Date on Master's Thesis/Doctoral Dissertation

12-2020

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Civil and Environmental Engineering

Degree Program

Civil Engineering, PhD

Committee Chair

Zhihui, Sun

Committee Co-Chair (if applicable)

Satyavolu, Jagannadh

Committee Member

McGinley, William Mark

Committee Member

Kim, Young Hoon

Committee Member

Sathitsuksanoh, Noppadon

Author's Keywords

cement; concrete; cementitious material; lignocellulosic biomass; chemical treatment; finite element

Abstract

The disposal of lignocellulosic biomass wastes imposes a huge economic and environmental burden on this society. Recycling lignocellulosic biomass wastes and applying them to cementitious materials provides a sustainable and value-added way for both agriculture and concrete industries. To comprehensively identify the effect of lignocellulosic biomass wastes at different scales on cementitious materials, the hydration, shrinkage, cracking, and mechanical properties of cementitious materials with lignocellulosic biomass wastes were studied. Given the three different forms (powders, chips, and fibers) of lignocellulosic biomass wastes in this study, the research was implemented in three stages. In the first stage, hemp powders were collected through grinding the residual of hemp products and then chemically treated using saturated lime water to partially remove hemicellulose, lignin, and impurities. The effect of untreated and treated hemp powders on the hydration of cement paste was studied. It was found that partially replacing cement with untreated and treated hemp powders can delay cement hydration. Compared with untreated hemp powders, treated (washed or nonwashed) hemp powders showed a lower delay effect on cement hydration, distilled-water-washed treated hemp powders delayed less than nonwashed treated hemp powders, and coarse hemp powders exerted a lower delay effect on cement hydration than fine hemp powders. In the second stage, ground wood chips were lightly or highly torrefied and then used to partially replace sand in mortar. The effect of non-torrefied and torrefied ground wood chips on the mechanical properties of mortar was studied. Compared to the mortar containing non-torrefied ground wood chips, those containing highly or lightly torrefied ground wood chips were found to have higher flexural strength and compressive strength due to the enhanced bonding between the wood chips and paste matrix. Although all the tested mortars with ground wood chips have lower strength than the mortar without any wood chips, their toughness was found to be comparable or higher, indicating better energy absorption capacity. In the third stage, kenaf fibers were chemically treated using different inorganic chemicals. The characteristics of raw and chemically treated kenaf fibers were investigated through a series of tests. It was found that chemically treated kenaf fibers have lower hemicellulose and extractives, lower moisture sorption capacity, and higher tensile strength and crystallinity index. And then, alkaline treated and alkaline-hydrogen peroxide treated kenaf fibers, together with raw kenaf fibers, were selected to be used as reinforcements in cementitious materials. The effect of these three types of kenaf fibers on the autogenous shrinkage, drying shrinkage cracking, and flexural behavior of cementitious materials was studied. It was found that compared to raw kenaf fibers, these two treated kenaf fibers can lead to reduced shrinkage and cracking and also improved flexural strength and toughness. This research provides some guidance for the future application of lignocellulosic biomass at different scales to non-structural concrete elements (such as pavement and roof). Hemp powders can be used to partially replace cement, with a dosage limit of 10% by weight of cement. Wood chips can be used to partially replace sand, with a recommended replacement level of 10% by weight of sand for OW and HTW, and a recommended replacement level of 5% for LTW. Kenaf fibers can be used as reinforcement, with a recommended dosage of 0.5% by weight of cement (or 0.12-0.24% by volume of the composites).

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