Semester

Fall

Date of Graduation

2018

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Roger H. L. Chen

Committee Co-Chair

Yoojung Yoon

Committee Member

Yoojung Yoon

Committee Member

Fei Dai

Committee Member

Hailin Li

Abstract

In this study, the modified double power law (MDPL) model is used to determine the tensile creep of concrete at an early age based on the ASTM C1581 restrained shrinkage ring test. Three concrete mixes using Ordinary Portland Cement (OPC) were tested. The three concrete mixes were cast, and each underwent the ring tests up to cracking. Mechanical properties of concrete at the age of 1, 3, 7, 14, and 28 days were tested to find the compressive strength, tensile strength and Young’s Modulus of concrete. The strength tests results were obtained from both 4x8 inch and 6x12 inch cylinders. The moisture distribution of the concrete inside the ring was simulated and solved theoretically by solving Fick’s law of diffusion equation. On the other hand, humidity sensors (SHT-21) were used at different depths to verify the theoretical solution. The interfacial compressive stress generated on the steel ring, caused by autogenous and drying shrinkages of concrete, is calculated using the experimentally measured steel strains during the restrained shrinkage ring testing. Meanwhile, the theoretical value of the interfacial compressive stress is calculated by a model with a known value of autogenous shrinkage and drying shrinkage of concrete. The tensile creep of the concrete at early age was then determined by comparing the theoretical interfacial compressive stress with the interfacial compressive stresses obtained from the strain gage measurements.

Finite Element Model (FEM) simulation was performed using ABAQUS to analyze the shrinkage and creep behavior in the concrete under the Restrained Shrinkage Ring Test. The calculated humidity was used as an input in the FEM to calculate the shrinkage in concrete for a 5-layer concrete ring model through a user-defined subroutine. Concrete tensile creep was also calculated from the subroutine using the shrinkage induced stress. The predicted creep behavior was verified by comparing the steel strain obtained from the experiment with what was solved using FEM. Furthermore, a stress analysis was performed to predict the critical time when the concrete is at risk of cracking in the concrete ring. Using this method, creep relaxation parameters were obtained for the concrete mix under different environmental temperatures and humidity, thus, can be used under any other ambient environment. The determined tensile creep, as a result, can be used in shrinkage-induced stress analyses, and further, be used for cracking control of concrete structures at early age.

Embargo Reason

Publication Pending

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