WO2023117979A1

WO2023117979A1 - Method of production of premix, for concrete or mortar, comprising portland cement, a superplasticizer and a defoaming agent

Info

Publication number: WO2023117979A1
Application number: PCT/EP2022/086761
Authority: WO
Inventors: Martin Mosquet; Karim BRAHMI
Original assignee: Holcim Technology Ltd
Priority date: 2021-12-20
Filing date: 2022-12-19
Publication date: 2023-06-29

Abstract

The present invention is directed to a method for producing dry premix for mortar or concrete comprising the steps of: al) introducing into a cement mill Portland clinker, a source of calcium sulphate and grinding at a temperature above 80°C to the desired fineness to form a hydraulic binder; a2) consecutively adding at a temperature above 80°C a superplasticizer and a defoaming agent, said superplasticizer is PolyCarboxylate Polyalkylene (PCP) and said defoaming agent comprising at least one function (PO), the function (PO) is chosen from *-(CH(CH3)-CH2-O)-* and *-(CH2-CH(CH3)-O)-*, where * represent bonding to the rest of the molecule; a3) collecting the hydraulic binder, the PCP and the defoaming agent forming together the dry premix. The present invention is directed to a method for producing mortar or concrete comprising the steps of: a) providing a dry premix of the invention; then b) mixing said premix with aggregates and water.

Description

METHOD OF PRODUCTION OF PREMIX, FOR CONCRETE OR MORTAR, COMPRISING PORTLAND CEMENT, A SUPERPLASTICIZER AND A DEFOAMING AGENT

The invention refers to a method of production of premix, for concrete or mortar, comprising Portland cement, a superplasticizer and a defoaming agent.

Superplasticizers are admixtures developed to give the cementitious materials greater fluidity for the same water to cement ratio (w/c). Polycarboxylate ether or ester- based admixtures, also referred to as "PCP" or "PolyCarboxylate Polyalkylene", are commonly used superplasticizers.

PCP-based admixtures are known to increase the amount of air in concrete or mortar compositions, in the form of small bubbles distributed across the volume of concrete or mortar. Excessive entrained air is detrimental to the strength of the hardened concrete or mortar at all ages.

Accordingly, defoaming agents are also added when mixing the cement with PCP-based admixture and water to prevent excessive amounts of air in concrete and mortar.

Adding the admixture when mixing cement with water requires specific equipment for accurate dosage of admixtures. An error in the dosage of the admixtures, either an over or an under dosage, can heavily impact the fluidity of the cemented paste. For some applications, one would prefer to provide cement already mixed with the desired admixture under the form of a dry premix. Then the premix can be mixed with water on the jobsite.

However, when cement is produced with PCP-based admixture, the amount of air entrained in mortar or concrete made with this cement increases significantly. Standard technology based on defoaming agent may not perform because most of defoaming agents lose their efficiency when they are added during cement production, at the cement mill entrance of after the cement mill.

The purpose of the invention is the selection of specific defoaming agents able to reduce efficiently the air content in concrete or mortar comprising PCP even when adding at a temperature above 80°C. The specific defoaming agent enables to prepare a dry premix comprising the cement, PCP and the defoaming agent. In particular, the admixtures can be added during the cement production. The defoaming agent comprises at least one function (PO), the function (PO) is chosen from *-(CH(CH3)-CH2-O)-* and *-(CH2-CH(CH3)-O)-*, where * represents bonding to the rest of the molecule. It was indeed found that these defoaming agents retain their performance after the grinding step of the cement, which is not the case of all types of defoaming agents.

The present invention is directed to a method for producing dry premix comprising the steps of: al) introducing into a cement mill Portland clinker, a source of calcium sulphate and grinding at a temperature above 80°C to the desired fineness to form a hydraulic binder; a2) consecutively adding at a temperature above 80°C a superplasticizer and a defoaming agent, said superplasticizer is PolyCarboxylate Polyalkylene (PCP) and said defoaming agent comprising at least one function (PO), the function (PO) is chosen from *-(CH(CH3)-CH2-O)-* and *-(CH2-CH(CH3)-O)-*, where * represent bonding to the rest of the molecule; a3) collecting the hydraulic binder, the PCP and the defoaming agent forming together the dry premix.

The premix can later be used for preparing a mortar or a concrete.

