METHOD AND APPARATUS FOR CUTTING HOLLOW-CORED CONCRETE SLABS

Abstract: Freshly cast hollow-cored concrete slabs are subjected to an immediate cutting operation prior to the hardening of the concrete mix in such a manner that exposes the cores, and the ends of the cores are automatically filled to avoid jointing mix from subsequently intruding into the cores. The cutting is performed by driving two sheet-like cutting blades (3), which are mutually placed in a V-shaped posture, through the slab so that cutting tips (10) of the blades (3) meet near the bottom of the slab; then driving an end cutting knife (1), whose sides (16) facing the mix are substantially parallel to the cutting blades (3), through the slab between the cutting blades (3) towards the cutting tips (10) of the blades (3) so that a homogeneous sheet (17) of the concrete mix is formed on the sides (16) of the end cutting knife; and, when the end cutting knife (1) reaches its lower position, lifting out the cutting blades (3) and pushing the formed homogeneous sheet (17) of mix by means of the end cutting knife (1) to adhere to the cut surface (18) of the slab formed by the cutting blades.

Description: The present invention relates to a method in accordance with the preamble of claim 1 for cutting hollow-cored concrete slabs. The invention also concerns an apparatus for implementing the method. In the production of hollow-cored concrete slabs, the slabs are conventionally cast on long beds using a continuous slip-forming extrusion method. In their typical form, the cored slabs are prestressed structures cast from relatively stiff mixes. Immediately after completion of the casting phase, openings and recesses are worked into the slabs according to the individual specifications of construction drawings. Working is performed using manual methods by first measuring the elements with a tape measure and marking the cutting points of elements. Referencing to the cutting point, the position of each opening is measured and marked, after which manual tools are used to scrape the openings free of unhardened mix that is then placed in a waste mix container. In some cases, the ends of slabs are trimmed immediately after the casting operation prior to the hardening of the mix. The immediate cutting is most typically performed using manual tools, e.g., a circular saw. In some cases the immediate cutting is made over such a wide length (10...20 cm) that the ends of hollow cores are visible from the cutting point, allowing the ends to be filled with concrete mortar or mix using manual methods. In the next phase the entire set of cored slabs is covered with a protective blanket until the final setting of the concrete. When the concrete has attained a sufficient strength, it is possible to cut the prestressing tendons at the ends of the slabs. Most typically, the slabs are cut by using a circular saw with a diamond-tipped blade, which is capable of cutting the set concrete, in addition to the tendons. Next, the elements can be transferred from the casting bed to be bundled and then put into final storage until they are later transported to the construction site. Prior to storage, however, the ends of the hollow cores are always stoppered by a suitable type of plug so that the jointing mix applied at the construction site to the joint between the element ends is not able to flow into and fill up the cores. Consequently, the stopper plugs of the hollow cores in the cored element, in practice, perform as casting plugs, but they may also be applicable as supports for the wall constructions resting on the ends of cored slab. The type of plug conventionally used is a cast concrete plug or a detachable, cut-shaped, molded plastic plug. Of the plugging methods described above, a disadvantage to be pointed out is that of the dominatingly high proportion of manual labour required. Each plugging operation calls for a dedicated work phase, and, also, quite frequently, the use of a dedicated and expensive plugging material. The present invention aims to overcome the disadvantages found in prior-art techniques and to provide an entirely novel method and apparatus for cutting prestressed hollow-cored concrete slab. The method is based on cutting the hollow-cored slabs immediately after the casting phase while simultaneously filling the ends of the hollow cores using the excess mix from the cutting phase as a filler. More specifically, the method in accordance with the invention is characterized by what is stated in the characterizing part of claim 1. Furthermore, an apparatus in accordance with the invention is characterized by what is stated in the characterizing part of claim 5. The invention provides remarkable advantages. When using the method in accordance with the invention, the labour-intensive sawing phase is shortened and the manual labour-requiring operation of filling the core ends is replaced by the filling of the core ends already in conjunction with the instant cutting phase. In the following, the invention will be examined in more detail by means of an exemplifying embodiment illustrated in the attached drawings. Figure 1 is a partially cross-sectioned side view of a cutting apparatus in accordance with the invention. Figure 2 is a partially cross-sectioned front view of the cutting apparatus shown in Fig. 1. The invention is based on arranging an instant-action cutting/-plugging apparatus 9 to be movable closely coupled to the slipforming extruder. The apparatus is movable on wheels 7 on side rails 8 of the casting bed. Drive means for the apparatus is provided by a separate transfer motor 12. The apparatus has preferably a distance measuring device 13, with help of which the apparatus is shifted forward on the casting line over the length of the slab element so as to locate an end cutting knife 1, which extends crosswise over the entire element width, at the separation point of the elements. After the apparatus is parked, cutting blades 3, mutually aligned in a V-shaped posture, are driven by means of an auxiliary mechanism 15 downward into the fresh unhardened mix, obliquely approaching each other in the mix. A tip 10 of the cutting blade 3 is preferably saw-shaped to advantageously help the blade 3 penetrate into the mix without distorting its cast shape. To aid penetration, the cutting blade 3 can be subjected to a sideways reciprocating motion by means of, e.g., a reciprocating actuator 6 implemented using a separate rotational drive and an eccentric cam disc. Sideways expansion of the mix is prevented by a mold wall 11 resting against the side of the fresh cast slab. The frequency of the reciprocating crosswise motion is 5 to 600 strokes/min, preferably approx. 300 strokes/min. The height of the cutting blade 3 is adjustable by means of a separate mechanical adjustment 4, which allows the adaptation of the apparatus into the fabrication of cored slabs of different heights. When the cutting blades 3 are driven sufficiently deep towards their lower position, the operation of a wedge-shaped end cutting knife 1, which extends over the entire width of the cored slab, is started. The end cutting knife 1 is pushed with help of a mechanical actuator 2 down into the fresh, unhardened mix close to the cutting blades 3. To improve the cutting effect of end cutting knife 1, a crosswise reciprocating actuator 6 and a saw-shaped tip, similar to those of the cutting blades, can be used. Sides 16 of the end cutting knife facing the concrete mix are substantially parallel to the cutting blades 3. Prior to the start of the end cutting knife operation, the concrete mix of the cast slab can be moistened with help of a separate water spraying nozzle 14 in order to plasticize the extremely stiff mix. The downward penetration of the end cutting knife 1 through the unhardened mix to its lower position simultaneously creates an instant cutting gap between the opposing ends of elements. The combination of the reciprocating motion, downward gravitational motion, and wedge-shaped form of the end cutting knife 1 works the mix between the cutting blade 3 and the knife 1 so that the mix is plasticized and transferred from the ridges as well as from the upper and lower surfaces of the slab into the open cores thus forming a homogeneous concrete mix sheet 17 from the original open core structure. When the end cutting knife 1 has reached the desired lower position, the cutting blades 3 are lifted by means of a mechanical actuator 15 to an upper position. Because of the extremely thin construction of the cutting blades 3 and the sustained downward pushing action of the end cutting knife 1, the homogeneous concrete sheet 17 formed at the cutting point is not severed but instead remains in place during all cutting phases. When the cutting blades 3 are at their upper positions, the end cutting knife 1 yet further finalizes the seam formed between an end 18 of the slab and the homogeneous concrete sheet 17, which forms a plug at the end of slab, by compacting the voids formed at the ends by the withdrawal of the cutting blade 3. At this stage, the pushing action and a small crosswise shearing motion of the end cutting knife 1 compacts the concrete sheet 17 to adhere to the end 18 of slab thus plugging the cores of the slab. Finally, the end cutting knife 1 is lifted up by means of the mechanical actuator 2 to allow the transfer of the cutting apparatus to the next cutting point. In the implementation of the method, the apparatus measures the lengths of elements, performs an immediate cutting of the hollow-cored slab, and works appropriate plugging material from the excess mix remaining from the cutting operation, and plugs the cores of the hollow-cored slab in a single work phase.

