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SLAB ON GRADE

VSL Slab on grade is the ideal cost-effective joint-free solution for industrial structures - highly durable, with very low maintenance.

  • West Swanson Intermodal Terminal
    Construction of a post-tensioned slab on grade for a heavily loaded pavement at the Port of Melbourne.
    Australia - 2012 read more

    West Swanson Intermodal Terminal

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  • North Dynon Rail Terminal
    Construction of 20,000m² of post-tensioned slab on grade in just 11 pours.
    Albania - 2012 read more

    North Dynon Rail Terminal

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  • Nestlé Distribution Plant
    VSL pours the world's largest joint-free surface..
    Chile - 2002 read more

    Nestlé Distribution Plant

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  • OCG Chocolate factory
    600 m2 of joint-free post-tensioned ground slab without passive reinforcement.
    France - 1997 read more

    OCG Chocolate factory

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The lightweight solution for the construction of economic and durable slabs

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VSL’s Slab on grade is a versatile method for producing slabs in industrial and commercial structures using the principles of post-tensioning to compensate for excess tensile stresses.

An industrial floor slab should be durable, free of excessive cracking, suitably flat and able to withstand traffic loads. The VSL Slab on grade greatly diminishes the risk of failures and so is widely used in the construction of such structures. The system uses post-tensioning technology in the design and construction of flooring and pavements.

There are expensive consequences to the failures that occur with conventionally reinforced concrete slabs or slabs with steel fibre reinforcement. Symptoms such as delamination and spalling, cracking, curling and abrasion increase the need for maintenance and repair, leading to higher service-life costs as well as the loss of production during any repair operations.

These issues are avoided by the use of the VSL Slab on grade system. Compared with conventional reinforcement, post-tensioning provides a longer service life and higher loading capacity. It requires almost no maintenance and retains a high resale value. The system has been used successfully worldwide in various types of logistics and manufacturing facilities, workshops and other structures including tanks and hangars.

Building a durable industrial or commercial structure requires consultation between the slab designer, owner, geotechnical specialist and builder. Many factors have to be considered before construction, such as the environmental and site conditions, traffic requirements, loads, slab thickness and reinforcement, joint locations and spacing as well as the method of slab construction. Each of these considerations affects one or more of the others.

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VSL's systems and services

VSL carries out the design, supply and construction of large joint-free reinforced post-tensioned concrete slabs. The slabs use axial compression forces in the concrete to counteract tensile stresses that would otherwise cause cracks. VSL’s services cover:

  • Full slab design
  • Earthworks
  • Subgrade preparation, including a sand base and plastic layer
  • Supply and installation of post-tensioning
  • Concrete works
  • Surface finishing

Advantages of VSL’s services

Supporting any load: The VSL Slab on grade can be designed to accommodate any loading requirement.

Crack control: Post-tensioned slabs reduce the risk of cracking more effectively than other reinforced slabs because of the compressive forces that are applied by the post-tensioning cables.

Fast-track construction: Post-tensioned slabs can be constructed much faster than conventional reinforced slabs. Time is also saved by using fewer joints and narrower footings with less excavation and less concrete. Large pours of more than 2,500m² are a common feature of post-tensioned slabs on grade.

Providing the ultimate choice in surface coatings: VSL Slab on grade produces the best possible base for surface finishes and gives the customer the ultimate freedom of choice in coatings. The eventual finish of the slab can be selected for appropriate texture, hardness and colouring, making it not only serviceable but also attractive.

Up to 30,000m² without joints: Large concrete areas can have their joint spacing increased to minimise the costs of the joints as well as the long-term maintenance and operational costs. Use of the slab-on- grade solution also reduces the wear and tear caused by moving equipment, extending the life of the joints.

Reduced maintenance: The use of fewer - or even no – joints significantly reduces the need for future maintenance. Studies have shown that the major costs over the life of a structure involve joint maintenance. With a post-tensioned slab, the costs of joint and crack repair are reduced as too is the damage to plant caused by the breakdown of joints.

More flexible slabs: A thinner slab is more flexible. In the event of a large overload that may induce cracking, the prestressing ensures that the slab returns to its previous state when the load is removed. In contrast, a weak point is more likely to remain in the substructure with a conventional reinforced slab, leading inevitably to deterioration.

Flatter slabs: The risk of slab curling is greatly reduced with fewer joints and greater joint spacing. This produces a smoother ride and less maintenance for vehicles.

Deflection control: Expansive soils, which expand when wet and shrink when dry, can cause foundation movements and cracking. Post-tensioning increases the slab’s flexural and tensile capacities, making it more resistant to problematic soils.

