Concrete works in Highway Engineering

Transcription

1 Concrete works in Highway Engineering

2 INTRODUCTION TO CONCRETE Concrete has been used as a construction material in largest quantity for several decades due to its excellent engineering properties and also due to the economy of this material. Except for cement all the other ingredients can be used from the locally available resources. When properly prepared its strength is almost equal to the strength of naturally occurring hard stone. The properties of concrete making materials influence the properties of concrete both in the fresh state as well as in the hardened state.

3 CONCRETE Constituents Water 7-15 % Cement % Fine Aggregate % Coarse Aggregate %

4 MATERIALS PRACTICES CEMENT AGGREGATES WATER ADMIXTURES BATCHING MIXING TRANSPORTING PLACING COMPACTING PROTECTING CURING

5 CONCRETE Code of Practice Bureau of Indian Standards published the code of practice for concrete (IS : 456) in Fourth Revision in Fourth Amendment in 2013

6 CONCRETE Specifications Standard Specifications for Roads and Bridges Published by Ministry of Road Transport and Highways - First publication in Fifth Revision 2013

7 ORDINARY PORTLAND CEMENT PHYSICAL REQUIREMENTS 1. CONSISTENCY 2. SETTING TIME 3. FINENESS 4. SOUNDNESS 5. COMPRESSIVE STRENGTH

8 Consistency of Cement : IS 4031 Part 4 Aim : Determination of Quantity of Water required to produce standard cement paste Apparatus : Vicat apparatus with Plunger Percentage of water corresponds to a consistency which will permit the plunger to penetrate to 5 mm 7 mm from the bottom of mould

9 VICAT APPARATUS

10 Initial Setting Time : IS 4031 Part 5 Aim : Determination of Initial Setting Time Apparatus : Vicat apparatus with Needle Initial Setting Time shall not less than 30 minutes

11 Final Setting Time : IS 4031 Part 5 Aim : Determination of Final Setting Time Apparatus : Vicat apparatus Final Setting Time shall not more than 600 minutes ( 10 hours )

12 NEEDLE FOR FINAL SETTING TIME

13 Fineness of Cement Fineness is a measure of particle size of Cement Particle size between 3 to 32 microns are optimum for cement performance Fine Cement reacts quickly with water Faster setting & High early strength depends on fineness

14 Fineness of Cement : IS Part 2 Aim : Determination of Specific Surface of Cement Apparatus : Blaine Air Permeability apparatus Specific Surface of Cement shall not be less than 225 m 2 /kg

15 Soundness of Cement : IS Part 3 Aim : Determination of Soundness Apparatus : Le Chatelier apparatus Expansion not more than 10 mm

16 Compressive Strength : IS 4031 Part 6 Aim : Determination of Compressive Strength Apparatus : Compression testing machine DAYS 43 GRADE CEMENT COMPRESSIVE STRENGTH (N/mm 2 )

17 Compressive Strength : IS 4031 Part 6 Aim : Determination of Compressive Strength Apparatus : Compression testing machine DAYS 53 GRADE CEMENT COMPRESSIVE STRENGTH (N/mm 2 )

18 AGGREGATES COARSE AGGREGATES : AGGREGATES RETAINED ON 4.75 MM SIEVE FINE AGGREGATES : AGGREGATES PASSING THROUGH 4.75 MM SIEVE

19 COARSE AGGREGATE SPECIFICATIONS (IS : 383) Particle size distribution Crushing value Impact value Abrasion value Soundness Flakiness index Elongation index

20 GRADED COARSE AGGREGATE IS : 383 TABLE 2 FOR 20 mm NOMINAL SIZE IS SIEVE DESIGNATION PERCENTAGE PASSING 40 mm mm mm mm 0 10

21 GRADED COARSE AGGREGATE IS : 383 TABLE 2 FOR 12.5 mm NOMINAL SIZE IS SIEVE DESIGNATION PERCENTAGE PASSING 20 mm mm mm mm 0 10

