Test III

Select the best possible answer out of the choices from the list to the statements (multiple choice):

1. The compressive strength of concrete and the tensile strength of steel… .

a. cannot easily withstand the stresses created by vibrations, wind, or other forces.

b. are enhanced by the roughening of steel bars.

c. form a strong bond to resist these stresses over a long span.

d. allow the stresses to be efficiently transmitted between the two materials.

2. Concrete consists of a cement and stone aggregate mixture … .

a. that withstands compression, bending, and tensile stresses.

b. that forms a rigid structure with the addition of water.

c. that can resist corrosion and consequently increase the life of the structure.

d. that does not require a protective layer to resist corrosion.

3. A film is formed on the steel … .

a. because of the alkaline environment created by lime.

b. because of the addition of water.

c. because of the roughening of steel bars.

d. because of the addition of polymer fibers.

4. When steel is embedded in concrete, … .

a. this RC is used extensively in all construction.

b. such mixtures are light, have a long life, and are at times more economical.

c. the composite material withstands compression, bending and tensile stresses.

d. that presents excellent mechanical properties.

5. The cohesive characteristics between the steel and concrete are enhanced …

a. with the addition of water.

b. by the roughening of steel bars.

c. due to the alkaline environment created by lime.

d. due to the internal stresses.

Test IV

Complete the sentences by filling in the correct word that fits a statement (gap fill). Choose the appropriate words from the word bank given below.

A. cellulose B. robust C. capability D. withstands

E. common F. corrosion G. load H. measure

I. contains J. moisture K. carried out L. resist

1. Reinforced concrete, or RC, is concrete that …… embedded steel bars, plates, or fibers that strengthen the material.

2. When steel is embedded in concrete, the composite material …… compression, bending and tensile stresses.

3. Reinforced materials are embedded in the concrete in such a way that the two materials …… the applied forces together.

4. Plastic reinforcement that can be as …… as steel, and does not require a protective layer to resist corrosion.

5. The most …… fibers used are glass fibers, synthetic fibers and steel fibers.

6. There is also the Natural Fiber Feinforced Concrete (NFRC) consisting of …… fibers.

7. If …… is present, then corrosion of steel embedded in the steel reinforced concrete will be an important concern

8. Damage due to …… of rebar may occur in large structures.

9. Techniques have been developed that can …… the gravity of rebar corrosive effects in the existing structures.

10. Measurements are …… on the rebar or on embedded rebar probes.

UNIT 7 Slipform Construction

Read, translate the following text and be ready to fulfil the tests:

Slipform construction is an economical way of working with the concrete. It works well for any kind of construction, be it working with plain concrete, reinforced concrete, or pre-stressed concrete. Accuracy and continual casting for constructing a monolithic structure are its greatest advantages. The slipform method is an efficient way of working with concrete because it reduces the overall construction time considerably. Slip forming is most commonly used for tall structures such as chimneys, silos, water towers, and building cores as well as horizontal structures such as roadways. The slipform technique of construction allows for the continuous pouring of concrete into walls of a structure and only stops when the full required height of the structure has been reached.

A major cost of concrete structure construction comes in the form of the required formwork to retain the concrete while it retains the necessary shape and gains the necessary strength till it can be able to support itself and other imposed loads. It also requires the formwork to be continually removed to newer locations and then re-erected. All this requires the continuous use of manpower and lifting equipment like cranes. In the case of slipform building, the formwork is erected only once and remains intact until the entire structure is completed.

A slipform assembly can only start after the foundations of the walls have been correctly laid and a starter for the walls laid out in its correct alignment with all the necessary steel for the walls already in position. The slipform shuttering is then firmly aligned to this starter with the means of yokes on each side of the shuttering that help to keep the panels in position. The yokes are all connected by horizontal crossbeams. Hydraulic jacks are then installed rigidly to the crossbeams that can all act simultaneously so that the entire slipform shuttering moves upwards. The heights of such slipform shuttering will normally be between 1.1 meters to 1.5 meters in height. The design of the working deck and the yokes and horizontal crossbeams are a very vital part of efficient slipform construction. It is very important that the entire structure be such that its rigidity and shape is maintained at all times. It is quite normal for the two sides of the shuttering to be inclined towards each other at the top with the correct wall dimension available at the center.

This allows the shuttering to move easily and eliminates any drag that concrete can cause on the shutters to prevent its free upward movement. The rigidity of the supporting platform is also essential so that all parts of the structure move simultaneously. If there is any lag from one part to the other, this can cause the shuttering to drag and make it difficult to be pulled up. It is also possible to reduce wall thicknesses as the construction gains height and arrangements have to be made in the slipform structure that will enable such reduction at regular intervals.

Slipform methods of construction can also be adapted to horizontal structures and are used for paving, canals, and tunneling. The technique is more in use for structures that have continuous walls like silos, chimneys, and piers for very tall bridges. It has also been successfully used for construction of buildings, although this requires the manner of leaving inserts for openings like doors and windows to be decided well in advance, as well as also any necessary inserts to support floor slabs after the walls are constructed.

Read and memorize the active vocabulary to the text: