FR2781568A1 - Method for forecasting the mechanical characteristics of a cement based material - Google Patents

Abstract

The method incorporates a calibration stage, consisting of submitting some test pieces made from the same material to a compression in a manner that establishes, for the element and for a family of given materials, a correlation relationship between the hardening time of non-compressed test pieces and the hardening times of compressed test pieces, leading to a similar value of the said mechanical characteristic. A method for forecasting at least one mechanical characteristic is possessed by a material obtained by casting, at the end of a determined hardening time. The material incorporates an element, notably of cement, that is the source of a dissolution precipitation reaction that leads to a hardening effect.

Description

The present invention relates to a method for rapidly predicting

  after they have been poured, the mechanical characteristics which materials, in particular cement-based, will have at different determined curing ages, and in particular at their standardized ages, namely, at seven days,

  twenty eight days, and ninety days.

  We thus know, for each type of cement, at least the most conventional, and each standardized addition, such as sand or standardized gravel, the hardness that will have on determined dates and in particular on standardized dates, the mortars and concretes obtained. from this cement. We also know that the cost of mortars and concrete depends for the most part on the amount of cement they contain. Insofar as, for certain specific applications, it is not necessary to have a mortar or a concrete having the predetermined maximum normalized characteristics, it is advantageous to replace a certain percentage of cement by a lower addition cost. However, these additions can be of very diverse origin, for example due to their location or their supply conditions. We are then faced with the problem of knowing the mechanical characteristics of this mortar or

  concrete at the standard ages mentioned above.

  To do this, it is of course possible to carry out quite conventional tests in this field, by making out of these materials, and according to a well-defined standardized protocol, test tubes of standardized dimensions and shapes Dsk 201 which will be tested when they have respectively reached said determined curing age, by mechanical strength tests such as in particular

  compression and / or bending tests.

  A disadvantage of such a method is that, by definition, it extends over time over long periods, which imposes on the user particularly long response times, which have the effect of lengthening the time periods. of construction and, consequently, the cost thereof The aim of the present invention is to propose a method making it possible to determine, with extremely short response times, the mechanical characteristics which such non-standardized materials will possess, in particular based on cement, at determined curing ages, and

  especially at their standardized ages.

  The present invention thus relates to a method of predicting at least one mechanical characteristic that a material obtained by casting will have, after a determined hardening time (T), this material comprising an element, in particular cement, source of a precipitation dissolution reaction leading to hardening, in which specimens of this material are produced and said mechanical characteristic thereof is measured at determined hardening dates of the specimens, characterized in that it comprises a step d calibration, consisting in subjecting test pieces made of the same material to a compression extending substantially from the end of the casting until at least the moment of development of the Dsk 201 resistances in this material, so as to establish, for said element and for a given family of materials, a correlation relation between the hardening time (T) of non-specimens and the hardening time (t) of the compressed test pieces, leading to the same value

  of said mechanical characteristic.

  The users will implement a use step during which: - after the determined hardening time (t), the said mechanical characteristic possessed by a test tube of a material belonging to the same family subjected to the said compression is measured, - we deduce from the value of this mechanical characteristic, using the correlation relation, the value of the mechanical characteristic that the material will have

  after a determined hardening time (T).

  The present invention is particularly interesting in that it allows a designer, engineer or architect, because of the rapid knowledge that he will have the technical characteristics of the specific material.

  he wants to use, to adjust the composition of it

  ci so that it meets the specifications imposed on it, while keeping this material a minimum cost price. Preferably, means will be used, at least during the compression phase, capable of eliminating

  the water exuded by the material during said compression.

  Dsk 201 According to the invention, it is possible to use as mechanical characteristic the compressive strength or

  the flexural strength of the material.

  An embodiment of the present invention will be described below, by way of nonlimiting example, with reference to the appended drawing in which: FIG. 1 is a perspective view of an example of a mold usable for making the casting of test tubes

measure according to the invention.

