Fiber-reinforced Geopolymer Research Articles

Performance characteristics of micro fiber-reinforced geopolymer mortars for repair

Abstract Fiber reinforced geopolymer materials are recently being considered as prominent sustainable repair materials for concrete retrofitting/repair due to their good bonding properties. The addition of fibers to geopolymers materials may considerably improve their mechanical properties but they also effect on physical properties such as setting, workability, density, porosity. It is crucial to understand these characteristics of micro fiber reinforced geopolymer mortars before optimizing the micro fiber for geopolymer mortars for repair. In this study, the effects of micro fiber type and fiber volume fraction on the physical characteristics and on flexural behavior are investigated. In addition, the influence of different heat curing durations on the properties of micro fiber reinforced geopolymer mortars is also examined. Six types of micro fibers (high-strength steel, waste steel wool, polyvinyl alcohol, polypropylene, polyester & carbon) at low fiber volume fractions of 0.5%, and 1.0% are considered to study the physical properties (workability, and total porosity) and flexural behavior of fly ash-based geopolymer mortars. High strength steel fibers imparted the least change in workability whereas with polyester fibers the flow was the lowest. Porosity as well was highest for polyester fiber reinforced mortars followed steel wool and polypropylene. Significant improvements in the flexural behavior and compressive strength due to micro fiber reinforcement are noted particularly in steel and polyvinyl alcohol fibers. Deflection hardening was observed for mortars with 1% polyvinyl alcohol fibers, and for both 0.5% and 1% steel fibers. The overall flexural performance of polyester, steel wool, and carbon fibers reinforced geopolymer mortars was dismal. Increasing the duration of heat curing from 4 h to 24 had little change in total porosity and compressive strength. In flexural behavior however, the effect of prolonged heat curing was more noticeable.

MECHANICAL AND MICRO-STRUCTURE CHARACTERIZATION OF STEEL FIBER-REINFORCED GEOPOLYMER CONCRETE

This paper aims to investigate the mechanical performance of steel fiber-reinforced geopolymer concrete made with fly ash and ground granulated blast furnace slag as blended aluminosilicate source material. To activate the binding phase, combinations of sodium silicate (SS) and sodium hydroxide (SH) solutions with three different molarities (8M, 10M, and 14M) were used. Steel fibers were added to the geopolymer concrete mix in varying proportions up to 3%, by volume. Constant binder, activator solution, and aggregate contents were adopted for all 13 mixes. Samples were cast and cured at ambient conditions for measuring the rheological and mechanical properties, including slump, modulus of elasticity, compressive strength, tensile splitting strength, and flexural strength. Experimental test results show that geopolymers made with higher molarity of SH were less workable but had improved mechanical performance. The effect of adding steel fibers on the mechanical performance was more apparent at an early age and in weaker geopolymer concretes. Additionally, scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy highlighted the co-existence of calcium aluminosilicate hydrate and sodium aluminosilicate hydrate gels.

Mechanical and Microstructural Properties of Polypropylene Fiber-Reinforced Geopolymer Composites

Mechanical and Microstructural Properties of Polypropylene Fiber-Reinforced Geopolymer Composites

Hybrid fibre-reinforced geopolymer (HFRG) composites as an emerging material in retrofitting aging and seismically-deficient concrete and masonry structures

Fibre-reinforced polymer (FRP) systems have recently become popular in repairing concrete or masonry structures because of their inherent advantages. In spite of these benefits, FRPs have drawbacks having low fire resistance, poor environmental sustainability and incompatibilty with the substrate concrete. The effort to address these issues has led to the development of an emerging strain hardening cementitious (SHC) material using an inorganic polymer known as hybrid fibre-reinforced geopolymer (HFRG) composites. Compared with cement-based SHC composites, HFRG has better bond performance to concrete substrates, higher fire resistance, greater corrosion durability and helps to reduce CO2 emissions. This paper reviews the recent development of HFRG composites as an emerging repair material. Literature reveals that flowability of a fresh HFRG mixture decreases with increasing fibre content though still workable up to 2% fibre volume. Fibre synergy could result in 10–181% higher flexural toughness of geopolymer composites than when just using mono fibres. The application of HFRG composites to RC beams increased displacement ductility by to 263%. To date, there has been no reported field application of HFRG as a repair material though mono-fibre FRG has been field-applied as a strengthening material in large-diameter sewer RC pipes, RC culverts, RC sewerage manholes and dam surface improvement.

