Once the concrete is thoroughly mixed and workable it should be placed in forms before the mixture becomes too stiff. During placement, the concrete is consolidated to compact it within the forms and to eliminate potential flaws, such as honeycombs and air pockets. For slabs, concrete is left to stand until the surface moisture film disappears, then a wood or metal handfloat is used to smooth off the concrete. Floating produces a relatively even, but slightly rough, texture that has good slip resistance and is frequently used as a final finish for exterior slabs.
If a smooth, hard, dense surface is required, floating is followed by steel troweling. Curing begins after the exposed surfaces of the concrete have hardened sufficiently to resist marring. Curing ensures the continued hydration of the cement so that the concrete continues to gain strength. Concrete surfaces are cured by sprinkling with water fog, or by using moisture-retaining fabrics such as burlap or cotton mats.
Other curing methods prevent evaporation of the water by sealing the surface with plastic or special sprays called curing compounds. Special techniques are used for curing concrete during extremely cold or hot weather to protect the concrete.
The longer the concrete is kept moist, the stronger and more durable it will become. The rate of hardening depends upon the composition and fineness of the cement, the mix proportions, and the moisture and temperature conditions. Concrete continues to get stronger as it gets older. Ministry of Ecology. Bitumens and mixtures Concrete and cement History Types of cement Concrete properties Stages of concrete Types of concrete Aspects of concrete Concrete: examples Relation with sustainable development The profession.
The setting of cement and hardening of concrete Published on 30 January updated on 13 February Cement hardens when it comes into contact with water. Return New search Print e-mail a friend. The basic hardening process When the constituents of concrete cement, aggregate and water are brought together, the cement and water chemically react and eventually set to form a hard mass which adheres to and binds together the aggregates to form concrete.
Acknowledgement : The Concrete Society. Privacy policy Contact us Members' area. Hardened Concrete Definition It is mainly the aggregate that provide strength to concrete especially coarse aggregates which act just like bones in the body. What Makes Cement Harden? What Causes Concrete to Harden? Why Does Concrete Harden? How Does Concrete Harden? How Does Cement Harden?
Properties of Hardened Concrete Strength : Hardened concrete has a number of properties, including Mechanical strength, in particular compressive strength. The strength of normal concrete varies between 25 and 40 MPa. Impermeability: The impermeability of hardened concrete may be defined as the property to resist- entry of water. This property is achieved by using extra quantity of cement in concrete mix. A concrete in hardened state must be impermeable.
Durability: Concrete is extremely resistant to the physico-chemical attack emanating from the environment frost, rain atmospheric pollution, etc. It is particularly well-suited for structures exposed to demanding and extreme conditions.
Dimensional Changes: Concrete is not a completely elastic material or. Shrinkage: The volume reduction that occurs primarily due to moisture loss after the concrete has hardened is known as drying shrinkage. Mechanical Properties of Concrete Performance of concrete is evaluated from mechanical properties which include shrinkage and creep, compressive strength, tensile strength, flexural strength, and modulus of elasticity.
Property of Concrete Strength : Hardened concrete has a number of properties, including Mechanical strength, in particular compressive strength. This property is achieved by using an extra quantity of cement in concrete mix. Modulus of Elasticity — NDT. Split-tension test — DT.
Flexural strength test — DT. Rebound hammer test — NDT. Penetration resistance test — NDT. Ultrasonic pulse velocity test — NDT. Maturity test — NDT. Concrete Hardening Cement hardens when it comes into contact with water. What Is Fresh and Hardened Concrete? How Is Concrete Hardened? Like this post?
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