DE1648538A1 - Method and device for the non-destructive determination of the strength of concrete or cement mortar - Google Patents

Description

Method and device for the non-destructive determination of strength of concrete or cement mortar.

Concrete or cement mortar consists of cement, water, aggregates and optionally additives. Cement and water make up the cement paste that makes the The aggregate structure is cemented and called cement stone in the hardened state will. The strength of a concrete or cement mortar is determined by its resistance the aggregates, through the strength of the cement paste and through the adhesion between aggregates and cement stone. B.i heavy concrete is the strength of the Aggregates without influence, since this is always above the strength of the cement block lies. Also the influence of the adhesion between aggregates and Cement stone can usually be neglected. The crucial size is in this case the strength of the cement paste. However, this is given by the ratio of water content to cement content, the so-called w / c value the degree of hydration of the cement and the air present in the cement stone (compression pores and artificially introduced air pores). Water and air content can be used as a room in Fresh concrete ". The influences of cement content and degree of hydration of the cement are determined by measuring the amount of hydration products formed recorded. The strength of the concrete or cement mortar can be considered accordingly as a function of the extent to which the resulting dratation products form the "space in fresh concrete ", i.e. as a function of the ratio of Hydration products to the space in the fresh concrete ". The amount of hydration products formed can be measured in a known manner using various methods, e.g. also due to the shrinkage.

Shrinkage refers to the fact that the water at the chemical bond through the cement reduces its volume by about a quarter. From the amount of water that a cement stone soaks up when it hardens is stored in water, the reaction state can therefore be checked in a manner known per se conclude. According to the invention in the method described here, the shrinkage related to the "space in fresh concrete" and related to strength. That has u.s. the advantage that the nature of the zenietes are not taken into account must, as is the case with other parameters for the hardening state, e.g. B. the surface of the hydration products formed is the case.

The shrinkage of a concrete is measured in the following way: One subtracted amount, about 10 to 20 kg of the concrete mix to be examined is in Weighed in a container, preferably made of strong sheet steel, the "shrink cup". The weight of the sample does not play a role for the shrinkage measurement, however it is advisable, for example, to sample a concrete clay at least 10 from a construction site kg, better 15 to 20 kg to choose so that this is representative of the site concrete is. Then, according to the invention, so much water is put into the shrink-fitting pot admitted that the concrete assumes a thin fluid consistency. Mostly are this requires a few liters of water. The water should be about the same Temperature like the concrete. By increasing the water content, the Cement stone so permeable to water that an obstruction of the swamping is excluded becomes, as is the case with dense cement stone. The shrinkage itself will practically unchanged by the addition of water, since the rate of hydration of the cement is largely independent of the w / c value. For w / c values below 0.40, which rarely occurs in practice, can reduce the shrinkage but only measure in the first days of hardening. After this time would have to the shrinkage values are corrected. A second advantage of increasing the water content results from the fact that the air contained in the concrete in a simple manner from the Concrete can be stirred out. When using certain gravel sands as aggregates was an additional one, however Action necessary. According to a Provisional execution of the invention was the shrinkage measuring pot after Fill in the concrete closed, with a small hand pump to below 0.5 at, preferably evacuated below 0.25 at and the evacuated pot rolled for about two minutes, to facilitate the escape of air from the concrete. After that the concrete was brought back to normal pressure and the pot finally with the tight-fitting Cover closed. This cover has two openings. One leads to one for example in ml graduated glass tube. The shrinkage measuring pot is inserted through this opening now filled with water until the water level has reached the zero mark. the Any air still in the pot is let out through the second opening in the lid. The shrinkage can then be read directly from the drop in the water level in the glass tube will. It is advantageous to use the ßchrumpfneäsopf before filling the concrete with a volume-resistant insert resting on the pot, for example a sheet metal or to lay out plastic film that absorbs the mixture to be tested and that includes The edge of the pot is tightly sealed, for example between pot and Lid is clamped. After the end of the shrinkage test, the Concrete, which then usually has a considerable strength, is simply orphaned can be removed from the shrink tube.

