Cementitious composition for forming mortars or concretes having reduced tendency to react with alkali

Abstract

The invention has as object a cementitious composition for forming mortars or concretes having reduced tendency to react with alkali, characterized in that it comprises as additive at least a compound of general formula:
[RN(CH.sub.2COOH).sub.n].sub.x(I)
R being an aliphatic or aromatic hydrocarbon chain, n=2 or 3 and x=1 or 2.

Claims

1. A method of reducing the tendency of mortars or concretes to react with alkali and reducing the deformation by expansion resulting therefrom, wherein the method includes; preparing a cementitious mixture; adding an acid of formula:
[RN(CH.sub.2COOH).sub.n].sub.x(I) where R being is aliphatic or aromatic hydrocarbon chain, n=2 or 3 and x=1 or 2, and an addition selected from the group consisting of fly ash, microsilica, granulated blast furnace slag, powdered glass, to the cementitious mixture; wherein said cementitious mixture does not include any salts of ethylene-diamino-tetraacetic acid; and forming the mortars or concretes from the combined mixture.

2. The method according to claim 1 wherein said acid of formula (I) is ethylenediaminetetraacetic acid, or EDTA, of formula:
(CH.sub.2COOH).sub.2N(CH.sub.2).sub.2N(CH.sub.2COOH).sub.2.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Characteristics and advantages of the present invention are described in grater detail in the following examples, provided by way of a non-limiting example of the present invention.

EXAMPLES

(2) In the described examples, EDTA was used for the preparation of mortar mixtures according to the invention, dissolving it in the mixing water in the mixer.

(3) Aggregate containing reactive silica and that is therefore susceptible to AAR was used; the reactive species content was 25% on average. NaOH was introduced to the mixtures as an alkali source, dissolved in the mixing water in the content of 1% by weight expressed as Na.sub.2O referring to the binder.

(4) Mortar specimens were prepared having 4 cm4 cm16 cm dimensions were prepared. The determination of performance was performed by measuring the deformation of the specimens, 24 hours from casting, under the following conditions: in a 1N of NaOH solution at 80 C., onerous both due to the high temperature and due to the continuous supply of alkali during exposure. in water at 60 C., onerous on account of the acceleration of the speed of the AAR due to the high temperature exposure.

Example 1

(5) The effect of EDTA in modifying AAR was evaluated in mortar mixtures containing fly ash, as shown in Table 1, using strongly accelerating conditions of exposure (NaOH 1N at 80 C.). or performance of the tests, the following proportions of mixture were adopted using a cement CEM II/A-LL 42.5 R: water-binder ratio equal to 0.55binder weightNaOH dissolved in the mixing water in a proportion of 1% by weight expressed as weight of Na.sub.2O relating to the binder, understood as the sum of the cement and pozzolanic addition. EDTA was added to one of the two mixtures in a proportion of 0.28% by weight of binder, equal to a value of 0.07% by weight referring to the mortar. A second mixture wherein EDTA was not added is shown as reference. It can be observed that using EDTA, the expansions were significantly reduced, the desired technical effect thereby being achieved.

(6) TABLE-US-00001 TABLE 1 Deformation (expansion) Maturation in NaOH 1N at 80 C. [m/m] 7 days 14 days 28 days 90 days Reference 581 931 1313 2144 EDTA 0.07% 331 463 731 1200 (present invention)

Example 2

(7) The positive effect of EDTA in reducing AAR was verified from tests on mortar mixtures containing fly ash, as shown in Table 2, using accelerating conditions of exposure (water at 60 C.).

(8) The following mixture proportions, using CEM II/A-LL 42.5 R, were adopted for performance of the tests: water/binder ratio equal to 0.55 aggregate/binder ratio equal to 2.25 fly ash in a proportion of 20% by weight of binder NaOH dissolved in the mixing water in a proportion of 1% by weight expressed as weight of Na.sub.2O referring to the binder.

(9) EDTA was introduced into one of the two mixtures in a proportion of 0.28% by weight of binder, equal to 0.07% by weight referring to the mortar. A second mixture wherein EDTA was not added is shown as reference.

(10) It can be observed the expansions were significantly reduced using EDTA.

(11) TABLE-US-00002 TABLE 2 Deformation (expansion) Maturation in water at 60 C. [m/m] 7 days 14 days 28 days 90 days Reference 210 150 191 263 EDTA 0.07% 110 63 47 113 (present invention)

Example 3

(12) The positive effect of EDTA in reducing AAR was verified by tests on mortar mixtures containing powdered glass as addition. The physicochemical characteristics of the powdered glass in question are shown in Table 3 and Table 4.

