Synergy Between Alkali-Aggregate Reaction and Other Deterioration Mechanisms in Concrete


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Title: Synergy Between Alkali-Aggregate Reaction and Other Deterioration Mechanisms in Concrete

Author(s): M. D. A. Thomas

Publication: Special Publication

Volume: 170


Appears on pages(s): 571-586

Keywords: Alkali-aggregate reactions; chlorides; concretes; durability; expansion; fly ash; freeze thaw durability; permeability.

Date: 7/1/1997

Laboratory and field studies were carried out to quantify the effect of AAR damage on other deterioration mechanisms in concrete. Laboratory concretes were cast with various mixture proportions selected to provide a range of AAR expansions after 3 months curing at 60°C. These specimens were then tested in compression and evaluated by an electrical test to predict chloride . permeability (ASTM C 1202), and oxygen permeability. and freezing and thawing tests. Expansions of 0.06% led to significant reductions in strength and stiffness, but no change in permeabilitv. Indeed, the perrneability characteristics were onlv adverselv affected in concretes that expanded bv 0.1 o%. The abilitv of concrete to tolerate low expansion (0.04 to 0.06%) without increases in permeability is probably a function of the discontinuous crack distribution. However, such cracks still result in a softening of the mechanical response. Cores extracted from ten hvdraulic structures exhibiting a wide range of distress due to AAR, were also tested in the laboratory. Quantitative petrographic damage ratings revealed damage ratings in the range 30 to 680. Concrete with minor levels of AAR gave damage ratings slightlv less than 100 and performed similarlyto undamaged concrete. Significant increases in permeability and electrical charge passed were observed when the damage rating exceeded 200. Concrete with damage ratings above 300 were characterized by extensive internal fracturing with crack widths frequently greater than 0.5 mm. These concretes had Coulomb ratings > 10,000 and og en perrneability coefficients > lO-15 m2 Cores -taken from fly ash concrete structures showed excellent performance (< 1, 0 00C and < IO-” m2) despite relatively high water-cementitious material ratios (:> 0.55).