DE4009062A1 - CONCRETE MIX - Google Patents

Abstract

In order to increase the resistance to high temperatures of concrete produced from a concrete mix, a proportion of the cement contained in the mix is replaced by ground granular blast furnace slag (GGBFS). Alternatively, in a pavement quality concrete mix containing naturally occurring aggregates of limestone and sand, a proportion of the naturally occurring aggregates is replaced by a pulverized fuel ash (PFA) in the form of a lightweight aggregate, so as to increase the resistance to high temperatures of concrete produced from the mix. The PFA may be incorporated into the mix in combination with naturally occuring sand and cement.

Description

The invention relates to an improved material for Production of a concrete paving for a runway to the Starting and landing of aircraft, especially of vertical take-offs.

Runways for vertical take-offs made of concrete are subjected to extensive test trials been used to determine the stresses of Vertical starters when starting on such runways be exercised. These test results have shown that while starting a whiz, e.g. B. one Harrier jets the runway concrete surface temperatures reached up to 300-350 ° C. The withdrawal duration for such Airplanes can take between five seconds for an experienced Pilots and up to seven seconds for a less experienced Pilots. Investigations of the damage to the Surface of the runway revealed that the destruction of the Surface of such runways by breaking open due to Exposure to heat instead of damage due to Weather conditions occur. From a study on the Influences of rapid heating of concrete to high Temperatures result in two processes when breaking up of the concrete are coupled together.

In one case, moisture evaporates with the concrete such a speed that the resulting Pressures created within the concrete, the material can break.

In the other case, the different thermal expansion of the material matrix generate internal stresses that cause the concrete to be blown apart.  

In the first case, water in the set concrete is reduced to three different types, namely as

• (1) Water that chemically combines in the cement hydrates is
• (2) Water contained in the gel of cement components (i.e. in the Gelporen) is absorbed, and
• (3) water in the capillary pores (usually as free Water) of the cement matrix.

The influence of increasing temperature on different Water content varies, but in general can vary be assumed that the largest when 100 ° C is reached Part of the free water turns into steam while that chemically bound water and the adsorbed water not evaporate until higher temperatures are reached when the Components in which the water is bound dissociate and dehydrate.

Different thermal expansion can result from either different coefficients of thermal expansion of the Aggregate and the cement paste or from the temperature gradient revealed by the concrete when the temperature of the surface increases rapidly. In this context, a Investigation of the temperature gradient in the concrete, the one is exposed to rapid heating of the surface that the Gradient is very steep, and that only a very thin surface layer of the material (from a few at most Millimeters) actually takes on very high temperatures.

Ordinary Portland cement (OPC) consists of four main components, namely dicalcium silicate (C₂S), tricalcium silicate (C₃S), tricalcium aluminate (C₃A) and tetrakalzium aluminoferrite (C₄AF) that hydrate and calcium silicate hydrates plus Calcium hydroxide, and calcium aluminate hydrate (C₃AH₆) together with various other hydrates.  

Ordinary Portland cement (OPC) loses on heating first the capillary water at about 100 ° C, and then its absorbed and combined water in certain higher temperature ranges before finally becoming anhydrous State is reached beyond which there are new ones form ceramic phases (at temperatures above 1000 ° C). A look at the differential thermal analysis curves of hydrogenated cement minerals indicates that ettringite (if present) dehydrated at about 150-200 ° C. Hydrogarnet (C₃AH₆), the hydrate of tricalzium aluminate and tetrakalzium- Aluminoferrite, breaks down at about 350 ° C. At about 500 ° C breaks down calcium hydroxide and forms free Lime and the calcium silicate hydrates lose their water Temperatures above 800 ° C. It is essential that the water donor reactions occur intermittently, and this can be critical to creating cracking. The Formation of lime is in the dehydration of potassium hydroxide a weak point in the OPC paste or paste because a subsequent wetting a strong tearing due to the high volumetric expansion (44%) if the Lime in calcium hydroxide hydrogenated again. Although a OPC concrete high temperatures when heated for the first time can withstand, it is unsuitable for use cases that Include conditions where the material repeats heated, cooled and exposed to moisture.