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Austrack project
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Ballerina project

Contributing to sustainable solutions

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In a project featuring the VSL Slab on grade system, sustainable practices and economic success go hand-in-hand as there are advantages over traditional reinforced concrete slabs:

  • A reduction in concrete volumes by up to 30%
  • Reduced energy demand
  • Reduced emissions of greenhouse gases (CO2).

The VSL Slab on grade system offers further advantages with regards to sustainable development:

  • Lower maintenance and repair costs throughout the life of the slab due to the inherent crack-inhibition properties of using prestressing
  • Lower whole-life costs due to the extended longevity of the system compared with plain reinforced concrete slabs
  • Reduced volume of end-of-life demolition and waste disposal with corresponding reductions in costs.
Awards
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The quality of the VSL Slab on grade system has been recognised through a number of prestigious awards:

2000: IVOR certificate stating that the VSL Slab on grade system is a recognised technique with regards to its durability

2002: Award from the Prestressed Concrete Institute and Association of US engineers for the world’s flattest pavement

2003: Award from Lockwood Greene Engineers/JA Jones Co. for the largest and flattest post-tensioned pavement system in the world

2007: Golden Trowel Award issued by FACE® for the flattest and most level slab of the year

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How it works

Resisting tensile stresses

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LMC project in HK, soil freezing to construct cross-passage between the 2 tunnels

Concrete has limited capacity to resist tensile stresses.

For conventional reinforced concrete slabs or slabs with steel fibre reinforcement, the thickness and primary reinforcement therefore have to be increased to prevent the stresses exceeding the concrete’s tensile strength. This ensures that the slab can satisfy all the design code requirements.

The VSL Slab on grade technology is based on the principle of post-tensioning where the prestress is permanently introduced into the structure after the concrete has hardened. Post-tensioning allows a balancing of the tensile stresses in the concrete, leading to thinner slabs and a great reduction in the amount of conventional reinforcement required. The system uses an optimum combination of post-tensioning, slab thickness and concrete tensile strength to produce a cost-effective slab-on-grade solution. Moreover, the design provides a wider joint-free and crack-free area with improved durability.

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Post-tensioning produces the most efficient solution, which takes into account:

  • External factors that affect the structure (including temperature, temperature differential and loadings);
  • Internal effects such as concrete shrinkage;
  • The size of the structure;
  • The quality of the supporting ground, which may require additional preparation to reach a given standard.

Main components

Stabilised subgrade

Concrete, which is placed in the same manner as for a traditional slab. The quantity of concrete for a VSL Slab on grade is slightly higher than for a conventional slab.

Post-tensioning (active reinforcement) has a critical function in the slab durability. It provides flexibility to the slab while preventing cracking. Post-tensioning can be either bonded or unbonded depending on local standards. It is normally designed and supplied by a specialist contractor. VSlab® is the VSL anchorage system that is commonly used for slab-on-grade construction.

Passive reinforcement, especially at the joints and for reinforcement of the local zone at the post-tensioning anchorages. In a VSL Slab on grade, the passive reinforcement ratio is typically about 25% of that for a conventional reinforced slab, although part of the saving is offset by the addition of post-tensioning. Overall, the quantity of steel reinforcement (active and passive) is decreased by about 25%.

Joints, are located at the periphery of each pour and ensure local continuity of the slab as well as allowing thermal movements of the structure.

Coatings and finishing

The finishing operation creates a concrete surface with the desired texture, smoothness and durability. The finish may be decorative or strictly functional. Different finishes and coatings are possible depending on the required appearance and material characteristics. Options include polished mirror finishing, half-polished finishing and quartz finishing. The slab’s mechanical properties also provide an ideal base for coatings belonging to the synthetic (polyurethane or epoxy), bitumen and cement families.

Key design aspects addressed by VSL

The VSL Slab on grade design can be tailored to individual needs:

- Use of few or no joints depending on the dimensions of the slab (up to 30,000m² of joint-free slab)

- Design detailing to match project-specific requirements such as a range of jointing treatments depending on the use

- Tendon positioning to suit the layout of fixed racking

- Subbase design to optimise slab and subbase costs for individual site conditions

- Concrete properties to maximise durability and strength while minimising the combined cost of the concrete and post-tensioning

- Pour size adapted to provide a slab that can be built taking into account available local resources

Adaptable and versatile

VSL Slab on grade can be applied to many commercial and industrial structures, including, but not limited to:

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Cool rooms and freezer storage facilities where wide temperature ranges act on the slab
Taxiways and aircraft hangars where a joint-free slab is of utmost importance
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Workshops with high loadings from heavy vehicles
Manufacturing facilities with heavy loads
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Lorry parks and roads subject to heavy loads
Warehouses and distribution centres subject to heavy loads
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Rail and seaport container terminals where heavy loads are encountered
Water storage tanks where water-tightness is a prerequisite

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