Effect of Polypropylene Fibre Addition on Properties of Geopolymers Made by 3D Printing for Digital Construction.

This paper investigates the effect of polypropylene (PP) fibres on the fresh and hardened properties of 3D-printed fibre-reinforced geopolymer mortars. Different percentages of PP fibres ranging between 0.25% and 1.00% by volume were added to an optimised geopolymer mixture. All samples showed reasonable workability and extrudability. In addition, shape-retention ability in the fresh state was investigated as a major requirement for 3D-printing. The compressive strength of the printed specimens was tested in the hardened state in three loading directions, viz. longitudinal, perpendicular, and lateral. The flexural strength of samples was also tested in the longitudinal and lateral directions. In addition, the interlayer bond strength was investigated. Fibre addition seems to influence compressive strengths positively only when the loading is perpendicular to the interface plane. This is due to the preferential fibre alignment parallel to the direction of extrusion. The addition of fibre significantly enhanced the flexural performance of the printed samples. The use of fibre dosages of 0.75 and 1.00 vol % caused deflection-hardening behaviour of the 3D-printed geopolymers and, hence, a significantly higher fracture energy in comparison to specimens without fibre or with lower fibre content. However, an increase in the fibre volume caused some minor reduction in interlayer bond strength. With respect to properties in the fresh state, higher fibre volumes caused better shape-retention ability in the printed samples. The results indicate the possibility of printing fibre-reinforced geopolymers which meet all the necessary properties in both the fresh and hardened states.

Effect of Type of Fiber on Inter-Layer Bond and Flexural Strengths of Extrusion-Based 3D Printed Geopolymer

Extrusion-based 3D concrete printing is analogous to fused deposition modeling method, which extrudes cementitious materials from a nozzle to build a complex concrete structure layer-by-layer without the use of expensive formwork. This study aims to investigate the influence of type of fiber on inter-layer bond strength and flexural strength of extrusion-based 3D printed geopolymer. An extrudable fly ash-based geopolymer composition previously developed by the authors was reinforced by three types of fibers, namely polyvinyl alcohol (PVA), polypropylene (PP) and polyphenylene benzobisoxazole (PBO) fibers. Control geopolymer specimens with no fiber were also 3D printed for comparison purposes. The results indicated that the incorporation of fibers reduced the inter-layer bond strength of 3D printed geopolymer. This pattern was true regardless of the type of fiber. On the other hand, the flexural strength of 3D printed fiber-reinforced geopolymer mixtures was substantially higher than that of the 3D printed geopolymer with no fiber. The rate of increase in the flexural strength depended on the type of fiber. The flexural failures of the specimens were due to the tensile failure of the bottom layer, rather than the shear failure of the interfaces.

Assessment of Na2SiO3 to NaOH ratio impact on the performance of polypropylene fiber-reinforced geopolymer composites

The aim of this project is to build and use a concrete with minimum irritating impacts on the environment, reasonable price and optimal properties. Geopolymer concrete is new class of mineral binder that due to the high durability, very low energy consumption, very low CO2 emission, low investment cost and also special properties, is distinguished of other mineral binder such as Portland cement. In this study, after construction of metakaolin-based geopolymer concrete containing 0.3, 0.5 and 1% polypropylene (PP) fibers with monomer ratios of 2, 2.5 and 3, engineering properties including compressive strength, flexural strength, displacement, Si/Al ratio, water absorption and electrical resistivity were assessed. Microstructural and structural changes of geopolymers as a result of lead addition/immobilization were evaluated via scanning electron microscopic (SEM) and X-ray Diffraction (XRD) tests. The obtained results showed that using PP fiber in geopolymer samples increased the flexural strength by 28%. Furthermore, as evidenced by XRD diffractogram, the compressive strength improved by increasing the SS/SH ratio due to the formation of crystalline nepheline in the geopolymer specimens. In addition, images of electron microscopy of hardened geopolymer paste confirmed the remarkable increase in the density and uniformity of polymer products in the presence of suitable monomer ratios. In general, it is reported that using 1% PP fibers along with the sodium silicate to sodium hydroxide ratio of 3 had an acceptable outcome in improving geopolymer concrete performance from point of view of environmentally, structurally and economically.

