What is Glass Fiber Reinforced Concrete (GRC)?

Glassfibre Reinforced Concrete or GRC is one of the most versatile building materials available to architects and engineers. Composed principally of cement, sand and special alkali resistant (AR) glassfibres, GRC is a thin, high strength concrete with many applications in construction.The GRC-Glass Fibre Reinforced Concrete, which was first invented by 'pilkington' in UK and developed successfully by rest of the continent, is a product having unique combination of properties unchallenged by any other existing material in the construction industry. Glass Fibre Concrete can be moulded into wide varieties of shapes and contours to become an architectural element of any building. In fact CRC is tailor made; it can take any profile or shape as per consumer's requirement. This flexibility is what gives the material its tremendous demand in a wide ranging variety of applications.

 

INTRODUCTION :- WHAT'S GRC?

Glass Fibre Reinforced Concrete (sometimes called Glass Fibre Reinforced Cement) is a mixture of Cement, fine aggregate, water, chemical admixtures and Alkali Resistant Glass Fibres. There are a number of different manufacturing processes, the most common are Hand Spray and Premix. Glass Fibre Reinforced Concrete (GRC) is a material which today is making a significant contribution to the economics, to the technology and to the aesthetics of the construction industry worldwide. The Alkali Resistant Glass fibre is generally used at the 3 to 5% level in Hand Spray GRC Process and 2 to 3% in Premix GRC Process to manufacture of factory finished prefabricated products.

 

ROLE OF FIBRES:-

 

When the loads imposed on concrete approach that for failure, cracks will propagate sometimes rapidly, fibres in concrete provide a means of assisting the growth. Reinforced Steel bars in concrete have the same beneficial effect because they at as long continuous fibres. Short discontinuous Glass Fibre has the advantage, however, being uniformly mixed and dispersed throughout the concrete.

 

WHY "ALKALI RESISTANT" GLASS FIBRE MUST BE USED IN GR Concrete?

 

When specifying the constituent materials of Glassfbire Reinforced Concrete it is an essential part of the overall Quality and Quantity Assurance in GRC products that a high zirconia alkali Resistant Glass fibre is used to manufacture GRC products. The reasons for this are clearly illustrated. Figure-1 shows the loss in weight of Glass Fibres held in a saturated cements solutions (PH=12.9) for 200 Hours at 80 degree Celsius ploated against the Zirconia content. As is seen, the higher the Zirconia cotent the lower the weight loss.visually illustrates the difference between high Zirnonia Alkali Resistant Glassfibres and standard E-glass, the type of glassfibre generally used in polyester resins and gypsum, quickly deteriorates and loses strength, where as the high Zirconia Resistant Glassfibre remains virtually unaffected. The cost of the Zirconia makes Alkali Resistant Glassfbires considerably more expensive than E-glass but, as seen the price for security is well work paying. GRC promise of thinner and stronger elements, reduced weight (1/3rd of Precast Concrete) and controlled cracking by simply adding a small amount of fibres an attractive feature of Fibre Reinforced Concrete.

Civil Engineering Interview Questions

Interview Question's

 

What are the steps involved in the concreting process, explain?

 

The major steps involved in the process of concreting are as follows:

1.     Batching: The process of measurement of the different materials for the making of concrete is known as batching. batching is usually done in two ways: volume batching and weight batching. In case of volume batching the measurement is done in the form of volume whereas in the case of weight batching it is done by the weight.

2.     Mixing: In order to create good concrete, the mixing of the materials should be first done in dry condition and after it wet condition. The two general methods of mixing are: hand mixing and machine mixing.

3.     Transportation and placing of concrete: Once the concrete mixture is created it must be transported to its final location. The concrete is placed on form works and should always be dropped on its final location as closely as possible.

4.     Compaction of concrete: When concrete is placed it can have air bubbles entrapped in it which can lead to the reduction of the strength by 30%. In order to reduce the air bubbles the process of compaction is performed. Compaction is generally performed in two ways: by hand or by the use of vibrators.

 

Describe briefly the various methods of concrete curing.

 

Curing is the process of maintaining the moisture and temperature conditions for freshly deployed concrete. This is done for small duration of time to allow the hardening of concrete. The methods that are involved in saving the shrinkage of the concrete includes:

(a) Spraying of water: on walls, and columns can be cured by sprinkling water.

(b) Wet covering of surface: can be cured by using the surface with wet gunny bags or straw

(c) Ponding: the horizontal surfaces including the slab and floors can be cured by stagnating the water.

(d) Steam curing: of pre-fabricated concrete units steam can be cured by passing it over the units that are under closed chambers. It allows faster curing process and results in faster recovery.

(e) Application of curing compounds: compounds having calcium chloride can be applied on curing surface. This keeps the surface wet for a very long time.

 

 

What do you understand by “preset” during the installation process of bridge bearings?

During the installation of bridge bearings the size of the upper plates is reduced to save the material costs. This process is known as preset. Generally the upper bearing plate comprises of the following components:

1. Length of bearing

2. 2 x irreversible movement.

3. 2 x reversible movement. The bearing initially is placed right in the middle point of the upper bearing plate. No directional effects of irreversible movement is considered. But since the irreversible movement usually takes place in one direction only the displaced direction is placed away from the midpoint. In such cases the length of the upper plate is equal to the length of the length of the bearing + irreversible movement + 2 x reversible movement.

 

Why are steel plates inserted inside bearings in elastomeric bearings?

 

In order to make a elastomeric bearing act/ function as a soft spring it should be made to allow it to bulge laterally and also the stiffness compression can be increased by simply increasing the limiting amount of the lateral bulging. In many cases in order to increase the compression stiffness of the bearing the usage of metal plates is made. Once steel plates are included in the bearings the freedom of the bulge is restricted dramatically, also the deflection of the bearing is reduced as compared to a bearing without the presence of steel plates. The tensile stresses of the bearings are induced into the steel plates. But the presence of the metal plates does not affect the shear stiffness of the bearings.

 

What reinforcements are used in the process of prestressing?

 

The major types of reinforcements used in prestressing are:

Spalling Reinforcement: The spalling stresses leads to stress behind the loaded area of the anchor blocks. This results in the breaking off of the surface concrete. The most likely causes of such types of stresses are Poisson`s effects strain interoperability or by the stress trajectory shapes.

Equilibrium reinforcements: This type of reinforcements are required where several anchorages exist where the prestressing loads are applied in a sequential manner.

Bursting Reinforcements: These kinds of stresses occur in cases where the stress trajectories are concave towards the line of action of load. In order to reduce such stresses reinforcements in the form of bursting is required.

 

 

What is the basic difference between QA and QC?

 

Quality Assurance is basically deals with defect prevention and Quality control deals with defect identification.