Que4.32. What do you mean by Poisson’s rate of concrete.
Answer Poisson’s rate 1. It’s determined as the rate of side to longitudinal strain in contraction test and may vary from0.13 to0.21.
2. The Poisson’s rate can also be determined from the abecedarian reverberative frequence of longitudinal vibration of concrete instance using ultrasonic palpitation haste system.
3. The Poisson’s rate can be determined from Concrete Technology 4 – 29 D( CE- Sem- 5) v2 2nL = 1) 1 2)( 1) where, v = palpitation haste, mm/ sec n = reverberative frequence of longitudinal vibration in Hz L = Distance between transducers, mm . The value of Poisson’s rate as determined by dynamic tests is slightly advanced and ranges from0.20 to0.25.
Que4.33. Define continuity of concrete. bandy the factor affecting concrete continuity.
Answer continuity
1. The continuity of concrete is defined as its capability to repel riding action, chemical attack, bruise, or any other process of deterioration.
2. Durable concrete will retain its original form, quality, and utility when exposed to terrain. Factors Affecting continuity Following are the factors affecting the continuity of concrete
1. Physical Factors Temperature Unfavourable temperature conditions can lead to loss cracks and volume changes. Variation in temperature changes beget secondary stresses in structures.
ii. humidity humidity induces erosion in sword. humidity also acts as a carrier of chemicals inside the body of concrete. humidity can also beget efflorescence on structural shells. Seepage/ Leakages beget vexation to inhabitants and deteriorates structures due to passable concrete. iii. indurating and Deliquescing Leads to expansion of concrete and cracking.
2. Chemical Factors
i. When we’re dealing with continuity, chemical attack which results in volume change, cracking and consequent deterioration of concrete come a major cause of concern.
ii. Ice- melting mariners beget corrosion of concrete.
3. Cement Content and w/ c rate of Concrete Volume change affect in cracks and cracks are responsible for decomposition of concrete. Workmanship Batching, mixing, transportation, placing, contraction and curing bear proper workmanship for a durable concrete.
5. Cover to Bedded sword( As per IS 4562000) i. For main underpinning up to 12 mm dia bar for mild exposures, the nominal cover may be reduced by 5 mm ii. Unless specified else, factual concrete cover shouldn’t diverge from the needed nominal cover by 10 mm.
6. Mineral Oil generally goods only fresh concrete in their hardening process( petrol, petroleum distillates etc) . Organic acid has sharp effect.
8. Vegetable and beast canvases and fats beget deterioration of concrete shells due to their sharp action.
9. Action of sugar has braking effect on fresh concrete and has gradational sharp effect on hardened concrete.
10. Action of Sewage Concrete seamsters running full remain innocent; but in incompletely filled seamsters where hydrogen sulphide gas is evolved and sulphuric acid is formed, concrete above sewage position gets affected due to sharp action of similar acids. Que5.1. What do you understand by high strength concrete? Write down its advantages and disadvantages. Answer High Strength Concrete For fusions made with normal- weight summations, high- strength concretes are considered to be those which have compressive strengths in excess of 40 MPa. Advantages of HSC 1. High compressive strength.
2. Increases rental space.
3. Reduces space enthralled by columns.
4. Reduces dead cargo. 5. Reduces quantum of sword.
6. High rise structures can be make by reduced columns.
7. To use the concrete service at early age,e.g., pavement in 3 days C. Disadvantages of HSC
1. Must be moxie in selection of constituents.
2. Damaged at high temperature i.e., lower resistance to fire.
Que5.2. bandy the guidelines to selection of accoutrements for HSC.
Answer 1. For the advanced target compressive strength of concrete, the outside size of concrete named should be small, so that the concrete can come more thick and compact and less void rate. 2. Up to 70 MPa compressive strength can be produced with a good coarse total of a maximum size ranging from 20 to 28 mm.
3. To produce 100 MPa compressive strength total with a maximum size of 10 to 20 mm should be used.
4. Concretes with compressive strengths of over 125 MPa have been produced with 10 to 14 mm outside size coarse total.
5. Using supplementary cementitious accoutrements , similar as blast- furnace sediment, fly ash and natural pozzolanas, not only reduces the product cost of concrete, but also addresses the depression loss problem.
6. The optimum negotiation position is frequently determined by the loss in 12 or 24 hour strength that’s considered respectable, given climatic conditions or the minimal strength needed.
7. While silica cloud is generally not really necessary for compressive strengths under 70 MPa, utmost concrete fusions contain it when advanced strengths are specified.
Que5.3. What are the colorful styles to achieve high strength in concrete? Also bandy their operations.
Answer styles to Achieve High Strength in Concrete Following are the special styles to achieve high strength in concrete
1. sowing This involves adding a small chance of finely ground, completely doused Portland cement to the fresh concrete blend. This system may not hold important pledge.
2. Revibration Controlled revibration removes all the blights like bleeding, water accumulates, plastic loss, nonstop capillary channels and increases the strength of concrete.
3. High Speed Slurry Mixing This process involves the advance medication of cement- water admixture which is also blended with total to produce concrete.