Claims: 1. A method of cutting a cast hollow-cored concrete slab, in which method: _ the cored slab is cut after the casting of the slab and prior to the hardening of the concrete mix, so that the hollow cores are exposed, and _ the exposed ends of the hollow cores are plugged in order subsequently to prevent jointing mix from filling the cores, characterised in that _ the cutting of the slab is performed by pushing from above two sheet-like cutting blades (3), which extend over the entire width of the slab and are mutually placed in V-shaped posture and aligned crosswise across the slab, into the slab close to its lower surface so that cutting tips (10) located at the lower edges of the cutting blades (3) are approaching each other, _ a wedge-shaped end cutting knife (1), which extends over the width of slab and has its sides (16) aligned substantially parallel to the cutting blades (3), is pushed with a mix-shearing action from above through the gap between the cutting blades (3) towards the cutting tips (10) of the cutting blades (3) in order to form a homogeneous concrete sheet (17) on the sides (16) of the cutting knife (1) facing the mix, and, when the end cutting knife (1) reaches a lower position where the end cutting knife (1) is in the immediate vicinity of the cutting blades (3), the cutting blades (3) are lifted up and the formed homogeneous concrete sheet (17) is pushed by a simultaneous shearing motion of the end cutting knife (1) to adhere to the cut surfaces (18) of the slab formed by the cutting blades and thereby plug the exposed ends of the hollow cores. 2. A method as claimed in claim 1, characterised in that the cutting blades (3) are pushed down by a cyclic movement. 3. A method as claimed in claim 1 or 2, characterised in that the shearing motion of the end cutting knife (1) is implemented by a cyclic crosswise reciprocating movement. 4. A method as claimed in any foregoing claim, characterised in that water is applied between the cutting blades (3) in order to improve the shearing action of the end cutting knife (1). 5. An apparatus for the immediate cutting of a cast hollow-cored slab, comprising: a frame (9) mounted on wheels (7), and cutting means (1, 3) mounted on the frame (9) characterised in that the cutting means comprise two sheet-like cutting blades (3), which are arranged on the frame (9) to extend over the entire width of the slab and are mutually placed in V-shaped posture and have cutting tips (10), a first set of actuator means (15), capable of pushing the cutting blades (3) towards each other close to the lower surface of the hollow-cored slab, a wedge-shaped and cutting knife (1), arranged on the frame (9) and extending over the entire width of the slab, with sides (16) of the knife being aligned substantially parallel to the cutting blades (3), and a second set of actuator means (2, 6), capable of pushing the end cutting knife (1) with a shearing motion through the gap between the cutting blades (3) down towards the cutting tips (10) of the blades in order to form a homogeneous sheet (17) of concrete mix over the sides (16) of the cutting knife (1) facing the mix. 6. An apparatus as claimed in claim 5, characterised in that the cutting tips (10) of the cutting blades (3) are saw-shaped. 7. An apparatus as claimed in claim 5 or 6, characterised in that the first set (15) and/or the second set (2) of actuators comprise means (6) for the generation of the cyclic crosswise reciprocating movement, implemented using, e.g., a rotational drive and an eccentric cam disc.

Inventors: TOMMINEN , HANNU
Applicants: LOHJA PARMA ENGINEERING LPE OY
Application year: 1988
Main classification: E04C2
IPC codes: B28B11