Details:

Creators:
Rambo-Roddenberry, Michelle ; Al-Kaimakchi, Anwer
Rambo-Roddenberry, Michelle ; Al-Kaimakchi, Anwer Less -
Corporate Creators:
FAMU-FSU College of Engineering (Tallahassee, Fla.). College of Engineering
Corporate Contributors:
Florida. Department of Transportation
Subject/TRT Terms:
[+]
Camber Curvature Girders Lightweight Concrete Lightweight Girder Mechanical Properties Pretensioning Stainless Steel
Resource Type:
Tech Report
Geographical Coverage:
United States ; Florida
United States ; Florida Less -
Edition:
December 2020
Corporate Publisher:
Florida. Department of Transportation
Abstract:
Benefits of lightweight concrete include reduction in the self-weight of the girder and reduction in transportation and handling costs, as well as potentially longer spans. Lightweight concrete can be produced with strength equivalent to normal-weight concrete. However, FDOT does not currently have an approved lightweight concrete mix for girders. The objective of this research was to study the implementation of lightweight concrete in girders. The following tasks were performed: a lightweight concrete mix was developed; the fresh and hardened mechanical properties were measured, lightweight concrete bridge girders were constructed, and the camber behavior of the girders was measured. At a later date, the flexural/shear behavior of girders may be studied. The self-consolidating lightweight concrete mix that was developed for use in the girders had a design compressive strength of 10 ksi, which is higher than the 8.5- ksi strength of FDOT’s standard concrete mix for girders. The 10 ksi strength was achieved 11 days after casting the test girders, and the strength at 28 days was 11.22 ksi – 12% higher than the specified strength. The measured unit weight was 0.126 k/ft³, slightly higher than the design unit weight of 0.122 k/ft³. The developed lightweight concrete mix satisfied FDOT’s mix design requirements. The fresh properties – including slump, air content, and penetration – were evaluated before casting the concrete. The hardened properties – including unit weight, compressive strength, modulus of elasticity, splitting tensile strength, and modulus of elasticity – were evaluated by testing concrete cylinders and small beams, which were cast from the batches used to fabricate the girders. The current AASHTO LRFD equations are limited to lightweight concrete compressive strength of 10 ksi. This study investigated the applicability of AASHTO equations for lightweight concrete compressive strength higher than 10 ksi. The average measured modulus of elasticity was 4,875 ksi, which was 15% higher than the calculated value using the AASHTO equation. Because no physical test was performed on the lightweight aggregate, the K1 factor was assumed as 1.0. The average measured splitting tensile strength of the lightweight concrete was 0.618 ksi, or 0.185√??c'. AASHTO LRFD Section 5.4.2.8 conservatively estimated the concrete density modification factor (??). The average measured modulus of rupture was 0.895 ksi, which is 19% higher than the value calculated using the AASHTO equation. It can be concluded that the current AASHTO equations conservatively estimate the hardened materials properties of the lightweight concrete mix used in this study, which had a compressive strength higher than 10 ksi. Five 42-ft-long AASHTO Type II girders were fabricated: two (2) used the lightweight concrete mix described above, and three (3) used normal-weight concrete. Girder cambers were monitored over time. Short-term camber measurements were compared between lightweight and normal-weight girders. The average measured cambers at 33 days were 0.605 in. and 0.688 in. for normal-weight Girders (A1, A2, and A3) and lightweight Girders (D1 and D2), respectively. Lightweight concrete girders had higher camber because of their lower elastic modulus. Long-term cambers of the lightweight girders were compared with values obtained using the PCI multiplier method and FDOT Prestressed Mathcad program v5.2. The short- and long-term cambers of lightweight girders were overestimated by both the PCI multiplier method and the FDOT program, where the PCI multiplier method was the most conservative. The average measured camber of lightweight girders at 380 days was 0.75 in., which was 67% of the calculated camber by FDOT program. The two lightweight concrete girders are currently stored at the FDOT SRC and will be experimentally tested in flexure or shear after adding a deck slab to investigate the structural behavior of high-strength lightweight concrete girders.
Format:
PDF
Funding:
BDV30-977-22
Collection(s):
US Transportation Collection
Main Document Checksum:
[+]
urn:sha256:82c8ff4b559b37fac2d85e4cc66b0018b8a752943c106769dfc172508e90d39b
Download URL:
https://rosap.ntl.bts.gov/view/dot/60647/dot_60647_DS1.pdf
File Type:

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