International Concrete Abstracts Portal

More and more today’s engineers are finding a growing need to develop and implement construction specifications that are characteristic of the distress mechanisms apparent in the performance of pavements. Such specifications will inherently motivate and empower contractors to seek for improved methods to narrow the deviation of quality and enhance the potential to construct longer lasting pavements at a lower cost.

The tensile strength used in the design of concrete structures, such as concrete pavement systems, has typically been determined based on small test specimens such as split tension cylinders and bending beams. It has been well known that strength values obtained from different specimens can be largely different. Naturally, one must question the applicability of strength values obtained from these conventional specimens to an actual structure. This deficiency is encompassed within effects of specimen (or structure) size and geometry on the strength. Given that fracture parameters can be used to determine the tensile strength of concrete structures, a simplified tension test method, based on the size effect law, is presented in this paper to determine fracture parameters. Cylindrical specimens are incorporated in the proposed method since such specimens have the advantage of being easily cast or cored. Special emphasis is given to concrete pavement systems where tensile strength is particularly important since most distresses in concrete pavements are due to tension-induced cracking.

This paper develops a finite-deformation viscoelastic material model to characterize the behavior of a silicone-based sealant material. A series of relaxation tests were performed on the test specimens for different levels of age and unit extension. Based on the experimental results, a master relaxation modulus curve is constructed. Unit extension and age effects are incorporated in the master relaxation curve by using the superposition principle. The shift factor equations developed were based on the relationship first suggested by William, Landel and Ferry (WLF Equation) and traditionally used for incorporating temperature effect. The unit extension and age dependence are accounted in the “reduced time”. The material model derived is of the generalized Maxwell (in parallel) type, which is simple and can be easily applied in finite element programs for stress analysis of joint sealants in concrete pavement.

This paper presents preliminary results of a laboratory and a finite element investigation of the behavior of joints in jointed concrete pavement systems in terms of load transfer derived through aggregate interlock. The results have thus far revealed that aggregate type, texture and shape have a pronounced effect on the load transfer mechanism of an undoweled joint in a concrete pavement system. Pure aggregate interlock is not sufficient to provide adequate load transfer over a long period of time. The load transfer mechanism of an undoweled joint was modeled by a two-phase system (cement matrix and aggregates). This approach produced results that were confirmed by experimental results. The finite element analysis demonstrated that the load transfer mechanism is sensitive to slab thickness, modulus of subgrade support, and joint stiffness (aggregate interlock factor). This analysis also indicates that the shear capacity of a joint is a function of the aggregate interlock factor, subgrade modulus, magnitude of load, and crack width. The finite element modeling indicated that undoweled joints in thinner pavements resting on weak subgrades tend to develop high shear stresses (and load transfer efficiencies) and subsequently a lower Endurance Index.

Concrete pavement design is still largely empirical, although, there are instances where analytical methods based on theoretical principals have been used. This paper presents the results of work to formulate the concepts for the development of a unified pavement analysis and design system for the improved performance of airport concrete pavements. The improved analysis and design system takes into account realistic material behavior over service life; environmental efffects; realistic pavement loading and a realistic assessment of pavement damage in the anlysis and design prcess, to come up with better performing pavements. Theses concepts are to form the basis of a pavement analysis and design system to be developed in subsequent applied research. A central component of the system proposed is a 3-dimensional finite element analysis based primary response model, applicable to the nonlinear analysis of concrete pavements. This primary response model incorporates the appropriate material constituitive models that will permit a realistic representation of the behavior of hte current and future materials used in concrete pavements. Using this primary response model, a data base of the outputs of nodal displacements, stresses, strains and local damage measures can be generated for a given pavement structure, for the applicable traffic and environmental loading conditions. The data generated is then used in a damage assessment procedure the results of which are used to predict the development of the key distress types and roughness for concrete pavements. This provides for greater design reliability and cost-effective pavement design. A major advantage of the mechanistic design procedure envisaged is its applicability to realistic rehabilitation design, which is likely to become very important in the coming decades, during which the demand for rehabilitation design is expected to supersede that for new construction design. The unified pavement analysis and design concept provides an effective system for the evaluation of the performance of existing concrete pavements from nondestructive testing results. This includes the evaluation of the in-situ material properties of existing pavements from the results of such nondestructive testing, using backcalculation procedures.