The present invention is directed to a method for producing mortar or concrete comprising the steps of: a) providing a dry premix of the invention; then b) mixing said premix with aggregates and water.

The premix is advantageously provided under a powder form.

Advantageously, the process of the present invention renders possible to reduce the amount of air in mortar or concrete from premix while the premix is obtained by a hot grinding of the hydraulic binder.

Another advantage of the present invention is mixing the defoaming agent with the hydraulic binder in a hot state for preparing a premix which reduces the amount of air in mortar or concrete.

The invention is based on selection of a specific defoaming agent which enables to be added to a temperature above 80°C to provide a dry premix that contains the admixtures which benefit from the PCP-based superplasticizer without losing compressive strength due to the air entrainment. According to the invention, the grinding step al is performed at a temperature above 80°C, preferably above 90°C, more preferably above 100°C and preferably at most at a temperature 140°C, preferably at most 130°C and more preferably at most 120°C.

According to the invention, step a2) is consecutive to grinding step al), meaning that the superplasticizer and the defoaming agent are added to the hot hydraulic binder before, during grinding or directly exiting the cement mill in step al).

Superplasticizer improve the rheological properties of cementitious paste. Superplasticizers are water reducers that are capable of reducing water contents of mixing water, for a given workability, by up to 30% while achieving suitable fluidity or those are capable of improving the flowability of the material for given water content.

The premix is designed as a dry mass, so that it can be stored for long times after having been pre-manufactured. In particular, providing the superplasticizer and the defoaming agent as a dry component of the premix reduces potentially the number of components to be mixed together at the jobsite. In fact, in some cases, only three types of components need to be mixed on site, namely the dry premix, the aggregates (including sand and/or gravels) and water. In other cases, additional admixture, preferably of other type, is further mixed at the jobsite.

According to the invention, the premix is provided in dry form. This includes embodiments, in which the residual water content of the premix is less than 2 wt.-%, preferably less than l wt.-%, more preferably less than 0,5 wt.-%. For example, the water content may be the result of a mixture of a dry hydraulic binder with a small amount of superplasticizer or a defoaming agent that is provided in liquid form. It must be noticed that due to the reaction capacity of the hydraulic binder any residual water will be converted in hydrates during transport and storage. A small amount of liquid admixture, such as a superplasticizer or a defoaming agent, may be mixed with a particulate hydraulic binder in different ways in order to obtain a homogenous mixture. For example, the liquid admixture may be added to the hydraulic binder at the entry of a mill, such as a ball mill or vertical mill, in which the coarse binder (typically clinker, gypsum and supplementary cementitious materials) is ground together with the admixture to obtain a fine binder powder homogenously mixed with the admixture. Alternatively, a particulate carrier may be impregnated with the liquid admixture, whereupon the impregnated carrier is mixed with the hydraulic binder. According to a preferred embodiment, the premix is provided in powder form.

The defoaming agent can be a molecule or a polymer.

The defoaming agent has preferably a molecular weight in weight, Mw, ranging from 200 g/mol to 4 000 g/mol, preferably ranging from 300 g/mol to 3 000 g/mol and more preferably 400 g/mol to 2 000 g/mol.

Then, the defoaming agent will preferably comprise (PO) blocks, chosen from -[CH(CH3)-CH₂- O]_n- and -[CH₂-CH(CH₃)-O]_n-, where n is an integer ranging from 1 to 60, preferably from 4 to 55, preferably from 10 to 50, preferably from 15 to 30.

The defoaming agent can be in particular triisobutylphosphate. Triisobutylphosphate is a molecule comprising three functions CH3-(CH(CH3)-CH₂-O)-* linked to the functional group *-P=O.

The defoaming agent can be a polymer. The polymer defoaming agent can further comprises (OE) blocks, of formula -[CH₂-CH₂-O]_m, where m is an integer ranging from 0 to 20, preferably from 1 to 20, preferably from 1 to 10, preferably from 1 to 4.

The defoaming agent is preferably a block copolymer (I) R-(PO)n(OE)m-R' , wherein n and m are as defined above, one of R or R' represents OH and the other of R or R' represents H or an alkyl group comprising 1 to 18 carbon atoms. Preferably R represents OH.

The defoaming agent is preferably a block copolymer (II) R-(OE)m'(PO)n(OE)m-R', wherein n, m, R and R' are as defined above, m' is an integer ranging from 0 to 10, preferably from 1 to 20, preferably from 1 to 10, preferably from 1 to 4 and more preferably from 2 to 4.

