66. Hydration c2s

The reaction of pure dicalcium C2S water is very similar to the above-described reaction of C3S. The primary products of hydration are also C-S-H-phases and Ca (OH) 2. Since C2S CaO content is less than C3S, is formed smaller calcium hydroxide produced during the initial hydrolysis (see. Eq 18). Reaction of dicalcium silicate and water is exothermic, but it is much slower than the reaction with water C3S.

Composition of C2S gidratsionnyh products depends on the temperature and water content. In general, the C2S hydration expressed as follows:

 

2CaO · SiO2 + xH2O uSaO → · SiO2 · (y (2)) H2O + (2-y) Ca (OH) 2 Equation 18

(= C-S-H) Portland

example:

2 C2S + 5H → C3S2H4 + CH

67. Reactions of hydration aluminate without participation of sulfates

According to studies, calcium aluminates have pronounced astringent properties, hardens quickly and reach a large mechanical strength. Very quickly it reacts with tricalcium aluminate water. In the presence of excess water formed numerous hexagonal plate-like crystals form. As a result of hydration is formed hydroaluminate

Rehbinder notes that the re-crystallization in the initial stage of structure formation plays a positive role, as a result of this process determines the dependence of the solubility of the size of the nuclei of the new phase, based on the coagulation structure is formed, the crystallization structure of tumors. Measurements have shown that the specific surface area of ​​tricalcium aluminate hydration at first increases, passes through a maximum and then decreases due to the predominance of the recrystallization process, which is expressed in the consolidation of the particles, ie. E. A decrease in the specific surface. Recrystallization leads to the disappearance of most small particles grow larger and that also experimentally proved by the example gypsum samples.

68. Reactions hydration aluminate with participation sulphates

To adjust the timing of cement clinker grinding with added 4-5% gypsum. Otherwise, it will be the so-called "false setting" when cement powder is mixed with water once it starts to thicken and set. According to GOST 10178-85 start setting cement paste should occur no earlier than 45 minutes, setting an end must occur not later than 10 hours. Setting time of cement is determined to Vicat apparatus.

As a regulator of cement setting time using dihydrate calcium sulphate CaSO4 · 2H2O (short formula CsHx). Regulator is mainly dihydrate or hemihydrate or a mixture of both types of calcium sulphate. When grinding clinker with additives in tube ball mills there is strong heating of cement, as expended in the process of grinding energy is used directly for grinding only partially. Thus, at high temperature gypsum dihydrate can be fully or partially dehydrated to hemihydrate. Total input sulfate dihydrate and attitudes entered and hemi to be agreed with the reactivity of the clinker and the requirements relating to the establishment of cement behavior (setting time). The high content of CaSO4 · nH2O delay the starting date and the end of the cement setting up the necessary limits. Depending on the concentration of the regulator setting can be various reactions: if the content of CaSO4 · nH2O the high C3A reacts with water and CaSO4 to form a compound, which is called "ettringite" (the title of the same name in the locality Ettringen Eifel)