Strength Of Geopolymer Binder Research Articles

Effect of mechanical activation of red mud on the strength of geopolymer binder

The growing interest in utilization of industrial waste and green construction has motivated the present work. Red mud is an industrial waste produced in the process of extraction of aluminum from bauxite by Bayer’s process. The paper presents the studies conducted to assess the influence of mechanical activation of red mud and curing methods on the strength of red mud-fly ash geopolymer paste. Red mud was used in both unprocessed and pulverised form and the alkali activated paste samples were cured thermally as well as in ambient condition. The percentage of red mud varied from 0 to 90% and alkalinity from 6 M to 12 M NaOH solution. X-ray diffraction (XRD) was carried out to identify the mineral phases in pulverised and unprocessed red mud. SAED (selective area diffraction diagram) test was done on the red mud, along with SEM (scanning electron microscopy), TEM (transmission electron microscopy) and HRTEM analysis (high resolution transmission electron microscopy) to study the effect of mechanical activation and validate the experimental findings. Mechanical activation increased the reactivity of silica and the hematite phase of red mud as reflected in the silica reactivity and Fourier transform infrared spectroscopy (FTIR) test results. Use of pulverised red mud enhanced the mechanical properties of ambient cured paste and the specimens possessed maximum 7 day compressive strength of 40 MPa at 6 M alkalinity with 30% mechanically activated red mud content.

Alkali activated materials vs geopolymers: Role of boron as an eco-friendly replacement

In this paper, the influence of boron ions on the strength development and microstructure variations of fly ash-based geopolymers and alkali-activated slag (AAS) was investigated through utilizing borax-based alkali-activators. In addition to cost-effective aspects, the substitution of boron ions in geopolymer and AAS matrixes meant to minimize the downside of the silicate compounds on the environment. The binders were produced by introducing borax to alkali-activator solutions. Granulated ground blast furnace slag (GGBS) and Class F fly ash were used to produce AAS and geopolymer specimens respectively. Results showed a decline in the strength of geopolymer binder as a result of the increase in the amount of borax. However, the formation of B-O bonds in geopolymer matrices prevented an unexpected behaviour of the strength derived from an imbalance in the alkali activator solution. Substitutions of more than 60% of sodium silicate in the fly ash-based geopolymer was not reasonable. The compensatory role of boron in the strength of AAS was undeniable where even introducing more than 30% of borax led to a slight growth in the AAS strength. It was concluded that borax-based binders could be potential candidates for high volume substitution of sodium silicate in both geopolymers and AAS.

The Effect of Chloride Environment on Mechanical Properties Geopolymer Binder with Fly Ash

This study is conducted to determine the effect of five variables on mechanical properties of geopolymer binders. These five variables are chloride environment, NaOH molarity, Na2SiO3/NaOH ratio, fly ash/alkaline activator (FA/AA) ratio and superplasticizer (SP) addition. The mechanical properties considered are compressive strength, porosity and density. Taguchi experimental design method is used to compile the binder composition of geopolymer to achieve the maximum compressive strength. Specimens binder used is a cylinder with 25 mm diameter and 50 mm height. Compressive strength test is performed at 28 days using SNI 03-6825-2002 (Indonesian National Standard) and porosity of the binder is determined using vacuum saturation apparatus similar to that developed by RILEM. The density of the binder is measured using Ultrasonic Pulse Velocity (UPV). This study concludes that the chloride environment has a beneficial effect on the compressive strength of the binder. In addition, the FA/AA ratio and NaOH molarity give a significant effect on the compressive strength of geopolymer binders.