Date of Award

Winter 12-20-2019

Level of Access

Open-Access Thesis

Language

English

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Eric Landis

Second Committee Member

Roberto Lopez-Anido

Third Committee Member

Warda Ashraf

Abstract

Cellulose Nanofibers (CNFs) are used as additives in cement-based products to modify their properties. Recent studies about the effects of CNFs on cement paste showed inconsistent results for several different important properties, including compressive strength and free shrinkage. There is reason to believe that the unsystematic results of the compressive strengths were affected by the lack of uniform dispersion of CNFs. As a potential remedy, two different mixing methods were applied. The first method used a basic mixer, but aggregates were added to the cement paste mixture to improve the blending process. The second method utilized a high-speed shear mixer to blend the cement paste. To understand the effect of CNF on cement product’s properties, different tests were applied to the specimens. For the specimen mixtures that followed the first method, tests were run for workability, compressive strength and drying shrinkage. Each experiment tested 24 batches. These batches can be divided into three groups of different water to cement ratios of 0.4, 0.45, and 0.5. Each group has batches with four different CNF percentages of 0%, 0.05%, 0.1%, or 0.2%. All of these groups also include two cement to sand ratios of 0.5 or 1.

The results from the compressive strength test showed a somewhat more systematic relationship with the CNF percentage. However, this trend shows a decrease in compressive strength when CNF concentration increases. The workability of the 24 batches were tested using the flow table test. The results showed a decrease of workability as the CNF percentages increased. An equivalent water-cement ratio was estimated based on the variations in workability. Free shrinkage results show a decrease in shrinkage over time but do not show a clear pattern with the CNF percentage of the mixtures.

For the second method, compressive strength was tested with the same water to cement ratio and CNF percentage used in the first method, but with no aggregates. The outcome of this compressive test showed a similar trend as the results of specimens blended with the same method. This finding also supports the hypothesis that aggregates were effective on increasing the quality of the blend. To test the effect of the high-speed shear mixer on the workability of the cement paste, different batches were used. A higher water to cement ratio has high workability, therefore it fails while using the flow table test. To avert that problem, water to cement ratio of 0.3, 0.35, and 0.4 were used with the same CNF percentages of 0%, 0.05%, 0.1%, 0.2%. This projects compares the workability of these batches mixed with the high-speed shear mixer compared to the basic mixer. Using the high-speed mixer resulted into a more workable mixtures which had a different texture in comparison to the mixtures blended with the basic mixer.

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