The Peculiarities of Hardening of Composite Anhydrite Cement Pozzolanna Binding Material with not Burned Natural Anhydrite

Abstract

The comparative investigations of gypsum cement pozzolana binding materials (GCPB) and anhydrite cement pozzolana
binding materials (ACPB) with not burned natural anhydrite were performed controlling kinetics of hardening, phase
composition of new formations generated in the course of hardening, structure, mechanical strength and water resistance.
It was established that the component of natural anhydrite with compact crystalline structure provides specific properties
to ACPB, i. e. long-term hardening, low porosity of the hardened matrix and good hydraulic properties. At the same
plasticity of moulding mix, ACPB density was higher by approximately 25 % than that of GCPB. ACPB early strength
is lower than GCPB, however, the gradual hydration of anhydrite over time makes the ACPB hardening structure more
compact and stronger. After 28 days ACPB strength was higher by ~11 %, after 4 months ~by 23 %, after 7 months by
~30 % than that of GCPB. During the ACPB hardening, the slower generating new formations of dihydrate gypsum
together with new formations of cement hydration make the hardening structure considerably more water resistant.
Contrary to GCPB, the hardened ACPB does not loose strength in water, but is developing it further. The process of
anhydrite hydration in the hardening ACPB is proceeding for many years and over time its influence on ACPB strength
becomes greater than that of cementitious component. It was established that ACPB still contains non- hydrated
anhydrite after 15 years of hardening. Basing on the results of investigations the performance characteristics of
composite anhydrite binding materials with not burned natural anhydrite were predicted, as well as a possibility to
replace cement binding materials by them.