JP2694883B2 - Recycled concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reclaimed concrete, and more particularly to retarders and accelerators used in the method of reclaimed concrete.

[0002]

BACKGROUND OF THE INVENTION The concrete required for major building operations is not mixed on site and is placed sufficiently close to the site that the concrete can be carried within about 90 minutes of mixing. Central mixed factory
It is common today to be supplied in a mixed state from (fresh concrete manufacturing plant). Especially at the end of the day's work, it is often the case that mixed trucks return from the scene loaded with unused portions of concrete. Such concrete that is returned from the site without being used is called return concrete. At present, this concrete cannot be used and is simply thrown into the dump before it hardens. Although such a situation is undesirable for both economic and environmental reasons.

[0003]

SUMMARY OF THE INVENTION Now such excess concrete adds sufficient retarder to prevent this concrete hardening even during the night or weekend, and then It has been found that the day-delayed concrete can be made usable by mixing it with fresh concrete and adding an accelerator which acts to counteract the action of the retarder.
In fact, with the proper choice of retarder, the process of mixing with fresh concrete is eliminated and the whole settling delayed concrete accelerates settling again, allowing it to be used as if it were fresh concrete. It is possible.

Accordingly, the present invention provides a method of reclaiming mixed virgin concrete, which method comprises: 1) an amount sufficient to delay hydration for a further 90 hours before the concrete hardens. 2) optionally, at the end of the desired setting retardation period, diluting the retarded concrete with fresh concrete, and 3) for restoring the retarded concrete to a hardenable state. Adding the accelerator of 1. to the delayed concrete.

If desired, water-reducing strength enhancers may be added to the diluted concrete along with accelerators.
The retarder used in the method of the present invention must be long-acting (ie, capable of delaying hydration over 6 hours or more) when used in an appropriate amount, and the addition of the accelerator is required. It must have a reversible effect so that the concrete can be substantially restored to its original condition. Preferred retarders are phosphonic acid derivatives, more preferably those containing hydroxy and amino groups that can act as calcium chelating agents. A particularly preferred retarder of this type is Monsanto.
Dequest for sale by Co. (St. Louis)
(Trademark) series compounds, in particular Dequest 2000: Aminotri (methylenephosphonic acid) Dequest 2006: Aminotri (methylenephosphonic acid) pentasodium salt Dequest 2010: 1-hydroxyethylidene-1,1-
Dephosphonic acid Dequest 2016: 1-hydroxyethylidene-1,1-
Tetrasodium Diphosphonic Acid Dequest 2041: Ethylenediaminetetra (methylenephosphonic acid) Dequest2047: Ethylenediaminetetra (methylenephosphonic acid) calcium sodium salt Dequest2051: Hexamethylenediaminetetra (methylenephosphonic acid) Dequest2054: Hexamethylenediaminetetra (methylenephosphonic acid) potassium salt Dequest 2060: Diethylenetriamine penta (methylenephosphonic acid) Dequest 2066: Diethylenetriamine penta (methylenephosphonic acid) sodium salt.

Other suitable retarders include hydroxycarboxylic acids (such as citric acid, gluconic acid, tartaric acid, glucoheptanoic acid) and salts thereof, polycarboxylic acids (fumaric acid, itaconic acid, malonic acid, polymaleic acid, polyfumaric acid). Acid, polyacrylic acid, polymethacrylic acid, etc., preferably low molecular weight ones) and salts thereof, antioxidants (ascorbic acid, isoascorbic acid, etc.), polymers (sulfonic acid-acrylic acid copolymer, polyhydroxysilane,
Polyacrylamide and the like, preferably of low molecular weight), carbohydrates (sucrose, corn syrup, etc.), lignosulfonates (calcium lignosulfonate, etc.) and the like. Of these, hydroxycarboxylic acids,
Polycarboxylic acid, isoascorbic acid, polyhydroxysilane and the like are preferable. More preferred retarders are at least one phosphonic acid type retarder and at least one.
It is a mixture with different types of retarders. Since many non-phosphonic acid type retarders also have water-reducing properties, they also have the effect of increasing the compressive strength of these final set concretes. A particularly preferred retarder is Deque
Mixture of st series and citric acid, especially Dequest 200
It is a mixture of 0 and citric acid. The preferred ratio of Dequest to citric acid is 1: 1 to 2: 1.

