FR2960538A1 - ANTI-REMOVAL AGENT BASED ON MINERAL NANOPARTICLES WITH MODIFIED SURFACE FOR MORTAR AND CONCRETE - Google Patents

Abstract

The invention relates to an anti-shrinkage agent for a 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 coated with a polymer coating formed predominantly poly (alikyl oxide). It reduces the shrinkage by more than 65%, without setting time, and also gives the mortar or concrete composition superplasticizing properties.

Description

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 young concretes to limit the rapid evaporation of the water of constitution of the concretes, to add an expansive compound which causes a swelling (compensation of withdrawal ), or use organic compounds (additives) "shrinkage reducers". The development of withdrawal reducing agents appeared in Japan in the early 1980s. These shrinkage reducing agents, also known as anti-shrinkage agents, are organic, water-soluble and hygroscopic products. 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, ifs reduce the surface tension and therefore reduce the capillary pressure of the microstructure resulting in a decrease in internal tensile stresses. The effectiveness of the anti-shrinkage agents is a function of the amount 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 and high strength concretes can reduce shrinkage by 35% at 50 ° C under 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, its action appears 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 hydration is also mentioned. 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 therefore 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 predominantly of poly (alkyl ether). Advantageously, the polymer coating of the mineral nanoparticles consists essentially of poly (ethylene oxide) chains adsorbed or grafted onto the surface of said nanoparticles. The mineral nanoparticles which thus serve as support for the polymer coating 20 are preferably oxides or carbonates selected from the group consisting of alumina, calcium carbonate, titanium dioxide, silica, zinc oxide and a mixture thereof. 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 desirably 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 mineral core fraction, 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. In this suspension, the surface-modified particle content is 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 Portland cement, possibly sand / or aggregates, and from 0.05 to 10% by weight. 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 advantageously containing 1% by weight of anti-shrinkage agent with respect to the binder characterized in that they 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 advantageously containing 1% by weight of anti-shrinkage agent with respect to the binder, characterized in that they exhibit a shrinkage at 28 days, measured according to the ASTM standard C596-07, at least 50% lower, preferably at least 65% lower than a reference concrete or mortar not containing said anti-shrink agent. These shrinkage-reducing 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 were prepared from a type I Portland cement of the following composition: Table 1 - Composition and performance of the Portland cement used and measured according to ASTM C114, C150, C1038, C191, C109, C185 and C204 (Bessemer Cement) Composition% by weight total SiO2 20.6 Al2O3 4.9 Fe2O3 3.8 CaO 65.1 MgO 1.1 SO3 3.5 C3S 60.4 C3A 6.5 Total Alkalis 0.56 Initial setting time 105 min. (Vicat) Compressive strength (MPa) at 1 day 15.9 at 3 days 24.3 at 7 days 30.8 at 28 days 37.7 Air content 5.3% Blaine fineness 359 m2Kg.1 Loss of fire 0.7 Insoluble residue 0.17 Adjuvants: Two types of adjuvants were used: B: a suspension of colloids made of alumina nanoparticles coated with a polymer of the polyethylene oxide type (marketed by BYK- CHEMIE 4 20 under the name BYK Nano3600) particle size of about 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 polymer type polyoxide ethylene s , dispersed in water (experimental product delivered by BYKCHEMIE 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 Name Particles Diameter suspension p Average aqueous density (nm) (% solid) A (Duraflux) ACP 5 35 7.3 1.1 B (BYK Nano Alumina 40 52.6 4.8 1.6 3600) coated C ( BYK LPX Alumina 60 54.2 5.74 1.6 20637) Coated Adjuvant particles B and C after ultrasonic treatment (i.e. for non-agglomerated particles) have an average hydrodynamic diameter of 138. + 2 mm with a unimodal grain 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 shown in Table 3 below. Table 3 - Mortar compositions tested BPE 0.4 BPE 0.45 BPE 0.5 Sand 1350 g 1350 g 1350 g Cement 740 g 740 g 534 g Water tempering 296 g 333 g 268 Prehumidif. Sand 11 11 g 11 g Antifoam 2.9 g - 2.9 g Water / cement 0.4 g 0.45 g 0.5 g The sand used is a siliceous so-called round silty 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 the NF EN-196 standard, and then the pre-moistening water by mixing for 2 min at a 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 tested adjuvant 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 active material relative 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 of measuring the

