FR2653890A1 - Installation and improved method for testing mortar and concrete - Google Patents

Abstract

The subject of the invention is an installation and an improved method for testing mortar and concrete, in particular for preventing silico-alkaline reactions. Test pieces (2) made under standardised conditions from granulates and cement to be studied are placed in leaktight containers (1) kept at a determined temperature, and are withdrawn at certain times to be subjected to an expansion measurement. According to the invention, the leaktight containers in which the test pieces are placed are themselves placed in a preservation reactor consisting of a heat-lagged enclosure (3) comprising, at its bottom, a grid (36) for supporting the containers (1), extending horizontally above a liquid tank (37) made in the bottom of the enclosure (3), and in which are immersed electrical resistors associated with a system for regulating the heating as a function of the temperature measured at the centre of the enclosure (3) and at the middle of the containers (1), in order to keep the temperature at a constant level.

Description

 The subject of the invention is a test installation for mortars and concretes, as well as an improved test method for testing and predicting the behavior of the various constituents of a mortar or concrete with respect to silico-alkaline reactions.

 It has long been observed that certain aggregates used for the manufacture of mortars or concrete have a particular reactivity with regard to the alkaline constituents of cements which could lead in the long run to a real deterioration of the concrete. Studies have shown in particular that some silica granules can be found to react with alkali, especially the sodium and potassium hydroxides commonly found in cements.

 While non-alkaline cements may be used, they are more expensive and, in any case, it is necessary for the manufacture of concrete and mortar to test the behavior of the aggregates - sand and gravel available, in particular. a function of the characteristics of the cement, which it is desired to use so as to predict and, consequently, to avoid triggering of silicoalkaline reactions.

 Some test methods have therefore been developed to test the behavior of the different constituents of concrete, ie aggregates, cement, admixtures and other additions.

 To obtain a reliable and representative result, the tests must be carried out under specific conditions governed by standards.

In particular, a chemical test defined by the ASTM C 289 standard is known, which has the advantage of great speed, since it provides results in less than three days, but is not sufficiently reliable. It is not uncommon, in fact, that we observe disagreements between
the results of the chemical test and the other tests.

 There is also known another method defined by ASTM C 227, which is to measure over time the longitudinal expansion of specimens made of standardized size mortar bars. These test specimens are made with the crushed aggregate in a precise grain size, the cement used being either the one that will be used for work on a given site, or a reference cement when it comes to comparing aggregates.

 From a mortar made in accordance with the proportions indicated by the standard, specimens are produced in molds of standardized dimensions. After 24 hours of hardening, the test pieces are demolded, measured and deposited in sealed containers containing a little water at the bottom.

 The containers are kept in a room whose temperature is maintained at a determined level, for example 380C. At certain times, for example every 14 days, the container is opened to extract the test pieces and measure the swelling after returning to 23 C, then the test pieces are placed in the container which is closed until the next measurement.

 This test method, which is very commonly used to evaluate the reactivity of grenuets, is quite easy to implement because the sample size is small and requires simple equipment. In fact, in general, the test installation comprises means for manufacturing test pieces, a plurality of sealed containers and a container storage room provided with means making it possible to keep the temperature as constant as possible. .

 It has been found, however, that the tests thus carried out were not absolutely reliable and, in particular, if comparative tests using the same granulate and the same cement were carried out in different organisms all implementing the instructions. of the standard, however, very different results can be obtained.

 The object of the invention is therefore to improve the known test methods and the installations used for this purpose in a way that makes it possible to obtain a reliable result.

 The studies carried out in this respect by the applicant company have made it possible, in particular, to verify that it was not sufficient to ensure compliance with the standard conditions imposed for the manufacture of specimens and the quality of the containers, but that, the very long duration of the test, the conditions of storage of the containers had a very important influence and that apparently small variations in the storage temperature and the hygrometric degree could lead to very variable results, although all the others conditions have been met.

 It was therefore necessary to perfect the method so as to ensure the conservation of the specimens throughout the duration of the test.

 According to the invention, the test installation comprises a specimen storage reactor consisting of an insulated enclosure provided with a container loading opening, closed by a sealed door, and comprising, at its lower part, a carrier grid for the containers extending horizontally over a reserve of liquid, normally water, formed in the bottom of the enclosure, the latter being further provided with heating means of the water reserve associated with a heating control system comprising at least one member for measuring the temperature placed in the center of the chamber and at the level of the middle of the containers and a device for controlled control of the heating means as a function of the measured temperature. , for maintaining the temperature at a constant level.

