Rebar corrosion is a significant deterioration problem in concrete that critically impacts the durability and structural integrity of reinforced concrete (RC) structures. The passivation and corrosion mechanisms substantially influence the service lifespan of steel rebar in the surrounding electrolytic environment. The passivation mechanism is a complex process dependent on the composition, microstructure, and surface condition of the steel rebar. The present work discusses the passivation and corrosion behavior of commonly used quenched self-tempered or thermos-mechanically treated bars (TMT), stainless steel (SS), and mild steel (MS) reinforcing bars in both chloride-free and chloride-contaminated simulated concrete pore solutions. Electrochemical techniques such as open circuit potential (OCP), linear polarization resistance (LPR), and cyclic polarization(CP) tests were carried out to evaluate passivation and corrosion behaviour of steel rebar specimens in chloride-free and chloride-contaminated simulated concrete environments. In addition, Mott–Schottky assessments were carried out to study the behavior and stability of passive oxide films formed on the rebar specimens. Results indicate that in chloride-free and chloride-contaminated simulated cementitious environments, the stainless-steel specimens exhibited stable and protective passive films characterized by low donor density, space charge thickness, and current density. Nevertheless, MS and TMT exhibited relatively higher current densities, which is due to the effect of lower capacitance. The n–type behavior was observed in TMT and MS specimens, which could be due to the inherent differences in the composition and microstructure.
This study is an experimental work that covers the development and production of alkali activated concrete (AAC) in a ready mix concrete (RMC) plant for the construction of a demo structure of a one-story with a plinth area of approximately 90m2 . AAC formulated with a glass granulated blast furnace slag (GGBS) to fly ash (FA) ratio of 70:30 serves as an ecofriendly and sustainable alternative to ordinary Portland cement (OPC) cement concrete. The research addresses the critical gap between laboratory study and on-site application, providing data to support the standardization and widespread implementation of AAC in the construction industry. The focus area of the research is a) High workability and its Retention at the site b) Ambient curing capability c) Validating structural performance through in-situ load testing. The AAC mix of grade M35 was developed after several iterations to achieve the desirable characteristics suitable for RMC construction as an alternative to OPC concrete. The collapsible slump is obtained at the batching plant, and after 1 hour, the slump is found to be around 150 mm for the mix. The temperature of the alkali activator initially reached around 70°C upon mixing. The temperature regulation is crucial to optimizing mixing conditions and ensuring safe handling. The successful retention of workability over an extended period led to the successful implementation of ready mix AAC. The Load-deflection testing of the structure confirmed more than 91 % recovery and compliance with safety criteria. Embedded and surface-mounted strain gauges revealed linear strain distribution, aligning with bending theory. The construction of demo structures with AAC using RMC helps in understanding the challenges of using AAC in construction projects. This study is an important step towards AACs viability in RMC applications, advancing sustainable construction practices.
This research work investigates the technical viability of producing artificial lightweight aggregates from municipal solid waste incinerated bottom ash (MSWIBA), municipal solid waste incinerated fly ash (MSWIFA), and cement through an autoclaving process. Before pelletization, MSWIFA underwent a washing process, resulting in a reduction of approximately 95 % chloride and 75 % sulphate content. The production of lightweight aggregates involved a single-step pelletization process using a disc-type pelletizer with optimum conditions of pelletizer speed of 35-45 RPM, pelletization duration of 20-30 minutes, and water/solid ratio of 0.30-0.35. Various ratios of MSWIBA, MSWIFA, and cement were trialed out with a proportion of MSWIBA : MSWIFA : Cement = 50:25:25 yielding the best results. The green pellets were cured in an autoclave and optimized for pressure, temperature, and retention time. The aggregates developed through the autoclaving process at a pressure of 3 bar with a temperature of 120°C, and a holding time of 60 minutes exhibited a bulk density of ~846 kg/m3, water absorption of ~11.5 %, and single pellet strength of ~2.8 MPa. After carbonation, an increase of ~2.5 times in single pellet strength and a 21 % reduction in water absorption is achieved due to the formation of phases like tobermorite, calcite and jennite. The developed lightweight aggregates sequester ~5.2 % of CO2 into it and gainfully utilize ~75 % of municipal solid waste incinerated ashes. The spherical-shaped lightweight aggregates are in the range of 4-15 mm in size and can be used in making non-structural elements like bricks, blocks, and roof insulation. The leaching behavior of heavy metals from MSWI bottom and fly ash showed significant reduction upon incorporation into concrete, confirming effective immobilization through cement hydration products and compliance with united states environmental protection agency (USEPA) limits. The embodied energy analysis of lightweight aggregates (LWAs) made from MSWI residues demonstrated relatively low energy input for raw materials (5.63 MJ/tonne) due to minimal pre-processing, and highlighted the potential for further reducing overall energy through optimized transportation and manufacturing processes.
Water absorption in unsaturated porous building materials plays a crucial role in determining their durability performance. The classical Richards equation has been widely used to model this phenomenon for materials that exhibit a linear relationship between the square root of time and the cumulative mass of water absorbed per unit exposed area. However, some materials, including brick, stone, and concrete, exhibit deviations from this behavior. To account for this anomaly, various improvements and alternatives for the Richards equation have been proposed. These include non-Fickian diffusion, timedependent diffusivity, time-dependent permeability, fractional differential equation, and fractal Richards equation. The fractal Richards equation accounts for the complex pore structure of the building materials by incorporating fractal dimensions. This study evaluates an approximate analytical solution to the fractal Richards equation for both power-law and exponential diffusivity functions. The analysis is based on water absorption profiles for seven different materials namely fired clay brick, siliceous brick, red-colored fired clay brick, cement-lime-sand mortar, standard cement-sand mortar, Lepine limestone, and Sandstone, sourced from the literature, using a leave-one-out cross-validation approach. Results indicate that the exponential diffusivity model fits the experimental data better compared to the power diffusivity model. It is also revealed that the power law-based solution exhibits an artifact, manifesting as an unexpected increase in saturation at greater depths.
August 2025
Volume - 99
Number : 08
July 2025
Volume - 99
Number : 07
June 2025
Volume - 99
Number : 06
May 2025
Volume - 99
Number : 05
April 2025
Volume - 99
Number : 04
March 2025
Volume - 99
Number : 03
February 2025
Volume - 99
Number : 02
January 2025
Volume - 99
Number : 01
December 2024
Volume - 98
Number : 12
November 2024
Volume - 98
Number : 11
October 2024
Volume - 98
Number : 10
