ITMI20110167A1 - DUST ADDITIVES FOR CEMENTITIOUS COMPOSITIONS - Google Patents

Description

Description

â € œ ANTI-DUST ADDITIVES FOR CEMENTITIOUS COMPOSITIONSâ €

The present invention relates to additives capable of reducing the formation of dust and relative emission that occurs during the handling of cement-based mortars for the construction sector, in particular during the emptying of the bags containing these products.

In particular, the invention concerns the use of liquid esters to be added to the cement-based mortar to reduce the formation of dust.

State of the art

The generation of dust from finely divided solid materials is a source of environmental problems. In particular, cement-based mortars for the construction sector can generate significant quantities of dust when handled, especially during bag emptying operations. If inhaled, this dust can deposit in the respiratory tract of the operators, with potentially dangerous effects for their health. The European standard EN 481 identifies various categories of dust; dust particles below 100 microns correspond to fraction E, which can be inhaled into the lungs, while particles below 10 microns correspond to fraction A, almost invisible, which remains in the air for a very long time, and can also be inhaled in the alveoli. Most of the cement particles are less than 10 microns in size and are therefore potentially harmful to health, due to the presence of alkaline compounds such as lime (calcium oxide), which is corrosive to human tissues as well as traces of crystalline silica. which is abrasive to the skin and can damage the lungs and traces of chromium which can cause allergic reactions.

The use of additives capable of reducing the development of dust in Portland cement-based formulations has already been known in the literature for almost 50 years. The patent GB 892015, published in 1962, describes an improvement in the production and properties of water-repellent Portland cement, with the aim of reducing its tendency to form dust, grinding it with 0.2-0.15% by weight of oil. mineral lubricant, mineral oil or mineral jelly. Patent GB 1227355 suggests the composition of a mortar based on Portland cement containing the addition of a mineral oil, with the aim of reducing the formation of dust. Further information on similar inventions is contained in JP 06-150847 in which the use of a dust formation inhibitor in the form of liquid paraffin is proposed and in US 3656979, in which an anti-dust cementitious composition is obtained with the addition 0.1-0.3% by weight of a paraffinic oil.

Description of the invention

It has now been found that liquid esters of fatty acids, applied for example by direct nebulization on the surfaces of cementitious materials such as adhesives, self-leveling compounds and joints, are particularly effective and advantageous with respect to known additives in reducing the development of dust.

The application can be carried out both on the single raw materials that make up the cement product and on the finished product itself, in percentages between 0.1% -2.0%, preferably between 0.4% and 1.0%.

The viscosity of the esters according to the invention must be such as to allow easy nebulization, thus having available the largest possible contact surface between the liquid particles of the additive and the solid particles of the cementitious material. Dust, estimated as a persistent dust value, is reduced by up to 90%, as measured using a DustMon® analyzer, manufactured by Anatac AS. The analyzer contains a measuring chamber in which the dusty sample to be evaluated is thrown. A light passes through the measuring chamber at a distance of 12 cm from the bottom, between the source and a detector. The light intensity measured by the detector decreases as the concentration of dispersed particles increases, and therefore this is a measure directly correlated with the dust levels of the sample. Figure 1 shows a typical graph obtained with the DustMon machine, showing the so-called “dust concentration index as a function of time” of a low-dust emission mortar compared to that of a conventional product. Both measures tend towards an asymptote which can be considered as an index of the persistent dust generated by the product.

The effect of reducing the dustiness is due to a mechanism of aggregation of the finer particles, which allows to increase the sedimentation speed of the particles, as roughly described by the following equation

where Ï pà the density of solid particles, Ï fà the density of air, g is the gravity coefficient and r is the radius of the particle. The equation allows to calculate the dependence of the falling speed on the size of the

particles, as shown in the following table.

Particle size µm Settling time

1 3 h

5 21 min

10 5 min

50 14 s

100 4 s

1000 0.3 s

The reported values show that the increase in the size of

allows particles to accelerate their rate of fall by reducing

considerably their time of stay in the air. Also, by increasing the

particle size decreases their potential danger to the

health.

Detailed description of the invention

The liquid esters of fatty acids can be selected from the esters of

fatty acids, saturated or unsaturated, monoethoxylated or polyethoxylated, with long-lasting

mono or multipurpose chain.

