Activated pulverised glass as an additive for mortars and cement, and related cementitious products

Abstract

The present invention relates to a cementitious composition adapted to form mortars or cements comprising glass as an additive having reduced tendency to reaction with alkali, characterized in that said glass is obtained by grinding and subsequent washing with water.

Claims

1. A cementitious composition suitable to form mortars or concretes including at least one hydraulic binder, water, optionally one or more aggregates, and comprising activated glass particles as an addition to mitigate an alkali-aggregate reaction, wherein a mitigation effect of the alkali-aggregate reaction is improved by activated glass particles obtained by firstly grinding to pulverization with an average diameter ranging from 10 and 200 micron, and an activation step consists of a subsequent washing of the grinded glass particles with fresh water that is renewed before it is saturated by the release of alkali into water by the finely subdivided glass, wherein the glass particles after grinding and washing with water have a ratio A between the specific surface SS.sub.BET, expressed in m.sup.2/g, and the laser specific surface Sv, expressed in m.sup.2/cm.sup.3, by the density, r, expressed in g/cm.sup.3, defined as activation parameter A=SS.sub.BET[m.sup.2/g]/Sv[m.sup.2/cm.sup.3]. [g/cm.sup.3], in a range from 1.9 to 4.0.

2. The cementitious composition as claimed in claim 1 wherein the grinded glass particles undergo washing with water carried out by a series of subsequent washings.

3. The cementitious composition as claimed in claim 1 wherein said activation parameter A ranges from 2.0 to 3.0.

4. The cementitious composition as claimed in claim 1 wherein said washing with water is carried out through the steps of: suspending in water the grinded glass particles separating the glass particles by settling and filtration submitting the glass particles to at least a further suspension in water followed by separation and filtration of the glass particles oven drying of the glass particles so washed.

5. The cementitious composition as claimed in claim 4 wherein said washing with water is carried out by the steps of: suspending in water the grinded glass particles in a concentration of 100 g/ liter and stirring for 24 hours separation of the glass particles by settling and filtration performing two further washings in water according to the same suspending, settling and filtration procedure oven drying at 105 C. of the glass particles so washed.

6. The cementitious composition as claimed in claim 1 including at least a hydraulic binder, water and optionally one or more aggregates, and/or one or more mineral additions, and/or fibres for cements, and/or one or more additives, wherein said glass particles as an addition have an amount by weight equal to 20% of said hydraulic binder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 to 4 attached hereto show electron micrographs of the samples of glass described in Example 3 below.

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLES

(2) In the examples described, activated ground glass according to the present invention has been used for the preparation of mixtures in mortar and cement by using directly in the mixer.

(3) Evaluation of the performances of the cement in relation to the AAR behaviour has been performed by testing both in mortar and in cement.

(4) For the purpose of demonstrating the efficacy of the invention, aggregate containing reactive silica and therefore susceptible to AAR has been used; the content of reactive species in the various factions of aggregates was measured as on average 23% of the total aggregate content.

(5) Into the mixtures of mortar and cement, the source of alkali was introduced in the form of NaOH dissolved in the mixing water in the quantity of 1% by weight, expressed as Na.sub.2O referred to the binder.

(6) Mortar test pieces of dimensions 4 cm4 cm16 cm and cement test pieces of dimensions 80 mm80 mm280 mm were manufactured.

(7) Performance was determined by measuring the expansion of the test pieces, it being desirable according to the purposes of the invention to obtain the lowest possible expansion values.

(8) In the case of testing in mortar, the test pieces were exposed in a 1N solution of NaOH at 80 C., having been turned out of the mould after 24 hours. These conditions should therefore be considered particularly severe both due to the elevated temperature and because of the continuous supply of alkali during the exposure.

(9) In the case of test pieces made of cement, the following conditions of exposure were used having turned out the test pieces from the mould after 24 hours: 20 C. and 95% RH 38 C. and 100% RH

(10) Chemical characterisations of the glass would also performed by fluorescence and SEM microanalysis.

Example 1

(11) Three cements of rheological class S3 were manufactured with CEM II/A-LL 42.5R, which cements had the following proportions in mixture: water/binder ratio equal to 0.44 binder content equal to 420 kg/m.sup.3

(12) comprising NaOH in a quantity equal to 1% of binder expressed as Na.sub.2O and containing respectively in a proportion by weight of 20% of binder: activated pulverised glass (APG) according to the present invention non-activated pulverised glass (preAPG), used as a reference material, outside the scope of the present invention, having an activation parameter A as defined above below 1.9.