  Figure 2 is a cross-sectional view of the mold shown in Figure 1 during a molding operation. FIG. 3 is a graph representing the variation in the compressive strength of specimens' produced from a CPA55 cement, as a function of the value of the compression applied to the specimen during casting and this at the end respectively 1 day, 2 days, 7

  days, 28 days and 90 days of hardening.

  FIG. 4 is a graph representing the variation as a function of time of the compressive strength of test pieces made of a mortar made from a CPA HP cement which were respectively obtained in a conventional manner and by subjecting the material to

  during its casting to compression.

  FIGS. 5a and 5b are graphs which represent the compressive strength of mortar specimens having been subjected to compression during casting, after 7 days and 2 days of hardening as a function of the resistance of conventional specimens in identical Dsk 201 materials after 90 days and 28 days of hardening for mortars in which 30% by weight has been replaced

cement by various sands.

  Figures 6a and 6b are graphs of the same type as those of Figures 5a and 5b in which the product

  Cement substitution is made up of fly ash.

  Figures 7a and 7b are graphs of the same type as those of Figures 5a and 5b in which the product

  Cement substitution is made up of slag.

  FIG. 8 is a graph showing the variation as a function of time of the compressive strength of test pieces made of a mortar obtained from a CLK-45P cement which were respectively obtained in a conventional manner and by subjecting the material at

  during its casting to compression.

  FIG. 9 is a graph representing the variation as a function of time of the compressive strength of test pieces made of a mortar obtained from a CPJL cement (CPJ-Laitier) which were respectively obtained in a conventional manner and in submitting

  the material during its casting to compression.

  FIG. 10 is a graph representing the variation as a function of time of the flexural strength of test pieces made of a mortar made from a CPJL cement (CPJ-Dairy) which were respectively obtained in a conventional manner and in subjecting the material to

  during its casting to compression.

  The tests which will be described below and which have been carried out by the applicant will establish that there is Dsk 201 for a given cement a correlation relation between on the one hand the hardening times necessary for a material, (such as '' a mortar or concrete), made from this cement and poured. following standard conditions, has a determined mechanical characteristic, (and in particular a certain resistance to compression or bending), and on the other hand the times hardening of a material belonging to the same family and having undergone compression during casting, under specified conditions described

below.

  These tests will also establish that the families of these materials are defined by the nature of the products that we have to replace the cement from which these

materials are made up.

  First of all, as shown in FIG. 3, we studied the effect, on the compressive strength of a mortar, namely a CPA-55, of a compression exerted on it as soon as it is poured and extending until at least the moment of the development of resistances in this

mortar.

  The compressive strengths of this mortar were measured on test pieces which were poured into a standard type mold, represented in FIGS. 1 and 2, which essentially consists of a base plate 3 on which two plates are fixed. transverse extremes 5, held thereon by bolting, between which are arranged and maintained four longitudinal plates 7 which thus define three housings. Each of these Dsk 201 housings is closed by a cover 8 which fits between

  the transverse walls 5 and the longitudinal plates 7.

  In the present case, porous plates 9 intended to absorb the exuded water during molding, as explained below, have previously been placed in the bottom of the mold and also under the covers 8. The mortar was poured into the mold 1 and it was placed in a machine capable of exerting on each upper cover 8 a vertical compressive force F, as shown in FIG. 2. The mortar was then compressed from the start of its casting up to an instant tr, at which the development of resistances begins therein and which the person skilled in the art knows perfectly how to determine. A series of test pieces was thus poured and allowed to harden respectively 1 day (curve a), 2 days (curve b), 7 days (curve c), 28 days (curve d) and 90 days (curve e ), that is to say durations of hardening which correspond to durations of standard type. It can be seen that for this mortar the compressive strength is maximum for a pressure

  of 3 MPa, regardless of the curing time considered.

