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The Relationship Between Glass Fiber Reinforced Cement Products and Terrazzo Products

Abstract: Cement-based building materials have a prominent feature is the high compressive strength and bending (folding) strength. Tensile strength and low impact strength. The use of fiber materials for cement-based materials to improve performance, after all, is an effective method. Some fibers can only improve the bending strength and tensile strength of cement base, but can not improve its impact resistance; some fibers can only improve the impact resistance of cement matrix, but can not improve its bending strength and tensile strength ; And glass fiber can not only improve the bending of cement-based. Tensile strength, but also can improve its impact strength. The high strength of the new materials in the terrazzo has a high value in the application.
Key words: glass fiber cement composite inorganic cementing material
 
 
 
Preface:
Glass fiber reinforced cement (Glass fiber Reinforced Cement, abbreviated as GRC) is a glass fiber reinforced material, cement paste or cement mortar as a matrix formed a composite material. Portland cement → mortar, concrete → reinforced concrete door (1850) → asbestos cement door (1900) → cement concrete door (1850) → cement concrete door (1900) → Prestressed Concrete (1929) → Admixture Concrete (1935) → Polymer Cement Concrete (1950s) → High Strength Concrete (1970s) → High Performance Concrete (20th century 90s). Fiber reinforced cement-based materials from asbestos cement to GRC (glass fiber cement) in the 1950s, steel fiber cement (SFRC) in the 1960s, carbon fiber cement (CFRC) in the 1980s, and later fiber-reinforced polymer cement, mechanics Performance greatly improved, with the subsequent expansion.
 
1. The development of glass fiber reinforced cement
    Cement-based building materials have a prominent feature, is the high compressive strength and bending (folding) strength. Tensile strength and low impact strength. The use of fiber materials for cement-based materials to improve performance, after all, is an effective method. Some fibers can only improve the bending strength and tensile strength of cement base, but can not improve its impact resistance; some fibers can only improve the impact resistance of cement matrix, but can not improve its bending strength and tensile strength ; And glass fiber can not only improve the bending of cement-based. Tensile strength, but also can improve its impact strength. The higher tensile strength (1770-2550 MPa for monofilament) and the higher elastic modulus (about 70 GPa, 2.5 times of the cement matrix) of the glass fiber can greatly enhance the cement matrix Strength and toughness provided the necessary guarantee. 30 years of domestic and foreign research on the performance of glass fiber reinforced cement, cement matrix added 4% -5% of the glass fiber can greatly improve its mechanical properties. General cement mortar tensile strength of 2-3MPa, the ultimate extension deformation of 100-150με, bending (folding) strength of 5-7MPa, impact strength of about 2kJ / ㎡, when adding 4% -5% of the Glass fiber, the tensile strength of the composite material reaches 9-12MPa, the ultimate extension deformation reaches 8000-12000με, the bending strength reaches 20-25MPa, and the impact resistance reaches 15-20kJ / ㎡. Of course, it is encouraging to add a small amount of glass fiber to the cementitious matrix to achieve such good results. As a material, especially for the manufacture of building elements, it is more concerned with its durability Sexual problems, all hope that building materials have a long service life and good safety and reliability. For glass fiber reinforced cement, whether the glass fiber can maintain its high strength and good toughness is the key to ensure the glass fiber reinforced toughening effect in the new composite material of glass fiber reinforced cement. In practice, it was found that the glass fiber in the cement matrix erosion and brittle problems, and began to identify the erosion and embrittlement mechanism, and through various methods to improve the glass fiber. On the one hand to improve the glass fiber resistance to alkali erosion, mainly from two aspects to improve, that is to change the chemical composition of glass fiber, or the glass fiber surface alkali treatment; the other hand, the substrate material Or adding pozzolanic material to Portland cement to increase the strength and toughness of the matrix or to add polymers to the matrix to prevent the substrate from being physically and chemically attacked, or to develop fibers that are suitable for glass fibers Use of low-alkalinity cement in the environment to reduce the amount of Ca (OH) 2 in cement hydration products. Japan, the United Kingdom and other technical line is used alkali-resistant glass fiber and modified Portland cement composite. China Building Materials Institute is used in alkali-resistant glass fiber and low-alkali cement match the "double insurance" technology line. Which solves the problem of long-term durability of glass fiber reinforced cement. Accelerated aging tests suggest that the GRC has a safe life of at least 50 years. The solution of the durability of glass fiber reinforced cement has laid a solid foundation for the wide application of this material.
    From the use of alkali-resistant glass fiber manufacturing GRC products and began to enter the industrial-scale production as a starting point, the international GRC products industry has so far experienced 30 years. At present, dozens of countries and regions around the world in different sizes of production and use of GRC products, the annual global production of GRC products is estimated at about 450,000 tons, of which the highest yield when pushed in Japan, the annual output of about 120,000 tons, the United States GRC Products with annual sales of more than 100 million US dollars, the whole of Europe GRC products is estimated annual production of not less than 100,000 tons, of which about half of Germany. In Asia, China's GRC industry has been growing in scale, the annual output has reached 4-5 million tons, Singapore, Malaysia and other countries as well as China's Taiwan, Hong Kong has also produced two GRC products for many years.
 