The polymer defoaming agent has preferably a molecular weight in weight, Mw, ranging from 500 g/mol to 4000 g/mol, preferably ranging from 600 g/mol to 3800 g/mol, preferably from 700 to 3500 g/mol, preferably ranging from 800 g/mol to 3200 g/mol and more preferably from 1000 to 3000 g/mol.

The premix preferably comprises from 0.1 to 10 wt.-%, preferably from 0.5 to 4 wt.-% of defoaming agent, compared to the weight of PCP. The quantity is expressed with reference to the dry weight of active defoaming ingredient to the dry weight of PCP. The supporting carrier, if any, does not form part of active ingredient.

The premix preferably comprises from 0.001 to 0.1 wt.-%, preferably from 0.002 to 0.01 wt.- % of defoaming agent, compared to the weight of the premix. The quantity is expressed with reference to the dry weight of active defoaming ingredient to the dry weight of premix. The supporting carrier, if any, does not form part of active ingredient.

The term "PCP" or "polycarboxylate Polyoxyalkylene" is to be understood according to the present invention as a comb polymer comprising a backbone bearing carboxylic groups and bearing pending polyoxyalkylene (POA) chains.

The PCP has preferably a molecular weight, Mw, ranging from 1 000 g/mol to 100 000 g/mol, preferably from 10 000 g/mol to 80 000 g/mol, more preferably from 20 000 g/mol to 40 000 g/mol.

The PCP can be prepared as disclosed in WO99/47468 (dispersant DI; page 1, line 26- page 5, line 9; page 5, line 31- page 6, line 27).

The premix preferably comprises from 0.02 to 1 wt.-%, preferably from 0.05 to 0.5 wt.-%, more preferably from 0.1 to 0,4 wt.-% of PCP. The quantity is expressed with reference to the dry weight of active ingredient compared to the total weight of the dry premix. The supporting carrier, if any, does not form part of active ingredient.

The hydraulic binder comprises Portland cement. Preferably the clinker is Portland clinker. Calcium sulphate is commonly added to Portland clinker to prepare a Portland cement. Calcium sulphate includes gypsum (calcium sulphate dihydrate, CaSO₄.2H2O), hemi-hydrate (CaSO₄.l/2H2O), anhydrite (anhydrous calcium sulphate, CaSO₄) or a mixture thereof.

Further, the hydraulic binder may also comprise other mineral components often called "supplementary cementitious materials (SCM)", in particular slag, fly ash, calcined clays, limestone, pozzolan, cement kiln dust, and mixtures thereof, preferably at a content comprised between 6 and 50 wt.-% of the total hydraulic binder.

The suitable cement used in the invention is preferably selected among cements described according to the European NF EN 197-1 Standard of April 2012 or mixtures thereof, preferably cement of the types CEM I, CEM II, CEM III, CEM IV or CEM V. Alternatively, the said suitable cement can be a mixture of a CEM I type with any one or several constituents listed in the European Standard of April 2012.

During step a2), the defoaming agent and the PCP are added at a temperature above 80°C to the composition comprising Portland clinker and source of calcium sulphate to form the premix. The defoaming agent and the PCP, also collectively called "the admixtures", can be added during the preparation of the cement, in particular at the cement mill entrance or directly after the cement mill.

A cement mill is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine cement powder. Most cement, currently ground in ball mills and also vertical roller mills operated in closed or open circuit, can be used.

In a first embodiment, at least part of the PCP and /or part of the defoaming agent is added during step al). Preferably, step al) comprises introducing Portland clinker, a source of calcium sulphate, PCP and defoaming agent into a cement mill. Supplementary cementitious materials can further be added. These components are ground together at a temperature above 80°C to the desired fineness. Accordingly, steps al) and a2) are at least partly concomitant. Preferably, the whole part of PCP and the whole part of defoaming agent are added during step al). Accordingly, steps al) and a2) are concomitant.

Step a3) comprises collecting at the exit of the cement mill the ground components forming the premix.

The method preferably comprises the following successive steps: all) introducing Portland clinker, a source of calcium sulphate, PCP and defoaming agent into a cement mill; al2) grinding the components of step all) at a temperature above 80°C to form hydraulic binder having the desired fineness; a3) stocking or wrapping the resulting premix.