  The tests which will be described below in which a mortar is subjected to compression as soon as it is poured have thus

  were carried out at a pressure of 3 Mpa.

  EXAMPLE 1: CEMENT-BASED MORTAR CPA HP

  Initially, a mortar was thus made from the same cement, namely a CPA HP cement.

  standardized by adding a standardized sand thereto.

  Dsk 201 This mortar was separated into two batches and, from the first batch, a first series of test pieces was poured in accordance with the standard in force in this field (standard CEN 196-1 1987F) in a mold of the type the one described above. We thus obtained a series of test pieces of standardized type which were left to harden during the standardized times, namely 7 days, 28 days and 90 days, and we then measured, at these different states of aging,

their compressive strength.

  This same mold 1 was then used to pour, from the second batch of mortar, a second series of test pieces, after having placed in the bottom of the mold as well as under the lids 8, porous plates 9 intended to absorb the water exuded during molding. These test pieces were subjected to compression during their casting as mentioned previously. These test pieces were then left to harden for shorter times than for the first series, which are respectively 30 hours, 50 hours, and 7 days, then, as for the

  previous, they were subjected to compression tests.

  The results obtained have been recorded in table I below and there is shown in FIG. 4 the variation in the compressive strength Rc of the two sets of test pieces as a function of the hardening time of the mortar which constitutes them. . The values corresponding to the first series of test pieces (obtained without compression) being represented on curve a and those corresponding to Dsk 201 the second series of test pieces (obtained without compression) being represented on curve a 'TABLE I (Figure 4 ) CPA - HP cement-based mortar - Compression Time Test Compressive strength (MPa) hardening Uncompressed mortar Compressed mortar 1.25 days (30 hours) / 49.2 2.1 days (50 hours) / 63.11 7 j 45.4 73.8 28 d 64.2 99 d 74, 0 109.3 It can be seen in this FIG. 4 that the compressive strength Rc of the test pieces from the second batch of mortar, that is to say the test pieces the mortar of which was subjected to compression during casting, have a compressive strength after 7 days equal to that of the first batch of test pieces after the standard hardening time of 90 days. Similarly, the test pieces subjected to compression have respectively after 4 days and 1.25 days compressive strengths identical to that of

  first batch after 28 days and 7 days respectively.

  The advantage of the present invention being in particular to allow the substitution of part of the cement forming these mortars by additions of a lower cost, we have, in a second step, substituted for 30% by weight of the cement contained in these mortars of the elements made up of four different sands Si, S2, S3, S4 and we renewed the

previously described tests.

  Dsk 201 FIG. 5a shows, for each of these sands, the 7-day resistance of the compressed mortar as a function of the 90-day compressive strength of the uncompressed mortar. It can be seen that the representative points S'1, S'2, S'3, S'4 are perfectly aligned. Similarly, FIG. 5b shows, and for the same sands, the resistance to 2 days of the compressed mortar as a function of the resistance to 28 days of the uncompressed mortar. The representative points S "il, S" 2, S "3, S" 4 are also distributed on a straight line. We thus obtain a correlation for a given cement and a family of additions

  data, namely the family of sands.

  It is understood, under these conditions that a user who wishes to use a mortar which must meet a given specification and who wishes to save on the cost of the cement used, may replace a certain percentage of it by the same percentage of sand, and then quickly test the mechanical qualities of the mortar obtained by applying the correlation which, for this given cement and for this family (namely the sands) will always be the same, so as to verify that it is at most close to its specifications. The rapid response times allowed by the present invention will thus allow it to ensure the best compromise between the cost of the mortar manufactured and the mechanical characteristics thereof. Similar type tests have been carried out using fly ash as part of

substitution of cement.