22 GRADED COARSE AGGREGATE IS : 383 TABLE 2 FOR 40 mm NOMINAL SIZE IS SIEVE DESIGNATION PERCENTAGE PASSING 80 mm mm mm mm mm 0 5

23 AGGREGATE CRUSHING VALUE IS : 2386 PART - IV AGGREGATE CRUSHING VALUE SHALL NOT EXCEED : 30 % FOR CONCRETE WORKS

24 AGGREGATE IMPACT VALUE IS : 2386 PART - IV AGGREGATE IMPACT VALUE SHALL NOT EXCEED : 30 % FOR WEARING SURFACES SUCH AS ROADS & PAVEMENTS 45 % FOR OTHER THAN WEARING SURFACES

25 AGGREGATE ABRASION VALUE IS : 2386 PART - IV AGGREGATE ABRASION VALUE SHALL NOT EXCEED : 30 % FOR WEARING SURFACES SUCH AS ROADS AND PAVEMENTS 50 % FOR OTHER THAN WEARING SURFACES

26 FINE AGGREGATE GRADING REQIREMENT - IS : 383 TABLE 4 SIEVE SIZE ZONE - I ZONE - II ZONE - III ZONE - IV 10 mm mm mm mm micron micron micron

27 Water Clean and free from injurious amount of Oil, Acid, Alkali, Sugar, Salt, and Organic materials Potable water is good for concrete Water having ph value less than 6 is not permitted Sea water is not permitted

28 CONCRETE Strength development Fresh Stage Concrete is Plastic, workable capable of being moulded Transition Stage Workability reduces, process of setting begins Hardened Stage Concrete becomes stiff and gains enough strength to support load

29 Concrete workability Slump Test Standard slump cone size Top dia = l0 cm Bottom dia = 20 cm. Height = 30 cm Standard tamping rod Length = 0.6 m Dia = 16 mm. Test Procedure Concrete shall be poured in four layers - each layer 25 blows. On removing the cone slowly, the slumped concrete height has to be measured. The difference between this reading and the original height of 30 cm is the slump of concrete.

30 Recommended Slump values Sl.No Type Slump (mm) 1. (a) Structures with exposed inclined surface 25 requiring low slump concrete to allow proper compaction (B) Plain Cement Concrete RCC, structures with widely reinforcement eg solid column, piers, abutment footing, well steining 3. RCC structure with fair degree of congestion of reinforcement eg.pier and abutment, Caps, Box culvert well curb, well cap, walls with thickness greater than 300 mm RCC PSC structures with highly congested reinforcement eg. Deck Slab Girders, Box Girders, walls with thickness less than 300 mm 5. Under water concreting through tremie eg. Bottom plug, cast- in-situ Pilling

31 CONCRETE Properties Strength Compression Bending Shear Torsion Bond Fatigue Elastic Modulus Creep Shrinkage Durability i) Porosity ii) Impermeability iii) Abrasion iv) Freeze thaw resistance

32 CONCRETE Strength Concrete is designated by its compressive strength only Eg : M 30 M refers to Mix Number refers to Compressive strength of 150 mm cube, cured in water for 28 days expressed in N/mm 2 (Mpa)

33 Grades of Concrete As per IS : 456 M 10, M 15, M20 : ORDINARY CONCRETE M 25, M 30, M35, M 40, M 45, M 50, M 55, M60 : STANDARD CONCRETE M 65, M 7O, M 75, M 80, M 85, M 90, M 95, M 100 : HIGH STRENGTH CONCRETE

34 Applications of Ordinary Concrete (M 10,M 15,M 20) Plain concrete works Lean concrete works Simple foundations Foundation for masonry walls Temporary RCC constructions Non load bearing structures

35 Ordinary Concrete Cement + Fine Aggregate + Coarse Aggregate + Water Ordinary Concrete

36 Applications of Standard Concrete (M 25 to M 60) Reinforced concrete works Prestressed concrete works Prefabricated concrete elements Load bearing structures

