Aggregates (Part - 02) PDF

## Segregation & Bleeding of concrete - When workability is very high - constituents of concrete tend to segregate - Very high w/c, improper grading of aggregates, Very high Specific Gravity of aggregates - More vibration for highly workable concretes leads to segregation - If the concrete is dropp...

## Segregation & Bleeding of concrete - When workability is very high - constituents of concrete tend to segregate - Very high w/c, improper grading of aggregates, Very high Specific Gravity of aggregates - More vibration for highly workable concretes leads to segregation - If the concrete is dropped from certain height - If the concreting is done in hot sun - segregation of water - bleeding - When the concrete segregates / bleeds and if the formwork is not leak proof - Honey combed concrete ## Transportation of Concrete - Manual transport - Rural areas - little concrete - When the concrete is dropped from height - segregation - Cranes - For two or more floors - Trolleys and place the concrete - Transit mixer - For more distances - Retarders to prevent setting of concrete during transit - Conveyor belts - Industries/ casting yards - For more heights - Concrete pumps - Self compacted concrete ## Compaction of concrete - Hand Compaction - Poking or Rodding - Crude method - Suitable for high workable concretes - Rural areas - Plat form Vibrators - Suitable in prefabrication yards & laboratory - Pan Vibrators - suitable for flat surfaces with shallow depths - Slabs, Pavements - Needle Vibrators - suitable for compaction at depths - beams, columns - Diameter of needle depends on the spacing between the rebars and thickness of the member - Shuttering Vibrators - Suitable for very low workable concrete - Effective - suitable for high strength concrete - Good finishing - Spinning - Centrifugal forces - Suitable for Hume pipes A graph showing the relationship between compressive strength and water/cement ratio. The graph shows vibration, hand compaction and the change in compressive strength for insufficiently compacted concrete and fully compacted concrete. ## Images of Compaction of concrete methods Two images show: Left Image: A man using a hand compaction rod to compact concrete in a formwork. Right Image: A man using a needle vibrator to compact concrete in a formwork. ## Images of other Compaction of concrete methods Two images show: Left Image: A man pushing a pan vibrator to compact concrete. Right Image: A table vibrator with 4 blue boxes on it. ## Images of additional Compaction of concrete methods Two images show: Left Image: A man placing a shuttering vibrator in formwork to compact concrete. Right Image: A man using a spinning machine to compact concrete. ## Curing of Concrete - Extremely important - Process to promote Hydration of cement – gain of strength and develop immunity (Improve Durability) - Evaporation takes place either due to temperature or wind - Never allow the concrete to dry - Immersion curing – Laboratory specimens, precast industries - Spraying water – vertical surfaces, covering with moist jute bags - more labour and more water is required. - Spraying Hydrophobic / Hydrophillic compounds and sealing the surface - Takes more time – Normally 28 days is required for full maturity. ## Images of Curing of concrete methods Three images show: Left Image: A man spraying concrete with a hose, along with a close-up of concrete being cured. Center Image: A man laying down jute sacks over freshly poured concrete. Right Image: A close-up of jute sacks laid over concrete. ## Images of additional Curing of concrete methods Two images show: Left Image: A large concrete slab covered in standing water Right Image: Large blocks of concrete submerged in a blue barrel of water. ## Images of additional Curing of concrete methods Three images show: Left Image: A man using a hose to spray a slab of concrete. Center Image: A large concrete slab, covered with a white plastic sheet. Right Image: A man laying down a white plastic sheet over a large slab of concrete. ## Advance Curing methods – Normal pressure steam curing - Normal pressure steam curing - Possible in pre-casting industries – Normally difficult on the site - But not impossible - Expensive - Rapid gain of strength - Better for PPC concrete - Retrogression of strength occurs. A diagram showing a graph of temperature within a steam enclosure over time. The graph shows an initial concrete temperature of 21 degrees Celcius, followed by a temperature increase to 60 degrees Celcius. After