Showing papers on "Geopolymer published in 2020"

Fiber-reinforced geopolymer composites: A review

Abstract: There is a burgeoning interest in the development of geopolymers as sustainable construction materials and incombustible inorganic polymers. However, geopolymers show quasi-brittle behavior. To overcome this weakness, hundreds of research have been focused on development, characterization, and implementation of fiber-reinforced geopolymers for a wide range of applications. This paper discusses the rapidly developing state-of-the-art of fiber-reinforced geopolymer composites, focusing on material and geometrical properties of construction fibers, and underlying mechanisms on fiber-binder interaction at fresh and hardened states, mechanical properties, toughening mechanisms, thermal characteristics, and environmental durability. It is intended to build a strong conceptual and technical background for what is currently understood on fiber-reinforced geopolymers by tying the subject together with knowns for other similar cementitious composites rather than a historical report of literature.

Review on the research progress of cement-based and geopolymer materials modified by graphene and graphene oxide

Abstract: Abstract In recent years, with the higher requirements for the performance of cement-based materials and the call for energy conservation and environmental protection, a wave of research on new materials has set off, and various high-performance concrete and more environmentally friendly geopolymers have appeared in the public. With a view to solving the defects of energy consumption, environmental protection and low toughness of traditional cement-based materials. At the same time, nanomaterials have become a focus of current research. Therefore, the research on the properties of cement-based materials and geopolymers modified by graphene and its derivatives has aroused extensive interest of researchers. Graphene-based nanomaterials are one of them. Because of their large specific surface area, excellent physical properties have been favored by many researchers. This paper reviews the research progress of graphene-based nanomaterials in improving the properties of cement-based materials and geopolymer materials, and points out the main challenges and development prospects of such materials in the construction field in the future.

Evaluation of Glass Powder-Based Geopolymer Stabilized Road Bases Containing Recycled Waste Glass Aggregate:

Abstract: As the concept of sustainable pavement gains prominence, a growing number of industrial wastes and recycled materials have been utilized in the pavement industry to preserve natural resources. This...

Chloride diffusion resistance and chloride binding capacity of fly ash-based geopolymer concrete

Abstract: This study evaluated the chloride diffusion resistance of low-calcium fly ash-based geopolymer concrete through electrical and bulk diffusion techniques. The geopolymer concretes were prepared using 12 different heat curing conditions; three temperatures of 60, 75 and 90 °C and four curing durations of 8, 12, 18 and 24 h, as well as ambient curing. The mechanical and transport properties and microstructural characteristics of the geopolymer concretes were examined. NT BUILD 492 chloride migration and ASTM C1556 bulk diffusion tests were carried out. Results showed that the chloride diffusion resistance and the chloride binding capacity of fly ash-based geopolymer concrete is very low. The fly ash-based geopolymer concrete appears to be suitable for applications where there are little or no chloride-related durability concerns.

Development of ultra-high performance geopolymer concrete (UHPGC): Influence of steel fiber on mechanical properties

Abstract: This study reports the development of ultra-high performance geopolymer concrete (UHPGC) and overcoming the brittleness feature of geopolymer matrix by using different steel fibers. Four straight steel fibers with different aspect ratios and two different deformed steel fibers were investigated. Flowability, compressive strength and flexural behavior including strengths and deflection, and energy absorption capacity of UHPGC, were systematically evaluated. A deformation ratio of steel fiber was introduced to quantitatively correlate the steel fiber shape and the mechanical performance. The flowability of fresh UHPGC mixtures decreased when the fiber content and length increased, as expected, and was inconspicuously influenced by fiber shape. The increase in fiber content and the decrease of fiber diameter contributed to the improvement of the mechanical strengths of UHPGC. The flexural behaviors of UHPGC improved as the fiber volume and length increased, while the compressive and first crack strengths were affected by both curing conditions and fiber dosages as well. Different from Portland cement-based composites, the corrugated fibers with a higher deformation ratio added in UHPGC, had an inferior strengthening and toughening efficiency, while for straight fibers, those longer and smaller in diameter were more preferred. Finally, based on the previous research, a new one with adjustment and simplification was proposed for that of newly-developed UHPGC, and the fitted results had higher correlation coefficients (r2).

Spalling behavior of metakaolin-fly ash based geopolymer concrete under elevated temperature exposure

Abstract: Fire-induced spalling is a serious risk to concrete structures, especially for high strength concrete structures. This paper presents results from high temperature spalling tests on geopolymer concrete. The effect of moisture content, concrete strength, heating rate and temperature level on the spalling behavior of geopolymer concrete is studied. The temperature-induced spalling mechanism in geopolymer concrete is investigated through the measurement of residual compressive and splitting tensile strength, variation in permeability (by sorptivity test) and chemical composition (by X-ray diffraction test) of geopolymer concrete after elevated temperature exposure up to 700 °C. The test results indicate that geopolymer concrete exhibit a good spalling resistance as compared to that of OPC concrete. The lower spalling risk in geopolymer concrete under high temperature exposure is facilitated from the highly connected pore structures and lower strength degradation with temperatures. Further results indicate that the pore structure (permeability) of geopolymer concrete gets a significant evolution with the exposure temperature, especially above 500 °C range. This is related to the sintering reaction in geopolymer binders at high temperatures.

