Yuvaraj Dhandapani

Bio: Yuvaraj Dhandapani is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Cement & Portland cement. The author has an hindex of 9, co-authored 17 publications receiving 503 citations. Previous affiliations of Yuvaraj Dhandapani include University of Leeds.

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.

Assessment of pore structure evolution in the limestone calcined clay cementitious system and its implications for performance

Abstract: Use of limestone and calcined clay together for clinker substitution makes an effective low clinker cement blend, which shows promising mechanical properties at early ages. The performance of these cementitious systems strongly depends on the pore structure, which is a dominant factor governing the durability characteristics because of its direct influence on the transport properties. The experimental study described in this paper on three different binder systems including Ordinary Portland Cement, Portland Pozzolana Cement - with 30% Type F Fly Ash (designated FA30) - and Limestone Calcined Clay Cement (LC 3 ) pastes shows that the LC 3 system attains greater refinement of the pore structure as early as 3 days, as seen from mercury intrusion porosimetry. Electrical measurements also reveal lower conductivity in the system, which suggests better resistance to ionic transport in the binder phase. The results of hydrate phase assemblage studied by X-ray diffraction also indicate that greater amount of hydrates contribute in a major way to the reduction in the (water-filled) porosity in all the systems. This change occurs at varying rates for the different systems due to the difference in hydration characteristics. The estimated permeability suggests that the LC 3 binder system attains much lower permeability compared to the ordinary Portland cement and FA30. A comparison of the formation factor shows distinct differences in the microstructural development and suggests a more durable binder with LC 3 cementitious system.

Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

Abstract: A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well.

Report of TC 238-SCM: hydration stoppage methods for phase assemblage studies of blended cements—results of a round robin test

Abstract: For many microstructural studies it is necessary to “stop” cement hydration—to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH)2 content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round robin test three recommendations are made. (1) Oven drying at 105 °C is not recommended. This dehydrates, alters and decomposes calcium aluminate hydrates significantly more than other methods and often produced carbonation artefacts. (2) Isopropanol exchange is the most appropriate hydration stoppage method for the study of the complete hydrate assemblage of cements, including calcium aluminate hydrates such as ettringite and AFm phases. (3) For quantification of portlandite (Ca(OH)2) all tested hydration stoppage protocols are satisfactory, with the exception of oven drying.

Service life and life cycle assessment of reinforced concrete systems with limestone calcined clay cement (LC3)

Abstract: This paper presents data on the chloride diffusion coefficient (Dcl), ageing coefficient (m) and chloride threshold (Clth) related to seven concrete mixes (four M35 and three M50) with OPC, OPC + PFA (pulverised fuel ash) and limestone-calcined clay cement (LC3). Using these, the service lives of a typical bridge pier and girder with the PFA and LC3 concrete were found to be much higher than those with OPC concrete of similar strength. From life-cycle assessment, the CO2 footprint of PFA and LC3 concrete were found to be significantly lower than those of OPC concrete of similar strength. Further, the CO2 emissions per unit of concrete per year of estimated service life, as a combined indicator of service life and carbon footprint, are similar for concrete with PFA and LC3, which are much lower than that with OPC.

Supplementary cementitious materials: New sources, characterization, and performance insights

Abstract: Conventional supplementary cementitious materials (SCMs), such as blast furnace slags or fly ashes, have been used for many decades, and a large body of knowledge has been collected regarding their compositional make-up and their impacts on cement hydration and concrete properties. This accumulated empirical experience can provide a solid, confident base to go beyond the status quo and develop a new generation of low-clinker cements composed of new types and combinations of SCMs. The need for new sources of SCMs has never been greater, as supplies of traditional SCMs are becoming restricted, and the demand for SCMs to reduce CO2 emissions from concrete production is increasing. In this paper, recent research on emerging SCM sources is reviewed, along with new developments in characterizing and qualifying SCMs for use and improved knowledge of SCMs on long-term concrete performance and durability.

Reactivity of supplementary cementitious materials (SCMs) in cement blends

Abstract: Supplementary cementitious materials (SCMs) are key components of sustainable, low carbon cements. To maximize their use in blended cements, the impact of SCMs on cement hydration needs to be understood and accurately captured by models. A central element in such models is the reactivity of the SCM, which is tedious to measure. Establishing relationships between SCM properties and their intrinsic reactivity is therefore highly important. Moreover, mechanisms enhancing or limiting SCM reactivity in blended cements need to be well-understood. This work reviews recent progress in the description and understanding of the reactivity of SCMs and their impact on Portland clinker hydration. Insights derived from fundamental work using synthetic SCMs, dissolution experiments and model systems are discussed as well as recent work studying the impact of common SCMs on hydration and microstructure of blended cements. Particular attention is paid to recent work on calcined clays, which are currently receiving substantial interest.

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.

Advances in alkali-activation of clay minerals

Abstract: To future-proof alkali-activation technology, there is a need to look beyond well-established precursors such as fly ash and blast furnace slag, due to resource competition, geographical distribution and technical limitations. Clay minerals are abundant and diverse aluminosilicate resources available around the world. However, due to the mineralogical complexity amongst the most common 1:1 (kaolinite, halloysite) and 2:1 (montmorillonite, illite) clay minerals, and practical issues such as workability, their use has been more limited. Recent advances have improved understanding both of pre-activation treatments (thermal, mechanical, chemical), and of the factors influencing clay reactivity, phase assemblages and properties of final products. This opens new opportunities for the exploitation of these resources to produce sustainable cements. A one-size-fits-all approach for processing and activating clay minerals is not viable. Instead, activation routes need to be tailored according to the clay mineralogy to achieve the binder properties required for key applications.

Durability, service life prediction, and modelling for reinforced concrete structures – review and critique

Abstract: Ever increasing attention is being paid to deterioration prediction and service life modelling of reinforced concrete structures. Research has progressed to a stage where service life models and design philosophies are, to varying degrees, included in some codes and standards, such as the fib Model Codes and ISO 13823. This has helped to base practical durability design on sound engineering approaches. This paper reviews service life modelling and prediction, and service life design, covering limit state design philosophies and deterioration models. An overview on recent developments, and a critical review on common assumptions in service life modelling and on the application and limitations of the various approaches, are presented. It is emphasised that design approaches and models need to be validated with field observations. It is argued that a performance-based approach is the most suitable engineering tool for durability design.