A Study of Self Compacting Cementitious Systems Using Metakaolin and Glass Powder

Abstract

Self Compacting Cementitious Systems (SCCS) are a modern technology in the field of high performance concrete which has been used extensively throughout the world. Some major applications of this technology involve massive placements in heavily reinforced sections such as tunnel linings, high rise buildings, rafts and pile foundations, bridge piers, transportation structures, prestressed concrete members and repair of structures like aircraft runways etc. This technology offers a uniform degree of compaction throughout the concrete placement and therefore, a uniform durability of the structure. SCCS contains high powder content with low w/p ratio than conventional concrete, hence, these systems provide a better overall response in terms of volumetric stability, packing density, ease of placement, evolution of heat of hydration, strength development and higher durability. In High Performance Concrete (HPC), all cement particles do not get hydrated. Therefore, in order to economize the system, secondary raw materials (SRM’s) are used. These SRM’s improve the microstructure and the overall response of concrete in both fresh and hardened state as well as make it more environment friendly. This research was undertaken to evaluate the feasibility of using Metakaolin (MK), an artificially manufactured pozzolan and Glass Powder, a pozzolan derived from finely crushing and grinding commercially manufactured glass, and to study their benefits in Self Compacting Mortars (SCM’s). The parameters studied include the particle characterization of SRM’s, flow behavior, strength development, and microstructural characterizations. The results indicate that Metakaolin and Glass Powder, when used to replace 10% of cement mass in replacement mode, enhance the properties of self compacting mortar formulation like flow, heat of hydration, strength development, microstructure and shrinkage etc. The finer particle size of Metakaolin leads to a higher water/SP demand and faster setting time for formulation with Metakaolin in replacement mode. This is also confirmed by its early and higher calorimetric peak. The formulation with Glass Powder in replacement mode requires more SP content owing to its larger particle size as compared with Metakaolin. This is also confirmed by its setting times and lower calorimetric peak which are delayed as compared with Metakaolin formulations. The Control mix formulation shows a lesser demand for water and SP but shows delayed setting time and slightly lower calorimetric peak as compared with Metakaolin but higher than Glass Powder. The strength development is also an important parameter as strength gain at a specified age varies and depends on the degree of pozzolanic activity which is in turn dependent on the physical and chemical characteristics of the SRM. Metakaolin vii shows a strength development similar to control mix while Glass Powder shows slightly less strength at comparative ages owing to its larger particle size and slower hydration. This strength evolution is also evident from MIP curves of SCM formulation in terms of pore refinement and at times discontinuous porosity for Metakaolin and Glass Powder. The volumetric stability of the cementitious system is also affected by Metakaolin and Glass Powder as Metakaolin produces more early linear shrinkage than Control mix due to its small size, latent reactivity and early evolution of heat of hydration whereas Glass Powder shows less shrinkage owing to its large particle size and delayed evolution heat of hydration. Thus, we can deduce that both SRM’s contribute positively towards enhancing the different characteristics of the cementitious systems and can be incorporated successfully in self compacting cementitious systems.