What are the steps in making concrete? Explain them.
The main steps in making concrete are as follows:
1. Batching
2. Mixing
3. Transporting and placing concrete
4. Compaction
Mixing: To obtain good concrete, the ingredients must be mixed first dry and then wet. The two most common mixing methods are manual and mechanical.
Concrete transport and placement: Once the concrete mix is ready, it must be transported to its final location. The concrete is placed on formwork and should always be deposited as close as possible to its final location.
Concrete compaction: When placed, concrete may contain air bubbles, which can reduce its strength by up to 30%. To reduce air bubbles, compaction is performed. Compaction is generally done in two ways: by hand or with a vibrator.
Briefly describe the different methods of curing concrete. Curing is the process of maintaining the humidity and temperature conditions of freshly applied concrete. It is cured for a short period of time to allow it to set. Methods to reduce concrete shrinkage include:
Water Spray: Curing can be done by spraying water on walls and columns.
Wet Surface Coating: Curing can be done with moist burlap or straw bags.
Sheathing: Horizontal surfaces, such as slabs and floors, can be cured by trapping water.
Steam Curing: In precast concrete units, steam curing can be performed on the units in a closed chamber. This allows for faster curing and recovery.
Applying Curing Compounds: Calcium chloride compounds can be applied to the cured surface. This keeps the surface moist for a longer period.
What is meant by "presetting" during the bridge bearing installation process?
During bridge bearing installation, the top plates are reduced in size to save material. This process is called presetting. Typically, the top bearing plate consists of the following components:
Length of the support
2 x irreversible movement
2 x reverse movement
The support is initially located in the center of the top bearing plate. The directional effect of irreversible movement is not considered. However, since irreversible movement usually occurs in only one direction, only the displaced direction moves away from the midpoint. In this case, the length of the top plate is equal to the length of the support + irreversible movement + 2 x reverse movement.
Why are steel plates inserted into elastomeric bearings?
For an elastomeric bearing to act like a soft spring, lateral bulging must be allowed. Furthermore, compressive stiffness can only be increased by increasing the lateral expansion limit. In many cases, metal plates are used to increase the compressive stiffness of the bearing. Once steel plates are incorporated into the bearings, the freedom of expansion is severely limited, and bearing deflection is reduced compared to bearings without steel plates. Steel plates generate tensile stress from the supports. However, the presence of metal plates does not affect the shear expansion of the supports.
What reinforcement is used in the prestressing process?
The main types of reinforcement used in prestressing are:
Breakdown reinforcement: Breakdown reinforcement creates stresses behind the loading zone of the anchor block. This causes the concrete to fail at the surface. The most likely causes of this type of stress are the Poisson effect, the interconnectedness of deformations, or the shape of the stress path.
Balanced reinforcement: This type of reinforcement is necessary when there are multiple anchors where prestressing loads are applied sequentially. Burst reinforcement: This type of stress occurs when the stress paths are concave to the line of action of the load. To reduce this stress, burst reinforcement is required.
Batching: The process of batching various materials for concrete production is called batching. Dosing is generally done in two ways: by volume and by weight. In the case of dosing by volume, the measurement is made by volume, while in the case of dosing by weight, it is done by weight.
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