37 Standard Concrete Ordinary Concrete + Chemical Admixture (High range water reducers) Standard Concrete

38 Applications of High Strength Concrete (M 65 M 100 ) High Rise Buildings Offshore Structures Nuclear Power Plants Spill ways of Dams Long span Bridges Ultra-thin whitetopping

39 Achieving High Strength Concrete Conventional Concrete + Chemical Admixture + Mineral Admixture High Strength Concrete

40 MINERAL ADMIXTURES RECOMMENDED BY IS : 456 Fly Ash Silica Fume Ground Granulated Blast Furnace Slag Rice Husk Ash Metakaolin

41 CONCRETE MIX DESIGN Name of Work Construction of bridge at km 62/2 of SH-57 Structural Member Grade of Concrete M 30 Target mean strength Cement Fine Aggregate Brand, Grade and Type Compressive strength at 28 days Type Grading Zone Percentage of water absorption Type Wearing Coat 42 Mpa Penna 53 Grade Ordinary Portland Cement Mpa River Sand II 0.86% Percentage of 20 mm size 45% Percentage of 12.5 mm Coarse Aggregate size 45% Percentage of 6 mm size 10% Percentage of water absorption 0.42% Crushed Stone

42 CONCRETE MIX DESIGN Materials Quantity required for 1 m 3 of Concrete Quantity required for 1 bag of Cement Cement Penna 53 Grade OPC kg kg Fine Aggregate (Dry) River Sand kg kg 20 mm size kg kg Coarse Aggregate (Dry) 12.5 mm size kg kg 6.0 mm size kg kg Water Free water + Water for Absorption of Fine and Coarse Aggregates lit lit

43 CONCRETE MIX DESIGN Concrete mix proportion by weight 1 : 1.66 : 3.26 Water Cement Ratio 0.40 Concrete Slump value achieved (Fresh Concrete) Compressive Strength of Concrete achieved at 28 days (Hardened Concrete) 32 mm Mpa

44 Acceptance Criteria for Strength of Concrete Strength of Concrete in Structure Strength of Concrete Sample 1 Sample = 3 Cubes

45 Minimum Frequency of Sampling Quantity of Concrete (m 3 ) Number of Samples and above for each additional 50 m3 or part

46 Sampling of Fresh Concrete Collect Samples from not less than 5 well-distributed positions immediately after discharge Quantity of sample shall not be less than 0.02 m 3 Avoid edge of the concrete mass to avoid segregation

47 Making and Curing Test Specimen Mould shall be thinly coated with oil Concrete shall be filled in 3 layers Each layer 5 cm deep Compaction with tamping bar Number of strokes per layer : 35

48 Making and Curing Test Specimen Specimen shall be stored at safe place at 22 0 c to 32 0 c for 24 hours After 24 hours, specimen shall be stored in clean water at 27 0 c ± 2 0 c until the date of testing

49 Testing of Concrete specimen Specimens stored in water shall be removed from the water Surface water shall be wiped off Specimens shall be tested while they are in the Saturated Surface Dry condition

50 Testing of Concrete specimen Load shall be applied perpendicular to Cast direction Top Top Rate of loading : 5.25 kn/sec Load shall be applied until the specimen breaks down Load at Failure Compressive Strength = Cross sectional area

51 Acceptance Criteria F c1 = Strength of cube 1 F c2 = Strength of cube 2 The values of F c1, F c2 and F c3 should be within ± 15 % of F c mean F c3 = Strength of cube 3 F c mean > (F ck + 3) F c1 + F c2 + F c3 F c mean =

52 F c1 = Test Result of Sample 1 F c2 = Test Result of Sample 2 F c3 = Test Result of Sample 3 F c4 = Test Result of Sample 4

