Showing papers on "Geopolymer published in 2015"
TL;DR: An overview of advances in geopolymers formed by the alkaline activation of aluminosilicates is presented along with opportunities for their use in building construction as mentioned in this paper, with respect to fresh and hardened states, interfacial transition zone between aggregate and geopolymer, bond with steel reinforcing bars and resistance to elevated temperature.
899 citations
TL;DR: In this article, the authors present a concise review of the current studies on the utilization of industrial by-products as the primary binder materials in the fabrication of geopolymer concrete.
369 citations
TL;DR: In this paper, a fly ash with partial slag substitution was used for GFC synthesis by mechanical mixing of preformed foam, and the GFCs exhibited 28 d compressive strengths ranging from 3 to 48 MPa with demolded densities from 720 to 1600 kg/m3 (105 °C oven-dried densities ranging from 585 to 1370 kg /m3), with the different densities achieved through alteration of the foam content.
Abstract: This study reports the synthesis and characterization of geopolymer foam concrete (GFC). A Class F fly ash with partial slag substitution was used for GFC synthesis by mechanical mixing of preformed foam. The GFCs exhibited 28 d compressive strengths ranging from 3 to 48 MPa with demolded densities from 720 to 1600 kg/m3 (105 °C oven-dried densities from 585 to 1370 kg/m3), with the different densities achieved through alteration of the foam content. The thermal conductivity of GFCs was in the range 0.15–0.48 W/m K, showing better thermal insulation properties than normal Portland cement foam concrete at the same density and/or at the same strength. The GFC derived from alkali activation of fly ash as a sole precursor showed excellent strength retention after heating to temperatures from 100 to 800 °C, and the post-cooling compressive strength increased by as much as 100% after exposure at 800 °C due to densification and phase transformations. Partial substitution of slag for fly ash increased the strength of GFC at room temperature, but led to notable shrinkage and strength loss at high temperature. Thin GFC panels (20–25 mm) exhibited acoustic absorption coefficients of 0.7–1.0 at 40–150 Hz, and 0.1–0.3 at 800–1600 Hz.
356 citations
TL;DR: In this article, the effects of sodium hydroxide and sodium silicate solutions on the properties of fly ash (FA)-granulated blast furnace slag (GBFS) geopolymer were investigated.
314 citations
TL;DR: In this article, a small proportion of ordinary Portland cement (OPC) was added with low calcium fly ash to accelerate the curing of geopolymer concrete instead of using elevated heat.
Abstract: Most previous works on fly ash based geopolymer concrete focused on concretes subjected to heat curing. Development of geopolymer concrete that can set and harden at normal temperature will widen its application beyond precast concrete. This paper has focused on a study of fly ash based geopolymer concrete suitable for ambient curing condition. A small proportion of ordinary Portland cement (OPC) was added with low calcium fly ash to accelerate the curing of geopolymer concrete instead of using elevated heat. Samples were cured in room environment (about 23 °C and RH 65 ± 10%) until tested. Inclusion of OPC as little as 5% of total binder reduced the setting time to acceptable ranges and caused slight decrease of workability. The early-age compressive strength improved significantly with higher strength at the age of 28 days. Geopolymer microstructure showed considerable portion of calcium-rich aluminosilicate gel resulting from the addition of OPC.
307 citations
TL;DR: In this article, the use of solid activators in the manufacture of geopolymer enhances its commercial viability as it aids the development of a one-part “just add water” mixture, similar to the conventional Portland cement-based materials.
250 citations
TL;DR: In this paper, the feasibility of generating geopolymers from fly ash using waste glass as an alkaline activator (waterglass family) was explored and the main reaction product in all the systems studied was the alkaline aluminosilicate hydrate gel.
243 citations
TL;DR: In this article, high compressive and flexural tensile strength of alkali activated fly ash geopolymer mortars were presented, where NaOH was used as alkali medium that provides high pH value.
223 citations
TL;DR: In this paper, the authors used the standard RILEM pull-out test to assess the development of the bond strength from 24h to 28 days after casting, with different heat curing conditions.
