1. For quality control of Portland cement, the test essentially done is : setting time , soundness , tensile strength , consistency .
2. Under normal conditions using an ordinary cement, the period of removal of the form work, is :
7 days for beam soffits
14 days for bottom slabs of spans 4.6 m and more
21 days for bottom beams over 6 m spans
2 days for vertical sides of columns
3. Wp and Wf are the weights of a cylinder containing partially compacted and fully compacted concrete. If the compaction factor is 0.95, the workability of concrete is high.
4. For given water content, workability decreases if the concrete aggregates contain an excess of thin particles , flat particles , elongated particles , flaky paticles .
5. M10 grade of concrete approximates 1 : 3 : 6 mix .
6. For ensuring quality of concrete, use graded aggregates.
7. According to I.S. : 456, the number of grades of concrete mixes, is 7 .
8. The mixture of different ingredients of cement, is burnt at 1400°C.
9. The risk of segregation is more for wetter mix , larger size of the maximum size aggregate , coarser grading .
10. Hydration of cement is due to chemical action of water with Tricalcium silicate and dicalcium silicate , Dicalcium silicate and tricalcium aluminate , Tricalcium aluminate and tricalcium alumino ferrite .
11. To obtain cement dry powder, lime stones and shales or their slurry, is burnt in a rotary kiln at a temperature between 1400° and 1500°C.
12. The maximum amount of dust which may be permitted in aggregates is 5% of the total aggregates for low workability with a coarse grading , 10% of the total aggregates for low workability with a fine grading , 20% of the total aggregates for a mix having high workability with fine grading .
13. The bulk density of aggregates depend upon : size and shape of aggregates , specific gravity of aggregates , grading of aggregates Note: does not depend on size of the container.
14. While compacting the concrete by a mechanical vibrator, the slump should not exceed 5 cm .
15. Construction joints are provided , where B.M. and S.F. are small , where the member is supported by other member , at 18 m apart in huge structures , in concrete wall at sill level of windows.
16. An aggregate is said to be flaky if its least dimension is less than 3/5th of mean dimension .
17. The increased cohesiveness of concrete, makes it less liable to segregation .
18. The ratio of the length to breadth of a wooden float, is 7.5 .
19. To ensure constant moisture content in aggregates , area of each aggregate pile should be large , height of each aggregate pile should not exceed 1.50 m , aggregate pile should be left for 24 hours before aggregates are used , conical heaps of aggregates should be avoided to prevent moisture variation .
20. Workability improved by adding : air-entraining agent , foaming agent , oily-agent , aluminium compound.
21. Curing a concrete for long period ensures better : volume stability , strength , water resistance , water tightness and durability .
22. For the construction of cement concrete floor, the maximum permissible size of aggregate, is 10 mm .
23. The process of proper and accurate measurement of concrete ingredients for uniformity of proportion, is known batching .
24. correct statement : Insufficient quantity of water makes the concrete mix harsh , Insufficient quantity of water makes the concrete unworkable , Excess quantity of water makes the concrete segregated , Excess quantity of water causes bleeding in concrete .
25. The preliminary test is repeated if the difference of compressive strength of three test specimens, exceeds 15 kg/cm2 .
26. correct proportions of chemical ingredients of cement : Lime : Silica : Alumina : Iron oxide : 63 : 22 : 6 : 3
27. Transport of concrete by pumps, is done for a distance of 400 m .
28. If X, Y and Z are the fineness modulli of coarse, fine and combined aggregates, the percentage (P) of fine aggregates to combined aggregates, is
29. The high strength of rapid hardening cement at early stage, is due to its increased lime cement .
30. correct statement : The weight of ingredients of concrete mix, is taken in kilograms , Water and aggregates are measured in litres , The finished concrete is measured in cubic metres , 20 bags of cement make one tonne .
31. Vicat's apparatus is used for consistency test .
32. The rock which is calcareous, is : lime stone , macl , chalk .
33. Internal friction between the ingredients of concrete, is decreased by using more water and coarse aggregates .
34. For road pavements, the cement generally used, is rapid hardening cement .
35. Construction joints are generally provided in concrete : roads , retaining walls , lining of canals , lining of tunnels .
