FI3914570T3

FI3914570T3 - Additive for concrete and method for producing said concrete

Info

Publication number: FI3914570T3
Application number: FIEP20796603.7T
Authority: FI
Inventors: Wolfgang Josef Klauck
Original assignee: Martellus Gmbh
Priority date: 2019-11-07
Filing date: 2020-10-29
Publication date: 2023-06-08
Also published as: EP3914570B1; WO2021089394A1; DK3914570T3; HUE062559T2; HRP20230515T1; LT3914570T; PL3914570T3; EP3914570A1; SI3914570T1; EP3914571C0; WO2021089401A1; EP3914571B1; EP3819273A1; EP3819274A1; DE202019004582U1; EP3914571A1

Description

EP3914570 1

Description Technical field

The invention relates to an additive for concrete, which is particularly suitable for layers in path and road construction, and to a method for producing this concrete.

State of the art

Layers consolidated or stabilized with the hydraulic binders cement or support layer binder are of great importance in traffic route construction. These layers are used both for the production of the substructure and for the production of the superstructure of roadway structures in high-ranking road networks as well as in roadway construction. The structural strength and fatigue resistance of the layers stabilized with hydraulic binders are of great — importance, especially for the service life of the superstructure of the traffic surfaces.

Additives for subgrade stabilization are known. In particular, the use of polymer dispersions to improve cementitious binders is also known. However, the addition of known polymer dispersions has the disadvantages that they have to be highly dosed in order to significantly lower the porosity and water absorption and to increase the adhesive tensile strength on a smooth substrate. To date, dispersion systems with active ingredient contents below 10 wt% have mostly been used as additives for subgrade reinforcement based on hydraulically bound base courses (HGTs). These dispersion systems are often viscous, so that the run-out times or waiting times of containers containing these dispersion systems on a construction — site can be long. Moreover, because of the transport of a lot of water, among other things, the life cycle assessments of these products are in need of significant improvement. Finally, the water resistance of these dispersion systems is limited due to their content of chloride- containing salt additives as well as hydrophilic polymers.

Previously known products are liquid polymer emulsions containing, among others, SiO,.

These products are described in the brochure "WALK THIS WAY" of NanoTera AG

Munich/Germany.

Publication EP 2 430 093 B1 discloses agueous polymer dispersions comprising a) at least one dispersed copolymer CP which is built up from at least two monomers selected from the group consisting of ethylene, propylene, butylene, isoprene, butadiene, styrene, acrylonitrile, acrylic acid, methacrylic acid, alkyl acrylate, alkyl methacrylate, vinyl ester and vinyl chloride;

EP3914570 2 and further b) at least one comb polymer KP having side chains attached to the main chain via ester or ether groups; and water.

WO 2011/086095 A1 describes the use of concrete aggregates having a coating with organic polymers to improve the stability of concrete against alkali-silica reaction. The polymer is, for example, a styrene-butadiene copolymer or styrene-acrylate copolymer, which are optionally carboxylated.

EP 2 256 098 A1 describes an agent for soil consolidation comprising a cellulose ether, an — alkali hydroxide, calcium chloride, a synthetic latex, and amorphous fumed silica having an average particle size in the range of 1 - 100 nm, wherein the synthetic latex used is in particular a polypropylene/styrene-butadiene block copolymer.

KR 100 975 581 B1 describes a polymer-modified ultra-crude-resistant concrete composition and a pavement repair method using it. This extends the curing time of concrete by adding a polymer modifier to reduce defects in the concrete. Such a polymer-modified ultra-raw concrete composition contains 5 to 25 wt% cement group binder, 30 to 60 wt% fine aggregate, 20 to 50 wt% coarse aggregate, 0.5 to 5 wt% water, and 0.1 to 6 wt% polymer modifier. The polymer modifier comprises 80 to 99 wt% of an ultra-micro-hydrophobic acrylic resin and 1 to 20 wt% of a styrene-butadiene emulsion.

Against this background, the object of the present invention was to provide an additive for concrete which allows use in a concentrated, yet comparatively low-viscosity form.

