Role of Polyfunctional Admixture Based on Silica Fume and Carbon Nanotubes in Forming the Structure of Gypsum Cement Composition

Abstract

One of the topical areas of regulating the structure of gypsum cement compositions is modifying the morphology with ultrafine and nanodisperse systems. The study has analyzed the possibility of changing the structure and properties of new formations of gypsum cement pozzolanic matrix by adding multifunctional admixture based on silica fume and multi-walled carbon nanotubes (MWCNTs) dispersed in a surfactant medium. The optimum content of complex admixture has been determined as 0.006% of MWCNTs and 10% volume content of silica fume as part of modified gypsum cement pozzolanic binder (GCPB) providing the increase of compressive strength by 55% and water resistance by 32%. Studying the structure of modified GCPB by means of physico-chemical analysis (scanning electron microscopy, infrared-spectral analysis and differential scanning calorimetry) has proved the improvement of physical and mechanical properties due to changes in mineralogical composition of new formations in hardening composition and morphology of the forming crystal hydrates in the structure of modified gypsum cement pozzolanic matrix. At the same time, it is noted that gypsum crystalline hydrates are coated with calcium silicate hydrates compacting the structure of the composition and increasing the total contact surface of the new formations. At the same time calcium silicate hydrates prevent water from the surface of crystals of calcium sulfate dihydrate, thereby increasing the water resistance of the composition.

The Use of Aluminosilicate Ash Microspheres from Waste Ash and Slag Mixtures in Gypsum-Lime Compositions

“…Experimental studies have established that the aluminosilicate product of the enrichment of ash and slag mixtures is an active mineral additive in compositions based on a gypsum-lime binder [ 27 ]. The increase in the strength of the modified gypsum stone with the joint introduction of aluminosilicate microspheres and slaked lime is due to the formation of a finely crystalline structure of the composition, which was also noted by the authors of the work [ 28 ]. The multi-directionality of crystals in the structure of the modified stone is noted.…”

“…There are several ways to increase the strength of gypsum stone, the most common today is the method of using finely dispersed mineral fillers [ 27 ]. To a lesser extent, the method of influence by introducing additives on the morphology of the resulting crys-talline hydrates in the structure of the modified gypsum matrix is known [ 28 ]. One of the ways to increase the strength of gypsum stone is also via the introduction of nanocomponents into the composition [ 29 ], however, this method remains the most expensive to date [ 30 ].…”

“…As a rule, a positive effect is due not only to packing density [ 43 ], but also to a change in the morphology of gypsum crystals formed during hydration and curing [ 43 ]. Thus, several approaches to the design of the structure were used at once [ 31 ], the introduction of an aluminosilicate component also plays the role of a filler [ 27 ] and affects the microstructure by changing the morphology and the formation of neoplasms [ 28 ].…”