Characterization of Alkali-Activated Nonwood Biomass Ash–Based Geopolymer Concrete Faris Matalkah 1 ; Parviz Soroushian, F.ASCE 2 ; Anagi Balchandra 3 ; and Amirpasha Peyvandi, A.M.ASCE 4 Abstract: The combustion ash of a common nonwood biomass (wheat straw) was evaluated for value-added use in production of geo- polymer concrete where alkali aluminosilicate hydrates are the primary binder constituents. The wheat straw ash was supplemented with other raw materials in order to achieve a desired chemical balance. The binder composition that performed well in experimental work comprised wheat straw ash:coal fly ash:metakaolin:gypsum at 0.50:0.25:0.25:0.05 weight ratios. The wheat straw ash–based concrete as well as a control portland cement concrete were subjected to a comprehensive experimental investigation. The workability, set time, compressive strength, residual compressive strength after immersion in boiling water, flexural strength, density, moisture absorption, voids content, capillary sorptivity, and acid and fire resistance of concrete materials were evaluated. The experimental results indicated that the nonwood biomass ash–based geopolymer concrete materials with proper binder formulation can provide desired mechanical attributes, moisture barrier qualities, durability, and fire resistance when compared with normal portland cement concrete. DOI: 10.1061/(ASCE)MT.1943-5533 .0001801. © 2016 American Society of Civil Engineers. Author keywords: Nonwood biomass; Combustion ash; Geopolymer concrete; Strength; Durability; Sorptivity; Acid resistance; Fire resistance. Introduction Biomass is finding growing applications as a renewable, carbon- neutral source of energy, and also as a valuable resource in biore- fineries (James et al. 2012). From agricultural lands, the United States can produce nearly 1 billion dry tons/year of biomass while still meeting food, feed, and export demands (Perlack et al. 2005). The relatively high silica and alkali contents of nonwood bio- mass ash suit production of alkali aluminosilicate hydrate binders in high-performance and sustainable geopolymer concrete materi- als (Matalkah et al. 2016). The high alkali content of nonwood biomass ash does not favor its use as a pozzolan in conventional portland cement concrete. The excellent impermeability, robust chemistry, molecular-scale pore structure, and high alkalinity of geopolymer binders based on alkali aluminosilicate hydrates enable value-added use of the relatively high silica and alkali contents of biomass ash, provide for stabilization of any harmful constituents of the ash, and effec- tively protect the steel reinforcement in concrete against corrosion (Chindaprasirt et al. 2013). Use of biomass ash as a source of alu- minosilicates and alkalis and the enabling role of biomass ash in alkali-activated aluminosilicate binder incorporating properly selected alkali-activators would benefit the sustainability and the economics of the new concrete materials versus ordinary portland cement–based concrete (Rajamma et al. 2012). The desired solidi- fication and stabilization, durability, and barrier qualities of alkali aluminosilicate hydrate binders translate into additional environ- mental benefits. Finally, biomass ash–based alkali-activated alumi- nosilicate formulations are amenable to development of one-part (all-inclusive) reactive powder blends which, similar to portland cement, require only the addition of mixing water to solidify. Various types of ash with properties similar to those of nonwood biomass combustion ash have found applications as raw materials in alkali-activated aluminosilicate (geopolymer) concrete materials (Autef et al. 2012). Coal fly ashes that meet the criteria for use as pozzolans in ordinary portland cement concrete have been common sources of aluminosilicates for production of alkali-activated con- crete. For example, Class F fly ash has been activated using sodium hydroxide solution (40.4% by weight) and sodium silicate solution (9.1% by weight Na 2 O, 28.9% by weight SiO 2 , and 62% by weight water) (Sarker et al. 2013). The binder in this alkali-activated con- crete comprised coal fly ash: sodium hydroxide solution:sodium silicate solution at 1.00:0.17:0.25 weight ratios. The resulting fresh concrete mixture was highly workable. It was cured at 60°C over 24 h (followed by exposure to ambient conditions), yielding desired engineering properties that surpassed those of ordinary portland cement concrete (Sarker et al. 2013). Fluidized bed combustion (FBC) is an efficient and environ- mentally friendly method of coal combustion. The fly ash from FBC contains high amounts of CaSO 4 and CaO due to the use of lime for SO 2 capture. These compounds hinder the use of FBC fly ash as a pozzolan in ordinary portland cement concrete because high CaSO 4 contents compromise the soundness of concrete (Chindaprasirt et al. 2013). Substantial amounts of FBC fly ash are thus disposed of in landfills. Geopolymers have been prepared successfully with FBC fly ash, using AlðOHÞ 3 to sup- plement the alumina content of solution, and adequate concen- trations of NaOH to control ettringite formation. The FBC fly 1 Ph.D. Student, Dept. of Civil and Environmental Engineering, Michigan State Univ., 1542 Linden St., East Lansing, MI 48823. E-mail: Matalkah@msu.edu 2 Professor, Dept. of Civil and Environmental Engineering, Michigan State Univ., 3546 Engineering Building, East Lansing, MI 48824-1226. E-mail: Soroushi@egr.msu.edu 3 Senior Scientist, Metna Co., 1926 Turner St., Lansing, MI 48906. E-mail: Abmetnaco@gmail.com 4 Project Manager, Stantec Consulting Services, Inc., 500 Main St., Baton Rouge, LA 70801 (corresponding author). E-mail: Amirpasha. peyvandi@gmail.com Note. This manuscript was submitted on May 23, 2016; approved on August 29, 2016; published online on November 11, 2016. Discussion per- iod open until April 11, 2017; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil Engineering, © ASCE, ISSN 0899-1561. © ASCE 04016270-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 04016270 Downloaded from ascelibrary.org by Michigan State University on 11/14/16. Copyright ASCE. For personal use only; all rights reserved.