The main component of alumina cement (HAC) is mono-calcium Aluminate (CA) together with small amounts of C₁₂A₇ and other components depending on the oxide composition. In simple terms, CA hydrates and forms CAH₁₀, C₂AH₈ and alumina gel (AH₃). There is no calcium hydroxide. Now it is known that these hexagonal hydrates are metastable are and themselves, especially at higher temperatures and at Presence of moisture, in the cubic hydrate hydrogarnet (CAH₆) and alumina level. Molecular Volumes of the conversion products are smaller than that of the original hydrates, so that a conversion to an elevated  Porosity and loss of strength. As a result the conversion process led to problems when HAC concrete has been used in building constructions.

When heated, HAC paste also loses its capillary water about 100 ° C. Adsorbed is between room temperature and 300 ° C Lost water and hydrated the calcium aluminate, and alumina gel breaks down; this process is usually completed at around 400-500 ° C. in the Unlike OPC, the hydrates decay into slower and more controlled way and cause less internal destruction. Calcium hydroxide is also not available Available to potentially destructive free lime too form. At very high temperatures (especially above 900 ° C) a heat-resistant HAC concrete begins to regain strength win if there are ceramic phases within the matrix form. Although a HAC concrete is more resistant when heated against breaking up is what by the way in the water disappears and the lack of free lime is the disadvantage in structural applications occur that the hydrates transform and thereby a Strength reduction occurs.

The object of the invention is to provide improved concrete mixes for To create runways for vertically taking off aircraft.

According to the invention, this is achieved in that a Proportion of cement in an otherwise conventional concrete mix of pavement quality through ground, granular Blast furnace slag (GGBFS) is replaced to withstand the Increase concrete against high temperatures.

Up to 50% of the concrete mix can go through the preferred Material will be replaced, however, it will account for 40% Exchange material preferred.

GGBFS is normally used in concrete mixes to make the Reduce heat of hydration in large inlets and / or the resistance of the material to sulfates in the soil  enlarge. It is interesting to note that a selective replacement of the cement with GGBFS the temperature resistance of the concrete increased.

According to a further embodiment of the invention Resistance of a pavement grade concrete mix (PQC) improved that part of the naturally occurring Aggregates in the mixture through powdered fuel ash (PFA) is replaced.

The PFA can take the form of pellets to large, in the Naturally occurring aggregates to replace that normally occur with the PQC mixture. A preferred material is that under the name LYTAG from the company Booral Lytag Limited material distributed.

The pellets can have a nominal size of about 10 mm.

The pellets can form a fine, light-weight aggregate ground used as a substitute for sand in the PQC mixture will.

The preferred PFA material is the waste product at Generation of electricity in coal-fired power plants; it will pelletized and sintered at 1200 ° C to hard, spherical Create nodes with a pore ratio of 40%.

The material has so far been used as a lightweight unit Cast concrete structures of low density have been used and can Building concrete with strengths in the range up to 60 N / nm² result. However, it has not yet been recognized that the introduction the resulting this material into a concrete mix Material much more resistant to breaking open can be made when the surface is high temperature is suspended while starting a whiz.

According to a third embodiment of the invention, the High temperature resistance of a concrete mix improved by the fact that coarse aggregate of low weight,  as in connection with the second embodiment of the Invention is described in connection with natural sand and cement is used.

In the following the invention is related to the data described that relate to a series of tests which were done to break up resistance to determine different concrete mixtures.

It was in a first stage of the investigation program necessary, in detail the possible mechanisms check that exist at breakup for alternative Mixed forms with the possibility of an improved breaking resistance to identify. It seems very little to give accessible information about this problem because OPC cements are not normally used for high temperature / cracking operations be used. Is related to this problem however the behavior of cementitious materials in heat-resistant applications (if OPC concrete is not ) and also the behavior of building concrete Fire damage.

There are two possible cases of concrete cracking, due to rapid heating. In one case it can Moisture vapor within the matrix at such a rate build up that the resulting pressures the Breaking concrete. In a set cement, water can in three different ways, namely as

• (1) water bound in the cement hydrates,
• (2) Water adsorbed in the gel by cement components (i.e. in the gel pores), and
• (3) water in the capillary pores of the cement matrix (as called free water).