Comparative Study of Strength of Fibre Reinforced Geo polymer Concrete and Conventional OPC Concrete

Comparative Study of Strength of Fibre Reinforced Geo polymer Concrete and Conventional OPC Concrete

Strength and Durability Characteristics of Steel Fibre Reinforced Geopolymer Concrete

Owing to the upturn inrepair and rehabilitation of structures that undergoes deterioration even before its intended life span; it has become necessary to study the durability properties of the structures. This paper deals with an experimental approach on the strength and durability characteristics of Geopolymer Concrete and Steel Fibre Reinforced Geopolymer Concrete with varying proportions of Fly ash, Waste Glass powder and GGBS (Ground Granulated Blast furnace Slag) as base material cured at room temperature. Sodium hydroxide (14M) and Sodium silicate are used as alkali activators. Steel fibres of length 60mm, 0.75mm diameter are used in two different proportions (0.25% and 0.50%). The results are compared with that of the Portland cement based plain and fibre reinforced control concrete. The durability characteristic involved in this study is Sorptivity test. The results reveal that Steel fibre reinforced Geopolymer concrete procures surpassing characteristics than that of Geopolymer concrete which in turn possess superior characteristics than that of conventional concrete.

Behaviour of Ambient Cured Steel Fibre Reinforced Geopolymer Concrete Columns Under Axial and Flexural Loads

This study investigates the behaviour of ambient cured geopolymer concrete column specimens reinforced with steel fibres under different loading conditions. Three types of steel fibres (straight micro steel fibre, deformed macro steel fibre and hybrid steel fibre) were used in reinforcing the geopolymer concrete column specimens. Also, geopolymer concrete column specimens without steel fibre were tested as reference column specimens. Sixteen circular geopolymer concrete column specimens of 150 mm diameter and 600 mm height were cast and tested. The influences of the addition of different types of steel fibres and the loading conditions (concentric axial load, eccentric axial load and four-point bending) on the performance of the geopolymer concrete column specimens were investigated. The test results showed that the peak axial load and bending moment of fibre reinforced geopolymer concrete column specimens were higher than those of the geopolymer concrete column specimens without steel fibres under different loading conditions. Also, the addition of different types of steel fibres resulted in significant improvements in the ductility of the geopolymer concrete column specimens. The addition of hybrid steel fibre showed the highest improvement in the peak axial load, bending moment and the ductility of ambient cured geopolymer concrete column specimens.

Mechanical Properties of Fibre Reinforced Geopolymer Composites Exposed to Operating Fluids

Geopolymers are amorphous aluminosilicate materials which combine low temperature, polymer-like processing with high temperature stability and fire resistibility without toxic smoke generation. For larger expansion of geopolymer composites in aircraft industry, it is necessary to know how it behaves in contact with operating fluids. The specimens were divided into groups exposed to fuel, hydraulic oil, jet oil, and salt mist. Hot/Wet condition until saturation was also applied for one group. Mechanical testing was performed by means of tension, compression, in-plane shear, flexion and interlaminar shear on both reference non-treated and exposed specimens. The largest decrease in all measured strength values was caused by the salt mist. As the most significant, in-plane shear strength was decreased by 85 % by this environment. Operating fluids and hot/wet conditions decreased the shear strength approx. by 15 %. Geopolymer composites are an interesting alternative to existing polymeric and ceramic matrix materials and offers high potential for cost-efficient applications dealing with temperatures up to 1 200°C.

Current Challenges in Average Residual Strength Evaluation of K-Silicate-Based Fiber-Reinforced Geopolymer Concrete

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Effects of cellulose, hemicellulose, and lignin on the morphology and mechanical properties of metakaolin-based geopolymer

Natural fiber-reinforced geopolymer has attracted wide attention in construction and building materials due to its low cost, low density, and excellent mechanical properties. Cellulose, hemicellulose, and lignin are the three basic components of natural fibres, and were investigated to reveal their influence on the metakaolin-based geopolymer. Comparative evaluations were investigated via morphology analysis and mechanical strength analysis. The results showed distinct microstructures and mechanical properties of the geopolymer-based materials with cellulose, hemicellulose, and lignin, respectively. A low content (5 wt%) of lignin, cellulose, and hemicellulose enhanced the flexural and compressive strength of pure geopolymer. Higher lignin and hemicellulose led to the porous morphology, lower density, and brittle fractures of geopolymer-based composites, which reduced the flexural and compressive strength in these geopolymer-based composites. It was noted that the degree of geopolymerization was clearly lowered by the alkaline degradation of hemicellulose. With the increase in cellulose content, in contrast, the denser structure and fewer pores of the geopolymer matrix were detected, as well as ductile failures of geopolymer-based composites. Good bonding was also shown between the geopolymer matrix and cellulose fibres without remarkable degradation. The results of this study will facilitate a better understanding of the effect of lignocellulosic biomass in natural fibre-reinforced geopolymers and should serve as the basis for further research and applications.