These esters are able to maintain the characteristics unaltered

dustproof of the cementitious material even in case of ester hydrolysis.

Liquid esters having a boiling point are particularly preferred

such as to guarantee the constancy of the percentage of the additive that interacts with

finished product and also having saponification and acidity values such as to

guarantee the least possible interaction with the cementitious formulation.

The preferred characteristics of the esters are reported below

usable according to the invention:

- kinematic viscosity (40 ° C) lower than 500 mm <2> / s, preferably lower than 20 mm <2> / s;

- density (20 ° C) lower than 1 g / cm <3>, preferably between 0.8 and 0.9 g / cm <3>

- boiling point higher than 100 ° C, preferably> 200 ° C;

- freezing point lower than -2 ° C, preferably between -10 ° C and -30 ° C;

- acidity value (expressed as quantity of potash necessary to neutralize 1 g of the substance under examination, index of the number of carboxylic groups present) lower than 10 mgKOH / g, preferably lower than 0.5 mgKOH / g;

- saponification value (expressed as the quantity of potash necessary to saponify 1 g of the substance under examination, index of the average length of the fatty acids present) lower than 500 mgKOH / g, preferably lower than 150 mgKOH / g;

- average chain length (as number of carbon atoms) greater than 10, preferably between 16 and 36;

- molecular weight greater than 100 g / mol, preferably greater than 300 g / mol;

- unsaturated bonds less than 3 or absent in the case of self-leveling formulations, where the isotridecyl-laurate works better than the analogous oleate, probably following an interaction of the corresponding dioxystearic derivative with the fluidifying agent.

From tests carried out with liquid additives of various chemical nature (esters, aliphatic or aromatic hydrocarbons of both synthetic and vegetable origin, alcohols, amines), the esters were found to have the greatest dust reduction capacity, in particular the category of acid esters fat. Furthermore, esters also have other desirable properties:

â € ¢ they are able to maintain the anti-dust properties well in a cement product stored for a prolonged time in various conditions;

â € ¢ they are easy to store and not dangerous;

â € ¢ they develop low quantities of volatile organic particles;

â € ¢ they do not influence the development of the mechanical properties of the cementitious product.

Before carrying out the tests with the additives, the dustiness of the different raw materials was evaluated and then combined to give the finished product. Among the formulation components, divided into four categories, inorganic binders (Portland cements, aluminous cements, slag, gypsum, anhydrites, hydraulic lime, metakaolin etc.), inert (sand, calcium carbonate, lightened aggregates, functional aggregates, recycled materials ), organic (redispersible powders) and additives (cellulose ethers, pigments, aerating agents, defoamers, thixotropic agents, hydrophobic agents, plasticizers, fluidifiers, anti-shrinkage agents, etc.), those that are among the main sources of dust are:

1) Portland cement

2) calcium carbonate having an average size greater than 100 µm 3) redispersible powder.

This study made it possible to identify a series of equations capable of predicting the contribution of each raw material and therefore allowing an estimate of the total dustiness value of the final product. Figure 2 shows the curves for the most significant raw materials.

The knowledge of the contribution to the dustiness of the various raw materials has therefore made it possible to identify the optimal dosage of the various anti-dust additives tested, with percentages from 0.1 to 2%, preferably between 0.4% and 1%, being able in some cases to exploit the tendency of certain raw materials to packing.

The same reduction in dustiness was observed both by applying the anti-dust additive on the individual raw materials and on the finished product.

The esters were tested in particular in the following generic cementitious formulation:

- Portland cement 10-70%

- aluminous cement 0-30%

- sand 10-70%

- calcium carbonate 0-30%

- 0-10% redispersible powder

- 0-2% additives.

The esters were tested by nebulization, in a percentage between 0.4-1.0%.

The reduction of dust has been estimated by comparing the persistent dust content, through measurements with the Dustmon apparatus, of the original cementitious product and the product on which the ester was sprayed.

The results obtained are discussed in the following examples

Example 1

The liquid additive used in this example is a glyceryl-trioleate which, although falling within the characteristics described above, has a rather high kinetic viscosity value.

