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Factors affecting the compressive strength of the concrete
Articles > Factors affecting the compressive strength of the concrete
Factors affecting the compressive strength of the Concrete:
The strength of the concrete indicates the ability of the
structure to withstand. In the world of construction, every
constructor wants its construction to be durable life long.
The durability of the concrete depends on the quality of the
material used in concrete. The strength of the concrete
exhibits the quality of material used in it. The strength of the
concrete can be measured by load parameters, which are the
dead weight of the concrete itself, load/burden of other
parts of the building on the concrete, live load, earthquake
load, and the wind load. Concrete strength is of two types;
one is compressive strength while the other is the tensile
strength of the concrete. The compressive strength is caused
due to the material and cement used in concrete structures,
while the tensile strength is caused partially by concrete
itself and a large part of this strength is caused by the
reinforced material (steel, iron) present in it. Concrete
strength may be affected by the following factors:
Factors affecting the tensile strength of the concrete:
The tensile strength largely depends on the reinforced steel used in the concrete, however, the concrete itself has also a partial role in
creating the tensile strength. In this article were are discussing in detail, the factors of compressive strength of the concrete material.
Factors affecting the Compressive Strength of the concrete:
1. Physical and Chemical Properties of Cement: Physical and chemical properties of the cement affect the durability and strength of
the concrete. OPC cement is suitable for dry weather where there is no salinity and sulfate attack. PPC cement is suitable for
underwater and water retaining constructions because they are resistant to chemical attacks. There is another type of cement-like
SRPC (sulfate resisting Portland cement), which is resistant to the sulfate attacks and is suitable in constructions near seashores.
Chemical and physical composition surely affects the durability of the concrete.
2. Quantity of Cement: The quantity of cement is another factor that affects the strength of the cement. Adding admixtures with
water and cement, the ratio of the cement is a basic determinant of strengthening the concrete structure. If the cement ratio is
lesser than the suggested ratio, the strength of the concrete will be reduced. Similarly, the ratio of the cement should also not
accede to the suggested level, because the access amount of the cement will create much distance from coarse aggregate, thus
reducing the bonding among the coarse aggregation.
3. Type of Coarse Aggregate: Coarse aggregate is the stone pebble and border. There are several shapes of the coarse aggregate.
Some are spherical, while some of the aggregates are conical. The conical-shaped aggregate has a much stronger bonding among
one another than the spherical. Speaking generally, the shape of the coarse aggregate has a deep impact on the strength of the
concrete structure.
4. Quantity of Coarse Aggregate: The coarse aggregate should neither be in access quantity nor should it be very less. The access
quantity of the aggregate will cause the concrete to lose its strength. Similarly, the reduced quantity of the coarse aggregate will
cause larger gaps between the pebbles of the aggregate, thus affecting the strength of the concrete structure.
5. Quality of Fine Aggregate: Fine aggregate means the very fine particles of the concrete mixture. Fine aggregate is composed of
sand and cement itself. The purpose of the fine aggregate is to fill the gaps among the particles of coarse aggregate. It the quality
of fine aggregate is good, the strength of the concrete will be greater, while if the fine aggregate/sand will not be pure and
impurities will exist in it, the concrete will lose strong bonding among the particles of the mixture.
6. Quantity of Fine Aggregate: Apart from the quality of the fine aggregate, its quantity also matters to a great extent. The
suggested ratio among, fine aggregate, coarse aggregate, and the cement will create strong bonding among the pebbles and
particles and pebbles of the concrete and cement. On the other hand, if the fine aggregate has been added to the mixture in
excessive quantity, it will definitely, affect the performance of the concrete structure.
7. Mixing level of the material: For better result, the mixture (admixture, water, and cement) are mixed very well. Equal mixing of the
concrete material will distribute all components of the mixture equally. If the materials are not mixed very well, the cement
concentrates at one side of the mixture. The structure made of an uneven mixed concrete will not evenly distribute the strength
among different parts of the structure.
8. Environmental Conditions: The environmental conditions are another strength determining factor of the concrete. In damp and
moist surroundings, the concrete structure does not need much water pouring and curing. While in dry and hot regions, the
concrete is cured intensively and for a long time. Moreover, environmental conditions also affect the durability of the concrete. In
rainy areas or in a humid atmosphere, the life of the concrete becomes shorter than that in dry and pleasant weathering region.
9. Water to Cement Ratio: The ratio of the weight of water to the weight of cement is called the Water/Cement ratio. It is the most
important factor for gaining the strength of concrete. The lower w/c ratio leads to a higher strength of concrete. Generally, the
water/cement ratio of 0.45 to 0.60 is used. Too much water leads to segregation and voids in concrete. The water/Cement ratio is
inversely proportional to the strength of concrete. As shown in the chart below when the w/c ratio has increased the strength of
concrete gets decreased and when the w/c ratio is decreased then the strength of concrete increases.
