Abstract
This paper presents the results of studying the properties of cement-based composites modified with a complex additive based on chrysotile nanofibers and carbon black. The optimal composition of complex additive was stated due to the particle size analysis of suspensions with different chrysotile to carbon black ratios and the mechanical properties study of the fine-grained concrete modified with the complex additive. It was found that the addition of chrysotile in the amount of 0.05% of cement mass together with carbon black in the amount of 0.01% of cement mass leads to a 31.9% compression strength increase of cement composite and a 26.7% flexural strength increase. In order to explain the change in the mechanical properties of the material, physical and chemical testing methods were used including IR-spectral analysis, differential thermal analysis, energy dispersive X-ray analysis as well as the study of the microstructure of the samples modified with the complex additive. They revealed the formation of durable hydration products including thaumasite and calcium silicate hydrates of lower basicity that form a dense structure of cement matrix, increasing the physical and mechanical characteristics of cement-based composites.
Highlights
Cement mortar and concrete are among the most widely used, durable and reliable materials in modern construction; improving their structure and properties has always been one of the main priorities of construction materials science
The creation of favorable conditions for the effective hydration of Portland cement is achieved by adding the additives that have high activity due to the large surface area and the ability to compact the cement matrix structure [14,15]
The results have confirmed the possibility of the combined use of chrysotile nanofibers and carbon black in order to improve the structure and properties of cement composites
Summary
Cement mortar and concrete are among the most widely used, durable and reliable materials in modern construction; improving their structure and properties has always been one of the main priorities of construction materials science. There is a wide variety of technical possibilities for modifying the cement-based composites and improving their physical and mechanical characteristics. These include decreasing the water-to-cement ratio [1,2], increasing the binder fineness [3,4], using plasticizers [5,6], varying the hardening conditions [7], introducing the various types of fiber [8,9,10], etc. The creation of favorable conditions for the effective hydration of Portland cement is achieved by adding the additives that have high activity due to the large surface area and the ability to compact the cement matrix structure [14,15]. The further recrystallization of hydration products into larger crystal blocks is limited due to the high surface energy of nanoparticles
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