Construction Techniques and Materials
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Questions and Answers

What is the primary advantage of using Tremie pipes in construction?

  • To prevent concrete contamination (correct)
  • To reduce the cost of concrete
  • To increase the speed of pouring concrete
  • To enhance the concrete's strength

Which formwork can typically be removed first in a construction project?

  • Beam Formwork
  • Foundation Formwork
  • Slab Formwork
  • Wall and Column Formwork (correct)

What is the role of a superplasticizer in concrete?

  • To enhance the concrete's thermal resistance
  • To improve workability and make it pumpable (correct)
  • To make concrete set faster
  • To reduce the drying time of concrete

Which type of joint is most effective for improving water tightness in precast structures?

<p>Wet Joint (A)</p> Signup and view all the answers

What type of construction pump is suitable for dewatering operations?

<p>Submerged Pump (A)</p> Signup and view all the answers

What is the critical temperature at which a building's structure loses half its strength?

<p>600°C (A)</p> Signup and view all the answers

For a super tall building, which formwork system is preferred to speed up slab construction?

<p>Fly Form/Table Form (C)</p> Signup and view all the answers

Which construction equipment is regarded as being quieter during operation?

<p>Hydraulic Vibrator Machine (D)</p> Signup and view all the answers

What is one advantage of using precast concrete in terms of operational efficiency?

<p>Production is less impacted by weather conditions. (D)</p> Signup and view all the answers

Which factor contributes to the environmental benefits of precast concrete?

<p>Reduction in noise and air pollution. (A)</p> Signup and view all the answers

How does the use of prestressed concrete help in construction?

<p>It fully utilizes the strength of both concrete and steel rebar. (C)</p> Signup and view all the answers

Why is a waterproofing layer recommended in precast toilets?

<p>To lower the risk of water leakage. (A)</p> Signup and view all the answers

What is a result of reducing the number of separate operations in construction?

<p>Enhanced management under a single entity. (C)</p> Signup and view all the answers

What operational challenge is directly addressed by the factory setting of precast concrete?

<p>Delays caused by adverse weather conditions. (D)</p> Signup and view all the answers

What safety advantage does precast production offer over traditional construction methods?

<p>Minimized exposure of workers to hazardous weather. (B)</p> Signup and view all the answers

Which material is suitable for achieving water tightness in jointing applications?

<p>Silicone (C)</p> Signup and view all the answers

Which of the following describes a benefit of using a vibration table in concrete compaction?

<p>It improves the density and strength of the concrete. (B)</p> Signup and view all the answers

What is the primary advantage of the unitised system in curtain wall construction?

<p>It is the most effective and economical option (B)</p> Signup and view all the answers

Which option is a common test used to assess the performance of piles?

<p>Sonic logging test (B)</p> Signup and view all the answers

What is the recommended method for basement depths exceeding 20 meters?

<p>Diaphragm wall plus top-down method (B)</p> Signup and view all the answers

Which of the following is NOT considered a potential risk when constructing a basement?

<p>Soil Stability Monitoring (C)</p> Signup and view all the answers

Which of these factors is an advantage of using precast concrete components?

<p>Ensures consistent and higher quality due to controlled environments (C)</p> Signup and view all the answers

What makes the steel H pile a popular choice in Hong Kong for displacement piles?

<p>Higher load capacity and adaptability (C)</p> Signup and view all the answers

Which of the following describes the effect of the top-down construction method?

<p>It allows concurrent construction of the basement and superstructure (B)</p> Signup and view all the answers

What is the main purpose of the temporary steel casing during the installation of machine dug piles?

<p>To prevent soil collapse during drilling (B)</p> Signup and view all the answers

Which of the following is NOT an important consideration for prefabrication on the site plan?

<p>The preferred material colors for the prefab items (A)</p> Signup and view all the answers

What is the minimum depth of penetration for the bellout formed at the base of the pile?

<p>300 mm (A)</p> Signup and view all the answers

In what scenario would a reversed circulation drill (RCD) be most appropriate?

<p>When working with a rock stratum (D)</p> Signup and view all the answers

What method is employed to clean the borehole base before placing the reinforcement cage?

<p>Air lifting (A)</p> Signup and view all the answers

Which factor must be considered when determining the area for storing prefabricated materials?