4. Use of cocktails Use of water reducing agents are known to produce increased compressive strength.
5. Sulphur Impregnation Satisfactory high strength concrete have been produced by macerating low strength pervious concrete by sulphur. The sulphur sneaked concrete has given strength up to 58 MPa.
6. Inhibition of Cracks If the propagation of cracks is inhibited, the strength will be advanced. Concrete cells made this way have yielded strength up to 105MPa.
Applications of High Strength Concrete
1. High strength concrete is needed in engineering systems that have concrete factors that must repel high compressive loads.
2. High strength concrete is generally used in the construction of high- rise structures. 3. It has been used in factors similar as columns( especially on lower bottoms where the loads will be topmost), shear walls, and foundations.
4. High strengths are also sometimes used in ground operations as well.
5. High strength concrete is sometimes used in the construction of trace islands.
6. Use of HSC in column section decreases the column size.
7. Use of HSC in column decreases quantum of sword needed for same column.
8. In high rise structure, use of HSC increases the bottom area for rental purpose.
9. In islands, use of HSC reduces the number of shafts supporting the arbor.
Que5.4. What’s tone compacting concrete? What are the parcels, advantages and disadvantages of tone compacting concrete?
Answer tone Compacting Concrete It’s defined as “ a concrete that’s suitable to inflow under its own weight and fully fill the formwork, while maintaining unity indeed in the presence of congested underpinning, and also consolidate without the need for wobbling contraction ”. Properties of SCC In fresh state, SCC have the following parcels . Filling Capability Flows fluently at certain speed into formwork.
2. Passing Capability Passes through underpinning without blocking.
3. isolation Resistance The distribution of aggregate patches remains homogeneous in both perpendicular and vertical direction.
Advantages of SCC Following are the advantages of SCC
1. A faster rate of placing, without vibration.
2. bettered pumpability.
3. bettered connection around underpinning.
4. Reduced permeability.
5. Reduced wear and tear and gash on forms from vibration.
6. Improves the quality, continuity, and trustability of concrete structures due to better contraction and unity of concrete.
7. Ease of placement results in cost savings through reduced outfit and labour demand.
8. lower noise from vibrators and reduced peril from hand- arm vibration pattern( HAVS).
9. Improves working conditions and productivity in construction assiduity.
10. Reduced construction period.
11. Elimination of problems associated with vibration.
Disadvantages of SCC Following are the disadvantages of SCC
1. More strict conditions on the selection of accoutrements .
2. Lack of encyclopedically accepted test norms and mix designs.
3. premium than conventional concrete grounded on concrete material cost exception to placement cost).
4. Requires further trial batches at laboratory as well as at ready-mixed concrete shops. 5. More precise dimension and monitoring of the element accoutrements .
Que5.6. Compare the hardened parcels of normal concrete and tone compacting concrete.
Answer Following are the comparison of parcels between normal concrete and tone compacting concrete
1. Compressive Strength The compressive strength of SCC when compared with normal concrete made for a particular strength is nearly the same. The tone- compacting property of SCC has veritably little effect on the strength of concrete.
2. Tensile Strength A comparison between cylinders made of SCC and normal concrete of the same grade shows that there’s no major difference between them.
3. Bond Strength The pull- out test carried out to determine the bond strength of SCC indicates superior bond strength of SCC.
4. Modulus of Pliantness The modulus of pliantness for SCC and for normal concrete is the same.
5. snap- thaw Resistance The low- strength of SCC has lower resistance to snap and thaw conditions as compared with low- strength normal concrete.
6. Creep SCC typically is more doughy as compared with normal concrete. So its creep is slightly advanced.
7. continuity continuity is slightly advanced in SCC because of the elimination of crimes which may do during placing and contraction of normal concrete. SCC is likely to have lower voids.
8. Exposure to Fire SCC has a more compact microstructure. This can lead to high vapour pressure. So SCC has a advanced threat of spalling when exposed to fire.
Que5.7. Explain the tests used for inflow parcels of tone compacting concrete.
Answer Following are the colorful test that carried out on tone compacting concrete is fresh state
1. Depression Flow and T50 Test Depression inflow test is used to find the stuffing capability of the SCC.
ii. The SCC sample is poured in to the depression cone also the depression inflow periphery is measured.
iii. The inflow time is measured and is known as T50 depression time.
iv. The advanced the depression inflow value, the lesser its capability to fill formwork under its own weight.
2. L- Box Test
i. The L- box test is used to find the end capability of SCC.
ii. The SCC sample is poured in to the L- box outfit, now the plate is removed to allow inflow.
iii. The L- box rate is calculated as H2/ H1.
iv. When the rate of H2 to H1 is larger than0.8, tone compacting concrete has good passing capability.
3. V- Funnel Test and V- Funnel Test at T- 5 twinkles
i. The V- channel test is used to find the isolation resistance of SCC.
ii. The SCC sample is poured in to the V- channel outfit, now it’s allowed to inflow by its weight.
iii. The evacuating time of V- channel is noted.
iv. This test measured the ease of inflow of the concrete, shorter inflow times indicate lesser inflow capability. After 5 twinkles of setting, isolation of concrete will show a lower nonstop inflow with an increase in inflow time