Chloride Content by Weight of Concrete. Q.: For corrosion protection, ACI 318-95, Building Code Requirements for Structural Concrete, specifies maximum water-soluble chloride ion in concrete as percent by weight of cement. What are acceptable levels when measuring chloride-ion content in existing concreteâspecifically, by weight of the concrete sample?
Plasma membranes are selectively permeable, regulating the cellâs molecular traffic. Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and. pass through the membrane rapidly. Polar molecules, such as sugars, do not cross the membrane easily. Transport Membranes Transport proteins allow passage of hydrophilic substances across the membrane.
In some membranes the water flux is very high and cannot be accounted for by water diffusion across lipid barriers. A consideration of this fact lead to the hypothesis that membranes must contain protein which provide an aqueous channel through which water can pass.ubstances which are water soluble typically do not cross lipid membranes easily unless specific transport mechanisms are present. It might be expected that water would likewise not cross cell membranes easily. Indeed, in artificial lipid bilayers, water does not cross easily and this is consistent with our expectation.