 Preferably, the means for heating the water reserve are constituted by a set of electrical resistances extending towards the inside of the enclosure from the side wall so as to plunge into the liquid and associated with a system. regulating the supply current.

 For a better understanding of the invention, the following will be described in detail below the improved methods according to the invention for the testing, respectively, of mortars and concretes, as well as the equipment employed, which is shown in the accompanying drawings.

 Figure 1 is a diagram, in vertical section, of a container.

 Figure 2 is a diagram, in vertical section, of the preservation reactor.

 We will therefore describe in detail the procedure used to test the alkali reactivity of natural rocks in the case of a mortar and a concrete.

1 - Mortar test
In general, an expansion test is carried out for prisms made of a mortar consisting of the granulate to be studied and a cement rich in alkali.

a - Preparation of mortar and test pieces
The pieces (greater than 5 mm) of the rock to be studied must be selected so as to obtain a sample that is mineralogically homogeneous.

These pieces are washed beforehand and dried at 800C, then crushed and separated by sieving into five granulometric slices. These slices are then recomposed in the proportions indicated below in order to obtain a perfectly defined granulometric curve of a sand ranging from 0.16 to 5 mm:
between 0.160 and 0.315 min 15% by weight
0.315 and 0.630 minutes 25%
0.630 and 1.25 minutes 25%
1.25 and 2.50 mm 25%
2.50 and 5.00 mn 10%
100%
it is preferable to dispose of the rock in the natural state. Nevertheless, although this is to be avoided, one may be led to study a sample of aggregates already crushed industrially with particles less than 5 minutes or in the form of sand: - if the largest dimension is greater than 5 min, the particles larger than 5 min are crushed and separated into five slices as before, if the largest dimension is less than 5 min, sieving is carried out according to the slices provided. and the coarsest slice is put in larger quantities, adding to the proportion predicted the proportions of the missing slices.

 If, in one slice, the quantity is insufficient and higher in another coarser slice, it is possible, by crushing, to ensure a better distribution of the quantities of material.

 Before recomposing the five tranchas, they must be washed separately to remove the dust from crushing that adheres to the particles, dry at 800C and homogenize.

 Note that this procedure aims to obtain a characterization of the rock in the natural state (> 5 min) vis-à-vis the alkali-reaction. it does not attempt to characterize the crushed sand that could be marketed from this rock.

 An alkaline rich CPA cement having an Na 2 O content of 0.9 + 0.2% is used.

This cement is then enriched in Ne2O by adding
NaOH with mixing water to bring the Na2O equivalent of the cement to 1.25%.

To prepare the mortar, the composition of a jail is as follows:
- 300 g of cement
- 675 g of dry granulates
water required to obtain at the ASTM shaking table, from a 100-mm diameter tale, a diameter spread of between 205 and 220 minutes after 10 shocks in 6 seconds.

 These 675 g of aggregates are prepared beforehand by reconstituting the granulometric curve from the five slices and homogenized.

 Deionized water containing the addition of NaOH is used.

The kneading is carried out in the known manner according to
ASTM C305 by checking the spreading at the table to adjust the water content. The establishment in the molds is immediately after.

 The molds defined by the ASTM C 490 standard are used to obtain 25x25x285 nm prismatic specimens.

At the ends of these prisms stainless steel studs are embedded in the mortar for the measurement of swelling. The distance between studs, which will be used for calculations, is 250 minutes.

 The setting of the mortar in the molds is done in two equal layers, compacted.

 For a type of rock four prisms are made from two different waste (two prisms per gachée).

b - Preservation of specimens and measurement of swelling
The mussels are kept at 200C, 100% RH for 24 hours. To prevent runoff, a glass plate with a rubber seal covers the molds without touching
the mortar.

 The prisms are demolded and the measurement of the initial length is performed with an ASTM retractometer provided for this type of prism.

 The prisms are then immediately introduced into a sealed container of the type shown in FIG.