For rough measurements it would also be conceivable to have just a single opening to be provided, which is necessary for the evacuation to be carried out as well as is also used for water replenishment. It is also possible with lower Temperatures or when using certain additives on the evacuation at all to renounce.

The shrinkage measurement can also be carried out without the lining lining the inside of the pot Use can be made, however, is removing the concrete from the shrinkage jar after the end of the attempt in this ball more difficult.

A special calibration of the ßchrmpfmßopfes is not necessary. However, it should be checked from time to time whether the lid and the openings can still be tightly closed. The easiest way to do this is to use the Pot only with water without concrete up to the zero mark of the glass tube replenishes. The water level must then not change.

Of course, the shrinkage measurement can be carried out on concrete in the same way as carried out on cement mortar.

The device used to carry out the method according to the invention therefore consists of a pot, a tightly fitting lid with at least one Opening, a graduated one that can be inserted or inserted into one of these openings transparent tube, and possibly an evacuation device assigned to the pot and optionally an insert lining the inside of the pot. The evacuation device is attached to the pot either via a closable evacuation nozzle provided on the pot or can be connected via one of the also tightly closable openings in the cover.

On a second sample, the percentage Water @t the concrete. This can be done in a known manner, e.g. by drying atf ccr * arre or even simpler and more shear with the alcohol method happen. Does the concrete contain larger amounts of air (compression pores or artificially introduced Pores), which can be found in the fresh concrete room calculation, see above the air is added to the water content. Water content and air content result in the "RAujm in fresh concrete". Since the air content is mostly in relation to the water content is only sticky, you will usually work with concrete without artificially introduced air pores Being able to equate the "space in fresh concrete" with the water content without being too big To commit mistake. The "space in the fresh concrete" is read from the shrinking cup Shrinkage related. De the shrinkage over the entire hardening process of a As cement increases steadily, there is the relationship between shrinkage and strength linear from a shrinkage value of approx. 5%. Below this shrinkage value, one applies Higher order function. This is caused by the fact that # during With this hardening time, the bridges of hydration products necessary for the firmness are necessary between the individual cement particles.

The exact form of the reference to the "space in FRischbston" related Shrinkage and strength result from the type of strength with which the shrinkage occurs should be compared. Such a Bozichung can be heartfelt for everyone Manifestation the strength, e.g. compressive strength of concrete cylinders, compressive strength of concrete cubes with 20 em edge length, compressive strength of concrete cubes with 10 cm edge length, compressive strength of mortar prisms, bending tensile strength of concrete prisms, tensile strength of Mortar prisms, splitting tensile strength of concrete cylinders, etc.

The relationship found between strength and on the "space in fresh concrete" 1 related shrinkage can according to the invention in practice, for example, be as follows be evaluated.

The hardening process should be observed in a component because this component must be exposed to a load as soon as possible. As examples for this, the stripping and loading of concrete parts, the application, should be mentioned a bracing the joint cutting in a concrete road, the release of a Concrete road for traffic, reworking, e.g. milling concrete blocks, that Transporting concrete blocks or precast concrete parts, etc. In these cases mostly the concrete composition, especially the w / c value and the hardening temperature only insufficiently known.

Here, through a shrinkage measurement in the manner described, the Strength, e.g. compressive strength, can be determined easily and non-destructively. The latter means that the measurement can be carried out until the required Compressive strength is reached. Besides knowing the percentage Water content no information about the concrete required, such as cement type, cement quality, any damage to the cement due to improper storage, grain composition the aggregates, cement content, degree of hydration of the cement, w / c host, admixtures, Hardening temperature etc.

If the concrete composition changes only a little, e.g. is often the case in concrete block and precast concrete plants, it is even possible with the help of already created shrinkage time curves, the hardening after a short time Time to assess and, if necessary, take appropriate measures in the evening (for example Heat supplyl) to meet the transport, the post-processing or the like Allow work the next day.

