6 FOCAL PROPERTIES OF CONCRETE IN FRESH AND HARDENED STATE

6 FOCAL PROPERTIES OF CONCRETE IN FRESH AND HARDENED STATE

PROPERTIES OF HARDENED CONCRETE 

1. STRENGTH:

 Concrete is robust in compression but relatively weak in tension and bending. It takes an excellent deal of force to crush concrete, but little or no force to tug it apart or cause bending cracks. Compressive strength is decided primarily by the quantity of cement used, but is additionally suffering from the ratio of water to cement, also as proper mixing and placing, and therefore the adequacy and extent of hydration and curing. Tensile strength usually ranges from 7 or V-E Day of compressive strength in high-strength mixes to 11 or 12% in low-strength mixes. Both lastingness and flexural bending strength are often increased by adding steel or fiber reinforcement. Required compressive strength is predicated on an analysis of the hundreds which will be applied and therefore the soil conditions at the project site. Actual compressive strength is verified by testing samples during a laboratory using standardized equipment and procedures. On commercial projects, numerous samples are tested throughout construction to verify that the concrete is put into place actually has the required strength. Laboratory testing isn't often required in residential work, except perhaps on large high-end projects or on projects with difficult sites where special foundation designs make concrete strength critical. Concrete that's stronger than necessary for its intended use isn't economical, and one that's not strong enough are often dangerous. 

2. DURABILITY: 

Durability could be defined because of the ability to take care of satisfactory performance over an extended service life. Satisfactory performance is said to the intended use. Concrete which will be walked or driven on must be abrasion resistant in order that it doesn’t wear away. Concrete which will be exposed on the surface of a building must be weather-resistant in order that it doesn’t deteriorate from repeated freezing and thawing. The durability of concrete exposed to repeated freeze-thaw cycles is often significantly increased by air entrainment. Concrete during which steel reinforcement is embedded must resist excessive moisture absorption so as to guard the metal against corrosion. Natural wear and weathering will cause some change within the appearance of concrete over time, but generally, durability also includes the upkeep of aesthetic also as functional characteristics. Just as concrete mix designs are often adjusted to supply a spread of strengths, appropriate concrete ingredients, mix proportions, and finishes can and will be adjusted on the idea of required durability. 

3. VOLUME STABILITY: 

All materials expand and contract with changes in temperature, and porous materials like concrete also expand and contract with changes in moisture content. Cement-based products like concrete, concrete masonry, and stucco experience initial shrinkage because the cement hydrates and excess mixing water evaporates. This initial shrinkage is permanent and is additionally to reversible expansion and contraction caused by later temperature or moisture changes. Excessive shrinkage can cause concrete to crack. The cracks allow moisture to penetrate, and a vicious circle of degradation may begin. Shrinkage cracking is often restrained to some extent by steel or fiber reinforcement, and therefore the location and weather resistance of shrinkage cracks are often controlled through the utilization of control joints which divide the concrete into smaller panels or sections. However, the combination design and ingredient proportions even have an impact on the potential for shrinkage cracking. The higher the cement content, the greater the tendency for shrinkage cracks to make while the concrete is curing and hardening. 

PROPERTIES OF FRESH CONCRETE 

4. WORKABILITY: 

Workability is that the relative ease with which a fresh concrete mix is often handled, placed, compacted, and finished without segregation or separation of the ingredients. Good workability is required to supply concrete that's both economical and high in quality. Fresh concrete has good workability if it is often formed, compacted, and finished to its final shape and texture with minimal effort and without segregation of the ingredients. Concrete with poor workability doesn't flow smoothly into forms and properly envelop reinforcing steel and embedded items, and it's difficult to compact and finish. Depending on the appliance, however, a mixture that has good workability for one type or size of the element could also be too stiff or harsh for an additional, therefore the term is relative. Each mix must be suitable for its intended use, achieving a balance among required fluidity, strength, and economy. Workability is said to the consistency and cohesiveness of the combination and is suffering from cement content, aggregates, water content, and admixtures. 

5. CONSISTENCY: 

Consistency is the aspect of workability associated with the flow characteristics of fresh concrete. It is a sign of the fluidity or wetness of a mixture and is measured by the slump test. Fresh concrete is placed during a metal cone. When the cone is removed, the concrete slumps a particular amount counting on how fluid it's. A wet, soft mix slumps quite a drier, stiffer one. A high-slump concrete is one that's very fluid, and a low-slump concrete is drier and stiffer. A high-slump mix may cause excessive bleeding, shrinkage, cracking, and a dusting of the hardened concrete surface. There is a particular range of consistency that's appropriate for every sort of work. Workability is at a maximum in the concrete of medium consistency with a slump between 3 and 6 in. Both very dry (low-slump) and really wet (high-slump) mixes are less workable. 

6. COHESIVENESS: 

Cohesiveness is that the element of workability which indicates whether a mixture is harsh, sticky, or plastic. Plasticity may be a desirable property in concrete, indicating that a mixture is often molded and hold a shape when formed. A harsh mix lacks plasticity and therefore the ingredients may tend to separate. Harshness is often caused by either an excess or deficiency of blending water (high- or low-slump mixes), a deficiency of cement (lean mixes), or a deficiency of fine aggregate particles. Harshness can also be caused by more than rough, angular, flat, or elongated aggregate particles. Harsh mixes can sometimes be improved by air entrainment or by increasing the fine aggregate or cement content, but adjustments must be made to the general mix to take care of the right proportion of all ingredients. A sticky mix may have a high cement content (fat mixes) or large amounts of rock dust, fine sand, or similar fine materials (over-sanded mixes). Sticky mixes don't segregate easily, but because they require tons of water to realize even minimal workability, sticky mixes often develop excessive shrinkage cracking. A plastic mix is cohesive without being either sticky or harsh, and therefore the ingredients don't easily segregate unless the concrete is handled improperly.

Er.SP.ASWINPALANIAPPAN., M.E.,(Strut/.,)

Structural Engineer

Madras Terrace Architectural Works

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