53 Acceptance Criteria Mean of the Four Non - Overlapping Consecutive Test Results F c1 + F c2 + F c3 + F c4 F c mean = Condition 1 F c mean > (F ck + 3) Condition 2 F c1 > (F ck - 3) F c2 > (F ck - 3) F c3 > (F ck - 3) F c4 > (F ck - 3)

54 ACCEPTANCE CRITERIA COMPRESSIVE STRENGTH OF CORES I ) AVERAGE EQUIVALENT CUBE STRENGTH OF CORE = 85 % of CUBE STRENGTH of SPECIFIED GRADE II ) STRENGTH OF ANY INDIVIDUAL CORE = 75 % of CUBE STRENGTH of SPECIFIED GRADE If the Concrete is not able to meet any of the Standards of Acceptance, the Structure is to be Investigated

55 Factors affecting Compressive Strength Water/Cement Ratio Cement Content Aggregate/Cement Ratio Type of Aggregate Placing & Compaction Curing condition Age of Concrete Environmental Condition

56 Steel Reinforcement for Structures Properties of Steel bars Properties Fe 415 Fe 415 D Fe 500 Fe 500 D 0.2 Percent Proof Stress Minimum (Mpa) Tensile Strength Minimum (Mpa) Elongation Percentage Minimum (%)

57 Prestressed Concrete Pre tensioned Concrete Steel tendons are stressed by Jacks anchored to fixed blocks in the casting yard, Concrete is then placed in moulds or casting beds around these tendons. When the concrete has hardened sufficiently, the tendons are released. As they try to return to their original length, large compressive forces are applied to the concrete. This process is nearly always carried out in a factory environment and is the usual way of manufacturing precast prestressed bridge girders.

58 Prestressed Concrete Post tensioned Concrete Tensioning forces are applied to the tendons after the concrete is placed and hardened. Ducts are incorporated into the formwork and the concrete is placed around them. After the concrete has hardened, the stressing tendons are threaded through the ducts and are stressed using Jacks. A special grout is injected into the ducts around the tendons to provide bond and protection from corrosion. Pos-tensioning is mainly carried out on site although it has been used for special precast girders.

59 Non Destructive Tests Non Destructive tests are used to obtain estimation of the properties of concrete in the structure. Non Destructive tests provide alternative to core tests for estimating the strength of concrete in a structure, or can supplement the data obtained from a limited number of core specimens tested. These methods are based on measuring a concrete property that bears some relationship to strength.

60 Non Destructive Tests The following Non destructive tests are commonly conducted on concrete structures: Ultrasonic Pulse Velocity Test as per IS : part Rebound Hammer Test as per IS : part

61 Non Destructive Tests Ultrasonic Pulse Velocity Test

62 Non Destructive Tests Ultrasonic Pulse Velocity Test Concrete Quality Grading Pulse Velocity (km/s) Quality Above 4.5 Excellent 3.5 to 4.5 Good 3.0 to 3.5 Medium Below 3.0 Doubtful

63 Non Destructive Tests Rebound Hammer Test POSITION OF REBOUND HAMMER - VERTICALLY DOWNWARDS POSITION OF REBOUND HAMMER - VERTICALLY UPWARDS

64 Inspection of Culverts Check whether the vents are choked with debris, vegetable matter, etc., and clear them. Check for cracks, distresses in body wall and correct them. Check whether the roadway is level on the culvert. If there is a depression suspect failure of pipes, slab, etc., and take action to rectify it. Observe during monsoons whether flow of water is proper or whether there is overtopping of the culvert/breach of road adjoining the culvert in which case collect hydraulic particulars, investigate and redesign the culvert for larger discharge.

65 Inspection of Bridges Check the backfill at abutments/approaches and if settlement is seen correct it to a level surface. Check abutment, and wing walls for distress. Check the slope projection works at abutment and replace / repack loose stones. The foundation is to be checked before monsoon for erosion of bed exposing footing, pile cap, pier cap to a larger extent or damage of concrete, abrasion of concrete. Aprons / Bed protection works to be ensured to avoid erosion of footings underneath piers and abutments.

