Permeability and Sorptivity
Concrete is a porous material which interacts with the surrounding environment. The durability of mortar and concrete depends largely on the movement of water and gas enters and moves through it.
The permeability is an indicator of concrete's ability to transport water more precisely with both mechanism that is controlling the uptake and transport of water and gaseous substances into cementitious material.
Permeability is a measure of flow of water under pressure in a saturated porous medium while Sorptivity is materials ability to absorb and transmit water or liquid through it by capillary suction. Uptake of water or liquid by unsaturated, hardened concrete may be characterized by the sorptivity.
This is a simple parameter to determine and is increasingly being used as a measure of concrete resistance to exposure in aggressive environments.
Sorptivity or capillary suction is the transport of liquid in porous solid due to surface tension acting in capillaries and is a function of viscosity, density and surface tension of liquid and also pore structure (radious, tortuosity and continuity of capillaries) of the porous solid
The Sorptivity can be determined by the measurement of the capillary rise Vs absorption rate on reasonably homogeneous material.
The following observations are made regarding the resistance of partially replaced fly ash for M-25:
(a) The water absorption and sorptivity of fly ash concrete shows lower water absorption and sorptivity at 10% replacement with fly ash for M-25. There after the water absorption and sorptivity shows a increasing trend.
(b) The water absorption and sorptivity of fly ash concrete shows lower water absorption and sorptivity at a replacement level of 10% with fly ash for M-25 grade concrete with respect to other % of fly-ash based concrete.
(c) The water absorption and sorptivity of fly ash concrete shows higher water absorption and sorptivity than traditional concrete with respect to % fly-ash and water cement ratio adopted.
IMPORTANT: The fly ash can be innovative supplementary cementitious Construction Material but judicious decisions are to be taken by engineers/consultant/contractor.
More ever a good designed concrete can not provide guarantee for placing, laying and finishing as per client’s requirement or industry requirement.
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