While the influence of increasing temperature on this different forms of water can be complex say that generally the capillary water is around 100 ° C converted into steam and the combined water forms (chemical  bound and adsorbed) moisture vapor at higher Form temperatures, depending on the temperature, where the various components dehydrate.

The second case concerns the different thermal Expansion of the matrix that causes the concrete to burst. These differential movement can be either different coefficient of thermal expansion of the Aggregates and the cement paste (cement paste) or the result of the temperature gradient through the concrete if the Surface is heated quickly; previous work have already shown that only the top few millimeters are exposed to these very high temperatures.

The resistance of concrete to these two mechanisms depends clearly depends on many factors. Related to water vapor induced errors come into question the water content of the Mixture, the chemical components of hydration and the Temperature at which they dehydrate, the permeability of the Matrix, the moisture content of the concrete and the strength of the concrete. In relation to the second mechanism, they are thermal expansion coefficient of the materials, their thermal conductivity and in turn the strength of the Concrete.

To try to break open the OPC Increasing concrete mix with pavement quality has been one Set of options checked:

• (i) The free water in the hardened concrete became thereby reduces the water / cement ratio of the Mixture was reduced (using a Super plasticizer);
• (ii) Increasing the permeability of the concrete (using of a coarser grain cement) in an attempt to Escaping water vapor more easily when heated allow;  
• (iii) changing the hydrate components of the mixture (under Use of cement-replacing materials) and thus the behavior when heated, and
• (iv) Reduce the influence of the different thermal expansion in concrete (using artificial aggregates, namely rough and / or fine).

Furthermore, the use of a high alumina cement as an exchange for the Portland cement in the Standard PQ-concrete mix examined. A plasticizer / retarder Admixture was used in this mixture to make up the Increase processing time because of an early Impairment of workability is known to possible problems and a perfect finish of a HAC concrete is prevented.

Cements

Three cements were used in this study, namely

• (i) ordinary Portland cement that complies with BS 12,
• (ii) coarse, ordinary Portland cement manufactured by Castle cement is delivered. This cement has one specific surface area of about 280 m² / kg compared with about 380 m² / kg for normal Portland cement, and
• (iii) ordinary high alumina cement (Fondu), supplied by Lafarge.

Aggregates

Standard PQ concrete aggregates were used, which consist of one fine aggregate of washed river sand and a coarse Aggregate with quartzite limestone existed in two maximum unit sizes (10 mm and 20 mm) were delivered.  

There were also two artificially produced aggregates used. Lytag aggregates were used in two forms, namely in a coarse aggregate with a grain size of 10 mm and a graded fine aggregate (about 4 mm down). Lytag consists of pelletized and sintered powdered Fly ash and is a lightweight building material aggregate in Trade.

An expanded, milled firebrick material (EFG), that from Alfa Aggregate Ltd. in three sizes (5-10 mm, 0-5 mm and 0-2.5 mm) was also delivered checked. EFG is low weight chamotte for medium Stress produced by sintering and grinding Fireclay materials as used in the refractory industry be used.

Cement exchange materials

Two cement exchange materials were tested, namely ground, granular blast furnace slag (GGBFS) to BS 6699 and powdered fly ash (PFA) for BS 3892.

Admixtures

An air entrapping agent was used, namely Fro-be manufactured by Sika Ltd. is distributed; this All mixtures were used to produce test panels with the exception of HAC limestone mix used. A super plasticizer, sicament, made by Sika Ltd. is distributed in a mixture used to make a To achieve a PQ mixture with a low water content.

A retarding plasticizer, Plastiment VZ, which is manufactured by Sika Ltd. is distributed in the alumina cement-limestone concrete mixes used.

In addition to the test panels or test panels that are in the as described using the aforementioned Ingredients were made, three more panels were made  from Proderite Ltd. used whose Hypol HTC mixture was used for comparison. It is a Special high-temperature concrete, the cementite-like and polymeric Contains materials, and that with a surface coating Aluminum base is finished.

