B. S. Dhanya

Bio: B. S. Dhanya is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Cementitious & Durability. The author has an hindex of 4, co-authored 8 publications receiving 37 citations. Previous affiliations of B. S. Dhanya include Government Engineering College, Sreekrishnapuram.

Sustainability-based decision support framework for choosing concrete mixture proportions

Abstract: A framework is proposed, along with two objective indices, for the selection of concrete mixture proportions based on sustainability criteria. The indices combine energy demand and long-term strength as energy intensity, and carbon emissions and durability parameters as A-indices, which represent the apathy toward these essential features of sustainability. The decision support framework is demonstrated by considering a set of 30 concretes with different binders, including ordinary portland cement (OPC), fly ash, slag and limestone calcined clay cement (LC3). In addition to the experimental data on compressive strength, chloride diffusion and carbonation, life cycle assessment has been performed for the concretes considering typical situations in South India. The most sustainable of the concretes studied here, for service life limited by chloride ingress, are those with LC3, OPC replaced by 50% slag, and ternary blends with 20% each of slag and fly ash. In the case of applications where carbonation is critical, the appropriate concretes are those with OPC replaced by 15–30% slag or 15% fly ash, or with ternary blends having 20% slag and 20% Class F fly ash.

Carbonation model for concretes with fly ash, slag, and limestone calcined clay - using accelerated and five - year natural exposure data

Abstract: Supplementary cementitious materials (SCMs) can be used in concrete to enhance sustainability and reduce the concrete industry's carbon footprint. However, some negative perceptions about their long-term carbonation resistance are obstacles for large-scale implementation of such concretes. This study evaluated the carbonation resistance of 34 concretes (with Ordinary Portland Cement, fly ash, blast furnace slag, and limestone calcined clay) in natural tropical exposure conditions (Open and Sheltered) for 5 years and in accelerated exposure conditions (1 and 3% CO2) for 112 days. Using these data and the square root of time function, the carbonation coefficients (KCO2, natl and KCO2, accl) of these concretes were estimated and a good correlation between them could not be observed. Hence, a more generic model (named as “A-to-N model”) to estimate the KCO2, natl using the KCO2, accl, CO2 concentration, and mixture proportion of concrete was developed, for which the mean absolute percent error is about 12% (reasonable accuracy). Using the A-to-N model, the carbonation depth at 50 years was estimated for various concretes. SCM concretes with low water-binder ratio and optimal binder content showed high resistance against carbonation at later ages; such information along with the target cover depth must be used while selecting materials for concrete design. Based on the model developed, a relatively simple ‘service life design chart’ was developed. This chart can be used by engineers to set the target KCO2, natl or KCO2, accl, and select the cover depth and binder type to provide the target service life (i.e., corrosion initiation time). This paper clearly shows that SCMs can be used to design concretes with comparable long-term carbonation depth as OPC concretes.

Performance evaluation of rapid chloride permeability test in concretes with supplementary cementitious materials

Abstract: Rapid chloride permeability test (RCPT) is one of the widely used test methods to rapidly assess the durability of concrete, specifically its resistance against chloride ion penetrability. Many researchers have questioned the applicability of RCPT in mixes having supplementary cementitious materials (SCMs). The present work analyses the performance of RCPT in concretes that contain different dosages of three SCMs such as slag, Class F fly ash and Class C fly ash. In addition to the conventional measurements of current at half an hour interval, other details of the tests such as initial current, temperature development during the experiment, and depth of chloride ion penetration are also measured. Good correlations are obtained between total charge passed and other additional measurements such as initial current, depth of chloride ion penetration, temperature reached during the experiment etc., which are reported by other researchers with mixes having only OPC as binder. Furthermore, the results of RCPT are well correlated with the results of Wenner 4-probe surface resistivity test, which is free from many of the criticisms of RCPT. The paper concludes that RCPT can be used as a reliable accelerated test method to assess chloride ion penetrability in concretes that have supplementary cementitious materials such as fly ash and slag.

Performance evaluation of concretes having different supplementary cementitious material dosages belonging to different strength ranges

Abstract: Production of durable concrete at lower strength levels is always a challenge for concrete technologists. One way to achieve this objective is by the use of Supplementary Cementitious Materials (SCMs). An attempt has been made in this paper to develop indicators called performance indicators, which combine both strength and durability criteria. Limiting values of these indicators are also suggested. Different mixes in the same strength range are classified into different performance classes based on these performance indicators. The durability parameters evaluated here include surface resistivity, charge passed, sorptivity index and oxygen permeability index. The database generated can act as a guideline for material selection and it demonstrates the potential of SCMs to improve durability.

