D. V. Reddy

Cement Stabilization of Highly Organic Subgrade Soils to Control Secondary Compression Settlement

Many flexible pavements in western Palm Beach County, Florida, are underlain at shallow depths by thick deposits of organic soils and peats. These soils undergo long-term secondary compression as a result of sustained overburden pressure of the pavement and thereby cause excessive premature structural distress in the form of cracking, rutting, and differential settlement. Although cementitious materials have been successfully used to stabilize soft, expansive, and inorganic soils, research and experience regarding the stabilization of highly organic soils are limited. The authors’ main motivation for doing this research was to investigate the effects of cement stabilization on the compressibility of soils consisting of organic content in the range of 67% to 90%. The undisturbed soil samples were collected from the subsurface of the SR-15 (US-98) roadway, which had experienced severe distress attributable to organic layers and had undergone frequent and costly rehabilitation in recent years. It was found that cement stabilization at dosages between 35% and 55% (by dry weight) drastically reduced the ratio of the secondary compression index to the primary compression index of the organic soils to values that resembled a nearly granular soil with desirable compressibility characteristics. This optimized mix design may provide appropriate guidelines for deep mixing methods in subsurface organic layers for the long-term preservation of roadways built over problematic soils.

Permanent Strain Characterization in Granular Materials using Repeated Load Triaxial Tests and Digital Image Correlation (DIC) Technique

An experimental investigation was conducted to evaluate the permanent strain characteristics of a granular pavement foundation layer using Repeated Load Triaxial (RLT) tests, assisted by a non-contact strain measurement system based on a Digital Image Correlation (DIC) technique. Permanent strains are generally determined from laboratory triaxial tests using global measurement of axial strains. Under cyclic loading there may be formations of localized strains and instabilities, which may not be captured by conventional measuring methods, but can have significant influence on the performance of the constructed granular layer. Results are reported from a series of 40 consolidated drained triaxial tests, to develop a better understanding of the permanent strain response of a granular material under simulated traffic loadings. The DIC technology was employed to record deformation measurements, which included acquiring high-resolution images of the specimen at every 100 cycles of repeated deviatoric stresses, using a Q-Imaging / QICAM 1394 camera, and VIC-2D image correlation software. Results indicate that there is a reasonable match between the LVDT and DIC measurements when the entire specimen length was used as the gage length. However, localized strains at the top, middle, and bottom of the specimens computed from DIC measurements deviated from the LVDT measurements. This factor should be taken into account during the pavement design phase, or for the development of pavement rutting performance models.

Durability-Based Ranking of Typical Structural Repairs for Corrosion-Damaged Marine Piles

Corrosion damage is a main cause of deterioration for concrete marine structures. It has become increasingly important to rehabilitate structures and develop repair techniques that prolong their life cycles. This investigation compares the performance of recognized repair techniques, in terms of corrosion resistance, structural integrity, and cost-effectiveness. Eight sets of three cylindrical piles were prepared to conduct seven types of repairs with one control set. Following initial exposure to corrosion, the specimens were repaired using the proposed techniques and tested for durability under simulated tidal conditions, with corrosion monitoring, determination of time-to-corrosion threshold, and visual inspections. The structural integrity was determined by crack scoring and ultimate load testing, and synthesized with a cost-effectiveness evaluation to rank the repair techniques. The repairs comprising carbon wrapping, high-density polyethylene (HDPE) jacketing, and MMFX steel outperformed the others, slurry-infiltrated fibrous concrete (SIFCON) repair, styrene-butadiene grout with woven roving fabric wrapping, normal concrete repair with spliced fiberglass reinforcing plastic (FRP) (glass) reinforcement, and the modified ASANO refresh method.

Fire Resistance of Structural Concrete Retrofitted with Carbon Fiber–Reinforced Polymer Composites

This paper presents an experimental investigation for evaluating the effects of fire exposure on properties of structural elements retrofitted by carbon fiber–reinforced polymers (CFRPs). Mechanical properties of CFRP-strengthened reinforced concrete (RC) members, protected with secondary insulation, were investigated, before and after (residual) direct fire exposure. Direct fire contact resulted in a reduction in capacity of 9% to 20% for CFRP-strengthened RC beams and 15% to 34% for CFRP-strengthened RC columns. Furthermore, a similitude analysis was developed for a heat transfer relationship between full-scale and small-scale specimens, allowing a one-fourth exposure time reduction for the latter. Results from the experimental investigations demonstrated the benefits of employing secondary fire protection to CFRP-strengthened structures, despite the glass transition temperature being exceeded in the early stages of the elevated-temperature exposure. Therefore, it is suggested that fire protection is necessary for a CFRP-strengthened structure to retain integrity throughout the duration of the fire exposure and on return to ambient temperature. The conclusions of this investigation will lead to recommendations and guidelines to designers and practicing engineers for using CFRP materials in retrofitting RC structures with adequate fire resistance by contributing to the missing information for fire protection requirements not available in codes of practice.