The concrete for the test panels was made according to a specification manufactured, which contained the following requirements:

• (1) maximum aggregate / cement ratio of 5.8;
• (2) maximum water / cement ratio of 0.45;
• (3) Fine aggregate content up to 32-37 percent by weight of total aggregate content;
• (4) volume of enclosed air 5% + 1%; and
• (5) Slump from 30-60 mm.

For test mixtures, the strength requirement is based on Compression tests with a cube of 150 mm, the mean of the three samples exceeds the target mean Strength of 32.3 MPa for seven days.

This specification was based on all table mixes Limestone aggregate / OPC base used. If artificial manufactured aggregates or HAC were used, the Mixing proportions based on recommendations from suppliers and Experience from previous investigations turned off. While the entire table production was in accordance with the requirements maximum water / cement ratio, workability and Seven-day firmness followed and these requirements Fulfills. However, it should be noted that in view on previous work the machinability using the Vebe method in contrast to the slump test (consistency check) was evaluated, with a time of about ten seconds Achieve satisfactory workability for this method is sufficient for the table production was found.  

For comparison purposes, a simple break up test was carried out performed to differentiate the relative performance To identify mixture forms, with the intention of suitable mixtures for the table production to the final Identify testing on an aircraft runway. This Test consisted of a 405 x 255 mm panel under one Oxy-acetylene flame at a fixed distance of 145 mm above to heat the surface. This height was chosen because they break up in an OPC-PQ control mix roughly gave twelve seconds; this is similar to the length of stay until for the first break, which under test conditions a Runway was reached.

The experimental mixtures were mainly concerned with perfect machinability (i.e. Vebe of about ten Seconds) and a usable surface finish. In some cases, the strength of cubes was 100 mm measured.

A total of ten test mixtures were used to manufacture and created for testing small boards. The blends were chosen to cover the range of materials that are described in Table 1.

Tests were made on one or two panels of each Mix type performed. Both on the top and on the Bottom of the panel was a minimum of six breakup tests carried out. The maximum length of stay was 40 Seconds. The results are summarized in Table 2, where (40) indicates that no breakup has occurred, and for averaging purposes it became a result without break-in rated as if there was a time until the first breakup of Would have 40 seconds.  

Results of a simple breakup test

The first observation is that this simple pry open test significantly different results with different Types of concrete revealed. The tests have shown that

• (i) When using a coarse OPC (Mix 23) only one little influence on the break-up time occurred,
• (ii) when using a super plasticizer to achieve a very low water content (mixture 22) poorly resistant top against breaking open, but a much more resilient floor area against breaking open. This difference can be caused by the very damp surface, the occurs during vibrating and finishing,
• (iii) a cement exchange material in an otherwise standard PQ Mixture (Mixtures 20 and 21) the resistance against Breakup has improved significantly, with PFA being far gave better results than slag,
• (iv) a light weight aggregate in combination with Limestone sand flours offer resistance to breakup has also improved, esp. on the top (Mixtures 23A and 23C), and the use of PFA In addition, there was a further improvement (mixture 32);
• (v) the use of HAC (blend 23D) a good one Resistance to breakup resulted, however, not exceptional, and
• (vi) the use of low weight Lytag aggregates (Mix 23C) consistently with a concrete high resistance to breakup resulted, only one Test from eighteen showed a breakup.

The test results show that a stronger against breakup more resistant concrete than the standard PSA-PQ mix can be made, and that test panels, the nine of these Mixing types showed that large-scale tests were carried out.  

Manufacture of test boards for soil erosion tests Details of the mixtures

The nine types of blends used to make panels for Large-scale tests are used in Table 3 (Mixtures 24-32); at this stage the PQ trial mix with low water / cement ratio excluded. All mixes except the HAC concrete contained an air entrapping agent. The use of PFA decreased the air content (up to 2%) was critical and it wasn't possible the air content of the mixtures that are artificial manufactured aggregates contained in the used Determine or record operating pressure.

The machinability of all blends was satisfactory and were in the range of 6-9 seconds. The seven- Daily strength at 150 mm cubes were all above the minimum required range (32 MPa) and were all within Range from 35.7 to 40 MPa (with the exception of the HAC mixture).

