Two main characteristics of the aggregates affect the water content of a mix:
total surface area and particle interference
. Both are functions of grading. The greater the surface area of the mix constituents, the larger will be the amount of water required to lubricate the surfaces of the particles.
How does aggregate size affect water demand?
As the maximum size of coarse aggregate reduces,
surface area of coarse aggregate increases
. Higher the surface area, greater is the water demand to coat the particles and generate workability.
How does gradation affect the concrete mix?
The grading or
size distribution
of aggregate is an important characteristic because it determines the paste requirement for workable concrete. … The more these voids are filled, the less workable the concrete becomes, therefore, a compromise between workability and economy is necessary.
What is the significance of grading of aggregates?
Significance of grading of aggregates
Grading of aggregates
gives uniformity in the specific weight of concrete
. Grading of aggregates reduces the chances of segregation in concrete. The graduation curve is also used to estimate the type of soil.
What is the effect of grading of aggregate on workability of concrete mix?
Grading of Aggregates
Well-graded aggregates tend to
fill up voids and easily get workability
. Less amount of water can make it workable. If grading is better, there will be fewer voids and excess paste will be available to give better lubricating effect.
How does the water absorption of the coarse aggregate affect the concrete mix?
On the other hand, the absorption of water by aggregate from fresh concrete may
enhance adhesion of cement paste to the aggregate and thus the tightness of hardened concrete
. It can result in higher strength and better durability of concrete, which was revealed in some research [4, 5, 6].
Why is aggregate sample reduction Important?
Aggregate and other materials sampled in the field
need to be reduced to appropriate sizes for testing
. It is, therefore, necessary to reduce field samples while minimizing the chance of variability during handling.
Why grading of fine aggregate test is important explain the impact if ungraded fine aggregate is used in concrete?
Gradation of aggregates play a very important role in increasing or
decreasing the compressive strength in
concrete. If aggregates aren’t properly graded it effects the compressive strength of concrete. The theory of gradation is basically based on the concept of to decrease the void ratio in concrete mix.
What is the effect of grading of coarse aggregate on workability and strength of concrete?
The workability of fresh concrete
increases with poor gradation of
the coarse aggregate. The workability of fresh concrete is higher for gap graded coarse aggregate concrete than for well graded coarse aggregate concrete. For the gap aggregates, the bigger the particle sizes removed, the higher the workability.
How can poorly graded aggregates affect the quality of concrete?
Poorly graded aggregate is characterized by
small variations in size
. This means that the particles pack together, leaving relatively large voids in the concrete.
What is the necessity of grading of aggregate in ready mix concrete?
Ideally
coarse and fine aggregate should be graded in such a way as to minimise the voidage
. After compaction the volume of the cement paste must be more than the voidage between particles. Underfilling will result in entrapped air and an unworkable mix.
Why is grading of aggregate important with regard to the properties of fresh concrete?
Grading of aggregates:
Grading of aggregates is an important aspect as they can influence the various properties of concrete such as cohesion, water demand, workability and strength.
Aggregates should be well graded and consistent in their grading
.
What is the requirements of grading of aggregate?
General requirements for fine aggregate include (i) fine
aggregate passing the 2.00 mm (No. 10) sieve shall consist of natural or crushed sand
, and fine mineral particles passing the 75 μm sieve; (ii) the fraction passing the 75 μm sieve shall not be greater than two-thirds of the fraction passing the 0.425 mm (No.
How does water content affects workability of concrete?
Higher the water/cement ratio
, higher will be the water content per volume of concrete and concrete will be more workable. Higher water/cement ratio is generally used for manual concrete mixing to make the mixing process easier.
How does coarse aggregate affect the strength of concrete?
They concluded that, in high-strength concretes, higher strength coarse aggregates typically yield
higher compressive strengths
, while in normal-strength concretes, coarse aggregate strength has little effect on compressive strength.
What is the influence of aggregate grading on density of concrete?
Effect of Grading
If grading of aggregate is varied, it also
changes cement paste content (cost economy), workability of the mix, density and porosity
. It is an important factor and has a maximum influence on workability. Well graded aggregates result in the least amount of voids in a given volume.
How does aggregate reduce water absorption?
Hi, the best way to reduce the wear and tear of recycled aggregate concrete is
to lower the w / c ratio of water to cement and add a fluidizing admixture
. Another way is to add a low water absorption aggregate in the proportion of 50/50%.
