Hydration hardening

From Cement Hydration Hardened Edoxv Resfn... 

For industrial Portland cements, tetracalcium aluminum monosulfate hydrate (C ASH ), which is a major component of fully hydrated hardened cement, reacts with gypsum to form secondary ettringite (C ASjHj ). This reaction also causes expansion of 57 vol.% of the solid components ... 

From Cement Hydration Hardened Eooxv Resin... 

These expressions are further used in the analysis of the behavior of AF as a function of the various parameters. The challenge here is to overcome the mental barrier associated with the traditional formal approach to this problem. Particular examples of real physical processes and states reflecting various types of behavior of AF include the peptization-coagulation transition in colloid sols and particle bridging in the course of the hydration hardening of mineral binders. 

In agreement with the concepts developed by Polak [10], the appearance of a contact nucleus may take place when the new crystalline phase forms in the contact zone between the newly formed crystals in the course of crystallization from metastable solutions. The bridging of crystals results in the formation of fine disperse polycrystalline products, such as those formed during hydration hardening of mineral binders and cements. 

Crystallization disperse structures can also form in aqueous suspensions of other singlecomponent mineral binders. For instance, the hydration hardening of MgO results in the formation... 

By all means, the most important and at the same time the oldest nanotechnology in the world is the hydration hardening of cements. Of special interest here is the fact that the nucleation taking place in the supersaturated phase controls both the formation of new phase particles and the formation of bridges between these particles. 

First, there is the formation and preservation of nanosize systems under conditions when kinetic and structural factors prevent the transition of the new phases into a macroscopic phase. This includes the processes of the hydration hardening of various mineral binders. 

In order to control the formation and development of structure in the processes of the hydration hardening of mineral binders, electrolytes are used in addition to surfactants. This allows one to... 

Formation of Contacts between the Particles and the Development of Internal Stresses during the Hydration Hardening of Mineral Binders... 

All of these processes indicate the need to examine the conditions of particle bridging as they relate to the origination of residual stresses in the products of hydration hardening. This approach is... 

Mechanical stresses are necessary for the crystallization contacts to be established in hydration structures in the course of hydration hardening. These stresses are either applied externally or originate from the directional growth of the crystals inside the already formed network. Mechanical stresses may also be caused by the weight of powders or result from the action of capillary forces acting in the drying menisci. 

In order to cause bridging between crystals and particles, one needs to apply external compressive forces. In the laboratory studies, these forces were introduced by applying suitable compression. However, in the course of hydration hardening, such forces are originated in the system internally. One is thus faced with the need to answer a number of questions. Specifically, what is the origin of those forces in the process of structure formation What are the nature, magnitude, and... 

Internal Stresses in Structures Obtained in the Course of the Hydration Hardening of Various Binders... 

Dependence of Internal Stresses on the Conditions of the Hydration Hardening... 

Effect of the Addition of a Filler (Amorphous Silica) on the Values of the True Width of the Interference Line, p, and on the Value of Ad/d in the Structures Formed in the Hydration Hardening of the Mg(OH)2 Samples... 

In summary, one can say that x-ray diffraction stndies have proven the presence of residual stresses in the strnctnres formed in the conrse of hydration hardening and have made it possible to quantitatively estimate their magnitude under varions physical-chemical conditions. The stresses that originate in the conrse of crystal bridging can reach hundreds of kg/cm and manifest themselves in many different ways depending on the hydration hardening conditions. In particular, the stresses can nndergo partial or complete relaxation in the course of the plastic deformation of the... 

FIGURE 7.63 Some ways to enhance the strength and durability of industrial catalysts magnesium oxide (a), calcium-nickel-phosphate (b), zeolite-filled aluminum silicate (c,d), magnesium oxide by hydration hardening (e), and sorbeats (f). 

Another possible way to substantially modify the nature of contacts is to use hydration hardening of the magnesium oxide followed by dehydration instead of mechanical pellet pressing (Figure 7.63e) [120,149,160]. This allowed one to establish stronger phase contacts while simultaneously removing the residual internal stresses. 

---