The preferred accelerators to be added in step 3) of the process of the invention are those as classified as type C mixtures in ASTM C494.
Preferred accelerator compositions are chlorine-free and include, for example, calcium salts such as calcium nitrate and calcium formate,
Includes thiocyanates, triethanolamine and glycolurils, such as trimethylolglycoluril, such as trimethylolglycoluril. A particularly preferred accelerator of this type is the Master Builders In
c. (Cleveland) under the trademark Pozzolith 555A. It can optionally be added in step 3) together with a promoter. Preferred water-reducing strength enhancers are those classified as type A mixtures in ASTM C94, i.e., water-reducing agents which themselves do not have a substantial retarding or promoting action. A particularly preferred material is Master Builders Inc.
Are sold under the trademark Pozzolith Polyheed by. Further, instead of using the combination of the type C mixture as the promoter and the type A mixture as the water reducing agent, it is also possible to add and use the type E mixture as the water reducing accelerator alone. However, it is preferred to use a combination of type C and type A.

The amount of retarder and accelerator that must be added as a percentage of the concrete weight in the process of the invention will be readily understood by those skilled in the art. It will vary according to many of the different factors. These include: 1) The composition of the retarder and accelerator used. 2) How long the delay is desired. This is usually 1 night (1
2-18 hours) or over the weekend (36-90 hours, preferably 60-72 hours). 3) ASTM type of cement. Types 1 to 4 are preferred, although types 1 to 4 can be used in the process of the invention. The degree of substitution of fly ash in the cement will affect the amount of accelerator to be added in step 3) of the process of the invention. In general, the greater the degree of fly ash substitution, the more accelerator is required. 4) The time of addition of the retarder to the concrete, defined as the length of time between mixing the concrete and addition of the retarder, the retarder may be added to the unused portion of the concrete immediately after use, or It may be added when the mixed truck is returned to the concrete manufacturing industry or as long as the concrete maintains the desired slump, air content and unit weight. Preferably, the retarder is added to the cement 1 to 4 hours after the initial mixing. Longer addition times would require more retarder. 5) Hardening time of the original concrete. If the concrete had a very low cure rate, less retarder would be needed and more accelerator would be needed than for longer cure times. 6) Temperature of concrete. The higher the temperature, the faster the cure rate and therefore the greater the amount of retarder that will be needed. 20 ° C (70 ° F) for faster cure
For concrete temperatures above 1.0, the retarder is preferably added within 3 hours of initial mixing. 7) The volume of concrete to be treated. More volume of concrete at a given initial temperature will cure faster than less volume concrete at the same initial temperature. This means that large volumes lose their heat of hydration less rapidly, thus giving a greater temperature rise and a higher cure rate. Thus, for example, 2 cubic meters of concrete would require more than twice the amount of retarder as 1 cubic meter of concrete would require. 8) Ratio of recycled concrete to fresh concrete in the final mixture. Old concrete may range from 5 to 100%, preferably 10 to 50% by weight of the total mixture. Obviously, the higher the proportion of recycled concrete, the higher the amount of accelerator. 9) Type and amount of mixture in original cement and freshly added cement.

In a preferred method of practicing the process of the present invention, the temperature of the load is probed to measure the volume of the load when the mixed trunk is loaded with virgin concrete back into the green concrete manufacturing plant. , And based on these data and known properties of the concrete batch, the amount of retarder needed to keep the load available until the next operating day is calculated. Advantageously, this is done by a suitably programmed microcomputer and the desired amount of retarder (preferably as an aqueous solution) is automatically metered into the shipment.
The shipments are mixed briefly and then left unmixed until the next working day. The desired amount of fresh concrete is then mixed into the recycled concrete, the temperature is measured again and the desired amount of accelerator (and water reducing agent, if necessary) is calculated. Again, the addition should be under automatic computer control.

The following examples serve to illustrate the invention.
is there. Parts and percentages are given by weight unless otherwise stated. An example                           Standard concrete composition Component       kg / m ³ concrete Kaiser Cement Type I / II 250 Fly ash (Jim Bridger, CF517 70 ° F) 46.5 Sand 864 Gravel 1008 Water 175 Retarder composition R 12.8% aminotri (methylenephosphonic acid) (Deques
t2000) and an aqueous solution containing 8% citric acid. Accelerator composition C Pozzolith 555A (Master Builders), 48.7%
Nitrate supplied as an aqueous solution containing the active substances of
Chlorine-free accelerator whose main component is rum. Water-reducing agent composition A Pozzolith Polytheed (Master Builders), 39%
Low delay rig supplied as an aqueous solution containing the active substance of
A water reducing agent whose main component is nosulfonate.