Current development of geopolymer as alternative adsorbent for heavy metal removal

Abstract: The deterioration of water quality is becoming serious due to continuous development. One of the major factors is heavy metal contamination, which is an extremely deleterious to the environment and human being. This work reviews current development of a potential alternative adsorbent, namely geopolymer, in removing heavy metal pollutants from water via adsorption techniques. Geopolymer adsorbent can be regarded as a sustainable material as it can be synthesized by utilizing waste material and by-products. Fabrication process, removal capability and factors governing the removal ability of geopolymer have been highlighted as well. As binding site is a salient criteria for the adsorption technique, enhancement in porosity of adsorbent, i.e. in porous and pervious geopolymer as well as different shapes of geopolymer, of which will influence the available binding sites, is also reviewed. The intention of this review is to provide some state-of-the-art of geopolymer technology in eliminating heavy metal pollutants from water.

Sulfate resistance of hybrid fiber reinforced metakaolin geopolymer composites

Abstract: This work aims to investigate the sulfate resistance of geopolymer composites prepared by alkali activation of metakaolin (MK) and reinforced with polypropylene fiber (PP), polyvinyl alcohol fiber (PVA) and wollastonite (WS). Compressive and flexural strength were measured to determine the optimum mix proportion of the composites. The sulfate resistance properties were evaluated by strength loss, mass loss, microstructure and pore structure changes after sulfate exposure. The experimental results show that the two groups containing 1% of PP + 1% of PVA and 2% of PVA +15% of WS, respectively, exhibit the highest compressive strength and flexural strength compared to non-reinforced mixtures. After sulfate exposure, the decreased compressive strength and mass loss are correlated to the concentration of sulfate and exposure period. In the simulated extreme marine environment, the deterioration of composites induced by high concentration of sulfate after 28 days of exposure reaches to the maximum level or a threshold. The average pore size and porosity increase after the sulfate exposure. The role of fibers in mechanical properties and microstructure after sulfate exposure were also investigated. The uses of hybrid organic fiber and inorganic mineral microfiber reinforcement are effective to enhance the resistance to sulfate attack.

Estimating strength properties of geopolymer self-compacting concrete using machine learning techniques

Abstract: There has been a persistent drive for sustainable development in the concrete industry While there are series of encouraging experimental research outputs, yet the research field requires a standard framework for the material development In this study, the strength characteristics of geopolymer self-compacting concrete made by addition of mineral admixtures, have been modelled with both genetic programming (GEP) and the artificial neural networks (ANN) techniques The study adopts a 12M sodium hydroxide and sodium silicate alkaline solution of ratio to fly ash at 033 for geopolymer reaction In addition to the conventional material (river sand), fly ash was partially replaced with silica fume and granulated blast furnace slag Various properties of the concrete, filler ability and passing ability of fresh mixtures, and compressive, split-tensile and flexural strength of hardened concrete were determined The model development involved using raw materials and fresh mix properties as predictors, and strength properties as response Results shows that the use of the admixtures enhanced both the fresh and hardened properties of the concrete Both GEP and ANN methods exhibited good prediction of the experimental data, with minimal errors However, GEP models can be preferred as simple equations are developed from the process, while ANN is only a predictor

Potential use of ceramic waste as precursor in the geopolymerization reaction for the production of ceramic roof tiles

Abstract: The red ceramic industry is responsible for generating high amounts of solid wastes around the world from manufacture process failures, such as ineffective firing and issues related to the products transportation. Besides the necessity of clean alternatives to discard the solid wastes, the civil construction industry has been demanding the development of better technological properties new materials. One an example of those new materials is the geopolymeric materials, characterized by the gain of mechanical strength at early ages, high fire resistance, low water absorption and refractoriness. All these characteristics imply that geopolymers are suitable for civil construction applications. The characterization of clay bricks waste, named chamotte, and its use as an alternative precursor to produce geopolymeric materials, such as roof tiles for buildings are the aims of this present work. The chemical characterization, particle size distribution, X-ray diffraction, specific mass, pozzolanic activity index (PAI) and scanning electron microscopy (SEM) were performed, in addition to the technological tests carried out on the geopolymer specimens, such as flexural strength, water absorption, linear shrinkage and apparent porosity. The chemical and mineralogical analysis proved that the waste is rich in silica and alumina, which are fundamental compounds for the geopolymers synthesis. The chamotte also has fine particles and high pozzolanic reactivity. Thus, this waste has great potential to be used as a raw material for obtaining of ceramic roof tiles by means of geopolymeric reactions.