Effect of bacteria on strength, permeation characteristics and micro-structure of silica fume concrete Rafat Siddique a , Abir Jameel a , Malkit Singh b,⇑ , Danuta Barnat-Hunek c , Kunal d,1 , Abdelkarim Aït-Mokhtar e , Rafik Belarbi e , Anita Rajor f a Department of Civil Engineering, Thapar University, Patiala, Punjab, India b Punjab State Power Corporation Limited, Patiala, India c Faculty of Civil Engineering and Architecture, Department of Construction, Lublin University of Technology, Nadbystrzycka St. 40, 20-618 Lublin, Poland d School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana, Punjab, India e Department of Civil Engineering, University of La Rochelle, France f School of Energy and Environment, Thapar University, Patiala, Punjab, India highlights  Effect of bacteria on strength and permeation properties of concrete is presented.  Concrete is made with 0, 5, 10, and 15% silica fume as cement replacement.  Economic study of bacterial SF concrete is also covered. article info Article history: Received 29 November 2016 Received in revised form 19 February 2017 Accepted 9 March 2017 Keywords: Bacteria Concrete Silica fume Compressive strength Sorptivity Porosity abstract Influence of bacteria on strength and permeation characteristics concrete incorporating silica fume (SF) as a substitution of cement has been investigated in this study. The cement was partially substituted with 5, 10 and 15% SF and with constant concentration of bacterial culture, 10 5 cfu/mL of water. Cement was substituted with silica fume in concrete by weight. At 28 d, nearly 10–12% increase in compressive strength was observed on incorporation of bacteria in SF concrete. At 28 d, the compressive strength of concrete increased from 32.9 to 36.5 MPa for SF, 34.8 to 38.4 MPa for SF5, 38.7 to 43.0 MPa for SF10 and 36.6 to 40.2 MPa for SF15 on addition of bacteria. Water absorption, porosity and capillary water rise reduced in the range of 42–48%, 52–56% and 54–78%, respectively, in bacterial concrete compared to cor- responding nonbacterial samples at 28 days. Reduction in chloride permeability of bacterial concrete was observed and the total charge passed through bacterial concrete samples reduced by nearly 10% com- pared to nonbacterial concrete samples at 56 d of age. At 28 d, total charge passed through concrete reduced from 2525 to 1993 C for SF, 1537 to 1338 C for SF5, 961 to 912 C for SF10 and 1186 to 1174 C for SF15 on addition of bacteria. Calcite precipitation on addition bacteria and confirmed by SEM and XRD analysis is considered as the reason for improvement in properties of concrete. Economic study of bacterial SF concrete has also been carried out in the present work. The Benefit/Cost Ratio of bacterial SF concrete got reduced with the increase in SF quantity. Compared to control concrete, bacterial SF con- crete containing 10% silica fume demonstrated highest benefit in improvement in its properties and cor- responding highest Benefit/Cost Ratio. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Supplementary cementing materials (SCMs) are extensively used in enhancing concrete properties. Waste/by-product materi- als used as SCM in concrete constructions not only check the envi- ronmental contamination but also enhance the concrete properties in fresh as well as in hardened state. Silica fume (SF) is generated by silicon metal or ferrosilicon alloys producing industry and has http://dx.doi.org/10.1016/j.conbuildmat.2017.03.057 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: siddique_66@yahoo.com (R. Siddique), abir47@gmail.com (A. Jameel), bhangal_ms@yahoo.co.in (M. Singh), d.barnat-hunek@pollub.pl (D. Barnat-Hunek), kunal_pau@yahoo.co.in ( Kunal), karim.ait-mokhtar@univ-lr.fr (A. Aït-Mokhtar), rbelarbi@univ-lr.fr (R. Belarbi), anitarajor@yahoo.com (A. Rajor). 1 Participated in this work when worked in Department of Civil Engineering, Thapar University till July 2015. Construction and Building Materials 142 (2017) 92–100 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat