Date of Award

Spring 1996

Document Type

Dissertation

Degree Name

Doctor of Engineering (DEng)

Department

Civil Engineering

First Advisor

Freddy Roberts

Abstract

The Louisiana Transportation Research Center (LTRC) recently conducted a research effort using the Accelerated Loading Facility (ALF). The objective of the research was to evaluate a limited number of alternative base materials and construction techniques envisioned to provide a significant reduction in the occurrence of shrinkage and reflected block cracking in the cement-stabilized bases. Nine test sections were constructed for this research, using the same wearing course material but having different thicknesses of crushed stone and soil cement bases and subbases. The soil cement base is the most commonly used base material in Louisiana, whereas crushed stone is a preferred base material in North Louisiana.

The objective of this study includes evaluating the ALF test results to determine the performance for each set of materials used in the test sections, and assessing the performance of those materials when constructed at other conditions and environment throughout Louisiana. To accomplish the objective, activities including literature review, data analysis, and performance modeling were performed.

From the analysis it was found that the combination of crushed stone base over a soil cement subbase, known as an inverted pavement, provided better performance than the soil cement bases while resisting rutting and retarding the occurrence of reflection cracking. This finding confirmed the results from other researches conducted previously.

Based on the analysis it is recommended that an inverted pavement section should definitely be considered for use in Louisiana. The pavement with crushed stone bases should also be considered even in those areas where the subgrade is relatively soft. In addition, soil cement bases of 4 percent cement and mixed in-place should be constructed and their performance observed and compared to the more standard 10 percent plant mixed soil cement bases.

When the ALF materials were used in the pavement structure in the regions having different soil conditions and traffic levels, pavement with soil cement bases outperformed those with crushed stone bases.

Therefore, it is recommended that crushed stone materials similar to those used in the ALF test sections be used only in the areas with ADT not more than 25,000 or the number of ESALs not more than 23,700,00 ESALs for 20 years design period. On the other hand, soil cement bases can structurally be used in any areas with ADT not more than 75,000 or the number of ESALs not more than 44,500,000 for the 20-year design period. However, one should be cautious when using this material in areas where rainfall or water table is high since water may weaken the structure and cause a substantial reduction of pavement life.

It is also concluded that none of the material combination used in the ALF test section can predictably perform satisfactorily in the areas with ADT more than 75,000. In such a situation, therefore, a rigid pavement should be a better candidate to handle the traffic.

Inverted sections such as those used in lone 009 of ALF test section can be considered as the best of all material combinations even though its performance is somewhat lower than those with soil cement bases. The results from the Louisiana ALF experiment showed that the inverted section has better performance due to its ability to substantially reduce the reflection cracking initiated in the soil cement material underneath.

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