Reinforcement of concrete monolithic structures with plastic materials is increasingly used in construction. This is due to such operational qualities as high strength, durability and the absence of corrosion. The latter circumstance is especially important in the construction of hydraulic structures, bridges and foundation foundations.
Classification
Manufacturers of building materials produce 5 types of composite reinforcement made of plastic:
- fiberglass or fiberglass - ASK;
- carbon composite - AUK;
- basalt composite - ABA;
- aramidocomposite - AAK;
- Combined - ACC.
From the name you can understand what material is the basic basis for the manufacture of plastic fittings.
General description and manufacturing technology
Due to the low cost and good performance, the most widely used fiberglass reinforcement. Its strength is slightly lower than that of other composites, but lower costs justify its use. For its manufacture use:
- staple fiberglass;
- epoxy thermosetting resins as a binder;
- special polymer additives to increase strength and improve other characteristics.
Composite fiberglass reinforcement for the foundation can have a smooth or corrugated surface. According to the manufacturing technology, bundles of the required diameter are initially formed from fiberglass and impregnated with epoxy resin. Then, to obtain a corrugated variable cross-section, the surface of a smooth rod is wrapped in a spiral cord, which is also woven from fiberglass. Then, the obtained preforms are polymerized in a furnace at high temperature and, after cooling, are cut into straight sections or wound into coils.
Specifications
Production of a periodic profile and technical characteristics of fiberglass reinforcement are regulated by GOST 31938-2012. The standard defines:
- types of plastic fittings depending on the materials used;
- nominal diameters ranging from 4 to 32 mm;
- length of straight rods from 0.5 to 12 meters;
- the possibility of supplying materials in bays with a diameter of up to 8 mm inclusive;
- marking and conventions;
- quality control methods;
- storage and transportation rules.
The weight of the material depends on the size of the cross section and can range from 0.02 to 0.42 kg / m.
The data on ultimate strength and elasticity given in GOST show that these parameters exceed the characteristics of rolled steel at the same diameters. This allows the use of polymer reinforcement in critical structures or, if necessary, to reduce the cross sections of reinforcing materials.
Scope and method of application
Plastic fittings are a modern alternative to rolled metal. The identical shape of the rods allows its use in technology similar to steel. The reinforcing cage made of composite plastic reinforcement is formed in the form of a flat grid or spatial structure designed to strengthen and increase the strength of reinforced concrete monoliths.
Polymeric reinforcing materials are used in the construction of roads, bridges, hydraulic structures, columns, walls, ceilings, foundations and other monolithic structures.
The main load falls on the longitudinal rods of the structure. They have a larger cross section and are located at a distance of not more than 300 mm from each other. Vertical and transverse elements can be at a distance of 0.5-0.8 m. The connection of individual rods at the intersection is carried out using polymer ties or knitting wire. Docking of individual rods on one horizontal line is overlapped.
The advantages of plastic fittings
When comparing composite rods with metal ones (we already performed a comparison in this article), a number of pluses and minuses of plastic reinforcement are clearly determined. These include:
- 5-7 times reduction in weight of the reinforcing cage;
- higher strength, allowing to reduce the diameter of the rods;
- resistance to corrosion and chemicals in concrete;
- simple installation and high assembly speed of reinforcing frames;
- simplified technology for creating structures of round and oval shape;
- excellent dielectric and thermal insulation properties;
- convenience of transportation.
In addition, it should be noted the unlimited length of rods for materials supplied in bays, as well as the simple cutting of workpieces of the required length.
Reinforcement made on the basis of fiberglass, 20-30% inferior in strength to other composites, but much cheaper. Therefore, such material is in higher demand in construction.
Disadvantages
Among the main disadvantages of composite reinforcing materials, experts call:
- low limit temperature of use, not exceeding 60-70 ° C;
- poor mechanical stability under transverse loads;
- the impossibility of bending with a small rounding angle and the need to use special elements.
It should be noted the lack of a regulatory framework for the use of polymers for concrete reinforcement and, often, inaccurate technical data from the material manufacturer. This makes it difficult to carry out calculations and forces to assemble structures with a margin of safety.
Technology for reinforcing foundations with composite materials
The light weight of plastic reinforcement for the foundation simplifies the assembly process of the reinforcing cage of any design. Moreover, due to the increased strength of the material, the cross-sectional diameter is taken one number less than for metal analogues.
The technological process of mounting concrete monolithic structures using polymer rods consists of the following steps:
- formwork installation and level marking of concrete mix;
- assembly and installation of a reinforcing frame;
- concrete pouring into the formwork;
- removal of shuttering boards.
Installation of reinforced monolithic structures must be carried out in accordance with the design decisions. The deck configuration should be fully consistent with the size and shape of the foundation. As formwork material, you can use factory-made standard boards, boards, moisture-proof plywood or chipboard. For fixed formwork, sheet polystyrene foam is most often used.
After assembling and fixing the shuttering boards, on their inner side, using the water level, make marks of the upper limit of pouring concrete mixture. This will reduce the lead time and help distribute concrete more evenly.
Spatial reinforcement cage for strip foundations
The scheme of reinforcing the foundation, laying and diameter of the rods are always indicated in the design. The use of composite reinforcement, especially based on carbon fiber, allows one to reduce the diameter of the rods. Laying the material must exactly match the calculated data. The frame is assembled on a flat platform.
Work begins with cutting blanks. To do this, unwind segments of the required length from the bay and install them on supports at a height of 35-50 mm above the support pillow or soil. After that, the transverse jumpers are laid, according to the drawing, and at the intersections they are connected with wire or ties. Thus, the lower row of the spatial reinforcing cage will be assembled.
At the next stage, it is necessary to assemble a lattice that is completely similar to the first, lay it on top and then cut the vertical posts of the design length. The first post is tied at the corner of flat lattices, the second - at an adjacent intersection, as a result, a spatial structure is gradually formed. If there are more horizontal rows, then the second lattice is fixed at the desired height, and then the next one is fixed. The vertical strut in this case represents one whole segment.
When assembling the frame, it must be remembered that the ends of the reinforcing bars should be 35-50 mm from the formwork. This will create a protective layer of concrete and increase the operational life of the structure. For this purpose, it is very convenient to use special plastic clips.
At the bottom of the trench, pour a sand and gravel pillow and tamp it well. After that, it is recommended to cover the sand layer with geotextile or waterproofing material. This will prevent the entry of moisture to the concrete and the germination of weeds.
Horizontal reinforcement of slab foundations
When pouring the foundation foundations of the slab type, the technology of horizontal reinforcement is used. Its main feature is the absence of turning and adjacent sections. Usually these are two grids located one above the other from long straight rods and uprights.
All work is done locally. First, according to the design drawing, the lower mesh is knitted, and the upper one is laid on top of it. After that, vertical racks are installed, as was described for tape structures. The bottom mesh must be installed on the stands.
Pouring concrete onto a plastic reinforcing cage
Technologically, pouring concrete mixture is no different from work when using steel reinforcement. However, given the lower strength of the material during lateral radial impact, vibrator compaction should be done carefully so as not to violate the integrity of the plastic rods.
It is not recommended to use manual tamper, as concrete pressure can change the configuration of the reinforcing structure.