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Title:Increasing residual structural capacity of cracked concrete railroad crossties with polypropylene fibers
Author(s):Ji, Dongshuo
Advisor(s):Lange, David A.
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Concrete crosstie
Polypropylene fibers
Flexural performance
Abstract:The purpose of this research was to employ polypropylene fibers into concrete railroad crossties to increase its residual structural capacity once the concrete has cracked. The center negative flexural cracking is considered as a serious failure mode in concrete railroad crossties, which decreases structural capacity and results in safety issues. It also leads to deterioration of prestressed concrete crossties and shortens the service life. The post-cracking flexural performance of fiber reinforced concrete (FRC) crossties is changed by the inclusion of polypropylene fibers. Fracture toughness, cracking resistance, and energy absorption capacity of the concrete are improved by incorporating fibers. Furthermore, restriction of crack size extends the service life of concrete railroad crossties and thus the maintenance cost decreases. Several tests were conducted to select the most suitable fibers in the following study. Six types of polyethylene fiber samples with different elastic modulus, surface texture, length, stiffness, and shape were evaluated. The performance of fibers was mainly evaluated by the workability of fresh FRC mixture, the compressive strength and the average residual strength (ARS) of hardened FRC specimens. The concrete mixture reinforced by Strux 90/40 macro polyethylene fibers had the best workability because no balling or clumping issue was found in the mixing process. It had the least effect on the reduction of compressive strength of hardened FRC specimens. The ARS value also indicates Strux 90/40 fibers can improve post-cracking performance of concrete. Therefore, Strux 90/40 macro polyethylene fibers were selected as the reinforcement material in this research. Flexural performance of full-scaled prestressed plain cement concrete (PCC) crossties and FRC crossties was evaluated by center negative bending test and rail seat positive bending test. Load-displacement curves of crossties in flexural tests were recorded. Fracture patterns of crossties in the flexural tests were also captured. Based on the experimental results, it was confirmed that the prestressed FRC crosstie had a higher fracture toughness. The FRC crosstie completely failed at a greater deflection in the flexural test. A numerical method was introduced to predict flexural performance of full-scaled prestressed FRC crossties in center negative bending test. The materials element modeling can be built based on experimental results from simple four-point bending tests on small FRC beams. The materials element modeling was input into an established structural member modeling of prototype prestressed crossties in Abaqus. For a given fiber volume fraction, the flexural performance of full-scaled prestressed FRC crossties can be simulated by inputting corresponding materials element modeling.
Issue Date:2018-12-04
Rights Information:Copyright 2018 Dongshuo Ji
Date Available in IDEALS:2019-02-08
Date Deposited:2018-12

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