Best practices for the use of siliceous river gravel in concrete paving.

Fracture toughness (K sub IC) value at early ages of concrete was used to represent the interfacial bond between aggregate and mortar of a variety of coarse aggregates types and concrete mixtures. A fractional factorial design based on Taguchi’s orthogonal array using four factors (i.e., aggregate type, w/cm, replacement of ultra-fine fly ash, and curing method) was selected to conduct the detailed laboratory study. The statistical analysis indicated the following decreasing rank order with respect to the relative importance of each factor to K sub IC: aggregate type, curing method, w/cm, and ultra-fine fly ash content. A comprehensive investigation of aggregate properties relative to physical, geometric, and chemical characteristics was conducted. The research findings indicated that the aggregate-mortar interfacial bond for a given cement paste was found not to be a simple function of any one of the aggregate properties, but a function of all three properties aggregated together. The application of utility theory to the evaluation of overall contribution of aggregate properties to the bonding performance of concrete, and feasibility of design combinations enables agencies to select the best aggregate type, modify aggregates by blending different aggregates, and optimize the design combinations for concrete paving construction, to relieve delamination and further spalling distresses. The interfacial fracture energy can be predicted once a design combination is known based on the linear relation with both concrete and mortar fracture energy. A fracture mechanics based approach was proposed with the facilitation of numerical analysis to predict the occurrence of delamination. The criterion for predicting early age delamination occurrence is that delamination occurs when the stress intensity factor (K sub I) > K sub IC. Through examples of practical design and construction methods, this approach is able to assess the probability of delamination occurrence, which will facilitate selection and evaluation of the effectiveness of pavement design methods to prevent delamination and spalling problems in concrete paving. Test sections of both winter and summer were established based on the research finding from laboratory investigations, theoretical modeling, and numerical analysis. Future performance of these sections will determine if the measures taken to arrest delamination were successful or not.