AGGREGATE BLENDING DESIGN FOR HOT-MIX ASPHALT WITH RISK ANALYSIS

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Ponlathep Lertworawanich

Abstract

Aggregates are one of the most important elements of hot-mix asphalt. Aggregate blending is a process to find the proportion of aggregates to satisfy the gradation specification. Traditionally, in Thailand aggregating blending is a trial-and-error technique. This study proposed a new method to solve for an optimal aggregate blend where the problem is formulated as a nonlinear program. The new model has an objective function to minimize the total cost of the aggregate blend. It incorporates the Bailey ratios as constraints to ensure aggregate interlock and aggregate packing of the blend. A concept of risk analysis is introduced as a constraint. This risk is quantified by the probability that the aggregate blend will violate the gradation specification. A case study is presented. It is found that the proposed model can generate an efficient frontier, a trade-off curve between the total cost of aggregate blend and the risk of violating the gradation specification. The minimum-cost aggregate blend produces the highest risk of violating the gradation specification while the minimum-risk aggregate blend produces the highest cost of the aggregate blend. The resulting grading chart indicates that the minimum-risk aggregate blend is somewhat close to the middle points of the gradation specification whereas the minimum-cost aggregate blend is close to the boundary of the gradation specification. The proposed model is helpful for engineers to weigh the trade-off between cost and risk and to select the most suitable blend with different risk perspective.            

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References

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