Preferably, this additive should also be suitable for the production of layers consolidated or stabilized with hydraulic binders for use in road construction, where it preferably causes an increase in the fatigue strength of the layers bound with the hydraulic binders. The object of the invention was also to provide a method for the production of this concrete.

The solution of this problem is achieved according to the present invention by an additive for a concrete as well as a method for the production of this concrete having the features of the independent patent claims. Preferred embodiments of the additive according to the invention are set forth in corresponding dependent patent claims. Preferred embodiments of the additive according to the invention correspond to preferred embodiments of the method according to the invention and vice versa, even if this is not explicitly stated herein.

Thus, the subject of the invention is an additive for concrete which contains (a) a butadiene-styrene copolymer;

EP3914570 3 (b) a styrene-acrylic ester copolymer; (c) water; (d) an alkali silicate; and (e) a fumed or colloidal silica.

The solids content in the additive is preferably in the range of 40 to 60 wt%, more preferably in the range of 45 to 55 wt%, based on the total weight of the additive.

The concrete is not limited according to the invention. But in a preferred embodiment of the additive, the concrete is a lean concrete having a cement content of less than 12 wt%, based on the concrete. In addition to cement, a lean concrete generally contains all the constituents that are also common in concretes with higher cement contents.

The cement used according to the invention is generally Portland cement.

Preferably, the additive according to the invention is an additive for concrete for soil consolidation.

The copolymers (a) and (b) are generally used in the form of their agueous emulsions. These copolymers are contained in commercially available emulsions sold, for example, under the designations KUMHO KSL 362 Latex of JUMHO PETROCHEMICAL or Acronal® of BASF

SE.

According to the invention, the butadiene-styrene copolymer (a) preferably has a glass transition temperature Tg1 in the range from -60°C to +30°C, preferably in the range from - 40°C to +10°C.

The butadiene-styrene copolymer (a) may contain further comonomers. Examples of suitable comonomers are ethylene, propylene, butylene, isoprene, acrylonitrile, acrylic acid, methacrylic acid, alkyl acrylates, alkyl methacrylates, vinyl esters, vinyl chloride and vinyl or methacrylic silanes. Where comonomers are present, their content is generally less than 6% by weight, based on the butadiene-styrene copolymer (a).

According to the invention, the styrene-acrylic ester copolymer (b) preferably has a glass transition temperature Tg2 in the range from -60°C to +40°C, preferably in the range from - 40°C to +10°C.

EP3914570 4

The above values for Tg1 and Tg2 refer to a measurement by differential scanning calorimetry (DSC) according to DIN EN ISO 11357-1.

The acrylic ester in the styrene-acrylic ester copolymer (b) is not restricted. Non-limiting examples of the acrylic ester in the styrene-acrylic ester copolymer (b) are ethyl acrylate, propyl acrylate, butyl acrylate, ethyl hexyl acrylate and vinyl or methacrylic silanes.

Preferably, the acrylic ester used is a butyl acrylate, so that the styrene-acrylic ester copolymer (b) is preferably a styrene-butyl acrylate copolymer.

In addition to copolymers (a) and (b), the additive according to the invention may contain further polymers and/or copolymers (h). Examples of further polymers and/or copolymers are pure acrylate dispersions, polyurethane dispersions, natural rubber latex or starch / cellulose derivatives. If these are additionally present in the additive, their content is generally limited to up to 5% by weight, based on the total mass of polymers and copolymers in the additive. — In this context, an acrylonitrile-butadiene copolymer can advantageously be additionally present in the additive as component (h).

In a preferred embodiment, the additive contains from 5 to 95% by weight, preferably from 20 to 80% by weight, and even more preferably from 40 to 80% by weight, of butadiene-styrene copolymer (a); and from 5 to 95% by weight, preferably from 20 to 80% by weight, and even more preferably from 40 to 80% by weight, of styrene-acrylic ester copolymer (b), based in each case on the sum of (a) and (b).

The styrene-acrylic ester copolymer (b) is preferably a styrene-butyl acrylate copolymer.

The additive preferably has a water content (c) in the range from 30 to 70% by weight, more preferably in the range from 40 to 60% by weight, in each case based on the total weight of the additive. Thereby, the pH is generally in the range of 9 to 12.5, preferably in the range of 9.5 to 12, and more preferably in the range of 10 to 11.5.