Should the strength curve be tracked in this way in a single part , of course, it is important to ensure that the shrinking mold similar Is exposed to temperature conditions like the component in question. Exist between the temperature of the concrete in the shrinkage pot at the beginning of the experiment and those if there are larger differences in a shrinkage reading, it is particularly useful at temperatures above + 10 ° C, the resulting changes in the volume of the water to be considered in the pot. This can easily be done with the help of a correction table.

The shrinkage measurement only applies to a water-saturated concrete. Evaporates Water from the component to be tested, so the cement can be hydrated there come to a standstill. Should the strength development over the beginning of the hardening also examined on thin-walled components and in the case of insufficient machinability then corresponding reductions must then be determined from that determined via the shrinkage Strength to be made The invention is illustrated by the following games exasperated.

Example 1: In the Hehrumpftopf described above a concrete mix filled with 870 g Portland cement, 610 ml water, 1390 g construction sand 0.1-1 mm, 1390 g building sand 1 - 4 mm, 1740 g building sand 4 - 8 mm and 2430 g building gravel 5 - 15 mm. Then this concrete mix was diluted with about two liters of water and vigorously stir the whole mixture with an iron stick. After that was the lid placed on the shrink mold and closed one of the two openings in the lid With the help of a small hand pump, which was connected to the second opening, was the pot evacuated to approximately 0.25 at. The second opening was now also closed, the hand pump removed and the evacuated pot about two Rolled for minutes to facilitate the escape of air from the concrete. Thereafter the two openings in the lid were opened and the concrete was back to normal pressure brought. Through the one opening that led to the graduated glass tube the pot is filled with water so far that the water spoon passes the zero mark in the glass door produced. The air in the pot above the concrete hole was thereby through the second Opening left out. This second opening was then closed again. The shrinkage was now followed by the drop in the water level in the glass tube based on the water content of 610 ml known from the Ausatz.

After 24, 48, -72, 120, 168, 240 and 336 hours it was started in parallel produced concrete cubes of the same composition as the undiluted shrink concrete determines the compressive strength.

Particular care was taken to ensure that the concrete cubes were the same At the same temperature as the shrink pot. The dates indicated on then determined Compressive strength was related to that observed on the water related shrinkage. The compressive strengths were between 66 and 344 kp / cm2, the Shrinkage based on water was between 3.75% and 8.69%. The relationship between shrinkage and compressive strength was linear.

In the same way, shrinkage and compressive strengths increased already mentioned dates determined on a second concrete mix of 1015 g Portlandzenent, 610 ml water, 1320 g building sand 0.1 - 1 mm, 1320 g Beusand 1 - 4 mm, 1650 g Beusand 4 - 8 mm, 2310 g construction gravel 5 mm, on a third concrete mix made of 1210 g Portland cement, 605 ml water, 1345 g building sand 0.1-1 mm, 1345 g building sand 1 - 4 mm, i68Q g construction sand 4 - 8 mm, 2350 g construction gravel 5 - 15 mm and finally on a fourth Concrete mixture of 1410 g Portland cement, 605 ml water, 11o5 g Bausend 0.1-1 mm, 1105 g building sand «- 4 mm, 1380 g building sand 4 - 8 mm and 1940 g building gravel 5 - 15 mm. at These tests showed compressive strengths of 66 to 552 kp / cm2 and shrinkage values determined from 375% to 12.9%.

The relationship between compressive strength and water Shrinkage was the same for all concrete mixes and therefore the cement content and the w / c value independent. The attached sketch shows the relationship between shrinkage and compressive strength again.

Example 2: In the shrink pot described above a concrete mix filled with 870 g Portland cement, 610 ml water, 1390 g construction sand 0.1 - 1 mm, 1390 g construction sand 1 - 4 mm, 1740 g Beusand 4 - B mm and 2430 g construction gravel 5-15 mm. Then this concrete mix was diluted with about 2 liters of water and the whole mix vigorously stirred with an iron stick. Then the lid was placed on the shrink measuring pot and one of the two openings in the lid is closed. With the help of a small hand pump that was connected to the second opening, the pot was on evacuated approximately 0.25 at. The second opening has now also been closed, the hand pump removed again and the evacuated pot rolled for about 2 minutes, to facilitate the escape of air from the concrete.

