Leca® HD - Low Weight / High Strength Aggregate LWAC
Structural applications where normal weight concrete is not the preferred solution and a Higher Strength Leca® Lightweight Aggregate Concrete (LWAC) is the solution, Leca® HD is the aggregate of choice.
Reduce deadloads and achieve high strength equivalent to Normal density concrete.
Leca® HD, Lightweight Aggregate (LWA) is a natural, unique and sustainable lightweight clay aggregate. Leca® LWA has remarkable properties which ensure its versatility for use in Lightweight Aggregate Concrete (LWAC) applications.
Concrete can be considered Lightweight when its density is not more than 2200 kg/m3.
The notation LC for strength class is typically used in specification, for Leca® HD e.g. LC 45/50 with a cylinder strength 45 MPa and a cube strength of 50MPa.
Typically, in LWAC concrete of same cylinder strength, the tensile strengths and strains and shear strengths are lower than Normal density concrete.
LWAC concrete is usually less stiff, consideration needs to be given to the reduction of self-weight and the resulting reduction in the depth of a beam or slab. Creep and Shrinkage should be considered at design stages.
Structural lightweight aggregate concretes have taken a leading role since the 1990s, being the chosen solution for the development of many bridges in Nordic countries, allowing structures to be established that defy gravity. In simple words, light weight concrete can be made with high resistance and reduced weight, of typically 25 %. Combining design parameters, structural LWAC can fit in wide range of density classes, from 1000 to 2000 kg/m3, and wide range of strength classes, from 8 to 80 MPa.
One of the big questions is how and where to utilize the LWAC. LWAC can be used in the same structures as NDA, using traditional admixtures and local cements. The only difference is the use of high-performance Leca LWA that allows to reduce weight without significantly reducing the mechanical characteristics.
Leca® LWA Material Characteristics
- Made of natural raw material
- Low to Mid density
- Greater pellet Strength
- Improved thermal Properties
- A1 fire rating
- Frost resistant
- Reduce transport cost
Leca® LWAC Concrete Characteristics
- Less reinforcement required
- Lighter than Normal Density concrete
- Good workability
- Low thermal conductivity
- High Temperature resistance
- Potential reduction in depth of beam and slab
- Reduction in deadload
- Improved Homogeneous properties
Can be pumped**
• The product complies with: EN 13055-1
• Fraction: 4-12 mm
• Loose bulk density: 610-700 kg/m 3 (approx. 320 kg/m 3 on average)
• Crush resistance: 5 N/ mm2
• Thermal conductivity: λ = approx. 0.100 W/mK*
• Reaction to fire: class A1 (non-flammable)
*For dry aggregate
Leca® HD - Low Weight / High Strength Aggregate
Leca® Lightweight Aggregate Concrete Applications
By using a lower density concrete longer span can be achieved. Thus, the positioning of the foundation are more flexible and large costs are saved.
The use of LWAC will create a slimmer and more cost-effective construction with lower amount of total use of concrete and therefore, also a greener construction.
The use LWAC in the deck structure of cable-stayed bridges either as a fully LWAC structure or in composite solutions of LWAC/NDC/steel structure.
In general, reduced construction costs are achieved due to lower need of concrete volume which can be proven during the design phase
• Floating Structures
The use of LWAC is in floating structures like Wind Turbines, barges, floating fish farms, floating bridge foundations etc.
The LWAC can be made with considerably lower density and keep much of the mechanical characteristics from NDC. LWAC service densities in the range of 1600-1950 kg/m3 will result in characteristic compressive strength of 35-65 MPa and achieve considerably better structure buoyancy.
High pumping power should be avoided for LWAC, since it can promote segregation, changing also the absorption and the consistency of the placed concrete
In general, LWAC can be easily pumped when pre-saturation is assured, until the internal moisture is circa 15%, assuming also that the viscosity is not too high. However, the pump selection depends a lot on the desired pumping performance and on the transport capacity (in height and in distance), being able to use, stationary pumps with compressor or; auto-pumps, with pressure technology applied by piston pump.
Batching of lightweight concretes is normally done from ready-mixed concrete producers.
At low work abilities, the concrete can easily be placed by skip or chute. Pumping lightweight concrete can be achieved, but care needs to be taken so that the concrete mix doesn’t separate. For pumpable mixes it is usual to use a natural sand, i.e. not to have a lightweight aggregate for the fine portion of the mix and to have a high workability so that increased pump friction and blockage is avoided. This is achieved with the use of admixtures. Over vibration of a lightweight concrete tends to cause segregation so a flowing concrete is best used when it is to be pumped as it requires only minimum vibration.