Journal Jul 2020

Can we formulate a geopolymer or an alkaliactived binder as a Portland cement? Martin CYR

Geopolymers and more generally alkali-activated binders represent possible alternatives to classical Portland cements. Their formulation seems however more difficult to manage compared to cements, which might restrain their industrial use. The complexity of their formulation is mainly linked to the wide variety of basic materials that compose them and the need to use activators. The purpose of this article is to present a few indications for the formulation of geopolymers and alkali-activated binders. It first defines the main precursors and activators, emphasizing the couplings between the two. Then it draws a parallel with Portland cements on the quantities of binders and water, two important notions in formulation. Finally, it describes some important details of the formulation of geopolymers compared to Portland cements, in particular the use of molar ratios of certain oxides. These ratios might complicate the formulation of the material, but they allow the optimization of the composition to meet the targeted performance.

Case study on field trials of developed geopolymer (slag and fly ash based) precast concrete paver blocks Lalit Yadav, Amit Trivedi, V. V. Arora, B.N. Mohapatra

The advancements in material sciences have led to development of altogether alternative binding material to concrete in form of alkali activated concrete. The alternative works out to be green and sustainable but there are apprehensions regarding costs, testing methods and field performance.

The study presents development of mixes in laboratory conditions. The mixes have been developed keeping view the optimal ratios of SiO2/Al2O3, SiO2/Na2O as per established researches and trials conducted in the laboratory.

The study also presents major difficulties that may arise during production and measures adopted to overcome the difficulties.

The selection of activator modulus (SiO2/Na2O) and Na2O content can not only help in cost optimization and also significantly influences the workability and strength of the mixes. The results of trials have been published in paper using different compositions.

The effect of activator modulus on strength properties of different mixes was studied.

A mix was also developed to cast precast plain concrete product (interlocking paver blocks) for economizing cost. The curing of blocks was done in ambient conditions (without use of water or curing compounds). The paver blocks developed using Geopolymer concrete were used to cast a trial stretch. The laid stretch was monitored for about a year regarding its field performance under low volume traffic flow.

The study includes strength development, abrasive behavior, water absorption etc. The findings of study indicate that with little modifications in testing, development and usage methodology, precast plain alkali activated products can be used as a substitute as well as supplement / compliment to conventional concrete products.

Efficient production of alkali-activated geopolymers using low-calcium fly ash G.V. P. Bhagath Singh, K.V. L. Subramaniam

An experimental investigation of fly ash activated with sodium based alkali-silicate activating solutions is presented. As the first step a detailed characterization of the low-calcium fly ash is performed. The reactive SiO2 and Al2O3 in fly ash are shown to be smaller proportions of the total SiO2 and Al2O3 indicated by the oxide analysis. In the experimental program, the roles of reactive oxide ratios, and the molarity of sodium hydroxide in influencing the compressive strength of alkali-activated fly ash are evaluated. The reactive silica content in the alkali-activated fly ash is taken as the sum of the reactive silica contributed by the fly ash and the soluble silica from the activating solution. The reactive alumina in the fly ash and the total sodium in the activating solution are used in determining the reactive oxide ratios. The ratio of reactive Al2O3/Na2O close to 2.5 produces the highest compressive strength. The maximum ultimate compressive strength is attained for a reactive SiO2/Al2O3 mass ratio equal to 2.0 in the activated system. The minimum required molarity of NaOH in the alkali-activated mixture is 3M. The results presented in this paper indicate that the composition of the activating solution for achieving the highest compressive strength would depend on the reactive oxide composition of the fly ash. Producing high strength geopolymers requires optimizing the activating solution for the specific reactive oxide ratios based on the reactive oxide content in the fly ash.