(13) Also given, as reference material no. 1, is a cement manufactured without addition of glass, wherein the weight corresponding to the missing additive is made up with cement.

(14) The chemical compositions of both glasses are presented in Table 1. The BET characterisations and the laser granulometry results are shown in Table 2.

(15) As shown in Table 3, in the case of maturation at 38 C. and 100% RH and in Table 4, in the case of maturation at 20 C. and 95% RH, the use of activated pulverised glass has led to a reduction in the deformation (expansion) of the test pieces relative to that demonstrated by the reference cements, in particular relative to reference material No. 1.

(16) This expansion reduction is to be considered as demonstrated by the technical effect of the invention. The activated pulverised glass was obtained from pulverised glass in the following way: suspending the pre-APG pulverised glass in water in a concentration of 100 g/liter and stirring for 24 hours separating the phase by natural settling/filtration performing two further washings according to the same procedure oven drying at 105 C. of the residue obtained.

(17) TABLE-US-00001 TABLE 1 APGactivated preAPGpulverised pulverised glass glass (reference 1) (present invention) Reactive SiO.sub.2 [%] 52.88 54.93 SiO.sub.2 [%] 69.0 69.1 Al.sub.2O.sub.3 [%] 2.70 2.62 Fe.sub.2O.sub.3 [%] 0.36 0.36 CaO [%] 8.84 8.86 MgO [%] 1.44 1.59 Na.sub.2O [%] 15.6 15.3 K.sub.2O [%] 0.84 0.82

(18) TABLE-US-00002 TABLE 2 APGActivated preAPGpulverised pulverised glass glass (reference 1) (present invention) SS.sub.BET m.sup.2/g 0.59 1.07 A = SS.sub.BET/Sv .Math. 1.5 3.0 Density - g/cm.sup.3 2.540 2.544 Laser - Sv m.sup.2/cm.sup.3 0.99 0.92 (specific surface) Laser -xp m 16.7 17.3 (mean diameter) Laser - n 1.23 1.28 (amplitude)

(19) TABLE-US-00003 TABLE 3 Maturation at 38 C. and 100% RH Deformation (expansion) 18 26 39 52 [m/m] weeks weeks weeks weeks Reference no 1 (no additive) 2411 2413 2477 2564 Reference no 2 836 911 1013 1255 (preAPGPulverised glass) APGActivated pulverised 282 471 636 786 glass (present invention)

(20) TABLE-US-00004 TABLE 4 Maturation at 20 C. and 95% RH Deformation (expansion) 18 26 39 52 [m/m] weeks weeks weeks weeks Reference no 1 (no additive) 1914 1882 1939 2018 Reference no 2 554 611 739 914 (preAPGPulverised glass) APGActivated pulverised 43 82 89 179 glass (present invention)

Example 2

(21) Four mixtures were prepared in mortar containing CEM II/A-LL 42.5R and having the following proportions in mixture: water/binder ratio=0.51 aggregate/binder ratio=2.25

(22) and containing NaOH in a quantity equal to 1% of binder expressed as Na.sub.2O and containing two different activated pulverised glasses according to the present invention (V1 and V2), in a proportion by weight of 20% of binder.

(23) Also given as a reference material is a mixture wherein the weight corresponding to the missing additive is made up with cement.

(24) The chemical compositions of the glass are presented in Table 5 and the results of the granulometric and laser analyses are presented in Table 6, together with the respective analyses of the pulverised glass prior to activation (pre-V1 and pre-V2 respectively), which are outside the scope of the present invention, having an activation parameter A below 1.9.

(25) Table 7 shows the deformations (expansions) measured for the various manufactured mixtures. Also mentioned therein as a reference is the APG glass already described in example 1.

(26) Table 7 also reveals that the glass of the present invention results in reduced expansion as compared with the reference.

(27) The activated pulverised glass was obtained in the following way: suspending the pulverised glass in water in a concentration of 100 g/liter and stirring for 24 hours separating the phase by natural settling/filtration performing two further washings in water according to the same procedure oven drying at 105 C. of the residue obtained.

