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Copy of Research Presentation
Transcript of Copy of Research Presentation
Cadatal, Calvin D.
Santos, Xriz CAST-IN-PLACE CONCRETE CAST-IN-PLACE CONCRETE Cast-in-place concrete is deposited in the place where it is required to harden as part of the structure. These are produced by setting forms in place, placing reinforcing materials in the forms and pouring the concrete over the reinforcing material, filling the form. TRANSPORTING, HANDLING, AND PLACING CONCRETE CAST-IN-PLACE CONCRETE Cast-in-place concrete structural members are usually heavier than steel, wood or precast concrete members. PREPARING CAST-IN-PLACE CONCRETE PREPARING CAST-IN-PLACE CONCRETE PREPARING CONCRETE Batching is the process of measuring concrete mix ingredients either by volume or by mass and introducing them into the mixture. Step I: BATCHING PREPARING CONCRETE Admixtures Percentage of Accuracy for Measurement for: Cement Aggregates Water PREPARING CONCRETE The mixing operation consists of rotating or stirring of all ingredients. This is to coat the surface the all aggregate particles with cement paste, and to bind all the ingredients of the concrete into a uniform mass. Step II: MIXING PREPARING CONCRETE STATIONARY MIXING PREPARING CONCRETE READY-MIX CONCRETE READY-MIX CONCRETE ADVANTAGES Better quality concrete is produced The time required is greatly reduced Wastage of basic materials is avoided Reduce cost READY-MIX CONCRETE DISADVANTAGES Concrete's limited time span between mixing and going-off Critical travel time from the plant to the site. PREPARING CONCRETE Concrete is often remixed at the job site to ensure proper slump is achieved. If this is the case, at least half the mixing time should occur during the remixing. Remixed concrete is likely to set more rapidly than concrete mixed only once. Step III: REMIXING TRANSPORTING, HANDLING, AND PLACING CONCRETE TRANSPORTING CONCRETE The main objective in transporting concrete is to ensure that the water-cement ratio, slump or consistency, air content, and homogeneity are not modified from their intended states. TRANSPORTING, HANDLING, AND PLACING CONCRETE TRANSPORTING CONCRETE Must meet the requirements of BS 5328 Part 3 or the specification for the procedures to be used in producing and transporting concrete.
The concrete shall be transported to the site in an approved type of truck mixer or agitator truck. TRANSPORTING, HANDLING, AND PLACING CONCRETE TRANSPORTING CONCRETE TRANSPORTING, HANDLING, AND PLACING CONCRETE
Segregation may occur HANDLING CONCRETE Delays in concreting work may reduce productivity. Early stiffening and drying out may create problem in placing and finishing. BELT CONVEYORS TRANSPORTATION AND HANDLING EQUIPMENTS TRANSPORTATION AND HANDLING EQUIPMENTS BUCKETS TRANSPORTATION AND HANDLING EQUIPMENTS CHUTE ON TRUCK MIXERS PUMPED CONCRETE TRANSPORTING, HANDLING, AND PLACING CONCRETE Grout shall be pumped through the concrete pump to provide initial lubrication. The initial discharge of any pumped concrete shall not be incorporated in the permanent works. The Contractor shall ensure that the shock is not transferred from the pipeline to the formwork and previously laid concrete. The slope of the chute or the pressure of the pump shall allow the concrete to flow without the use of any water additional Trailer-Mounted Boom Concrete Pump PUMPING EQUIPMENTS Trailer-Mounted Concrete Pump PUMPING EQUIPMENTS PLACING OF CONCRETE TRANSPORTING, HANDLING, AND PLACING CONCRETE In placing concrete, care being taken to avoid separation of the constituent materials. Concrete shall be carefully placed in horizontal layers which shall be kept at an even height throughout the work. Concrete is placed after the base for on-grade pours ready or the forms for walls, columns, and beams are erected and reinforcing is in place. No concrete shall be placed until the Engineer has inspected and approved in writing the surfaces upon which the concrete is to be placed. Never place concrete on frozen ground or onto ice or snow. DURING COLD WEATHER… The best way to protect concrete from the cold is to cover it with blankets after it's been finished Concrete placed in cold weather gains strength slowly. Fresh concrete must be protected from freezing. When the freshly mixed concrete is in danger due to the rate of moisture loss and cement hydration, hot-weather concreting methods is important. DURING HOT WEATHER… Ready mix producers in hot climates use chilled water or ice to lower the concrete temperature. Using cool water is a way to get cool concrete. It is the process of consolidating, leveling, and creating concrete surface of a desired texture, smoothness, and durability. It can be decorative or functional. Finishing makes concrete attractive and serviceable. FINISHING CONCRETE Exterior slabs must be sloped to carry away water. It must provide a texture that will not be slippery when wet. The final texture, hardness, and the joint pattern on slabs, floors, and driveways depend on the concrete’s end use. FINISHING Flatten or level the concrete using a darby, or highway straight edge to smoothen the surface, and this process should be completed before water appears on the surface. STEPS IN FINISHING CONCRETE FINISHING OF CONCRETE Finishing processes should start after the concrete has stopped bleeding. STEPS IN FINISHING