Factors affecting the compressive strength of the concreteArticles > 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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 Well-graded 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.
- 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.
- 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.
- 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.
- 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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