36. Separation of coarse aggregates from mortar during transportation, is known segregation .
37. According to the recommendations of IS : 456-1978, the expansion joints : are provided where plane changes abruptly , are provided to ensure minimum resistance , are supported on separate columns , do not carry reinforcement across them .
38. Grading of sand causes great variation in : workability of concrete , strength of concrete , durability of concrete , handing and placing of concrete .
39. Shrinkage in concrete can be reduced by using : low water cement ratio , less cement in the concrete , proper concrete mix , presaturated aggregates .
40. IS. Sieve Nos. 10 mm and 4.75 mm are geneally used for grading of coarse aggregates , fine aggregates .
41. correct statement: The free water is the amount of water added while mixing and the amount of water held on the surface of the aggregates prior to mixing , The total water is the free water and the amount actually absorbed by the aggregates .
42. Addition of pozzolana to ordinary port land cement, causes : decrease in early strength , reduction in chemical action with sulphates , increase in shrinkage , reduction bleeding .
43. Too wet concrete may cause : weakness of concrete , excessive laitance , segregation , lower density.
44. Addition of pozzolana to cement causes : reduction in permeability , loss of heat of hydration , reduction in bleeding , increase in curing time .
45. Lime in excess, causes the cement to expand and disintegrate.
46. Silica in excess, causes the cement to set slowly.
47. Alumina in excess, reduces the strength of the cement.
48. Magnesium oxide in excess, remains in free state and makes the cement unsound.
49. Higher workability indicates unexpected increase in the moisture content
50. Higher workability indicates deficiency of sand
51. If the concrete mix is dry, the slump is zero
52. Concrete mix having zero slump, is unsuitable for high strength.
53. to construct a massive dam - low heat cement
54. Water required per bag of cement, is 35 kg .
55. For construction of structures in sea water, the cement generally preferred to, is Portland-pozzolana cement .
56. Percentage of pozzolanic material containing clay upto 80% used for the manufacture of pozzolana cement, is 30% .
57. The process of hardening the concrete by keeping its surface moist is known curing .
58. C.R.R.I. charts are used to obtain a relatioship between strength of concrete and water cement ratio .
59. Proper batching ensures : economy , durability , workability , strength .
60. Workability of concrete for a given water content is good if the aggregates, are rounded aggregate.
61. Bulking of sand is caused due to formation of a thin film of surface moisture
62. Fine sand bulks more than coarse sand
63. With 10% moisture content by weight, the bulking of sand is increased by 50%.
64. The volume of fully saturated sand, is equal to the volume of dry and loose sand.
65. For compacting plain concrete road surface of thickness less than 20 cm, we use screed vibrator.
66. Expansion joints need not be provided in foundation concrete .
67. Specified compressive strengh of concrete is obtained from cube tests at the end of 28 days.
68. The strength of concrete decreases as the water cement ratio increases
69. If the water cement ratio is less than 0.45, the concrete is not workable and causes honey-combed structure
70. The percentage of the aggregate of F.M. 2.6 to be combined with coarse aggregate of F.M. 6.8 for obtaining the aggregates of F.M. 5.4, is 50% .
71. The final operation of finishing floors, is known as troweling.
72. The internal dimensions of a ware house are 15 m x 5.6 m, and the maximum height of piles is 2.70 m, the maximum number of bags to be stored in two piles, are 3000 bags .
73. The maximum thickness of concrete floor of a cement warehouse, is 25 cm.
74. A construction joint is provided where: bending moment is small , shear force is small, the member is supported by other member.
75. The compaction of concrete, improves : density , strength , durability .
76. Water cement paste hardens due to hydration
77. During hardening cement binds the aggregates together
78. Cement provides strength, durability and water tightness to the concrete
79. The light weight aggregates are obtained from volcanic source.
80. According to the petrological characteristics, concrete aggregates are classified as heavy weight, normal weight and light weight.
81. According to the shape of the particles, concrete aggregates are classified as rounded irregular, angular and flaky.
82. According to the surface texture of the particles, the concrete aggregates are classified as glassy, smooth, granular, rough, crystalline, honey combed and porous.
