MixDesignCalc 2026 β LECA, Sintered Fly Ash & Pumice LWA: Density Class Selection, Pre-Saturation Requirement, Modified Absolute Volume Method, Floating Aggregate Control, VMA Dosage, Structural LWC Design & Batch Quantities
Lightweight concrete (LWC) uses lightweight aggregates (LWA) β materials with particle density below 2000 kg/mΒ³ β to produce concrete with fresh density between 1000 and 2000 kg/mΒ³ (vs normal weight concrete at ~2400 kg/mΒ³). The primary motivation is reduced structural dead load β which allows smaller section sizes, less reinforcement, and smaller foundations in high-rise construction. Secondary benefits include improved thermal insulation and better fire resistance.
Mix design for LWC requires significant modification from normal concrete procedures because LWA particles are porous β they absorb water over time during mixing and placement. This creates the two defining challenges: pre-saturation (LWA must be wetted before batching to prevent mix water absorption) and floating (LWA Sg β 1.0 is close to water density β particles can float upward during vibration at high slump).
LECA (Lightweight Expanded Clay Aggregate) is produced by firing clay or shale at 1100β1200Β°C until it bloats and forms a porous internal honeycomb structure with a harder ceramic outer shell. IS 9142:1979 governs LWA quality in India. LECA has very high water absorption (8β25% by mass in 24 hours) β pre-saturation before batching is mandatory. Its Sg of 0.80β1.20 means particles are close to water density β floating during vibration is a significant risk at high slump. Excellent thermal insulation properties (thermal conductivity 0.08β0.18 W/mΒ·K).
EN 206 and ASTM C330 classify lightweight concrete by fresh/hardened density. IS 9142 and IS 456 use density broadly, but EN density classes provide a useful design framework internationally. Select the target density class for your application.
Select LWA type, density class, enter mix parameters and click Calculate LWC Mix. Results include LWC mix proportions, fresh density estimate, pre-saturation water requirement, floating risk assessment, IS 456 compliance, step-by-step workings and batch quantities.
| LWA Type | Sg (SSD) | Bulk Density (kg/mΒ³) | 24h Absorption (%) | Max Size (mm) | Suitable For | IS 9142 |
|---|---|---|---|---|---|---|
| LECA β 4β8mm | 0.80β1.05 | 280β420 | 12β25 | 8 | All LWC; fine CA replacement | Cl.3.1 |
| LECA β 8β16mm | 0.85β1.20 | 300β480 | 8β20 | 16 | Structural; precast; bridge deck | Cl.3.1 |
| Sintered Fly Ash | 1.50β1.80 | 750β900 | 10β20 | 14 | Structural LWC; higher strength | Cl.3.2 |
| Expanded Shale | 1.20β1.60 | 500β750 | 5β15 | 20 | Structural LWC, M25βM35 | Cl.3.3 |
| Pumice (Natural) | 0.60β1.10 | 400β700 | 20β40 | varies | Non-structural; insulating fills | Cl.3.4 |
| Normal Weight (ref) | 2.65β2.70 | 1450β1700 | 0.5β2 | 40 | Reference β normal concrete | IS 383 |
LWA must be pre-wetted for a minimum of 24 hours (LECA: 48 hours recommended) before use. Dry or partially dry LWA placed in a drum absorbs 8β25% of its own mass from the paste within the first 5β10 minutes β destroying workability before placement. Pre-saturation water is NOT counted as mix water (it stays inside the aggregate pores). Measure LWA mass in SSD condition; batch water is designed for SSD aggregates. The additional water to bring dry LWA to SSD must be added as a separate pre-wetting step.