  Dsk 201 From a standardized mortar made of the same CPA-HP cement, four mortars were thus formed, replacing 30% by weight of the cement with four fly ash of different natures CV1, CV2, CV3, CV4. Tests of the type of those previously carried out were then carried out and, in each of these mortars, the resistance to 7 days of the compressed mortar is shown respectively in FIG. 6a as a function of the resistance to 90 days of the uncompressed mortar . It can be seen that the representative points CV'1, CV'2, CV'3, CV'4 are perfectly aligned. Similarly, FIG. 6b shows, for the same fly ash, the resistance to 2 days of the compressed mortar as a function of the resistance to 28 days of the uncompressed mortar. The representative points CV "1, CV" 2, CV "3, CV" 4 are also distributed on a straight line. Thus a correlation established for a fly ash could be

  kept for any other fly ash.

  We also note that the correlation coefficients are the same for fly ash and for sands. It was also established that these correlation coefficients could be adopted for elements of substitution for cement made up of limestones, so that these elements belong to the same family as sands and fly ash, namely that of non-additives.

assets.

  Identical tests were also carried out using slags L1, L2, L3, L4, as partial substitutes for cement in a proportion as previously of 30%. The results were recorded on the Dsk 201 figures 7a and 7b which represent respectively the resistance at 6 days and at 4 days of the compressed mortar as a function of the resistances at 90 days and at 28 days of the uncompressed mortar. The correlation is well preserved for all types of slag, but the correlation coefficients are different from those obtained for sands and fly ash, so that the slags belong to another

  family, namely that of active additives.

  We could of course apply this

  invention to any other type of cement.

  The same type of test was thus carried out with a CLK 45 cement (CLK CEM III / C)

  EXAMPLE 2: CLK 45 CEMENT-BASED MORTAR (CLK CEM III / C)

  The same type of tests were carried out as those carried out previously with another standardized mortar consisting of a CLK 45 cement (CLK CEM III / C) and standardized sand. The results are shown in Table II below and the corresponding graph is the subject of the

figure 8.

  As in the previous series of tests, it can be seen that the mortars subjected to compression during casting have, after 3 days, 5 days and 12 days, respective compressive strengths which are identical to those obtained by the standardized process. from the prior art after 7 days, 28 days and 90 days. We obtain here a correlation whose coefficients are different due to the difference of

nature of the cement.

Dsk 201 TABLE II (Figure 8)

  Cement-based mortar CLK 45 (CLK CEM II / C) -

  Compression test Time of Resistance to compression (MPa) hardening Uncompressed mortar Compressed mortar

1.75 / 35.9

4 / 47.2

6 / 53.4

7 33.9

28 47.6

52.5

  Of course, as in the case of CPA-HP cement, a given percentage of the cement can be replaced by inactive additives such as sand, fly ash or limescale, or by active additives such as slag. We also know that there are cements which contain original ash or slag, such as

  for example CPJ Ash cements and CPJ- cements

  Dairy. With such cements, we do not know the mechanical characteristics of the standardized mortars that they make it possible to obtain, so that we are forced, before their use, to carry out tests of the type mentioned above. The present invention is

  of course applicable to such cements.

  EXAMPLE 3: CEMENT-BASED MORTAR CPJL (CEM II / B)

  , Tests were carried out of the same type as those carried out previously with another standardized mortar Dsk 201 consisting of a CPJL cement, that is to say a cement containing slag, and standardized sand. The results are shown in Table III below and the graph

  corresponding is shown in Figure 9.

TABLE III (Figure 9)

  CPJL cement-based mortar (CPJ CEM II / B) -

  Compression test Time of Resistance to compression (MPa) hardening Uncompressed mortar Compressed mortar

3/40

I 53.3

7 36.8

12 / 68.5

28 53.4

68.4

  As in the previous series of tests, it can be seen that the mortars subjected to compression during casting have, after 1.75 days, 4 days and 6 days, respective compressive strengths which are identical to those obtained by the standardized process of the prior art after 7 days, 28 days and 90 days. A correlation is obtained here, the coefficients of which are different due to the difference in the nature of the cement. Of course the correlation relationship could also be established on the basis of another mechanical parameter such as in particular the bending strength of the material. Dsk 201 A series of tests was thus carried out from which the variation in the RF flexural strength of two series of test pieces made in a CPJL cement-based mortar was measured as a function of the time of O hardening of this mortar. A first series of test pieces was produced without compression (curve a) and the other series of test pieces was obtained under compression in the

  conditions described above (curve a ').