According to the invention, the additive additionally contains as component (d) an alkali silicate (sodium, potassium, lithium), preferably a sodium silicate with a weight ratio SiO, to

Na;O in the range from 1.5 to 5. Preferably, the proportion of Na,O in the liquid component (d) is in the range from 5 to 15% by weight, based on the total weight of component (d).

Preferably, the sodium silicate (d) is present in the additive in an amount of 0.3 to 5% by weight, based on the total weight of the additive. Betol& from Woellner, for example, which is a purely inorganic binder and additive based on sodium silicate, is suitable. The use of

EP3914570 sodium silicate in such quantities in the additive according to the invention is very unusual, since it is considered to contribute to the so-called concrete cancer. However, this undesirable effect is not observed in the present invention. 5 The viscosity of the additive according to the invention is preferably in the range of 100 to 3,000 mpas. The viscosity is measured by a Brookfield RV rheometer (spindle 4, 50 revolutions / min at 20°C).

Finally, the additive according to the invention additionally contains as component (e) a fumed or colloidal silicon dioxide, preferably a fumed silicon dioxide. The silicon dioxide (e) is preferably present in an amount of 0.1 to 2% by weight, based on the total weight of the additive. A suitable silicon dioxide is, for example, Aerosil 200 from Evonik.

Furthermore, the additive preferably contains a defoamer as component (g). The defoamer is generally present in an amount of 0.01 to 0.2%, based on the additive. Suitable defoamers, in particular non-ionic defoamers, contain, for example, modified fatty substances, silicic acid, oxalkylated compounds and emulsifiers. AGITAN® 351 from MUNZING CHEMIE GmbH, for example, is suitable. However, cationic or anionic defoamers can also be used. Their use will generally depend on the pH of the additive.

Moreover, the additive may contain hydrophilic polymers such as cellulose derivatives or starch derivatives (methyl cellulose, methyl hydroxypropyl cellulose, methyl hydroxyethyl cellulose or hydroxypropyl starch). However, according to the invention, it is even advantageous that the hydrophilic polymers can be dispensed with.

In particular, the additive is dosed into the mixture with water, so-called addition water, during the production of aggregates bound with hydraulic binders.

The invention also relates to a process for producing a lean concrete, comprising a step of mixing a cement with one of the aforementioned additives and with an aggregate.

The aggregate for concrete and its properties are defined and measured according to EN 12620. They are explained in detail in the standard reference book "Cement Pocket Book 2000, ISBN 3-7640-0399-5".

In a preferred embodiment, the method according to the invention is a method for producing a road or path structure, comprising a step of producing a hydraulically bound layer, in which

EP3914570 6 a soil material is mixed with the cement and the additive described above, and a subgrade layer obtained therefrom is compacted.

The soil material consists of existing soil constituents and/or aggregates necessary for a hydraulically bound base layer.

A method for producing a road or path structure is preferred in which the hydraulically bound layer contains cement in an amount of 0.3 to 10% by weight, preferably in an amount of 2 to 5% by weight, based on the weight of the layer.

Moreover, according to the invention, a method is preferred in which the hydraulically bound layer contains the additive in an amount of 0.05 to 0.5% by weight, based on the weight of the layer. — According to the invention, a method is also preferred in which a top layer is applied to the hydraulically bound layer, preferably a top layer containing bitumen or concrete. This method is documented in detail in the standard reference work "Road Construction and Maintenance,

ISBN 3 503 06094 4".

A road body in road and path construction generally contains a subdivided superstructure that carries a surface course, namely the road surface, and possibly a so-called binder layer.

The subdivided superstructure generally consists of support layers, which are in turn subdivided into unbound support layers (frost protection layer, gravel and ballast layer, soil improvement layer) and bound support layers.

