Anti-bleed grouts are often used to fill voids in post-tensioning ducts that result from bleeding and shrinkage of older portland cement grouts. This repair, however, exposes the strands to environmental differences from dissimilar grouts, differences that may cause rapid corrosion. Portland-cement grout, gypsum grout, and four commercially available prepackaged grouts were analyzed to determine the chemical composition of the resulting pore solutions and tested to determine the potential for accelerated corrosion. Grouts and simulated pore solutions were paired to evaluate their potential to cause corrosion of, respectively, grout-encased and bare prestressing strands using the rapid macrocell test. Strands were also evaluated in simulated pore solutions containing chlorides and in deionized water. Unprotected prestressing strands can exhibit rapid corrosion. Gypsum grout, with its low pH and high sulfate content, will cause accelerated corrosion of strands when used in conjunction with any of the other grouts tested. None of the prepackaged grouts resulted in significant corrosion when used in conjunction with portland-cement grout. The highest corrosion measured for a prepackaged grout occurred for the grout with the highest pore solution sulfate content.

The injection of cementitious grouts by vacuum techniques is increasingly used in repair and new construction of posttensioning members. A research program was undertaken to assess the effect of thixotropy on water retention and behavior of grouts placed using such techniques. Tests were conducted using specimens sampled right after mixing as well as after being subjected to vacuum to extract part of the free mixing water. Test results have shown that the partial or complete extraction of free mixing water due to vacuuming decreases flowability (flowtime and mini-slump cone) and increases thixotropy of grouts, mostly due to increased cohesiveness and internal friction within the solid particles. Good correlations were established between extracted water and variations in thixotropy, air entrainment, wick-induced bleeding, unit weight, setting time, and compressive strength. Mixtures exhibiting more than 35% normalized extracted water are not suitable for grouting by vacuum techniques due to increased cohesiveness that hinders proper penetrability. A set of regression models was proposed to simplify product development and predict grout properties either in the fresh or hardened states.

The current industry practice for acceptance testing of post-tensioning grouts includes an accelerated corrosion test (ACT), as recommended in Post-Tensioning Institute (PTI) M55.1-03, “Specification for Grouting of Post-Tensioned Structures.” The most significant downside of the current ACT method is the length of time required to run the test, which typically ranges from 1 to 2 months to complete. The linear polarization resistance (LPR) technique, on the other hand, requires only a few hours to complete; and the research presented in this paper indicates a strong correlation between the time to corrosion, as measured by the ACT method, and the system polarization resistance, as measured by the LPR technique. Based on the test results to date, the authors recommend the use of the LPR method as a prescreen for very high-quality grouts so that lengthy ACT testing is not necessary.

A 12-month long strand corrosion test program with 298 specimens was conducted to identify and quantify parameters influencing corrosion and tension capacity of strands in post-tensioned bridges. The parameters investigated were grout class, moisture content, chloride concentration, void type, and stress level. The test specimens were 41 in. (1041 mm) long, in unstressed or stressed conditions, partially or completely embedded in cementitious grout, and exposed to various environmental conditions representing possible field conditions. After the exposure period, the grout material was removed and the strand surfaces were cleaned and visually evaluated for corrosion damage. The tension capacities of the strands were then determined. Results indicate that the corrosion was most severe at or near the grout-air-strand (GAS) interface. Corrosion evaluation and statistical analysis of the strand tension capacity results show that orthogonal, inclined, and bleedwater void conditions caused more corrosion and tension capacity loss than parallel and no-void conditions. The change in grout class did not result in statistically significant changes in the tension capacity of the strand samples evaluated. Statistically significant changes in tension capacity were observed with changes in the GAS interface, stress level, moisture content, and chloride concentration.

Cement grouts used for crack injection, anchorage sealing, and post-tensioning applications are proportioned to exhibit high flowability to facilitate casting and adequate cohesion to prevent phase separation and bleeding. An experimental investigation was carried out to evaluate the effect of different types of supplementary cementitious materials (SCMs) on rheological properties, stability, and compressive strength of structural grout. Substitutions of cement by 3% silica fume, 10 to 30% Class F fly ash, and 40% granulated blast-furnace slag were considered. Various binary systems that resulted in good performance were also combined to investigate the effect of ternary cement blends on grout performance. The use of SCMs in structural grouts is shown to increase water demand in mixtures made with portland cement. When incorporated in well-dispersed systems, the use of binary and ternary cements led to higher fluidity, lower yield stress, higher plastic viscosity, and greater resistance to forced bleeding compared with reference mixtures made with portland cement. This paper discusses the performance of various grout mixtures prepared with binary and ternary binders and different concentrations of high-range waterreducing admixture.