A Study of Self Compacting Cementitious Systems Using Bagasse Ash and Bentonite

Abstract

Self Compacting Cementitious Systems (SCCS) fall in the domain of modern concrete technology which has been used successfully through out the world. The major applications of such systems involve massive placements with heavily reinforced sections such as tunnel linings, bridges piers, transportation structures, high rise buildings, rafts, prestressed concrete members and repairs of structures. Such systems offer uniform degree of compaction as well as have uniform durability and contain higher powder content with lower w/p ratio compared with the conventional concrete. These environmental friendly systems have better overall response in terms of volume stability, better packing, placement ease, economy, lesser heat of hydration, strength development and higher durability. In high performance concrete (HPC) systems, all cement particles do not get hydrated, therefore secondary raw materials (SRM) are used to replace a part of cement in order to economize, to make an environmental friendly concrete with improved microstructure and to get better overall response in terms fresh and hardened properties of concrete. Extensive successful research work has been carried out through out the world on use of secondary raw materials in self compacting cementitious systems and now this practice is quite popular. However, in Pakistan, despite the availability of various pozzolanic materials in abundance, both in natural as well as artificial form, the coordinated and well planned research work on these resources is still in the elementary stage due to non availability of response data. Accordingly, their usage in the cementations systems is very limited. This study was made to evaluate the feasibility of using Bentonite (BN), a naturally occurring pozzolan and Bagasse Ash (BA), an artificial pozzolanic material, in self compacting paste systems with ultimate aim to produce self compacting concrete with desired properties. The parameters studied include secondary raw material’s particle characterization, flow behavior, strength development, calorimetric investigations, volume stability, X – ray diffraction (XRD) study and microstructural analysis by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) of self compacting paste systems. The results showed that the internal porosity of secondary raw material particles adversely affects the water demand and super plasticizer demand of self compacting paste system. While the shape, size and surface texture of secondary raw materials along with their chemical and physical properties all have vital effects on the flow behavior, strength and the durability. The rate of strength gain of self compacting cementitious system is also an important aspect besides the strength at a specified age as it varies with secondary raw material being used. Furthermore, the addition of secondary raw materials in replacement mode causes an overall reduction in the total amount of heat released and has a better effect on the volume stability of the mix. After the detailed analysis of all the results, it can also be stated that both secondary raw materials investigated, can be successfully used in self compacting cementitious systems as each contributes positively towards enhancement of certain properties of concrete and the use of their blends can further optimize the response of self compacting concrete. The research was carried out both at NUST, Islamabad and TU Freiberg, Germany under DAAD sponsorship.