When using the additive according to the invention in the method according to the invention, for example, a soil material, aggregates, recycled material, cement and the additive according to the invention can be mixed in advance with optimized water content in a mixing plant in a stationary or mobile mixing plant. This mixture can then be taken to a construction site where it can be spread, for example, as a support layer for a soil layer. Generally, a grader is then used to produce a subgrade, followed by compaction of the homogenized and improved soil layer using vibrating rollers. In further operations, surface layers of chippings, asphalt and/or concrete can then be applied. For example, a surface course of grit and bitumen emulsion can be produced, as described in detail in the reference book Asphalt im — StraBenbau, ISBN 978-3-7812-1782-9.

EP3914570 7

However, processing of the additive according to the invention can also be carried out on site at a construction site. For example, a fixed quantity of cement can be spread on the existing soil and the soil can be milled up to, for example, 50 cm with a soil milling machine. In this process, the cement is incorporated with an optimized amount of water.

The invention has numerous advantages. Cost and quality advantages can be achieved, while construction time and CO, emissions can be reduced. The latter in particular also due to a shorter operating time of construction machinery. It is possible to achieve improved flexural strength regardless of the amount of Portland cement generally used. Layer thicknesses of concrete or asphalt pavements can possibly be reduced. Water sensitivity and thus frost sensitivity are reduced. The service life of the support layers or of the road or path pavements constructed with them is extended, and so are the maintenance periods of roads built with recycled materials.

The additive according to the invention not only catalyzes the cement reaction but also prevents leaching of pollutants such as coal tar. It increases the flexural strength and thus the elasticity of the layers containing this additive. The road structure and layer thickness can be simplified without compromising guality. Cement stabilizations with all types of existing soils as well as with recycled aggregates, bitumen, organic components and pollutants are made possible. High savings in disposal, transport and material costs can therefore be realized. The additional improvement in elasticity and frost resistance leads to significantly reduced cracking in the stabilized layer over its entire service life. Indeed, winding roads, especially winding mountain roads, are subject to extreme shear forces, so that rapid abrasion generally occurs. In addition, weather conditions and their changes can put a lot of — stress on the subgrade, especially from heavy rainfall and storms. Increased cracking of the base course may eventually occur, so frost resistance and elasticity of the base course are important. This reduces cracking and the base course absorbs additional tensile forces. This leads to significantly longer durability and better guality. In addition, a recycled pavement can be safely incorporated into the support layer.

An additive is also provided that can enable use with a high active ingredient content with comparative thinness. When the additive is used, high flexural strength values of the base layer can be achieved. Thus, for the first time, a liguid ultra-concentrate can be provided for soil stabilization. Compared to known systems, only about 1/6 of the previously used amount has to be used. Despite the high solids content that can be realized, an absolutely environmentally compatible product is obtained that is thin-bodied and can therefore mix very guickly with the incoming water on a construction site. Moreover, salt additives and

EP3914570 8 hydrophilic polymer components can be dispensed with. Load simulations have also shown an extended service life of the road.

In road construction, a particularly elastic hydraulically bound base course (HGT) and an asphalt surface course can be combined. The additive according to the invention can be used to increase the elasticity of the HGT and thus significantly reduce cracking. This also makes it possible to reduce the thickness of an asphalt surface course, e.g. from 14 cm to 8 cm. Compressive strength is also increased without the use of stress-relieving rollers. A thinner asphalt surface is made possible in a shorter construction time, and it can be — achieved that neither cracking nor settling occurs. In some cases, no transport and use of primary raw materials (gravel, chippings) is reguired for the HGT, so that the reduced use of construction vehicles can also reduce CO, emissions. Stabilization of roads, e.g. forest roads in alpine areas under high freeze-thaw loads, can be achieved. Stabilization is already achieved with cement and additive, without a base layer.

Examples

The following non-limiting example serves to illustrate the present invention. In the example, an additive according to the invention with the following composition was used, which is also referred to as additive Z hereinafter: 70.00 wt.% butadiene-styrene copolymer dispersion 28.75 wt.% styrene-butyl acrylate copolymer dispersion 1.00 wt.% sodium silicate 0.25 wt.% silicic acid in each case based on the weight of the additive.

For this purpose, the individual components were mixed, the butadiene-styrene copolymer (Tg1 = +1°C, pH = 10.0, solids content = 48 wt.%) as well as the styrene-butyl acrylate copolymer (Tg2 = -8*C, pH = 8.0, solids content = 59 wt.%) in the form of their agueous emulsions being used for the mixture.

