To execute the base from FBS blocks the hands it will hardly turn out — all the same it is necessary to employ hoisting crane. However it is worth spending for special equipment nevertheless if it is necessary to build quickly the dwelling, the base from blocks is the most economic and pre-fabricated.
Foundation blocks have been thought up especially for mass, pre-fabricated housing in 1960. Volumes of release of precast structures and construction from them just strike. Today foundation blocks use not only at construction of multi-storey buildings, but also in individual construction.
Main data on the combined bases
The base — the most responsible and expensive part of residential building. Costs of the base can reach third of all estimate on the house. However you should not save on this part of the building — the durability of construction depends on it.
The base is meant as all designs executed below than "zero" — to floor height of the first floor. The base is intended for distribution of overall load from the building on basis soil. There is a lot of types of the bases, but main types only three: pile, tape and continuous monolithic plate.
FBS is deciphered as "foundation block wall". It is made of high-strength concrete, is the load-carrying structure intended for operation in soil with high aggression in relation to concrete. The block is not reinforced by principal reinforcement, is not intended for the device of columns and crossing points. Has two assembly loops in special deepenings.
Sizes of blocks longwise: 2400, 1200 and 900 mm. Height of all blocks — 600 mm; width — 300, 400, 500 and 600 mm. Marking is put at production at faces of blocks and can look so: FBS 24-4-6t that means length of 2400 mm, width of 400 mm, height of 600 mm. Letter T means "concrete of high specific weight". All sizes in construction are specified in millimeters. Mass-dimensional characteristics of blocks can be found in any construction catalog easily.
Base merits and demerits from FBS blocks
It is worth carrying to advantages of the block base:
- Fast construction. At the correct planning and the coordinated work of crew the combined part of the base of the small house can be established in one day.
- Simplicity of mounting. Even unskilled workers quickly master methods of installation of blocks.
- Opportunity to make dismantling of the block and again to put it on use: or sorting the old base, or incorrectly established.
- Lack of need to fill gaps between blocks. At correctly established FBS of these gaps simply should not be.
The subjective shortcoming from FBS blocks nevertheless is available for the base — the lifting equipment is necessary for performance of work. Of course, if for some reason the crane and the tractor are not able to approach site, it is necessary to carry out the base on other technology. Also it is necessary to make quite great physical efforts at installation of blocks — working with scrap, by the end of change you are ready to drop.
If to compare the cost of construction of the monolithic and combined base for owner-occupied dwelling, then the special overweight is not observed. Therefore the only argument for FBS blocks is construction speed.
The sequence of construction of the bases from FBS blocks
Let's consider option of the device of continuous footing with walls from FBS blocks and basement of 2.2 m in depth. The building small — 8x12 meters according to the plan. It is supposed that the working draft on hands and is carefully studied, the site under the base is planned, middle lines of the building are taken out and fixed.
Sequence of performance of the base (from below up):
- Ditch fragment.
- Device of base course. Depending on basis soil it can be charge crushed stone or preparation from lightweight-aggregate concrete of class B3.5 (on old — brand 50). It is not necessary to do any charges by sand under base of foundation.
- Device of continuous footing. Basic element of the base.
- Laying of the FBS wall blocks. Creation of walls of the basement, basis under overlying floors.
- Device of armoshv or reinforced concrete belt. Settles for forming of the top belt of strengthening under overlapping over the basement. The belt is arranged on the weak bases — on collapsible soil.
- Laying of panels of overlapping or the device of monolithic overlapping over the basement. Completion of works is below zero.
Now we will consider each stage in more detail.
Earthwork operations
For the specified base we tear off ditch. Excavating depth depends on depth of the basement and height of socle of the building — in our case of 2.5 m. We carry out the ditch size in the plan 1.0 m more for the device of protection of ditch, waterproofing of walls of the basement, convenience of works. It is desirable to get away the top, fertile layer of earth to one place and upon termination of works to carry out recultivation of sites around the house. Other soil if it is not necessary to take out.