In particular, the assessments performed with the following additions

a) 100% cementitious formulation

b) cementitious formulation 99.6% glyceryl trioleate 0.4%

c) cementitious formulation 99.4% glyceryl trioleate 0.6%

d) cementitious formulation 99.2% glyceryl trioleate 0.8%

gave dust reduction values (index of persistent dustiness generated by the product) of 23.4, 10.8, 6.4 and 3.1 respectively, which highlight how the additive is difficult to atomise, leading to an initial contact surface with the finer particles lower than the optimal one and therefore the initial reduction in dustiness is decidedly low. Only at high quantities does this additive begin to prove effective.

Example 2

The liquid additive used in this example is an isobutyl oleate which, even though it falls within the characteristics described above, is made up of a monovalent alcohol with a rather short chain, with a not particularly high boiling point.

In particular, the assessments performed with the following additions

a) 100% cementitious formulation

b) cementitious formulation 99.6% isobutyl oleate 0.4%

c) cementitious formulation 99.4% isobutyl oleate 0.6%

d) cementitious formulation 99.2% isobutyl oleate 0.8%

gave the following dustiness values: 23.4, 4.4, 2.1, 1.2. However, by repeating the test after keeping the added powder in an open plastic bag for 7 days, dust reduction values of 7.5 and after another 7 days of 11.0 were obtained, starting from values of 4.4. The results show that this additive, while being effective both in terms of reducing the initial dustiness and in terms of interaction with the cement matrix (the mechanical properties of the product remain almost unchanged if compared with those of the initial dusty product), is not able to maintain these anti-dust capacities over time, given a not particularly high boiling point and a partial saponification of the ester to release the monovalent short-chain alcohol: this is an effect of the partial hydration of the cement surface left exposed under ambient humidity conditions.

Example 3

The liquid additive used in this example is an ethylhexyl laurate which, although it falls within the characteristics described above, has a rather high saponification value.

In particular, the assessments performed with the following additions

a) 100% cementitious formulation

b) cementitious formulation 99.6% ethylhexyl laurate 0.4%

c) cementitious formulation 99.4% ethylhexyl laurate 0.6%

d) cementitious formulation 99.2% ethylhexyl laurate 0.8%

have highlighted how the presence of a high number of carboxyl groups leads to a greater interaction with the cement matrix, creating a depressant effect on the development of the final mechanical strength of the product.

Example 4

The additive used in this example is an isotridecyl-oleate, which falls perfectly within the general characteristics described above.

In particular the assessments performed with the following additions

a) 100% cementitious formulation

b) cementitious formulation 99.6% isotridecyl oleate 0.4%

c) cementitious formulation 99.4% isotridecyl oleate 0.6%

d) cementitious formulation 99.2% isotridecyl oleate 0.8%

they gave the following dustiness values: 23.4, 3.0, 1.7, 1.0. These results show that the additive is more effective as the concentration increases. Experiments carried out by keeping the sample open for prolonged times show that this additive is also effective in maintaining its properties over time. The interaction with the cement matrix has proved to be negligible since the final performance of the product is identical to that of the formulation without additive.

A full correspondence with the characteristics described above allows therefore to select a dust suppression additive already effective at low dosages and efficient with all types of cementitious formulations.

Claims (6)

CLAIMS 1. Use of liquid esters of fatty acids as agents capable of reducing the dustiness of cementitious materials. Use according to claim 1 of fatty acid esters, saturated or unsaturated, monoethoxylated or polyethoxylated, with mono or polyvalent long-chain alcohols. Use according to claim 1 or 2 wherein the cementitious materials are Portland cement, adhesives, self-leveling compounds and grouts. 4. Use according to one or more of claims 1 to 3 in which the ester is applied on the cementitious material in percentages between 0.1% -2.0%, preferably between 0.4% and 1.0% . Use according to one or more of claims 1 to 4 wherein the esters are selected from isodecyl trioleate, ethylhexyl laurate, isobutyl oleate, glyceryl trioleate. 6. Process for reducing the dustiness of cementitious materials which comprises the nebulization of liquid esters of fatty acids on said materials in percentages between 0.1% -2.0%, preferably between 0.4% and 1.0%.