Despite presenting a very high global warming toll, Portland cement concrete is the most widely used construction material in the world. The eco-efficiency, economy, and the overall mechanical and durability performances of concrete can be improved by incorporating supplementary cementitious materials (SCMs) as partial substitutions to ordinary Portland cement (OPC). Naturally found bentonite possesses pozzolanic properties and has very low carbon footprint compared to OPC. By applying activation techniques, the reactivity of bentonite can be improved, and its incorporation levels can be maximized. In this study, the influence of mechanical and thermo-mechanical activation of bentonite is investigated on properties of concrete. Bentonite was used for 0%, 10%, 15%, 20%, 25%, 30%, and 35% mass replacements of OPC. Mechanical (compressive strength and split tensile strength) and durability (water absorption, sorptivity coefficient, and acid attack resistance) properties were studied. Results of experimental testing revealed that, concrete containing bentonite showed good mechanical performance, while durability was significantly improved relative to control mix. Application of thermo-mechanical activation can enhance the incorporation levels of bentonite in concrete. At 15% and 25%, bentonite produced optimum results for mechanical and thermo-mechanical activation, respectively. Bentonite inclusion is more beneficial to the durability than the mechanical strength of concrete.

Tire-bead steel wires derived from the pyrolysis of waste-tires can be converted into the discrete reinforcement for fiber-reinforced concrete (FRC). This study for the first time presents the information about selecting the optimum dosage of recycled steel-fibers (RSF) in FRC application. Therefore, two most common types of RSF i.e., plain RSF (PRSF) and twisted RSF (TRSF) were incorporated in a high strength plain concrete (PC) at seven different volume fractions i.e., 0%, 0.25%, 0.5%, 0.75%, 1%, 1.5% and 2%. Both physical and mechanical properties of FRCs were studied including density, compressive strength-f_CU, modulus of rupture-f_R, splitting-tensile strength-f_SP, ultra-sonic pulse velocity-UPV, and water absorption-WA. The results revealed that TRSF performed better than PRSF in overall mechanical performance. Maximum compressive strength-f_CU, 9-12% higher than PC, was achieved with a 0.75% volume fraction of PRSF or TRSF. TRSF was extremely useful in upgrading the f_SP and f_R by more than 82% and 109%, respectively, at a 1.5% volume fraction w.r.t PC. PRSF-FRC showed lower permeability than TRSF-FRC at the same volume fraction. Lower volume fractions i.e., 0.25-0.5% RSF reduced the permeability of FRC, while higher volume fractions were detrimental to WA and RCP resistance. Experimental values of mechanical (i.e., f_SP and f_R) and permeability properties (i.e., WA and RCP) were accurately related to predicting RSF-FRC as a function of strength class of PC and reinforcement index. Graphical Abstract

Researchers have conducted numerous investigations on various repair techniques to restore the mechanical properties of fire-damaged concrete. However, most of the techniques are either expensive or require high technical skills. As a continuous work, this study involved an experimental investigation of the effects of various low-cost repair techniques to restore the mechanical properties of fire-damaged concrete. Sixty cylindrical concrete samples were subjected to heat ranging from 400°C to 800°C in a propane gas furnace. The samples were categorized into six groups, including the following: undamaged, fire-damaged, and fire-damaged and repaired using water curing; fire-damaged and repaired using cement-based slurry injection; re-curing fire-damaged and repaired with steel wire mesh along with epoxy resin wrapping; and fire-damaged and repaired using epoxy injection. The samples were tested for non-destructive and destructive tests, including ultrasonic pulse velocity, rebound hammer, and compressive strength. The results showed that the use of cement-based slurry injection along with the water-curing repair technique could regain almost 90% of its ultimate strength and secant stiffness, making it the most effective low-cost repair technique for fire-damaged concrete exposed up to 700°C.

Pounding occurs when the adjacent buildings start vibration out of phase during the seismic activity which causes collision amongst the adjacent buildings. There are many mitigation techniques to avoid or minimize the effects of pounding including the provision of minimum separation gap between the adjacent buildings. Although all codes have provided the minimum separation gap requirements for the buildings, still a lot of study is required on this topic. This research aims at finding the minimum gap requirement for midrise buildings in Pakistan. Adjacent Buildings with different geometry and height are modelled in Sap2000 software with varying gap elements. Pushover and In-elastic time history analysis of these buildings are carried out using ground motion of Kashmir earthquake. Buildings are assumed to be resting on stiff soil. Material and sectional properties are also remained same for all cases. In order to reduce the pounding effects of two buildings, they were attached with each other and top displacements of buildings were compared with separate buildings with inadequate gap. Column shear, maximum peak displacements and square root of sum of squares of maximum peak displacements were studied and the results were plotted graphically. It was found out that pounding can occur up to separation gap of six inch. Maximum pounding occurs at the top floor level of smaller building. The requirement for minimum gap in UBC 97 is found out to be conservative.