It is necessary to stop sample of soil 100 mm above design mark of bottom of ditch. No damages of the basis and dosypok under the base are allowed. Under continuous footing soil manually is chosen. The superficial trench in form of future base at the bottom of ditch turns out.
Device of the bases
After the termination of earthwork operations and secondary breakdown of axes and the sizes at the bottom of ditch, we start the direct device of the base.
- Preparation under the base. It is made of "lean" concrete with the content of cement 1:3 or 1:4. Thickness of preparation is 100 mm. Basic purpose — protection of base of foundation against soil aggression. Smoothes all roughnesses at the trench device under tape. Carefully leveled preparation — pledge of ideally flat base and walls up to roof.
- Device of continuous footing. It is carried out from base slabs of FL. Laying of plates is carried out by the crane. Plates keep within on layer of cement and sand solution of structure 1:2. Sand under solution needs to be taken sifted. It is impossible to put concrete under plates.
- Laying of FBS blocks. To carry out laying of blocks of the lower row in strict accordance with the project. On each wall of the basement in the project the development with marking of each block is executed. Blocks keep within on cement and sand solution of structure 1:2. We verify correctness of installation of each block level. After installation of the lower row to execute seal of edge bosoms of blocks, it is possible concrete of class B3.5. To stack the second row of blocks also on solution with obligatory bandaging of seams of underlying row. So, all ranks consistently keep within, forming basement walls. We do not forget to leave window and door openings at laying of blocks, being verified with the project.
- Device of armoshv or can of belt. Are carried out on all perimeter of the basement. Armoshov has thickness of 50 mm, is made of concrete of class B 7.5, is reinforced by one number of principal reinforcement. Intended for the top binding of blocks and alignment of the basis under overlapping. Settles in option with monolithic continuous footing. The reinforced concrete belt is carried out at construction on the weak basis — collapsible soil. Is power element of building frame. The belt is also intended by the basis under floor slabs over the basement, at the same time being crossing point over apertures. It is carried out from class B15 concrete of high specific weight, reinforced by 2 rows of the principal reinforcement united in space framework.
After seal by concrete of all openings the base from FBS blocks is ready. It is necessary to execute waterproofing of walls outside. The waterproofing is usually carried out plastering for 2 times cold bituminous mastic of all concrete surfaces adjoining to soil. At high level of underground water the backing waterproofing — full gluing of outer surface of blocks roofing material on special mastic and clamping wall from ceramic brick is arranged. We dismantle boards, we carry out layer-by-layer backfilling of bosoms of ditch, we plan surface.
Safety rules
The well-known phrase "do not stand under arrow" when mounting FBS it is very relevant. All works on preparation of solution have to be performed out of crane area of coverage.
At strapping of blocks the hooks of rope of the elevator should be clung edges inside. Let's remind that assembly loops at the FBS block two. Naturally, about any drivings on the block at installation out of the question.
At lifting and moving blocks you should not help to direct them — the crane operator will make everything, excessive vanity only irritates him. It is necessary to stand far away as at rise the block can leave sharply aside. At reception of the block below if it was untwisted, it is not necessary to try to stop rotation — on its one and a half tons of weight of the person insufficiently.
If ditch quite deep — up to 2 m and more — actions for strengthening of earth walls have to be executed by wooden boards, at least from work of heavy machinery. It is obligatory to strengthen boards struts. It is not necessary to save on tree — life and health, undoubtedly, is more expensive than cubic meter of boards. Even the small collapse which was filling up leg can cause serious consequences.
The mass concrete needs to be sustained to full (28 days) or partial (7 days) achievements of design durability. It is impossible to stack blocks on the base executed the day before. In rainy weather or at strong wind it is better not to carry out works.
In construction there are no trifles. It is not necessary to save on the base. Everything should be done precisely and accurately. These rules are simple, are quickly comprehended.