83. Segregation is responsible for: honey-combed concrete , porous layers in concrete , surface scaling in concrete , sand streaks in concrete .
84. The datum temperature for maturity by Plowman, is - 11.7°C.
85. The degree of grinding of cement, is called fineness.
86. The process of changing cement paste into hard mass, is known as setting of cement
87. The heat generated during chemical reaction of cement with water, is known as heat of hydration.
88. Slump test of concrete is a measure of its consistency .
89. Pozzolana cement is used with confidence for construction of dams , massive foundations , abutments , R.C.C. structures .
90. Efflorescence in cement is caused due to an excess of alkalis .
91. If the engineer-in-charge approves, the 10 cm cubes may be used for the work test of concrete provided maximum nominal size of aggregate, does not exceed 20 cm .
92. The diameter of the Vicat plunger is 10 mm and its length varies from 40 mm to 50 mm .
93. The shrinkage of concrete is proportional to water content is the mix .
94. The shrinkage of concrete is proportional to cement concrete .
95. The shrinkage of concrete increases with age of concrete .
96. Separation of water or water sand cement from a freshly concrete, is known bleeding .
97. According to Water-Cement Ratio Law, the strength of workable plastic concrete : depends upon the amount of water used in the mix , does not depend upon the quality of cement mixed with aggregates , does not depend upon the quanity of cement mixed with aggregates .
98. In properly graded aggregates, bulk density is more.
99. In single size aggregates, bulk density is least.
100. Saw dust can be rendered chemically inert by boiling it in water containing ferrous sulphate .
101. High percentage of C3S and low percentage of C2S cause rapid hardening .
102. High percentage of C3S and low percentage of C2S make the cement less resistive to chemical attack
103. Low percentage of C3S and high percentage of C2S contribute to slow hardening
104. Low percentage of C3S and high percentage of C2S provide greater resistance to chemical attack.
105. The factor which affects workability, is : water content and its temperature , shape and size of the aggregates , grading and surface textures of the aggregates , air entraining agents.
106. The cement whose strength is a little lower than the ordinary cement during the first three months but attains afterwards the same strength, is known as low-heat Portland cement.
107. Sand stones may be divided into calcareous, siliceous and ferrugineous sand stones.
108. Concrete using sand stones, cracks due to excessive shrinkage.
109. Very hard and close grained crystallined lime stones are suitable aggregates but provide low strength.
110. Broken bricks produce a concrete having good fire resisting qualities.
111. Water enables chemical reaction to take place with cement.
112. Water lubricates the mixture of gravel, sand and cement.
113. Only a small quantity of water is required for hydration of cement.
114. Strength of concrete structure largely depends upon its workability.
115. Calcium chloride acts as a an accelerator.
116. Gypsum (calcium sulphate) acts as a retarder.
117. Joints in concrete structures, are provided : to reduce the tensile stresses likely to be developed due to evaporation of water , to minimise the change in the dimensions of the slab ,to minimise the necessary cracking.
118. The condition applicable to water cement ratio law, is : internal moisture conditions on hydration continue till complete strength is gained , concrete specimens need be of same age , concrete specimens need be of same size.
119. High temperature decreases the strength of concrete.
120. The bulk density of aggregates, is generally expressed as kg/litre.
121. Allowable shear strength of concrete, depends upon shear strength.
122. The most useless aggregate is one whose surface texture is glassy .
123. To obtain a very high strength concrete, use very fine grained Granite.
124. Concrete containing silicious aggregates, has higher co-efficient of expansion.
125. Concrete containing igneous aggregates, has intermediate coefficient of expansion.
126. Concrete containing lime stones, has lowest co-efficient of expansion.
127. An ordinary Portland cement when tested for its fineness, should not leave any residue on I.S. seive No. 9, more than 10% .
128. The top diameter, bottom diameter and the height of a slump mould are : 10 cm, 20 cm, 30 cm .
129. Workability of concrete mix with low water cement ratio is determined by compaction factor test .
130. While designing an air entrained concrete : water cement ratio is reduced , proportion of aggregates is reduced , an allowance for the entrained air is made , strength of the concrete, is reduced .