207 citations
TL;DR: In this paper, the effect of the addition of graphene nanoplatelets (GNPs) on the microstructure and mechanical properties of a fly ash based geopolymer was reported.
206 citations
TL;DR: Porous fly ash-based geopolymer material was produced using fly ash and sodium water glass as original material and H 2 O 2 as foaming agent in this paper, where the changes caused by the geopolymersization and decomposition of H 2O 2 on the properties of the final products were investigated by applying curing on geopolym mortars with different amounts of sodium waterglass (60, 80 and 100 ǫ) and H2 O 2 (4, 6 and 8 g) added at various curing temperatures.
TL;DR: In this article, the compressive strength of concrete, bricks and tiles collected from various demolished buildings were mixed with the activating solution (NaOH and Na 2 SiO 3 ), and various synthesis conditions (curing at 60-90°C, 8-14 m NaOH molarity, particle size) were considered.
TL;DR: In this article, one-part "just add water" geopolymer binders are synthesized through the alkali-thermal activation of the red mud which is relatively rich in both alumina and calcium.
Abstract: In this study, one-part “just add water” geopolymer binders are synthesized through the alkali-thermal activation of the red mud which is relatively rich in both alumina and calcium. Calcination of the red mud with sodium hydroxide pellets at 800°C leads to decomposition of the original silicate and aluminosilicate phases present in the red mud, which promotes the formation of new compounds with hydraulic character, including a partially ordered peralkaline aluminosilicate phase and the calcium-rich phases C3A and α-C2S. The hydration of the “one-part geopolymer” leads to the formation of zeolites and a disordered binder gel as the main reaction products, and the consequent development of compressive strengths of up to 10 MPa after 7 d of curing. These results demonstrate that red mud is an effective precursor to produce one-part geopolymer binders, via thermal and alkali-activation processes.
TL;DR: In this paper, the joint effect of several mix parameters on the properties of foam geopolymers was investigated through a laboratory experiment of 54 different mortar mixes were, sodium silicate/sodium hydroxide mass ratio (2.5, 3, 4.5), activator/binder mass ratio(0.6, 0.8, 1.0), chemical foaming agent type (H2O2) and sodium perborate (NaBO3)) and foam agent mass ratio content (1, 2, 3%).
TL;DR: In this paper, the microstructure, reaction products, and reactivity of fly ash/slag binders synthesized at various mixture ratios of two raw materials were examined using various experimental techniques (NMR, ICP-OES, EDS, FT-IR and TGA).
TL;DR: In this article, the assessment of a number of key durability parameters for geopolymer concrete made from fly ash activated with sodium silicate and sodium hydroxide is presented. But, there is a concern over the long term performance of the concretes with activator modulus of 1.00 and 1.25 when considering chloride induced corrosion of reinforcing steel.
Abstract: The environmental impact from the production of cement has prompted research into the development of concretes using 100 % replacement materials activated by alkali solutions. This paper reports the assessment of a number of key durability parameters for geopolymer concrete made from fly ash activated with sodium silicate and sodium hydroxide. Properties investigated have included workability, compressive strength, water sorptivity, carbonation, chloride diffusion and rapid chloride permeability. Microstructure studies have been conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. The results showed that both the geopolymer concretes with activator modulus 1.00 and 1.25 gave durability parameters comparable to Ordinary Portland and blended cement concretes of similar strength, while the geopolymer concrete with an activator modulus of 0.75 displayed lower durability performance. However, there is a concern over the long term performance of the geopolymer concretes with activator modulus of 1.00 and 1.25 when considering chloride induced corrosion of reinforcing steel due to the initial pH and long term chloride diffusion coefficient.
TL;DR: In this article, the authors combined various proportions of class-F fly ash (FA) and residual rice husk ash (RHA) with an alkaline solution to produce geopolymers.
TL;DR: In this paper, the authors investigated the utilization of high calcium fly ash geopolymer mortars (GPM) containing ordinary Portland cement (PC) for use as Portland cement concrete (PCC) repair material.
