Plant fiber reinforced geopolymer – A green and high performance cementitious materialRui Chen (Graduate Student), Saeed Ahmari (Graduate Student), Mark Gregory (Undergraduate Student), Lianyang Zhang (Advisor)

Department of Civil Engineering and Engineering Mechanics, The University of Arizona

Background Sweet Sorghum Fiber Preliminary Results (Cont.)

Preliminary Results

Preliminary Results (Cont.)

Conclusions & Future Work

Research Approach

Ordinary Portland cement (OPC) is widely used in construction industry; but the utilization of OPC imposes an enormous impact on the environment. The manufacturing of OPC not only consumes significant amount of natural materials and energy but also releases substantial quantity of greenhouse gases. To produce 1 ton of OPC, about 1.5 tons of raw materials is needed and 1 ton of CO2 is released to the atmosphere. Worldwide, the cement industry alone is estimated to be responsible for about 7% of all CO2 generated. Another drawback for OPC is that it may not provide the required properties for specific applications, such as rapid development of mechanical strength and high resistance to chemical attack.

Recently, geopolymer has been of great research interest as an ideal OPC alternative for sustainable development. Geopolymer not only provides performance comparable to OPC in many applications, but has many additional advantages, including rapid curing, high acid resistance, excellent adherence to aggregates, immobilization of toxic and hazardous materials, and significantly reduced energy usage and greenhouse gas emissions. As OPC, however, geopolymer exhibits brittle behavior with low tensile strength and is sensitive to cracking. These shortcomings not only impose constraints in structural design, but also affect the long term durability of structures. Research has been conducted on utilizing steel, carbon, and glass to reinforce geopolymer. Although these fibers can effectively increase the tensile strength, ductility and toughness of geopolymer, they are all produced by a high energy-consuming process and there is concern about how to do with them at the end of their life cycle. Growing environmental awareness and the need to ensure sustainability of construction materials have led to efforts to look for alternative fibers. Recent years have witnessed an increasing interest in natural plant fibers because they are abundant, reproducible and environmentally friendly. So far researchers have studied utilization of natural fibers to reinforce OPC cementitious materials and very promising results have been obtained; but very little research has been conducted on utilizing natural fibers to reinforce geopolymer.

This project investigates the reinforcement of fly ash-based geopolymer with sweet sorghum fiber, a residue after sweet sorghum is used for production of biofuel.

The project takes a multi-scale and multi-disciplinary approach to investigate sweet sorghum fiber reinforced fly ash geopolymer.

Conclusions:The unit weight of geopolymer paste samples decreases

with higher sweet sorghum fiber content, which is beneficial for producing light weight cementitious material.

The inclusion of sweet sorghum fibers in geopolymer paste samples slightly decrease the UCS.

The tensile strength increases with the content of sweet sorghum fibers up to 2% and then decreases to be lower than that of the plain geopolymer paste sample.

The post-peak toughness increases significantly with the content of sweet sorghum fibers up to 2% and then slightly decreases but is still much higher than that of the plain geopolymer paste sample.

There is a clear transition from the brittle failure of the plain geopolymer specimen to the “ductile” failure of the geopolymer paste specimen containing sweet sorghum fibers.

Future Work:Conduct DEM simulations to investigate how the distribution

and orientation of fibers affect the mechanical properties.Conduct wet/dry cycling experiment to test the durability of

the composite.

Fly Ash-Based GeopolymerThe fly ash-based geopolymer is produced by using Class F fly ash in reaction with an alkaline hydroxide solution of 10 M concentration at ambient or slightly elevated temperature, which has an amorphous to semi-crystalline interconnected polymeric structure.

Fly ash Alkali (NaOH) Geopolymer pasteWater

Unit Weight & Unconfined Compression Strength

(a) Unit weight versus fiber content; and (b) UCS versus fiber content for sweet sorghum reinforced geopolymer paste samples

Split Tensile Test

(a) Split tensile test load and displacement curves; and (b) Effect of fiber content on tensile strength of geopolymer paste samples

(a) Definition of post-peak toughness; and (b) Effect of fiber content on post-peak toughness of geopolymer paste samples

Different failure modes

Different failure modes of geopolymer paste samples containing (a) no fibers; and (b) 1% sweet sorghum fibers

SEM Imaging

AcknowledgementThe research is supported by the National Science Foundation. The Campus Agriculture Center (CAC), University of Arizona, provided the sweet sorghum bagasse and the Salt River Materials Group, Phoenix, Arizona provided the Class F fly ash.

(a) (b)

Sweet sorghum bagasse: (a) As received; and (b) After treatment

Sweet sorghum is a potential crop for large scale production of biofuel. After the juice is extracted from sweet sorghum stalks for ethanol production, a large amount of bagasse is left behind. For large scale bioethanol production, it is a great challenge to handle the significant amount of bagasse. Because the bagasse contains high content of fibers, however, it has a great potential to be used for reinforcement of cementitious materials.

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Toughness

DEM Simulations

Durability Tests

Unconfined Compression Tests

Split Tensile Tests XRD Characterization

SEM/EDS ImagingFlexural Tests

AFM Nano-indentation

Pull-out Test

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