<p>The anticipated construction speed (B)</p> Signup and view all the answers

What is the primary purpose of using spacers with the reinforcement cage during pile installation?

<p>To maintain adequate concrete cover (B)</p> Signup and view all the answers

What sequence follows the insertion of the temporary steel casing in pile installation?

<p>Boring the hole using a rotary auger (A)</p> Signup and view all the answers

What is the role of the beam and slab system in this construction method?

<p>To provide lateral support to the diaphragm wall. (A)</p> Signup and view all the answers

Which step directly follows the backfilling of bored holes with soil?

<p>Exposing the upper portion of stanchions. (D)</p> Signup and view all the answers

What is the purpose of the temporary openings made in the slabs?

<p>To provide access for excavating machinery. (C)</p> Signup and view all the answers

At what stage of the construction process is soil removal facilitated by ramps?

<p>While excavating for the first level of the basement. (A)</p> Signup and view all the answers

What is the first step in the construction procedures for the top-down method?

<p>Constructing diaphragm walls. (B)</p> Signup and view all the answers

What is the primary purpose of the tremie pipe during the concreting process?

<p>To allow concrete to flow without contamination (D)</p> Signup and view all the answers

Which operation is conducted after the concrete acquires adequate strength in piling?

<p>Removing the excess contaminated concrete (A)</p> Signup and view all the answers

What role does bentonite slurry play during the excavation of diaphragm walls?

<p>It provides hydrostatic pressure to support the soil (A)</p> Signup and view all the answers

How is the panel width of typically excavated trenches determined for stable soil?

<p>Between 4 m to 6 m (C)</p> Signup and view all the answers

What is required at the end of each panel during diaphragm wall construction?

<p>Vertical tubes to form a semicircular recess (B)</p> Signup and view all the answers

When is the tremie pipe tip required to be placed during the concreting process?

<p>Around 2 to 3 metres below the surface (A)</p> Signup and view all the answers

What happens to the bentonite slurry once the concrete has hardened?

<p>It is pumped to a de-sanding plant for reuse (D)</p> Signup and view all the answers

What is the function of the box-outs attached to the reinforcement cage in diaphragm wall constructions?

<p>To form junctions of floors and walls (A)</p> Signup and view all the answers

Flashcards

Pile Types

Steel-H Pile and Barrettes are two common types of piles used in construction. Steel-H Piles are driven into the ground using a hammer, while Barrettes are drilled into the ground and filled with concrete.

Tremie Pipe Technique

Tremie pipes are used to pour concrete underwater, preventing contamination by water and ensuring the concrete stays fresh.

Formwork Removal Order

Formwork for walls and columns can be removed earlier than formwork for beams and slabs because they are self-supporting, meaning they can stand on their own.

Dewatering Pumps

Submerged pumps and suction pumps are commonly used in dewatering, which is the process of removing water from an area.

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Self-compacting Concrete

Self-compacting concrete is a type of concrete that is highly flowable and can easily fill complex shapes without requiring vibration.

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Superplasticizer

Superplasticizer is a chemical admixture added to concrete to improve its workability and flow, making it easier to pump and fill complex shapes.

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Fly Forms/Table Forms

Fly forms or table forms are large, reusable formwork systems that can be moved to a new location after the concrete has cured, speeding up the construction process.

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Precast Joint Types

Dry joints rely on sealant and gaskets for water tightness, while wet joints create a monolithic structure by filling gaps with concrete, providing better water tightness.

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Precast Concrete Advantages

Precast concrete elements can be produced in a controlled environment, often in a factory, with benefits such as increased quality and accuracy, faster construction, and reduced costs.

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Faster Construction

One major benefit of precast concrete is the ability to produce and assemble elements off-site, leading to faster construction schedules.

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Predrilling

A process that involves preparing a hole in the ground before the actual pile construction. It's done to identify the founding rock level and ensure the pile's stability.

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Environmentally Friendly

Precast concrete production relies on controlled environments, minimizing waste and imperfections, leading to a more sustainable and efficient building process.

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Steel Casing

A temporary metal tube inserted into the ground to guide the drilling process and prevent soil collapse.

