GRAIN FOR CONSTRUCTION MATERIAL

Abstract: Disclosed is an improved granular material used for for­ ming construction materials such as concrete and mortar. The grain material comprises a main material of fly ash or slug powder and reinforcing fibers (12). The reinforcing fibers (12) are mixed with the main material together with a binder to form a grain body (11) such that the reinforcing fibers (12) project outward from the surface of the grain body (11). The reinforcing fibers (12) mixed in this fashion permit increasing the bonding strength between the grain and the binder such as cement so as to improve the mechanical strength of the resultant construction material.

Description: The present invention relates to a granular material for forming construction materials such as concrete and mortar, particularly, to a granular material prepared by mixing reinforcing fibers with the grain body such that the fibers project outward from the surface of the grain body. Because of the fiber projection, the bonding strength between the grain body and a binder such as cement is increased. As known well, construction materials such as concrete and mortar are prepared by bonding grains such as stones, sand and artificial aggregate with a binder such as cement, lime, plaster or resin. It should be noted that the grains are bonded to each other by only the bonding strength of the binder, leading to an insufficient reliability of the resultant construction material in mechanical strength. Also, it is known to the art to mix reinforcing fibers with a binder. In this case, it is certainly possible to improve the mechanical strength of the binder itself. However, the reinforcing fibers mixed with the binder fail to improve the bonding strength between the aggregates, i.e., grains, and the binder. It follows that the resultant construction material such as concrete remains insufficient in its mechanical strength. What should also be noted is that skill of very high level is required for uniformly dispersing the reinforcing fibers within the binder. Prior art document EP-A-1 0 126 167 discloses a fiber-bearing aggregate in which concrete grains are reinforced by fibers which extend beyond the surface of the concrete grains. Further, prior art document FR-A-538 085 describes a ring-like aggregate whose surface is protected with a shield and which has a plurality of appendices. Finally, prior art document FR-A-2 117 647 discloses a method for improving the strength of an aggregate by addition of a hydraulic binder, e.g. cement, and document "Chemical Abstracts", volume 97, November 26, 1982, page 384, abstract number 22 1853k, Columbus, Ohio, USA, describes a method for producing concrete aggregates by mixing shag with cement or self-hardening resin. An object of the present invention is to provide a grain for construction material having an improved bonding strength with a binder so as to provide a construction material having a sufficiently high mechanical strength. To solve this object the present invention provides a grain as stated in claim 1 or in claim 3. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 schematically illustrates a grain for construction material according to one embodiment of the present invention; Figs. 2 and 3 are photos each showing in a magnified fashion a grain for construction material of the present invention; and Figs. 4 and 5 are graphs each showing the effect produced by the grain for construction material of the present invention. Fig. 1 schematically illustrates a grain for construction material according to one embodiment of the present invention. As seen from the drawing, the grain comprises a grain body 11 and a plurality of reinforcing fibers 12 mixed with the grain body 11 such that the fibers 12 project outward from the surface of the body 11. The grain body 11 is prepared by mixing 90 to 50 parts by weight of a main material such as fly ash, slug powder or a mixture thereof, 50 to 10 parts by weight of a binder, e.g., cement, and a suitable amount of water. The grain body 11 is further mixed with 0.3 to 3% by volume of reinforcing fibers 12 and, as required, additives such as thickening agent, water reducing agent, foaming agent and nucleating agent. The resultant mixture is granulated by a high speed mixing granulator, followed by subjecting the resultant grains to a wet, steam or autoclave curing so as to obtain the desired grains for construction material of non-baked type. The grain for construction material of the present invention may be baked, as desired. In this case, the grain body 11 is prepared by mixing 90 to 50 parts by weight of a main material such as fly ash, slag powder or a mixture thereof, 50 to 10 parts by weight of a binder such as shale powder, clay or silica fume, and a suitable amount of water. The grain body 11 is further mixed with 0.3 to 3% by volume of reinforcing fibers 12 and, as required, additives such as water reducing agent, foaming agent, nucleating agent and sintering aid like feldspar. The resultant mixture is granulated by a high speed mixing granulator, followed by drying and, then, sintering the resultant grains at 800 to 1,300°C so as to obtain the desired grains for construction material of baked type. The reinforcing fibers 12 used in the present invention are fibers of nylon, aramid, carbon, glass, ceramics, metal or asbestos. The diameter of the reinforcing fiber 12 is from 5 to 50 microns (µm). On the other hand, the length of the fiber 12 is at least equal to the diameter of the grain body 11 and not greater than 10 times the diameter of the grain body 11. In the case of preparing the baked-type grains for construction material, the reinforcing fiber 12 is formed of a heat-resistant material such as carbon, glass or ceramics. In the grain for construction material prepared as described above, the reinforcing fibers 12 project outward from the surface of the grain body 11 as shown in Fig. 1. Naturally, the reinforcing fibers 12 permit the grains for construction material of the present invention to be strongly bonded with the binder. It follows that the construction material such as concrete or mortar prepared by using the grains of the present invention is markedly advantageous over the conventional construction material in mechanical strength such as flexural strength, compressive strength, impact resistance and cracking resistance. Figs. 2 and 3 are photos showing in a magnified fashion the grain for construction material of the present invention, which was prepared by granulating a mixture consisting of 80 parts by weight of fly ash (main material), 20 parts by weight of cement (binder), 10 parts by weight of shale powder (thickening agent), and a reinforcing fiber "Kureha C-106T" (which is a trademark of a pitch-type carbon fiber having a diameter of 18 microns, a length of 6 mm and a specific gravity of 1.65), using an Irish reverse flow type high speed mixer, followed by subjecting the resultant grains to a steam curing for 6 hours. The grain for construction material of the present invention is sized 2.5 mm or less in diameter, which fully meets the fine aggregate specified in Standards of Reinforced Concrete by Civil Engineering Institute of Japan. Also, the grain for construction material has an absolute dry specific gravity of 1.20. The construction material prepared by using the grain of the present invention has a mechanical strength higher than that of the conventional construction material in which the reinforcing fibers are mixed with the binder. Fig. 4 shows the flexural strength of the construction material with respect to the mixing proportion (% by volume) of the reinforcing fibers in the construction material. The marks "o" in Fig. 4 denote the construction material prepared by using the grain of the present invention in which the reinforcing fibers project outward from the surface of the grain body, with the marks "x" denoting the conventional construction material in which the reinforcing fibers are mixed with the binder. Further, Fig. 5 shows the compressive strength of the construction material with respect to the mixing proportion (% by volume) of the reinforcing fibers in the construction material. The marks "o" and "x" shown in Fig. 5 are equal to those shown in Fig. 4. In these experiments, the mixing ratio of cement to the grains, i.e., aggregates, was 1 : 2, and the water-to-cement ratio was 32%. Also, 3% of "Mighty 50", a trade-mark of a high performance water reducing agent, was used as an additive. As apparent from Figs. 4 and 5, the construction material prepared by using the grain of the present invention is superior to the conventional construction material in both the flexural strength and compressive strength. Clearly, the improved mechanical strength in the present invention is derived from the mechanism that the reinforcing fibers projecting outward from the surface of the grain body permit increasing the bonding strength between the grain, i.e., aggregate, and the binder in the present invention. What should also be noted is that the grain for construction material of the present invention can be readily used in the construction site because the reinforcing fibers are mixed in advance with the grain. In the prior art, however, the reinforcing fibers must be uniformly dispersed in the binder in the construction site, which is considerably troublesome.