During step al), in particular step all), the PCP and the defoaming agent are preferably added separately, especially when the defoaming agent is a molecule.

Advantageously, the temperature of the grinding of step al2) is above 90°C, more preferably above 100°C and preferably at most at a temperature 140°C, preferably at most 130°C and more preferably at most 120°C.

When the hydraulic binder further comprises the mineral component disclosed above, it is added during step al), in particular step all).

In a second embodiment, at least part of PCP and /or part of the defoaming agent is added after step al). Accordingly, at least part of PCP and /or part of the defoaming agent is directly added to the hot hydraulic binder exiting the cement mill. Step a2) comprises adding to the hot hydraulic binder, at the exit of the cement mill, PCP and defoaming agent, and ensuring turbulence in order to distribute the admixtures in the hydraulic binder. By hot hydraulic binder is meant above a hydraulic binder existing the cement mill at a temperature above 80°C, preferably above 90°C, more preferably above 100°C and preferably at most at a temperature of 140°C, preferably at most 130°C and more preferably at most 120°C.

Accordingly, the method comprises the following successive steps: all') introducing Portland clinker and a source of calcium sulphate into a cement mill; al2') grinding the components of step all') to form hydraulic binder having the desired fineness; a2) at the exit of the cement mill, adding to the hydraulic binder having a temperature above 80°C the PCP and the defoaming agent, ensure a minimum turbulence in order to distribute the admixture in the hydraulic binder and a3) stocking or wrapping the resulting premix.

When the hydraulic binder further comprises the mineral component disclosed above, it is added during step al), in particular step all').

During step a2) the PCP and the defoaming agent are preferably added separately, especially when the defoaming agent is a molecule.

Step a2) is advantageously directly consecutive to grinding process, meaning that the admixtures are added to the hot ground hydraulic binder exiting the cement mill, ensuring a minimum turbulence in order to distribute the admixture in the hydraulic binder without intermediate step of stocking or wrapping step of the ground hydraulic binder.

The invention is also directed to a dry premix comprising hydraulic binder, a superplasticizer and a defoaming agent, said superplasticizer is PCP and said defoaming agent comprising at least one function (PO), the function (PO) is chosen from -(CHfCHa)- CH₂-O)- and -(CH₂-CH(CH₃)-O)-.

The dry premix is as described above.

The invention is also directed to a dry premix obtained by the method previously disclosed.

The premix is preferably under a powder form The premix is then later mixed (step b)) with aggregates and water to prepare concrete or mortar. The aggregates can comprise sand and/or gravels.

The invention is also directed to a method for preparing a concrete or a mortar, comprising the following steps: a) providing a premix as disclosed previously; then b) mixing said premix with aggregates and water.

Preferably, the premix is a dry premix, in particular is provided under a powder form.

EXAMPLES

The present invention will now be illustrated in more detail by reference to the following examples compared to the total weight of the premix. a) Materials

If not specified otherwise, the percentages of compounds in the examples here-under are expressed in weight of dry active ingredient.

• Cement

The following cements were used in the tests:

CEMII-325R Le Teil comprising 80 wt.-% Portland cement and 20 wt.% limestone ;

CPC30 Salvador comprising 65 wt.-% Portland cement, 25 wt.% pozzolan and 10 wt.% cement kiln dust

• Superplasticizer

A superplasticizer PCP as disclosed in WO99/47468 was prepared and used in the following tests.

The PCP is prepared by grafting a polymethacrylic backbone of 5000 Daltons with methoxypolyoxyethylene side chains of 2000 Daltons using the process used in Patent WO99/47468. The molar ratio between carboxylic groups and side chains is 5. The polymer is then neutralized at pH 6 and diluted with water at 50% active ingredient.

• Defoaming agent

The following defoaming agents were used in the tests:

b) Process of preparation of mortar First a premix comprising the cement and the admixture(s) is prepared. Cement and admixture(s) are ground together at 100°C.

Cement (5kg) is introduced in a lab ball mill pre-heated at 100°C. Then admixtures are added on top of cement. 500 revolutions are operated before emptying the mill and collecting the cement. Tests are done after 24h cooling at 20°C.

