Some Studies on Use of Microfine Additives in Cement Paste and Mortar

Abstract

Concrete is the widely used human made material in our civilization and most of its own properties are controlled by its main component, cement paste. The impor- tant property of concrete after strength is its workability. The main measurement of workability, the slump test, is not always applicable; at the same slump value, two concretes may exhibit different workabilities. On the other hand, hundreds of tests were designed over the years to measure the workability of concrete. The question is how to select the proper test for the application at hand and how to interpret the results obtained to predict the performance of the concrete in the field in the fresh state. To address these questions, it is necessary first to define workability in terms of fundamental physical entities, as described in the science of rheology. To see the importance of durability of structure and the escalation in replacement costs of structures and the growing emphasis on the life-cycle cost rather than the first cost are forcing engineers to pay serious attention to durability issues. Next,there is a realization that a close relation exists between durability of materials and ecology. Two types of durability test are conducted as per their importance in construction industries. One is rapid chloride permeability test and chloride migration test. Experimental investigation comprises preliminary investigation to find the effect of salient parameter on rheology of cement paste. Total five types of parameters are se- lected such as specific surface, particle size distribution, types of mineral admixture, water to cement ratio and co-relation between empirical test and fundamental test. Result of these parameters are used for selecting the types of different micro-fines, dosage of w/c ratio, and types of test for rheological investigation of cement paste. For further investigation of rheological properties of micro fines, total seven types of microfines are selected at three different level of replacements 5%, 7.5% and 10% and w/c ratio are 0.45, 0.5, 0.55 and 0.6 respectively. Rheological properties like mini slump ow, yield stress, viscosity, zeta potential are investigated and compared with the different cement pastes. Also a co-relation between minislump ow diam- eter and yield stress is developed. For measurement of yield stress and viscosity of cement paste viskomat Nt rheometer is used and for mini slump ow diameter mini slump cone is used. Result have indicated that among the seven different cement pastes containing different microfines at various dosages and w/c ratio tested, the paste with containing classified Fly Ash (P-100) was found giving the superior results by reducing the yield stress and viscosity, on the other hand, the Undensified silica fume gave the worst result. The cement paste rheological data were also compared using simpler tests, such as mini slump test. The goal was to determine whether the simpler tests could be used to characterize the rheology of cement paste adequately. The conclusions are that mini slump test is reliable to co-relate slump ow with yield stress. Rapid chloride permeability and chloride migration two types of test is conducted for durability study of microfines. For durability test mix proportion of mortar is kept as 1:3 and w/c ratio-0.4. The performance of RCPT test on cement mortar evaluate based on charged passed and penetrability class. For chloride migration test performance is evaluate based on penetration depth of chloride ion and co-efficient of migration. Result of durability study indicated that the RCPT test value and mi- gration co-efficient value of, Undensified Silica fume mix shows very low value while Alccofine mix shows very high value of RCPT compared to control and mix with Fly Ash shows higher value of migration co-efficient. The co-relation between RCPT and chloride migration test shows co-relation factor around 0.88. Classified Fly Ash (P-100) is the suitable material for improvement of rheological properties of concrete, hence the pumpability and Silicafume is the suitable material for improve the durability of cocncrete against chloride ion.