Efficiency of Limestone Powder in SCC
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Efficiency of Limestone Powder in SCC
K. Ganesh Babu and B. Chandra Sekhar Department of Ocean Engineering, Indian Institute of Technology, Chennai – 600036.
ABSTRACT Self-compacting concretes have been of topical interest due to the ease of adoption and the significant savings in compaction efforts particularly at the congested reinforcement locations, in spite of the leak- proof forms required. However, many of the aspects regarding their production with different powder or pozzolanic additions and their corresponding mechanical strength characteristics are not yet fully understood. This paper deals exclusively with the compressive strength characteristics of these concretes incorporating limestone powder as a mineral admixture through the water cement ratio to strength results of concretes reported in literature. The basic idea is to get an idea of the SCCs at the lowest and the highest possible amounts of the limestone powder in it. INTRODUCTION Self-compacting concrete (SCC) as the name suggests are concretes that are fluid, cohesive and have the ability to compact under their own weight without any imparted external compaction effort, yet resulting in a homogeneous compact matrix devoid of segregation or bleeding. This requires a delicate balance in the proportioning of the constituent material, particularly the fines content and in some cases this is augmented or supported by introducing a special viscosity modifying admixture. In general, the higher fines content demanded by these concretes cannot be addressed by cement alone, neither from the economy point of view nor from the associated shrinkage and hydration temperature effects. Also, in the present- day context, with the increasing pollution levels due to the different industrial processes and also the need to optimize the mineral resources to achieve a low carbon foot print, the use of mineral additives to cements for concrete that are produced with a significant energy input is not only appropriate, but is also a basic necessity. With this broad perspective, there have been several investigations in recent years to accommodate and arrive at the cementitious compositions using pozzolans, both, several of the industrial waste by- products and also the natural pozzolanic minerals and clays. This aspect assumes a high significance in SCC’s as the additional fines that are needed can be introduced without sacrificing the economy. However, the effect of the addition of limestone powder (LSP), to concrete which really is not possible to be classified under either of the categories of pozzolans, industrial or natural, has never been fully understood. Initially it was assumed that this material is inert and performs only the pore filling effect in the matrix. The double peak in the heat of hydration results from experimental calorimeter studies suggests that apart from accelerating the hydration reactions limestone powder is not just an inert additive but may be an active constituent in the hydration
process. Some of these aspects were reported by earlier
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