What is the effect of moisture content in aggregates?
The moisture content of an aggregate is expressed as: If the moisture content is positive,
the aggregate has surface moisture and will contribute water to the PCC
, while if the moisture content is negative the aggregate is air dry to some degree and will absorb moisture from the PCC.
What is water absorption of aggregate?
Water absorption gives
an idea on the internal structure of aggregate
. Aggregates having more absorption are more porous in nature and are generally considered unsuitable, unless found to be acceptable based on strength, impact and hardness tests.
Why water absorption of aggregates is important?
The authors accept that absorption of water by aggregates is important per se; it also allows
indirect assessment of pore structure
by characterising the pores, not in terms of sizes (based on assumptions about their shapes) but in terms of accessibility to water under simple immersion, low pressure (0.2 N/mm
2
) and …
What is aggregate in concrete mix?
‘Aggregate’ is a term for
any particulate material
. It includes gravel, crushed stone, sand, slag, recycled concrete and geosynthetic aggregates. … Aggregates make up some 60 -80% of the concrete mix. They provide compressive strength and bulk to concrete.
What is aggregate sampling?
WHAT is Aggregate Sampling? … At a ready mixed concrete plant aggregates are typically stored in a bin or a stockpile. The
process of taking a sample of aggregate that is truly representative of the nature and condition of the aggregate in the
stockpile, bin or transfer point is called aggregate sampling.
What difficulties arise in the use of aggregates which absorb water?
The water cement ratio is the water added to unit weight of cement. If the aggregates absorbs water and equivalent water for this absorption is not added above the required w/c ratio,
the workability reduces, maybe becoming unworkable
, depending on the dryness of the aggregates.
What is the effect of water cement ratio on strength and durability of concrete?
If the water-cement proportion is higher, it brings about wider spacing between the cement aggregates and thus, influences the compaction. Correspondingly, concrete’s durability and compressive strength are
decreased due to increased dampness levels
.
Why are aggregates used in concrete?
Aggregate materials
help to make concrete mixes more compact
. They also decrease the consumption of cement and water and contribute to the mechanical strength of the concrete, making them an indispensable ingredient in the construction and maintenance of rigid structures.
How does aggregate size affect concrete?
The tensile strength of the concrete is severely affected by
increasing the size of the aggregate
. … On increasing the aggregate size, homogeneity of the concrete deteriorates, and the values Rp and R
pb
approach each other, even on specimens of the same cross-sectional dimensions.
What is grading of coarse aggregate?
The graded coarse aggregate is defined by its nominal size i.e.,
40 mm, 20 mm, 16 mm, 12.5 mm, etc
. For example, a graded aggregate of nominal size 12.5 mm means an aggregate most of which passes the 12.5 mm IS Sieve. … For a given quantity of water and paste, bigger size of aggregate will give higher workability.
What is grading of aggregate explain standard grading curve?
The grading curve graphically represents
the proportion of different grain sizes which the aggregate is composed of and which form part of the shotcrete mix
. It provides useful information to find out: Whether the distribution of the different aggregate sizes is suitable for pumping.
What are the effects of aggregate shape on the properties of concrete?
Aggregate shape and surface
texture influence the properties of freshly mixed concrete more than the properties of hardened concrete
. Rough-textured, angular, and elongated particles require more water to produce workable concrete than smooth, rounded compact aggregate.
What are the benefits of using well graded aggregates?
A well graded aggregate consists of particles which have a broad range of sizes.
Aggregate should be such that the smaller particles should fill the voids between the larger particles
. As a result, the compacted mass will contain less voids and need less quantity of fine aggregates and cement paste.
How can grading of aggregate be controlled?
Factors that affect the grading of aggregate are: 1
. Surface Area of the Aggregate 2. Relative Volume Occupied by the Aggregate 3. Workability of the Mix 4
.
Which type of aggregate gives more workability of concrete with the same amount of water content?
The irregular shape of aggregate requires more water to make it workable, due to greater surface area. Rounded shape aggregate requires less water to make it workable, due to less surface area. Hence for fixed water content
rounded aggregate
has more workability.
What kind of aggregates can be said to have caused a decrease in workability if kept at same water content?
Answer: Explanation: Other than that, the
round aggregates
also have less surface area compared to elongated or irregular shaped aggregates. This will make less requirement of water for same workability of concrete.