In the examples below, the addition of all additives to concrete is based on the cementitious material in the concrete.
It is given as a weight percent based on the dry weight of (ie cement + fly ash). % Are based on dry active material unless otherwise stated. Example 1 Four samples are prepared according to the above standard concrete composition, each of which is left in a 5 gallon container for about 2 hours. To three of the vessels is added 5% by weight (based on the weight of all materials in the vessel) of an aqueous solution of Dequest 2000, alone or with citric acid, as shown in Table I. 4th
For the second sample, as a reference, only 5% by weight of water is added. Mix concrete samples and leave overnight. After 24 hours, 3 delayed samples
Dilute with fresh concrete at a ratio of 1 part recycled concrete to 5 parts fresh concrete, 3.1
Reactivate with% accelerator composition C and 0.3% water reducing agent composition A. Table I shows the compressive strength measured after 14 and 28 days. Table I No. Dequest 2000% Citric Acid% Compressive Strength (kg / cm ² ) 14 days later 28 days later 1 0.318-290 390 2 0.227-277 370 3 0.3318 0.200 321 432 4 − − 265 325

Example 2 0.318% Dequest material and 0.2 for each sample
00% citric acid (all based on the weight of the cementitious material in the sample) was used as a retarder, and these were 2.5% by weight as an aqueous solution (based on the weight of all the materials in the container). Example 1 was repeated with the addition. Reactivation was performed as in Example 1. Table II shows the results for% air content, cure rate to initial setting (initial) after reactivation and compressive strength after 1 and 7 days. In the case of No. 10, like the other samples, a sample having a standard concrete composition is placed in a container and left for 2 hours. Only 2.5% by weight of water was added and allowed to stand, the curing rate (however, the time after addition of water only) and 1 day and 7
The compressive strength after day was measured. Table II No. Dequest Material Air% Curing rate (hour) Compressive strength (kg / cm ² ) After 1 day After 7 days 1 2000 2.0 4.0 153 443 2 2006 2006 1.8 4.25 147 418 3 2010 1.9 3 .875 140 402 402 4 2016 1.8 4.0 144 419 5 2041 1.8 1.8 5.0 121 121 423 6 2051 2.0 3.5 138 416 716 2054 1.9 3.25 144 416 8 2060 1.8 1.8 3. .875 135 414 9 2066 2.2 3.75 156-10 None 0.7 5.5 86 256 (reference)

Example 3 Retarder R for overnight delays and weekend (2 days) delays
Appropriate usage (one solution per 100 kg of cementitious material) was expressed as a function of the concrete temperature and the amount of concrete to be treated (delayed), the experimental results of which are shown in Table III. Table III Concrete Temperature Usage for one night delay Weekend (three nights) Usage for delay (1/100 kg (cementitious material)) 1.5 m ³ 1.5 m ³ (1/100 kg ° an amount greater than to F ° C. (about) (cementitious material)) 90-99 30-35 3.5 4.4 9.0 80-89 25-30 3.1 4.0 8.4 70-79 20- 25 2.5 3.4 7.8 60-69 15-20 2.2 2.8 7.1 50-59 10-15 1.5 1.5 1.5 6.5 40-49 5-10 1.2 1 .2 5.9 32-39 0-5 0.9 0.9 0.9 5.3 The delayed concrete was mixed with 5 parts of fresh concrete for 1 part of the concrete and then promoted as shown in Table IV below. The agent composition C can be reactivated with a predetermined amount (one solution per 100 kg of cementitious material). Table IV Concrete Temperature Amount Used for One Night Delay Weekend (3 nights) vs. Delay (1/100 kg (Cement usage (1/100 ° F ° C (approx.) Material)) kg (cement material)) 80-89 25-30 1.9 5.3 70-79 20-25 2.5 6.5 60-69 15-20 3.1 7.1 50-59 10-15 3.7 7.5 40-49 5-10 4.4 7.8 32-39 0-5 5.0 8.1

