EP2576475A1

EP2576475A1 - Anti-shrink agent based on surface-modified mineral nanoparticles for mortar and concrete

Info

Publication number: EP2576475A1
Application number: EP11726891.2A
Authority: EP
Inventors: Laurent Bonafous; Laure Regnaud; Angélique Vichot
Original assignee: Ciments Francais SAS
Current assignee: Ciments Francais SAS
Priority date: 2010-05-25
Filing date: 2011-05-24
Publication date: 2013-04-10
Also published as: FR2960538A1; WO2011148092A1

Abstract

The invention relates to an anti-shrink agent for a cementitious composition, such as cement paste, mortar or concrete, characterized in that it is in the form of surface-modified particles constituted of mineral nanoparticles covered with a polymer coating formed predominantly of polyalkyl oxides. It makes it possible to reduce the shrinkage by more than 65%, without retardation of setting, and also gives the mortar or concrete composition superplasticizing properties.

Description

Anti-shrinkage agent based on surface modified mineral nanoparticles for mortar and concrete

The present invention relates to the field of admixtures for cementitious compositions such as cement pastes, mortar or concrete, and more particularly the anti-shrinkage adjuvants, as well as cementitious compositions containing them.

Withdrawal, in the broad sense of the term, is the first cause of cracking of concrete or mortar structures and is therefore at the origin of many disputes on site. The solutions proposed to date to limit the shrinkage are essentially of three types: applying an effective cure to the concrete concretes to imitate the rapid evaporation of the water of constitution of the concretes, to add an expansive compound which causes a swelling ( shrinkage compensator), or use organic compounds (additives) "shrinkage reducers". The development of withdrawal reducers appeared in Japan in the early 1980s.

These shrinkage reducing agents, also known as anti-shrinkage agents, are organic products, which are soluble in water and hygroscopic. These are generally fatty acid molecules, polyalkylene glycol ethers such as propylene glycol ethers, alkanes diols and polyaliphatic or cycloaliphatic ethers.

It is accepted that they can limit shrinkage by acting on the surface tension of the water in the pores of the hydrated cement. Indeed, they reduce the surface tension and thus reduce the capillary pressure of the microstructure resulting in a decrease in internal tensile stresses.

The effectiveness of anti-shrinkage agents depends in particular on the quantity introduced, their chemical composition, the water content added to the cement (W / C ratio) and the humidity level of the ambient air. The optimum dosing specified is about 2% by mass with respect to the cement.

Several studies have shown that the use of conventional anti-shrinkage agents in conventional, high-strength concrete reduces shrinkage by 35% to 50% in dry conditions.

This type of agent, while reducing the short-term withdrawal (28 days), actually produces very limited results in the longer term (> 90 days). In addition, his action seems to be dependent on the chemical and mineralogical composition of the cement.

On the other hand, it is reported in the literature that the use of anti-shrinkage agents also leads to a decrease in the strengths and the elastic modulus of the concretes. A delay effect on the hydration is also mentioned, which can pose difficulties on the building sites.

Finally, many anti-withdrawal agents are classified as harmful according to the European classification, which is problematic from the point of view of the health of the user.

A first object of the invention is therefore to provide an anti-shrinkage agent which overcomes the disadvantages enumerated above, and more particularly which does not reduce the mechanical strengths, nor does it cause setting retardation.

The inventors have surprisingly discovered that certain types of surface-modified mineral particles make it possible to act as an anti-shrinkage agent.

The present invention thus relates to an anti-shrinkage agent for a cementitious composition, such as a cement paste (also called a grout) mortar or concrete, characterized in that it is in the form of surface-modified particles consisting of mineral nanoparticles coated with a polymer coating formed essentially of poly (alkyl oxide) chains, preferably poly (ethylene oxide), adsorbed or grafted onto the surface of the nanoparticles, said mineral nanoparticles being oxides or carbonates selected from the group : alumina, calcium carbonate, titanium dioxide, silica, zinc oxide and a mixture thereof.

By "essentially poly (alkyl oxide) chains" is meant here that the polymer coating does not comprise polymer chains of different natures, and in particular no chains having acrylic or carboxylic units.

It has been found that the polymer coating of the inorganic nanoparticles can be from 1 to 30% by weight, preferably from 5 to 20% by weight, and advantageously about 10% by total weight of the surface-modified particles. The particles of the anti-shrinkage agent according to the invention thus consist of a fraction mineral heart, majority.

