DEVICE AND PROCEDURE FOR COOLING FRESH CONCRETE AT ELEVATED TEMPERATURES

Abstract

The device and procedure for cooling fresh concrete at elevated temperatures enable efficient cooling of fresh concrete, which is achieved by the subject device comprising of: cooling station (1) with measuring and regulating equipment (2) and safety equipment (3), solenoid valves (5), pressure transmitter (6), cryogenic shut-off valves (7), collector (17) made of stainless steel pipes with temperature probes (8), concrete mixer (9) and manometer (10) with safety valves (11).

The procedure of cooling fresh concrete using liquid nitrogen in the mixer is carried out as follows: first aggregate-separated gravel is added, then cement, then water and finally, if necessary, additives-chemical additives. Mixing of added raw materials lasts from 15-20 seconds, until a homogeneous mixture is obtained, after which liquid nitrogen is added at a pressure of 6 bar, giving cooled fresh concrete on which no surface cracks and fissures appear at external temperatures of 30-35 C.

Claims

1. Device for cooling fresh concrete at elevated temperatures, characterized by comprising: a cooling station (1) with measuring and regulating equipment (2) and safety equipment (3), by means of seamless stainless steel pipes (4), via four solenoid valves (5) connected to a pressure transmitter (6) and via four manual cryogenic shut-off valves (7) connected to a collector (17) with two temperature probes (8) for measuring the temperature of fresh concrete in the concrete mixers (9) with filter (20), manometer (10) and four safety valves (11), and by the cooling station (1) being fixed to the stainless steel frame (12) made of boxes, and by the control cabinet (13) containing PLC (14) and elements (15) for automatic control, and by the control box (16) having a display with a button for remote control of the operation of concrete cooling equipment from the container, and by the collector (17) made of seamless stainless steel pipes connected to a liquid nitrogen tank (21) with brass nozzles (18) installed on pipes with connectors (19).

2. Procedure for cooling fresh concrete at elevated temperatures, characterized by the fact that, first aggregate-separated gravel, then cement, then water and finally, if necessary, additives-chemical additives are added in given and accurately measured mass percentages into the mixer (9), after which the procedure of mixing the raw materials begins, and after 15 seconds liquid nitrogen is added by pipeline at a pressure of 6 bar, and then the procedure is continued for a total of 30-40 seconds, until a homogeneous mixture is obtained, which is then cooled to the required temperature and transported to the construction site.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to facilitate the understanding of the invention, the author refers, only by way of example, to the attached application drawing where:

[0039] FIG. 1 presents the technological scheme of the device which enables the process of cooling fresh concrete mixture using liquid nitrogen in the mixer.

DETAILED DESCRIPTION OF THE INVENTION

[0040] It is known that concrete is basically made of three main ingredients: aggregate 70-80%, water 5-10% and cement 10-20%. Concrete hardens after mixing and installation, due to a chemical process called hydration. Water reacts with cement, which hardens and binds the other components in the mixture, which eventually results in a hard stone material. The term concrete generally means a wide range of artificial building materials of composite type obtained by agglomeration of grains of very different aggregate types. Agglomeration also involves the use of certain binders. Having in mind this definition, it follows that in principle there are gypsum concrete, lime concrete, water glass concrete, asphalt concrete and others. Certainly, the most widely used are concretes with cement used as a binder, which should formally be called cement concretes, but in practice, it is common for materials of this type to be called only concretes and are used the most of all artificial materials in the world, primarily for making roads, buildings, foundations, bridges, stone blocks, etc.

[0041] Knowledge and problems related to the use of fresh concrete, which are especially pronounced during the summer months when the cement delivered to the concrete factory is at a temperature between 60 and 70 C., aggregates used for the production of fresh concrete are at a temperature of 30 to 35 C., and the water used in the production of fresh concrete is at a temperature between 10 and 15 C. and lead to fresh concrete having a temperature usually up to 32-33 C. This type of concrete is considered to be of poor quality and very quickly forms surface cracks and fissures, which occur as a result of plastic shrinkage.

[0042] The solution to this problem was the basis on which the inventive idea of defining a device that enables the process of efficient fresh concrete cooling at elevated temperatures using liquid nitrogen was realized, with the device designed so that it can precisely determine lowering temperatures of concrete and control during the entire concreting process.

[0043] This is achieved by the device comprising: a cooling station 1 with measuring and regulating equipment 2 and safety equipment 3, by means of seamless stainless steel pipes 4 (AISI304L, 21.32.77 mm sch40 S), via four electromagnetic valves 5 connected to the pressure transmitter 6 and via four manual cryogenic shut-off valves 7 connected to the collector 17 with two temperature probes 8 for measuring fresh concrete temperature in the concrete mixer 9, and a manometer 10 with four safety valves 11. The cooling station 1 is mounted on a stainless steel frame 12 made of 50502 mm boxes, the operation of which is controlled by a control cabinet 13 with PLC 14 and elements 15 for automatic control, control box 16 with display and button for remote control of the concrete cooling equipment operation from the container where the operator is located. The collector 17 made of seamless stainless steel pipes (AISI304L, 33.42.77 mm sch10S) is connected to the liquid nitrogen tank 21 and via brass nozzles 18 mounted on the pipes (A151304L, 21.32.11 mm sch10S) with connections 19 enables the injection of liquid nitrogen into the concrete mixer 9. The number of brass nozzles 18 depends on the volume of the mixer 9.

[0044] The invention device provides injection of liquid nitrogen directly into the mixer 9 after 15-20 seconds of mixing the concrete components, with the use of liquid nitrogen for cooling fresh concrete achieved without negative effects on consistency, workability, air content, curing time and w-c ratio for fresh concrete.

[0045] Nitrogen injected in this way, which is an inert gas that does not chemically react with other components in the concrete mixture during cooling, is partially released into the atmosphere without any environmentally negative effects, which is very important for the application process itself given the stricter regulations of PAB 87 and other national and international regulations that apply and are valid and binding, and according to which the fresh concrete temperature must not exceed 30 C.

[0046] The process of cooling fresh concrete using liquid nitrogen in the mixer is carried out on the device simply with flexible cooling capacity, controlled nitrogen consumption and control of concrete mixture cooling to the desired temperature as follows: first add aggregate-separated gravel is put, then cement, then water and finally, if necessary, additives-chemical additives. Mixing of added raw materials lasts 30-40 seconds, until a homogeneous mixture is obtained, and after 15-20 seconds of mixing, liquid nitrogen is injected into fresh concrete mixture via the pipeline from the liquid nitrogen tank 21, at a pressure of 6 bar, through installed nozzles, during which liquid nitrogen in contact with fresh concrete mixture evaporates and thus cools it to a given temperature, and the evaporated gaseous nitrogen and air exit through a filter 20 at the top of the pipeline connected to the mixer 9. This freshly cooled concrete mixture is transported to the installation site.

INDUSTRIAL OR OTHER APPLICATION OF THE INVENTION

[0047] According to the present invention, industrial or other way of carrying out the process of cooling fresh concrete at elevated temperatures is absolutely possible by means of the device and the parameters specified in this description.

[0048] Experts in the subject field can, without any problems, make the device and carry out the procedure for making fresh concrete, at the temperature defined by the PBAB 87 regulations, valid and binding for the field.

[0049] In accordance with the good results of experimental tests, conducted under conditions of particularly high temperatures, on the construction site of the ortanovci-Sremski Karlovci high-speed railway, it was determined that the invention application achieves cooling of fresh concrete using liquid nitrogen without any negative effects on consistency, workability, air content and setting time.