CONCRETE Round over the outside corners with an edging tool. STEPS IN FINISHING CONCRETE Joint the concrete when required. A jointing or a grooving tool is used to section concrete to manage cracking. STEPS IN FINISHING CONCRETE Smooth the surface with a steel trowel, if required, after it is partially hardened. STEPS IN FINISHING CONCRETE Drag a broom across the concrete after floating it to create a non-slippy surface. Adjust the downward pressure to create the desired amount of texture. STEPS IN FINISHING CONCRETE CURING CONCRETE CURING CURING CONCRETE Concrete should be protected from losing moisture until final finishing. After final finishing, the concrete surface must be kept continuously wet to prevent evaporation for a period of at least several days after finishing. Temperature is an important factor in proper curing. Generally, concrete temperature should be maintained above 50 F for an adequate rate of strength development. Also, uniform temperature should be maintained through the concrete section while it is gaining strength to avoid thermal cracking. Curing can be defined as a procedure for insuring the hydration of the Portland cement in newly-placed concrete. Effects of Curing on Concrete: CURING CONCRETE Increase concrete strength Increase concrete abrasion resistance Lessen the chance of concrete scaling Lessen the chance of surface dusting Lessen the chance of concrete cracking Effects of Curing on Concrete: CURING CONCRETE Ponding of water on a slab is an excellent method of curing. The water should not be more than 20 F cooler than the concrete. WAYS IN CURING CONCRETE Subject the concrete to higher temperature, in order to gain strength faster, and maintain the required wetness. This can be achieved by exposing the concrete to steam curing. WAYS IN CURING CONCRETE Concrete could be covered with membrane which will effectively seal off the evaporation of water from concrete. WAYS IN CURING CONCRETE Formwork is the structure of boards that make up a form for pouring concrete in construction. FORMWORKS TYPES OF
FORMWORK This type of formwork is built on site out of timber and plywood or moisture-resistant particle board. 1.Traditional Timber Formwork CAST-IN-PLACE ON-GRADE
economical and durable structure
suitable for a variety of floors and foundations
usually reinforced, and various types of joints are used CAST-IN-PLACE ON-GRADE CONCRETE SLABS ON-GRADE CONCRETE SLAB Types of Slabs Advantages: They rely entirely upon the earth for support against tension forces Aluminum and Steel Formwork Advantage: STEEL REINFORCING BARS CONCRETE REINFORCING MATERIALS Various materials are used to reinforce concrete. Round steel bars with deformations, also known as deformed bars, are the most common type of reinforcement. Others include steel welded wire and fiber reinforcements. UNREINFORCED SLABS LIGHTLY REINFORCED SLABS They are reinforced with welded wire fabric or fiber reinforcements Advantages of Welded Wire Reinforcement: WELDED WIRE REINFORCEMENT Welded Wire Reinforcement (WWR) is an assembly of steel reinforcing wires made from rods that is cold-drawn or cold-rolled, or both. FIBER REINFORCEMENT Fiber-reinforced normal concrete is mostly used for on-ground floors and pavements. Concrete reinforced with fibers are less expensive than hand-tied rebar, and it has the characteristic of increasing the tensile strength. Shape, dimension and length of fiber are important. STRUCTURALLY REINFORCED SLABS • Fiber-reinforced polymer (FRP) Different Kinds of Fiber Reinforcements: They contain steel reinforcing bars and often welded wire fabric and/or fiber reinforcing •Glass Fiber Reinforced Concrete (GFRC) •Steel CAST-IN-PLACE ON-GRADE CONCRETE SLABS JOINTS necessary when building concrete slabs on grade to help control cracking
reduce the size of the pour
separate the slab from surfaces where it should not bond Types of Joints Types of Joints Contraction joints Control joints They are placed to control random cracking They are reinforced with welded wire fabric or fiber reinforcements Construction joints They help prevent cracking because each joint serves as a control joint Isolation joints They are used to relieve flexural stresses due to vertical movement of slab-on-grade applications. Expansion joints They are used primarily to relieve stress due to confinement of a slab. CAST-IN-PLACE CONCRETE WALLS LIFT-SLAB CONSTRUCTION Lift slab construction has become a basic method of economical concrete construction, especially for office buildings, apartments, parking garages, hotels and other structures characterized by repetitive framing from floor to floor. They are made with ready-mix concrete
They may rest on a continuous concrete footing and below grade or extended above grade CAST-IN-PLACE BEAMS They rest on end supports and the stirrups are held in place
The beam ties the structure together from column to column CAST-IN-PLACE COLUMNS They are typically round, square and rectangular
They are reinforced with vertical bars
Tied columns have vertical bars tied together with small-diameter smooth steel bars placed horizontally and wired to the vertical bars
