Pozzolanic Efficiency of Calcined Clays in Blended Cements with Focus on the Early Hydration

The fundamental knowledge about the reaction mechanism of calcined clays in cement and the mutual interaction is important for their assessment as supplementary cementitious material and the resulting concrete properties. In this study, the hydration of two cements differing in alkali content and with the addition of a highly reactive, aluminum-rich metakaolin and one calcined common clay with low kaolinite content was investigated during the first 48 hours. For this purpose, four established methods that describe the early hydration were used: isothermal calorimetry, thermogravimetry, in-situ X-ray diffraction and chemical analysis of pore solution. This so far unique combination of methods enabled the understanding of the complex binder (cement-calcined clay) hydration behavior. The results showed considerable differences depending on type of calcined clay, its chemical-mineralogical composition, fineness and especially towards its reaction mechanism with aluminate clinker phases controlled by the composition of pore solution. The impact of calcined clay on the early clinker hydration exceeds significantly physical effects only.

A Study on Differential Characteristics of HSC Containing RHA and M-Sand as an Aggressive Environment

Concrete is a versatile material and can be extended to applications requiring to perform in aggressive environments. In these environments, concrete should be highly durable for longer service life. The present thesis is an effort directed towards the achieving high performance in concrete by using RHA as supplementary cementitious material. To achieve high Strength in the concrete, it is necessary to have better understanding of the behavior of constituent materials. Thus, the behavior of RHA in concrete in terms of efficiency was assessed through the results available from literature. A mix design method was suggested and a wide range of concretes varying from 85-87Mpa with replacement levels varying from 0 to 15 Percentage were attempted. These concretes could be produced with the mixing, compaction, curing procedures conventionally used and with the available RHA. A maximum strength of about 86Mpa was obtained which compares well or was even better with the results reported hitherto in literature.

Behaviour of Self-Compacting Concrete incorporating Natural Perlite used as Part of Cement and as Aggregates

Perlite, a natural glassy volcanic rock could be used as supplementary cementitious material to reduce environmental pollution and the consumption of precious natural resources in the concrete industries. The aim of this work is to assess natural perlite used as 50% aggregates substitution by volume (sand or gravel) and as 10%, 15%, 20% cement substitution in self-compacting concrete. Workability characteristics and mechanical properties were analysed. Results showed that replacing 50% of natural aggregates with 50% of perlite aggregates or substituting cement with 10% of perlite powder generated the best workability characteristics and improved compressive, flexural strength, and elastic modulus of concrete at 28 days. Moreover, the results were combined to develop correlations that prove to be good between mechanical properties of self-compacting. Using perlite as aggregates offers a new source of supply and saves natural aggregates. Also, perlite used as cement substitution helps to reduce PC consumption, cost, and CO2 emission.