Microbial Technology—A Sustainable Alternative to Improve Concrete Quality

The aim of this research is to experimentally study the application of powder coating sludge (PCS) and metakaolin as geopolymer. The PCS is a lot of waste which is released after the powder coating production process. While metakaolin comprises SiO2 and Al2O3 which can be used to produce geopolymer. Therefore, this study aimed to determine a suitable geopolymer mix ratio, using PCS as part of the mixture. This research also investigated the effect of metakaolin/PCS ratio, sodium hydroxide (NaOH)/sodium silicate (Na2SiO3) ratio, curing time, NaOH concentration and solid/liquid ratio on compressive strength of geopolymer. The coefficient of thermal conductivity was tested by using a suitable composition. Kaolin in this experiment was calcined at 700 °C for 2 h. Alkaline activators for molding were NaOH and Na2SiO3. Samples were hardened in an electric oven at 80 °C for 4 h before being removed from the moulds and cured at room temperature within 7, 14 and 28 days. Metakaolin/PCS ratios of 90:10, 80:20, 70:30 and 60:40, and solid/liquid ratios of 0.8 and 0.6 were performed. Concentration of NaOH were 6, 8, 10, 12 and 14 molars and NaOH/Na2SiO3 ratios were 1:1.5, 1:2 and 1:2.5, respectively. The experiments were conducted in triplicate. Results of 3 PCS tests showed that the highest composition of Al2O3 and SiO2 were 3.37 and 1.99 % w/w, respectively. The sample which is based on 60 % metakaolin and 40 % PCS, 10 molars NaOH, NaOH/ Na2SiO3 of 1:1.25, solid/liquid of 0.6 and curing time of 28 days had a maximum compressive strength of 81 kg/cm2, while the coefficient of thermal conductivity was 0.1766 W/(mk). Therefore, it can be concluded that the PCS has the potential to partially replace metakaolin as geopolymers material. 
HIGHLIGHTS 
 
Geopolymer comprises alumina (Al2O3) and silica (SiO2) and the advantages of geopolymer production are environmentally friendly and reduce energy consumption  
 
 
The appropriate metakaolin/PCS ratio and concentration of activators provide the highest compressive strength 
 
 
The geopolymer of this study has low thermal conductivity coefficient therefore it is a good insulation material  
 
 

Effect of Composition on Characteristics of Powder Coating Sludge (PCS)-Metakaolin-Based Geopolymer

The review study identifies research gaps in bacterial concrete as well as the benefits of using different bacillus strains to rehabilitate charred structures. A structural fire accident is an unfavourable circumstance that can occur at any time on the building. As a result, the structure's strength and durability will deteriorate, resulting in significant economic losses. Fire in the structure leads to prominent increase in crack and spalling of the surface concrete and to address this issue, retrofitting is one of the most effective techniques to ensure that a badly burnt structure is safe for future use with the help of bacterial concrete. Biomineralization is one of the most eminent techniques over a decade in auto-healing of cracks in the structure by itself with different bacillus strains such as Bacillus subtilis, Bacillus pseudofirmus, Bacillus pasteurii, Bacillus sphaericus, Escherichia coli, Bacillus cohnii, Bacillus balodurans, Bacillus halodurans, etc. Strengthening with the bacillus strain is the emerging techniques that give a good improvement in results and performance of the scorched structure. In this review paper we compiling the many research authors work in the understandable manner with subheading of appropriate techniques with results from the experimentation of various authors.

An absolute review on strengthening of scorched concrete by means of bio influenced self medicate mechanism

In recent years, concrete has become an important versatile construction material. This paper evaluates the strength obtained by concrete with the influence of bacteria. The bacterial strains were isolated from calcareous sludge and urea ware house. The bacterial strains were identified through 16srRNA gene sequencing as Bacillus pumilus and Bacillus flexus.  Using these strains, an experiment on cylinder and prisms cast was performed. Compressive strength, split tensile and flexural tests were conducted at the age of 7, 28 and 56 days with ultrasonic pulse velocity and rebound hammer. The results were compared with Bacillus cohnii MTCC 3616 obtained from microbial type culture collection and gene bank, Chandigarh, India. Based on the experimental results, the improvement in the mechanical strength is due to the deposition of calcite crystals on the bacterial cell surfaces within the pores which enhanced the strength of concrete and reduced porosity and permeability.

Anand Elumalai

Papers

An Experimental Study on Performance of Bacillus pumilus KC845305 and Bacillus flexus KC845306 in Bacterial Concrete