The sodium silicate used was an aqueous solution with 36 wt% solids content, a pH of 11.4, and a SiO,/Na;O molar ratio of 3.3.

EP3914570 9

The silica used was a fumed silica with a BET specific surface area of 200 m?/g.

Different concretes were prepared using additive Z (M3 and M4) and their properties were compared with those of lean concretes that did not contain additive Z (M1 and M2).

For this purpose, an aggregate was first selected. The aggregate used was a graded mixture of grain size 0/16 mm (round grain) for the production of the mixtures bonded with cement. A grain mixture with a maximum grain size of 16 mm was deliberately used in order to produce mixtures that were as homogeneous as possible for the tests. The grain size distribution was determined on the grain mixture by means of wet sieve analysis in accordance with the specifications of EN 933-1.

To determine the optimum water content of the aggregate mixed with cement, the Proctor density was determined according to the specifications of EN 13286-2, with 4% by weight of

CEM Il cement mixed into the aggregate.

Preparation of the cement-bound concretes Mi to M4 — Four mixtures bonded with cement CEM II /B-M (SL) 32.5 R were produced as concretes Mi to M4, which had the compositions given in Tables 1 and 2:

Table 1 - Mixtures without additive Z

Components Mixture No. 1 (M1) Mixture No. 2 (M2) (% by weight) (% by weight)

EP3914570 10

Table 2 - Mixtures with additive Z

Ingredients Mixiure No. 3 (M3) Mixture No. 4 (M4)

Additive Z *} Addition of additive Z in each case related to the cement weight.

The mixtures were prepared in a compulsory mixer, with a mixing time of 120 s. The additive

Z was dosed with the addition water.

The concretes produced, Mi to M4, were subjected to comparative tests on specimens. For this purpose, a test program was defined that corresponded to the specifications of the

Austrian guideline and regulation for road construction, RVS 08.17.01 "Support layers stabilized with binders”, for the execution of the suitability test on support layers stabilized with hydraulic binders. The test program was extended to include the "Determination of the shrinkage behavior of the mix stabilized with cement” and the "Determination of the resistance to fatigue of the layers stabilized with cement”.

Production of test specimens - tests within the scope of a qualification test according to RVS 08.17.01 (1) Production of test specimens

Test specimens (dimensions d: 150 mm, h: 125 mm) were produced from the aggregates mixed with cement at optimum water content according to the Proctor density method (1- point method) in accordance with EN 13286-2. The specimens were removed from the

Proctor molds 24 hours after fabrication and stored at the standard climate (20°C, 65% relative humidity) until testing. (2) Tests performed

The tests described below were performed on the specimens prepared from the cementitious mixtures:

EP3914570 11 - Determination of the compressive strength after 7 and 28 days in accordance with the specifications of EN 13286-41 - Determination of the splitting tensile strength after 7 and 28 days in accordance with the specifications of EN 13286-42 (Note: Immediately before the tests, the specimens were stored under water for more than four hours).

Further tests

After the results of the tests were available, as they are carried out within the framework of the suitability test for support layers stabilized with cement, it was decided that the further tests described below would be carried out on the following mixtures:

Mixture No. 1 (concrete M1: exclusively bound with cement).

Mixtures No. 3 and No. 4 (concretes M3 and M4): prepared with different content of additive

Z

(i) Determination of the shrinkage behavior of the cement-bound concretes produced with and without the addition of additive Z. — The comparative test was carried out in accordance with ÖNORM B 3329 "Grouting mortars - Requirements and test methods”, item 7.3 "Swelling and shrinkage”, in so-called shrinkage/swelling troughs. Here, the change in length of the freshly produced, cement- bound mixture {concrete) was continuously recorded by means of a displacement transducer in a standard climate (20°C, 65% relative humidity) during hardening over a period of up to 14 days. This test arrangement was used to determine whether the mixes prepared with the addition of additive Z had a lower shrinkage tendency than the mix prepared with the addition of cement alone. (ity Recording the fatigue resistance of the layers stabilized with cement.