2. Glass fiber reinforced cement products characteristics
The main properties of cement for its cost, adaptability and high compressive strength. The main drawback is low tensile strength and brittleness. Thus, as mentioned above, the above disadvantages of the cementitious material can be improved by the addition of glass fibers. The advantage of glass fiber reinforced cement is that the product is thinner than reinforced concrete (typically above 10 cm) and has a lighter component capacity. And reinforced concrete must have 25mm or more protective layer. Glass fiber reinforced cement in many ways similar to ordinary reinforced concrete, such as weather resistance, non-combustion, easy maintenance, low heat flow and corrosion resistance. And has a number of advantages over concrete, such as high strength and weight ratio, it can use thinner cross-section; with early high impact resistance; easy to shape to various shapes; easy to form with other materials, high-strength semi-structural insulation components; Can be used simple tool modeling and cutting; have broad smooth surface available. The main drawback is that it is not yet allowed for load-bearing structures. It can be used for semi-structural applications, such as various wall (curtain wall), and metal wall and plastic wall material competition.
 
2.1 Physical properties
    Density The density of the GRC material is not affected by age. A 1-square-meter, 6-cm-thick flatboard weighs about 12 kg, and GRC weighs less than 20 percent of a normally prefabricated concrete slab.
    Shrinkage and Water Movement As with all cement-based materials, the volume change of GRC occurs in two ways: irreversible shrinkage at initial hardening, a function of C / W, and long-term moisture transfer caused by normal temperature changes. Glass fiber reinforcement had no effect on the amount of GRC shrinkage, but silica sand was added to the matrix as a supplement to hardness to reduce both shrinkage. The larger the sand / cement, the smaller the amount of shrinkage, and the addition of 25% of the sand in the matrix, the theoretical limit of shrinkage may be 1.5cm / m. Practical GRC Curtains In the UK weather conditions, water movement is only half of this limit, but this value is slightly larger than the ordinary concrete moisture movement of 2 times. If the plate has a protective film, because it limits the movement of water within the GRC surface, shrink smaller.
    Permeability and condensation GRC can prevent water penetration, but has a lower vapor permeability. Therefore, under normal conditions of use, no vapor barrier is required. However, in some special cases, such as refrigerated panels, consideration should be given to the possibility of inter-layer condensation and the installation of a vapor block in the building where appropriate.
    Humidity and heat flow The same as other cement-based materials, GRC thermal expansion is very low, the temperature difference of 70 ℃ for each m is less than lmm. In the UK, hot and cold conditions vary widely, thermal expansion and contraction can offset each other, which can reduce the size of the change. In the Middle East, hot and dry climates have little impact on GRC's long-term performance compared to temperate climates, which can withstand complex cycles of long-term sub-zero temperatures and freeze-thaw cycles.
    Chemical Resistance GRC has the same chemical resistance as concrete, but has lower porosity than most concrete or mortar. Therefore, GRC has a slightly better resistance to chemical attack. But the acid and sulfate corrosion is poor, use special cement instead of ordinary Portland cement as the GRC matrix material.
    Fireproof The GRC does not burn at all and disperses the fire inside the building. Has excellent incombustibility and to prevent the spread of fire performance, fire classification is not easy to fire.
2.2 Durability
    (1) the length, content and orientation of the glass fiber; (2) the matrix material / cement / cement composition, and the mechanical properties of the GRC; (2) the mechanical properties of the GRC, which are different from those of the reinforcing materials, Water and air ratio; (3) the product of a spraying method or pre-mixing method; (4) hardening time and hardening; (5) age; (6) conditions of use. The combination of the above six items can determine the scope of a material performance benchmark. However, mixing, manufacturing methods and hardening are components of the design and specifications of the function, the age of the GRC also have a fundamental impact on performance. 1968 - 1969 alkali-resistant glass fiber reinforced cement products development, a large number of tests used to verify the long-term performance of GRC. The main conclusions drawn from the 5-year experimental program are the reduced tensile properties and some embrittlement of the material, especially GRC, where exposure to permanent moisture or temperate weather is most severe. In high temperature and high humidity areas, such as the tropics, embrittlement is very significant.
 
