Alternative Construction Methods Flashcards
What is Modular/Hybrid-Concrete construction?
• fasterdelivery
• improvedquality
• improvedsafety
• BUTit’snotbeingusedinSouthAfrica!?Whynot?
• InsupportoftheNationalDevelopmentPlan
• HCChasthepotentialtoassistinimproved projectdelivery
• CurrentstatusinSouthAfrica:
–Limitedapplicationofprefabrication;
–Lackofknowledgeamongstdesignersand contractors;
–Wrongperceptions(labour,quality,visually…..)
–Procurement
Advantages if HCC for the Building Industry?
• High-Quality Product for less cost
• Minimise Time of Completion
• High-Quality Finished Surfaces
• Optimise Use of Resources (Raw Materials)
• Transfer of Skills to Unskilled Labour Force (Major Task in SA)
-> PROVIDE MORE SUSTAINABLE SOLUTIONS
what are motivations for using precast concrete?
- Safety
- Economy
- Construction Time Savings
In-Situ Concrete vs Precast Concrete:
In-Situ:
- Manufacture in an uncontrolled environment
- Lengthy Construction Procedure
- Multistage casting procedure
- Quality often lacking (rushed jobs, minimum supervision)
- Inefficient reuse of materials (scaffolding, shuttering)
- Unskilled Labour Force
Pre-cast:
- Manufacture in a controlled environment (Quality Control)
- Rapid construction (simultaneous site work and precast yard)
- Single-stage casting procedure
- High-quality product (high level of supervision)
- Minimum requirement of temporary supporting structures
- Skilled Labour Force
In-Situ Concrete vs Precast Concrete Social and Environmental Benefits?
- Prefabrication carried out away from residential areas and city centres at more suitable, accessible sites (less noise/air pollution)
- More economical use of concrete implies less production and consumption of cement
- Effective transfer of skills among workforce resulting in enhanced, more fulfilled workforce (teamwork)
What are some design considerations for precasting?
- Speed of Construction
- Aesthetics
- Connections
Name three pre casting floors used in South Africa.
- Hollow-Core
- Rib-and-Block
- Permanent Shuttering
What are some site considerations for precast floors?
- Delivery and Installation on Site
- consider all load possibilities,
during installation as well
- consider all load possibilities,
- Safety and Order on Site
Quality management of In-Situ vs Precast?
In-Situ – Production of Readymix Concrete Mixture
Precast – Series of closely monitored processes (batching, mould preparation, casting, stripping) to ensure quality
Precast manufacturers rely on in-house mix designs developed according to specified codes and standards over years of experience, resulting in an enhanced quality of the final product
Production Cycle of Precast?
Batching
Automated processes, selection of constituent materials and proportions according to the intended use of the final product
Casting
- High degree of automation in hollow-core casting procedure (high-strength, low workability, prestressing)
- Lesser degree of automation in casting procedure of Rib-and-Block and Permanent Shuttering
Quality Control
- Regular testing of concrete samples (cube crushing)
- Quality of raw materials (ISO & SABS certified)
- Long-line extrusion process useful when inspecting defects in manufacture. Areas of imperfection, due to cracks or variations in the mixture, can be identified and removed by cutting
- High-quality product from extrusion process, associated with a high degree of automation.
- Low degree of automation – experienced skilled workers, high-quality result.
Learn Potential for Skills Development graph
slide 55:
RELATIONSHIP BETWEEN SKILLS DEVELOPMENT AND MACHINE INTENSITY
With intensity of machinery use in production processes:
Skills development potential goes down, and
Speed of production goes up.
What are the limitations of Precast?
- Flexibility of precast floor systems layouts (Modular layout more suitable to certain floor systems)
- Transportation Considerations (Location of Precast Yard with respect to Project Site
- Special attention required for joints once members are placed (proper connection to existing structure and between different units ensures monolithic action, prevents differential effects)
- More complex connections with prestressed systems (Hollow-core) than with Normally Reinforced (Permanent shuttering)
- Criteria for selection dependent on project requirements (longer spans achievable with prestressed systems, but lifting equipment needed for installation of large, heavy prestressed units)
what is the pre-requisites for precast:
- Design for precast from the start
- Repetitive use of elements
- Early collaboration between designer and contractor
Parameters in construction projects?
Mid Circle:
1. Project (technical solutions)
All around it:
- Procurement model
- Cost
- Construction time
- Labour
- Sustainability
- Safety/Quality
- Aesthetics
- Skills
