reactive aggregates but also coatings, lightweight particles, unstable materials, etc.

Deleterious Materials

Soft and unsound fragments, clay lumps, coal, lignite, porous chert, shells, materials finer than #200 sieve, conglomerates and cemented particles

Gradation and Particle size

Describes the particle size distribution of the aggregate

Unit Weight and Voids

It is the weight of unit volume, cubic feet or cubic meter of the sand or coarse aggregate

Density

It is the weight of a unit volume of a solid rock

Void Cement

It is the measure of the voids or spaces between the aggregate particles

Gradation and Maximum Size

It describes the particle size distribution of the aggregate. The particle size distribution is an important attribute of the aggregate. Large aggregate are economically advantageous in Portland cement and asphalt concrete, as they have less surface area and therefore requires less binder. However, large Portland cement concrete are harsher and more difficult.