Vineet Shah

A Correlation Study Between Lime Reactivity Strength Test and Calorimeter for Different SCMs

Supplementary cementitious materials (SCMs) are added to improve various mechanical and durability properties of cement and concrete. One of the indirect benefits of binary and ternary blended cements is to reduce CO2 emissions. As per Indian standards (IS), reactivity of pozzolanic material is observed in the presence of calcium hydroxide (CH) using lime reactivity test. A pozzolana should qualify lime reactivity test before adding it to the cement. In this study, reactivity of SCMs was observed using lime reactivity strength test and isothermal calorimeter. For this purpose, different calcined clays, fly ashes (FA), and slags were selected. Lime reactivity test was used to study the mechanical strength potential of SCMs and calorimeter was performed to measure total energy evolved during the reaction of SCMs with CH in the presence of water at 27 °C. Strength data from lime reactivity test was then finally correlated with the calorimeter heat evolved data in different conditions.

Change in Microstructure Properties of Concrete on Accelerated Carbonation

Carbonation of concrete is a complex physicochemical process. The overall volume of the system changes due to carbonation of different hydration products. During carbonation, t products formed on conversion of calcium hydroxide have a higher volume as compared to the initial products, thus the surplus volume fills up the empty space in the capillary system, resulting in a reduced porosity. Supplementary cementitious materials (SCMs) consume calcium hydroxide by pozzolanic reaction, which is the majorly responsible for high alkalinity. Volume change due to CSH transformation is most uncertain, and the type of polymorph formed depends on the calcium-to-silica ratio and water content of the silica gel. Therefore, the change in the microstructure of concrete due to carbonation depends upon the type of cement. In this study, the effect of accelerated carbonation on the microstructure of concrete, made from different cements, was analysed. Change in properties of concrete such as porosity, sorptivity and permeability with carbonation was studied. Accelerated carbonation was carried out at 1 and 3% CO2 concentration. From the results, it can be inferred that irrespective of the type of cement used, the porosity of the system increases on carbonation. Similarly, results were also obtained for sorptivity and air permeability.

Applicability of Lime Reactivity Strength Potential Test for the Reactivity Study of Limestone Calcined Clay Cement

Limestone calcined clay cement (LC3) allows clinker replacement up to 50% but it can also be designed for other replacement levels based on the quality of raw materials and required properties. In this study, LC3 was prepared with different proportions using clinker replacement levels of 50%. Two different types of calcined clay and three different types of carbonates were used as supplementary cementitious materials (SCMs) for preparing LC3. The compressive strength of LC3 cement mortar cubes were checked for the age of 28 days. The pozzolanic strength potential of limestone and calcined clay (LC2) blends were tested with the lime reactivity test as per Indian Standard 1727. The lime reactivity test showed the highest reactivity for blends comprising clay and limestone in the proportion of 2:1. Similar result was observed in the case of LC3 mortar strength. The 28 days cement mortar strength results were correlated with the lime reactivity strength potential test and good correlation was observed. On the basis of results, it was concluded that the lime reactivity strength potential test could be directly applicable to the reactivity study of LC3 even at varying proportions of limestone and calcined clay.

Durability Characteristics of Sustainable Low Clinker Cements: A Review

Cement is an important industrial product for economic development. Global consumption of cement is predicted to continue to grow from current level of 450 kg per capita with escalation in economic growth of world. Cement production is an energy intensive industry and the industry is facing major challenges in terms of the air pollutants produced during production along with that amount of energy resources invested in the production process and consumption of natural resources. Use of low clinker cement can ensure to provide sustainable explanation to minimize the total environmental impact. Use of various supplementary cementitious materials as clinker replacement is being carried out since past 70 years. In order to mitigate the long term impacts on structures built using such binders, the durability study is of utmost importance. In this paper a comparative study of various low clinker cements consisting of fly-ash, slag, calcined clay, limestone and their subsequent effect on durability is reviewed.

Protocol for Prediction of Durability of New Cements: Application to LC3

As Ordinary Portland Cement has been the most widely used binder till 1990s, its long term behaviour in concrete is well understood. However, environmental concerns and resource availability has driven cement industry to move to use of supplementary cementitious materials and developing new binders with less environmental footprint and more utilisation of locally available resources. As more such cements suiting local needs get developed, it will be critical to rapidly understand the durability of concretes containing these blends so as to reduce the typical period required to standardise cements. Since durability related tests are, by definition, time-consuming, this paper suggests a framework that can be used to gain a faster prediction of the performance of these cements when subjected to different deterioration processes. The application of this framework to Limestone Calcined Clay Portland Cement is also described. This framework promises to significantly reduce the time required for the standardisation of new cements, saving precious resources in the process.

Use of Marble Dust as Clinker Replacement in Cements

Around 6 million tonnes of marble dust, which is a waste product of marble polishing and grinding, is currently being dumped annually in three states in India. Though previous studies have investigated the use of this material as a replacement of fine-aggregate, since its particle size distribution is closer to that of cement, it could be more suitable as a clinker replacement. As the primary molecule in marble dust is calcium carbonate, the same as limestone, this study looks at the possible use of marble dust in ways similar to crushed limestone. Blends of ordinary Portland cement (OPC) with marble dust, with and without fly-ash and calcined clays as sources of alumino-silicates, were prepared and tested in the laboratory. The role of activators such as gypsum and sodium sulphate was also studied. The results show that although marble dust may be less reactive in such systems than limestone, it offers the advantage of better workability in concretes using these blends.