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Improved Quality & Accuracy

Precast concrete allows for the construction of elements in a factory setting, where skilled workers and specialized equipment can achieve precise and consistent results.

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Reduced Formwork Costs

Precast concrete promotes efficient and cost-effective construction by reducing the need for formwork on site, saving both time and resources.

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Rotary Auger

A method used to excavate soil during pile construction. It removes soil by rotating a special bit and lifting it to the surface.

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Reversed Circulation Drill (RCD)

A specialized drill used to create a widened base for the pile, increasing its bearing area on the bedrock.

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Safer Construction

Precast concrete construction involves less work at height, reduces the need for scaffolding, and minimizes potential safety hazards.

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Complex Designs

Precast concrete elements can be produced in highly specialized factories, enabling the incorporation of complex designs and intricate details that may be difficult to achieve on-site.

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Bellout

A widened section at the bottom of the pile, designed to distribute pressure and increase its stability.

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Air Lifting

A technique used to clean debris from the bottom of the pile using air pressure.

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Weather Independence

The controlled environment of precast production helps to reduce delays and disruptions caused by unpredictable weather conditions, ensuring a consistent workflow.

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Steel Reinforcement Cage

A metal cage containing steel bars that provides reinforcement to the concrete pile.

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Tremie Pipes

A method of pouring concrete into the pile using a long pipe to prevent separation of the materials.

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Watertight Joints: Best Material

Silicone is the best material for water tightness joints. It effectively seals gaps and prevents water leaks.

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Most Popular Curtain Wall System

Unitised Curtain Walls are the most popular in Hong Kong due to their efficiency and cost-effectiveness. Modular panels are prefabricated off-site and then assembled on-site.

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Popular Displacement Pile in HK

Steel H Piles are the most common type of displacement pile used in Hong Kong. They are driven into the ground, displacing soil to create a foundation.

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Top-Down Construction Method

The top-down method is a construction technique where the upper levels of a building are built first, working downwards. This allows simultaneous work on basement and superstructure, saving time.

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Deep Basement Construction Method

Diaphragm walls and the top-down method are ideal for deep basements (more than 20 meters). They provide strong support and allow for excavation and construction in stages.

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Advantages of Pre-Cast Concrete

Pre-cast concrete offers several advantages, including semi-skilled labor requirements, consistent high quality, and reliable quality control due to factory production.

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Basement Construction Risks

Soil collapse, worker safety, disruption of underground utilities, neighboring building foundation settlement, and ground water/flooding are potential risks associated with building basements.

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Common Pile Tests

Common pile tests include dynamic load, static load, sonic load, sonic logging, standard penetration, core drilling, vibration, lateral load, and tension tests. These tests ensure the piles are strong enough to support the structure.

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Diaphragm Wall

A continuous wall constructed using a trenching method, often used to enclose basements and underground structures.

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Top-Down Construction

A method of building a structure where excavation and superstructure construction occur simultaneously, with the basement floors constructed progressively.

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Diaphragm Wall Panels

Large, pre-cast concrete panels used to form the walls of a basement in a top-down construction method.

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Beam and Slab System

A method of supporting the diaphragm wall during the excavation process, using steel beams and slabs to provide lateral support.

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Temporary Openings in Slabs

Temporary openings made in the floors of a top-down construction project to allow access for excavation equipment and the removal of soil.

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Bentonite Slurry

A specialized slurry made from bentonite clay used to support the sides of trenches during diaphragm wall construction, preventing soil collapse and groundwater infiltration.

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Alternate Panel Excavation

Excavating a trench in sections, alternating between panels to maintain stability and ensure the bentonite slurry can circulate effectively.

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Stop-End Tubes

Vertical tubes placed at the end of a panel to create a recess, allowing for a watertight joint when connecting to the next panel.

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Reinforcement Cage

A cage made of reinforcing steel, placed in the trench to provide strength to the diaphragm wall.

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Concrete Placement in Diaphragm Wall

Concrete is poured into the trench using tremie pipes, displacing the bentonite slurry, which is then cleaned and reused.

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Box-Outs

Small openings built into the reinforcement cage to create connections between the diaphragm wall and the floors or walls of the building.