2.3 Mechanical properties
    It is important to understand how the GRC is deformed under load, and the relationship between stress and strain is important because the mechanism of alkali-resistant glass fibers in cement-based materials is different from that of general glass fibers in reinforced plastic composites. For plastic materials, glass fibers are much more rigid than plastic substrates, so when a load is applied to the composite, the glass fiber reinforcements bear most of the load. For GRC, the glass fibers are harder at the margin than the cement matrix, and when a load is applied to the GRC compound, three different phenomena occur: (1) the cement matrix acts with the glass fibers, although partially bearing the cement; (2) the cement matrix is characterized by a small crack, a sudden transfer load on the glass fiber, and the matrix to be combined with fiber to obtain the load continuity; (3) load completely by the glass fiber to bear, micro-cracking until failure. The elongation of the fibers, without breaking away from the cement matrix, imparts considerable ductility to the GRC. Because the properties of glass fiber reinforcements in the GRC are similar to those of conventional reinforced concrete, the load transfer to the fiber, similar to the load in the reinforced concrete, is transferred to the reinforcing steel and the cement matrix produces the same microscopic cracking.
 

JS-HX-600 Rotating type tile press

JS-HX-600 Rotating type tile press

3. High durability glass fiber reinforced cement composite
    Since the early 70s of the 20th century, many countries competing to develop glass fiber reinforced cement (GRC) products, the development of GRC in the West based mainly on lead-based alkali-resistant glass fiber (ARGF) as a reinforcing material, Portland cement as Matrix, but the test and use of the results show that the AGRF-OPC made GRC mainly the following two major problems:
    (1) exposure to the atmosphere or in a humid environment, the ultimate tensile strength. Ultimate bending strength, impact strength and toughness with time and more significant decline, especially in toughness worse.
   (2) GRC wall panels mounted on a metal skeleton are warped, cracked, and peeling off the ceramic sheets.
    Western countries to solve the long-term durability of GRC, to explore a number of technical measures to take, such as alkali-resistant glass fiber surface covered with protective layer to adjust the alkali-resistant glass fiber active ingredients, cement doped with pozzolanic active material. Doped acrylic polymer emulsion, but the effect is not significant. To this end, in the 1980s the Western countries of the GRC industry was low. China in the 20th century, since the mid-70s research and development of a new generation of GRC, take ARGF and low-alkalinity sulphoaluminate cement compound 'double insurance' technology line. Accelerated aging test in steam at. 20 ℃ water immersion test, accelerated aging test in 80 ℃ hot water and atmospheric exposure test in Beijing show that GRC made of LASC + ARGF (low alkalinity sulphoaluminate cement and alkali resistant glass fiber composite) The flexural load and ultimate flexural strength retention of the test were significantly higher than those of GRC of OPC + ARGF, GRC of low basicity sulphoaluminate cement and medium alkali glass fiber (LASC + AGF), Portland cement and medium alkali glass fiber (OPC + AGF). The GRC prepared by LASC4-ARGF accelerated aging at 50 ℃ for 180 h, and its flexural toughness was not significantly lower than that of the GRC with the same composition in the atmosphere for 28 days. The dry shrinkage of GRC made of LASC + ARGF is lower than that of OPC + ARGF. Therefore, it can be considered that GRC made of LASC + ARGF has higher durability. At present, this combination of GRC not only for the production of Po Wa, bath, digesters, etc., but also for the production of certain secondary load-bearing components or products, such as granaries, pressure pipes. Racks and roof racks and so on. In the mid-1980s, Japan's Central Glass Company, Chichibu Cement Corporation and Nippon Electric Company jointly developed a new generation GRC made of high-alumina content ARGF and low-alkalinity cement. Compared with the GRC made by OPC + ARGF, Sex has significantly improved.