For use in mortars or concretes, the anti-shrinkage agent described above is advantageously in the form of a suspension, preferably in the form of a colloidal aqueous suspension, of said surface-modified particles. Surprisingly, the incorporation into water of these nanoparticles does not cause the detachment of the polymer from the inorganic support, that is to say the coating of the mineral nanoparticles. In this suspension the content of surface-modified particles is large, that is to say advantageously between 10 and 70% by weight, preferably between 40 and 60% by weight. The size of the surface-modified particles is advantageously between 5 nanometers and 1 micrometer, preferably between 5 and 500 nanometers, more preferably between 10 and 200 nanometers.

The present invention also relates to a cementitious composition, such as a cement paste, a mortar or a concrete, comprising a hydraulic binder such as Portiand cement, possibly sand / or aggregates, characterized in that it contains 0 0.5 to 10% by weight of anti-shrinkage agent as described above, relative to the binder.

The inventors have also surprisingly found that the anti-shrinkage agent described above also exhibits superplasticizing properties on mortar and / or concrete.

The present invention therefore also relates to concretes or mortars prepared from such a composition, characterized in that they contain 1% by weight of anti-shrinkage agent relative to the binder, so as to have a shrinkage measured according to the ASTM C596-07 standard less than 0.05% (ie 500 pm / m), preferably less than 0.035% (ie 350 pm / m) at 28 days.

The invention also relates to concretes or mortars prepared from such a composition, characterized in that they contain 1% by weight of anti-shrinkage agent relative to the binder, so as to have a measured 28-day shrinkage. according to ASTM C596-07 at least 50% lower, preferably at least 65% lower than a reference concrete or mortar which does not contain said anti-corrosive agent. withdrawal.

These shrinkage reduction properties are observed without retarding the hydration of the cement and without decreasing mechanical compressive strength, even in the long term. The invention is illustrated below by the following nonlimiting examples: EXAMPLE 1

Different mortars have been prepared from a Portiand type I cement of the following composition:

Table 1 - Composition and performance of Portiand cement used and measured according to ASTM C114, C150, C1038, C191, C109, C185 and C204 (Bessemer Cement)

Composition In% total mass

Si0 ₂ 20.6

Al ₂ 0 ₃ 4.9

Fe ₂ 0 ₃ 3.8

CaO 65.1

MgO 1.1

n ₃ 3.5

C ₃ S 60.4

C _{3 to} 6.5

Total Alkalis 0.56

Loss of fire 0,7

Insoluble residue 0.17

Fineness Blaine 359 m ² Kg ^"1

Air content 5.3%

Initial setting time 105 min. (Vicat)

Resistance to compression (MPa)

to 1 day 15,9

at 3 days 24,3

to 7 days 30.8

to 28 days 37.7 Adjuvants: Two types of adjuvants were used:

B: a suspension of colloids consisting of alumina nanoparticles coated with a polymer of the polyethylene oxide type (marketed by BYK-CHEMIE under the name BYK Nano3600) with a particle size of around 40 nanometers dispersed in water, or

C: a suspension of colloids consisting of alumina nanoparticles having a particle size of about 60 nanometers coated with polyethylene oxide type polymer, dispersed in water (experimental product delivered by the BYK-CHEMIE company under the reference BYK-LP X 20637). The products B and C each have a percentage of organic matter close to 10% by weight relative to the dry product, corresponding to their polymer coating. Table 2 summarizes the main properties of the adjuvants used.

Table 2

Adjuvant particles B and C have after sonication (i.e. for non-agglomerated particles) an average hydrodynamic diameter of 138 ± 2 mm with a unimodal particle size distribution. The Zeta potential measured after dilution of a drop of B or C in 15 ml of water is respectively 8 mV and 3 mV, that is to say less than 10 mV, which corresponds to particles not loaded. Various mortar compositions have been tested in the examples below. They are presented in Table 3 below:

Table 3 - Mortar Compositions Tested

The sand used is a so-called round siliceous rolled alluvial sand of controlled particle size less than or equal to 4 mm. The mortar compositions were prepared according to the following protocol:

The sand is introduced into the bowl of a mixer in accordance with standard NF EN-196, the sand then the prehumidification water by mixing for 2 min at low speed. The mixture is then allowed to stand under a wet cloth for 5 minutes. Then, the cement is introduced and kneaded for 30 seconds at low speed before introducing the mixing water while kneading a further 30 seconds at low speed and 30 seconds at high speed. After these steps, the mixture is allowed to stand for 1 min 30 seconds while scraping the bottom and around the bowl. The adjuvant tested is then introduced with a syringe by dispersing it on the mortar. Finally, we end with a mix of 30 seconds at low speed followed by a minute 30 seconds at high speed.