TL;DR: In this article, the authors investigated the durability and microstructure of fly ash and metakaolin-based geopolymer exposed to elevated temperatures and acid attack and found that the densities of the pore structures of the fly ash-metakaolin mixture are higher than those of OPC.
TL;DR: In this article, a systematic approach for selecting mix proportions for alkali activated fly ash-based geopolymer concrete (GPC) is presented for low calcium Class F fly ash activated geopolymers using sodium silicates and sodium hydroxide as activator solutions.
TL;DR: In this paper, the effect of various influential factors on compressive strength of sludge-fly ash geopolymer was investigated with the intention to develop an alternative green construction and building materials, without the usage of Portland cement as a cementing agent.
TL;DR: In this article, an amorphous geopolymer, synthesized from waste fly ash, was used as a sorbent material for copper from aqueous solutions, which has much higher removal efficiency compared to the raw fly ash.
Abstract: This work aims to evaluate the effectiveness of an amorphous geopolymer, synthesized from waste fly ash, as sorbent material for copper from aqueous solutions. The obtained geopolymer was found to be highly amorphous in structure due to the dissolution of fly ash glass phases. It has much higher removal efficiency compared to the raw fly ash. The removal efficiency was affected by solid/liquid ratio, temperature, reaction time, and Cu2+ initial concentration (C0). The highest Cu2+ removal capacity was obtained at pH 6. The kinetic data were found fit to the pseudo second order kinetic model. Furthermore, it was found that Langmuir model is better than Freundlich model within the temperature range (25–45 °C). The maximum sorption capacity (qm) occurred at 45 °C, reaching a value of 152 mg/g. The sorption process by the obtained geopolymer is endothermic in nature and more favorable at higher temperatures with enthalpy of adsorption of 39.49 kJ/mol. The activation energy of the sorption process at the optimum conditions was found to be 34.9 kJ/mol.
TL;DR: In this article, compressive strength of metakaolin-based geopolymers with molar Si/Al ratios of 1.12, 1.77 and 2.20 was analyzed.
TL;DR: In this article, a fly ash-based engineered geopolymer composite (EGC) with relatively low-concentration activator combinations was used to improve the mechanical properties of the composite.
Abstract: This paper is aimed to improve the mechanical properties (namely compressive and tensile strengths) of a recently developed fly ash-based engineered geopolymer composite (EGC) with relatively low-concentration activator combinations. In this regard, four different activator combinations (including two Na-based solutions and one K-based activator solution, and one lime-based activator combination in the form of powder) were used to develop the fly ash-based EGCs exhibiting strain hardening behavior under uniaxial tension. Randomly oriented short polyvinyl alcohol (PVA) fibers (2% v/v) were used to reinforce the relatively brittle low-calcium (Class F) fly ash-based geopolymer matrix. The matrix and composite properties of the developed fly ash-based EGCs [including workability of the fresh matrix, density, compressive strength, matrix fracture properties (comprising elastic modulus, fracture toughness, and composite crack tip toughness), and uniaxial tensile behavior] were evaluated. A counterpart ...
TL;DR: In this article, the incorporation of nano-silica in fly ash based geopolymer binders has been investigated in order to understand its effect on the strength and microstructural development.
TL;DR: Results showed that geopolymer inorganic membrane efficiently removes Ni(2+) from wastewater because of the combined actions of the adsorption and rejection of this membrane on Ni( 2+) during membrane separation.
TL;DR: In this paper, a study on low calcium fly ash based geopolymer concrete cured in ambient temperature (23oC) without additional heat was presented. And the results showed that inclusion of additives with fly ash significantly enhanced the early age properties.
TL;DR: In this paper, the properties of lightweight geopolymer specimens aerated by aluminium powder were investigated and the compressive strength of all aerated specimens were in the range of 0.9-4.35-MPa.
TL;DR: In this article, the workability of a geopolymer was investigated and the negative zeta potential of fly ash was identified as assisting gel formation with the smaller the negative zero potential of the fly ash, the more gel formation and high compressive strength observed.