Pumping effect to accelerate liquid uptake in concrete and its implications on salt frost durability

- Characteristics associated with pumping effect is demonstrated.
- A major pumping mechanism to accelerate liquid uptake in concrete is proposed.
- Implications of pumping effect on salt frost scaling are elucidated.

Pumping effect is studied by means of bulk moisture uptake in low water-binder (w/b) ratio concrete mixes under freezing-thawing (F-T) exposure. The added absorption is clearly demonstrated under either water or salt exposure with no appreciable difference noted. Air void degassing and subsequent saturation accelerated by the pumping effect is shown to cause void infillings commonly observed in concrete pavement exposed to prevalent freezing weather and deicing procedures in winter. Measured moisture uptake at two different minimum temperatures (−10 °C and −20 °C) indicates equally significant absorption suggesting external moisture forced into the concrete interior upon freezing is a major pumping effect. Concurrent investigation on the cumulative mass loss and internal damage reveals the decoupling of salt scaling and internal frost damage governed by different mechanisms. This is enhanced by the silane and temperature effects on the mass loss and relative dynamic modulus (RDM) change. Silane treatment and a higher minimum temperature (−10 °C) are found to create much less scaling attributed to the restricted ice growth. However, the hydrophobic effect is neutralized by the hydraulic pressure at instant freezing, which maintains the universal pore saturation in concrete and eventually causes cracking.