Adjuvants B and C were introduced at a content of 1% by weight of material active with respect to the cement, in a BPE mortar composition 0.45 as described above.

The shrinkage was measured according to ASTM C 596-07. This test consists in measuring the length variation, at certain deadlines, of square section mortar specimens, with side equal to 25 mm and length equal to 250 mm. The preparation of the test pieces is as follows: introduction of the mortar into the molds (3 molds for each type of mortar), compacting and evacuation of the air by vibration. Then, the molds are placed in a temperature controlled room at 23 ° C ± 2 ° C with a humidity equal to 95% for 24 hours. The test pieces are then demolded and immersed in a solution saturated with lime for 48 hours. At the end of this curing period, the specimens are kept in the open air in a room regulated at a temperature of 23 ° C ± 2 ° C with a relative humidity of 50%. The initial withdrawal measurement (3 days) is carried out just after the cure period in saturated lime and then during storage in the open air after 7, 14, 21 and 28 days for each of the specimens.

The measurement is carried out using a comparator which makes it possible to measure the length variation of the test piece relative to a reference metal rod.

The% withdrawal is then obtained at each maturity by the following formula:

_{AL =} ^{dl ~ dl} ^ * ioo with

AL =% of withdrawal,

dL = variation in the length of the specimen relative to the metal rod

L = initial length of the bar

The% withdrawal at maturity taken into account corresponds to the arithmetic mean of the values obtained for each of the three test pieces. The results obtained with the two adjuvants B and C were compared with those obtained under the same conditions on a non-additive mortar sample, and are presented in Table 6 below.

The withdrawal values shown in Table 4 are expressed in% shrinkage (0.01% withdrawal corresponds to a withdrawal of 100 pm / m.).

Table 4

These results show that regardless of the time frame considered, the two adjuvants B and C decrease the withdrawal significantly (> 65% compared to the unadjuvanted formula at 28 days). Moreover, it seems that the product C is more effective than the product B, which could mean differences in performance as a function of the average diameter of the alumina nanoparticles constituting the core of the particles of the adjuvant according to the invention.

EXAMPLE 2

The inventors have found, surprisingly, that adjuvants B and C have, in addition to their anti-shrinkage properties in a mortar composition, superplasticizing properties, in particular the maintenance of fluidity over time, without setting delay.

These superplasticizing properties were evaluated on the mortars prepared according to the previous protocol by means of a modified cone test. For this test a bottomless cone is used whose upper diameter is equal to 5 cm, the lower diameter equal to 10 cm and the height equal to 15 cm. The cone is filled with a volume of mortar stitched 15 times with a metal rod. After having leveled the upper surface of the cone, the latter is lifted rapidly as vertically as possible. The diameter of the slump obtained at the center of the upper part of the mortar is then measured. Significant sagging shows that the adjuvant has an effective superplasticizing property. This measurement of the slump is carried out 1 min 30 after the end of the mixing mortar and every 15 minutes up to 45 minutes for rheological monitoring over time. For rheological monitoring, the mortar is put back into the bowl of the mixer, covered with a damp cloth until the next deadline. Before the new test, the mortar is remixed 15 s at low speed. Similarly, the setting time of the mortar was evaluated according to a thermal monitoring test which allows, by recording the temperature of the mortar at the first ages of its hydration (24 or 48 hours), to draw a curve of temperature evolution. as a function of time and thus to evaluate the delay effect due to the use of the adjuvant by the determination of the "half-slope time". It involves introducing the mortar at the end of rheological monitoring into a semi-adiabatic heat box in which a thermal probe is immersed. The mortar temperature is recorded for 24 to 48 hours. From this temperature curve as a function of time, the "half-time" is defined as the abscissa corresponding to half the temperature rise of the mortar during its hydration. The effectiveness of adjuvant C at different concentrations was tested on the BPE 0.4 mortar composition described in Table 3, compared to a non-adjuvanted reference composition, and a composition containing a superplasticizer A of the invention. prior art (Duraflux 44). The results are summarized in Table 5 below:

Table 5

If we first look at the initial subsidence (15 min) obtained, we observe that the increase in the C adjuvant dosage increases the slump of the mortar, which accounts for the fluidizing properties of this product.

