The trouble is that water, chlorides, and sulfates travel through these voids. Once they reach the reinforcing steel, the bridge dies from the inside.
[ Absorption = [(B-A)/A] \times 100 ] What it means: The concrete’s appetite for water. High absorption (typically >8% for normal concrete) suggests a permeable matrix vulnerable to freeze-thaw damage and chemical attack. astm c642 density absorption voids in hardened concrete
Armed with ASTM C642 data, the owner rejected the deck. The contractor demolished and repoured. The test cost less than $500 per core. The replacement cost $2.3 million. Concrete is not a rock. It is a manufactured geology, and its performance depends entirely on the geometry of its emptiness. ASTM C642 is not glamorous. It involves no high-speed cameras or finite element models. It is just a scale, an oven, a boiling pot, and a calculator. The trouble is that water, chlorides, and sulfates
Note: Values >20% permeable voids generally indicate poor-quality concrete or a mix design error. The test cost less than $500 per core
| Property | Typical Value | | :--- | :--- | | Dry Density | 125 – 155 lb/ft³ (2000 – 2480 kg/m³) | | Absorption | 4 – 8% | | Permeable Voids | 12 – 18% |
[ D_dry = [A / (B-C)] \times \rho_water ] What it means: The mass of solid concrete per unit volume, including pores. A low dry density might indicate lightweight aggregate or excessive voids.
The sample is placed in a ventilated oven at 110 ± 5°C (230 ± 9°F) for at least 24 hours, or until it stops losing weight. This is the – the skeleton of the concrete, stripped of all free water. Step 2: The Flood (Saturation) Now comes the counter-intuitive part. To find the voids, you must fill them. The dry sample is placed in a water bath at 21 ± 2°C (70 ± 4°F) for at least 48 hours. But that’s not enough to reach full saturation. Air gets trapped in fine pores.