Board making

Three panels of 600 × 600 × 100 mm were made from each mixture produced, with the exception of mixture 31 (two plates 800 × 600 × 100 mm) and mixture 32 (a plate of the same size). The compression technique used on all test panels and finishing was the same as in the previous one Test program (2), namely

• (1) complete filling of the mold with a slight overload,
• (2) compression with internal vibrator,
• (3) Equalize with two passes of the vibrating screed,
• (4) Remove the supernatant with two passes of the Scraper (channel section),
• (5) closing the surface with 102 passes of the vibrating plank, and
• (6) Smooth the surface for the finish.

The boards were in the laboratory under plastic cladding, for example Hardened for 28 days. No curing component was used however, the surface of each panel became occasional wetted.

Test process

The aim of the test program was the performance of the different Evaluate types of mixtures under jet blowing conditions. The experimental setup was therefore made with a Harrier jet nozzle with a beam exit temperature of 700 ° C at a Height distance of three nozzle diameters above the board surface and operated at a pressure ratio of 1.5.

Each plate (which was kept in its steel form) was opened attached to the rails of a soil erosion rack and then positioned centrally under the jet nozzle, with their Surface perpendicular to the beam axis and in a certain Height was arranged. Before the plate's blasting effect Test pressure and temperature were exposed to one the heat shield protecting the samples. As soon as the perfect operating conditions were achieved, the Heat shield with the help of a driven by a linear motor Removed trolley of the soil erosion frame and the Exposed concrete to the blow jet.

Each plate was blasted with a minimum of 40 seconds checked. If no breakup is found the experiment was continued for 120 seconds until was switched off.

Complete visual and thermal image data for everyone Test runs were recorded on videotape for analysis.  

Relationship between surface temperature and length of stay

The maximum surface temperature of the boards, which are obtained from the thermal image recordings, is plotted in FIGS. 1, 2 and 3 over the residence time; the mixtures are grouped according to OPC / cement exchange, aggregate and HAC variants.

A comparison with the result of the OPC-PQ control mixture shows that the cement exchange materials have reduced the rate of temperature increase ( Fig. 1). The rate of temperature increase of the mixture based on the EFG aggregate was similar to the OPC-PQ control, while that of the Lytag mixtures was greater ( Fig. 2). The Hypol-HTC and a HAC panel were similar to the OPC control; however, the other HAC panel has reached temperature at a much slower rate ( Fig. 3).

Dwell time until the first break up

The time to first break up for each panel is shown in Table 4 and shown graphically in Figure 4 (with a 120 second dwell time indicating that no breakup occurred at the end of this test period). The results show:

• (i) The OPC-PQ concrete mix showed slightly better results than in the previous tests, with an average residence time of 15 seconds to a first break-up (compared to about 10 seconds in the previous tests, Fig. 5);
• (ii) the coarse OPC-limestone mixture was slightly worse than the tax mix with an average of 10 Seconds;
• (iii) the result of the mix, the PFA as a cement exchange contained, was disappointing and gave only an average from about 15 seconds to the first break;  
• (iv) in contrast, the panels with GGBFS showed as Cement exchange much better results than that PQ control with an average of 32 seconds over a test duration of 40 seconds (with no breakup was evaluated as a value of 40 seconds);
• (v) The two HAC concrete panels tested showed significant better results than the aforementioned OPC blends; they had an average length of stay of 77 Seconds before the first break. The departures, though they actually occurred were related to sudden Appearance and size extraordinary;
• (vi) of the three panels produced on EFG, this resulted a breakup after 15 seconds while the not the other two even after 120 seconds had left;
• (vii) all Lytag blends operating under Harrier conditions tested lasted the full period of 120 seconds without a break (one of the Lytag / Sand plates had some very small break-up points over large sand particles were ordered, but were not counted); and
• (viii) the two Hypol-HTC panels showed after 120 seconds no departure.

