CONCRETE

It is hard to imagine today’s construction processing without concrete. Concrete is one of mass construction materials that identifies the development level of the civilization the most. Alongside, concrete is the most complex artificial composite material having exclusively unique properties. Concrete is used in the most diverse operational conditions, it can be well combined with the environment, it has unlimited base of raw materials and relatively low cost. It is also worth adding high architectural and construction expressivity, comparative simplicity and availability of technologies, small power consumption, ecological safety and operational reliability. It is doubtless that these are the reasons why concrete will remain the main structural material in the nearest future.

Concrete is an artificial composite material that occurs due to hardening of well-mixed and compacted mix of cohesive substance, water, small and big aggregates and special admixtures taken in definite proportions. Before it hardens, this mix is called a concrete mix.

Currently there are different types of concrete used in construction. The concrete classification helps to understand their diversity. Concretes are classified by average density, type of cohesive substance, technological peculiarities and purpose.

Many properties of concrete depend on its density that is influenced by density of cement stone, type of aggregates and concrete composition. As on density, concretes are divided on extra heavy, density over 2500 kg/m³, heavy – 1800…2500, light – 600…1800, extra light – below 600 kg/m³.

Heavy concrete, density 2100…2500 kg/m3 with dense rock aggregates (granite, limestone, toadstone, etc.).

The main component of concrete that defines its properties is a cohesive substance differing concretes such as cement, silicate, gypsum, lime-slag, polymer concrete, polymer cement and special ones.

Cement concretes are made using different cements and they are most widely used in construction. The main place among then is taken by concretes based on Portland cement and its varieties used for different types of structures and their operational conditions.

Silicate concretes are based on lime. In this case, there is autoclave-hardening method used for fabrication of elements.

Gypsum concretes are used for internal partitions, suspended ceilings and finishing elements of buildings.

Lime-slag concretes are based on ground slags created on lime mortars.

Polymer concretes are made of different types of polymer cohesive substance that is based on resins (polyester, epoxide, etc.) or monomers (furfural-acetone, etc.) hardening in concrete due to special additives. These concretes are more appropriate for operation in aggressive environments and special impact conditions (wear, cavitation, etc.)

Polymer cement concretes are made on mixed cohesive substance consisting of cement and polymer substance. As a polymer, water-soluble resins and latexes, for example, are used.

Properties of concretes based on non-organic cohesive substances may be increased via monomer treatment with their further hardening in pores and capillaries of concrete. Such materials are called concrete polymers.

Special concretes are made using special cohesive substances. Glass with sodium fluosilicate, phosphate, magnesia and other cohesive substances are used for acid and heat resistant concretes.

Depending on the application area, the following is differed:

• regular concrete for reinforced concrete structures (foundations, columns, floor slabs, bridges and other types of structures);
• maritime engineering concrete (for dams, floodgates, cladding of channels, etc.);
• concrete for cladding structures (light);
• special purpose concretes, for example, for radiation protection, acid resistant, heat resistant, flooring concrete, road and airfield surfaces, etc.

General requirements to concretes and concrete mixes are the following: prior to hardening, concrete mixes shall be well mixed, have relevant workability, shall not get layered; concretes shall have definite speed of hardening according to given period of formwork removal and commissioning of structures or buildings.

It is possible to get concrete meeting all of the stated requirements only if the following conditions are observed: right selection of concrete composition, use of materials for concrete production of high quality, strict adherence to manufacturing technology, pouring and hardening of concrete mix as well as right concrete curing at the initial period of its hardening.

At our plant, there are three stages of concrete control: entrance, operational and acceptance ones.

Entrance control is control of materials received at the plant for concrete mixing on meeting GOST requirements.

To make concrete we use the following materials:

• Portland cement M500 is used as a cohesive substance for concrete mixes;
• Sands of Bagyevsky sand pit, grain 2.5-3.0, are used as a small aggregate;
• Granite crushed stone, grain 5-20 mm, is used as a big aggregate;
• As a plasticizing admixture, superplasticizers based on polycarboxylates and modified lingnosulfonates of well-known manufacturers are used;
• FROST 20 is used as a frost resistant admixture.

At the plant, there is operational control (control of technological processing) during all period of concrete manufacturing. Concrete mixes are prepared in accordance with the requirements of the technological regulations and GOST 7473. The conveying screw supplies cement from the warehouse to the concrete mixing unit. A skid steer loader supplies the aggregate from the warehouse to the concrete mixing unit; every receiving tank is for acceptance of a definite type of the aggregate. Aggregate mixing is not allowed in the acceptance tanks. The aggregates from the acceptance tanks are supplied to the dozer of the skip loader in the amount required for preparation of the mix amount specified by the operator. The maximal mix amount is 2000 l. the dozing of cement, aggregates, water and admixtures is performed by Stetter automatic weight dozer under the computer input program depending on the ordered class and workability of a concrete mix; provided that water and admixtures are spread in all mix via nozzles thus providing maximal uniformity of concrete.

All concrete mixes are subject to mandatory acceptance control according to the requirements of the approved technological regulations and GOST.

The certificate of conformity proves the quality of our concrete.