131. For performing compressive strength test of cement water is added at the rate of + 3.0 percentage of water where P is the percentage of water for standard consistency , A cube mould of 10 cm x 10 cm x 10 cm is used , The perpared moulds are kept in a atmosphere of 50% relative humidity , The temperature of water in the submerged tank for curing moulds, should be 27° ± 2°C. .
132. For concreting tunnel linings, tran-portation of concrete is done by pumps .
133. The operation of removing humps and hollows of uniform concrete surface, is known as screeding .
134. The void ratio of single size coarse aggregate is roughly 0.45..
135. The void ratio of graded coarse aggregate is roughly 0.040 .
136. The void ratio of fine aggregate is roughly 0.45.
137. The type of aggregates not suitable for high strength concrete and for pavements subjected to tension, is rounded aggregate .
138. For the construction of R.C.C. slabs, columns, beams, walls, etc. the grade of concrete mix used, is 1 : 2 : 4 .
139. The type of aggregates of same nominal size, which contain less voids when compacted, are rounded spherical .
140. For the construction of cement con-certe dams, the maximum permissible size of the aggregates, is 40 mm,
141. For preparing a test-specimen, it is necessary : to mix cement and fine aggregate by dry hand , to mix coarse aggregates , to mix water to the cement, fine aggregates and coarse aggregates , to oil inner surface of the mould and the base plate, before placing concrete.
142. The aggregate containing moisture in pores and having its suface dry, is known as saturated surface dry aggregate.
143. The commercial name of white and coloured cement in India & Nepal , is colocrete , rainbow cement , silvicrete , snowcem .
144. An increase in water content must be accompanied by an increase in cement content.
145. Angular and rough aggregates reduce the workability of the concrete.
146. Large size aggregates increase the workability due to lesser surface area.
147. The slump of the concrete mix decreases due to an increase in temperature.
148. To hydrate 500kg of cement full water needed, is 130 kg.
149. Concrete gains strength due to hydration of cement.
150. If aggregates completely pass through a sieve of size 75 mm and are retained on a sieve of size 60 mm, the particular aggregate will be flaky if its minimum dimension is less than 40.5 mm.
151. Non-uniform compaction may cause the concrete : porous , non-homogeneous , reduced strength .
152. Log Angles machine is used to test the aggregate for abrasion resistance.
153. If fineness modulus of sand is 2.5, it is graded as fine sand .
154. Pozzolanic properties exist in : shales , fly ash , pumicite , diatomaceous clay .
155. An aggregate which passes through 25 mm I.S. sieve and is retained on 20 mm sieve, is said to be flaky if its least dimension is less than 13.5 mm .
156. Expansion joints are provided if the length of concrete structures exceeds 45m .
157. Workability improved by adding : fly ash , hydrated lime , calcium chloride , bentonite .
158. If the slump of a concrete mix is 60 mm, its workability is medium .
159. Sand obtained from pits, is washed to remove clay and silt.
160. Sand obtained from flooded pits, need not be washed before use.
161. Sea shore sand contains chlorides which cause effloresance.
162. The chloride in sea shore sand and shingle may cause corrosion of reinforcement if the concrete is porous.
163. The strength and quality of concrete, depend upon: grading of aggregates , surface area of aggregates , shape of aggregates , surface texture of aggregates .
164. The process of mixing, transporting, placing and compacting concrete using Ordinary Port land Cement should not take more than 30 minutes.
165. While performing preliminary test on concrete proportions of the material and water should be the same as to be used at the work site.
166. While performing preliminary test on concrete cement should be mixed by hand in order to maintain uniformity .
167. While performing preliminary test on concrete concrete mix should be stored in air-tight containers .
168. Sand requiring a high water cement ratio, belongs to Zone I .
169. Ordinary Portland cement is manufactured from gypsum and lime .
170. A flaky aggregate is said to be elongated if its length is twice the mean size .
171. To prevent segregation, the maximum height for placing concrete, is 150 cm .
172. Water cement ratio is generally expressed in volume of water required per 50 kg .
173. For a good concrete : aggregates should be hard and durable , cement should be sufficient to produce the required strength , water should be free from organic materials , mixing of ingredients should be done thoroughly so as to produce homogeneity .
