L Box Apparatus

The L-Box Apparatus is a standard testing instrument used to evaluate the passing ability, filling behavior, and flow rate of fresh Self-Compacting Concrete (SCC) through congested reinforcement. By quantifying how the concrete maneuvers through narrow rebar gaps and flows along a horizontal trough, the apparatus assesses whether a mix can achieve uniform compaction in complex formwork without aggregate blocking or segregation.

Constructed from a rigid, heavy-gauge steel frame with smooth internal surfaces, the unit consists of a vertical hopper connected to a horizontal trough via a quick-release sliding gate and a standardized rebar obstacle. Once the gate is lifted, the concrete flows through the reinforcing bars across a set distance, allowing operators to measure the vertical heights at the gate and trough ends to calculate the blocking ratio (H2 / H1) for clear compliance verification.