Undergraduate Kaldybaev Т.S., c.т.s., professor RАS Kolesnikov А.S.,

PhD doctor Zhakipbayev B. E., c.t.s. Kocherov Ye.N., master Estauova А.А., master Кulmahanova А.N., master Besbaeva N.А., master Аykenova S.Zh., master Shegenova G.К., master Каsimova Zh.Zh., student Ayazbekov M.

A study of aluminum-containing accelerators used for Torbert concreting

At the present time when carrying out concrete work, which require quick setting and hardening concrete and mortar additives are put accelerators of setting and hardening. Instead of alkaline additives are increasingly used supplements boosters that do not contain compounds of alkali metals, with the purpose of increasing the strength at the later stages of hardening and resistance of concrete to internal corrosion caused by the interaction of alkalis with aggregate and thereby increase the durability of structures made of concrete. Of particular importance supplements boosters have sprayed concreting when the concrete mix with the concrete spraying machine is supplied under pressure and compacted under the action of impact. In shotcrete adhesion of concrete or mortar mix should occur within seconds. As alkali-free accelerators are the most used aluminium compound is a finely dispersed amorphous modification of hydroxides and oxides of aluminum, aqueous solutions of sulfates and hydroxocuprate aluminum. High reactivity of these additives in cement paste caused by intensive education in the interaction with components of the test vysokoplotnogo hydrosulphate-minata calcium 3CaO∙Al₂O₃∙3CaSO₄∙32H₂O (ettringite phase).

The rotor is a high - tech way of concrete, which are nowadays solved various tasks in the construction industry, mining, agriculture. Invented in the early XX century in the USA, this mechanized method of laying concrete quickly spread worldwide [1,2]. The rotor allows you to perform special, a particularly challenging work such as tunnel driving, fastening the coastal slopes, the device shaft lining and many others. With more than 90% of the total use of concretestone have to mount mine workings [2]. The use of this technology in Kazakhstan has received active development in recent years is that associated with the construction of sports facilities in Almaty and Astana for holding the Asian games, the development of the metro. To build infrastructure in the mountainous terrain necessitated the construction of long transport tunnels.

In shotcrete, the concrete mixture using a special device (shotcrete machine)is applied to the surface under pressure and compacted by the impact energy [2]. Layers of Torreblanca, in some cases reaching a thickness of more than 25cm, and must quickly gain a firm foothold on rough vertical surfaces, the vaults of tunnels, mines, hard to reach areas and components of the equipment. In addition, when spraying should be provided with minimum rebound of the concrete mix. The rotor may be "dry" or "wet" methods [3-4]. During the "dry" shotcrete at the nozzle of the gunning apparatus with compressed air is a dry mixture of components (aggregate, cement, powdery additives), where it is mixed with water or an aqueous solution of additives and then discharged onto the surface. When wet spraying in the nozzle of the gunning apparatus is supplied ready concrete mixture, compressed air and a solution of additives (figure 1).

a

b

Figure 1 – is a Conventional diagram of the installation for the preparation of sprayed concrete in the dry (a) wet and (b) methods of production [5].

With its advantages of wet shotcrete method to date, is most prevalent, especially when performing major works.

As subjects of the study selected highly dispersed amorphous aluminum hydroxides, one of which is a product of Russian manufacturer (JSC "Boksitogorsky alumina") of AmGA, another product of the company "Industrias Químicas del Ebro" (Spain) Geloxal. Chemical composition of aluminum hydroxides according to the manufacturers is presented in table 2.

Table 2–Chemical composition of aluminum hydroxides

№ Number of indicator	Наименование показателей	Name of indicators	Geloxal	АmGА
1.	Mass fraction of Сl^-	% by weight.	not more than 0,5	–
2.	Mass fraction of SO4^2-	% by weight.	not more than 2	–
3.	Mass fraction of SiO2	% by weight.	–	0,16
4.	Mass fraction of Na2O	% by weight.	not more than 1	0,15
5.	Mass fraction of Al2O3	% by weight.	50	50

Thus, the requirements of modern accelerators for shotcrete are not only in the fact that at a moderate cost, they provided almost immediate grasp of the concrete mix and quick set early strength, but also in the fact that they do not adversely affect the properties of concrete in adulthood and did not serve the cause of reduction of its durability.

Bibliography

1. Yoggy, G.D. The history of shotcrete / Shotcrete. 2005 (Summer). P. 26–32.

2. Melbye, T. Sprayed concrete for rock support / Garshol – MBT International Underground Construction Group, Division of MBT: Switzerland- 2001. -247 pp.

3. EFNARC (1999) – Guidelines for Specifiers and Contractors: UK- 1996. – 35 pp.

4. William, D. Brown. Standard practice for shotcrete. Engineer Manual No. 1110–2–2005. Washington – 1993 – 49 pp.

5. American Concrete Institute ACI 506R–90: Guide to Durable Concrete. Farmington Hills. –1995. – 41 pp.