This set of Construction Materials Questions and Answers for Experienced people focuses on “Cement Concrete Construction – Water-Cement Ratio”.
1. According to the __________ law given by Abram as a result of many experiments, the strength of well compacted concrete with good workability is dependent only on the water cement ratio.
a) Water-cement ratio
b) Cement content
c) Water-sand ratio
d) Water content
View Answer
Explanation: It is to be noted that to apply Water-cement ratio law, the concrete is assumed to be fully compacted. The lower water content produces stiff paste having greater binding property and hence the lowering of water cement ratio within certain limits resulting in the increase strength.
2. The water enters into chemical action with cement and this action causes ________ and ________ of concrete.
a) Swelling, shrinkage
b) Expansion, contraction
c) Setting, hardening
d) Strong, weak
View Answer
Explanation: The water lubricates the aggregate and it facilitates the passage of cement with the voids of aggregates. This mean that water makes the concrete workable.
3. The ratio of the amount of water to the amount of cement by weight is termed as the _______
a) Aggregate-sand ratio
b) Water-cement ratio
c) Cement-water ratio
d) Sand-aggregate ratio
View Answer
Explanation: It is found theoretically that the water required for Function is about 0.50 to 0.60 times the weight of cement. The strength and quality of concrete primarily depend upon the water cement ratio.
4. For structures which are regularly wetting and drying, the water cement ratio by weight should be ______ and _________ for thin section respectively.
a) 0.55, 0.45
b) 0.45, 0.55
c) 0.55, 0.65
d) 0.65, 0.55
View Answer
Explanation: The water cement ratio for structure which are exposed to weather should be carefully decided. For structures that are continuously underwater, the water cement ratio by which should be 0.55 and 0.65 for thin sections and mass concrete respectively.
5. The term _________ is used to describe the ease or difficulty with which concrete is handed, transported and placed between the forms with minimum lost of homogeneity.
a) Water-cement ratio
b) Homogeneous mixture
c) Setting time
d) Workability
View Answer
Explanation: The workability, as a physical property of concrete alone irrespective of a particular type of construction, can be defined as the amount of useful internal work necessary to produce full compaction. For instance, the workability suitable for mass concrete is not necessarily sufficient for thin, inaccessible or heavy reinforced sections.
6. If the concrete mix is too wet, the ______________ settle at the bottom of concrete Masha and the resulting concrete becomes of non uniform composition.
a) Fine aggregate
b) Coarse aggregate
c) Sand
d) Cement
View Answer
Explanation: On the other hand, if the concrete mixture is too dry, it will be difficult to handle and place it in position. Both these conflicting condition should be correlated by proportioning carefully the various component of concrete mixture.
7. The _________ is used to measure the workability of concrete mixture which is commonly used in the field.
a) Vee-bee test
b) Slump test
c) Compaction factor
d) Workability test
View Answer
Explanation: The first to suggest the concept of Slump was probably C.M. Champman as a measure of concrete consistency in 1913 and it first appeared in USA book of standard in 1922. Thus the slump test is too old and very few test method of concrete technology have beaten this record.
8. In ________ test, the workability of concrete is measured in the terms of internal energy required to compact the concrete fully.
a) Compaction factor test
b) Vee-bee test
c) Rotating table test
d) Slump cone test
View Answer
Explanation: In Compaction factor test, the concrete is allowed to fall in a lower cylindrical mould of 150 mm diameter and 300 mm height through into vertical placed conical Hopper. The surplus concrete appearing about the top of the mould is removed with a trowel. The weight of concrete in the mould is then found out.
9. The presence of moisture in the sand _____________ the volume of the sand.
a) Increases
b) Decreases
c) Shrink
d) Contract
View Answer
Explanation: The increase in volume of sand is due to the fact that the moisture causes film of water around sand particles and it results in the increase of volume of sand. For moisture content of about 5% to 8%, this increase of volume may be as much as 20% to 40%, depending upon the grading of sand.
10. The finer the material, the more will be increasing volume for a given moisture content and this phenomenon is known as the _____________
a) Shrinkage of sand
b) Contraction of sand
c) Bulking of sand
d) Expansion of sand
View Answer
Explanation: When moisture content is increased by adding more water, the sand particles pack near each other and the amount of bulking of sand is decreased. Thus the dry sand and the sand completely flooded with water have practically the same volume.
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