The resistance to fatigue was tested by means of the 4 point - bending test on prismatic specimens in accordance with EN 12697-24, Annex D. Appropriately sized mixes of the three selected concretes were prepared and layers of the cement-bonded aggregate with dimensions 500 mm x 300 mm x 160 mm were produced by means of a roller segment compactor {sliding plate method) in accordance with EN 12697-33. The aggregates bound with cement were compacted to the degree of compaction of 98%, based on the Proctor density.

EP3914570 12

The boards produced from the cement-bound mixiures were stored for 30 days at the standard climate (20 °C, 65 % relative humidity). Subsequently, 18 specimens with dimensions of 500 mm x 60 mm x 60 mm were cut out for each mixture.

The slabs of the aggregates bonded with cement were prepared in the time frame such that the three mixtures (formulations) were tested for fatigue resistance at the age of 40 - 50 days, respectively. Fatigue resistance testing was performed in a displacement-controlied servo-hydraulic testing machine at the frequency of 30 Hz. Three different strain amplitudes were selected to record the fatigue resistance of the hydraulically bonded mixtures. The — stifiness modulus was determined at the frequency of 8 Hz.

Results of the tesis 1 Result of the tests, which are relevant to prepare a suitability test for siabilized — support layers in accordance with RVS 08.17.01

Particle size distribution of the aggregate

The particle size distribution of the aggregate from which mixtures bound with cement were prepared was as follows:

Table 3 < 0.063

Swelling and shrinkage behavior of aggregates consolidated with cement

The comparative tests yielded the following results:

Mixture No. 1:

Mix stabilized with cement without additive Z.

EP3914570 13

Mixture M1 showed an average swelling of up to 66 pm/m, i.e. the swelling behavior of the

STZ overlapped the shrinkage behavior of the hardened cement paste at the beginning of setting. The shrinkage behavior (after completion of the swelling behavior) in a period of 11 days was linear idealized 1.7 um/day.

Mixture No. 3:

Mix stabilized with cement with addition of 3 wt.% additive Z, based on the cement quantity. — Mixture M3 showed an average swelling of up to 50 pm/m, i.e. the swelling behavior of the

STZ overlapped the shrinkage behavior of the hardened cement paste at the beginning of setting. The shrinkage behavior (after completion of the swelling behavior) in a period of 13 days was linear idealized 1.2 um/day.

Resistance to fatigue

Four-point bending test according to ONORM EN 12697-24:2012.

The M4 mix showed swelling averaging up to 50 pm/m, i.e. the swelling behavior of the STZ overlapped the shrinkage behavior of the hardened cement paste at the beginning of setting.

The shrinkage behavior (after completion of the swelling behavior) in the period of 14 days was linear idealized 0.7 pm/day.

The variation of the measuring range of about 5 um was caused by the slight temperature fluctuations or humidity variations in the climatic chamber. The specimens were stored at 20 °C + 1 °C and a relative humidity of 65 % + 10 %.

Fatigue strength of the cement-reinforced layers

The results of the comparative fatigue strength testing of the cement stabilized layers are shown in Table 4.

Table 4

Characteristic Unit Mi M3 M4 value 4 % by weight | 4 wt.% cement | 4 wt.% cement cement 3 wi.% additive | 5 wt.% additive

Z Z

EP3914570 14 rr rr

Durability of the layer against p/m 87 107 97 fatigue at 10° cycles at the freguency of 30

Hz

Stiffness of the layer at the MPa 9.821 8.205 10.731 frequency of 8 Hz at the age of 40 to 50 days

The above comparative material engineering tests allow the following conclusions to be drawn.

The strength values of the mixtures bonded with cement:

The mixtures prepared with the addition of additive Z show a slower strength development than the mixture prepared on the basis of cement alone, at the same cement content. The slower strength development increases as the proportion of additive Z increases.

Shrinkage behavior of mixtures bonded with cement:

The shrinkage of the cement-bound mixtures prepared with the addition of Additive Z is — significantly lower than that of a mixture prepared on the basis of cement alone. With the addition of 5% by weight of additive Z, based on the weight of cement, the shrinkage is more than 50% lower than that of the concrete produced using cement alone (lean concrete). The significantly lower shrinkage reduces the risk of cracking in the layers stabilized with cement.