 Each container 1 has a rectangular section and comprises a side wall 1 closed at its bottom by a bottom 11 and provided, at its upper part, with a hole closed by a lid 12 which is associated, preferably, a dome 13 allowing to avoid the fallout of condensation.

 The container preferably has the same dimensions as that used for the ASTM C 227 test and therefore normally has a section of 280 x 230 min and a height of 400 min.

 At a certain height above the bottom 11, nor malement 50 min, is stretched a stainless steel grid 14 for supporting the prismatic specimens 2. These are positioned by a second grid 15 extending transversely towards the middle of the container. Below the gate 14, the container contains a quantity of water 16 to ensure a degree of humidity of 100% at 380C.

 Each container is designed to store 30 prismatic specimens.

After storing the test pieces, the containers are sealed and placed in a storage reactor shown schematically on the
Figure 2

 The reactor consists of a parallelepipedal enclosure 3 covered with a heat insulator 31 and provided, at its upper part, with one or more insertion orifices 32 each closed by a cover 33. The inner wall of the enclosure 3 is constituted by a stainless steel sheet 34.

 Normally, the enclosure 3 is designed to contain nine containers of the type shown in Figure 1. It has horizontal dimensions of the order of 1300x1100 minutes and a height of 950 mm.

 At a certain height above the bottom 35 of the enclosure 3, of the order of 250 to 300 minutes, is stretched a stainless steel grid 36 strong enough to support the nine containers loaded. This grid 36 therefore limits a lower space which is filled, up to a certain height, of the order of 200 minutes, by a water reserve 37.

 the reactor 3 is further provided with a plurality of electrical resistors 4 which extend horizontally inwardly from the side wall 33 of the enclosure so as to plunge into the water supply 37. The resistors 4 are connected to a power supply station 41 controlled by a regulating device 42 as a function of the temperature of the enclosure, the latter being measured by a probe 43 placed in the axis of the enclosure 3, substantially in the center geometrically thereof, and at the middle of the containers arranged on the gate 36. The measured temperature is displayed on an input 44 of the regulating device 42.

 Thanks to these provisions, the containers can be kept in an atmosphere saturated with water vapor ensuring better temperature regulation. This is in fact maintained at a constant level by the regulating device 42 and, in practice, the temperature is regulated so as to be maintained, at the level of the container medium, at 380 ° C, to a maximum of 10, the hygrometric degree being 100% inside the containers.

 The equipment normally used includes containers designed to receive thirty prismatic test pieces, the reactor 3 being able to contain nine containers.

 Before each swelling measurement, the container 1 is removed from the reactor and, while remaining closed, is left at 200 ° C. for about 18 hours. The container is then green and the test pieces 2 are removed, measured and then reintroduced into the container 1. The latter is then closed and returned to the storage reactor 3. All these operations must be done as quickly as possible.

 At each measurement, we reverse the direction of the specimens 2 by turning down the end that was up before and we change their place in the container l.

 Thanks to the provisions which allow a perfect maintenance of the temperature and the hygrometic degree during an indeterminate time, the measurement can be carried out over a sufficiently long duration to predict the behavior of the cement and aggregates in the long term. In practice, the deadlines for the measurements may be 1 - 2 - 3 - 4 - 6 - 8 - 10 - 12 - 15 - 18 - 24 months.

For each mortar, at least four specimens will be made on which the measurements will be carried out according to the indicated deadlines. At each maturity, we measure the variation of length dL compared to the original length
L equals normally 250 minutes and 1 tone calculates the dL / L ratio.

 The result expressed is the arithmetic mean of the four values.

 If one follows the method that has just been exposed, a container must be cooled and opened at each expiry.

It must therefore contain specimens that all arrive on the same day at a time. For example, it is possible to make the same day several mortars of different compositions so as to fill a container. However, in practice, it may be necessary to place in the same container specimens maturing at different dates.

 In this case, the container is left inside the reactor maintained at 380 ° C. and, having opened it, only the prisms to be measured are taken out and introduced into an additional container preheated to 380 ° C. with water at the bottom. The reactor container and the lid 33 of the latter are then closed and the additional container is allowed to cool at 200 ° C. for about 18 hours. The measurements are then carried out as indicated above and the test pieces are re-introduced into the original container by operating in a reverse manner as quickly as possible.

