**2.4 "Agglomeration" stage**

After the accumulation of a sufficient number of particles in the system, when the probability of particles meeting and growing together becomes co-measurable with the probability of their molecular growth, the process of agglomeration begins.

There comes a second evolutionary transition "particle growth agglomeration." In this case, the main phenomenon is the topological selection of ordered aggregates, which consists in the fact that the medium destroys and eliminates disordered aggregates and contributes to the formation of ordered forms consisting of particles with similar morphological parameters.


**Table 2.**

*Modifiers of nano-, ultra-, and micro-sized levels of dispersion and their mechanism of action.*

In real technologies of materials, the stage of agglomeration can be regulated by the addition of additives of surface-active substances (surfactants), widely used plasticizers, and superplasticizers (SP) [7–10].

#### **2.5 "Spontaneous structure formation" stage**

The evolutionary changes of the hardening system are objectively related to the third evolutionary transition "agglomeration → spontaneous structure formation." At the end of the growth stage and the agglomeration stage, the state of the system is far from the equilibrium state, therefore at a certain period inside. Systems of substance and energy redistribution develop simultaneously, which leads to spontaneous ordering of the system. The phenomenon of morphological selection is observed, and a "change in the geometry of the system" takes place; ordered aggregates of a certain shape and size are formed instead of less ordered shapes.

Technologically, the management of the spontaneous structure formation stage can be based on different temperature processing, on the use of various types of forced compaction by pressing, on the introduction of additives of microparticles, etc. (**Table 3**).


*Nano-Modification of Building Composite Structures DOI: http://dx.doi.org/10.5772/intechopen.86388*

> **Table 3.**

*Systematics of structural modification mechanisms on the main transitions of the evolutionary route solid substance formation.*

The stage of spontaneous structure formation is completed by the formation of coagulation (thixotropically reversible) and condensation-crystallization (irreversible-decaying) structures that are capable of further evolutionary transformation when interacting with the external environment, which is associated with an evolutionary transition "spontaneous structure → response to external influence. In this case, the principle of equalization and equal distribution of substances and energies in the volume of each phase is implemented.

Summarizing the analysis of the evolutionary route of the solid state and the related analysis of engineering and technological methods and means of nanomodifying the structure, it is possibly reasonable to present a systematics of the main phenomena and driving forces of structural transitions between the stages of the route, factors controlling these transitions, and their mechanism effects on the hardening system (**Table 3**).

Using the method of introducing nanoscale particles, effects of structure formation control are being implemented. Those associated with the nano-size particles are playing the role of (a) structure-forming nuclei, (b) substrates for crystallization, (c) centers of new formation zoning in the matrix substance of the material, and (d) nano-reinforcing matrix element. In all of these cases, the essential point is the lowering of the energy threshold for activating the processes of synthesizing hardening systems and accelerating hardening. Another important point is the spatial geometric modification of the structure, which, as was noted, is its zoning and the corresponding effect on the characteristics of homogeneity-inhomogeneity and, as a result, on the mechanical properties of the material [11, 12]. Finally, we should also keep in mind the effects of disperse reinforcement [13, 14].

The effects of structure formation control could be observed when the method of introducing nanoscale particles is applied. These are associated with the nanosize particles playing the role of (a) structure-forming nuclei, (b) substrates for crystallization, (c) centers of new formation zoning in the matrix substance of the material, and (d) nano-reinforcing matrix element. In all these cases, the essential point is the lowering of the energy threshold for activating the processes of synthesizing hardening systems and accelerating hardening.

Another important point is the spatial geometric modification of the structure, which, as was noted, is its zoning and the corresponding effect on the characteristics of homogeneity-inhomogeneity and, as a result, on the mechanical properties of the material [11, 12]. Finally, one should also keep in mind the effects of disperse reinforcement [13, 14].