  The results of these measurements and the variation as a function of the curing time of the flexural strength RF of

  these test pieces have been shown in FIG. 10.

  TABLE IV (Figure 10) CPJL cement-based mortar - Bending test Time of Resistance to compression (MPa) hardening Uncompressed mortar Compressed mortar Demoulding 3, 1 4.8 h 1.25 d / 5.0 h 2.1 d / 6.3 7 d 6.0 8.4 28 d 7.6 9.9 d 7.8 10.4 It can be seen on curves a and a 'in FIG. 10 that the test specimens produced under compression have respectively at the end of 2 days and 4.5 days the same flexural strength as the test pieces produced without compression after the standard durations of 7 days and 28 days. There is therefore also a correlation between the Dsk 201 curing times of respectively compressed and uncompressed cement-based materials and resulting in

  the same resistance to bending.

  One could of course establish correlation relations of the same type from materials highlighting

works with other cements.

  Although the various examples of implementation of the invention relate to mortars, it has been established that the results of the invention are also verified in the

case of concrete.

  The present invention therefore proves to be particularly advantageous for designers, engineers or architects who can extremely quickly either verify for themselves the mechanical characteristics of the mortars or concrete obtained from these cements, or determine the mechanical characteristics of specific mortar or concrete in which the standardized quantities of cement have been partially replaced by inactive additives such as sand, fly ash or limestone, or by active additives such as slag. The present invention will also be of interest to cement manufacturers since it will enable them to make available to their customers, for each of these cements, correlation tables enabling them to obtain according to the

  additives used the previously mentioned results.

  The results of the invention will also be found when using cements of other Dsk 201 elements which may be the source of a reaction of

  dissolution precipitation leading to hardening.

Dsk 201

Claims (8)

  1.- Method for predicting at least one mechanical characteristic that a material obtained by casting will possess, after a determined hardening time (T), this material comprising an element, in particular cement, source of a reaction of dissolution precipitation leading to hardening, in which test pieces are made of this material and the said mechanical characteristic thereof is measured at determined hardening dates of the test pieces, characterized in that it comprises a calibration step, consisting in subjecting test pieces made of the same material to compression extending substantially from the end of the casting until at least the moment of development of the resistances in this material, so as to establish, for said element and for a family of given materials, a correlation relation between the hardening time (T) of the uncompressed test pieces and the hardening time (t) of the compressed specimens, leading to the same value   of said mechanical characteristic.   2.- Method according to claim 1 characterized in that it comprises a step of use during which: - after measuring the hardening time (t) determined, said mechanical characteristic possessed by a test piece of a material belonging to the same family subjected to said compression, Dsk 201 - we deduce from the value of this mechanical characteristic, using the correlation relation, the value of the mechanical characteristic that the material will have   after a determined hardening time (T).   3.- Method according to any one of   previous claims characterized in that one realizes   a material from said family by substituting part of the cement an additive.   4.- Method according to claim 3 characterized in that the additive is a sand, a fly ash or a slag.   5.- Method according to one of claims   previous characterized in that the compression value to which the material is subjected at the end of the casting is around 3 Mpa.   6.- Method according to claim 1 characterized in that the mechanical characteristic of the material is its compressive strength.   7.- Method according to claim 1 characterized in that the mechanical characteristic of the material is its resistance to bending.   8.- Method according to one of claims   previous characterized in that one implements, at least during the compression phase, means capable of removing the water exuded by the material during said compression. Dsk 201