Pradip Sarkar

Enhancement of properties of recycled coarse aggregate concrete using bacteria

ABSTRACT Due to rapid construction, necessity for raw materials of concrete, especially coarse aggregate, tends to increase the danger of early exhaustion of the natural resources. An alternative source of raw materials would perhaps delay the advent of this early exhaustion. Recycled coarse aggregate (RCA) plays a great role as an alternative raw material that can replace the natural coarse aggregate (NCA) for concrete. Previous studies show that the properties of RCA concrete are inferior in quality compared to NCA concrete. This article attempts to study the improvement of properties of RCA concrete with the addition of bacteria named as Bacillus subtilis. The experimental investigation was carried out to evaluate the improvement of the compressive strength, capillary water absorption, and drying shrinkage of RCA concrete incorporating bacteria. The compressive strength of RCA concrete is found to be increased by about 20% when the cell concentration of B. subtilis is 106 cells/ml. The capillary water absorption as well as drying shrinkage of RCA are reduced when bacteria is incorporated. The improvement of RCA concrete is confirmed to be due to the calcium carbonate precipitation as observed from the microstructure studies carried out on it such as EDX, SEM, and XRD.

Effect of Nonureolytic Bacteria on Engineering Properties of Cement Mortar

AbstractBacterially induced mineral precipitation is a general phenomenon in nature. Ureolytic bacteria have been used in many studies as an environmentally friendly method for the protection and i...

Investigation of cement mortar incorporating Bacillus sphaericus

ABSTRACT Ureolytic-type bacteria has been used to improve the strength of cement mortar by the precipitation of calcium carbonate. In the present study Bacillus sphaericus has been used to improve the properties of cement mortar such as setting time, compressive strength and sorptivity. The setting time is found to be unaffected by the presence of bacteria. It is found that compressive strength at both 7-days and 28-days of mortar cube increases with the increase of bacteria concentration. At the optimum bacteria dosage of 107 cells/ml, the average compressive strength increases by 58% (at 7 day) and 23% (at 28 day) over the control specimen. The sorpitivity coefficient decreases as the concentration of bacterial cells increases. The mineralogy and morphology of the calcium carbonate precipitation have been tested by XRD and FESEM.

Vertical Irregularity of Buildings: Regularity Index versus Seismic Risk

AbstractThe seismic performance of buildings with irregular distribution of mass, stiffness, and strength along the height may be significantly different from that of regular buildings. Design code...

Studies on Identifying Critical Joints in RC Framed Building Subjected to Seismic Loading

A beam-column joint is very critical element in reinforced concrete (RC) framed structure where the elements intersect in all three orthogonal directions. In normal design practice for gravity loads, the design check for joints is not usually critical in reinforced concrete (RC) frames and hence not warranted in general. However, failures of RC frames during recent earthquakes have revealed heavy distress in the joints and resulted in the collapse of several structures due to joint shear failure. Despite the critical role of joints in sustaining large deformations and forces during earthquakes, specific guidelines are not explicitly included in current Indian codes of practice IS 1893:[1], IS 13920:[2] and IS 456:[3]. On account of this, it is tacitly assumed in practice that adequate lapping of the main reinforcement and provision of transverse ties satisfies the integrity and strength of joints. However, the kind of reinforcement detailing given in the design codes is not consistent with the Indian practice of construction in terms of implementation. This paper aims to study the behaviour of beam-column joints in multi-storeyed RC framed structure with an objective to identify the location of deficient joints and developing alternative design scheme suitable for Indian construction industry. A family of multi-storeyed building of 2 bay × 2 bay (at 5 m) frames from 3 storey (10.5 m height) to 10 storey (35 m height) is studied. Shear force demand in the joint is estimated from the concept of capacity design. The shear capacity is calculated for the interior joints at different height (i.e., at different floor level) of the buildings as per selected international building codes and other methods available in literature. This result shows that the maximum joint demand occurs not in the lowest storey level of the building but somewhere in the second, third or fourth storey level. The maximum joint shear demand found to be more than the corresponding capacity for all building above 5 storeys (i.e., 17.5 m height) studied here. An effort has been made for correlating the joint shear demand in any interior joint with the height of the joint. This will be helpful for identifying the critical joint location in a building.

Seismic Evaluation of RC Stepped Building Frames

‘Stepped building’ frames, with vertical geometric irregularity, are now increasingly encountered in modern urban construction. This chapter proposes a new method of quantifying irregularity in such building frames, accounting for dynamic characteristics (mass and stiffness). The proposed ‘regularity index’ provides a basis for assessing the degree of irregularities in a stepped building frame. This chapter also proposes a modification of the code-specified empirical formula for estimating fundamental period for regular frames, to estimate the fundamental time period of the stepped building frame. The proposed equation for fundamental time periods is expressed as a function of the regularity index. It has been validated for various types of stepped irregular frames. A new approach to determine the lateral load pattern, considering the contributions from the higher modes, is proposed that is suitable for pushover analysis of stepped buildings. Also, a modification to the displacement coefficient method is proposed, based on time history analysis of 78 stepped frames. When the newly proposed load pattern is combined with the modification of the displacement coefficient method of FEMA 356, the target displacement for the stepped building frame is found to match consistently the displacement demand given by the time history analysis.