174. If the effective plan area of a warehouse is 54 sq. m, and maximum height of piles permitted is 270 cm, the number of cement bags to be stored, is 2700 bags .
175. Gypsum is added for controlling setting time .
176. A concrete having a slump of 6.5 cm, is said to be plastic .
177. Strength of concrete with passage of time increases .
178. Cement used for normal concrete construction, is obtained by burning a mixture of silicious, argillaceous and calcareous materials .
179. The concrete gains strength due to hydration of cement.
180. The concrete cured at a temperature below 23°C, gains strength up to 28 days.
181. The concrete does not set at freezing point.
182. The strength of concrete increases with its age.
183. Admixtures does not accelerate hydration.
184. Admixtures make concrete water proof .
185. Admixtures make concrete acid proof .
186. Admixtures give high strength.
187. Higher workability of concrete is required if the structure is thick and heavily reinfored..
188. Setting time of cement increases by adding gypsum .
189. The dimensions of a 35 litre forma for measuring aggregates by volume, are : length 27 cm, breadth 27 cm, height 48 cm
190. The shuttering of a hall measuring 4 m x 5 m, can be removed after 7 days .
191. correct statement : There should not be any loss of cement from the charged drum of the mixer , Cement should be mixed for at least one minute , 10% of water is placed in the rotating drum before adding dry material , 10% of water is added after placing the other ingredients in the drum.
192. The entrained air in concrete increases workability.
193. Tricalcium silicate (C3S) hydrates rapidly .
194. Tricalcium silicate (C3S) generates more heat of hydration .
195. Tricalcium silicate (C3S) develops early strength.
196. In slump test, each layer of concrete is compacted by a steel rod 60 cm long and of 16 mm diameter for 25 times.
197. If the average compressive strength is 4000 kg/cm2 and standard deviation is 500, the co-efficient of variation is 12.5% .
198. For preparing ordinary concrete, the quantity of water used, is 5% by weight of aggregates plus 30% of weight of cement.
199. According to IS : 382-1963, a good aggregate should be : chemically inert , sufficiently strong , hard and durable .
200. The 28 days cube strength of mass concrete using aggregates of maximum size 5 cm for gravity dams should be below 200 kg/cm2 .
201. If P, Y and Z are the weights of cement, fine aggregates and coarse aggregates respetively and W/C is the water cement ratio, the minimum quantity of water to be added to first batch, is obtained by the equation 0.3P + 0.1Y + 0.01Z = W/C x P.
202. For the construction of thin R.C.C. structures, the type of cement to be avoided, is blast furnace slag cement .
203. Space between the exterior walls of a warechouse and bag piles should be 30 cm.
204. Cement bags should preferably be piled on wooden planks.
205. Cement bags should be placed such that bags of one layer does not touch the bags of the adjacent layer.
206. Width and height of the pile should not exceed 3 m and 2.70 m respectively.
207. For the construction of the retaining structures, the type of concrete mix to be used, is 1 : : 3
208. An ideal ware house, is provided : water proof masonry walls , water proof roof , few windows which remain generally closed , 15 cm thick concrete floor laid on a dry course of soling.
209. Concrete is unsuitable for compaction by a vibrator if it is plastic.
210. Inert material of a cement concrete mix, is aggregate.
211. Sands of zone I are coarse.
212. The lower water cement ratio in concrete, introduces : smaller creep and shrinkage , greater density and smaller permeability , improved frost resistance , greater wear resistance and improved bond strength .
213. The cement becomes useless if its absorbed moisture content exceeds 5%.
214. A concrete using an air entrained cement is more plastic and workable.
215. The maximum size of a coarse aggregate, is 75 mm and minimum 4.75 mm.
216. The maximum size of the fine aggregate, is 4.75 mm and minimum 0.075 mm.
217. The material having particles of size varying from 0.06 mm to 0.002 mm, is known as silt.
218. The material having particles of size less than 0.002 mm, is known as clay.
219. Placing of concrete should preferably be done at a temperature of 27 ± 2°C.
220. The aggregate impact value of the aggregate used in building concrete is less than 45, road pavement concrete is less than 30, runway concrete is less than 30.
