(SEM V) THEORY EXAMINATION 2018-19 CONCRETE TECHNOLOGY

CONCRETE TECHNOLOGY (RCE-052)

B.Tech (SEM-V) – AKTU                                                                 Time: 3 Hours  Total Marks: 70

SECTION A

(Attempt all questions in brief – 2 × 7 = 14 marks)

Q1 (a) What is bulking of sand?

Bulking of sand is the increase in volume of sand due to the presence of moisture. A thin film of water forms around sand particles, pushing them apart and increasing the volume. Bulking is maximum at about 4–6% moisture content and affects concrete mix proportions if not corrected.

Q1 (b) What are the thermal properties of aggregates?

Thermal properties of aggregates include thermal conductivity, specific heat, and coefficient of thermal expansion. These properties influence heat flow, temperature variation, and thermal cracking in concrete structures, especially mass concrete.

Q1 (c) What is workability of concrete?

Workability of concrete is the ease with which concrete can be mixed, transported, placed, compacted, and finished without segregation. It depends on water content, aggregate size, shape, grading, and use of admixtures.

Q1 (d) Define setting time of cement.

Setting time of cement is the time required for cement paste to lose its plasticity and gain sufficient hardness. It includes initial setting time and final setting time and is important for handling and finishing concrete.

Q1 (e) What is creep of concrete?

Creep is the gradual increase in strain in concrete under sustained load over a period of time. It depends on stress level, age of concrete, humidity, and temperature.

Q1 (f) Define durability of concrete.

Durability of concrete is its ability to resist weathering, chemical attack, abrasion, and other environmental effects while maintaining strength and serviceability throughout its life.

Q1 (g) What is segregation of concrete?

Segregation is the separation of coarse aggregates from cement mortar in concrete. It results in non-uniform concrete and reduces strength and durability.

SECTION B

(Attempt any three – 7 × 3 = 21 marks)

Q2 (a) Explain the wet process of cement manufacturing.

In the wet process, raw materials like limestone and clay are crushed and mixed with water to form a slurry. This slurry is fed into a rotary kiln where it is heated to high temperatures. Chemical reactions produce clinker, which is cooled and ground with gypsum to produce cement. The wet process ensures uniform mixing but consumes more fuel.

Q2 (b) What are supplementary cementitious materials? Explain their benefits.

Supplementary cementitious materials include fly ash, silica fume, ground granulated blast furnace slag, and rice husk ash. These materials improve workability, strength, durability, reduce heat of hydration, and lower cement consumption, making concrete more economical and eco-friendly.

Q2 (c) Explain shrinkage of concrete and its types.

Shrinkage is the reduction in volume of concrete over time. Types include plastic shrinkage, drying shrinkage, autogenous shrinkage, and carbonation shrinkage. Shrinkage may cause cracks if not properly controlled.

Q2 (d) Explain factors affecting strength of concrete.

Strength of concrete depends on water-cement ratio, type and quality of cement, aggregate properties, curing conditions, age of concrete, and compaction. Lower water-cement ratio generally results in higher strength.

SECTION C

(Attempt any one part from each question – 7 × 2 = 14 marks)

Q5 (a) Explain how you would determine the various elastic moduli for concrete.

Elastic properties of concrete include modulus of elasticity, Poisson’s ratio, and shear modulus. These are determined through laboratory tests by applying compressive loads and measuring stress-strain relationships. The modulus of elasticity is obtained from the slope of the stress-strain curve.

Q5 (b) What do you understand by carbonation of concrete? How is it tested?

Carbonation is a process in which carbon dioxide from air reacts with calcium hydroxide in concrete, reducing alkalinity. It may lead to corrosion of reinforcement. Carbonation depth is tested using phenolphthalein indicator, which changes color in alkaline concrete.

Q6 (a) Write a brief note on flexural strength of concrete.

Flexural strength is the ability of concrete to resist bending. It is measured using beam tests under two-point or three-point loading. Flexural strength is important for pavements and slabs.

Q6 (b) Discuss the influence of mix proportions of concrete on shrinkage.

Higher water-cement ratio increases shrinkage. Rich mixes shrink more than lean mixes. Aggregate content and type also affect shrinkage, with higher aggregate content reducing shrinkage.

Q7 (a) What is the need to study fiber reinforced concrete? Explain briefly the factors affecting its properties.

Fiber reinforced concrete is used to improve tensile strength, crack resistance, toughness, and durability. Properties depend on type of fiber, fiber content, aspect ratio, orientation, and bond between fiber and matrix.

Q7 (b) Differentiate between high performance concrete and high density concrete.

High performance concrete is designed for superior strength, durability, and workability. High density concrete is designed mainly for radiation shielding and uses heavy aggregates like barite or magnetite.