Mechanical properties and durability performance of concretes with Limestone Calcined Clay Cement (LC3)

Abstract: The adoption of any binder system for structural concrete depends on the performance characteristics desired for addressing the long-term deformation and durability concerns. The major properties influencing the performance includes the shrinkage characteristics governing the long-term deformation, and durability characteristics related to various transport mechanisms, governing the performance in different service conditions. This paper describes the potential of Limestone Calcined Clay Cement (LC3) for use in structural concrete in comparison with Ordinary Portland Cement (OPC) and fly ash based blended cement (FA30). Three types of concrete mixtures were designed for the study, two based on achieving an equivalent strength grade (M30 and M50 concrete grade) with each binder, and the third with equal binder content and w/b ratio. Mechanical properties such as compressive strength and elastic modulus, and autogenous and drying shrinkage, along with various durability parameters of the different concretes were assessed. Oxygen permeability, rapid chloride penetration, chloride migration, resistivity development and water sorptivity were the various parameters considered for evaluation of durability performance. The results indicate the superiority of LC3 binder over other binders in producing durable concrete, especially in a chloride laden environment. The major reason for the better performance was attributed to the more compact and dense microstructure of the system with the LC3 binder against OPC and FA30. The drying shrinkage performance was seen to be similar for concrete with all three binders.

Limestone calcined clay cement and concrete: A state-of-the-art review

Abstract: This article reviews the rapidly developing state-of-the-art literature available on the subject of the recently developed limestone calcined clay cement (LC3). An introduction to the background leading to the development of LC3 is first discussed. The chemistry of LC3 hydration and its production are detailed. The influence of the properties of the raw materials and production conditions are discussed. The mixture design of concrete using LC3 and the mechanical and durability properties of LC3 cement and concrete are then compared with other cements. At the end the economic and environmental aspects of the production and use of LC3 are discussed. The paper ends with suggestions on subjects on which further research is required.

Sustainable materials for 3D concrete printing

Abstract: This paper explores the sustainability aspects of binders used in concrete 3D concrete printing. Firstly, a prospective approach to conduct sustainability-assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing. The potential of the material production phase is emphasized to enhance the sustainability potential of 3DCP by reducing the embodied impacts. The literature on the different binder systems used for producing 3D printable mixtures is reviewed. This review includes binders based on portland cement and supplementary cementing materials (SCMs) such as fly ash, silica-fume and slag. Also, alternative binders such as geopolymer, calcium sulfo-aluminate cement (CSA), limestone calcined clay cement (LC3) and reactive magnesium oxide systems are explored. Finally, sustainability assessment by quantifying the environmental impacts in terms of energy consumed and CO2 emissions of mixtures is illustrated with different binder systems. This paper underlines the effect of using SCMs and alternative binder systems for improving the sustainability of 3D printed structures.

Macro–meso–micro experimental studies of calcined clay limestone cement (LC3) paste subjected to elevated temperature

Abstract: In this study, the macro properties (residual compressive strength), meso properties (mesoscopic images), and micro properties (reaction products and pore structures) of paste specimens with various limestone and calcined clay contents at elevated temperatures (20, 300, 550, and 900 °C) are experimentally investigated. According to the experimental results, (1) the strengths of all samples increase at 300 °C, while those of the LC3 ternary blended pastes increase more significantly because of the formation of katoite and the further hydration of binders. After the treatments at 550 and 900 °C, the reduction in the strengths of the LC3 samples is greater than that of the plain paste. (2) With further increasing temperature, all samples generate more meso cracks. (3) At 900 °C, a large gehlenite crystalline phase is formed in the samples with calcined clay. In summary, the microscopic explanation for the macroscopic and mesoscopic properties of LC3 paste at elevated temperature is investigated.

Effects of adding sugarcane bagasse ash on the properties and durability of concrete

Abstract: Ashes from biomass burning, such as from sugarcane bagasse, have great potential as supplementary cementitious materials. The sugarcane bagasse ash (SCBA) possesses high pozzolanicity. However, limited studies have investigated the influence of SCBA on the durability of concrete. A knowledge gap exists regarding the influence of these ashes on the lifetime of reinforced concrete in terms of chloride migration and carbonation. Moreover, additional studies on the effects of SCBA on the alkali–silica reaction (ASR) are essential because this ash generally has a high alkali content. In this study, the effects of adding 5%, 10%, and 15% SCBA on the properties and durability (chloride migration, carbonation, and alkali-aggregate reaction) of concrete were investigated. Furthermore, the SCBA pozzolanicity was evaluated and lifetime estimations in terms of chloride ingress and carbonation were performed. The studied ash demonstrated high pozzolanic activity, which reduced the porosity and water absorption by capillarity and increased the mechanical strength of the concrete. However, because the alkaline reserve was reduced, the concrete with SCBA exhibited a higher carbonation rate (up to 69%) and a shorter lifetime regarding carbonation. Nevertheless, all concrete specimens had a lifetime of more than 50 years in an industrial environment, except for that with 15% SCBA. Adding SCBA also reduced the chloride diffusion coefficients, increasing the lifetime by up to 97.3%. SCBA addition of up to 5% mitigated the ASR owing to the pozzolanic reaction and additional C-S-H formation.