    (3) Ca (OH) 2 crystals have been found to be chemically resistant to ARGF in the presence of ARGF (1, 2, 3, 4, 6, 7) The deposition of the original silk gap, growth of the original wire to lose flexibility and become brittle. Secondly, it is considered that the hydration product of cement matrix is the key of GRC durability. For this purpose, a low basicity cement or a cementitious system of silicate cement should be used to substantially reduce its alkalinity. Even with an aqueous solution of certain salts (CaCl 2, AgCl 2, CdCl 2, etc.), the glass fiber surface can be protected. It has been proposed to add 2% to 10% of calcium chloride to the molding sand to prevent alkali corrosion in the hardened cement. The calcium chloride in the aqueous medium acts with Portland cement while the reactant - Calcium acid and calcium silicate hydrate are deposited on the surface of the fiber to prevent corrosion (Japanese Patent No. 1321711).
    The method of treating the surface of the glass fiber can not only stabilize the glass fiber strength but also enhance the strength of the glass fiber to a certain extent. One of the methods is the low-temperature ion exchange, which relies on the K <sup> + </ sup> ions in the KNO3 salt melt to replace the Na <sup> + </ sup> ions in the glass to form the compressed surface layer (<5min) in the glass fiber KNO3 melt depends on the glass fiber composition and the glass transition temperature from the plastic state to the hard brittle state. Under these conditions, the strength of the cement stabilized glass fiber can be increased by 40%, and a new type of mixture based on epoxy gypsum and epoxymethylpropylene derivatives can be used. To prevent corrosion of the glass fiber surface by alkali.
    A series of physical-chemical studies have shown that epoxy gypsum can modify the new hydrate boundary layer, and greatly reduce the amount of calcium hydroxide, increasing the content of low-alkali hydrated silicate. This facilitates the diffusion of the weak alkaline ions to the surface of the glass member. Epoxy masticated methyl acrylic polymer is acidic, with long-lasting elasticity. The adsorption of hydrated silicate on the surface of the fiber can be accumulated, the alkaline environment can be converted to acidic, and the formation of insoluble loose structural compounds. The rate at which the protective layer is polymerized in an alkaline environment depends on its composition, as well as its chemical interaction with the cement matrix, glass, and surface-active groups. When such polymers are used, the migration of alkaline oxides of the glass framework into the cement matrix is reduced by two to three orders of magnitude. Therefore, the thickness of the protective layer should be in the range of 100 to 150 με in order to improve the strength properties and extend the durability. The presence of the polymer protective layer forms a barrier to diffusion of the film, allowing the CaZ to pass at a speed of not less than 10 m / m to ensure the chemical stability of the glass material. The polymer interfacial layer is filled with pores to reinforce the glass reinforcement and the matrix .
    For fiberglass, the erosion of the cement matrix can be reduced by reducing the cement alkalinity. Add fly ash
To the cement, can promote the reduction of hardened cement liquid phase "and" OH-ion concentration. Practice has pointed out that the glass fiber in the hardened bauxite cement is relatively stable. The solidification hardening process of hydrated bauxite cement appears to be similar to that of Portland cement, which is actually different from that of Portland cement. If the Portland cement hydration composition consists of calcium hydroxide and calcium aluminate hydrate, Soil hydration results in the formation of aluminum hydroxide and calcium aluminate hydrate, which will crystallize and reduce the recrystallization process. When the bauxite cement hardens, the pH of the liquid phase is smaller than that of the Portland cement, and has a low C-OH content for slag Portland cement solidification, due to slag-related reasons. This property is favorable for corrosion stability, indicating the possibility of relatively stable products based on glass fiber and slag Portland cement.

 

 

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