Ravindra Gettu

This paper focusses on the influence of cement type (Ordinary Portland Cement, OPC; and Fly ash based Portland Pozzolana Cement, PPC), polycarboxylic ether (PCE) superplasticizer and calcium nitrite inhibitor (CNI) on the corrosion resistance of cracked reinforced concrete in chloride-rich environments. U-shaped specimen reinforced with 12 mm diameter bar was used for initiating flexural cracks of required width. Accelerated impressed current test results show that the weight loss of rebar for concrete with PPC is found to be significantly lower and the weight loss of rebar for concrete with CNI is significantly higher, when compared to that of the weight loss of rebar for concrete with OPC alone. The results show that the relative service life of PPC based concrete is found to be at least twice that of corresponding OPC based concretes.

In this work, limestone‐calcined clay (LC2) is studied as an alternative supplementary cementitious material (SCM), combining two widely available resources – calcinated kaolinitic clay and limestone, to partially substitute portland clinker. The primary goal is to assess the potential of LC2 to produce moderate to high strength concretes with design compressive strengths of 20 to 50 MPa. For this purpose, 27 mixes with LC2 were prepared with a range of binder contents and water‐binder ratios, and the performance was benchmarked against those of mixes having fly ash (PFA). In addition to the quantification of strength and concrete resistivity, life cycle assessment was performed for the concretes considering a typical situation in India. The efficiency of concretes made with LC2, PFA and ordinary portland cement (OPC) was analyzed using the energy intensity index (eics) and apathy index (A-index) as sustainability indicators. This framework establishes the sustainability potential of the LC2 with insights on the influence of strength on the indicators. It is concluded that the LC2 concretes with 45% replacement level, w/b≤0.45 and binder content lower than 400 kg/m3 possess the highest sustainability potential, among the concretes studied here.

The significance of the creep behaviour of fibre reinforced concrete (FRC) in the cracked state is a matter of debate. As FRC in service could be in the cracked state, the serviceability and failure will depend on the stability of the cracks, and the alteration of the capacity to transfer stresses. Based on the present knowledge, this paper discusses factors influencing the creep of cracked FRC to facilitate further discussions. Effects of load, temperature and humidity, and the importance of progressive debonding and pull-out, creep of the fibres and crack propagation under sustained loading have been discussed for steel and polymer fibres.

Evaluating and quantifying the scientific output of a researcher is a complex problem that may not benefit from standardized or uniformly accepted solutions. Over the past few decades, various indices, including the most popular h-index, have been introduced for assessing the output and quality of research publications. The uniform application of a single index to researchers with varying age, tenure, gender, economies, funding opportunities, nature of tasks performed, etc., can introduce significant bias, eventually leading to inappropriate assessment results for promotion and tenure. Further, no indices explicitly account for the time spent on teaching-related tasks, advising students for their projects not necessarily resulting in publications, and administration work leading to a situation that favors colleagues who are focused only on research. A new metric, called GG-index, for internal use by institutions of higher education, is proposed to evaluate researchers who have spent a minimum of five continuous years at the academic/research institution. This GG-index is calculated from the h-index, the logarithm of the scientific tenure, citations/paper over the recent 5-year period, and a correction factor that considers the relative dedication to research and the researcher’s field. A survey was conducted of some top researchers in various fields, and their publication parameters and responses are used to illustrate the robustness and characteristics of the GG-index. We further demonstrate how the GG-index complements the h-index and helps mitigate the bias against researchers with long-term breaks for maternity, childcare, and other personal reasons. Further, young researchers with good recent publication impact (reflected by high citations per paper) and those working in fields with low citations would also be benefited. It is, however, to be noted that the GG index strongly relies on data available with the institutions, thus making it suitable for the internal assessment of faculty/researchers.

In order to move towards a circular economy, it is relevant to maximize the usage of waste materials in construction activities. One such resource that could be extracted from abundant waste are Recycled Concrete Aggregates (RCA). Many methods have been proposed in the last few decades to improve the quality of RCA, with limitations in terms of energy demand or low yield. In the present study, an attempt has been made to employ thermo-mechanical beneficiation to obtain high-quality coarse and fine aggregates, with high yield (>90%). Heating temperature, feed size and residing duration are variables that have been optimized. When waste concrete chunks are heated for about 60 min at 500 °C (932°F) and milled with steel ball charge, the resulting RCA fractions conform to the limits set by stringent codes and guidelines. The beneficiated coarse RCA thus obtained could give concrete performance comparable to that of pristine granite aggregate concrete.

