The efficiency of plasticizing surfactants in alkali-activated cement mortars and concretes

Functionality of mortar and concrete mixes is regulated by surfactants, which act as plasticizers. The molecular structure of these admixtures can be changed during hydration of alkali-activated cements (AAC). The objective was to determine the chemical nature of plasticizers effective for property modification of mortars and concretes based on AACs with changing content of granulated blast furnace slag from 0 to 100 %. The admixtures without ester links become more effective than polyesters when content of alkaline component increase. The admixtures effective in high alkaline medium 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 MPa) and in ready-mixed concretes (consistency class changed from S1 to S3, S4 with consistency safety during 60 min; 3 d compressive strength of modified concrete was not less than the reference one without admixtures)

Analysis of Plasticizer Effectiveness During Alkaline Cement Structure Formation

The problem of plasticization of alkaline cements was analyzed and the ways of its solution were offered. The problem is related to the structural instability of a number of chemical admixtures that are effective in plasticisation of clinker cements in the highly alkaline media of hardening cement. Superplasticizers based on polyesters lose their steric effect due to the hydrolysis reaction. On the other hand, selectivity of action of chemical admixtures is associated with the changes in a wide range of compositions of alkaline cements. In addition, the degree of changes in the structure of admixtures depends not only on the medium pH but also on the nature of the alkaline component, the production process and use of such cements. Generalization of the problems made it possible to proceed with the expansion of the range of substances from the class of surface active substances (SAS), their experimental verification and the application proposal for plasticization of alkaline cements. As plasticizing SAS characterized by stability of molecular structure in alkaline media, low- and high-molecular compounds from the class of acyclic (aliphatic) compounds or fatty compounds were considered. The polyester-based superplasticizers traditionally applied in plasticization of calcium cement systems were used for comparison. Variation of the nature and ratio of components in the composition of alkaline cements as well as the chemical admixture nature were taken as the main factors in the study of features of cement plasticization. Comparative evaluation of effectiveness of these admixtures indicates selectivity of use taking into account composition of alkaline cements. As a result of this research, systematization of classes of chemical compounds according to their effectiveness as plasticizers for alkaline cements was proposed. Such a systematization can be used in development of commercial products in a form of plasticizing additives for concretes and mortars