Combined harmful processes affecting the cementitious materials

(Hugo Eguez Alava)

There are several mechanisms that can deteriorate reinforced concrete and reduce its service life.
One common aggressive mechanism acting in concrete is carbonation, a process occurring when CO2 diffuses through it and reacts with cement hydration products such as calcium hydroxide and calcium silicate hydrates, to produce calcium carbonate in the presence of water. This process can induce corrosion of the reinforcement, due to reduction of the pH in the surroundings and also due to removal of the passive film that protects the reinforcement surface.

 
         hugo1                    hugo2
  Carbonation in concrete in which 50% of the Portland             Spalling of concrete due to rebar’s corrosion.
      cement binder is replaced by blastfurnace slag.

Corrosion products may grow in volume up to almost 5 times the initial metal volume, and the expansive force derived from this volume increase easily exceeds the low tensile strength of concrete, causing cracking. This latter phenomenon is enhanced after chloride ions reach the concrete rebar through diffusion. This case is typically found in concrete which is in contact with any source bearing chloride.

Combinations of environmental and mechanical loads have proven to be more deleterious for concrete than any harmful mechanism distressing concrete’s structures in an isolated manner.
In order to obtain a more realistic reflection on concrete’s durability, the contribution of environmental and mechanical load, when they simultaneously act on this material, should thus be taken into account. The objective of this research  is to investigate the combined attack effects on concrete made with ordinary Portland cement, high sulfate-resistance cement and blast furnace slag cement, when they are subjected to the combined action of chloride attack under loading, and also the influence of carbonation on deicer scaling resistance for these concretes.

         hugo3           hugo4

Simulation of chloride attack to concrete under splitting tensile stresses (left) and detail of the test setup (right).