Temperatures the first time you break open

The surface temperatures at the first cracking for the panels showing cracking are given in Table 4 and shown graphically in Fig. 6. The OPC-PQ control mix panels gave first break temperatures in the range of 320-370 ° C, which is a lot compared to values found in previous studies ( Fig. 7). The two large OPC panels, for which the thermal images have been successfully awarded, showed the first break temperatures of 350 ° C and 415 ° C.

The first break-up temperatures for the tablets, with a OPC / limestone concrete were made, one of the two Cement exchange materials used (PFA and GGBFS) contained, were all in the range of 390 ° C to 425 ° C. The Average of the first break temperature for the HAC panels was at 435 ° C.

In comparison, the maximum surface temperatures were those using Lytag based Panels were reached before the test was completed showed no breakup at all in the 510- 540 ° C.

The broken areas of the test panels which became defective within 40 seconds are shown in Table 4 and shown graphically in FIG. 8. While the area of breakup size was large, the middle breakup area is similar, between 53 and 96 cm². For these materials, the extent of damage that occurs is a similar value, while the time it takes to break open varies considerably.

Because of the good results of some of the mix types four panels were placed under Harrier blasting conditions tested tougher conditions. The test device was with a beam exit temperature of 1000 ° C and one Pressure ratio operated by 4.0. These tests served two Purposes: First, an attempt should be made between the breaking resistance of the four best blends that haven't yet had broken out when they passed the previous blast test were exposed to differentiate, and secondly one wanted some information about the usability of these materials win for the future.  

The four mixtures tested were HAC (Mix 30), Hypol HTC (blend 33), OPC Lytag / Sand (blend 28), and OPC / only Lytag (mix 31). The results of these four test runs are summarized in Table 5.

The increase in the surface temperature with the residence time is shown in FIG. 9, and the respective residence time until the first break in FIG. 10. From the results it follows that the HAC and Lytag / Sand mixtures differ both in terms of the speed of the The increase in temperature and the time until the first breakup behaved similarly (about one second). Both tests were terminated after 20 seconds due to excessive break-up.

The surface of the Hypol-HTC tablet heated up more slowly and showed breaks after 6 seconds. At the end of the test (after 40 seconds) the panel showed considerable break-up and Signs of erosion.

In contrast, the mixture based on OPC also showed Lytag coarse and fine aggregates show no signs of breaking open within the test duration of 40 seconds. After testing the surface of the panel showed discoloration, although fine cracks were seen, as was to be expected.

Simple lab breakdown tests

The easy lab breakdown test using one Oxy-acetylene flame gave very different break-up times for the area of examined concrete mixtures. The Mix types were in decreasing order of resistance to breakup

The relationship to the result of the mixtures tested was in the soil erosion rack under jet blowing conditions generally good, the main exception is the OPC-PQC- Mix with PFA, which is bad under jet blowing conditions Results.

Comparative performance of mixtures under jet blowing conditions

The radiation erosion tests have confirmed that the types of mixture had a wide range of break resistance, with all but two were significantly better than the OPC-PQC Control. The most useful indicator of break-up resistance is the length of stay until the first departure. On the Basis of the tests under Harrier conditions (700 ° C, Pressure ratio 1.5) and the subsequent tests at 1000 ° C with a pressure ratio of 4.0 (ASTOVL) on most resistant materials is the detection of the breaking resistance the mix type as follows:

The performance of the Hypol HTC tablet can be classified as very good (it remained undisrupted after 40 seconds Harrier conditions), but the surface material was clearly damaged after 120 seconds, it discolored and became fragile (could easily be removed with a fingernail will).

The time / temperature profiles showed that the surface of the artificially produced aggregate panels heated up more quickly as the OPC-PQC concrete; this can affect the general insulation properties be attributed. Conversely, they heated up Concrete materials with cement exchange slower than that OPC-PQC concrete materials, increasing their thermal Conductivity suggests.

The OPC-PQC concrete gave temperatures at a first Breaking up in the order of the values of previous ones Work has been identified (i.e. 320-370 ° C). The OPC / limestone aggregate mix, which is one of the cement exchange materials (PFA and GGBFS) included resulted in higher first break temperatures (in the range of 390-425 ° C). The HAC concrete showed no signs of cracking up to about 435 ° C were achieved, and the mixtures, the Lytag aggregates contained, reached surface temperatures of over 500 ° C without signs of breakage.  