Mortar is prepared according to ASTM C109 (2021): 1 part of premix for 2,75 part of standard sand (gradel Sand according to ASTM C778 - 2017) and enough water to reach a diameter of 205-215mm (starting from a 100mm diameter cone) on the shock table (25 shocks). c) Measurement methods

Air content is measured according to EN 1015-7 (1999).

Example 1 - air content of reference mortar

Without any superplasticizer, mortar made of the hydraulic binder have a low air content.

Example 2 - air content of mortar with superplasticizer

The addition of superplasticizer in the hydraulic binder increases the air content of the resulting mortar.

Example 3 - air content of mortar with superplasticizer and defoaming agent comprising (PO) function

The addition of defoaming agent comprising (PO) function reduces air content increase due to the superplasticizer in the resulting mortar.

Example 4 - air content of mortar with superplasticizer and defoaming agent comprising (PO) function

Example 5 - air content of mortar with superplasticizer and various defoaming agent comprising (PO) function

Example 6 - air content of mortar with superplasticizer and defoaming agent lacking (PO) function

The addition of defoaming agent lacking (PO) function when grinding at 100°C does not reduce air content increase due to the superplasticizer in the resulting mortar.

Claims

1. A method for producing dry premix for mortar or concrete comprising the steps of: al) introducing into a cement mill Portland clinker, a source of calcium sulphate and grinding at a temperature above 80°C to the desired fineness to form a hydraulic binder; a2) adding at a temperature above 80°C a superplasticizer and a defoaming agent, said superplasticizer is PolyCarboxylate Polyalkylene (PCP) and said defoaming agent comprising at least one function (PO), the function (PO) is chosen from *-(CH(CH3)-CH2-O)-* and *-(CH2- CH(CH3)-O)-*, where * represent bonding to the rest of the molecule; a3) collecting the hydraulic binder, the PCP and the defoaming agent forming together the dry premix.

2. The method according to claim 1, wherein the grinding step al is performed at a temperature above 90°C, more preferably above 100°C and preferably at most at a temperature 140°C, preferably at most 130°C and more preferably at most 120°C.

3. The method according to the preceding claims, wherein, the defoaming agent comprises (PO) blocks, chosen from -[CH(CH3)-CH2-O]_n- and -[CH2-CH(CH3)-O]_n-, where n is an integer ranging from 1 to 60.

4. The method according to the preceding claims, wherein the defoaming agent further comprises (EO) blocks, of formula -[CH2-CH2-O]_m, where m is an integer ranging from 1 to 20.

5. The method according to claim 4, wherein the defoaming agent is a block copolymer of general formula (II) R-(OE)m'(PO)n(OE)m-R', wherein n, m is an integer ranging from 0 to 20, preferably from 1 to 20, preferably from 1 to 4 one of R or R' represents OH the other of R or R' represents H or an alkyl group comprising 1 to 18 carbon atoms, m' is an integer ranging from 0 to 10, preferably from 2 to 20, preferably from 1 to 4.

6. The method according to anyone of the preceding claims, wherein the defoaming agent has a molecular weight in weight, Mw, ranging from 200 g/mol to 4 000 g/mol.

7. The method according to anyone of the preceding claims, wherein the premix comprises 0,001-0,1 wt.-%, preferably 0,002-0,01 wt.-% of defoaming agent

8. The method according to anyone of the preceding claims, wherein the PCP has a molecular weight, Mw, ranging from 1 000 g/mol to 100 000 g/mol, preferably from 10 000 g/mol to 80 000 g/mol, more preferably from 20 000 g/mol to 40 000 g/mol.

9. The method according to anyone of the preceding claims, wherein the premix comprises 0.02-1 wt.-%, preferably 0.1- 0,4wt.-% of PCP, compared to the total weight of the premix.

10. The method according to anyone of the preceding claims, wherein at least part of PCP and /or part of the defoaming agent is added during step al), preferably steps al) and a2) are concomitant.

11. The method according to anyone of the preceding claims, wherein at least part of PCP and /or part of the defoaming agent is added to the hot hydraulic binder directly at the exit of the cement mill.

12. The method according to anyone of the preceding claims, wherein the PCP and the defoaming agent are preferably added separately.

13. A dry premix obtained by the method of claims 1 to 12.

14. A method for producing mortar or concrete comprising the steps of: a) providing a dry premix obtained by the method of claims 1 to 12; then b) mixing said dry premix with aggregates and water.

15. The method according to claim 14, wherein the premix is provided in powder form.