Claims: A grain for construction material comprising a grain body (11) and reinforcing fibers (12) outwardly projected from a surface of the grain body (11), characterized in that (a) said grain body (11) comprises 90 to 50% by weight of a main material consisting of fly ash, slag powder or a mixture thereof, and 50 to 10% by weight of a binder of cement, (b) a suitable amount of water and reinforcing fibers consisting of nylon, aramid, carbon, glass, ceramics, metal or asbestos are added to the main material, (c) said grain is formed by a high-speed mixing granulator and subjected to a wet, steam or autoclave curing to provide a cured grain body (11) having a particle size of 2.5 mm or less, said reinforcing fibers (12) projecting outward from the surface of the cured grain body (11), and (d) said reinforcing fibers (12) have a diameter of 5 to 50 microns (µm) and a length at least equal to, but not greater than 10 times the diameter of said grain body (11) and are added in an amount of 0.3 to 3% by volume of said grain for construction material. A grain according to claim 1, characterized in that the grain body (11) is further mixed with additives such as thickening agent, water reducing agent, foaming agent and nucleating agent. A grain for construction material comprising a grain body (11) and reinforcing fibers (12) outwardly projected from a surface of the grain body (11), characterized in that (a) said grain body (11) comprises 90 to 50% by weight of a main material consisting of fly ash, slag powder or a mixture thereof, and 50 to 10% by weight of a binder selected from the group consisting a shale powder, clay and silica fume, (b) a suitable amount of water and heat-resistant reinforcing fibers consisting of carbon, glass or ceramics are added to the main material, (c) said grain is formed by a high-speed mixing granulator and, then, dried and sintered at 800 to 1300°C to provide a sintered grain body (11) having a particle size of 2.5 mm or less, said reinforcing fibers (12) projecting outward from the surface of the sintered grain body (11), and (d) said reinforcing fibers (12) have a diameter of 5 to 50 microns and a length at least equal to, but not greater than 10 times the diameter of said grain body (11), and are added in an amount of 0.3 to 3% by volume of said grain for construction material. A grain according to claim 3, characterized in that the grain body (11) is further mixed with additives such as water reducing agent, foaming agent, nucleating agent and sintering aid like feldspar.

Inventors: OHAMA, YOSHIHIKO, SUZUKI, SEISHI, YAMAMOTO, TADASHI
Applicants: OHAMA YOSHIHIKO, THE TOHOKU ELECTRIC POWER CO., INC., TOHOKU POLE COMPANY, INCORPORATED
Application year: 1986
Main classification: C04B20
IPC codes: E04C5, E02D5, C04B14, C04B18, C04B20