Spiral columns; also restrain the concrete inside them The most common formwork materials for casting concrete in place are steel, aluminum, and wood. It is also used to shape reinforced concrete while it is setting. FORMWORKS •It has light weight and very flexible. •It is easy to produce and damaged parts can be replaced with new one. •It is easy to disassemble. Disadvantages: •It can’t be used for a long time, and can only be re-used for 5 or 6 times. •If the timber is dry, it will absorb moisture from wet concrete which could weaken the resultant concrete member. •Timber has high moisture content so wet concrete will shrink & cup leading to open joints & leakage of grout. This type of formwork is favored over wood formwork because of the greater speed of stripping the formwork. •It possesses greater strength and durability. •It can be used for a long time and easy to assemble. •It is safer than wood formwork. Disadvantages •It is more expensive Steel Reinforcing bars are also called as rebars which may be hot rolled steel rods that may be plain or deformed. The smooth type is used for special applications while the deformed type has surface ridges, which gives better bonding to concrete. CAST-IN-PLACE COLUMN •The welded grid pattern reduces labor by eliminating the need to tie individual rebar together. •Wires are precisely machine spaced and welded when sheets are manufactured so field inspections are quick and easy. •WWR is custom manufactured to your design specifications, providing the exact steel area required. CAST-IN-PLACE ON-GRADE CONCRETE FRAMING SYSTEMS CAST-IN-PLACE CONCRETE FRAMING SYSTEMS A typical cast-in-place concrete framing system utilizes cast-in-place columns, concrete slabs, and cast-in-place joists, beams and girders.
Several types of reinforced concrete framing system are used with cast-in-place concrete construction. CAST-IN-PLACE CONCRETE FRAMING SYSTEMS Two commonly used reinforced concrete floor and roof systems:
This is a reinforced concrete slab supported directly by concrete columns without the use of beams.
This is much like the flat slab but it is supported by columns that do not enlarge when the columns and slab meet. GENERAL CONSTRUCTION PROCEDURE The walls and columns are poured when the foundation is in place, and if cured, the forms for the slab are built.
The beams are formed and poured with the floor, forming a monolithic unit.
The forms are supported with temporary joists and beams of wood or metal.
Wood or plastic inserts are placed in the form to produce a beveled or rounded corner. GENERAL CONSTRUCTIONPROCEDURE The interior surfaces of the forms are coated with a form-release compound.
As mentioned earlier, usually beams, girders, joists, and floor or roof slab are poured monolithically.
After the structure has reached its sufficient strength, the formwork for the next floor is constructed. Types of Frames Rigid Frames
-Rigid frame structures are built at the site which may or may not be poured monolithically.
-Rigid frame structures provide more stability.
- Rigid frame structures resist rotations more effectively. Advantage:
Rigid frame structures feature positive and negative bending moments throughout the structure due to interaction of walls, beams and slabs. Braced Frames
- Braced frame structures resist lateral forces by the bracing action of diagonal members.
- Braced frame structures are used to resist sideway forces.
- Buildings are braced by inserting diagonal structural members into the rectangular areas of a structural frame.
Lift-slab system is a hybrid structural scheme comprised of cast on site post-tensioned concrete slabs supported on steel columns.
The post-tensioned slabs are cast on top of each other on the ground or podium floor with plastic sheets or an oil-based separator dividing them.
The lowest slab is cast first, with subsequent slabs poured directly on top of preceding one.
Steel shear heads are embedded within the slab around the columns to form an opening to facilitate the lifting process as well as lifting attachment point and a welded connection point to the steel columns. WHAT IS A LIFT-SLAB? HISTORY
The concept of lift-slab construction originates in Columbia, South America and in the United States as the Youtz-Slick lift slab method in the 1950's.
It was generally used for buildings up to 8-storey high.
Canadian Lift Slab construction started in Winnepeg in the early 1960's with Lount Construction Corporation founded by Graham Lount. LIFT-SLAB CONSTRUCTION ADVANTAGES AND DISADVANTAGES OF
LIFT-SLAB CONCRETE ADVANTAGES TILT-UP CONSTRUCTION This involves site-casting concrete walls of a building on its floor slab or on a separate casting bed and then tilting and lifting them into position by crane.
After the wall has gained sufficient strength, it is lifted into position by a crane and secured to the footing.
Panels generally range in thickness from about 140 to 190 mm and may contain openings for windows and doors.
Pick-up hangers must be carefully located in the panel where the crane can attach to and lift the wall. History of Tilt-Up Construction Tilt-up was born in the early 1900's, when architect contractor Robert Aiken built several buildings in the Midwest. WHAT IS TILT-UP CONSTRUCTION? Tilt up construction involves site-casting the concrete walls of a building on it's floor slab or on a separate casting bed and then tilting and lifting them into position by crane.
The result is rapid construction arising from a well-planned process. BENEFITS OF TILT-UP CONCRETE WALL CONSTRUCTION FLEXIBLE FINISHES
HEALTH AND SAFETY
MAINTENANCE AND DURABILITY