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Factors such as paste content, concrete slump, compressive strength, and evaporation rate affect the tendency of concrete to crack, which can lead to corrosion and rapid deterioration in structures...

United States Department of Transportation Federal Highway Administration under Contract No. DTFH61-03-C-0013

Internal curing (IC) using prewetted lightweight aggregate (LWA) has often been used to improve the cracking performance of concretes with low water-to-binder (w/b) ratios (

Techniques for making epoxy-coated reinforcement more corrosion resistant, including epoxies with increased adhesion to the steel; concrete with a decreased water cement ratio; concrete containing calcium nitrite or one of two organic corrosion inhibitors; bars with a primer coating containing microencapsulated calcium nitrite applied prior to epoxy application; and bars coated with zinc prior to epoxy application are compared based on the chloride content required to initiate corrosion and corrosion losses using the southern exposure and cracked beam tests. The coatings on all bars are penetrated prior to testing to simulate damage in the field. The results indicate that, even when damaged, conventional epoxy coatings result in much higher concrete chloride contents at corrosion initiation and much lower corrosion losses than exhibited by conventional reinforcement. A reduced water-cement ratio, corrosion inhibitors, and the primer coating containing microencapsulated calcium nitrite provide prot...

Three commercially available corrosion inhibitors—calcium nitrite, a solution of amines and esters, and an alkenyl substituted succinic acid salt—are evaluated in conjunction with conventional reinforcement in concrete based on corrosion rate, metal loss, the critical chloride corrosion threshold (CCCT), pore solution analyses, and concrete compressive strength. All three inhibitors increase time to corrosion initiation and decrease corrosion rate, but are less effective in cracked concrete than in uncracked concrete. Of the three inhibitors, the alkenyl-substituted succinic acid salt results in the greatest decrease in corrosion rate, but exhibits the lowest CCCT—below that measured in concrete with no inhibitor. The compressive strengths of concretes containing the amine-ester inhibitor and the alkenyl-substituted succinic acid salt were 15% and 60% lower, respectively, than concrete without an inhibitor. For the latter inhibitor, pore solution analyses indicated elevated sulfate contents at 1 and 7 days, which may explain the low CCCT and strength. Paste containing the amine-ester inhibitor had an elevated sulfate content at 7 days.

Determination is made of the chloride content required for galvanized reinforcing bar corrosion initiation. With the exception of there being no chromate treatment application so that the degree of hydrogen evolution for untreated bars could be evaluated, the bars conform to ASTM A767. There is comparison of bridge deck chloride surveys with test results, as well as with results for 316LN stainless steel, low carbon chromium (ASTM A1035, MMFX), and conventional (ASTM A615) reinforcement. There is a greater average galvanized reinforcement critical chloride corrosion threshold than for conventional steel. The threshold is lower when compared to ASTM A1035 and 316LN steel. Concrete porosity in the non-chromate treated bars did not increase through hydrogen gas evaluation relative to that observed for conventional reinforcement. Compared with 15 years for ASTM A1035 steel and 2.3 years for conventional steel, there is a 4.8 year average time to corrosion initiation for galvanized steel at bridge deck crack locations. There is no corrosion of 316LN stainless steel.

The bond strength of four sets of reinforcing bars is evaluated, two each with No. 5 and No. 10 (No. 16 and No. 32) bars, which have, respectively, nominal diameters of 0.625 and 1.27 in. (15.9 and 32.3 mm). One bar of each size satisfies the criterion for maximum deformation spacing in ASTM reinforcing bar specifications, while the other has deformations that exceed the maximum spacing. All bars exceed the requirements for minimum deformation height. Research related to the effect of deformation properties on bond strength, including the research used to establish the requirements for deformations in ASTM reinforcing bar specifications, is also reviewed. The test results match earlier research and demonstrate that (1) bond strength is not governed by the specific value of deformation height or spacing, but by the combination of the two as represented by the relative rib area of the bars and (2) the bond strength of the bars with deformation spacings that exceed those in ASTM reinforcing bar specifications is similar to the bond strength of the bars that meet the specification. Based on this and prior research, it is recommended that ASTM reinforcing bar specifications be modified to allow for deformation spacing up to 90 % (currently a maximum of 70 %) of the bar diameter provided the ratio of deformation height to deformation spacing is greater than or equal to the minimum ratio for bar deformations meeting the current requirements in ASTM reinforcing bar specifications.