GLASSFIBER REINFORCED CONCRETE: MATERIALS

The table below contains the major technical specifications for materials used in GRC product manufacture.

* if the average sand-to-cement ratio is 1:1;
** equipped with bar-and-auger spreaders.

As we have said earlier, GRC can be sprayed both in workshop and building site conditions:

In production plants, GRC can be sprayed onto rigid and special embossed forms in commercial production of precast single-layer thin-walled panels (up to 20 mm thick) and multilayer (heat-insulated) structural membes. The special embossed forms can be made of plastic, rubber, or polyurethane, and their reuse values are 150-200, 300-400, and up to 600 times, respectively. Generally, the choice of materials for formwork manufacture is unlimited – these can include profiled sheet metal, alabaster, and sealing compounds;

On construction sites, GRC can be effectively sprayed onto rigid and inflated formwork to produce space frames such as monolithic thin-walled (up to 30 mm thick) panels for sectional insulation and other structures. This technique is also used to make thin-layer waterproof coatings (with a maximum thickness of 15 to 20 mm) for reservoirs, swimming pools, and other facilities.

The premixing and compaction process is recommended for large-scale shop production of precast GRC panels where the product range is relatively small but the production volume is high.

The following components are used for manufacture of GRC structures designed in compliance with VSN 56-97:

1. GOST 26633 fine grained concrete with a minimum average density of 2000 kg/m3:

1.1. Aggregates for fiber reinforced concrete (coarse or fine) depend on the type and aggregative state of the fiber, product application and size, concrete grade and quality class, and the type of process used and must conform to the requirements of the applicable standards. The most multipurpose aggregate, for instance, is GOST 8736 high-silica sand with a grain size ranging from 1.5 mm to 2.5 mm (for low-speed GRC spraying, the maximum allowable sand grain size is 1.5 mm). The cement mortar may not contain more than 50% of sand;

1.2. GOST 10178 Portland Cement or GOST 969 Cement Fondu graded not lower than ̀400. Where the structures must conform to some exclusive standards, Expansive Portland Cements are permissible, provided that the cement self-stressing value must not exceed 200 kg/cm2 and the linear expansion must not be greater than 1%;

1.3. To obtain the desired mixture lowability and placeability values, depending on the specific process requirements, it is recommended to use chemical additives. Chemicals added to the concrete mixed for GRC manufacture can be the same as the additives used in conventional high-grade concretes; plainly speaking, all that can be added to traditional concrete can as well be added to GRC mortars. A mandatory requirement for GRC manufacture is to use a plasticizing agent;

2. The length of glass fiber used for reinforcement of GRC structures can range from 10 mm up to 60 mm (depending on the panel size, reinforcement type, and the process equipment chosen for preparation and casting of the GRC mixture). The initial material can be:

2.1. Alkali-resistant glassfiber rovings (STs-6 grade alkali-resistant glassfiber). One can also use imported fiberglass manufactured by Fibre Technologies International Ltd. (Bristol, UK), L’Industrielle De Prefabrication (Saint Priest, France), Cem-Fil (Chicago, USA), or other companies;
Note. Only alkali-resistant fiber can be used for reinforcing fine grained portland cement concrete.

2.2. GOST 17139 alumina borosilicate AlBSi-fiberglass rovings (note: non-alkali-resistant AlBSi-fiber can be used for reinforcement of limited durability concretes based on cement fondu, gypsum-retarded Portland cement, or densified cement). The use of AlBSi-glassfiber strings for reinforcement of portland cement based GRC is only allowable to ensure resistance to technological loads on a product that will not be used for more than one month (longer service time is permissible if it is experimentally tested and approved by respective controlling authorities), e.g. for permanent formwork components.