Date of Graduation

12-2020

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Cameron Murray

Committee Member

Kevin Hall

Second Committee Member

Andrew Braham

Keywords

1993 AASHTO, Cement Stabilized Base, MEPDG, pavement design, Spring Constant, Structural Number, Transportation

Abstract

Approximately 70 – 80% of state departments of transportations (DOTs) utilize the 1993 AASTHO Guide for Design of Pavement Structures (1993 AASHTO) [1] for structural design of pavements. A growing portion of DOT’s are beginning to implement the Mechanistic-Empirical Pavement Design Guide (MEPDG), referred to as AASHTOWare Pavement ME [2]. The 1993 AASHTO flexible guide applies empirically derived unitless strength values referred to as structural layer coefficients and structural numbers (SN) to pavement thickness and pavement types. The 1993 AASHTO rigid flexible guide utilizes the depth and strength of the concrete pavement, with the composite spring constant (kc), which is calculated from subgrade resilient modulus, subbase modulus of elasticity (MOE), and the subbase depth. The ME instead includes material properties such as MOE and Poisson’s ratio, in addition to a large list of other inputs toprovide a pavement design that can resist required traffic loadings and other impacts.

Cement Stabilized Crushed Stone Base Course (CSCSBC) is a subbase alternative that is usually provided to prevent loss of subbase support over time. Often, CSCSBC is designed based on prescribed strength values, regardless of the range of cement contents used. CSCSBC can have varying strength properties that are often not accounted for. The goal of this research was to provide a structural coefficient, spring constant, MOE, and Poisson’s ratio based on the actual strength of CSCSBC for use in Arkansas DOT (ARDOT) projects. This research is not focused on the benefits or disadvantages of 1993 AASHTO to MEPDG, and instead will only be focused on the inputs of both.

A range of tests were performed to characterize the strength and stiffness of a test strip located in central Arkansas. The tests conducted were the Static Plate Load Test (StPT), unconfined compression strength, MOE, and Poisson’s ratio. The recommended design values for the 1993 AASTHO Guide, the structural coefficient and spring constant, was an a2 minimum of 0.21 and kc = 2,000 psi/in, respectively. a2 would be acceptable to be kept in a range of 0.21-0.30, based on the 7-day compression strength. For the MEPDG, an equation was provided to relate the MOE to the cement content, and the Poisson’s ratio is suggested to be taken from Table 11-7 from the Mechanistic-Empirical Pavement Design Guide: A Manual of Practice [3].

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