2 - Concrete test
It is another test of expansion of test pieces made of a concrete made from the aggregates to be studied, a non-reactive alkaline sand and a cement rich in alkaline.

a - Preparation of concrete and test pieces
The aggregates to be studied, between 5 and 20 minutes, must be selected so as to obtain a homogeneous and representative sample of the aggregates to be studied.

 These aggregates are washed beforehand and dried at 800C.

 They are then separated by sieving, without crushing, in three slices granulometric: 5 - 10 min, 10 - 14 min, 14 - 20 min.

 Each slice is homogenized separately.

 Aggregates <5 minutes and> 20 minutes, if present in the seal, must be rejected.

 The cement used is an alkaline rich CPA cement having an Na 2 O content of 0.9 + 0.2%.

This cement is then enriched with Na2O by adding
NaOH with mixing water to bring the Ne2O equivalent of the cement to 1.25.

 We use a sand sandstone particle size 0 to 7 minutes very pure and whose alkali reactivity was verified by the mortar test at 380C indicated above.

 The composition of the sand is as follows: 7% from 2 to 7 minutes; 18% from 1 to 2 minutes; 35% from 0.5 to 1.5 minutes; 30% from 0.35 to 0.7 minutes; 10% <0.8 min.

To prepare a mixture of concrete, the test granules taken in equal proportions are mixed in the three granulometric units indicated above, respectively 5 to 10 minutes, 10 to 14 minutes and 14 to 20 minutes, which leads to a share of granulates of 1170 kg of concrete
These aggregates are mixed with a sand sandstone grain size 0-7 min, very pure, and which has been verified nonreactivity to alkali by the mortar test described above.

 the quantity of sand is of the order of 640 to 690 kg / m3 of concrete as the case may be, this quantity being dependent on the density of the aggregates tested, the quantity of water required and the amount of air that is measured. the aerometer according to the standard NFP 18-353 of June 1985.

 The cement dosage is 410 kg / m3 of concrete.

Demineralised water with added
NaOH to reach the value of 1.25% Na2O equivalent. The amount of water is determined beforehand to obtain a slump with Abrams cone of about 8 cm.

 The kneading is carried out in a room at 200 ° C. and 70% humidity in a 20-liter kneader and is continued for 3 minutes at 17 rpm.

The concrete is poured into 7 x 7 x 28 cm prismatic molds. Stainless steel studs are embedded in the ends in the concrete for the measurement of swelling, the distance between studs being 247 mn
For the same type of aggregates, three prisms are produced from the same waste.

b - Preservation and measurement of swelling
After casting, the molds are stored at 200C in a 100% humidity atmosphere for 24 hours. The prismatic specimens are then demolded and immersed in demineralized water at 200C for 30 minutes. The measurement of the initial length is then made with a retractometer provided for this type of prism.

The prisms are then immediately introduced into a sealed container of the type described in FIG. 1 and thus comprising a lateral envelope 1 closed by a bottom
It and a lid 12 and containing at its lower part a water reserve 16 surmounted by a grid 14 on which are standing test tubes. These are held by a grid 15 stretched horizontally in the middle of the container and provided for the storage of six specimens in the container.

 The containers 1 are then stored in a preservation reactor of the same type as that described above and shown in FIG. 2. The reactor 3 therefore contains a water reserve 37 into which electrical resistors 4, the power supply of which is controlled, are dipped. by a control system 42 as a function of the temperature measured by a probe 43 placed in the axis of the reactor, substantially at the level of the middle of the containers.

 The reactor is regulated so that the temperature at the height of the middle of the container is maintained at 380C to 10C.

 As for the mortar test, this arrangement makes it possible to maintain around the containers an atmosphere saturated with water vapor which ensures an excellent regulation in temperature. The inside of the containers is thus perfectly maintained at the chosen temperature of 380C, with a degree of humidity of 100%.

 The swelling measurement is done in the same way as above, for the mortar test. at deadlines of 1 - 2 - 4 - 5 - 6 - 8 - 10 - 12 - 15 - 18 - 21 - 24 less.

 For each mortar composition, three specimens were made and, at each time, for each specimen, the dL / L ratio of the variation of length dL compared to the original length L equal to 247 minutes was calculated. The result expressed is the arithmetic mean of the three values thus calculated.

