115. Areas of use alumina cement

Aluminous cement strength (GOST 969-77) is divided into grade 400, 500 and 600, determined by the test results in compression size prisms halves 4X4X16 cm, made of low ductility of a 1: 3 (GOST 310.1-76 rev.) And tested through 3 days hardening. After 1 day of hardening cement 80-90% three-day prochnosti.Dlya hardening alumina cement are most favorable water conditions. Both air and combined air-wet storage is accompanied by a significant drop in the strength of concrete in this cement in the late periods of hardening (at 50- 60% in 10-20 years). Durability decreases sometimes willows first month hardening. GOST 969-77 not allowed to decrease the tensile strength of samples 28-sous-exact age strength compared to three-day-aged samples more than 10%. At low temperatures (5-10 ° C), aluminous cement hardens quite rapidly due to significant heat release, as indicated on ranee.Betony alumina cement are characterized by high resistance to water, frost and heat resistance. The water resistance of cement due, in particular, the lack of products of hydration calcium hydroxide, characterized by, as is known, a considerable water solubility (1.2 g / L at ordinary temperature CaO).

116. Softeners (plasticizers), added during the production concrete

Breakers, sometimes referred to as plasticizers (Engl. "Plasticizer"), reduce the viscosity (in professional language "Concrete Technology" is called "consistency") concrete. Building material becomes thinner and thus easier to handle. One of the other applications is the so-called plasticisers less water (water saving) in concrete or cement and / or gypsum solutions. In this case, by using a plasticizer water / cement ratio, without degrading the consistency can be reduced or the processing capabilities of the construction material.

The most widely used is the lignosulfonate (sometimes referred to as lignin sulfonate, or sulfonated lignin). They are the Na, Ca salts of lignosulfonic acid, is used in liquid, solid or powder form. This thinning effects was discovered in 1920 during the construction of roads in the United States. At the time, it was customary to give a dark colored certain lane carriageway by spraying the waste lye containing lignin. It was found that lignin product will not only change the color of the concrete road, but also thins (plasticized) it. Thus, it was found lignosulfonate plasticizing effect. Today, in the construction industry uses annually about 600 000 tons of lignosulphonate. Thus, this additive count occupies first place among the construction of chemical additives.

Lignosulfonate is made from wood lignin (lat. Lignum = wood). Wood contains an average of from 20 to 30% lignin (mainly cortex), 60-70% golotsellyulozy (hemicellulose and cellulose fibers) and 10% water. Depending on the type of tree having various lignins. There are lignins from soft wood (eg fir and pine trees), solid lignin trees (eg oak, beech and eucalyptus) and lignin from grasses. In each case, a different part of the lignin. Figure 2.1 shows the approximate composition of spruce lignin, which is often used in the form of raw materials [219]. Lignin from herbs in the chemical industry is almost never used. The hydrophobic lignin protects plants from injuries caused by a fungus, microbes and insects. In addition, it gives a certain toughness plant material.