It is known that, due to shrinkage, transverse cracks usually occur in the layers stabilized — with cement without additional measures such as cutting, notching or stress-relieving rolling, and longitudinal cracks occur more rarely. These cracks reflect into the bonded layers above, such as asphalt or concrete structures. The possible prevention of these damage patterns typical of cement stabilized layers by reducing shrinkage is a major technical advantage of the present invention.

Fatigue strength of the mixtures bonded with cement:

EP3914570 15

The cement-stabilized layers prepared with the addition of additive Z have a more favorable fatigue strength than the layer bonded with cement alone.

In addition to the improved fatigue strength, the blend with 5 wt.% additive Z was also shown to have a high stiffness modulus. This means that a longer service life can be expected for this layer than for the layers bonded exclusively with cement.

The investigations shown herein have shown that the use of the additive according to the invention for the production of the cement-bonded layers results in a slower hardening of the layers, combined with significantly lower shrinkage stress. This circumstance reduces the risk of cracking in the cement-stabilized layers. The additive according to the invention reduces the shrinkage tendency of the layers bonded with hydraulic binders. Furthermore, with regard to the fatigue resistance of the layers, it was found that the fatigue resistance of the layers modified with the additive according to the invention is better than that of the layers bonded exclusively with cement. This circumstance has a positive effect on the extension of the service life of the layers under the same traffic load.

Claims

EP3914570 PATENT CLAIMS

1. A concrete additive, characterized in that it contains (a) a butadiene-styrene copolymer; (b) styrene-acrylic ester copolymer; (c) water; (d) alkali silicate; and (e) fumed or colloidal silica.

2. An additive according to claim 1, characterized in that the styrene-acrylic ester copolymer is a styrene-butyl acrylate copolymer.

3. Additive according to one of claims 1 to 2, characterized in that it contains 5 to 95% by weight of butadiene-styrene copolymer (a); and 5-95% by weight of styrene-butyl acrylate copolymer as styrene-acrylic ester copolymer (b), calculated from the sum of (a) and (b).

4. An additive according to claim 3, characterized in that it contains - 80% by weight of butadiene-styrene copolymer (a); and 20% to 80% by weight of styrene-butyl acrylate copolymer (b), calculated from the sum of (a) and (b).

5. An additive according to one of claims 1 to 4, characterized in that its water content is between 30 and 70% by weight, preferably between 40 and 60% by weight, — the total weight of the additive calculated in each case.

6. Additive according to claim 5, characterized in that the pH is between 9 and 12.5, preferably between 9.5 and 12 and more preferably between 10 and 11.5.

—

7. Additive according to one of claims 1 to 6, characterized in that it contains as component (d) sodium silicate, the weight ratio of SiO 2 and Na 2 is preferably between 1.5 and 5. 1

EP3914570

8. A method for producing lean concrete with a cement content of less than 12% by weight calculated from the concrete, which method comprises a step in which cement is mixed with an additive and aggregate according to one of claims 1-7.

9. A method for making a road or path structure, which method comprises the step of mixing cement with an additive and aggregate according to any of claims 1-7, and which comprises a step of preparing a hydraulically bound layer by mixing earth material with cement and any of the — any of claims 1-7 with the additive and compacting the base layer obtained from it.

10. The method according to claim 9, characterized in that the hydraulically bonded layer contains 0.3 to 10% by weight of cement, preferably 2 to 5% by weight, based on the weight of the layer.

11. The method according to one of claims 9 or 10, characterized in that the hydraulically bonded layer contains an additive of 0.05 to 0.5% by weight, calculated from the weight of the layer.

12. The method according to one of claims 10-11, characterized in that a surface layer, preferably a surface layer containing bitumen or concrete, is applied to the hydraulically bound layer.

13. Use of an additive according to any of claims 1 to 7 in concrete.

14. Use according to claim 13, characterized in that the concrete is lean concrete with a cement content of less than 12% by weight, calculated from the concrete.

15. Use according to claim 13 or 14, characterized in that it is a concrete additive for soil compaction. 2