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Study Notes

Pile Types

  • Two main pile types exist: displacement piles (Steel-H Piles) and replacement piles (Barrettes)

Tremie Pipe Advantages

  • Prevents concrete contamination

Formwork Removal Priority

  • Walls and columns can be removed first due to their structural independence from beams and slabs.

Dewatering Pumps

  • Submerged pumps and suction pumps are used for dewatering

Self-Compacting Concrete

  • Highly workable and pumpable

Concrete Additives

  • Superplasticizer increases workability and flowability of concrete

Slab Formwork

  • Fly form or table form is suitable for speeding up tall building slab construction

Continuous Beam Steel

  • Top steel (cantilever) and bottom steel (span) are important reinforcing components

Simply Supported Beam Steel

  • Bottom steel is the main reinforcing component for a single-span beam.

Joint Problems in Precast Structures

  • Wet joint (Monolithic Joint) using in-situ concrete topping is superior to a dry joint for preventing water leakage, since it fills gaps and doesn't rely on unreliable gaskets or sealants.

Construction Equipment Noise

  • Hydraulic vibrator machines are known for their quiet operation contrasted with other construction equipment.

Design Considerations for Fire-Damaged Structures

  • Temperature of 600°C for steel and concrete structural failure

Moving Wall Tiles

  • Material hoist machinery is specifically designed to move items (but not personnel).

Concrete Joint Material

  • Epoxy is used for concrete spalling repair whereas silicone provides lasting water tightness.

Formwork Cover Material

  • Plastic sheets are commonly used to cover formwork spaces.

Curtain Wall Systems

  • The unised system is the most prevalent and efficient curtain wall system.
  • Steel H pile is the most popular displacement pile in Hong Kong (HK).

Bored Pile Installation

  • The process of bored pile installation involves a temporary steel casing, a hydraulic oscillator, chisel, reinforced cage, and tremie pipe.

Common Pile Tests

  • Pile tests may include dynamic load tests, static load tests, sonic load tests, sonic logging tests, standard penetration tests, core drilling, vibration tests, lateral load tests, and tension tests.

Top-Down Construction Advantages

  • Reduced construction time, simultaneous basement & superstructure construction, and enhanced weather protection.

Deep Basement Construction Methods

  • Diaphragm wall plus top-down method for depths exceeding 20 meters; Steel sheet piling and cofferdams (bottom-up method) for shallower basements (10-20 meter).

Basement Risk Factors

  • Soil collapse, worker safety, disruption of utilities, differential settlement affecting neighboring structures/MTR, and ground water/flooding

Precast Concrete Advantages

  • Skilled labor demand reduced in favor of semi-skilled labor on site for precast elements installation, lower labor costs, reliable quality control (factory QC), consistent quality (indoor shielded from weather and rain environments), use of robots and machinery, vibration tables for improved compaction, controlled curing chambers for temperature, humidity, and pressure control, time efficient process in the construction workflow.

Precast Construction Site Considerations

  • Ensuring tower crane capacity in relation to working radius to safely handle prefabricated materials.
  • Choosing appropriate storage area for prefabricated materials based on construction rate and material delivery timing.
  • Planning internal access pathways for prefabricated material delivery vehicles.

Machine Dug Piles Installation

  • Precise site location determination, initial hole boring using rotary auger, positioning and protection using temporary steel casing, continuous boring until required depth, forming a bell-out, cleaning the borehole, embedding reinforcement cage, pouring concrete with tremie pipes ensuring no spillage, removing casing, excavating to the concrete cut-off level, removing contaminated concrete, and finally casting pile cap.

Diaphragm Wall Installation

  • Creating guide walls for trenching machinery, using hydrofraise or hydro-mill cutters, utilizing bentonite slurry support, recirculating bentonite, placing stop-ends, building the semicircular wall recess to ensure watertight connections, and removing excess soil

Top-Down Construction Method

  • Forming bored holes, establishing steel stanchions, creating a ground floor slab, and subsequently excavating the basement and constructing the structure iteratively, progressively working upwards.

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Description

This quiz covers essential construction techniques and materials used in modern building projects. Topics include pile types, self-compacting concrete, formwork removal, and reinforcement in beams. Test your knowledge on the fundamental concepts that enhance construction efficiency and safety.

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