Then the two openings in the lid were opened and the concrete so brought back to normal pressure. Through the one opening that led to the graduated Glass tube led, the pot was filled with water so far that the water level reached the zero mark in the glass tube. The one still in the pot above the concrete Air was let out through the second opening. This became exclusive second opening closed again. The shrinkage was now due to the lowering of the water level followed in the Glasrchr and the water content known from the approach of 610 ml based. After 10, 16 and 24 hours as well after 3 and 7 days it became on standard mortar prisms produced in parallel using the same Portland cement determines the compressive strength. Particular attention was paid to that the mortar prisms were stored at the same temperature as the shrink pot. the Compressive strength determined on the dates given was related to the observed shrinkage related to the water. The compressive strengths were between 9 and 358 kgf / cm2, the shrinkage related to the water was between 1.67% and 7.05%. The relationship between shrinkage and compressive strength was ab a linear shrinkage related to the water of about 5.0%. In the same way the shrinkage and compressive strengths were determined on the dates indicated Concrete mixtures with a total of 12 different cements, including one Cement without tricaloium aluminate content, an iron Portland cement and a blast furnace cement found. In these tests, compressive strengths were between 3 and 429 kp / cm2 and a shrinkage value of 1.08% to 7.85% was determined.

The relationship between the compressive strength and that of the water related shrinkage was for all concrete mixes the same and thus regardless of the nature of the cement used.

EXAMPLE 3: -In the shrink pot described above a concrete mixture filled with 1210 g portland cement, 605 ml water, 1345 g Beusand 0.1 - 1 mm, 1345 g building sand 1 - 4 mm, 168Q g building sand 4 - 8 mm and 2350 g building gravel 5 - 15 mm.

Then this mixture was diluted with about 2 liters of water and the whole Mix vigorously with an iron stick. Then the lid was on the The shrink-fit pot is attached and one of the two openings in the lid is closed.

With the help of a small hand pump that is connected to the second opening the pot was evacuated to about 0.25 atm. The second opening was now also closed, the hand pump removed and the evacuated pot. Rolled for about 2 minutes to allow the air to escape from the concrete. Then the two openings in the lid were opened and the concrete was opened again Normal pressure brought. By the one opening leading to the graduated Glass tube led, the pot was filled with water so far that the water level reached the zero mark in the glass tube. The one still in the pot above the concrete Air was let out through the second opening. Then this second opening closed again. The shrinkage was now due to the lowering of the water level followed in the glass tube and the water content known from the approach of 605 ml based. After 24 and 48 hours, concrete cubes produced in parallel were used the same composition as the undiluted shrink concrete has the compressive strength certainly. The compressive strengths were 126 and 222 kp / cm2, the corresponding Shrinkage values were 4.90% and 6.80%.

Shrinkage and compressive strength were determined in the same way on a concrete mix of 1800 g Portland cement, 900 ml water, 2550 g construction sand 0.1 - 1mm, 715 g Beusend 1 T 4 mm, 612 g construction sand 4 - 8 mm and 1730 g construction gravel 5 - 15 a.

This concrete mix thus differed from the first mentioned above mainly due to the composition of the additives. The plump was a relative one cheap, in the second a relatively unfavorable aggregate mixture is used. The height Fine portion of the second mixture makes the much higher cement paste content necessary, so that the concrete can be compacted .. On this second concrete mix were Compressive strengths after 24 and 45 hours determined from 1Q1 and 169 kp / cm2. The corresponding Shrinkage values were 4.25% and 5.70%.

The relationship between water shrinkage and compressive strength was the same for both concrete mixes and corresponded to the one shown in the sketch 1 is shown in Example 1. So it was neither due to the grain composition the aggregates, nor by the percentage of that used for the concrete Cement line affected.

