Technology of building erection in special conditions

Contents

Job for Course Project

1 Formwork

1.1 Formwork Requirements

1.2 Design and Calculation of Formwork

1.3 Reinforcement works

1.4 Methods of providing the design protective layer of concrete

2 Concreting technology of the structure

2.1 Design of concrete mix composition

2.2 Transportation of concrete mixture to the place of laying

2.3 Laying and compaction of concrete mixture

2.4 Concrete Care, Smelting and Quality Control

3 Concreting technology in extreme conditions

3.1 Operation procedure

3.2 Calculation of basic parameters

4 Technical and economic part

4.1 Calculation of labor costs

4.2 Technical and economic characteristics of the main machines and mechanisms

5Safe Health and Safety Measures

List of literature used

Formwork

Formwork Requirements

When exposed to monolithic structures of residential buildings, increased surface quality is required, so a number of additional requirements are imposed on the formwork.

Formwork shall have high rigidity in addition to strength parameters.

Not only the strength and quality of the monolithic structures, but also the labor intensity of the formwork and finishing work, the durability and cost of the formwork depend on the deformation of the formwork. In addition to surface curvatures, violation of geometric dimensions and other deviations with insufficiently rigid formwork, shells on the surface and air bubbles are formed when compacting concrete.

The main requirement for formwork is the uniformity of deformation of elements of one functional purpose (for example, large-sized panels of walls and floors). During thermal treatment of concrete in thermoactive formwork it is necessary to take into account additional loads and deformations of formwork during heating.

When exposed to monolithic structures, depth vibrators are usually used to seal concrete of vertical structures. The use of external vibrators reduces the labor costs of concrete work. However, the formwork is significantly heavier and, in addition, the quality of concrete surfaces is deteriorated due to suction of air during vibration.

All formwork connections are recommended to be quick detachable; they must be sufficiently tight and impermeable. Prefabricated seams, as well as sharp corners and formwork edges, shall be machined.

Accuracy of formwork fabrication shall be one or two classes higher than accuracy of monolithic structures. Higher tolerances are prescribed for thermoactive formwork, since in addition to additional deformations of the mold, dimensional changes during cooling and heating should be taken into account. Most formwork structures are manufactured according to the 7th accuracy class. Universal formwork systems designed for additional service life, high turnover rate and use in different conditions must be performed according to a higher accuracy class. It should be borne in mind, however, that unreasonable overstatement of manufacturing accuracy significantly increases the cost of formwork .

The surface of the formwork in contact with the concrete has a significant impact on the surface quality. Good surfaces are obtained by applying a lubricant layer to a metal formwork. Formwork made of specially selected wood allows you to get a beautiful texture in some cases. Special absorbent linings give good results. As the degree of material absorption increases, the number of shells and voids on the concrete surface decreases. In addition, the reuse of the formwork also changes the degree of absorption and color of the concrete surface. Also, composition of concrete, technology of laying and method of compaction are changed.

The beautiful surface of the concrete can be obtained using solid wood-fibre slabs and plywood coated with grease. The surface in this case is slightly better than with the metal surface of the formwork. Formwork with a completely impermeable surface often causes the appearance of voids and shells. To reduce them, you need to consume more emulsion grease. For these reasons, it is desirable to apply lubricants to surfaces having little adhesion to concrete (plastic formwork, synthetic plywood).

Metal formwork and its accessories are manufactured in mechanical workshops or metal structures workshops. Metal formwork parts are made of steel of grade St.0. Workpieces of formwork elements are processed with a sufficiently high accuracy class. Permissible deviations from design dimensions in length and width by 1 linear meter of metal panel formwork boards shall not exceed 2 mm, deviations in the arrangement of holes for connecting elements (wedges, bolts, etc.) - 0.5 mm

The metal formwork passes the control assembly. Its parts touching concrete are coated with lubricant, and the rest are painted, after which all elements of the formwork are marked.

Transportation of concrete mixture to the place of laying

The permissible duration of transport depends on the temperature of the mixture at the exit from the mixer: it should not exceed 1 hour at a temperature of 2030 ° C; 1.5 h - 19-10 ° С; 2 h - 9-5 ° С. Long transportation on bad roads leads to its delamination. Therefore, in vehicles without inducing a mixture in transit, it is not recommended to transport more than 10 km on good roads and more than 3 km on bad ones .