Geopolymeric materials in infrastructure development: A way forward Md. Reyazur Rahman, Rakesh Paswan, S. K. Singh

Geopolymer material has emerged as a potential substitute for the ordinary Portland cement and research on this material has grown rapidly around the globe. The synthesis chemistry of this alternative inorganic binder has been studied in the laboratory extensively to understand the basic structural framework and the underlying parameters, which influence the material properties at large in a scientific manner. After so many year of research work at lab level, in recent past geopolymer has started to grow into the field in the form of demonstration and implementation projects. In this paper an overview of applications of geopolymer materials in different prospective areas has been presented. The development of products and demonstrations for up-scaling carried at CSIR-CBRI, Roorkee, India is also described briefly. The challenges associated with the large scale implementation and acceptance in practice has been pointed out. There is need of systematic approach towards the development of geopolymer technology at commercial scale in order to bring the beneficial attributes associated with geopolymer to the industry and society as a whole.

Utilization of ferrochrome ash as a source material for production of geopolymer concrete for a cleaner sustainable environment Jyotirmoy Mishra, Shaswat Das, R.S. Krishna, Bharadwaj Nanda

This paper addresses the importance of implementing circular economy for a sustainable future by focusing on the merits of the utilization of industrial wastes in the production of ecofriendly/ green construction materials: preferably Geopolymers. The first part of the paper describes a circular economy business model, review of modern concretes concerning waste utilization and the second part demonstrates an experimental investigation on the development of open-air cured ferrochrome ash (FCA) based geopolymer concrete with regard to its workability and compressive strength along with various geopolymer reaction models. ground granulated blast furnace slag (GGBFS) was introduced to the system at appropriate substitution levels; scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR) analysis of few hardened concrete samples are discussed.

Bond strength characteristics of fly ash admixed self-compacting alkali activated concrete mixes Manjunath R., Mattur C. Narasimhan, Suryanarayana L. R.

Bonding in any type of concrete plays a crucial role in the performance of reinforced concrete structures, which are profoundly determined by many factors such as concrete compressive strength, diameter, type and size of the bar along with length of embedment and confinement of concrete. Herein, an attempt has been made to develop fly-ash admixed self-compacting alkali activated slag concrete mixes cured under laboratory ambient conditions and to evaluate the bond strength characteristics using direct pull out test along with their bond stress-slip behaviour at the age of 28 and 56 days.

These self-compacting alkali activated slag concrete mixes were developed using Fly-ash and GGBFS as the major principal binder. Naturally available river sand was used as the fine aggregate; 12.5 mm down size crushed granite chips (Jelly) constituted the coarse aggregate fractions in all these mixes. The alkaline solutions basically consisted of mixtures of sodium hydroxide flakes dissolved in the calculated quantity of water and mixed with the liquid sodium silicate solution.

The experiments were planned based on Taguchi’s design of experiments methodology. A total of fifteen mixes were developed and evaluated for their flow ability characteristics as per the requirements of EFNARC guidelines along with compressive strength values at the age of 7, 14, 28 and 56 days. In an initial, calibration phase, bond strength characteristics of a set of nine mixes were utilized for performance evaluation purposes. Strength prediction equations were then derived on the basis of such results, whose predictive capacity was then evaluated and ascertained in the prediction phase with actual results of experiments on a set of three new mixes. Test results indicated higher flow ability characteristics for all the mixes satisfying the requirements as per the EFNARC guidelines. Higher compressive strengths values in the range of 46 – 85 MPa were obtained at the age of 56 days. Further acceptable bond strength values were obtained varying in the range of 8.0 – 14.5 MPa as compared to control OPC based reference concrete mix.

Experimental study on behavior of geopolymer structural masonry Radhakrishna, Venugopal K.

Burnt clay bricks and concrete blocks are very popular traditional units used in structural masonry. Both are energy-intensive with the use of thermal input or cement. Geopolymer masonry units were manufactured using class F fly ash and ground granulated blast furnace slag (GGBS) as binding materials. The activator solution was prepared using sodium hydroxide and sodium silicate. Samples were cured in the open air without using water or thermal input. These masonry units exhibited better properties compared to traditional units. The performance of geopolymer masonry prisms and wallettes was found excellent when subjected to axial and eccentric loading. This article demonstrates the potential of effectively utilising Fly ash and GGBS in making geopolymer masonry units which will bring a ‘green initiative’ in the construction of structural masonry.

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