Example 4: A concrete is to be prestressed as soon as it has a compressive strength of 250 kp / cm2. From the relationship found in example 1 it follows that that this requires a shrinkage of 7.4% in relation to the water is. Complete compaction of fresh concrete is a prerequisite. Stand for the concrete work available an aggregate and a cement, about which nothing further is known is. The work should be carried out at a temperature of 20 ° C. the The question is, after what time will the necessary strength be achieved if the w / c value in one case 0.60, in the other case 0.80 and what value must the w / c value so that the strength is already reached after 30 hours. It became that put a concrete in the shrink pot with 1000 g of the intended for the work Cement and 600 ml of water. Then there was such an amount of dry aggregate added, in the example described 9 kg, that the concrete with the on the construction site, given possibilities could be completely condensed. Are the aggregates moist, so it is not necessary to dry them for the shrinkage measurement, it has to be however, in this rebound the prosentuelle water content of the concrete can be determined. The concrete was then diluted and evacuated in the manner described above. Thereupon the writing was carried out on the sinking of the water level into the graduated glass tube tracked and on the water content, in the example described 600 ml related. It was found that the required shrinkage value of 7.4 ", accordingly in the example described, 44.5 ml, is reached after 92 hours. After this time In other words, a concrete in the examined composition has the required strength.

It was also necessary to check the time after which the strength of a w / z-RNert of 0.80 is achieved. For this purpose, the water content of the examined is thought of Concrete mix increased from 600 to 800 ii. The necessary shrinkage value of 7.4 % then corresponds to 59.2 ml. The shrinkage is continued until the Shrink volume is 59.2 ml. This is the case after about 250 hours. At a w / c-value of 0.80 the concrete can only be prestressed after 1012 days.

Finally, it should be determined at which w / c value the Required strength is reached after 30 hours. In this example investigated concrete mix with w / c = 0.60 the shrinkage was after 30 hours only 35 ml. Based on the water That’s just a salary of 600 il around 5.8%. You now mentally reduce the water content of the concrete mix in this way far, that these 35 ml make up 7; 4 ffi again. That. is at a water content of 470 ml is the case. Since 1000 g of cement were used for the experiment, corresponds to that has a w / c value of 0.47. The w / z-wbrt would have to be reduced to 0.47 so the concrete can already be prestressed after 30 hours. For this theoretical Considerations it does not matter that in practice the concrete is then too dry and one could no longer process it. The water content must be the same here If the cement content remains high enough that a w / c value of 0.47 results.

It should be fixed so that it is possible to get out of a single Shrinkage measurement for a concrete with a certain cement and a certain Additive, about which nothing more needs to be known, to unite the strength to be calculated at any time and for any w / z currency.

Claims (7)

Patent claims 1. Method for the non-destructive determination of the Strength of concrete or cement mortar, characterized in that one has to testing concrete or cement mortar the shrinkage of the cement and then "space in the Prischbetonn determined and based on the relation of the shrinkage volume to the "space in Fresh concrete "which Oasu derives from the concrete's relative strength. 2. The method according to claim 1, characterized in that the Pour the concrete to be tested into a closable vessel, dilute the concrete, if necessary the air is removed from the concrete, then with water or another, the hardening of the cement does not affect the liquid to an arbitrarily defined volume and the amount of shrinkage is determined based on the decrease in volume the space ii brings fresh concrete into relation and from this relation the strength of the concrete. 3. The method according to claim 2, characterized in that the air from the concrete to be tested by applying a vacuum of less than 0.5, preferably below 0.25 at is removed, with air removal by rolling the evacuated Pot is supported. 4. Device for performing the method according to the claims 1 to 3, characterized by a pot, a tightly fitting lid with at least an opening, a graduated which can be inserted or inserted into one of these openings transparent tube, and possibly an evacuation device assigned to the pot. 5. Apparatus according to claim 4, characterized in that the pot is provided with an evacuation nozzle. 6. Apparatus according to claim 4 or 5, characterized in that the pot an insert made of volume-resistant material, for example made of sheet metal or Plastic film, assigned to accommodate the mixture to be tested. 7th Device according to claim 6, characterized in that the insert tightly with the The edge of the pot or lid closes off. Blank page