Indian Concrete Journal

Computational modelling of early-age temperature development in large concrete elements constructed in horizontal layers and exposed to solar radiation Yunus Ballim

This paper presents a finite-difference computational approach to modelling the early-age temperature development in a layer of sequentially cast concrete, that is subjected to heat input from the still-hydrating concrete layer below and, after a given time interval, receives a fresh layer of concrete above. Importantly, the model presented includes the effects of net solar radiation on the exposed top and side surfaces of the concrete as a component of the boundary conditions. The model results are compared with measured results obtained from a 1997 dam construction project. The results indicate that the model approach is reliable in predicting the temperature profiles and underlines the importance of including the effects of solar radiation in temperature prediction studies for large concrete elements.

Experimental study on mechanical and durability properties of steel, glass and hybrid fiber (steel and glass) based geopolymer concrete Kallempudi Murali, T. Meena

After water, concrete is the resource with the second highest available commodity on the whole planet. There is still widespread adherence to the practise of using Portland cement as a binder in concrete. The output of cement in India is expected to reach around 502 million tonnes in 2018, and the country's annual CO₂ emission rate is estimated to be 634 kg/ton. It is not recommended to use Portland cement for achieving environmental sustainability and the manufacture of Portland cement is associated with a number of environmental issues. The geopolymer supply (GGBFS, FA, glass fiber, and crimped steel fiber) and the alkaline activator (consisting of NaOH and Na₂SiO₃ with a molarity of 8M) have been taken into consideration as the framework for this study. The ratio of Na₂SiO₃ to NaOH used in this is 2.5 to 1. In this experimental study, some of the variables include the following: the binder 360, 420, and 450 kg/m³, the percentage of FA and GGBFS were taken in the ratio of 70:30, 60:40, and 50:50 respectively and the grades of Geopolymer concrete (GPC) are GPC 20, GPC 40, and GPC 60. Crimped steel fibers were added in amounts ranging from 0.1, 0.2 %, 0.3 to 0.4 %, and 0.5 %. In general, the addition of steel fibers to Geopolymer concrete results in an increase in both flexural and split tensile strengths of the material. The optimal dosage of steel fibers was found to be 0.4 percent (by volume fraction), and it was discovered that this dosage is reduced with the addition of steel fiber further. According to the findings of the tests, the addition of glass fibers to fiber-based GPC led to an increase in both split tensile strength and the flexural strength of the material. It was determined that around 0.3 percent of the volume of concrete comprise of glass fiber. In a similar manner, the mechanical and structural properties of steel and glass combined at a percentage of 0.3 percent are improved when the fibers are introduced in a hybrid form.

Comparison of stripping-times of formwork for reinforced cement concrete structures in selected codes of practices Kumar Neeraj Jha, Siddharth Shankar, Amarjit Singh

Reinforced Cement Concrete (RCC) is one of the most widely used composite construction materials worldwide for constructing shelters and infrastructure. Formwork is needed in RCC work to give different dimensions to various concrete elements. Estimating the stripping time of formwork is a big issue in RCC work as safety and the economy are both dependent on this. In the study, a review of codal provisions of the Indian, British, American, Japanese, German, and Ugandan Standards on stripping time of formwork was carried out. It was found that there is no uniformity across countries on the formwork stripping issue. Some codes rely on achieving a minimum strength while some codes rely on specifying the minimum time for stripping and some codes specify both. Our findings showed that most of the codes are silent on the stripping time when the temperature is less than 15 degrees Celsius. All codes do specify that formwork should not be removed if it results in excessive deflection or if it results in cracks and damages in the newly constructed RC structures. Some of the codes have suggested carrying out field tests and NDTs to determine the stripping time in case there is a variation in the conditions specified in the Standards. In general, for flexural members, stripping time for bottom formwork is recommended when the compressive strength of the freshly placed concrete achieves a strength of more than or equal to 70% of the concrete design strength. The stripping times of different concrete elements as specified in codes of practices followed in different countries vary from twelve hours to twentyeight days. However, some codes have listed the stripping period of formwork in terms of compressive strength of in situ concrete varying from 3.5 MPa to 14 MPa (N/mm²).

Assessment of acid and chloride resistance of ferrochrome slag based geopolymer concrete Satya Ranjan Prusty, Sanghamitra Jena, Ramakanta Panigrahi

In order to find sustainable alternative to the conventional concrete, several researchers have explored addition of different industrial wastes to develop geopolymer concrete offering improved durability properties. The current study examines the chemical resistance of geopolymer concrete (GPC) utilizing fly ash (FA), ferrochrome slag (FS) and alkaline activators exposed to acid environment along with its microstructural properties. Different tests such as change of weight and compressive strength were performed to find out resistance of GPC after immersions for 28, 56 and 90 days into 3 % solutions of sulphuric acid. Rapid Chloride Permeability test was conducted to study quantity of ionic charge entered into the GPC. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) analyses were conducted to study properties of GPC at microstructural level. The FS30 mix that contained 30 % FS has achieved the greater strength as well as better resistance against chemical attacks due to the crosslinked polymeric chain.

Development of structural forms using textile reinforced concrete Sachin Paul, Komathi Murugan, Ramakrishna Samanthula, Anusha S.Basavaraj, Stefie J Stephen, Ravindra Gettu, Raúl L. Zerbino

Textile reinforced concrete (TRC) is a composite material consisting of fabric reinforcement embedded in fine-grained concrete. Being an efficient construction material with high tensile strength, as well as strain-hardening behavior, it has the potential to be used in thin structural applications, such as roofs, façades, water tanks and other precast elements. The present work focusses on the fabrication of TRC elements with different techniques to obtain two- and three-dimensional structural forms. Description of the fabrication processes, including those used for the application of TRC in retrofitting of a structural column and modular tanks, is given in this paper. A brief review of the advantages of TRC and previous usage at the international level is also presented.