(13) TABLE-US-00003 TABLE 3 reactive SiO.sub.2 [%] 52.88 SiO.sub.2 [%] 69.0 Al.sub.2O.sub.3 [%] 2.70 Fe.sub.2O.sub.3 [%] 0.36 CaO [%] 8.84 MgO [%] 1.44 Na.sub.2O [%] 15.6 K.sub.2O [%] 0.84

(14) TABLE-US-00004 TABLE 4 BET m.sup.2/g 0.59 Density - g/cm.sup.3 2.540 Laser - Sv (specific surface) m.sup.2/cm.sup.3 0.99 Laser - xp (average diameter) m 16.7 Laser - n (amplitude) 1.23

(15) The following mixture proportions were adopted for performance of the tests: fly ash in a proportion of 20% by weight of binder aggregate/binder ratio equal to 1.88 water/binder ratio equal to 0.49 NaOH dissolved in the mixing water in a proportion of 1% by weight expressed as weight of Na.sub.2O referring to the binder.

(16) Binder means the sum of cement and powdered glass.

(17) EDTA is added to one of the two mixtures in a proportion of 0.28% by weight of binder, equal to 0.1% by weight of mortar. A second mixture wherein EDTA was not added is shown as reference.

(18) Table 5 shows the results of tests of the expansion tests in mortar under strongly accelerating conditions of exposure of the AAR (NaOH 1N at 80 C.). It can be observed that by using EDTA the expansions were significantly reduced as follows.

(19) TABLE-US-00005 TABLE 5 Deformation (expansion) Maturation in NaOH 1N at 80 C. [m/m] 7 days 14 days 28 days 90 days 126 days Reference 3363 4131 5119 7456 8844 EDTA 0.1% 2494 3394 3638 4638 4644 (present invention)

Example 4

(20) The present example shows that, although EDTA is an acid, its use as an additive for concrete according to the present invention has not shown abatement of the mechanical characteristics arising from negative interactions with a strongly basic cementitious matrix.

(21) Table 6 records the determinations of dynamic elastic modulus of the same specimens for which the expansions were recorded in the preceding Table 1 and Table 2.

(22) It can be derived from Table 6 that it there has been no decrease in elastic modulus in the time, but that there has been, on the contrary, an increase between 30 and 50%, between 1 and 90 days, in all examined cases.

(23) TABLE-US-00006 TABLE 6 Dynamic Dynamic Specimens the elastic elastic expansions of modulus modulus which are shown (1 day) (90 days) in [MPa] [MPa] % increase Table 1 Reference 16691 22110 28 EDTA 17077 26191 42 Table 2 Reference 15745 28170 57 EDTA 17417 29545 52 Table 5 Reference 15269 17528 14 EDTA 15913 21895 32

Example 5 (Comparative)

(24) The effect of the use of a disodium salt of the EDTA instead of the EDTA in a cement mixture is studied in the present invention. Table 7 shows the test expansion data on mortar under strongly accelerating conditions of exposure (NaOH 1N at 80 C.).

(25) The following mixture proportions were adopted for performance of the tests: aggregate/cement ratio equal to 1.88 water/cement ratio equal to 0.49 NaOH dissolved in the mixing water in a proportion of 1% by weight expressed as weight of Na.sub.2O referring to the binder. Na-EDTA added in a proportion of 0.5% and 2% on cement, respectively equal to 0.1% and 0.3% by weight of mortar.

(26) The behaviour of a mixture used as reference wherein Na-EDTA has not been used, is also recorded.

(27) Table 7 shows only a mild effect reduction effect of the expansions with respect to the reference, probably to be attributed to the two non-complexing functional groups present in the disodium salt molecule of the EDTA.

(28) The present example highlights that the use of a salt of EDTA, in this case a disodium salt, does not produce appreciable effects on the reduction of the expansions. In addition, the use of high sodium salt contents has led to undesirable variations of the rheology and of the mechanical characteristics of the mixtures. More in particular, the higher dose of Na-EDTA (0.3%) caused a strong reduction to 1 day of the elastic modulus with respect to the reference.

(29) The use of a salt of EDTA must therefore be considered excluded from the scope of the present invention.

(30) TABLE-US-00007 TABLE 7 Deformation (expansion) [m/m] Dynamic Dynamic Use of (Maturation in NaOH Rheology elastic elastic disodium 1N at 80 C.) (Spreading) modulus modulus salt of 7 14 28 [mm] [MPa] [MPa] the EDTA days days days UNI 7044 (1 day) (7 days) Reference 3650 6006 8919 115 18461 19424 Na-EDTA 3344 5381 8106 131 18420 20215 (0.1%) (outside the present invention) Na-EDTA 4488 5975 8894 180 7809 18315 (0.3%) (outside the present invention)