 The use, according to the invention, of a storage reactor for maintaining a saturated atmosphere at constant temperature by controlled heating of a water reserve and the respect of the operating conditions which have just been described allow both for mortars and concretes to ensure excellent reproducibility of the results, and consequently to carry out much more reliable tests than by the methods used so far.

 By way of example, Table I below gives the results of tests carried out for a mortar and for a concrete, under the conditions just indicated.

The same aggregates and the same cement were used by three different operators, labeled 1, 2, 3 in Table I. Tests 1, 2, 3 were started with an interval of one month. Table I below gives, for the mortar and for the concrete respectively, the results of the tests at 1, 2, 3, 6, 8, 10 months and one year as well as the average of the results. We see that the results differ little from the average, with the differences not exceeding 10% after six months.

TABLE I Due date for measurements and swelling in

i <SEP> I <SEP> i
<tb> 1 <SEP> mo <SEP> i <SEP> s <SEP> 2 <SEP> mo <SEP> i <SEP> s <SEP> 3 <SEP> mo <SEP> i <SEP> s <SEP > 6 <SEP> mo <SEP> i <SEP> s <SEP> 8 <SEP> mo <SEP> i <SEP> s <SEP> 10 <SEP> mo <SEP> i <SEP> s <SEP> 1 <SEP> year
<tb> MDRTIER
<tb> i <SEP> I <SEP> i <SEP> i
<tb> Assay <SEP> 1 <SEP> 230 <SEP> 755 <SEP> 1370 <SEP> 2840 <SEP> 2990 <SEP> 3090 <SEP> 3200
<tb> Assay <SEP> 2 <SEP> 255 <SEP> 840 <SEP> 1650 <SEP> 3060 <SEP> 3280 <SEP> 3440 <SEP> 3500
<tb> Assay <SEP> 3 <SEP> 200 <SEP> 1090 <SEP> 1820 <SEP> 2630 <SEP> 2970 <SEP> 3030 <SEP> 3110
<tb> Medium <SEP> 228 <SEP> 902 <SEP> 1616 <SEP> 2843 <SEP> 3080 <SEP> 3190 <SEP> 3270
<tb> i <SEP> i <SEP> i <SEP> i <SEP> i <SEP> I <SEP> i <SEP> I
<tb> BETON
<tb><SEP> Assay <SEP> 1 <SEP> 730 <SEP> 990 <SEQ> 1480 <SEP> 1590 <SEQ> 1700 <SEP> 1770
<tb> Test <SEP> 2 <SEP> 320 <SEP> 600 <SEP> 1080 <SEP> 1230 <SEQ> 1310 <SEQ> 1380
<tb> Assay <SEP> 3 <SEP> 400 <SEP> 700 <SEQ> 1170 <SEP> 1290 <SEQ> 1340 <SEP> 1360
<tb> Average <SEP> 450 <SE> 763 <SE> 1240 <SE> 1370 <SE> 1450 <SEP> 1500
<tb><SEP> I
<Tb>
Comparative tests were also conducted to show the importance of the storage conditions and in particular the combined use of the sealed containers and the preservation reactor. These comparative tests are carried out on test pieces of the same mortar made with a granulate deemed highly reactive and a cement
CPA whose alkaline content was increased to 1.25% equivalent Na 2 O, by addition of sodium hydroxide in the mixing water.

 Three storage conditions were compared: 1 - The specimens were placed directly, that is to say without a container, in a preservation reactor such as the one just described, that is to say heated to 38 C by electrical resistors immersed in water placed at the bottom of the reactor.

 2 - The test pieces were placed in a metal container such as that described above but it was kept during the time of measurement, in an air chamber simply maintained at 38 C.

 3 - The test pieces were placed in the same sealed container but it was locked in a storage reactor as described above.

 These measurements were carried out with a maturity of 14 days, 1 month, 2 months, 3 months, 4 months, 8 months, 1 year.