Experimental Investigation on the Effect of Corrosion on the Bond Between Reinforcing Steel Bars and Fibre Reinforced Geopolymer Concrete

This paper investigates the effect of corrosion on the bond between reinforcing steel bars and fibre reinforced geopolymer concrete. An accelerated corrosion method was used to corrode the reinforcing steel bars embedded in geopolymer concrete. Three types of steel fibres including straight micro steel fibre, deformed macro steel fibre, and hybrid steel fibre were used in this study. A total of ten geopolymer concrete mixes were used to evaluate the effect of corrosion of steel bar on the bond between steel bar and fibre reinforced geopolymer concrete. The pull-out test specimens were composed of concrete cubes with a side length of 160mm and reinforced with a deformed steel bar of 16 mm diameter located at the centre of the specimens. The test results showed that the addition of steel fibres in geopolymer concrete (fibre reinforced geopolymer concrete) significantly enhanced the bond strength of reinforcing steel bar. The bond strength of reinforcing steel bars embedded in steel fibre reinforced geopolymer concrete specimens reduced due to corrosion of reinforcement. However, the reduction of bond strength in steel fibre reinforced geopolymer concrete specimens was less than the reduction of bond strength in plain geopolymer concrete specimen.

An integrated design method of Engineered Geopolymer Composite

Strain-hardening ductile fiber-reinforced geopolymer composite, named Engineered Geopolymer Composite (EGC), is a promising material for achieving green and durable civil infrastructure. Despite increasing attentions of the unique material, inefficient trial-and-error approaches are often employed in the material design, which slows the research and development. This paper proposed a new design methodology of EGC that integrates three design techniques: Design of Experiment (DOE), micromechanical modeling, and Material Sustainability Indices (MSI). The mix design of a preliminary version of EGC was optimized to achieve higher compressive strength, maintain high tensile ductility, and enhance the material greenness simultaneously. With the aid of the systematic design process, an optimized EGC with improved compressive strength of 43.1 MPa and high tensile ductility of 4.7% was developed, while achieving 11% less embodied energy and 55% less CO2 equivalent emissions compared with a standard Engineered Cementitious Composite (ECC). Therefore, the applicability and effectiveness of the proposed design method were successfully demonstrated.

Development of Abaca Fiber-reinforced Foamed Fly Ash Geopolymer

The growing environmental and economic concerns have led to the need for more sustainable construction materials. The development of foamed geopolymer combines the benefit of reduced environmental footprint and attractive properties of geopolymer technology with foam concrete’s advantages of being lightweight, insulating and energy-saving. In this study, alkali-treated abaca fiber-reinforced geopolymer composites foamed with H2O2were developed using fly ash as the geopolymer precursor. The effects of abaca fiber loading, foaming agent dosage, and curing temperature on mechanical strength were evaluated using Box-Behken design of experiment with three points replicated. Volumetric weight of samples ranged from 1966 kg/m3to 2249 kg/m3. Measured compressive strength and flexural ranged from 19.56 MPa to 36.84 MPa, and 2.41 MPa to 6.25 MPa, respectively. Results suggest enhancement of compressive strength by abaca reinforcement and elevated temperature curing. Results, however, indicate a strong interaction between curing temperature and foaming agent dosage, which observably caused the composite’s compressive strength to decline when simultaneously set at high levels. Foaming agent dosage was the only factor detected to significantly affect flexural strength.