variation in length, at certain times, of test pieces of square section mortar, 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% shrinkage is then obtained at each time by the following formula: ## EQU1 ## with L AL =% shrinkage, dL = variation in length of the test piece relative to the metal rod L = initial length of the bar The% withdrawal at maturity taken into account corresponds to the arithmetic average 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 shrinkage values shown in Table 4 are expressed as% shrinkage (0.01% shrinkage is a shrinkage of 100 pm / m 2).

Table 4 Deadlines (days) Without adjuvant B (1%) C (1%) 7 0.043 0.025 0.005 14 0.072 0.029 0.008 21 0.089 0.028 0.009 28 0.102 0.032 0.013 These results show that regardless of the time frame considered, the two adjuvants B and C decrease the shrinkage significantly (> 65% compared to the unadjuvanted formula at 28 days). Furthermore, 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 found, surprisingly, that adjuvants B and C had, in addition to their anti-shrinkage properties in a mortar composition, superplasticizing properties, in particular the maintenance of fluidity over time, without delay. of taking. 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 kneading of the mortar and every 15 min up to 45 min to obtain the rheological follow-up in the 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, we obtain the "half-slope time" 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 art. previous (Duraflux 44). The results are summarized in Table 5 below: Table 5 BPE mortar composition 0.4 Adjuvants Reference Duraflux 44 Adjuvant C (% by weight of 0% 0.1% 0.25% 0.5% 1%) cement) Settling at 15 26 85 55 73 96 min (mm) Falling at 45 11 42 40 61 83 min (mm)% loss 58 51 27 16 14 sagging Time at half-slope 4 hrs 9h20 4:32 4:48 4:53 (hours; min) If one first looks at the initial settlement (15 min) obtained, it is observed 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. 2960538

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 maintaining (51 ° Io slump 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 0 / o of slump 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 up the 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 carried out, as well as a measurement of the resistance at 28 days according to ASTM C109 / 109M. The results are collated in Table 6 below: Table 6 BPE mortar composition 0.5 BC Adjuvant Reference BYK-Nano 3600 BYK LP-X 20637 Determination (% by weight of material 0% 1% 1 ° Io active relative to cement) Slump 7 min (mm) 48 98 102 Sagging 30 min (mm) 33 81 89 Time mid slope (hr; min) 5 h 46 5 h 58 5 h 37 Resistance to 28 days (MPa) 45.1 48, 49.1 These results show that products B and C show similar performances 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. io

Claims (3)

REVENDICATIONS1. 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 inorganic nanoparticles covered with a polymer coating mainly formed of poly (oxide) alkyl). 2. anti-shrinkage agent according to claim 1, characterized in that the polymer coating of the mineral nanoparticles consists essentially of poly (ethylene oxide) chains adsorbed or grafted to the surface of the nanoparticles. 3. anti-shrinkage agent according to claim 1 or 2, characterized in that the mineral nanoparticles are oxides or carbonates selected from the group: alumina, calcium carbonate, titanium dioxide, silica, zinc oxide and a mixture of these 4, anti-shrinkage agent according to any one of the preceding claims, 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 particles to modified surface. 5. 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. 6. 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 6, 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. 8. 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. 9. 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, and from 0.05 to 10% by weight, relative to the binder, of anti-shrinkage agent according to any one of claims 1 to 8. 10. Concrete or mortar prepared from a composition according to claim 9, containing 1% by weight of agent anti-shrinkage with respect to the binder, characterized in that it has a shrinkage measured according to the ASTM C596-07 standard of less than 0.05% (ie 500 μm / m), preferably less than 0.035% (ie 350 μm / m) at 28 days. 11. Concrete or mortar prepared from a composition according to claim 9, containing 1% by weight of anti-shrinkage agent relative to the binder, characterized in that it has a 28 days shrinkage measured according to ASTM standard C596-07 at least 50% lower, preferably at least 65% lower than a reference concrete or mortar not containing said anti-shrink agent.