In order that the concrete mixture at the place of laying has the specified mobility and uniformity, and the concrete made from it is a design grade for strength, it is advisable to deliver the concrete mixture without overloading or with a minimum number of overloads, while observing the following conditions:

packagings for transportation of concrete mixture shall provide convenient unloading of the mixture;

Gradual emptying;

absence of mixture hanging;

The construction of the container for the transportation of the concrete mixture should allow it to be systematically washed and cleaned from adhered and solidified concrete particles.

When transporting the concrete mixture from the concrete plant to the object under construction, it is necessary to maintain its homogeneity and compliance with the design indicators of mobility or rigidity. Violation of the homogeneity of the concrete mixture, that is, its stratification, can be caused by excessive amount of water, shocks during loading, transportation or unloading from a high height. It is forbidden to lay the stratified concrete mixture in concreted structures. If conditions allow, then before laying it is again mixed until the homogeneity is completely restored. At the same time, the reasons for the stratification of the concrete mixture are found out and measures are taken to eliminate them.

Deviation of mobility or stiffness indicators from design ones can be caused by harmful effects of atmospheric precipitation, wind, sunlight, as well as increased time of transportation of concrete mixture to the place of laying.

In course work, the mixture is transported by a car dump truck.

The dump truck is unloaded in badges. Concrete mixture is fed by crane to place of laying.

Buckets with a capacity of 1.0 m3 are used.

Concrete care, smelting and quality control

During hardening, concrete must be protected against precipitation or moisture loss. In the future, maintain the temperature-moisture mode with the creation of conditions that ensure the growth of its strength.

To avoid mechanical damage to freshly laid concrete, it is forbidden to move people, install scaffolding and formwork until concrete reaches a strength of at least 1.5 MPa. Movement along concreted floors of vehicles, concrete laying machines and other machines is prohibited until concrete reaches design strength .

As soon as the concrete reaches the strength at which the surface and facets of the structure can be preserved during fracturing, the side elements of the form are expanded.

Strength of laid concrete is evaluated by results of tests of control samples for compression.

Control samples in the form of cubes with a size of 20x20x20 cm are made at the concreting sites of the structure and stored in conditions close to the conditions for holding the structure.

Concrete is considered to have passed the tests if the average strength of the control samples is not less than 85% of the design.

Quality control and acceptance of structures

1 Concrete work log shall be kept on the site every day.

2 At acceptance of concreted structures, in accordance with the requirements of the current state standards, determine:

- concrete quality in terms of strength, and in necessary cases of frost resistance, waterproofness and other indicators specified in the design;

- quality of surfaces;

- availability and compliance with the design of holes, openings and channels;

- presence and correctness of deformation joints;

- permissible deviations of structures as per table 11 SNiP 3.03.01-87 *

Documents (invoices, certificates, concealed works certificates, etc.) confirming the quality of applied materials, products and semi-finished products shall be submitted.

Technology of concreting in extreme conditions

3.1 Operation procedure

Selection of work methods.

When choosing winter concreting methods, the following factors must be taken into account:

- Dimensions and purpose of the structure;

- Ambient temperature;

- Distance to RBU;

- Formwork material.

Finally, the winter concreting method is adopted based on economic feasibility and local conditions.

According to recommendations [3], the most expedient method of winter concreting of monolithic columns is the laying of heated concrete mixture with thermal cooling in the formwork. It should be borne in mind that the strength of concrete of the monolithic structure at the time of possible freezing should be at least 40% of the design strength at the grade of concrete 300.

Thermos method

Concrete laid in winter conditions is maintained mainly by method of thermos based on application of insulated formwork with device on top of protective layer. Concrete mixture with temperature of 2080 0C is laid in insulated formwork, and open surfaces are protected from cooling. It is not necessary to heat it at the same time, since the amount of heat introduced into the mixture during preparation, as well as the resulting physical and chemical processes of the interaction of cement with water (exothermy), is enough to harden it and gain critical strength. When designing thermal maintenance of concrete, the type of formwork and the degree of its insulation are selected. The essence of the thermos method is that the concrete, cooling to 0 0C, can gain critical strength during this time. Given this, the thickness and appearance of the formwork insulation are assigned. Insulation of the formwork is carried out without gaps and slots, especially in places of connection of heat insulation. To reduce blow-off of the formwork and prevent it from moistening, a layer of toli is laid along the skin.

The protective layer is represented by tol, cardboard, plywood, straw, on which sawdust, slag, slag-butter and glass wool can be laid. Formwork can be double, then the gaps between its shields are filled with sawdust, slag or filled with mineral wool, foam.

Formwork and insulation are dismantled when concrete reaches critical strength. The surfaces of the split structure are protected from a sharp temperature difference in order to avoid the formation of cracks.

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