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor David A. Lupuyan               44022, Cha, Ohio, United States               Green Falls, Longview               Rail 10500 (72) Inventor Fredrick Dee. Kinney               44147, Bro, Ohio, United States               Dview Heights, Twin Oaks                 Drive 7956                (56) References JP-A-59-195564 (JP, A)                 JP-A-53-5222 (JP, A)                 JP-A-50-25623 (JP, A)                 JP 61-40854 (JP, A)                 Japanese Patent Publication Sho 51-15856 (JP, B2)                 Admixture materials for cement and concrete               Edited by Yoshio Kasai, published on May 15, 1986,               Published by Technical Shoin, pages 325-345

Claims (1)

(57) [Claims] (1) A step of adding a retarder in an amount sufficient to delay hydration before the concrete is hardened and after the concrete is poured and before the lapse of 4 hours from the initial mixing for a further 90 hours. And (2) adding an accelerator to the delayed concrete to restore the delayed concrete to a settable state by the end of the desired setting delay period. A retarder for delaying the setting of return concrete before curing, which is used in the method for reclaiming returning concrete and contains at least one phosphonic acid derivative. 2. Use according to claim 1, characterized in that between the steps (1) and (2) there is a step in which the concrete with delayed setting is diluted with fresh concrete. Delay agent. 3. The phosphonic acid derivative is aminotri (methylenephosphonic acid), aminotri (methylenephosphonic acid) pentasodium salt, 1-hydroxyethylidene-1,1-diphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid tetrasodium salt, ethylenediamine. Tetra (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid) calcium sodium salt, hexamethylenediaminetetra (methylenephosphonic acid), hexamethylenediaminetetra (methylenephosphonic acid) potassium salt, diethylenetriaminepenta (methylenephosphonic acid) and diethylenetriaminepenta The retarder according to claim 1 or 2, which is at least one selected from (methylenephosphonic acid) sodium salt. 4. The retarder further comprises hydroxycarboxylic acids or polycarboxylic acids and their salts, ascorbic acid and isoascorbic acid, sulfonic acid-acrylic acid copolymers,
The retarder according to any one of claims 1 to 3, comprising at least one compound selected from polyhydroxysilane, polyacrylamide, carbohydrate and lignosulfonate. 5. The retarder according to claim 4, comprising at least one compound selected from hydroxycarboxylic acid, polycarboxylic acid, isoascorbic acid and polyhydroxysilane. 6. 3. The retarder according to claim 1 or 2, comprising aminotri (methylenephosphonic acid) and citric acid. 7. 7. The retarder according to claim 6, wherein the ratio of aminotri (methylenephosphonic acid) to citric acid is 1: 1 to 2: 1. 8. (1) A step of adding a retarder in an amount sufficient to delay hydration before the concrete is hardened and after the concrete is poured and before the lapse of 4 hours from the initial mixing for a further 90 hours. And (2) adding an accelerator to the delayed concrete to restore the delayed concrete to a settable state by the end of the desired setting delay period. A accelerating agent for accelerating the hardening of reverted concrete, the hardening of which is delayed by the addition of a retarder, which comprises at least one compound selected from the group consisting of calcium salt, thiocyanate, triethanolamine and glycoluril, which is used in the method for reclaiming rejuvenated concrete. 9. 9. Use in a method for reclaiming return concrete, characterized in that there is a step between the step (1) and the step (2) in which the concrete with delayed setting is diluted with fresh concrete. Accelerator. 10. 10. Accelerator according to claim 8 or 9, consisting of a mixture of calcium nitrate, sodium thiocyanate, triethanolamine and trimethylolglycoluril. 11. (1) A step of adding a retarder in an amount sufficient to delay hydration before the concrete is hardened and after the concrete is poured and before the lapse of 4 hours from the initial mixing for a further 90 hours. And (2) adding an accelerator to the delayed concrete to restore the delayed concrete to a settable state by the end of the desired setting delay period. A retarder for delaying the setting of return concrete before curing, which contains at least one phosphonic acid derivative for use in the method of reclaiming return concrete, and at least one selected from calcium salt, thiocyanate, triethanolamine and glycoluril. It is necessary to use an accelerator for promoting the hardening of reverted concrete, which contains a compound and whose hardening is delayed by the addition of a retarder. A component, return concrete regenerant. 12. Use in a method for reclaiming reconstituted concrete, characterized in that there is a step between the step (1) and the step (2) in which the concrete with delayed setting is diluted with fresh concrete. With a retarder and an accelerator as essential components,
Return concrete reclaiming agent.