the initial temperature increase, the temperature is reduced until it is within 10 degrees Celcius of the outside air. ## High Pressure Steam Curing - Requires Autoclave for developing High Pressure - Precast industries only - No Retrogression of strength is observed - Steam curing - rapid gain of strength - formwork can be released - normal curing by spraying or immersion should continue for the remaining period. An image shows an autoclave, used for high pressure steam curing of concrete. ## High Pressure Steam Curing - Requires Autoclave for developing High Pressure - Precast industries only - No Retrogression of strength is observed - Steam curing - rapid gain of strength - formwork can be released - normal curing by spraying or immersion should continue for the remaining period. - IS 9013-1978 - Accelerated curing of concrete An image shows an autoclave, used for high pressure steam curing of concrete. ## Internal Curing – High Strength Concrete High Strength Concrete - W/C ratio is low - In complete Hydration - Good Gradation of Aggregates - Impermeable - Requires reservoirs of water inside the concrete as and when required A diagram showing 4 squares. The top left square shows normal aggregate with external curing. The top right square shows a water filled intrusion. The bottom left square shows normal aggregate with internal curing. The bottom right square shows a cured zone. Saturated sponge like aggregates as a partial replacement of normal aggregates - Light Weight Aggregates - Recycled aggregates - Super absorbent polymers (SAP) **STRENGTH IS COMPROMISED** Use of Hydrophillic or Hydrophobic materials in Concrete Plyethylene Glycol (PEG), Paraffin Wax etc., ## Other Methods of Curing - Electrical Method - Using Alternative Current - Temperature increases due to resistivity - Used in Cold environments - expensive - Infrared Method - Used in Cold environments - Expensive - early rate of gain of strength - ## Self Compacting Concrete - Will Compact due its own weight. - No external compaction (vibration) is required - No noise due to vibration - Minimum labours are required - Rapid work progress - Suitable where the reinforcement is very congested. - Excellent surface finish - More dense internal structure - enhanced durability - More fines are required ## Self Compacting Concrete - EFNARC: European Federation of National Associations Representing for Concrete. - EFNARC GUIDELINES FOR SELF COMPACTING CONCRETE - 2005 - Flowability Test - Passing ability Test - Segregation Resistance Test - Viscosity test A diagram showing the different components of Conventional Concrete and Self-Compacting Concrete. Such concrete will be suitable for 3D printing of strutures ## GUIDELINES FOR SCC Acceptance values as per EF-NARC Guidelines | No. | Methods | Property | Minimum | Maximum | |---|---|---|---|---| | 1 | Slump flow | Filling ability | 650 mm | 800 mm | | 2 | T50 cm slump flow | Filling ability | 2 s | 5 s | | 3 | V-funnel | Filling ability | 6 s | 12 s | | 4 | L-box (ratio) | Passing ability | 0.8 | 1.0 | | 5 | J-ring | Passing ability | 0 mm | 10 mm | ## FLOWABILITY-SLUMP FLOW TEST Two images show: Left Image: A slump cone sitting on a piece of plywood, being filled with concrete. Right Image: A close-up of the spreading concrete, as measured by the slump flow method. The image shows measurements of D1 (Diameter 1) and D2 (Diameter 2). ## GUIDELINES FOR SCC Acceptance values as per EF-NARC Guidelines | No. | Methods | Property | Minimum | Maximum | |---|---|---|---|---| | 1 | Slump flow | Filling ability | 650 mm | 800 mm | | 2 | T50 cm slump flow | Filling ability | 2 s | 5 s | | 3 | V-funnel | Filling ability | 6 s | 12 s | | 4 | L-box (ratio) | Passing ability | 0.8 | 1.0 | | 5 | J-ring | Passing ability | 0 mm | 10 mm | **ALL THE TESTS ARE TO BE SATISFIED SIMULTANEOUSLY THEN ONLY IT CAN BE CALLED AS SELF COMPACTED CONCRETE** ## PASSING ABILITY TEST-L BOX TEST A diagram showing the L-box test for concrete flow. ## PASSING ABILITY TEST - U BOX TEST A diagram showing the U-box test for concrete flow. ## SEGGREGATION RESISTANCE - J RING TEST A diagram showing a top view and side view of the J-Ring test. The side view shows the concrete sample and indicates the maximum height (H) of the concrete between the J-Ring and the base plate. The side view also shows the various height measurements to be taken: Aht, Aho, Ahy, Ahx, and Ahx2. The top view shows the J-ring, the base plate and a marking of 500 mm. The top view also shows the placement of 16 plain steel rods.