(28) TABLE-US-00005 TABLE 5 preV1 preV2 (outside (outside the scope of the scope of V1 V2 the present the present (present (present invention) invention) invention) invention) Reactive 34.93 43.43 38.98 45.59 SiO.sub.2 [%] SiO.sub.2 [%] 69.5 69.2 69.3 69.4 Al.sub.2O.sub.3 [%] 2.51 2.58 2.39 2.54 Fe.sub.2O.sub.3 [%] 0.33 0.34 0.34 0.34 CaO [%] 8.63 8.64 8.69 8.73 MgO [%] 1.42 1.44 1.55 1.58 Na.sub.2O [%] 15.7 15.7 15.5 15.2 K.sub.2O [%] 0.86 0.85 0.85 0.85

(29) TABLE-US-00006 TABLE 6 preV1 preV2 (outside (outside the scope the scope of the of the V1 V2 present present (present (present invention) invention) invention) invention) SS.sub.BET m2/g 0.370 0.384 0.434 0.739 A = SS.sub.BET/ 1.8 1.5 2.0 2.8 Sv .Math. Density - g/cm.sup.3 2.541 2.542 2.546 2.544 Laser - Sv m.sub.2/cm.sub.3 0.51 0.65 0.56 0.67 (specific surface) Laser -xp m 47.74 30.09 38.17 28.48 (mean diameter) Laser - n 1.06 1.16 1.15 1.2 (amplitude)

(30) TABLE-US-00007 TABLE 7 Deformation (expansion) Maturation in NaOH 1N at 80 C. [m/m] 7 days 14 days 28 days Reference 2919 4784 8081 V1 (present invention) 2213 3225 4419 V2 (present invention) 1888 2481 4594

Example 3

(31) From the qualitative point of view, an activated pulverised glass according to the present invention has a surface texture different from that of a non-activated pulverised glass. The non-activated pulverised glass being obtained by crushing processes, the fracture surfaces of the non-activated particles show fracture lines FL1 derived from the crushing process that can be demonstrated using an electron microscope, as shown in FIG. 1.

(32) As shown in FIG. 2, following the activation process, the facture lines FL2 present on the surfaces of the activated particles of pulverised glass are less evident or even non-demonstrable.

(33) More particularly, the activated pulverised glass FIG. 2 was obtained from the pulverised glass of FIG. 1 in the following way: suspending the pulverised glass in water in a concentration of 100 g/liter and stirring for 24 hours separating the phase by natural settling/filtration performing two further washings in water according to the same procedure oven drying at 105 C. of the residue obtained.

(34) Another example of non-activated pulverised glass is presented in FIG. 3. The non-activated pulverised glass being obtained by crushing processes, the fracture surfaces of the non-activated particles show fracture lines FL1 derived from the crushing process that can be demonstrated using an electron microscope.

(35) A corresponding case of activated pulverised glass is presented in FIG. 4. As shown in FIG. 4, following the activation process, the fracture lines FL2 present on the surfaces of the activated particles of pulverised glass are less evident or even non-demonstrable. In general terms, according to the present invention it is surprising that a treatment of the pulverised glass by a series of washings with water can increase its capacity to mitigate the AAR.

(36) This technical effect is all more surprising considering the merely marginal impact of the washing operations on the chemical composition of the glass, more particularly on the proportion of silica and on the content of alkali.

(37) It is therefore possible to use the technical solution proposed in the present invention, for example, to reduce the costs associated with the process of compression comminution, which would make it necessary to obtain a non-activated glass having comparable performances, when such a pulverised glass is not already available as a byproduct of an industrial process.

(38) Furthermore, the release of alkali into water by finely subdivided glass can be very rapid and can lead to a rapid saturation of the solution in contact, and for this reason renewal is necessary to achieve the desired degree of activation of the glass. Such alkaline aqueous solutions have a potential use in the construction materials sector as activators of ground blast-furnace slag, even if the latter is used as an additive to cement in accordance with the harmonised European standard EN 15167.

(39) Alkaline aqueous solutions could also be used in the construction materials sector for markedly reducing CO.sub.2 associated with the production of clinker associata alla produzione del clinker, even if the following reactions are made the basis of the process of eliminating installation fumes:
Na.sub.2O.sub.(aq)+CO.sub.2(g).fwdarw.Na.sub.2CO.sub.3(s)