Abstract

Lightweight cellular concrete (LCC) consists of a mixture of cement, water, and a pre-formed foam. The pre-formed foam entrains a high proportion of air voids into the cement water slurry at the time of casting, decreasing the product's overall weight. LCC is also a viable alternative when low native soil strengths prevent the use of traditional backfill methods through mitigating settlement and increasing strength. Due to these benefits, the use of LCC behind mechanically stabilized earth (MSE) walls is gaining popularity. Despite LCC gaining popularity behind MSE walls, the exact nature of the failure envelope is poorly understood. The pullout resistance of welded wire reinforcement within LCC is poorly understood as well. This research attempts to add knowledge of LCC behind MSE walls by (1) performing pullout tests on welded wire reinforcements, (2) defining the apparent friction coefficient versus vertical stress, (3) defining LCC strength properties, and evaluating methods for global stability with welded-wire reinforcement. A large-scale test box (10 feet wide by 12 feet long by 10 feet high) supported by a steel resisting frame, was constructed, and filled with LCC backfill. The east wall consisted of a free face wall while the west wall consisted of a MSE concrete wall. The east free-face wall contained two different sizes of reinforcements (5.5 feet long and 4.5 feet long by 1.2 feet wide), six each, for a total of 12 welded wire reinforcements for pullout resistance testing. To determine the frictional component of the reinforcements, different uniform surcharge loads were applied consisting of the LCC self-weight, concrete reaction beams, and hydraulic jacks at the top of the backfill. After the pullout tests were completed, a surcharge was applied to the free-face wall until failure to determine the failure of lightly reinforced LCC. The west MSE wall contained 8 welded wire reinforcements (8 feet long by 2.5 feet wide) placed 2.5 feet vertically and 2.5 feet horizontally. A surcharge was placed on the west side until failure to determine the failure of reinforced LCC behind a MSE wall. Slope stability analyses were performed to back-calculate F* for the MSE wall test. These F* values were in good agreement with results from pullout tests and confirmed the validity of slope stability analysis for MSE wall with LCC backfill. Finally, a total of 120 LCC cylinder specimens were used to identify LCC material properties. Results of these tests show that the unconfined compressive strength of LCC is greatly dependent on the cast and cured unit weight, as well as the sample maturity. Comparing the UCS results to other work reveals a wide variation of UCS versus cured density, even though the same ASTM standard was applied for all tests. An equation for the secant modulus of LCC was created using UCS data from this thesis. Direct shear tests were also conducted on LCC cylinders cut to fit the confinement of a direct shear machine. Back-calculated shear strength parameters from the large-scale test box indicate a friction angle of 34 degrees and a cohesion of about 1700 psf.

Degree

MS

College and Department

Ira A. Fulton College of Engineering; Civil and Environmental Engineering

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2024-08-14

Document Type

Thesis

Keywords

lightweight cellular concrete, mechanically stabilized earth, MSE wall, welded wire reinforcement, pullout strength, pullout resistance, normalized pullout resistance, slope stability

Language

english

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