10. Compaction of Concrete: Compaction of concrete increases the density of the concrete because it is the process in which air voids
are removed from freshly placed concrete which makes the concrete compact and dense. The presence of air voids in concrete
greatly reduces its strength. Approximately 5 % of air voids can reduce strength by 30 to 40 %. As we can see in the above chart,
even at the same water/cement ratio strength is different with different compaction accuracies. In the fully compacted concrete,
strength is higher than the insufficiently compacted concrete.
11. Ingredients of Concrete: The main ingredients of concrete are cement, sand, aggregate, and Water. The quality of each material
affects the strength of the concrete. All materials, therefore, should fulfill the standard criteria for use in concrete like
12. Type of Cement: The type of cement used in the concrete affects the strength of the structure to a large extent. Keeping in view
different surroundings and challenges different types of cement can be used. OPC is used in dry, clean, and chemical-free regions.
While PPC is used in wet and humid regions because it is resistant to water penetration. The SRPC is another type of cement which
is resistant to sulfate attacks. In areas like off-shore and water-logging and salinity regions, this type of cement is very successful.
There are some of the cement, which hardens very rapidly, suitable in the regions where environmental conditions do not allow
another type of slow hardening cement.
13. Quality of Water: Quality of water also affects the strength and durability of the concrete structures. In areas where water is very
pure and does not contain any sulfate and chloride, OPC and PPC are recommended to be used, as the cost of the cement is very
reasonable, while in areas where the water is enriched with minerals like sulfate and chloride, then the sulfate and chloride resisting
cement will be used.
14. Relative Humidity: Relative humidity means the ratio between the long term humidity of the atmosphere of a particular region and
the highest possible humidity in that region. If the difference between the two humidities is greater, then the risk of affecting the
concrete structure is also greater.
15. Curing of Concrete: Curing of concrete is the most essential to prevent plastic shrinkage, temperature control, strength
development, and durability. Curing provides the desired moisture and temperature at the depth and near the surface after placing
and finishing of concrete for the development of strength. In other words, curing provides sufficient water to concrete for
completing the hydration process without interruption which is important for strength development. Commonly 7-day curing
corresponds to 70 % of compressive strength. The curing period depends on the types of cement and the nature of the work.
Generally, it’s about 7 to 14 days for Ordinary Portland Cement. There are many methods of curing like Ponding and immersion,
Spraying and fogging saturated wet coverings, etc.
16. The shape of Aggregate: There are many shapes of aggregate like angular, cubical, elongated, elongated and flaky, flaky, irregular,
and rounded. Angular aggregates are rough-textured, and rounded aggregates are smooth textured. Thus, the rounded
aggregates, create the problem of lack of bonding between cement paste and aggregate. Angular aggregates exhibit a better
interlocking effect in concrete, but the angular aggregate contains a larger amount of voids. For this, you needed a well-graded
aggregate. The shape of aggregates becomes more important in the case of high strength and high-performance concrete where a
very low w/c ratio is used. In such cases, cubical shape aggregates with uniform grading are required for better workability.
17. Size of Aggregate: Larger size aggregates give a lower strength because they have a lower surface area for the development of gel
bond which is responsible for strength. Larger size aggregate makes concrete heterogeneous. It will not distribute loading
uniformly when stressed. Due to internal bleeding, the problem of development of the microcracks in concrete happens when
larger size aggregates are used in concrete.
18. Grading of Aggregate: Grading of aggregates determines the particle size distribution of aggregates. It’s the most important
factor for concrete mix. There are three types of graded aggregate Gap Graded Aggregate, Poorly graded aggregate, and Wellgraded aggregate. Well-graded aggregate contains all sizes of particles of aggregate. So, they have less amount of voids. The use of
well-graded aggregates gives higher strength to the concrete.
19. Weather Condition: Weather condition also affects the strength of concrete due to different reasons. In a cold climate, exterior
concrete is subjected to repeated freezing and thawing action due to the sudden change in weather. It produces deterioration in
concrete. With the change in moisture content, materials expand, and contract. It produced cracks in concrete.
20. Temperature: With a certain degree of temperature increase, the rate of hydration process increases in it which, gains strength
rapidly. Sudden temperature changes create a thermal gradient, which causes cracking and spalling of concrete. So, the final
strength of concrete is lower at a very high temperature.
21. The Rate of Loading: The strength of concrete increases with the increase in the rate of loading because at the high rates of
loading, there is less time for creep. Creep produces permanent deformation in the structure at constant loading. So, the failure
occurs at limiting values of strain rather than the stress. In rapid loading, the load resistance is better than the slow loading.
Read also:
Determinants of tensile stress of the concrete
Environmental Factors affecting the strength of the concrete structure
Concrete Properties
Properties of normal strength Portland cement concrete
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