A study on the use of amorphous metallic fibers (AMFs) in concrete was undertaken to combine its action with that of hooked-ended steel fibers for improving flexural strength and toughness. Tests on mixtures with various dosages of AMF (10, 20, and 30 kg/m3 [16.9, 33.7, and 50.6 lb/yd3]), and 15 kg/m3 (25.3 lb/yd3) of steel fibers were carried out, along with hybrid mixtures with two dosages of AMF. The results showed a significant increase in the flexural strength of concrete with the addition of AMF, even at low dosages. The performance of concretes with the hybrid combinations is significantly enhanced. For example, the equivalent flexural strength for the concretes with just 10 kg/m3 (16.9 lb/yd3) of AMF and 15 kg/m3 (25.3 lb/yd3) of steel fibers is 35% higher than with only steel fibers and is approximately 3.5 times that obtained with only 10 kg/m3 (16.9 lb/yd3) of AMF. The load-deflection behavior and the toughness parameters clearly indicate a significant synergy in the hybrid combination.

This study presents a series of tests for characterizing the structural behaviour of fibre reinforced concrete beams subjected to shear loading. The experimental program involves three types of fibres; two steel fibres and a polypropylene fibre. As a reference, plain concrete and conventionally reinforced concrete specimens have also been tested. The ultimate shear capacity of the beams is calculated and these values compared with those predicted by existing formulations. The study confirms that the toughness and shear crack resistance of the material is greatly enhanced by the fibres. However, the incorporation of 1% of fibres yielded lower shear strength than conventionally reinforced beams with the same amount of steel in the form of transversal stirrups. Existing design methods seem sufficiently robust to estimate the maximum shear load, even when using material properties (toughness, tensile strength) extrapolated from code formulae.

The rate of ingress of external elements (that is, chlorides, carbon dioxide, oxygen, moisture, and so on) through the cover concrete is a key parameter influencing the durability of concrete structures. It can take several decades to estimate the realistic rates of ingress of these elements through concrete systems in the field - under natural exposure. Therefore, several accelerated test methods have been developed by various researchers to qualitatively estimate and compare the durability of various concrete mixtures in a reasonable period of time. Three such methods are (i) Wenner resistivity test, (ii) Rapid Chloride Penetration Test (RCPT) [ASTM C1202] and (iii) Accelerated Chloride Migration Test (ACMT) [NT Build 492]. This work presents a study on the correlation between the results from the Wenner resistivity tests and the RCPT and ACMT methods. The experimental design included 20 types of concrete (selected combinations using four independent variables). These independent variables and their levels were: (i) water-binder ratio (0.5, 0.55, 0.6 and 0.65); (ii) total binder content (280, 310, and 340 kg/m3); (iii) supplementary cementitious materials (SCMs) content (slag, class C fly ash and class F fly ash with 0%, 15% and 30% replacement); and (iv) curing period (28 and 90 days).

Organic repair products for concrete can be exposed to accidental incidents, like fire. The increase of temperature produces a modification in some of their properties. In general, these types of repair products have organic fibers to increase their tixotropic properties, but they are more sensible to the high temperature than the Portland cement or aggregates. In order to analyze the behavior of organic repair mortars with temperature three types of repair mortars are studied. These repair products have the organic components composed by acetate fiber of polyvinyl like Vinyl Acetate Acrylate (VAA), Copolymer of Vinyl Acetate Vinyl Versatate (VeoVA) and Acrylic polymers fibres. The repair products are tested increasing the temperature from 1.7°C /min until 200°C, 400°C or 600°C respectively during 20 minutes. After that, the samples are cooled in four different cooling conditions two of them slow and two others fast, and with and without oxygen. These conditions are used in order to simulate the different conditions that can occur during the cooling after fire. After the testing the visual aspect, the color and brightness and the open porosity is analyzed in each condition of test. In this work the relationship between the temperature of exposition, the cooling conditions and the change in some physical properties are studied.

The characterization of the complete uniaxial compressive stress-strain curve of concrete is crucial for a more rational and reliable design of concrete structures. However, without intrinsic knowledge of the influence of different experimental control variables and the failure mechanisms of concrete, it is impossible to obtain a stable softening response in a test. This paper discusses the various aspects to be considered while performing the characterization, provides a comprehensive description of the different steps involved in the post-processing of the obtained experimental data. The influence of different test variables such as the type of contact, specimen size, rate of loading, the grade of concrete and fibre dosage on the compressive response is also elucidated. The complete stressstrain curves for different concretes have been obtained using the proposed procedure, which can serve as guidelines for such characterization. The brittleness of higher strength concrete is clearly manifested by a stress-strain curve that descends more sharply than those of conventional concretes. Further, it is seen that the incorporation of steel fibres mitigates the brittleness by improving the compressive toughness through bridging of the cracks and internal confinement.