Concrete containing marginal aggregates: - Mechanical behavior and application in concrete pavement

Concrete is made up of three phases i.e. the aggregate phase, the hydrated cement paste and the Interfacial Transitional Zone (ITZ) between the hydrated cement paste and the aggregate phase. The aggregate phase is generally thought of as the strongest phase while the ITZ is the weakest phase and thus dictates the strength of hardened concrete. For normal concrete, the aggregate phase mostly has no influence on the strength except in the case of highly porous and weak aggregates such as pumice. In view of the above, the strength of the aggregate is mostly not taken into consideration when producing normal concrete. However, with the ever increasing depletion of good quality aggregates, weaker aggregates have been considered to be used for some concrete application. These weaker aggregates are mostly considered as marginal or borderline aggregates and do not meet current standards and specifications. Key among these weak aggregates is natural aggregates that do not meet current standards and specifications.;This research studied the physical properties of selected marginal aggregates in Florida. A laboratory testing program was conducted to evaluate the properties of concrete made with aggregates which do not meet current Florida Department of Transportation (FDOT) aggregate specifications and compared them with those made with aggregates which meet the current FDOT specifications. Ten different aggregate sources were selected for use in this study, involving two control aggregates which met the 2010 FDOT aggregate specifications, and eight aggregates which did not meet at least one of the aggregate specification requirements. The required aggregate properties which were not met included the maximum allowable LA abrasion loss, percent passing No. 200 sieve, and shell content.;Base on the results from this study, it was found that the strength of concrete was dependent on the strength of the coarse aggregate used. The workability of concrete containing marginal aggregate was found to be similar to concrete containing normal concrete when the Shilstone mix design method was used to optimize the mix. Various relationships between aggregate properties and concrete properties were also developed. New predictive equations for different mechanical properties of concrete containing marginal were developed. Based on these results a developmental three-tier aggregate specification was recommended for use by FDOT. The first tier (Category A) aggregate would have the same requirements as the current FDOT aggregate specifications. The second tier (Category B) and third tier (Category C) aggregates have relaxed requirements in maximum allowable LA abrasion loss, sodium sulfate soundness loss, and materials passing No. 200 sieve. Possible uses for Category B aggregates include all nonstructural concrete applications, manholes, inlets, and junction boxes. Category C aggregates are recommended only for non-structural concrete applications.;Results of analysis in this study indicate that when carefully designed, concrete containing marginal aggregates can be successfully used in concrete pavement applications.