However, it is necessary to add about 0.7% by weight of adjuvant C to obtain a slump equivalent to that obtained with the addition of 0.1% of the superplasticizer Duraflux 44.

On the other hand, if one now looks at the maintenance of the fluidity over time represented by the% of sagging loss between 15 min and 45 min, it can be seen that unlike the superplasticizer Duraflux which does not generate a good maintenance (51% sag loss at 45 min), the adjuvant C according to the invention makes it possible to obtain a very good maintenance of the fluidity after 45 min (only 14% sag loss).

Finally, the half-slope time, determined by the thermal monitoring of the hydration of the mortar, is inversely correlated with the resistances obtained at 24 hours, and thus makes it possible to obtain a qualitative indication of the setting time of the mortar. It is found, as is often the case with conventional PCP-type superplasticizers, that Duraflux 44 gives rise to a significant retardation of setting compared with the nonadhered mortar (approximately 5 hours) while the adjuvant C according to the invention almost no setting delay, which is interesting for setting mortar or concrete on site (no increase in the stripping time, for example).

EXAMPLE 3

The effectiveness of the two adjuvants B and C was tested on the BPE 0.5 mortar composition described above, and compared to a composition without adjuvant. The same tests as in Example 2 were performed, as well as a 28-day strength measurement according to ASTM C109 / 109M.

The results are summarized in Table 6 below: Table 6

These results show that products B and C show similar performance in mortars. In fact, they make it possible to obtain the same initial initial settlement and after 30 minutes they do not give rise to any significant setback.

Their similar behavior makes it possible to deduce that the size of the basic inorganic nanoparticles of the particles of the adjuvant according to the invention does not have a decisive influence on their efficiency of fluidification of the mortar.

In addition, it is found that the presence of these two adjuvants B and C in the mortars significantly improves their resistance to 28 days.

Claims

1. Anti-shrinkage agent for cementitious composition, such as cement paste, mortar or concrete, characterized in that it is in the form of surface-modified particles consisting of mineral nanoparticles covered with a polymer coating formed essentially of chains poly (alkyl oxide), preferably poly (ethylene oxide), adsorbed or grafted on the surface of the nanoparticles, said mineral nanoparticles being oxides or carbonates selected from the group: alumina, calcium carbonate, dioxide of titanium, silica, zinc oxide and a mixture thereof.

2. Anti-shrinkage agent according to claim 1, characterized in that the polymer coating of the mineral nanoparticles represents from 1 to 30% by weight, preferably from 5 to 20% by total weight of the surface-modified particles.

3. anti-shrinkage agent according to any one of the preceding claims, characterized in that the size of the surface-modified particles is between 5 and 1 micrometer, preferably between 5 and 500 nanometers.

4. anti-shrinkage agent according to any one of the preceding claims, characterized in that it is in the form of a suspension, preferably an aqueous suspension, said surface-modified particles.

Anti-shrinkage agent according to claim 4, characterized in that the content of the surface-modified particles in the aqueous suspension is between 10 and

70%, preferably between 40 and 60% by weight.

6. Anti-shrinkage agent according to any one of the preceding claims, characterized in that it also has superplasticizing properties on the mortar and / or concrete.

7. Cementitious composition, such as cement paste, mortar or concrete intended to be mixed with water comprising a hydraulic binder such as Portland cement, possibly sand and / or aggregates, characterized in that it contains 0.05 to 10% by weight, based on the binder, of anti-shrinkage agent according to any one of claims 1 to 6.

8. Concrete or mortar prepared from a composition according to claim 7, characterized in that it contains 1% by weight of anti-shrinkage agent relative to the binder, so as to have a shrinkage measured according to ASTM standard C596-07 less than 0.05% (ie 500 pm / m), preferably less than 0.035% (ie 350 pm / m) at 28 days.

9. Concrete or mortar prepared from a composition according to claim 7, characterized in that it contains 1% by weight of anti-shrinkage agent relative to the binder, so as to have a 28 day shrinkage measured according to the ASTM C596-07 standard is at least 50% lower, preferably at least 65% lower than a reference concrete or mortar which does not contain said anti-shrink agent.