These surface temperatures and assigned dwell times the first time you break open, compare with conditions, which were previously determined in use, which leads to the conclusion is that the mixtures based on HAC and Lytag Harrier operating conditions give good results. The Mixtures based on OPC / slag-PQC concrete and EFG units can also be expected to produce flawless results, although these materials are not as tough are against breaking open.

Mechanisms of breakup

Previously, two possible mechanisms were thought to do this Cause breakup

• (1) one associated with water vapor formation and
• (2) the other with a differential thermal expansion effect.

In practice, it is likely that these mechanisms together cause the PQ concrete to break open.

A comparison of the breakup behavior of the different Mixing types with that of the OPC-PQ concrete shows that the Modification of the cementitious matrix (using PFA or GGBFS) has brought some improvements that far predominant increases in resistance to breakup however, when natural aggregates were achieved by artificially produced were replaced (in particular the Low weight Lytag unit). This can be due to this are based on the fact that these porous aggregates are released Can absorb water vapor, or more likely that they introduce less differential thermal expansion (or better resist it).

It is interesting to note that concrete materials often result in a substantial increase in their coefficient of thermal expansion at temperatures above 320 ° C, and this has contributed to the dehydration of the cement paste. A value of 8 · 10 ^-6 per ° C below and 20 · 10 ^-6 per ° C above this temperature for a lime-gravel aggregate concrete is known from the literature, while interestingly, an expanded slate clay aggregate an increase of only 6.1 -7.5 x 10 ^-6 per ° C.

In view of the fact that the PQ / limestone concrete shows cracking at a temperature of 320-370 ° C under test conditions (ie just above the critical transition temperature of 320 ° C) and that the artificially produced Lytag aggregate concrete (also with a coefficient of thermal expansion of about 7 x 10 ^-6 per ° C) shows no cracking, the most likely mechanism that causes cracking is likely to be a differential thermal expansion effect between the top, very hot layer of the concrete and the underlying cooler layers . This effect is enhanced compared to all natural aggregate particles that are close to the surface, since the particles on the surface have a significantly lower coefficient of thermal expansion than the paste.

The results clearly show the superiority of the Lytag blend in terms of resistance to jet conditions. They also show that it is possible to use this mixture to make paving concrete that is suitable for the next generation of vertically taking off and landing aircraft.

Claims (12)

1. Concrete mix with pavement quality, characterized in that a proportion of cement contained in the mixture is replaced by ground, granular blast furnace slag (GGBFS) in order to increase the resistance to high temperatures of the concrete obtained from the mixture. 2. Concrete mixture according to claim 1, characterized in that up to 50% of the mixture is replaced by GGBFS. 3. Concrete mixture according to claim 2, characterized in that 40% of the mixture is replaced by GGBFS. 4. Concrete mix with pavement quality, the naturally occurring Contains aggregates of sandstone and sand, thereby characterized in that at least part of the course aggregates occurring through pulverized fuel ash (PFA) in the form of a low-weight unit is replaced to the resistance of the mixture recovered concrete against high temperatures. 5. Concrete mixture according to claim 4, characterized in that the PFA is in the form of pellets. 6. Concrete mixture according to claim 5, characterized in that the pellets have an aggregate size of 10 mm. 7. Concrete mixture according to claim 5, characterized in that the pellets to a fine aggregate of low weight are ground. 8. Concrete mixture according to claim 4, characterized in that the PFA is owned by Boral Lytag Limited the name LYTAG is sold concrete mix.   9. Concrete mixture according to claim 4, characterized in that the PFA is a waste product in the generation of electricity in Has coal-fired power plants, the waste product pelleted and sintered at 1200 ° C to hard, spherical tubers with an empty ratio of Generate 40%. 10. Concrete mixture according to claim 4, characterized in that the PFA in the mixture in conjunction with natural Sand and cement is installed. 11. Concrete mixture according to claim 1 or 4, characterized by an air entrapping agent. 12. Concrete made from a concrete mix according to claim 1 or claim 4.