66 Inspection of Bridges The abutment and piers are to be checked for cracks, if any, at points just below bearings. The deck slab has to be checked for spalling of concrete/delaminating by visual observation and by tapping with a hammer for dull hollow sound. Spalling is due to corrosion of rebars and subsequent pressure caused due to swelling of bars. The beams of the deck may be inspected for cracks and the cracks may be identified whether due to shear, bending or otherwise (shrinkage etc.,). The bearings may be inspected for proper functioning. Especially, Neoprene pads may be inspected for distresses by way of squeezing out of plates in the bearing, tearing of the polymer or puncture of beam into the bearing or bearing into the concrete.

67 Inspection of Bridges Vegetation present on the structure at drainage spouts are to be removed. All drainage spouts are to be cleaned regularly. The wearing coat of bridges are to be inspected and all the joints are to be raked, cleared and joint filler board with joint sealant to be applied. Clogging of joints does not allow free movement of the slabs and result in cracks. Expansion joints of all bridges are to be checked for proper functioning, cleaned and filled with bitumen sealants wherever applicable. The deck and beams near expansion joints and drainage spouts are to be checked for corrosion of bars due to water logging

68 Repairs and Rehabilitation Crack Repair First identify whether cracks are active or inactive. Active means the crack is live either expanding and contracting or extending in length. Inactive cracks are dead cracks which do not vary in size for quite a period of time. Inactive cracks may be filled with resins or cement grouts (nonshrink type). Filling may be done by simply pounding or pressure injection Cracks of width > 10 mm. may be filled with single size aggregate and then with non shrink cement grouts.

69 Repairs and Rehabilitation Crack Repair First identify whether cracks are active or inactive. Active means the crack is live either expanding and contracting or extending in length. Inactive cracks are dead cracks which do not vary in size for quite a period of time. Inactive cracks may be filled with resins or cement grouts (nonshrink type). Filling may be done by simply pounding or pressure injection Cracks of width > 10 mm. may be filled with single size aggregate and then with non shrink cement grouts.

70 Repairs and Rehabilitation Crack Repair Active Crack:- Cracks to be cleared properly by water jetting, compressed air, etc., Sealing with a flexible sealant or filling with a resin, providing a chase and filling it with flexible sealant.

71 Repairs and Rehabilitation Repair of Spalled concrete Corrosion is the process of rusting of steel due to action of saline water (chlorides). Structures near the coast (upto15 kms from sea or creek) and those on backwaters are prone to corrosion. The corrosion product (rust or iron oxide) is larger in volume and creates great pressure on the concrete and concrete ultimately cracks. This cover concrete separates, (called delaminating) and falls from the structure (called spalling of concrete).

72 Repair of Spalled Concrete All loose concrete should be chipped off and the spalled area should be cleaned by water jetting. Any damaged reinforcement to be replaced with new piece of bar by welding and placing in position. The reinforcement may be protected by applying zinc rich coating. Then a bonding agent may be applied, to ensure proper bond between old and new concrete. The epoxy mortar, either ready-to-use or prepared by adding admixtures to normal cement mortar may then be applied layer by layer up to a maximum thickness of 1 inch at a time.

73 Guniting Guniting is used for large scale repairing of structures (such as decks of bridges, columns, beams etc.,)which have damaged extensively. Mortar is applied over the area to be required by pressure from a gun. A guniting machine with compressor is required for the above work. It has to he done by skilled workmen as loss of mortar (rebound) will be high. For large repairs proper temporary supports, frameworks are to be provided.

74 Repair of Wearing Coat in Bridges When the wearing coat of bridges are extensively damaged, they may be replaced by a new wearing coat. The cracks on the wearing coat may be repaired by filling with non-shrink cement based grouts or by filling with sand mastic (a mix of bitumen and sand).