Is Durability directly related to strength of concrete?
Strength of concrete is affected by a lot of factors which in turn does affect its durability. However, such losses in strength during construction and operation ought to be given due consideration in design. Thus if concrete retains the desired minimum strength through out its design life despite fall of strength with time (reasons being creep, shrinkage, fatigue, relaxation, impact loads, weathering, abrasion etc.), we can’t question its performance and durability. Infact, losses such as time dependent losses can’t be dealt with otherwise. Any loss below the desired minimum strength however would indeed lead it to failure upon further loading (as soon as it reaches worst conditions of loading). Like a few others have rightly pointed out, concrete is simply supposed to resist weathering action, chemical attacks and abrasion while maintaining its desired engineering properties.
Quality Control at site ought to ensure that desired strength is achieved during construction. Design, on the other hand, also plays a vital role, from ensuring strength to bear temporary loads during construction to durability through out its design period specifying apt grades and dimensions. Defect liabilities are well thought out during the contract/tender/award period and the responsibilities distributed accordingly. Maintenance and operation is an important part of any project.
It’s also worth noting here that while durability is affected by strength, it’s not the only factor. There’s also a service life and a functional life. It’s likely that a concrete structure would reach functional obsolescence (You might want to look this up: )or be rendered unserviceable due discomfort (due to overly large deflections and incurable permeability) despite enough strength. All these reasons add together with possibilities of natural calamities and other contingencies to define a design service life for any concrete structure which may range from about 30 to 100 years.