Lightweight Aggregate Concrete Structures

LWAC is classified by density classes ranging from 1.0 to 2.0 according to EN 206-1, with corresponding oven-dry densities from 800-2000 kg/m³. Density class 1.0 represents the lightest concrete (800-1000 kg/m³), while class 2.0 approaches normal-weight concrete (1800-2000 kg/m³). The classification reflects the proportion and type of lightweight aggregates used—natural volcanic materials or sintered artificial aggregates like expanded shale or expanded polystyrene. For structural design, the oven-dry density ρ is used to calculate material properties and dead loads. Plain and reinforced concrete density tables account for typical reinforcement quantities, enabling simplified dead load calculation.

LWAC properties differ from normal concrete due to lower aggregate stiffness and different hydration characteristics. Tensile strength is reduced compared to compressive strength, requiring strength modification coefficient η1 = 0.4 + 0.6(ρ/2200). For density class 2.0 (ρ = 2000 kg/m³), η1 ≈ 0.95; for density class 1.0 (ρ = 1000 kg/m³), η1 ≈ 0.67. Elastic modulus decreases with density per formula ηE = (ρ/2200)². Strength classes for LWAC designated LC8/10 to LC60/68 replace normal concrete classes C8/10 to C60/75. Design strengths are obtained by dividing characteristic strengths by material factor γM = 1.5 (same as normal concrete).

LWAC structures follow standard limit state design procedures with modifications for material properties. Reduced elastic modulus necessitates higher deflection checks, particularly for long-span elements. Increased creep requires second-order effect evaluation for slender columns. The reduced unit weight (40-55% normal concrete) enables lighter columns and foundations, offsetting the higher material cost per unit volume. Load combinations remain per EN 1990 with partial factors unchanged. Durability provisions are equivalent to normal concrete, with cover requirements based on exposure classes in EN 206-1. Temperature and shrinkage effects are more significant in LWAC and warrant careful analysis.

Shear design of LWAC members follows truss model principles with modifications for reduced aggregate interlock. Shear resistance without reinforcement (VRd,c) incorporates reduced tensile strength through η1 coefficient. The strength reduction factor ν for concrete strut crushing is modified for LWAC, generally becoming ν = 0.5 for LWAC. Punching shear resistance similarly uses modified strength values through density-dependent coefficients. Critical perimeter location and control section placement remain per normal concrete, but resistance values are reduced appropriately. Members with inclined prestressing tendons require evaluation of longitudinal tension forces from combined bending and shear.

Serviceability requirements for LWAC follow normal procedures with increased emphasis on deflection control due to reduced modulus. Stress limitation checks apply with characteristic loads and appropriate combination factors. Crack control provisions are similar to normal concrete but accounting for lower tensile strength and higher creep. Deflection calculation requires evaluation of cracking patterns and time-dependent deformations. Durability provisions are equivalent to normal concrete in EN 206-1 with environmental exposure classes determining minimum cover and concrete composition. The closed structure of LWAC provides excellent frost and weathering resistance, particularly when compared to normal-weight concrete of equivalent strength.

LWAC production requires careful aggregate selection and mix design to achieve specified density and strength. Lightweight aggregates absorb water, necessitating pre-wetting to prevent workability loss and strength reduction. Placement and consolidation procedures are similar to normal concrete but vibration intensity should match aggregate strength to prevent fragmentation. Quality control testing includes density measurement and strength verification per EN 206-1 requirements. LWAC exhibits excellent self-consolidating properties in many formulations, enabling reduced vibration and improved surface finish. Curing conditions significantly affect strength development, particularly for early strength requirements in precast applications.