Effect of microbes addition on the properties and surface morphology of fly ash-based geopolymer paste
Introduction
Geopolymers, also known as zero-cement concrete, are one of the innovations to produce sustainable green materials in order to replace concrete [1]. Geopolymers can be produced by reacting pozzolanic materials with alkali solutions [2]. Fly ash is one of the pozzolanic materials which has a spherical and hollow form that could substitute Portland cement in the making of concrete to reduce its energy consumption [3,4]. Fly ash-based geopolymers have resistance to sulphate attack, fire, and acidic environments, better than normal concrete. It can also immobilize toxic metals [[5], [6], [7]].
Nowadays, lightweight concretes are highly produced. Lightweight concretes are usually produced for non-structural purposes by adding a foaming agent into the mixtures [8,9]. Foamed concrete has a high flow ability, low weight, minimal consumption of aggregates, controlled low strength, and excellent thermal-insulation properties [10]. A new technology that is currently being developed by researchers is by the addition of microbes to concrete as a natural method that can be used to improve concrete properties. Previous research conducted by Emdadi et al. [4] and Iswarya et al. [11] showed that the strength of concrete was improved by adding microbes such as bacteria into the concrete. In other studies, the addition of microbes into the mixtures has enhanced the strength of fly ash-cement-based paste and fly-ash based geopolymer paste due to an increased amount of calcite that fills any micropores, thereby increasing its compressive strength [9,12,13].
Various studies have mentioned that the addition of microbes can have an additional function, namely as a self-healing agent in concrete, or the ability of concrete to repair hairline cracks that occur in itself [12,14,15]. Rhizopus oligosporus is one species of fungi who had been proven of producing hyphae as a good environment for bacteria to live in Ref. [16]. Sporosarcina pasteurii is a known bacterial species to have a capability to adapt the highly alkaline condition while inducing the calcite precipitation [17,18]. The interaction of both microbes may result in the self-healing activity of concrete [15,19]. While the development of geopolymer as the substitution of concrete is currently rapid, analysis on the effectiveness of microbes addition in performing self-healing activity for geopolymer was currently still limited and scattered [20].
The changes in properties, that are supported by observations of the surface morphology which occur due to the addition of microbes into geopolymers, has not been specifically studied, including when microbes are added to fly ash-based geopolymer paste with additional materials such as foaming agents and bottom ash. Research on this specific topic may become the first indication of self-healing activity of geopolymer by the addition of microbes into the paste. The aim of this study was to investigate the effect of microbes additions to the properties and surface morphology of fly ash-based geopolymer paste cast with variations of foaming agent and bottom ash additions. The results of this research show the potential of microbes as self-healing agents on geopolymer paste and the suitability of applying self-healing technology based on the geopolymer's mixing proportions.
Section snippets
Raw materials characteristics
Fly ash (with 2.273 g/cm3 density) and bottom ash (with 2.353 g/cm3 density) in this study were obtained from the Suralaya Coal Fire Power Plant, Banten, Indonesia. Chemical compositions of the fly ash and bottom ash were determined from previous research by Wulandari et al. [9] as listed in Table 1.
The fly ash used in this study was 100 mm in size and the bottom ash was 4.75 mm. An alkali activator (consisting of 4 M sodium hydroxide (NaOH), sodium silicate BE-52, that consists of 15% Na2O,
Compressive strength analysis
The strength development as a result of this test was observed at the age of paste at 7, 14, and 28 days as presented in Fig. 1. Based on Fig. 1, it shows that the compressive strengths increased by day for all mixtures. PGB has the highest result of compressive strength in every age of observation. PGB (23.53 ± 1.18 MPa) has a higher compressive strength than PG (16.44 ± 0.82 MPa). The compressive strength of PGB increased by 43.75% compared to PG at the end of the test period. The addition of
Conclusions
The addition of microbes can increase the compressive strength of PGB up to 43.75% (23.53 ± 1.18 MPa) higher than the PG (16.44 ± 0.82 MPa) at the end of the test period. The addition of bottom ash (MG and MGB) also increased the compressive strength of the geopolymer paste (compared to PG, PGF, and PGFB). All microbe-added specimens showed a slightly higher closed porosity amount compared to the non-microbial-added specimens. The result of SEM indicated that the mixture with the foaming agent
CRediT authorship contribution statement
Kiki Dwi Wulandari: Investigation, Formal analysis, Writing - original draft, Project administration. Januarti Jaya Ekaputri: Supervision, Funding acquisition, Resources. Triwulan: Supervision, Methodology, Resources. Setyo Budi Kurniawan: Formal analysis, Validation, Visualization, Writing - review & editing. Widya Emilia Primaningtyas: Writing - original draft. Siti Rozaimah Sheikh Abdullah: Writing - original draft. Nur ‘Izzati Ismail: Writing - original draft. Muhammad Fauzul Imron: Writing
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by PPNS, ITS and Universitas Airlangga through the scheme of international collaboration with grant No. 443/UN3.14/PT/2020 and Universiti Kebangsaan Malaysia through a collaboration research work under DCP-2018-006/3 grant.
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