Civil Engineering ETDs

Rick Grahn

Publication Date

8-30-2011

Abstract

Self-consolidating concrete (SCC) is a relatively new type of concrete that has the ability to flow under its own weight such that it can pass through tightly spaced reinforcement and fill corners of molds without the use of mechanical vibration. Due to the favorable plastic properties of SCC, there has been an increased interest in using SCC in precast and pre-stressed bridges. However, SCC achieves this flowability by reducing the maximum aggregate size in the concrete mix, significantly increasing the volume of the cement paste and incorporating large content of powder fillers. This mix design of SCC was hypothesized to affect two critical criteria for concrete used in bridges: creep and crack propagation. Therefore, this study is focused on investigating creep and fracture toughness of SCC. Furthermore, we compare creep and fracture toughness of SCC with that of normal vibrated concrete (NVC) typically used in bridge applications in New Mexico. Five different SCC mixes were designed using two different New Mexico aggregate sources and varying amounts of fly ash ranging from 20-40% by weight of Portland cement. Two NVC mixes using the same local aggregate were produced for comparison. Creep of SCC was measured experimentally and compared to commonly used code prediction models including AC1 209R-92 and CEB-FIP MC90-99. Three of the SCC mixes with varying amounts of fly ash (20%, 30%, and 40% by weight of Portland cement) were also tested to classify SCC fracture toughness as a function of fly ash content. Two fracture tests including the stiff tension fracture test and the notched beam level II test were conducted. The two tests provided good information on the significance of increasing powder content (here fly ash) on fracture toughness of SCC. Based on the experimental observations, it was concluded that SCC with high volume fly ash exhibited higher creep strains than conventional vibrated concrete mixes. However, the aggregate source also played an important role in controlling creep of SCC. SCCs produced using Placitas aggregate showed significantly higher creep compared with that produced using Griego and Sons aggregate. A modification of the ACI code was necessary to enable the prediction of creep in SCC. On the other hand, the CEB-FIP code was able to successfully predict creep of all SCCs mixes. It was also concluded that fracture toughness of SCC decreased as the fly ash content in the mix increased. The significance of increasing the cement paste volume and eliminating the large aggregate on reducing fracture toughness of SCC is evident.

Keywords

Self consolidating concrete, Concrete--Creep, Concrete--Fracture, Fly ash.

Sponsors

New Mexico Department of Transportation

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Gerstle, Walter

Second Committee Member

Maji, Arup

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