THE EFFICIENCY OF PLASTICIZING SURFACTANTS IN ALKALI-ACTIVATED CEMENT MORTARS AND CONCRETES

Abstract

Application of alkali-activated cements (AAC) allows to provide high quality functional and durable mortars and concretes in the view of efficient application of raw materials and energy supplies. There are five types of AACs depending on their composition. Thus the basic factor of AAC composition change can be considered as part of granulated blast furnace slag (GBFS) that changing from 0 % to 100 % in aluminosilicate component of cement. Compounds of alkaline metals are considered as AAC structurization components, which contents depend on AAC type. Functionality of mortars and concretes is regulated by surfactants, which act as plasticizing admixtures. However modification of AAC by admixtures has certain features connected with risk of molecular structure degradation in hydration medium of AAC due to alkaline hydrolysis (saponification). The emergence and speed of this process are determined first of all by AAC composition including nature (group) of alkaline component. The objective was to determine the chemical nature of plasticizers effective for property modification of mortars and concretes based on AACs with various content of GBFS (from 0 to 100 %) and appropriate alkaline component content. Stability of plasticizers’ molecular structure in hydrated medium of AAC with different content of GBFS was investigated by means of infrared spectroscopy. It was shown that admixtures with ester bonds undergo of molecular structure degradation as a result of alkaline hydrolysis at increasing pH values that is caused by content of alkaline component and depends on the nature of alkaline component. Admixtures without ester bonds (sodium lignosulphonate,ones based on polyethylene glycol and acyclic polyamine) are characterized by stability of molecule regardless of alkaline component content. The effective admixtures were used in dry mixes for anchoring (consistency of mortar 150 mm by Vicat cone; 1 d tensile strength in bending / compressive strength of mortar = 6,6 /30,6 MPа) and in ready-mixed concretes (consistency class changed from S1 to S3, S4 with consistency safety during 60 min; 3 d compressive strength of concrete was not less than the reference one without admixtures).