221. Workability of the concrete mix decreases with an increase in the moisture content.
222. Concrete for which preliminary tests are conducted, is called controlled concrete.
223. Bulking of sand depends upon the fineness of grains.
224. Concrete mix 1 : 6 : 12, is used for mass concrete in piers.
225. The impurity of mixing water which affects the setting time and strength of concrete, is sodium carbonates and bicarbonates.
226. Continuous grading is not necessary for obtaining a minimum of air voids.
227. The omission of a certain size of aggregate is shown by a straight horizontal line on the grading curve.
228. The omission of a certain size of aggregate in concrete increases the workability but also increases the liability to segregation.
229. Di-calcium silicate (C2S) generates less heat of hydration.
230. On a grading curve, the gap grading is represented by a horizontal line.
231. Bulking of sand is swelling of sand when wetted.
232. Curing of pavements, floors, roofs and slabs, is done by ponding method.
233. After a period of 24 months, the strength of cement reduces to 50%.
234. The concrete made with storage deteriorated cement, gains strength with time.
235. The surface where two successive placements of concrete meet, is known as Construction joint.
236. An excess of flaky particles in concrete aggregates decreases the workability .
237. An excess of flaky particles in concrete aggregates increases the quantity of water and sand.
238. An excess of flaky particles in concrete aggregates affects the durability of concrete , more than 15% are not desirable .
239. For given workability the grading requiring the least amount of water is one that gives greatest surface area for the given cement and aggregates.
240. The minimum percentage of chemical ingredient of cement is that of magnesium oxide .
241. The specifications of a cement bag for storage, are : weight 50 kg , height 18 cm , plan area 3000 sq. cm , volume 35 litres .
242. The bulk density of aggregates, depends upon : shape , grading , compaction
243. The bulk density of fine aggregate is usually about 10 per cent more than that of coarse aggregate of similar composition .
244. The specific gravity of aggregate is important for the determination of the moisture content.
245. The absorption and porosity of an aggregate influence the property of the concrete.
246. A highly absorptive aggregate reduces the workability of concrete considerably.
247. Horizontal construction joints in concrete walls are generally provided at : soffit level , window sill level , floor level .
248. Construction joints in columns are provided a few cm below the junction of beam \.
249. Construction joints in columns are provided at the bottom haunching.
250. Construction joints in beams and slabs are provided within middel third.
251. Constructionjoints are generally provided in positions subjected to least shear force.
252. For a concrete mix 1:3:6 and water cement ratio 0.6 both by weight, the quantity of water required per bag, is 14 kg.
253. The concrete mix which causes difficulty in obtaining a smooth finish, possess harshness .
254. Le-Chatelier's apparatus is used for testing soundness of cement .
255. 'Ware house pack' of cement means pressure compaction of the bags on lower layers .
256. In the method of voids for determination of the quantity of cement paste, it is assumed that : Voids in coarse aggregates are filled by fine aggregates , Voids in fine aggregates are filled by the cement paste , Volume of fine aggregates is equal to total voids in coarse aggregates plus 10% extra , Volume of cement paste required is equal to total volume of voids in fine aggregates plus 15% extra .
257. The size of fine aggregates does not exceed 4.75 mm .
258. An aggregate is known as cyclopean aggregate if its size is more than 75 mm.
259. The main object of compaction of concrete, is: to eliminate air holes , to achieve maximum density, to provide initimate contact between the concrete and embedded materials .
260. The quality of water governs the strength of concrete.
261. The quantity of water required for concreting, depends upon the grading of aggregate amd method of compaction.
262. 10% excess of water reduces the strength of concrete by 15%.
263. 30% excess of water reduces the strength of concrete by 50%.
264. Particles of 0.002 mm size are that of clay.
265.
Comments
Post a Comment