Indian Journal of Chemical Technology Vol. 15, July 2008, pp. 349-354 Adsorption of comb –type superplasticizers on calcium carbonate in alkaline medium in presence of electrolytes and rheological properties Sarita Rai & N S Gajbhiye* Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India Email: nsg@iitk.ac.in Received 1 October 2007; revised 8 May 2008 Adsorption behaviour of polycarboxylate type superplasticizers (PC) on CaCO 3 suspension in a basic medium has been studied in the presence of NaCl, Na 2 SO 4 and CaCl 2 having same ionic strength. The amount of PC adsorbed was found out by determining the amount of PC present in supernatant solution with the help of total organic analyzer. It is found that the adsorption decreased when the POE chain length decreased. The adsorption was increased in presence of CaCl 2 while NaCl and Na 2 SO 4 decreased the adsorption. The adsorption is not a competitive process but depends on ionic strength. Rheological measurements of suspensions have also shown that lower the POE chain length, higher the viscosity of the CaCO 3 suspension. Keywords: Polycarboxylate, Superplasticizer, Adsorption, Cement Superplasticizers are essential ingradients for the production of high performance concrete which includes high strength and high fluidity concrete. In recent years a new class of superplasticizers often referred to as polycarboxylate based comb – polymers, has emerged as having the unique ability to improve the quality and economics of concrete products 1-4 . The polycarboxylate (PC) type superplasticizers (SP) contain polycarboxylic acid backbone with attached polyoxyalkylene groups. PC based superplasticizers have gained much more acceptance in cement industry due to their higher efficiency in reducing water /cement ratio, and preventing slump loss in comparison with the traditional superplasticizers based on naphthalene sulfonate and melamine sulfonate condensates. Further, polycarboxylate based superplasticizer is a safer material for health because it does not contain formaldehyde, so its application is expected to expand in future. An exhaustive literature survey on concrete admixtures, with particular emphasis to PC superplasticizers and their functions have recently been publsihed 5,6 . Polycarboxylate type superplasticizers with a polyethylene oxide (PEO) grafted chains is one of the materials used to make self compacting concrete (SCC) because of its superior dispersing ability for cement, especially at low water/cement ratio. A large number of variations in these polymers are possible by varying the length of the backbone, the content of ionic groups, and the length, the amount and the type of side chains. These structural variations of the polymer have great influence on the performance of the PC. Sodium salts of formaldehyde condensates of β-naphthalene sulphate disperse cement particles by electrostatic repulsion that results from the adsorption of superplasticizer on cement surfaces. Polycarboxylate type superplasticizers with graft chains disperse cement agglomerates by steric hindrance 1,7,8 . By varying the polymer structure, properties like adsorption, electrostatic and steric effects of the superplasticizers can be optimized. When the same level of superplasticizers is used, the surrounding environment of the concrete or ingredients significantly affect the rheological properties of the concrete as an initial slump or slump loss 9,10 . Such problems were known as an incompatibility phenomenon between the cement and the superplasticizer 11-14 . Different studies have shown that the amount of alkaline sulphate significantly affects the adsorption of superplasticizers on the surface of cement particles 15,16 . Portland cement consists of four mineral phases namely Ca 3 SiO 5 , Ca 2 SiO 4 , Ca 3 Al 2 O 6 and Ca 4 Al 2 Fe 2 O 10 , which are abbreviated as C 3 S, C 2 S, C 3 A and C 4 AF. In addition to these phases there is a small amount of gypsum also. For these cement