Biomineralization is a process that leads to the formation of minerals using the biologically or biotechnologically mediated route. Calcium carbonate is one such biomineral that is secreted by the ureolytic bacteria which contributes for the strengthening and improvement of cementitious and sandy materials. It is a new and innovative area in the geotechnological engineering and structural engineering due to its wide range of implications in strengthening of soil, sand, stone, and cementitious materials. The shape and size of the calcium carbonate particle vary with the strain of the bacterium used, and it is species specific. This paper aims in the critical review of the mechanism of calcium carbonate precipitation by the bacterium, various bacteria involved, and the useful outputs of the technique of biomineralization. Based on the critical review, it also recommends the future development and research in the field to develop a technology that can strengthen the existing and the proposed structures.

No abstract

This paper presents the development of ambient temperature cured ultra-high-performance geopolymer concrete (UHPGPC). Ultra-high-performance concrete (UHPC) mixtures were developed by completely eliminating Portland cement and activating industrial by-product materials such as ground granulated blastfurnace slag and silica fume.Local standard sand (maximum size 2 mm), quartz sand (600 ìm) and 0 . 16 mm diameter steel fibres of 13 and 6 mm length were used. Fresh properties (density and flowability) and mechanical properties (compressive strength) of the UHPGPC produced under ambient temperature curing conditions were evaluated. Four mixtures with fibres and one mix without fibre addition were studied as the UHPGPC mixtures. The highest average compressive strengths obtained were 175 MPa for UHPGPC with steel fibres (1% 6 mm and 2% 13 mm) and 124 MPa for UHPGPC without fibres. Prismatic specimens (100 3 100 3 500 mm) were cast to determine the flexural strength, which was found to be 10 . 3-13 . 5 MPa and 9 . 1 MPa for mixes with and without steel fibres respectively. The compressive and flexural strengths obtained in this work are comparable to UHPC strengths presented in the literature. Production of this innovative material with industrial by-products and without the conventional curing regimes used for UHPC will improve sustainability and lead to cast-in-situ applications of UHPC.

A methodology of design for seismic performance enhancement of buildings by using linear viscous fluid dampers (VFDs) is proposed. It also gives the procedure for arriving at an efficient distribution of VFDs in the building. The peak base shear and inter-storey drifts determined from a time history analysis of the building subjected to design basis earthquake (DBE) are used for satisfying the Uniform Building Code 1997 specified target performance criteria for base shear and inter-storey drifts. The methodology proposed is used for designing the linear VFDs to increase the effective damping with chevron, upper toggle, and scissor jack mechanisms in a 20-storey benchmark building subjected to DBE to meet the performance criteria. The time histories of the N-S component of El Centro, N-S component of Kobe, N-S component of Northridge, and S-E component of Taft scaled to a PGA of 0.2 g are considered to be representatives of DBE for the place where the 20-storey benchmark building is located. It is observed that the optimum location of the dampers with different mechanisms in the building is the ground floor or the first few storeys from the ground floor.

The effect of amorphous nanosilica particles on the mechanical properties and durability of two high-strength concrete (HSC) mixes was investigated. Nanosilica in powder form was used as a partial replacement of cement at dosages of 1 wt% and 2 wt%, and significant improvements in performance were observed for 2 wt% replacement of cement by nanosilica. Micromechanical studies were performed on the nano-modified HSCs to determine the impact of nanosilica on pozzolanic reactivity. Durability assessments such as the rapid chloride penetration test, water sorptivity test and water absorption test revealed significant resistance to chloride penetration, sorptivity and water absorption. These improvements can be mainly attributed to the larger specific surface area of nanosilica, which effectively stimulates both pozzolanic reactivity and the filler effect over the cementitious matrix. Notation a exposed area of specimen (mm 2 ) d density of water (g/mm 3 ) I absorption I 0 , I 30 , I 60 … I 330 , I 360 current (A) at 0, 30, 60 … 330, 360 min m t change in specimen mass (g) at time t Q charge passed (C)