Flexural performance and toughness of hybrid steel and polypropylene fibre reinforced geopolymer

In this study, the effects of steel and polypropylene fibre hybridization on the flexural performance of fibre-reinforced geopolymer were investigated. Fibre reinforcement has emerged as a way to improve the brittleness of geopolymer. There are currently several types of fibres available on the market. When polypropylene fibre is used, it usually yields a large drop in strength immediately after the first crack, as well as a lower post-peak response, owing to its high flexibility and low stiffness. To resolve these issues, a hybrid system is introduced using fibre with high strength and stiffness such as steel fibre. In the present study, two hybridization systems are investigated: replacement and addition systems. For a replacement system, the polypropylene fibre is replaced gradually with steel fibre at a rate of 0.2% by volume. For an addition system, the steel fibre is added into the mixture at the same rate. The results indicate that the hybridization of steel fibre can improve the flexural response, toughness, and residual strength of polypropylene fibre reinforced geopolymer to different degrees. Both the load dropping and second peak are found to improve almost instantaneously. The toughness and residual strength also increase gradually with an increase in steel fibre content.

Fracture Behaviour of Fibre Reinforced Geopolymer Concrete

Geopolymers have several applications and concrete is one of the materials that can be produced with geopolymer as binder. Since industrial byproducts/wastes such as fly ash, iron slag, micronized biomass silica, silica fume, red mud, etc. can be used as a binder instead of Portland cement, geopolymer concrete (GPC) has generated lot of interest among the scientific and engineering community. This has also resulted in reduced carbon footprint of concrete and an effective method of disposing industrial waste. In this study GPC with a blend of class-f fly ash and ground granulated blast furnace slag as binder has been developed, and its flexural and fracture characteristics have been studied. The GPC developed has a 28-day compressive strength in the range 40-50 MPa. Incorporation of steel fibres resulted in increased flexural strength, enhanced fracture properties and ductility. The residual strength of steel fibre reinforced GPC was also determined in the study.

Chemical Treatment of Waste Abaca for Natural Fiber-Reinforced Geopolymer Composite.

The use of natural fibers in reinforced composites to produce eco-friendly materials is gaining more attention due to their attractive features such as low cost, low density and good mechanical properties, among others. This work thus investigates the potential of waste abaca (Manila hemp) fiber as reinforcing agent in an inorganic aluminosilicate material known as geopolymer. In this study, the waste fibers were subjected to different chemical treatments to modify the surface characteristics and to improve the adhesion with the fly ash-based geopolymer matrix. Definitive screening design of experiment was used to investigate the effect of successive chemical treatment of the fiber on its tensile strength considering the following factors: (1) NaOH pretreatment; (2) soaking time in aluminum salt solution; and (3) final pH of the slurry. The results show that the abaca fiber without alkali pretreatment, soaked for 12 h in Al2(SO4)3 solution and adjusted to pH 6 exhibited the highest tensile strength among the treated fibers. Test results confirmed that the chemical treatment removes the lignin, pectin and hemicellulose, as well as makes the surface rougher with the deposition of aluminum compounds. This improves the interfacial bonding between geopolymer matrix and the abaca fiber, while the geopolymer protects the treated fiber from thermal degradation.

Low carbon building: Experimental insight on the use of fly ash and glass fibre for making geopolymer concrete

Abstract Due to the environmental impacts resulting from the production of Ordinary Portland cement (OPC), the drive to develop alternative binders that can totally replace OPC is gaining huge consideration in the construction field. In the current study, attempt was made to determine the strength characteristics of glass fibre-reinforced fly ash based geopolymer concrete. Sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3 ) were used as alkaline solutions (for activation of geopolymer reaction) at 12, 16, 20 M. Glass fibres were added to the geopolymer concrete in varying proportions of 0.1–0.5% (in steps of 0.1%) by weight of concrete. A constant weight ratio of alkaline solution to fly ash content of 0.43 was adopted for all mixes. British standard concrete test specimens were cast for measuring compressive strength, split-tensile strength, and flexural strength. Concrete specimens were cured by heating in oven at 90 °C for 24 h and natural environment, respectively. From the results, thermally cured concrete samples had better mechanical properties than the ambient (natural) cured samples. Thermally cured concrete specimen, containing 0.3% glass fibre and 16 M NaoH, achieved a maximum compressive strength of 24.8 MPa after 28 d, while naturally cured samples achieved a strength of 22.2 MPa. There was substantial increase in tensile strength of geopolymer concrete due to the addition of glass fibres. Split tensile strength increased by 5–10% in glass fibre-reinforced geopolymer concrete, containing 0.1–0.5% glass fibre and 16 M NaoH when compared to the unreinforced geopolymer concrete (1.15 MPa).