TABLE II
Measuring times and swelling in m / m

<tb> Condition <SEP> 14
<tb> of <SEP><SEP> days <SEP> 1 <SEP> mo <SEP> i <SEP> s <SEP> 2 <SEP> mo <SEP> i <SEP> s <SEP> 3 <SEP> mo <SEP> i <SEP> s <SEP> 4 <SEP> mo <SEP> i <SEP> s <SEP> 8 <SEP> mo <SEP> i <SEP> s <SEP> 1 <SEP> year
<tb> servation
<tb> I <SEP> l <SEP> l <SEP> i <SEP> i
<tb><SEP> 1 <SEP> + <SEP> 20 <SEP> + <SEP> 90 <SEP> + <SEP> 300 <SEP> + <SEP> 320 <SEP> + <SEP><SEP> 380 <SEP> + <SEP> 380 <SEP> + <SEP> 380
<tb> i <SEP> i <SEP> i <SEP> i <SEP> i <SEP> i <SEP> i
<tb><SEP> 2 <SEP> i <SEP> - <SEP> 180 <SEP>
<tb><SEP> I <SEP> i <SEP>
<tb><SEP> i <SEP> i <SEP>
<tb><SEP> 3 <SEP> 0 <SEP> + <SEP> 450 <SEP> + <SEP> 650 <SEP> + <SEP> 960 <SEP> +969
<Tb>
We see that the condition 1, that is to say the conservation of the specimens in a reactor heated by submerged resistors but without container, shows a swelling, but it caps quickly, and does not show the reactivity well known from this granulait.

 Condition 2, that is to say the conservation in a metal container simply disposed in an air chamber is even less convincing since, after fourteen days, there is a withdrawal. It appeared, in fact, that under these conditions, the temperature was not sufficiently homogeneous, and that one could observe, between the top and the Sac. of the test piece, temperature differences of up to 20C. However, at 380C, a temperature difference of 10C varies the relative humidity by about 5%.

 This is why the test was stopped after fourteen days and the container deposited in the preservation reactor.

 After a further fourteen days, the withdrawal was gone and, beyond that, the swelling was sufficiently manifest to qualify the granulate reagent. Note, however, that a significant part of the swelling was lost initially, during the first fourteen days.

 These tests therefore show that, although the preservation reactor plays an essential role in obtaining reliable test conditions, it is nevertheless preferable to place the test pieces in sealed containers themselves arranged inside the reactor.

 Of course, if it is preferable to use the operating conditions just described, they could however be subject to changes.

Claims (4)

 I. Installation for the implementation of a test method for mortars and concretes in which test pieces (2 made under standardized conditions from the aggregates and the cement to be studied are placed in sealed containers (l) stored at a predetermined temperature, the specimens being removed from their container (l) at certain times, subjected to a swelling measurement, then placed back into the container which is closed until the next expiry, the installation comprising means of manufacture of the test pieces and a plurality of sealed containers (1) for the storage of the test pieces (2) and being characterized in that it further comprises a specimen storage reactor consisting of a heat-insulated enclosure (3) provided with an opening (32) for loading the containers (1), closed by a sealed door (33) and comprising, at its lower part, a grid (36) for supporting the containers (1) extending horizontally above a liquid reserve (37) formed in the bottom of the enclosure (3) and means (4) for heating the water supply associated with a heating control system comprising at least a temperature measuring member (43) placed in the center of the enclosure (3) and at the middle of the containers (i) and a device (42) for the controlled control of the heating means (41, 4) according to the measured temperature for maintaining the temperature at a constant level.  2. Test installation according to claim 1, characterized in that the heating means of the liquid reserve are constituted by a set of electrical resistances (4) extending towards the inside of the enclosure ( 3) from the side wall (31) so as to plunge into the liquid (32) and associated with a system (41, 42, 43) for regulating the supply current.  3. Installed installation according to one of claims 1 and 2, characterized in that each sealed container (1) is equipped with a grid (14) for supporting specimens placed at a certain height above the bottom ( li) and overcoming a reserve of liquid (16).  4. Test method for mortars and concretes in which test specimens 52) are made from the aggregates and the cement to be studied under standard conditions, the specimens (2) are placed in sealed containers (1) kept at a temperature determined and, at regular intervals, the specimens (2) are removed, their swelling is measured and then placed back in the sealed container (1) until the next expiry, characterized by the fact that the sealed containers (1 ) containing the specimens are placed in a closed enclosure (3) insulated, and above a water reserve (37) and that the temperature prevailing in the chamber and measured in the center of the enclosure and at the level of medium of the containers, is kept constant by a heating of the water reserve (37), regulated according to said measured temperature.